Staphylococcus aureus (MSSA) PJIs.Staphylococci and streptococci are the most frequent pathogens isolated from prosthetic joint infections (PJIs). The aim of this study was to analyze the outcome of streptococcal and methicillin-susceptible All monomicrobial streptococcal and MSSA PJIs managed in a French Referral Center (2010–2017) were sampled from the prospective PJIs cohort study. The primary outcome of interest was the cumulative reinfection-free survival at a 2-year follow-up.P = .012), but differed according to the strategy. After exchange arthroplasty, no outcome differences were observed ; after debridement, antibiotics and implant retention (DAIR), the reinfection-free survival rate was higher for patients with streptococcal PJI . For patients managed with prolonged suppressive antibiotic therapy (SAT) alone, those with streptococcal PJIs had a 100% infection-free survival .Two hundred and nine patients with 91 streptococcal and 132 staphylococcal infections were analyzed. Patients with streptococcal PJI were older, and infection was more frequently hematogenous. Reinfection-free survival rates at 2-years after all treatment strategies were higher for patients with streptococcal PJI (91% vs 81%; Reinfection-free survival after DAIR and SAT was better for patients with streptococcal than those with MSSA PJIs. No difference was observed after prosthesis exchange.The online version contains supplementary material available at 10.1186/s12879-022-07532-x. Staphylococcus aureus being the most frequent species, responsible for 19–29% of PJIs, and streptococci, being the second most frequent microorganism with Gram negative bacilli, found in 9–16% of PJIs , and then compared with the non-parametric Mann–Whitney U-test. The reinfection-free–survival rate was analyzed using the Kaplan–Meier method and expressed as the mean ± standard deviation. The Mantel–Cox log-rank test was used to calculate survival-distribution difference. A P value < 0.05 was considered significant. All statistical tests were computed with SPSS.20 software.The primary outcome of interest was the cumulative reinfection-free survival at a 2-year follow-up. Qualitative variables were expressed as number (%) and compared using χWritten informed consent was obtained from all patients and the cohort was approved by the Ethics Committee of Île-de-France (N° PP 14–034).During the 7.5-year study period, 988 PJIs in 918 patients were managed in our center. Two hundred and nine patients, 86 with 91 streptococcal and 123 with 132 MSSA PJIs, for a total of 223 PJIs, were included . Patients with MSSA experienced more prior PJI treatment failures in another center .Patients with streptococcal PJI were significantly older than those with MSSA PJI, had cancer more frequently within the last 5 years and their PJIs were often hematogenously acquired , Streptococcus dysgalactiae (20%) and Streptococcus mitis/oralis (16%).Streptococcal species isolated from these 86 patients’ PJIs are detailed in Additional file Details on treatment strategies and antibiotic therapy are given in Table P < 0.0001). Furthermore, 8 patients with streptococcal and 9 with MSSA acute PJIs of a loosened prosthesis or hematogenous infection lasting > 2 weeks underwent exchange arthroplasty: 16 underwent one-stage and one MSSA PJI-patient underwent two-stage exchange arthroplasty. All but 2, received preoperative antibiotic therapy for a median of 7 [One-stage exchange arthroplasty was by far the most frequent operation. Among these 124 patients, prior treatment failure was significantly more frequent in patients with MSSA PJIs .P = 0.001). None of the SAT-patients underwent surgery for their ongoing PJI. All streptococcal PJI-patients received first-line antibiotic therapy with amoxicillin, intravenously and then orally, except for 5 patients who had oral amoxicillin right away. All SAT-patients with MSSA PJIs received intravenous cefazolin or oxacillin, followed by oral cloxacillin (n = 8), clindamycin (n = 2) or cefalexin (n = 2).SAT was prescribed significantly more often to treat streptococcal PJI patients  and 5 new infections.However, after DAIR, reinfection-free survival was higher for patients with streptococcal PJIs Fig. C. Three P = 1.000).For patients with streptococcal PJIs treated with prosthesis exchange or DAIR, no outcome differences were observed between those who were on rifampicin or not (2 relapses among 30 treated with combination therapy vs 3 among 35 given beta-lactam monotherapy)  patients with MSSA PJIs relapsed: 1 following treatment discontinuation after 1 year of cloxacillin relayed by cephalexin and four others while taking oral cloxacillin.Among patients treated with SAT, those with streptococcal PJIs Fig. D had betMains results are summarized in an overview figure Fig. .Fig. 4ReThe results of our large observational cohort study on outcomes and characteristics of streptococcal and MSSA PJIs showed that patients with streptococcal PJIs were older, more frequently had cancer, and their hematogenous infection rate was higher. These findings are consistent with previous observations , 22. PriOur analysis showed also that streptococcal PJIs had better outcomes than MSSA for all therapeutic strategies combined, with differences observed