Commonly used humidity sensors are based on metal oxides, polymers or carbon. Their sensing accuracy often deteriorates with time, especially when exposed to higher temperatures or very high humidity. An alternative solution based on the utilization of Portland cement-based mortars containing in-situ grown carbon nanofibers (CNFs) was evaluated in this study. The relationship between the electrical resistivity, CNF content and humidity were determined. The highest sensitivity was observed for samples containing 10 wt.% of the nanomodified cement which corresponded to 0.27 wt.% of CNFs. The highest calculated sensitivity was approximately 0.01024 per 1% change in relative humidity (RH). The measured electrical resistivity is a linear function of the RH in the humidity range between 11 and 97%. The percolation threshold value was estimated to be at around 7 wt.% of the nanomodified cement, corresponding to ~ 0.19 wt.% of CNFs. Uncontrolled or improper moisture diffusion, especially in an early stage of hydration, can result in a number of negative effects. These include increased shrinkage, lower long-term strength and durability problems3. An insufficient water content, e.g. related to an excessive evaporation, can hinder the hydration process4. Therefore, monitoring the humidity is crucial for concrete technology. The humidity defined as the amount of water vapour present in the gas phase and can be expressed as absolute or relative value. The relative humidity (RH) is the ratio between the measured amount of water vapour and the water vapour required to reach the saturation state at a certain temperature. Measuring the mass of water vapour contained in a unit volume determines to the absolute humidity (AH).Humidity sensing plays an important part in, e.g. production processes or building maintenance. Cement hydration is controlled by moisture content and thus humidity7. The capacitive sensors are the most commonly used with an estimated 75% of the total market share8. They are built of two metal plates separated by a thin layer of an non-conductive polymer film9. The non-conductive polymer film attracts moisture from the air, which changes the dielectric constant of the hygroscopic layer. Various types of materials have been used for the moisture sensitive layer. The most common include for example polyimide film (DuPont 5878), polymethyl methacrylate (PMMA), porous ceramics, porous silicon, porous silicon carbide, hygroscopic polymers or porous alumina (Al2O3 )11. Capacitive sensors tend to have a variable sensitivity depending on the measured humidity levels. For example sensors using plasma-etched polyimide as the sensing layer showed low sensitivity at a RH up to 70% and very high sensitivity at a RH between 70 and 90% 11. Similar problems were observed when using porous silicon. In that case, hysteresis was observed at a RH above 60%9. The required power demand is rather low but the production technology of this type of sensors is complicated12. Resistive sensors overcame some of the problems typical for the capacitive sensors. They also are easier and cheaper to fabricate, have high sensitivity and low power consumption. Metal oxide, polymers, and carbon-based materials are the most frequently used materials for their production. Unfortunately, some of these materials degrade when exposed to high humidity, including for example, metal oxide or polymer sensors13. Slow response/recovery time and high operating temperatures remain the main design challenges for these sensors. Sensors based on matrixes containing Portland cement measure also changes of resistivity14. In this case, the measured changes were related to alterations of the pore structure leading to either shrinkage or expansion of the matrix, water absorption or desorption hysteresis at the interface. Humidity sensing of such matrixes depends also on the amount of the incorporated conductive material like carbon fibers (CFs). Chen et al.15 revealed that cementitious matrixes containing less CFs better sense changes of the internal humidity. Different curing conditions are known to affect the sensing capability as well. Sun et al.16 reported that a cementitious matrix reinforced with CFs cured in air had a more than 2-times lower electrical resistivity compared to the same material being oven cured. Results obtained by Han et al.17 showed the same trend. Optic fiber humidity sensors can be classified according to their working principles including optical absorption of materials, optical fiber Bragg gratings (FBG), interferometric method, and evanescent wave. The FBG-based sensors have been used to monitor strain and temperature20 as well as humidity in highways19. FBG uses a permanent periodic modulation of the reflective index which is formed by an exposure of the core of the optical fiber to an intense optical interference pattern of the light21. The humidity sensing is based on an interaction of water molecules with the sensitive core layer. This results in a change of the effective refractive index of the fiber core and in a shift of the Bragg wavelength22. Several polymeric materials such as polymide24, di-ureasil21 and PMMA26 have been coated onto an etched FBG to improve the humidity sensitivity. Etching of cladding and coating with graphene oxide27 or CNTs22 layer showed sensitivity of ∼31 pm/%RH. Furthermore, the modified sensor could detect the relative humidity over a wide range between 20 and 90% at a constant temperature of 25 ˚C22. PMMA-based microstructure polymer optical fiber Bragg were studied by Woyessa et al.28. The results showed a response having a very low hysteresis and an improved humidity sensitivity (∼35 pm/%RH at 90% RH).Humidity measurements rely on converting the detected amount of water molecules into a signal that can be measured, analysed, interpreted and quantified. The interaction between water molecules and sensors is controlled by various physical phenomena. The physical phenomenon being measured defines which type of sensor is used. The most conventional types include capacitive, resistive, impedance, quartz crystal microbalance (QCM), optic-fiber, surface acoustic wave (SAW) or resonance sensing32, Sun et al.33 and Ou et al.34 induced piezoresistive properties of cementitious composites by incorporating CFs. Camacho-Ballesta et al.35 reported that composites containing only 0.05 wt.% of CNTs showed electrical properties sufficient to be used for monitoring. Yu and Kwon36 revealed CNT/cement composites have high sensitivity of the composite stress response when the CNT doping level is high. Composites based on Portland cement with directly grown CNFs showed even better results in stress/strain monitoring reaching approximately 90% compared with the conventional cementitious material37. CNTs and CNFs are commonly added as aqueous dispersions. Unfortunately, their strong hydrophobicity results in a formation of agglomerates. The effect is even stronger in high pH solutions present during the Portland cement hydration. The formation of agglomerates prevents the uniform distribution of the fibers throughout the binder matrix, which is the key condition to create an effective electrically conductive network. Surface functionalization of CNTs and CNFs enhanced the mechanical properties of cement matrixes through a better bond but it also increased the agglomeration38. The usage of ultra-sonication in the presence of surfactants produced stable suspensions of well dispersed MWCNTs and functionalized CNTs/CNFs39. However, the results showed also that an increasing amount of CNTs/CNFs tends to worsen the fresh mix workability.Yet, carbon-based materials are widely used to induce the sensing capability into the monitored material. For example, Chung et al.41. Replacing part of Portland cement with this nanomodified cement ensured a uniform distribution of CNFs. It mitigated also the loss of workability and thus significantly increased the maximum amount of CNFs, which could be incorporated into the binder matrix. This method seems to be potentially beneficial to create electrically conductive matrixes sensitive in many aspects including humidity variations. The research described in the present paper focused on investigating potential applicability of nanomodified cement to manufacture sensors for humidity measurements.The development of an alternative technology enabling to synthesize CNFs directly on cement have limited some of these problems. This method uses a chemical vapour deposition process to grow CNFs directly on cement particles by utilizing naturally embedded Fe and Al as catalysts37. The morphology of grown CNFs is shown in Fig. Test sensors were produced as mortar beams composed of a mixture of an ordinary Portland cement (OPC) type CEM I 42.5 provided by Cementa-Sweden and the so-called SmartCem. The SmartCem is a nanomodified Portland cement having CNFs synthesized directly on the surface of pristine cement through Chemical Vapour Deposition (CVD). The total amount of carbon nanofibers (CNFs) grown on the SmartCem was approximately 2.71 wt.%. The used synthesis processes is described in detail elsewhereSieved and clean sand with the maximum particle size of 150 μm was used as fine aggregate. The superplasticizer (sp) type Glenium produced by Grace Chemical with a solid content of 30% was used to control the workability of the fresh mix. The water-to-binder ratio and the sand-to-binder ratio (s/b) were constant at 0.35 and 1 respectively. The mix proportions used for the test mortars are shown in Table Mortars were mixed using a Bredent vacuum mixer and poured into Teflon moulds. The size of test specimens in this research was selected having dimensions of 12 mm × 12 mm × 60 mm since no standard size setup test for electrical resistance measurement at present. Different specimen geometries can be used; however, the measured resistance should be converted to resistivity by using an appropriate geometry correction factor. Four copper electrodes having dimensions of 5 mm × 15 mm × 0.25 mm were immersed 7.5 mm and 30 mm apart into these samples and connected by electrical wires with the measuring system, Fig. 2CO3), sodium chloride (NaCl) and potassium sulphate (K2SO4) which can maintain relative humidities of 11%, 43%, 75%, and 97%, respectively. A commercial humidity sensor type SHT85 produced by Sensirion was installed in each container as reference. Values measured after 24 h showed less than 5% variation within 24 h.The effects of the curing conditions on the electrical resistivity were determined a using reference sample (Ref) and the mix containing 4 wt.% of the SmartCem (S4). After casting, the samples were cured at 11%, 43%, 75%, and 97% RH for 28 days, followed by storage in laboratory conditions at 20 ± 2˚C. The samples used for the actual humidity measurements were cured for 28 days at 20˚C and 97 ± 5% RH. The produced humidity sensors contained 0% (Ref), 2% (S2), 4% (S4), 6% (S6), 8% (S8) and 10% (S10) of the SmartCem, calculated as the total binder weight. Before measurements were started, all sensors were kept in humidity chambers at 11%, 43%, 75% or 97% RH for 24 h. The humidity chambers consisted of sealed glass containers containing various types of saturated salt solutions. These included lithium chloride (LiCl), potassium carbonate  and a combination of 96% of OPC with 4 wt.