according to the medical–surgical strategy. Notably, no difference was observed after prosthesis exchange. Although outcomes were better in patients treated with DAIR for their streptococcal PJIs, the difference was not significant, probably because the study lacked power. The median time to DAIR was significantly shorter and the rate of mobile components exchange was higher in patients with streptococcal PJI, but the difference wasn’t significant. These results could partly explain the better outcome of streptococcal PJI after DAIR.S. aureus was previously identified as a risk factor for DAIR failure [ failure , 35, 36. failure . As Wout failure  emphasizThese crucial points of the pathophysiology of foreign-body infection could also explain the good and similar outcomes of our patients with streptococcal or MSSA PJIs treated with prosthesis exchange. The strength and originality of our study was to include many patients treated with exchange arthroplasty, especially one-stage exchanges, which had not been addressed previously. Exchange arthroplasty removes the entire foreign body containing the bacteria embedded in biofilm. In our experience, one-stage exchange arthroplasty has a very low relapse rate (≤ 5%) in chronic prosthetic hip infections , even MSAnother important and unresolved question is the benefit of rifampicin against streptococcal PJIs. During the first 3 years of this cohort, patients received combination therapy with rifampicin before being stopped because of the absence of data supporting its use and the occurrence of rifampicin-induced adverse events in one-third of patients (data not shown) , 39. NotStreptococcus spp. and high bioavailability yielded very good outcomes with good tolerance. No relapses occurred and only one patient stopped amoxicillin because of Clostridioides difficile colitis. Although this strategy avoids surgery and achieves good infection control, it should be reserved for patients at high surgical risk or those with frequent, recurrent infections. On the other hand, five MSSA PJI patients relapsed, four while taking oral cloxacillin. Lower S. aureus antibiotic susceptibility and cloxacillin bioavailability could explain the difference observed. American guidelines recommend cephalexin, dicloxacillin or clindamycin for SAT [Finally, streptococcal PJI patients treated with SAT had better outcomes than those with MSSA infections. This therapeutic option was prescribed more frequently to streptococcal PJI patients, especially those very old and frail, or with relapsing PJIs. These patients did not undergo surgery. Amoxicillin having excellent activity against  for SAT .Our study has several limitations. First, it was a monocenter study conducted in a highly specialized referral center for treatment of complex BJI, thereby limiting the generalizability of our findings and carrying a risk for selection bias. For example, more MSSA PJI-patients had prior management of their PJI before admission to our center. This may have had an impact on our results. Moreover, as already mentioned in the methodology section, there were different antibiotic treatment protocols during the study period. The number of DAIR- or SAT-treated patients was small. Unlike the MSSA group, several streptococcal species were included, resulting in heterogeneity of the population.S. aureus or Streptococcus spp., is one of several important factors guiding medico-surgical strategy decision, in addition to infection duration, underlying comorbidities, functional state and surgical procedure complexity.In conclusion, we described a large cohort study analyzing streptococcal and MSSA PJIs. DAIR obtained a better reinfection-free survival rate for patients with streptococcal than MSSA PJIs, making it a valid therapeutic option for acute streptococcal PJI, if initiated very early. Outcomes after one-stage exchange arthroplasty were comparable with low relapse rates, highlighting the crucial role of this treatment strategy for chronic PJIs, even after DAIR failure. SAT is an alternative option for very old and frail patients at high surgical risk who develop streptococcal PJIs. The microorganism type, in this case Additional file 1: Table S1. Streptococcal Species Isolated from 86 Patients’ PJIs.


Wearable sensors and invasive devices have been studied extensively in recent years as the demand for real-time human healthcare applications and seamless human–machine interaction has risen exponentially. An explosion in sensor research throughout the globe has been ignited by the unique features such as thermal, electrical, and mechanical properties of graphene. This includes wearable sensors and implants, which can detect a wide range of data, including body temperature, pulse oxygenation, blood pressure, glucose, and the other analytes present in sweat. Graphene-based sensors for real-time human health monitoring are also being developed. This review is a comprehensive discussion about the properties of graphene, routes to its synthesis, derivatives of graphene, etc. Moreover, the basic features of a biosensor along with the chemistry of sweat are also discussed in detail. The review mainly focusses on the graphene and its derivative-based wearable sensors for the detection of analytes in sweat. Graphene-based sensors for health monitoring will be examined and explained in this study as an overview of the most current innovations in sensor designs, sensing processes, technological advancements, sensor system components, and potential hurdles. The future holds great opportunities for the development of efficient and advanced graphene-based sensors for the detection of analytes in sweat. The healthcare system is facing rising prices and difficulties as the world population grows fast and human life expectancy rises dramatically ,2, necesSensors, especially wearable and implanted sensors, are key components of health monitoring systems and the interface to the human body because they can detect and analyse numerous analytes or signals with high sensitivity and specificity . StandarWearable and implanted sensors for health monitoring are being developed, and graphene is a desirable 2D material because of its amazing multimodal features, i.e., ultrahigh carrier mobility ,17, exceThe necessity and significance of monitoring systems and the advantages of graphene in sensing devices and its non-toxicity are explored. In the next part, we examine the most recent sensors based on graphene, covering non-invasive and invasive condition monitoring, as well as their distinctive architectures, detecting methodology, and pace of innovation. Various sensor system components are also shown. Graphene-based sensing systems are also examined in terms of their potential drawbacks and advantages in the future.To be effectively used in agency, graphene must be manufactured at a price comparable to that of currently available materials. It is a significant problem to create production methods that are cost efficient, highly dependable, and scalable, as well as that produce high yields and quality products ,37. As aThe top-down approach is defined as a tactic that concentrates on the attack of powdered raw graphite. Eventually, the attack will split its layers and create graphene sheets. Chemical synthesis and mechanical or chemical exfoliation, for example, are classified as top-down strategies . Some of2O4) and nitrogen dioxide (NO2)  solution to compare the redox properties of pristine LIG with PtNPs and acetic acid-treated LIG with PtNPs according to electrodeposition cycles, with a scan rate of 50 mV/s. Hyosang Yoon et al.  recommen2O2 (hydrogen peroxide), may be quantified using an electrochemical sensitive membrane based on rGO-TEPA/PB (rGO-tetraethylenepentaamine)-modified paper electrode layer covered with Prussian blue. As a consequence, this microfluidic electrochemical biosensor based on 3D paper may be used to sense glucose quantitatively. For a detection limit of 25 mM, the proposed biosensor may be utilised to measure quantitative glucose across an ideal 0.1–25 mM linear range. Finally, a 3D paper-based microfluidic electrochemical biosensor was used to detect glucose levels in sweat and blood, and the findings were extremely comparable to those acquired with Roche’s blood glucose metre. Furthermore, the anticipated paper-based 3D electrochemical device showed outstanding anti-interference properties, stability and repeatability, suggesting that it has a lot of potential for monitoring glucose in complex biological fluids. Preparation of a three-dimensional microfluidic electrochemical biosensor based on paper is shown in Photolithography and screen-printing methods were employed by Liangli Cao et al.  to build2O2, GOx needs a cofactor that facilitates the reaction. The redox potential measures the produced H2O2 amperometrically on the working electrode’s surface, allowing the current to be linked to the glucose concentration. O2, electrons, and an H+ ion will be formed from the H2O2. To prevent the sensor from delaminating from the skin, a waterproof band is placed beneath the flexible sensor to help in sweat collection.When it comes to non-invasive sweat glucose monitoring, the patch-based electrochemical biosensor developed by Xuan et al.  is the b−1 while fasting, hyperglycaemia develops [−1 glucose in blood equates to 0.3 mM glucose in sweat. Because of this, it is predicted that the glucose level may be detected using a sweat sensor for diagnosis of diabetes. As a result, the quantity of glucose in sweat may be used to determine a person’s health. A sensor that does not adapt to the skin and does not have adequate mechanical stability would deform due to the skin’s mobility, making it impossible to reliably monitor pH and glucose levels in sweat [This century’s pandemic of diabetes is not only impacting adults but also children, regardless of gender or age, and it has become one of the main reasons of mortality among the other noncommunicable diseases (NCDs) . For exadevelops . Detectidevelops  convinciin sweat . As key in sweat . For exain sweat . As a biin sweat . There ain sweat ,492. As in sweat . The fooin sweat . As a rein sweat . The hig2O2). An electrochemical reaction restores the oxygen concentration by oxidising it, and a proportionate response is obtained [There are several applications for lactate concentrations outside clinical diagnosis in sports medicine, shock/trauma, and the food business. As an indicator of food quality and freshness, lactate may be utilised in the food