% of the SmartCem (S4).In general, the electrical resistivity increased with the curing age due to the consumption of water by the hydrating cement. The electrical resistivity of the S4-samples tended to be lower at all ages and exposures in comparison with the corresponding OPC samples, Table In the next stage, all sensors produced from the reference mix and the S4 mix and cured at different conditions were used to determine their humidity sensing capability. Before the measurement, all produced sensors were stored for 24 h at 60% RH and 20 ± 2 ˚C. The exposure conditions included 11%, 34%, 75% and 97% RH. The resistivity measurements started 24 h later. The obtained results are shown in Fig. Figure Samples containing only the unmodified Portland cement showed a generally low sensitivity to humidity; independently of the used curing conditions. While samples containing 4 wt.% of the SmartCem showed a significantly higher sensitivity to humidity. In both cases, the lowest sensitivity was measured for samples cured at 11% RH and the highest for cured at 97% RH. The highest calculated sensitivity of 0.00874/%RH was reached for the sensor cured at 97% RH and the sensitivity of the S4 sensor significantly increased when exposing to a humidity greater than 75% RH, Table 43. The hydration degree of tricalcium silicate, measured after 90 days dropped from 36% to only 2% when the RH decreased from 98 to 85%44. Furthermore, the hydration is believed to stop when Portlandite, C-S–H and tricalcium silicate are in equilibrium which can occur at a lower RH. Limited hydration leads to a decreased amount of gel pores and coarsening of the pore structure. Tests showed a nearly three times coarser pore structure for samples cured at 80% RH in comparison with water curing45. These results can be directly related to the observed research trends that show that the electrical resistivity of the matrix decreased when exposed to high humidity and vice versa. Furthermore, it can be assumed that the presence of CNFs enhances the connectivity between moisture filled pore network and thus increases the electrical sensitivity of the entire system. The tunnelling effect developing between CNFs was strengthened through the presence of water molecules at the fiber–fiber and fiber-matrix interfaces47.Access of moisture during curing of Portland cement affects the hydration process that controls also the developed pore structure. The pore structure and especially connectivity of capillary pores define transport of moisture within the solidified binder matrix. This in turn will ultimately affect the efficiency of a moisture sensor based on Portland cement. It has been shown that hydration of Portland cement stops when the relative humidity drops to around 80%The described results were used in a second set of sensor production and measurements. These sensors contained different amounts of CNFs to determine what kind of effect the CNF quantity has on the humidity-sensing capability. These sensors contained 0% (Ref), 2 wt.% (S2), 4 wt.% (S4), 6 wt.% (S6), 8 wt.% (S8) and 10 wt.% (S10) of the SmartCem. Based on the best results obtained in the first part of the study, a 97% RH was used for curing. To ensure the stability and exclude any possible effects of moisture or temperature variations on the measured electrical resistivity, the produced sensors were stored in laboratory condition for 72 h before testing.2 was over 0.95 in all cases, Table The test results showed a nearly linear relationship between the measured electrical resistivity and the relative humidity, Fig. Comparison between sensing capability of cementitious matrixes incorporating different types of carbon-based materials is shown in Table 50. A comprehensive micromechanical model was proposed by Jang et al.51 to predict the effective electrical conductivity of cementitious matrix containing carbon-based filler. This model confirmed that moisture affects the sensing of smart cementitious-based composite.Summarising, the humidity sensing mechanism of the developed SmartCem sensors is related to an alteration of the electrical resistivity. Absorption or desorption of water molecules due to variation of RH in this study change the interconnection between matrix–matrix, fiber–fiber and fiber-matrix resulting in a change in the ultimate electrical resistivity of sensors. For example, water molecules in gaseous state adsorb on the external surface of the sensor and later diffuse into the matrix due to capillary condensation, Fig. The study aimed to determine the sensitivity of novel sensors to variations in the humidity. These humidity sensors are based on mortars containing various amounts of the nanomodified Portland cement (SmartCem). It was found that the electrical resistivity of the sensors tended to increase with longer wet curing time due to the alternation of the microstructure and hydration processes. Samples cured at 97% RH showed the highest sensitivity with the sensitivity value reaching 0.01024/%RH. According to the percolation theory, the percolation threshold amount of the nanomodified cement using for humidity monitoring is estimated at 7 wt.% of the SmartCem (~ 0.19 wt.% of CNFs). The humidity sensitivity of the nanomodified cement was related to the intrinsic electrical property, water absorption property, the connectivity as well as the amount of the nanomodified cement to change the contact point between fiber–fiber and fiber-matrix due to the presence of water vapour in the air.


The effects of molecular weight (MW) and degree of esterification (DE) of soluble soybean polysaccharide (SSPS) on the stability of casein under acidic conditions were investigated. The ability of SSPS to stabilize casein was characterized by the content of SSPS–casein complex, the LUMiSizer instability index, average particle size, zeta potential, and storage experiments. The long-term storage stability of the mixtures was related to their ability to combine casein and the stability of the complexes. At the same DE, SSPSs with medium MW formed more complexes with casein than SSPSs with high or low MW; and at the same MW, SSPSs with medium or low DE formed more complexes than SPSSs with high DE. In addition, SSPSs with higher MW had a better stabilizing behavior due to the large steric repulsion between complexes. SSPSs with high MW and low DE showed the best ability to stabilize casein under acid conditions. Acidified milk drinks are a series of beverages produced by dilution, acidification, and homogenization, such as yogurt drinks, milk drinks with fruit, buttermilk, and whey drinks ,2,3,4,5.The instability of milk proteins under acidic condition is generally believed to be caused by the structural instability and aggregation of casein micelles. The diameter of casein micelles ranges from 80 nm to 400 nm ,7. It isFor a long time, pectin, propylene glycol alginate, and carboxyl methyl cellulose (CMC) have been used to stabilize proteins in acidified milk drinks ,14,15. TRecently, soluble soybean polysaccharide (SSPS), a new polysaccharide extracted from soybean dregs, has attracted attention due to its ability to stabilize milk proteins under acidic conditions ,16,21,22HMP has been shown to be adsorbed on casein micelles by electrostatic interaction during acidification, preventing the casein from aggregating through electrostatic and steric stabilization ,20,28,295 Da) had better ability to prevent aggregation and precipitation of proteins than a low MW fraction (5 × 103 Da) [6 Da) could stabilize acidified milk drinks better than SSPS with a lower MW (5.5 × 105 Da), and this was mainly due to the larger steric repulsion formed by complexes [6 Da) obtained through de-esterification still showed good stabilizing behavior, and a DE value between 25% and 17% was better for stabilizing due to the larger steric repulsion between complexes [Previous studies have indicated that SSPS with high molecular weight (MW) and low degree of esterification (DE) has good ability to stabilize acidified milk drinks ,32,33,34omplexes . Howeveromplexes . Xiong eIn this work, nine SSPSs extracted from soybean dregs with different MWs and DEs were used to explore the influence on stabilizing casein ability. The focus stability in this work was to protect casein from aggregation. The quantity of SSPS–casein complexes formed at different SSPS concentrations was quantified by size exclusion chromatography (SEC)-HPLC). The ability of SSPS with different MWs and DEs to stabilize casein was analyzed by the instability index, complex content, average particle size, zeta potential, and storage experiments.The acid casein 741 was obtained from Fonterra Co-operative Group , and contained 90% protein. CSSPS and soybean dregs were purchased from Pingdingshan Jinjing Biotechnology Co., Ltd. . Citric acid was obtained from Sino pharm Group Chemical Reagent Co., Ltd. .g, 20 °C) to separate the supernatant and precipitate. Ethanol was added to the supernatant at a volume ratio of 1/3, followed by centrifugation  to obtain the SSPS sediments. The sediments were dried at 45 °C for 12 h to obtain SSPSs with different MWs. Degreasing was achieved under different alkali treatment conditions (w/v), and the solutions were adjusted to specific pH values. Ethanol was added to solutions at a volume ratio of 1/3 to precipitate SSPS and the sediments were dried at 45 °C for 12 h. Nine SSPSs with different MWs and DEs were obtained sequentially—high MW and high DE (HH), high MW and medium DE (HM), high MW and low DE (HL), medium MW and high DE (MH), medium MW and medium DE (MM), medium MW and low DE (ML), low MW and high DE (LH), low MW and medium DE (LM), and low MW and low DE (LL).Nine SSPSs with different DEs and MWs were extracted from soybean dregs. First, soybean dregs were dispersed in distilled water at a ratio of 1/27, and SSPSs with different MWs were extracted under the acid treatment condition shown in nditions . SSPSs wMW was analyzed by analytical gel-filtration chromatography equipped with a Waters 2695 Separations Module and Waters 2410 Refractive Index Detector. Samples were analyzed using a TSK-gel 5000PWXL column (7.8 mm × 30 mm) in 50 mM sodium acetate buffer (pH 6.8).v/v) ethanol = 1:19) and stirred for 10 min. Then, the SSPS solution was filtered and washed thoroughly six times using the ethanol–HCl mixture and 70% (v/v) ethanol, sequentially. The filter residue was washed using 20 mL of anhydrous ethanol and dried at 60 °C for 12 h. Then, 200 mg of dried sample was dissolved in 40 mL of distilled water with 0.8 mL of anhydrous ethanol with stirring. The SSPS solution was titrated by 0.1 M NaOH solution (V1) using phenolphthalein as an indicator. NaOH solution  was added to the SSPS solution with stirring for 30 min to demethylate. After stirring, 5 mL of HCl solution (0.5 M) was added to the SSPS solution to neutralize the NaOH solution. The SSPS solution was again titrated with 0.1 M NaOH solution (V2). The DE was calculated using Equation (1):DE was analyzed with titration. SSPS (500 mg) was dissolved in 100 mL of ethanol–HCl solution (12 M HCl:70% (w/v). The nine SSPSs and the commercial SSPS solutions were prepared using distilled water and stirred with a magnetic stirrer at 60 °C until dissolved. The casein and SSPS solutions were mixed at equal volume proportions. The mixtures were acidified to pH 4.0 by adding 40% citric acid solution at 25 °C, and the process of crossing the isoelectric point of casein was controlled within 10 s. The final concentrations of the mixtures were calculated to obtain mixtures with contents of 1% (w/v) casein, the ratios of SSPS to casein were 1/10, 2/10, 3/10, 4/10, 5/10, 6/10, 7/10, 8/10, 9/10, and 10/10. A mixture of 1.0% commercial SSPS and 1.0% casein at pH 7.0 was also prepared.Casein was dissolved in distilled water at a concentration of 2.0% . LUMiSizer evaluated the stability of products through centrifugal acceleration technology based on the Lambert–Beer and Stokes’ laws .The instg for 8400 s. For the measurement program, the time interval was 15 s and the temperature was 25 °C.Approximately 4 mL of sample was injected into a standard cuvette and centrifuged at 2150× The casein, commercial SSPS, and their mixture at pH 4.0 and 7.0 were quantified by SEC-HPLC. The HPLC was composed of a Waters 1525 binary HPLC pump, Waters 2487 dual λ absorbance detector, and Waters 2707 autosampler. The samples were analyzed by size exclusion columns . The absorbance of ultraviolet radiation was detected at a wavelength of 280 nm. Phosphate buffers with sodium chloride were used as mobile phases. The mobile phase consisted of 50 mM phosphate and 0.3 M sodium chloride at pH 7.0, and 50 mM phosphate and 0.1 M sodium at pH 4.0. The mobile phase was filtered using a 0.45 μm cellulose membrane and degassed by ultrasonic cleaners for 30 min. The sampling volume was 10 µL, and the sampling time was 25 min at a flow rate of 1.0 mL/min. The UV wavelength was 220 nm. The temperature was set at 30 °C. All the prepared samples were stored at room temperature for 4 h before being injected.The contents of the nine SSPS–casein complexes were measured as above.The particle size distribution and diameter of the mixtures were characterized using a Zetasizer Nano ZS, ZEN 3600 . The refractive index of the sample and dispersant were 1.590 and 1.330, respectively. Measurements were performed at 25 °C. All samples were diluted to 1/10 with 0.02 M citric acid buffer at the same pH value to avoid the effects of high concentrations of multiple scattering.Samples obtained were kept at 4 °C for 30 days, and photos were recorded.p value < 0.05 was statistically significant throughout the study.All experiments were performed at least in triplicate, and drawings were performed using Origin 2017 . Statistical significance was analyzed with Statistic software 9.0 . The data were reported as the means ± SD, a 6 Da), and LL had the smallest MW (4.7 × 105 Da). The vigorous extraction conditions  accelerated the hydrolysis of SSPS. After de-esterification, the MW of HH (1.42 × 106 Da) decreased from 1.42 × 106 Da to 1.15 × 106 Da (HM) and 1.06 × 106 Da (HL), which demonstrated that both the DE and MW of SSPS decreased during de-esterification. Changes in MW and DE can affect the ability of SSPS to stabilize casein.The MW and DE of major fractions of nine SSPSs are shown in The stabilities of SSPS with different MWs and DEs were evaluated by LUMiSizer instability index. The instability index was calculated by the change in the transmission profile over time and space during centrifugation. For LH, LM, and LL SSPSs, the mixtures were not measured when the ratio was lower than 6/10 due to the sediment. The instability index of casein stabilized by the nine SSPSs is shown in 5 Da showed a lower instability index than HH (1.42 × 106 Da) and LH (5.2 × 105 Da). However, for medium or low DE, when the SSPS/casein ratio was below 5/10, there was little difference between SSPSs with high MW (HM and HL) and SSPSs with medium MW (MM and ML). When the ratio was >5/10, the instability index of SSPSs with high MW (MM and ML) was lower than SSPSs with medium MW (MM and ML). Meanwhile, the stabilizing ability of SSPSs with low MW at the same DE  to stabilize casein was worse than that with high or medium MW. Nobuhara et al. (2014) reported that SSPS with higher MW (2.85 × 106 Da) had better ability to prevent casein aggregation than that with a lower MW (5.5 × 105 Da) due to the strong steric repulsion of complexes [In terms of MW, comparing the SSPSs without de-esterification , the casein stabilized by SSPS with a medium MW (MH) of 8.8 × 10et al. 20 reportedThe complexes formed by SSPS with high MW had larger steric repulsion; but high MW might make it difficult for SSPS to form complexes with casein. However, SSPS with low DE could not only provide larger electrostatic repulsion for complexes but also contribute to the electrostatic interaction between SSPS and casein. These results suggest that the ability of SSPS to stabilize proteins is not only related to the stability of the complexes themselves but might also be associated with the ability to form complexes.The complexes formed by SSPS and casein under acidic condition were quantified to investigate the influence of MW and DE on the ability of SSPS to combine casein. Zhao, Li, Carvajal, and Harris (2009) reported that the polysaccharide–protein complexes driven by electrostatic interactions could be detected using SEC-HPLC . A Water6) was much larger than that of SSPS (7.4 × 104) and casein (1.1 × 105). This confirmed that complexes were formed between positively charged SSPS and negatively charged casein at pH 4.0, and only the content of complexes was detected, as reflected by the UV absorption value (area) at the elution time of 5.8 min.This result indicated that the casein and SSPS formed complexes mainly through electrostatic interaction. At pH 7.0, there was little interaction between SSPS and casein, which may be because both SSPS and casein had negative charge. When acidified to pH 4.0, which is below the isoelectric point, the casein surface became positively charged . MeanwhiThe UV absorption value (area) at the elution time of 5.8 min of SEC chromatograms reflected the SSPS–casein complex content. The higher UV absorption value (area) reflected more SSPS–casein complexes formed, which was beneficial to stabilize casein under acid conditions.The content of complexes  showed sAt the same DE, for SSPS without de-esterification, SSPS with medium MW (MH) was easily adsorbed on the casein surface to form more complexes than SSPS with high or low MW (HH and LH). Compared with SSPS with high MW (HM and HL), SSPS with medium MW (MM and ML) formed more complexes with casein and showed similar instability indexes as before at a ratio of 5/10. Moreover, HM and HL had better stability than MM and ML as the ratio of SSPS increased, which was consistent with the results in For HM and HL, the ratio of SSPS/casein showed some specific results. The SSPS–casein complex content reached a maximum a and casThe previous study reported that MW or DE was essential to the stabilizing ability of SSPS due to their effects on steric or electrostatic repulsion between complexes ,31,33,38As shown in At the same MW, SSPS after de-esterification showed a smaller Z-average size and a lower PDI due to the formation of more complexes, which corresponded to the instability index .In terms of the effect of MW on Z-average size, for SSPS without de-esterification, the casein stabilized by MH was smaller than with HH and LH because more complexes were formed. At the medium and low DE, there was a small difference between SSPS with high MW and medium MW. However, the casein stabilized by LM and LL showed small Z-average size and low PDI until the SSPS/casein ratio was greater than 6/10, due to the weak steric repulsion between complexes.For HL, the Z-average size and PDI of casein decreased to a minimum at the saturation ratio. Meanwhile, LL formed most complexes and showed the lowest instability index at this ratio . These rThe zeta potential of casein, commercial SSPS, and their mixtures at different pH values is shown in The zeta potential of casein with the nine SSPSs  showed sThe stability of casein stabilized by SSPS with different MWs and DEs after storing at 4 °C for 30 days is shown in For SSPS without de-esterification, the casein stabilized by MH was more homogeneous, whereas precipitates could be easily seen for SSPS stabilized by LH. For low and medium DE, when the ratio was 2/10 and 3/10, the SSPS with medium MW had better stability. When the ratio exceeded 4/10, there was no significant difference between the high and low MW. For LM and LL, the results were similar to those for the instability index. When the ratio of SSPS/casein was below 5/10, casein precipitated completely. When the ratio was greater than 6/10, the transmittances of the solutions were lower although the solutions were homogeneous.For HL, there was a large amount of precipitation when the ratio of SSPS/casein was below 2/10. With increasing ratio of SSPS, the amount of precipitation decreased and the light transmittance increased, which might be related to the decreasing particle size of the complexes. However, in contrast to the results for the instability index, excess SSPS could not reduce the stability although the particle size increased. The same results were found for HM, MM, and ML.Combined with the instability index and the complex content, the long-term stability of casein stabilized by SSPS needed to be measured with the content of complex and the stability of the complexes. For the complex with good stability, only a small amount of complex could provide excellent stabilizing ability. For the complex with weak stability, a large amount of complex was needed. The more complexes the solution had, the more stabilized the solution was and the higher the transmittance.The ability of SSPS to stabilize casein was related to the content of SSPS–casein complexes and the repulsion between complexes. At pH 4.0, SSPS was adsorbed on the surface of casein to form complexes before casein aggregated, which could be detected by SEC-HPLC. With regard to the ability of SSPS at the same MW to combine casein, the SSPS with medium or low DE could form more complexes than SSPS with high DE due to more negative charge on the main chain. At the same DE, the SSPS with medium MW was adsorbed on the casein surface more easily and formed more complexes with casein. The stability of the complexes themselves was also an important factor when a large number of complexes was formed. This was mainly due to the strong steric repulsion of the complexes and the weak electrostatic repulsion between complexes. The increasing number of complexes with good stability could effectively reduce the average particle size and improve the stability. The excess SSPS could not increase the complex content, and this might be related to further multilayer adsorption of SSPS on the casein surface. This could increase the particle size of complexes but have no negative effect on the long-term stability. For the complex with good stability, only a small amount of complex provided excellent stabilizing ability. For the complex with weak stability, a large amount of complex was needed. The more complexes the solution had, the more stabilized the solution was and the higher the transmittance.These results showed that, considering the complex content and the stability of complexes, the SSPS with high MW and low DE (HL) showed the best ability to stabilize casein under acid conditions. These results contribute to a better understanding of the interactions between SSPS and casein and the stabilizing of acidified milk protein.


It is necessary to systematically evaluate the efficacy and adverse reactions of pirfenidone in the treatment of patients with idiopathic pulmonary fibrosis (IPF).Pubmed et al. databases were searched up to March 15, 2021 for randomized controlled trials (RCT) of pirfenidone in the treatment of IPF. Two authors collected and compared the indicators including progression-free survival (PFS), vital capacity (VC), forced vital capacity (FVC), and adverse reactions. RevMan 5.3 software and Stata 15.0 software were used for meta-analysis.P < 0.001), slow down the VC of IPF patients , and decrease FVC . The main adverse reactions of pirfenidone were gastrointestinal reactions, photosensitivity and skin rashes.A total of 8 reports with 9 RCTs involving 1824 IPF patients were included. Meta-analysis results showed that compared with the control group, pirfenidone could prolong the PFS phase of IPF patients (HR = 0.65, 95% CI 0.55 ~ 0.76, Pirfenidone is beneficial to prolong the PFS of IPF patients, improve lung function, and it is safe for clinical use. However, more high-quality RCTs are still needed to provide reliable evidence for the treatment of IPF. Idiopathic pulmonary fibrosis (IPF) is a kind of unexplained, chronic progressive fibrotic interstitial pneumonia, and it is more likely to occur in middle-aged and elderly people . The gloThe previous treatment of IPF often included hormones and immunosuppressive agents, with the goal of reducing inflammation as much as possible and delaying the progression of inflammation to fibrosis , 8. WithThis meta-analysis and systematic review was conducted and reported in comply with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) .Two investigators conducted computer search of Cochrane Library, PubMed, EMBase, China national knowledge infrastructure (CNKI), Chinese Biomedical Literature Database and Wanfang Database for RCTs on the applications of pirfenidone in the treatment of IPF, the search time limit was from the establishment of each database to March 15, 2021. Following search terms were applied: "Pirfenidone"," idiopathic pulmonary fibrosis ", “IPF”, “pulmonary fibrosis”, “randomized controlled trial”, “RCT”.The inclusion criteria for RCTs in this meta-analysis were: ① RCT design on the pirfenidone use in the treatment of patients with IPF; ② all patients met the diagnostic criteria for IPF, and the experimental group was treated with pirfenidone and other clinical treatments were the same as the control group, the control group adopted conventional treatment methods using placebo or blank control, and the treatment duration was at least 3 months; ③ evaluation indicators were reported such as disease progression-free survival (PFS), vital capacity (VC), forced vital capacity (FVC), adverse reactions, etc.The exclusion criteria in this meta-analyses were: ① duplicate publication; ② studies with failure to provide sufficient original data.Two investigators independently screened and cross-checked the literature according to the inclusion and exclusion criteria. In case of disagreement, they discussed or consulted a third party to assist in the judgment. Then two authors extracted the following information independently according to the designed data extraction table: author, publication year, basic information of the research population, sample size, treatment plan, outcome indicators and related data. The original authors were contacted as much as possible for the lack of related outcome data.The Cochrane Collaborations risk of bias tool  was usedP > 0. 1, I2 < 50%, it was considered as homogeneous among multiple studies, and a fixed effects model was used for meta-analysis; if P < 0. 1. If I2 ≥ 50%, it was considered that there was heterogeneity in the effect size, then the source of heterogeneity was analyzed by conducting subgroup analysis, sensitivity analysis and applied random effects model. The effect size of each study was calculated according to the method of Parmar et al., and the combined effect size, combined weight and 95% CI were calculated. Publication bias was evaluated by using funnel plots, and asymmetry was assessed by conducting Egger regression test. In this meta-analysis, the difference was statistically significant with P < 0.05.RevMan 5.3 software and Stata 15.0 software were used for meta-analysis. Firstly, a heterogeneity test on the synthesized data was conducted. If As shown in Fig. We used the bias risk assessment tool recommended by Cochrane Network for quality evaluation. Among the 9 included RCTs, 7 of the included studies , 16–20 hPFS 5 RCTs [I2 = 0%, P = 0.525), and the fixed effects model was selected. Compared with control group, pirfenidone significantly prolonged the PFS of IPF patients , and the fixed effects model was selected. Compared with control group, pirfenidone could slow down the decline of VC in IPF patients , and the random effects model was selected. Compared with control group, pirfenidone could delay the decline of FVC in IPF patients , and fixed-effect models were selected. Compared with the control group, at 48–52 weeks and 72 weeks, Pirfenidone slowed down the decline of FVC in IPF patients . studies –19 reporAdverse complications The included reports had reported the adverse reactions of pirfenidone in the treatment of IPF, but there is a large heterogeneity among the studies , because it is impossible to determine the source of heterogeneity, descriptive integration is used. As shown in Table P > 0.05).We attempted to evaluate publication bias by using a funnel plot if ten or more RCTs were included in outcome meta-analysis. Limited by the number of included RCTs, we could not perform funnel plot. Egger regression tests indicated that there was no significant publication of biases (all Sensitivity analyses, which investigate the influence of 1 study on the overall risk estimate by removing one study in each turn, suggested that the overall risk estimates were not substantially changed by any single study.The pathogenesis of IPF is complex, and it is not yet fully clear. There are fewer effective drugs for the treatment of IPF in the clinic, so although the incidence of the disease is low, the prognosis is extremely poor , 23. SevA number of studies –33 have Studies  have repThis meta-analysis has certain limitations. First of all, among the 8 included reports, most of the studies have scientific and rigorous experimental design, with high patient compliance, low loss to follow-up, and high quality. However, there are still several RCTs did not explained the specific random allocation methods and blinding design. The above factors are the main reasons for the high-risk bias, and it may be the important reasons for the large heterogeneity of the results. Additionally, the included RCTs did not report in detail whether pirfenidone can reduce the mortality of IPF patients. Therefore, more large samples and high-quality RCTs are needed to further confirm the efficacy and safety of pirfenidone on IPF.In summary, pirfenidone is beneficial for prolonging the PFS phase of patients with IPF, improve lung function with good safety. It is recommended for clinical IPF treatment, but clinicians still need to make a reasonable choice based on the patient's condition. With the development of medicine, it is still necessary to design larger sample size and more scientific RCTs to verify the therapeutic effect and safety of pirfenidone in patients with IPF, to provide more reliable medical evidence for the treatment of IPF.


By combining microbial culturing and high-throughput sequencing, we can better understand microbe-microbe and microbe-host interactions. To support our proposed model, we used carbon-based and nitrogen-based media to capture the simple state communities. We used 16S rRNA amplicon sequencing and assigned taxonomic identity to the bacterial populations before and after simple state communities. We showed that simple state communities were a subset of the original microbial communities at both phyla and genera level. We further used shotgun metagenomics to gain insights into the functional potential of the assembled simple state communities. Our proposed model supported the goal of simplifying the complex communities across diverse systems to provide opportunity to facilitate comprehension of both the structure and function of the subset communities. Further applications of the concept include the high-throughput screening of simple state communities using the BIOLOG® system and continuous culturing (Chemostat). This concept has the potential to test diverse experimental hypotheses in simplified microbial communities, and further extend that knowledge to answer the overarching questions at a more holistic level.Microbial interactions in natural environments are intricately complex. High numbers and rich diversity of microorganisms, along with compositional heterogeneities complicate the cause. It is essential to simplify these complex communities to understand the microbial interactions. We proposed a concept of “ From the soil under our feet to the corals in the ocean, and the millions of microbes in our gastrointestinal tract, microbes inhabit nearly every environment on Earth . The micsimple state community” of the microbiome in the laboratory from a variety of environments, to enable us to understand the building blocks of stability in these systems and facilitate the further investigation of the microbe-microbe and host-microbe interactions. We defined “Simple State Community” as a subset of microbes and/or microbial functions of the original population that is required to build a stable community . This would include targeted screening, cultivation, and monitoring platforms. The concept drives in the direction to capture the sub-communities (SSC) so that defined systems can be generated and further analyzed by transcriptome, proteome, metabolome, or other approaches. We used the word SSC to refer to the sub-community because it is a simplified subset based on targeted substrate utilization of the original complex community (pre-SSC). We proposed substrate utilization as a primary screen and then monitor the expression of the sub-communities. In this way, responses of multiple organisms and clades, distinguished through the initial screen, can be recorded with changing dynamics and complexity of the system, resulting in more clarity on the functional aspect of the communities toward the host.We proposed a concept of a reductionist approach – the “The approach of SSC will not only allow the relatively easy study of complex communities in the laboratory but also would help to monitor if any defined biotic and/or abiotic disturbances are taking place on the population over time. Integration of all these data together would be perfect to understand the complexities.The basic goal for our SSC model is that to provide a framework to dissect complex microbial community members in a high-throughput manner . Here, w2S04 (1 g), KH2PO4 (4.7 g), K2HPO4 *3H20 (17.7 g), MgSO4 – 7H20 (0.1 g), NaCl (2.5 g), glucose (4 g) as the carbon source, and NH4Cl (1 mM concentration) as the nitrogen source (–1 – 10–6) and spread on the Petri plates. We incubated the plates at 37°C for 48 h to enable optimal growth of distinct colonies from both the soil and fecal samples. The samples were cultured in Petri-plates for this study as the nutrient cross-feeding interactions are well observed when microbes are isolated on conventional agar plates  following the manufacturer’s protocol. We used the E.Z.N.A Stool DNA Kit  to extract microbial DNA directly from stool samples following the manufacturer’s protocol. Extracted DNA was sequenced on an Illumina MiSeq platform to profile 16S rRNA V4 amplicons using 515F and 806R [515F-GTGCCAGCMGCCGCGGTAA and 806R-GGACTACHVGGGTWTCTAAT] primers with appropriate barcodes . We used Qiime 2 v2019.10  to proceWe observed that following incubation and media screening, the SSC structure revealed a simpler subset of the pre-SSC microbial community. We observed that the SSC members were representative of the parent community both at the phyla level as well as the genera level. These compositions were also reproducible in the replicated samples . We beliPseudomonas  and Micrococcaceae (0.14 ± 0.02) were the most dominant bacterial genera. For the soil SSC structure, there was a dominance of Bacillus (0.76 ± 0.05) followed by Enterobacteriaceae (0.16 ± 0.05) and Paenibacillus (0.01 ± 0.003). The common genera between pre-SSC and SSC structures included Streptomyces, Dehalococcoidia, Chloroflexi KD4-96, Tumebacillus, Bacillus, Pantoea, Enterobacteriaceae, Pseudomonas, and Paenibacillus , followed by Clostridium sensu stricto 1 (0.02 ± 0.01) and Streptococcus (0.01 ± 0.002)  of the complex fecal community . At the g others . The fec± 0.002) .Obs, Shannon index: H = 9.46, p = 0.02; Faith PD index: H = 9.46, p = 0.02; observed OTUs: H = 9.7, p = 0.02; In the preliminary study for our proposed model, we demonstrated a significant reduction in the complexity of the SSC as compared to the original community. We used the Kruskal-Wallis statistical analyses and showed statistical differences in the bacterial α-diversity between the SSCs and the original communities   and The Beyond taxonomic identity that was provided by 16S amplicon sequences, we assigned gene functional potentials to the MAGs using numerous databases. We recovered 27 highly resolved MAGs from carbon-based SSC treatment from the soil samples. We also recovered 37 MAGs from carbon-based treatment appended with Polyethylene Glycol. On the other hand, we recovered only two and eight MAGs from the more nutrient-limited, nitrogen-based SSC treatment for both the fecal and soil samples, respectively . We usedComparing the Pre-SSC and SSC microbial populations, we showed that the SSC communities were a subset of the Pre-SSC communities in the level of phyla and genera. Furthermore, the possibility of elucidating the functional potential of the simplified community indicated that information about nutrient utilization can be deduced. This supported our goal in simplifying the complex communities from different systems  that would help toward easier understanding of both the structure and the function of the subset communities. In validating this approach, we utilized Petri plates as the environment in which different media could be designed and allowed only certain microbial communities to grow. The proposed framework simplified microbial community complexity as well as laid a foundation to apply the concept by conjugating with high-throughput plates and chemostats.® microplates are well-suited for this cause; coupling these microplates with different types of nutrient source utilization is useful to identify subsets of the initial complex community  technologies (Chemostats to be used as a tool to establish SSC communities . Chemostnologies . The goanologies . This coAs a final point, one should keep in mind that the targeted media approach in our SSC model would result in capturing microbial members that are highly competitive for space and nutrients. Careful planning of future studies, taking into consideration the biases and pitfalls of culture-based assays is necessary.The original contributions presented in the study are included in the article/SS conceptualized, performed the experiments, analyzed the data, and wrote the manuscript. KW and AK performed the experiments. QR analyzed the data. BF, TR, and NR analyzed the data and reviewed the writing for the manuscript. SL conceptualized, supervised, analyzed the data, was responsible for resource acquisitions, and wrote the manuscript. All authors contributed to the article and approved the submitted version.The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.