business, while in sports medicine, lactate levels are used to assess an athlete’s physical fitness . Lactateobtained . LOx mayobtained . In the obtained . The eleobtained . ET’s frobtained . During obtained . The conobtained . Biosensobtained . Anti-inobtained . Lineariobtained . Figure Low volume sensing platforms were developed by Kai-Chun Lin et al.  using grSchiff base ligand was used to concurrently reduce and alter graphene oxide (GO) utilising a one-step technique to create functionalized reduced graphene oxide, as reported in Bravo et al. . The lacAn electrochemical biosensor for lactate measurement has been devised and manufactured by Raquel Sainz et al. . The enz+ and Na+) or glucose molecule alterations in sweat during exercise. According to clinical investigations, the amount of uric acid in sweat is strongly linked to the quantity of uric acid in blood [Sweat includes a wealth of physiological information that may represent a person’s current health status . Figure in blood . Cardiov2+ or deprotonated to O as the pH rises. As a result, OH2+ makes n-doped graphene, and O makes p-doped graphene, depending on the arrangement of the graphene/electrolyte interface. Doping holes or electrons into graphene may modify channel conductance, which is consistent with previous graphene research [research .It is possible to collect data on a person’s health using sweat monitoring rather than blood sampling since sweat sampling may be performed directly on the skin. Other uses include diagnosing illnesses and other conditions. If wearable biosensors are to be widely used for longer monitoring of physiological data in addition to sweat sensing, they must include low-cost, high efficiency, multibiometric sensing-capability platforms. The authors of Chan-Woo Lee et al.  suggest −, K+, Na+ and pH. This wearable potentiometric sensor offers a high level of accuracy, strong potential stability, and low limits of detection, making it suitable for application in healthcare and clinical analysis. The potential responses of the ISE electrodes were investigated in solution containing the positive and negative ions of interest in various concentration from 10−7 to 1 M.  (+ concentrations. The slope rises to 52.0 ± 0.53 mV/decade (R2 = 0.9990) if the linear range is decreased from 10−1 to 10−4 M. The advantages of the graphene transducer are shown by the K+-GPE’s response slope, which is 57.0 ± 0.25 mV/decade  a. Since V/decade b. Na+ ann slopes c,d. Swea−, Na+, K+ and pH present in the sweat. The indications are consistent. Following are the measurements made of the target ion concentrations: K+, Na+, Cl− are 6.5, 49.5, and 61.4 mM and pH (6.91). Sweat was centrifuged and ICP-MS examined to provide a baseline for comparison  with CB-SPEs, and the impedance measurements of SPE/CB/Na + ISM and SPE/Na + ISM are displayed.In order to conduct a voltammetric experiment employing cyclic voltammetry in a solution of 0.1 M NaCl in the −0.8 V to 1 V potential range, Vincenzo Mazzaracchio et al.  used botFor the study of human performance, the diagnosis of stress-related disorders, and the monitoring of mental health, it is essential to comprehend and evaluate the endocrine response to stress. The majority of current methods for stress monitoring rely on subjective questionnaires to achieve non-invasive, continuous, real-time stress measurement at the molecular level and prevent stress-inducing blood sample. Utilizing a wireless (integrated) device of sensing, Rebeca M. Torrente-Rodriguez et al.  examinedPowerful bioanalytical analytical techniques based on graphite and polymer-based electrochemical sensors have evolved in recent years. However, the majority of manufacturing techniques are not beneficial to the environment due to the usage of hazardous chemicals and the waste they create. Using graphite powder and thermal laminating sheets, Anderson A. Dias et al.  offered Non-enzymatic sensors have a long way to go in terms of commercialisation. In the majority of investigations, materialistic techniques based on a variety of substances and structural engineering have taken precedence. A practical sensor for detection of analytes from sweat cannot be developed using today’s experimental setups, which makes it evident that the systems and materials under consideration have significant functional constraints. These studies need a wide range of unique materials, which may provide new opportunities for breakthroughs in electrode and protective film technology. A more thorough investigation of the sensing mechanism is required for mass manufacturing, however, to identify the issues that prevent reliable functioning in clinical samples. It is common for diseases to develop slowly over time, with no outward symptoms or warning indications being visible to the individual affected. The commercialization of electrochemical biosensors, with the exception of diabetes, is still in its early stages. Glucose sensors are readily accessible in the market due to their widespread commercialization. Due to graphene-based transducers’ superior sensitivity and lesser cost, non-enzymatic glucose sensors are presently the most studied than enzymatic glucose sensors. Electronic biosensors are still in their infancy as a technology for