In this work, soluble soybean polysaccharides (SSPS) were employed together with multifrequency ultrasound to fabricate zein nanocomposites which were conducive to enhancing the stability of high internal phase emulsions (HIPEs). Compared with non-ultrasonic treated zein colloidal particle samples (132.23 ± 0.85 nm), the zein nanoparticles samples induced by dual-frequency ultrasound exhibited a smaller particle size (114.54 ± 0.23 nm). Furthermore, the particle size of the zein composite nanoparticles (256.5 ± 4.81) remarkably increased with SPSS coating, consequently leading to larger fluorescence intensity together with lower zeta-potential (−21.90 ± 0.46 mv) and surface hydrophobicity (4992.15 ± 37.28). Meanwhile, zein-SSPS composite nanoparticles induced by DFU showed remarkably enhanced thermal stability. Fourier transform infrared (FTIR) spectroscopy and Circular dichroism (CD) spectroscopy were also used to characterize zein-SSPS composite nanoparticles. The results confirmed that DFU combined with SSPS treatment significantly increased β-sheets (from 12.60% ± 0.25 b to 21.53% ± 0.37 c) and reduced α-helix content (34.83% ± 0.71 b to 23.86% ± 0.66 a) remarkably. Notably, HIPEs prepared from zein-SSPS nanocomposites induced by dual-frequency simultaneous ultrasound (DFU) at 40/60 kHz showed better storage stability. HIPEs stabilized by DFU induced zein-SSPS nanoparticles exhibited higher storage modulus (G′) and loss modulus (G″), leading to lower fluidity, together with better stability contributing to the water-binding capacity and three-dimensional (3D) network structure of the HIPEs emulsion. The findings of this study indicate that this method can be utilized and integrated to further extend the application of zein and SSPS and explore HIPEs. Pickering emulsions are stabilized by solid particles, which retain the basic properties of conventional emulsions stabilized by surfactants. In particular, the solid particles adsorb onto the oil-water interface of the emulsions, which endows these emulsions with excellent interfacial properties, thereby acting to prevent droplet aggregation. In comparison with conventional emulsions, Pickering emulsions exhibit a thicker interface, higher surface loads, and better stability . In receHIPEs  are biphasic systems with minimal dispersed phase volume fractions exceeding 74% . Low molNowadays, a wide variety of bioderived polymers, such as proteins, carbohydrates, and fats, have been investigated to fabricate Pickering emulsions. Protein-based particles in Pickering emulsions’ stability were realized, possibly attributed to the many promising physicochemical properties and functional groups, which endows the protein particles with a strong ability to adsorb onto the oil-water interface. Protein particles can be derived from various biomass sources, including soy protein isolate , pea proIn recent years, many attempts have been made to explore the synergistic effects of zein and other biological substances on the stability of emulsions, such as polyphenols , proteinMany auxiliary methods have been used to assist in the preparation of stabilizers for Pickering emulsions, including microfluidics , chemicaHence, the effects of different multimodel frequency ultrasound treatments on the preparation and properties of the zein-SSPS complex were investigated in this study. Furthermore, the zein-SSPS complex was used to prepare a HIPE Pickering emulsion, and properties of the HIPE Pickering emulsion were studied subsequently.Therefore, the main objective of this work was to explore the promising potential of nanoparticles fabricated from zein and SSPS in food-grade Pickering emulsion stabilization. First, zein and SSPS dispersions were subjected to either intact or thermal treatments. The effects of DFU and SSPS treatments on the interfacial properties of zein particles were then investigated. Furthermore, the potential application of these nanoparticles in Pickering stabilization was monitored and compared with that of zein particles subjected to similar treatments.Storage stability is an important indicator for judging the quality of the emulsion. As shown in The size of the colloidal particles affects the stability of the suspension and the emulsion formed by the colloidal particles . As showp > 0.05) effect on the zeta-potential of the zein colloidal particle. It could be concluded that the surface charge of the zein colloidal particle was not changed upon DFU treatment, even though this treatment significantly decreased the particle size of the zein colloidal particle. Furthermore, DFU treatment decreased the PDI of the zein colloidal particle from 17.47% to 11.30%, indicating that the complex became more uniform owing to ultrasonic cavitation.The zeta-potential of native zein colloidal particles was found to be positively charged with +18.7 mV and became highly negative (−21.90 mV) after zein particles were coated with soluble soybean polysaccharide. Similar results were also observed in other studies, which confirmed that soluble soybean polysaccharide was successfully coated on the surface of zein nanoparticles by electrostatic interactions ,32. HoweAtomic force microscopy (AFM) provides an alternative to image and manipulate single biological macromolecules with high resolution . Figure The intrinsic fluorescence property is usually used to evaluate the interaction between proteins and polysaccharides, which is mainly contributed by aromatic amino acids such as tryptophan and tyrosine. The fluorescence emission spectroscopy of the samples was evaluated at the excitation wavelength and emission wavelength 280 nm and 290–450 nm, respectively. As shown in −1, caused by the stretching vibration of N–H [−1, N–H stretching) position, revealing that DFU could not destroy hydrogen bond of zein. For the samples of zein coated with SSPS under ultrasonication, the hydrogen bond positions shifted from 3310 cm−1 to 3410 cm−1, indicating that zein and SSPS interacted with each other by hydrogen bonds, facilitating the formation of new complex. In addition, amide II band  positions shifted from 1540 cm−1 to 1526 cm−1 and 1530 cm−1, respectively. These results indicated that the electrostatic interactions between zein and SSPS treated with DFU. Furthermore, 1700–1600 cm−1 is the peak position of the amide I band and the peak position of the α-helix is 1650–1660 cm−1. After zein was coated with SSPS under ultrasonication, the peak position shifted from 1658 cm−1 to 1680 cm−1, indicating that the addition of SSPS changed the secondary structure of zein. Moreover, after adding SSPS to the zein suspension, a new peak appeared at 1080 cm−1, which might be attributed to the combination of zein and SSPS leading to the formation of a stable complex.FTIR is a common way to analyze the secondary structure of organic matter. As shown in n of N–H . CompareCD spectroscopy is a technical method to used evaluate protein conformation in dilute solutions . As showLong-term heat treatment induced protein aggregation. As the heating time and temperature increased, the larger colloidal particles formed . As showRheological properties are of great significance to the stability of the emulsions. The strength of the emulsion interface film can be reflected by the interface modulus (G′ and G″) and result in the stability of the emulsion. Compact interface film and great mechanical strength of emulsions could decrease the probability of collision, which is necessary to prevent the accumulation of oil droplets, thereby stabilizing the emulsion. As shown in Confocal Laser Scanning Microscopy (CLSM) is usually used to observe the distribution of oil droplets and proteins in the emulsion. 2 can reflect the degree of freedom of moisture in emulsions, and the change of T2 characterizes the distribution and mobility of various states of moisture in emulsions after heating treatment for different times, that is, the binding state and free movement of moisture in each state. Furthermore, the relaxation peak area percentage can estimate the relative content of hydrogen protons, thereby reflecting the content of various states of water groups, and its changes can characterize the changes in the content of various states of water molecules in emulsions after heating treatments for different times. As described in the precious reference, the distribution of the relaxation time T2 presented three peaks: 0–10, 10–100, and 100–1000 ms. According to the peak time and the percentage of the total area occupied by each peak, the three peaks were considered to correspond to the three components of water, namely bound water (T2b), non-flowing water (T21), and free water (T22) [2 of emulsion stabilized by zein treated with DFU combined SSPS  . As shower (T22) . Howeverned SSPS C did notThe HIPE Pickering emulsions were fabricated using zein and SSPS induced by DFU. The zein treated with DFU at 40/60 kHz contributed to great storage stability, following the ultrasonic frequency at 20/40/60 kHz. When treated with DFU, the size of the zein colloidal particles decreased significantly, and the fluorescence intensity and surface hydrophobicity increased; however, the zeta-potential did not exhibit any significant change. Based upon coating with SSPS, the particle size and fluorescence intensity of zein composites nanoparticles were obviously increased. Moreover, the zeta-potential and surface hydrophobicity were relatively decreased compared with colloidal particles treated with DFU. FTIR and CD spectroscopy were further used to characterize the secondary structure of zein, revealing that DFU did not change the secondary structure unless zein was coated with SSPS. Furthermore, the thermal stability of zein colloidal particles was obviously improved after DFU treatment and coating with SSPS. The rheological properties of the HIPE Pickering emulsions stabilized by zein-SSPS composite nanoparticles induced by DFU were improved. By means of LF-NMR analysis, it was proved that the water-binding capacity of zein colloidal particles was improved upon coating with SSPS. Using CLSM, the formation of a three-dimensional network structure in emulsions stabilized by zein-SSPS composite nanoparticles was confirmed, resulting in an improvement in the stability of the Pickering emulsion. Thus, this study reveals that DFU and SSPS treatment can be employed to design and fabricate high stability HIPE Pickering emulsions in the food industry.Zein (protein content of 90%) was purchased from Sigma-Aldrich, Steinheim, Germany. Soluble soybean polysaccharide (SSPS) was provided by Henan Wan Bang Industrial Co., Ltd. . Soybean oil was produced by Yihai Kerry Arawana Holdings Co., Ltd. and purchased from a local supermarket . Other reagents used were of analytical grade and were purchased from Sinopharm Chemical Reagent Co., Ltd. .w/v) were kept in the valve bags and treated with three different frequency models: single-frequency ultrasound (SFU) with frequency of 20, 40, 60 kHz, dual-frequency simultaneous ultrasound (DFU) with frequency of 20/40, 20/60, and 40/60 kHz, and multifrequency simultaneous ultrasound (MFU) with frequency of 20/28/40 kHz. The ultrasound time was 40 min and the pulsed on/off time was 10 s/3 s. The temperature of 25 ± 2 °C was maintained by placing the samples in a thermostatic water bath. After ultrasonication, the samples were dropped into 3 times volumes of SSPS solution a zein/ssps ratio of 1:0.4 (w/w). A magnetic stirrer  was used to ensure the mixer was fully dispersed. As control, native zein and zein treated with DFU was dropped 3 times into water under magnetic stirring The resulting suspension was rotationally steamed in a water bath at 45 °C to remove some of the water and ethanol so that colloidal suspension with zein concentration of 3% (w/v) was obtained. The colloidal solids and emulsions prepared with native zein were marked as native zein in the figures, the colloidal solids and emulsions prepared with zein treated with DFU were marked as DFU, and the colloidal solids and emulsions prepared with zein treated with DFU combined with SSPS were marked as DFU+SSPS. Finally, part of the obtained composite colloidal particle solution was stored in 4 °C refrigerators, and the other part was freeze-dried for further use.The ultrasound equipment with different model frequencies was developed by a research team at Jiangsu University and manufactured by a company named Meibo Biotechnology Co. . The instrument is equipped with three frequency generators  that can work sequentially or simultaneously. The maximum output power of the generators is 300 W and the maximum capacity of this instrument is 3L. Samples with zein concentration of 3% (v/v). Briefly, 7.5 mL of soybean oil was added to 2.5 mL of colloidal particle suspension in a sample vial with a maximum capacity of 15 mL. Then, the mixtures were sheared using a digital display high-speed dispersive homogenizer  at 10,000 rpm for 2 min. The freshly prepared emulsions were stored in refrigerator at 4 °C.The HIPEs was prepared according to a previous report with slight modifications . The preParticle size (average diameter), PDI, and zeta-potential were determined according to the previous method with slight modifications . In brieThe emulsions were assessed with a AFM  according to  with sliThe measurements of fluorescence spectroscopy and surface hydrophobicity were performed on a fluorescence spectrophotometer  referring to the reported methods ,41. For −1 in 64 scans. The atmosphere was used as a baseline. Briefly, about 2 mg of samples were weighed, and an 200 mg of KBr was added under the infrared lamp. After grinding for 5 min, the tablet (with a diameter of 1.3 mm) was pressed, and a full-band (500–4000 cm−1) scan was performed using attenuated total reflection (ATR) cell . Subsequently, the spectra were collected using a software named Omnic.The FTIR spectra were obtained using a Fourier transform infrared spectroscopy  with the wavelength of 400–4000 cmFar-UV CD spectra between190 and 260 nm were monitored with a CD spectropolarimeter  as described in a previous study . The colThe thermal stability of zein-SSPS colloidal particles was evaluated according to a previous study  with somThe rheological properties of the HIPEs were investigated with a rheometer  according to a previous study . A plate2) was measured using a Carr-Purcell-Meiboom-Gill pulse sequence (CPMG), and the time corresponding to the peak value of each component in the relaxation diagram was taken as T2.Low-field nuclear magnetic resonance (LF-NMR) was used to analyze the water migration of the HIPEs during heat treatment using an LF-NMR analyzer  equipped with a Windows analysis platform and a multi exponential fitting analysis (T-invfit) program. The evaluative method was modified according to a previous study . Brieflyw/v) Nile Red and 10 mg/mL Fast Green for staining for 1 h. An appropriate amount of stained samples were applied to glass slides, covered with the coverslip, and placed upside down on the loading table for observation. The excitation wavelength was set at 488 nm and 633 nm, and the wavelength at 488 nm was used to detect Nile Red (stained oil) and the wavelength at 633 nm was used to detect Fast Green (stained protein). Photos taken by confocal microscope were processed using LAS AF Lite 2.3.5 .Confocal microscope  was used for CLSM analysis according to the method described by  with sliThe data were processed and reported as mean ± standard deviation. A one-way analysis of variance was performed at the probability level of 0.05 according to Duncan’s multiple range tests. Statistical analysis was carried out using SAS 8.0 software .


The CV results demonstrated a distinctive behavior of the supercapacitor, while the modified CoFe2O4-G (5 wt.%) electrode demonstrated a strong reduction in the Rct value (~94 Ω). The highest corrosion current density valves and corrosion rates were attained in the CoFe2O4-G (5 wt.%) composite materials as 5.53 and 0.20, respectively. The high conductivity of graphene that initiated the poor corrosion rate of the CoFe2O4-graphene composite materials could be accredited to the high conductivity and reactivity.A two-step process was applied to synthesize the cobalt ferrite-graphene composite materials in a one-pot hydrothermal reaction process. Graphene Oxide (GO) was synthesized by a modified Hummer’s method. The synthesized composite materials were characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and Fourier-transform infrared spectroscopy (FTIR). The XRD and FTIR results were in good agreement with the TGA/DTG observations. SEM and TEM disclosed the spherical shape of the nanoparticles in 4–10 nm. The optimized CoFe Nanostructured materials have caught the attention of the materials’ community over the past few decades. It was discovered that materials could be involved in multiple applications, specifically the ones related to batteries and sensors ,2. NanosCobalt ferrite is known for its magnetic properties, in addition to its outstanding stability, both structurally and chemically . BecauseRecently, the field of research in materials has involved graphene as a secret component in the fabrication of composites to produce them with outstanding properties for various applications, such as energy storage and sensors ,9. Graph2O4 composites had a great impact in terms of morphology and structural and electronical performance.In this work, a two-step process was used to synthesize the cobalt ferrite-graphene composite materials. The first step was to fabricate the graphene oxide by a modified Hummer’s method, and the second step was to combine GO as a raw material with cobalt and iron salt after proper mixing in a one-pot hydrothermal reaction process. The composite materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). The outcome of the results revealed that the effect of graphene oxide ratio in the CoFe3)2•6H2O) and iron (III) nitrate nonahydrate (Fe(NO3)3•9H2O) were dissolved in 100 mL of double-distilled water. The mixture was kept under continuous stirring for an hour. Afterwards, sodium hydroxide (NaOH) was added to the mixture above dropwise until the pH reached ~12, and stirring was continued for an hour. Finally, the solution was transferred into two hydrothermal vessels (with 100-mL capacity), and they were placed in the furnace at around 200 °C for 5 h. The vessels were taken out of the furnace after cooling down naturally. The resulting product appeared to be a dark-colored solution. The solution was washed several times for 10 min each by double-distilled water and ethanol using a centrifugation process at 3000 rpm to remove the byproducts. The resulting precipitate was finally dried at 80 °C in an electric oven overnight.The synthesis of the cobalt ferrite nanoparticles was accomplished through the hydrothermal technique. Typically, a ratio of 2:1 of Cobalt (II) nitrate hexahydrate . Twenty mL of 30% H2O2 were added into the mixture to remove the excess KMnO4 in the mixture. To remove the manganese salt in the mixture, 250 mL of 5% HCl (34 mL of HCl with 216 mL of H2O) was added into the mixture. After obtaining the final product of this chemical synthesis, graphene oxide needed to be purified continuously by double-distilled water until the pH reached to ~7. A one-hour sonication step was performed to separate the graphene oxide sheets, which produced excellent dispersed graphene oxide sheets. Finally, the graphene oxide sheets were dried overnight in an electric oven.Initially, graphite flakes were used to synthesize graphene oxide chemically by an optimized Hummer’s method . In the 2O4/graphene nanocomposites were synthesized by a one-pot hydrothermal route. Usually, 1% of GO was dispersed in 100 mL of double-distilled water and sonicated for an hour using UIP 1000hdT . In the meantime, 3.96 g of Co(NO3)2•6H2O and 1.98 g of Fe(NO3)3•9H2O were dissolved in 80 mL of double-distilled water under continuous stirring. The dispersed GO sheets were added slowly in the solution under stirring. The NaOH (10 M) solution was added dropwise until the pH reached to 12 in the above solution under continuous stirring for 5 h. The basic conditions uphold a decline in the defects present in the resulted nanocomposite materials, while acidic conditions lead to higher number of defects in the resultant materials [The CoFeaterials . The finGlassy carbon electrodes (GCE) were cleaned and polished very well to have a reflective surface first with a 0.1-µm polishing diamond solution and then a 0.05-µm polishing alumina solution to remove the absorbed species on the surface of the electrode. The working electrodes for the electrochemical investigations were prepared. To prepare an ink of the active materials, it was done by mixing active materials and binder (PVDF) in a ratio of 9:1 using a few drops of n-methyl 2-pyrrolidone (NMP) in a mortar. An appropriate amount of materials were placed on the surface of an electrode using a digital micropipette. The prepared electrode was placed in the oven at 80 °C overnight.To understand the quality, phase, and crystallinity of the synthesized materials, the X-ray diffraction technique was utilized. X-ray diffraction studies were carried out by Shimadzu PXRD-7000,  with Cu Kα (1.54 Å) as a radiation source. The samples were scanned from 10–80°.−1 and 200 scans . FTIR spectra were recorded in the range of 500–4000 cm−1.Fourier-transform infrared spectroscopy (FTIR) studies were carried out to understand the structural and bonding features of synthesized composite materials. FTIR spectra on the synthesized composited materials were collected on a Nicolet iS50 FTIR spectrometer using the KBr pellet technique with a spectral resolution of 4 cmThe thermal stability of the synthesized composite materials was characterized by Thermogravimetric Analysis (TGA). The TGA analysis was scrutinized using an SDT Q600 instrument , and the spectra were recorded from room temperature to 900 °C at a constant heating rate of 5 °C/min in a nitrogen atmosphere.Field emission scanning electron microscopy (FE-SEM), model JSM-7600F , was used to investigate the microstructures of the samples. In addition, the elemental compositions of the samples were checked through energy-dispersive X-ray analysis . Furthermore, transmission electron microscopy (TEM), model JEM-2100F , was utilized to understand the morphological information and size of the synthesized materials.The electrochemical measurements were carried out on a multi-channel electrochemical analyzer  with PBS solution as the electrolyte. A three-electrode cell system was immersed in PBS . The synthesized materials  were used as working electrodes, whereas Ag/AgCl and Pt wire were used as a reference and as counter-electrodes. Cyclic voltammograms (CVs) were recorded at different scan rates (10–100 mV/s) within a potential range of −1.1–0.1 (Vs. Ag/AgCl) for cobalt nanoparticles and composite materials. Electrochemical impedance spectroscopy (EIS) investigations were conducted with the frequency range of 0.01 Hz~1 MHz at an amplitude potential of 0.1 V. Potentiodynamic polarization (PD) was performed to investigate the corrosion stability of cobalt ferrite nanoparticles and cobalt ferrite/graphene nanocomposites with different graphene ratios  in a 3.5 wt.% NaCl solution, where the electrodes were immersed in the solution for 18 h.2O4. The peak positions and relative intensities match well with the standard XRD data for cubic spinel structures [2O4, which is in good agreement with the JCPDS card no. 01-1121 [−1. Six vibration bonds were observed in the spectrum at 552 cm−1, 647 cm−1, 1055 cm−1, 1407 cm−1, 1563 cm−1, and 2934 cm−1. The peaks at 552 cm−1 and 647 cm−1 had a cobalt ferrite spinel structure related to the stretching vibrations of metal oxide (Fe3+–O2−) bonds [−1 would indicate the vibration of COO-, either in symmetric or asymmetric bond groups [−1 would indicate the stretching vibration of C-O [−1 revealed the rebuilding of π-π conjugation of graphene sheets [ructures . The dif 01-1121 . One ind 01-1121 ,21,22,23 01-1121 . No othe−) bonds . The pead groups , while tn of C-O ,27. Howee sheets ,29.2O4 [2O4 .The mass loss of the nanocomposite samples with different graphene ratios  was found to be increased when it was compared with the mass loss of pure nanoparticles. Therefore, the increase in mass loss of the nanocomposites happened due to the existence of graphene in the composition of the nanocomposites. Moreover, this goes to the decomposition of the carboxylic that occurred from the graphene oxide, which resulted in the release of carbon dioxide . Due to 2O4 nanoparticles on graphene sheets. 2O4 nanoparticles. The studies exposed that the particles were spherical and in the range of 4–8 nm. 2O4 nanoparticles with average sizes ~4–8 nm. The agglomeration of the nanoparticles can be seen in the images of the TEM. It occurred in the nanocomposites, as it is shown in the images below. It happened due to the nature of the nanoparticles according to work of Montoya et al. [A high-resolution transmission electron microscopy investigation was executed to understand the distribution of decorated CoFea et al. . Moreovea et al. .2O4 nanoparticles and CoFe2O4-G (1 wt.%), CoFe2O4-G (3 wt.%), and CoFe2O4-G (5 wt.%) modified electrodes. The CV plots were recorded at a constant scan rate of 30 mV/s in the potential range of −1.0 to 0.0 V. It can be seen from the results that CV curve of CoFe2O4-G (5 wt.%) occupies the largest area in a rectangular shape as compared to CoFe2O4 nanoparticles, CoFe2O4-G (1 wt.%), and CoFe2O4-G (3 wt.%). The modified electrode with the higher graphene wt.% reveals the characteristic electrical double-layer (EDL) capacitive behavior [2O4-G (5 wt.%) [behavior . Moreove(5 wt.%) .ct). The Rct of CoFe2O4 nanoparticle-coated GCE electrodes demonstrated, comparatively, the largest semicircle (396 Ω), whereas the Rct valves of CoFe2O4-G (1 wt.%), CoFe2O4-G (3 wt.%), and CoFe2O4-G (5 wt.%) modified electrodes were recoded as 123 Ω, 111 Ω, and 94 Ω, respectively. The modified CoFe2O4-G (5 wt.%) electrode demonstrated a strong reduction in Rct value (~94 Ω) and a sharper line. However, a smaller semicircle in EIS plots discloses the lower electrical resistance of the synthesized material [2O4-G modified GCE electrodes proved their excellent electron transfer property and their status as excellent electronic conductivity materials [EIS measurements were carried out to understand the electrical conductivity and the effect of graphene-decorated cobalt ferrite nanoparticles. material . The dataterials . A notabaterials . This reaterials ,46. Ther2O4 nanoparticles and CoFe2O4-G (1 wt.%), CoFe2O4-G (3 wt.%), and CoFe2O4-G (5 wt.%) nanocomposites. The above-labeled samples were immersed in a 3.5 wt.% NaCl solution for 18 h prior to the corrosion experiment. A potential window of −1.2 V–−0.2 V was applied at the scan rate of 1 mV/s. Corrosion studies were recorded and are displayed in 2O4-G (5 wt.%) composite materials as 5.53 and 0.20, respectively. corr, Ecorr, βa, βc, Rp, and Rcorr, which were calculated by Tafel plots. The potentiodynamic polarization results showed that CoFe2O4 nanoparticles demonstrated higher corrosion resistance due to their lower icorr values as compared to CoFe2O4-G (1 wt.%), CoFe2O4-G (3 wt.%), and CoFe2O4-G (5 wt.%) composite materials [2O4-graphene composite materials could be accredited to the high conductivity and reactivity. 2O4 nanoparticles appeared with nominal cracks, while cobalt ferrite/graphene nanocomposites with different graphene ratios  demonstrated the deformations in the composite as a function of graphene wt.%. The image of composite materials with graphene 5 wt.% in the CoFe2O4 showed the highest number of deformations. The SEM morphological studies are in good agreement with the potentiodynamic polarization results  composite demonstrated a distinctive behavior of the supercapacitor, while the modified CoFe2O4-G (5 wt.%) electrode demonstrated a strong reduction in the Rct value (~94 Ω). The Rct of CoFe2O4 nanoparticle-coated GCE electrodes demonstrated a comparatively large semicircle (396 Ω). The highest corrosion current density valves and corrosion rates were attained in the CoFe2O4-G (5 wt.%) composite materials as 5.53 and 0.20, respectively. The high conductivity of graphene that initiated the poor corrosion rate of the CoFe2O4–graphene composite materials could be accredited to the high conductivity and reactivity.A one-pot hydrothermal reaction process was utilized to successfully synthesize composite materials with different ratios of GO. SEM and TEM disclosed the spherical shape of the nanoparticles in 4–10 nm. The CV results on CoFe


Graphene-based nanocomposites are largely explored for the development of sensing devices due to the excellent electrical and mechanical properties of graphene. These properties, in addition to its large specific surface area, make graphene attractive for a wide range of chemical functionalization and immobilization of (bio)molecules. Several techniques based on both top-down and bottom-up approaches are available for the fabrication of graphene fillers in pristine and functionalized forms. These fillers can be further modified to enhance their integration with polymeric matrices and substrates and to tailor the sensing efficiency of the overall nanocomposite material. In this review article, we summarize recent trends in the design and fabrication of graphene/polymer nanocomposites (GPNs) with sensing properties that can be successfully applied in environmental and human health monitoring. Functional GPNs with sensing ability towards gas molecules, humidity, and ultraviolet radiation can be generated using graphene nanosheets decorated with metallic or metal oxide nanoparticles. These nanocomposites were shown to be effective in the detection of ammonia, benzene/toluene gases, and water vapor in the environment. In addition, biological analytes with broad implications for human health, such as nucleic bases or viral genes, can also be detected using sensitive, graphene-based polymer nanocomposites. Here, the role of the biomolecules that are immobilized on the graphene nanomaterial as target for sensing is reviewed. Th. Th21]. 2O2) was exploited to obtain a sensitive biosensor with a detection limit of 0.6 μM for glucose. The performance of this type of sensor can be ascribed to the large surface area and the fast electron transfer of graphene and Pt nanoparticles. This sensor showed good reproducibility and long-term stability, with negligible response to other compounds such as ascorbic acid and uric acid. The GOD/Pt/FGS/chitosan-sensitive nanocomposite can be useful for both clinical and home-care devices for rapid monitoring of glucose.Nanocomposite films based on glucose oxidase (GOD), platinum (Pt), functional graphene sheets (FGS), and chitosan were developed for glucose sensing . The eleGlucose sensing was also performed with composite films made of graphene, chitosan and uric acid, which were deposited onto glassy carbon electrodes . A molecN-(trimethoxysilylpropyl) ethylenediamine triacetic acid (EDTA-silane). The selectivity was investigated by using dopamine and ascorbic acid. Experimental tests demonstrated that the sulfuric groups of Nafion and the carboxylic groups of EDTA-RG interfere with the diffusion of ascorbic acid, thus enabling the selective detection of dopamine.Sensitive films based on EDTA-modified reduced graphene (EDTA-RG) and Nafion were fabricated and tested as dopamine detectors . GraphenMore recently, biosensing has seen advances towards more complex structures that are able to enhance the overall sensitivity of the detecting surface. A sensing composite material was realized using fractal nanoplatinum with a cauliflower-like morphology, which was developed on a reduced graphene oxide paper . PlatinuRecent trends in the development of graphene-based polymer nanocomposites (GPNs) with sensing properties were examined, with emphasis on applications in the fields of environmental and human health monitoring. In this review article, the methods that are traditionally used to synthetize and functionalize the graphene filler were included. These methods can be classified into two main categories, namely bottom-up and top-down approaches, and allow for the production of graphene sheets with various dimensions  and purity. Next, we discussed methods for the fabrication of GPNs, taking into account the role that the interactions between the polymer and the graphene nanomaterial have on the composite’s final properties. Typically, in situ polymerization is a good choice for obtaining homogeneous nanocomposites by creating a polymer network directly around the fillers, thus avoiding energetic methods—which might cause damage to the conductive capability of graphene—for dispersion. For environmental monitoring, graphene/polymer nanocomposites with metallic or metal oxide nanoparticles immobilized on the graphene filler possess the ability to detect harmful gas molecules  or measure humidity. Graphene-based nanocomposites with UV-sensing properties have recently been developed by immobilizing DNA strands on graphene: the proof-of-principle experiments were successful, opening the way to their potential use as lightweight, sensitive components of radiation monitoring systems on Earth or in space. The application of specific graphene/polymer nanocomposites for examining human health parameters was also discussed. Integration of (bio)molecules with the graphene surface was reviewed, and their role was explained, taking into consideration the interactions with the material and how they affect the overall sensing properties of the nanocomposites. One of their most important characteristics is the loading capacity of nanocomposites towards the biological analyte acting as the sensing element. The use of fractal-type nanoparticles with high surface roughness represents a great advantage for the immobilization of large quantities of enzymes or RNA for biosensing purposes.


High accuracy measurement of mechanical strain is critical and broadly practiced in several application areas including structural health monitoring, industrial process control, manufacturing, avionics and the automotive industry, to name a few. Strain sensors, otherwise known as strain gauges, are fueled by various nanomaterials, among which graphene has attracted great interest in recent years, due to its unique electro-mechanical characteristics. Graphene shows not only exceptional physical properties but also has remarkable mechanical properties, such as piezoresistivity, which makes it a perfect candidate for strain sensing applications. In the present review, we provide an in-depth overview of the latest studies focusing on graphene and its strain sensing mechanism along with various applications. We start by providing a description of the fundamental properties, synthesis techniques and characterization methods of graphene, and then build forward to the discussion of numerous types of graphene-based strain sensors with side-by-side tabular comparison in terms of figures-of-merit, including strain range and sensitivity, otherwise referred to as the gauge factor. We demonstrate the material synthesis, device fabrication and integration challenges for researchers to achieve both wide strain range and high sensitivity in graphene-based strain sensors. Last of all, several applications of graphene-based strain sensors for different purposes are described. All in all, the evolutionary process of graphene-based strain sensors in recent years, as well as the upcoming challenges and future directions for emerging studies are highlighted. With the advent of the internet-of-things (IoT), smart, ubiquitous, pervasive sensing is rapidly gaining importance for providing reliable information at unprecedented sensitivity to enable new applications in consumer electronics ,2,3, heaTypically, sensors based on piezoresistivity rely on transducing external mechanical loading into resistance change, which usually follows a linear relationship . CommonlTo date, various materials have been investigated for use as strain sensing elements, in an effort to optimize the response of the strain sensor with respect to the attributes mentioned above. Realizing a strain sensor operating at a wide strain range with good sensitivity has been an especially huge challenge. To overcome the problem of low sensitivity, different approaches have been proposed including doping, defect deformation and exploiting different piezoresistive sensing mechanisms along with sensing materials ,19,20,21Among the most typical strain sensing materials are metals. However, strain sensors based on metals, otherwise known as metal-foil gauges, primarily rely on resistance change due to dimensional change of electrically conducting thin lines typically structured in the form of a serpentine, and as such the gauge factors are typically limited to single digits ,22. SeveAs an alternative to some of these conventional materials like metals, metal oxides, semiconductors and ceramics which suffer either from intrinsic hardness, brittleness, low strain range or poor scalability, in recent years, carbon-based materials have been on the forefront of “sensor research”, including strain sensing ,23,24,25To date, there have been multiple studies which have reported graphene-based strain sensors built on a variety of substrates; however, the fabricated strain sensors display a wide range of gauge factors ,34,35,36Along these lines, in this work we critically survey the current state-of-the-art in graphene as a strain sensing material along with actual sensor demonstrations and relevant applications. To begin, we first discuss the fundamentals on graphene including electrical and mechanical properties, and the piezoresistive effect in graphene ,27. Then2 hybridized carbon atoms. After its exploration in 2004, graphene it has drawn a lot of attention due to its excellent electrical, mechanical, optical and magnetic properties . T. T72]. TDespite its superior electrical and mechanical properties, the challenges in obtaining pristine graphene limit the widespread use of this 2D material in device applications. In an effort to address this problem, numerous techniques were investigated to obtain thin graphitic films and few layer graphene (FLG). Initial demonstrations primarily through mechanical exfoliation followed by transfer of graphene onto silicon substrates, marked a major breakthrough in graphene research . Even thTherefore, research on obtaining high-quality graphene along with its integration to different substrates which often requires transfer methods, has received serious effort especially over the past two decades. The method with which graphene is obtained directly affects the quality of graphene including its electrical, mechanical and piezoresistive properties. Different methods which are classified as bottom-up and top-down processes have been utilized in order to obtain high-quality graphene. The most commonly used methods are: chemical exfoliation , chemicaThis approach, which is classified as a bottom-up method, can be used to produce mono- or multiple-layers of graphene on a catalytic transition metal substrate. Since its first demonstration in 2006, CVD-based synthesis of few-layer graphene (FLG) witnessed continuous progress transitioning into an established method today for providing scalable and reliable production of high quality, large-area graphene ,80,81,824) source takes place on the surface of Cu substrate to form the graphene lattice. Graphene islands, which show different lattice orientations in atomic scales enlarge and grow together on the substrate  sou3) and complexities during transfer of graphene to receiving substrates . All in all, this makes fabrication of sensors (including strain gauges) and electronic devices in general, difficult on CVD graphene.CVD technique provides many opportunities such as low cost, easy film transferring, employment of various transition metals as catalysts, and the ability to produce large-area films with high uniformity and low defects, which makes it a promising route to obtain graphene . Despite2/V·s at room temperature and the approach is low-cost with minimum investment on experimental setups ..99]. Altl setups . Additiops . . 168]. SGraphene nanopapers which are three-dimensional, highly stretchable structures composed of crumpled graphene and nanocellulose are also employed in strain sensing applications. As such, stretchable nanopapers were made by vacuum filtering of free-standing flexible nanopapers, and their 3D microporous structure allows for their effective embedment in elastomer matrix. Stretchability was effectively increased from 6% for flexible nanopaper to 100% for stretchy nanopaper. Stretchy nanopaper-based high-strain sensors had a gauge factor of 7.1 at 100% strain, which is more than ten times greater than stretchable CNT and AgNW sensors . In anotStrain sensors have been utilized in a broad range of applications. In the following parts, two major application areas of graphene-based strain sensors, namely, wearable devices and physical sensors  are discussed.One major area where strain sensors are used vastly as different applications is wearable electronics. For healthcare applications, wearable sensors have been attached to gloves, organs, and skins to observe physiological activities of the body such as monitoring heart rate, wrist pulse, motion, blood pressure, intraocular pressure, vibration of vocal cords, movement of joints and other health-related situations ,184,185.In another study, a device for detecting and identifying sound-signals with the help of strain sensing mechanism of the graphene woven fabric (GWF)-based sensor on PDMS was investigated . The senA single strain gauge is typically capable of measuring the strain that has the same direction with the position of the gauge . That isAlong with wearability, applications deeming stretchability and flexibility are yet another area where the use of graphene as a strain sensing element offers advantages. For instance, a highly sensitive graphene embedded viscoelastic polymer nanocomposite was reported as a flexible strain sensor, which could measure very small pressures of pulse, blood pressure and even the minute mechanical loading due to walking of small insects. In this work, the mobility of graphene fillers was enhanced by a lightly cross-linked polymer matrix providing high viscosity. The resulting nanocomposite exhibited a remarkable change in resistance as it was subjected to an applied strain. It yielded a high gauge factor of more than 500, and the temporal relaxation of electric resistance upon deformation .Measuring and monitoring the acceleration is vital in various cases such as monitoring activity in biomedical and healthcare applications ,191, staSo far, several studies have reported piezoresistive-based accelerometers employing graphene ,202,203.Likewise, graphene-based suspended, planar, spongy and double layer microstructures have been produced as highly flexible and sensitive pressure sensors. Zhu et al.  fabricat2 layer where the membrane was able to deflect due to pressure differences in the sealed cavity and in the pressure chamber. A superior sensitivity in pressure sensing was observed compared to silicon and CNT-based pressure sensors. The maximum GF of the piezoresistive sensor was 4.33 with an average value of 2.92 which, unlike silicon piezoresistive sensors, was unaffected by dopant concentration or crystallographic orientation (Another suspended graphene membrane was fabricated on rectangular and circular cavities (with diameter of 24 μm and depth of 1.5 μm) etched into SiOentation c 64]..2 layer Strain sensors have rapidly developed in the modern era due to the wide range of applications that they find use in, and graphene is a compelling candidate in this field. Graphene stands out as a suitable sensor material due to its remarkable physical, mechanical, and electrical properties as well as high flexibility and stretchability. Existing methods to synthesize, pattern and transfer graphene have resulted in different types of graphene with diverse electrical and mechanical properties that can be helpful towards development of ultra-sensitive and stretchable strain sensors, provided that the said properties can be accurately controlled with excellent run-to-run repeatability.It is due to the shortcomings of accurate process control in graphene synthesis methods  and material to device integration challenges that cause graphene-based strain sensors to have a wide range of gauge factors which also reflect in the scattered gauge factor values reported in published literature. Essentially, using different types of graphene on different kinds of substrates calls for different fabrication schemes, and results in strain gauges with varying performance and form factors. Although huge progress has been made in developing and studying graphene-based strain sensors in recent years, it is clear that further research is necessary. Future efforts should focus on minimizing the challenges in synthesis techniques and improving transfer/integration approaches, as well as exploring the underlying mechanisms to improve device sensitivity and stability.