detecting lung cancer, heart disease and asthmatic symptoms. The discovery of biomarkers for various diseases must be based on genuine samples/analytes. Simple solutions for biomolecule immobilisation and material functionalization may lead to practicality and commercialization at a lower cost. When used in the manufacture of transducers, nanomaterials incorporated with graphene-based materials have showed high performance in the detection of different analytes, namely the limit of detection in the region of ng/mL with greater selectivity and sensitivity. In order to achieve such high electrochemical performances, graphene nanosheets are uniformly distributed across a large surface area, allowing for fast electron transportation and an efficient immobilisation of bioreceptors. However, there are still a few obstacles that need to be overcome, such as the development of non-invasive electrochemical biosensors, a universal technique for the generation of graphene-based materials with the desired sizes and layers, the synthesis of a fine layer of graphene with zero defects, the best performing nanocomposite for electrode modification on diabetes detection, the best functionalization method for the development of immunosensors at a lower cost, and so on. There is now a focus on the point-of-care testing (POCT) market for biosensing platforms, where they provide significant advantages to healthcare providers and patients alike. POCT has a number of advantages, including the ability to be utilised at the patient’s bedside, quick detection, consistent results, ease of use, portability, and miniaturisation. From the selection of electrode materials, biological recognition element, chemicals preparation and immobilisation techniques, and 2D materials functionalization strategies, all these benefits may be attributed to the manufacturing procedures of nanodevices/biosensors. POCT is divided into two categories: tiny hand-held devices and big bench-top devices. The advancements in microfabrication and nanotechnology led to the development of the compact hand-held devices. In disease diagnostics, such compact hand-held devices also make it feasible to test the quality and quantity of a broad variety of analytes and to improve the diagnostic methods. As a result, disease identification processes may be streamlined by integrating biosensors and readout software with a real-time smartphone display. As a result, affordable POCT biosensors for routine health monitoring and management are now within reach of the majority of people. Health care facilities prefer non-invasive wearable sensors because they pose less danger and may continue to perform their functions even when they are removed from the body. Wearable technology has evolved from a novelty to a need in modern medicine. It will be a long time before medical devices can be made using these materials. Because of its potential to offer long-term authentic precise monitoring of tissues/organs/systems as well as support in diagnosis and therapy, implanted medical devices are progressively displacing conventional wearable and portable equipment. This is due to the advancement of materials and manufacturing techniques. Implantable devices, however, face a number of difficulties, including biocompatibility, biofouling, and power supply. Biodegradable and transient/biodegradable electronics have a wide range of implanted applications that can be destroyed without the need for further procedures or danger of infection. Biodegradable electronics for implants might use myeloperoxidase, an enzyme generated from human neutrophils, to break down the extensively scattered GO sheets. Non-invasive and invasive sensors used to monitor human health might be called an “augmented sense,” which extends the human senses. As a result, the development of a closed-loop illness management system that incorporates multifunctional sensors and feedback point-of-care treatment is critical. These gadgets, particularly implanted ones, need a source of power, especially in long-term use. An increasing trend in the construction of self-powered systems is the use of sensors and energy harvesting technologies, such as triboelectric nanogenerators (TENG), photovoltaics, radio frequency (RF), biofuel cells and thermoelectric. Finally, throughout the commercialization process, it is unavoidable to address issues of pricing and cost management. In order to produce vast quantities of graphene and graphene-based sensors at high throughputs, cost-effective and simple manufacturing techniques with outstanding uniformity need be devised. Materials have distinct benefits and disadvantages; thus, trade-offs must be made in order to meet the needs of various industries and applications. Although graphene has a wide range of unique properties, it also has limits. When it comes to biological applications, graphene’s zero gap structure has a low on/off ratio, which makes it less suitable for use. Functionalized organic molecules may be able to bridge the gap in its bandgap. Additionally, spintronics and strain-engineered lattice distortions have been tested. Due to its extreme sensitivity to environmental stimuli, graphene also lacks selectivity for target analytes. To enhance selectivity, one way is to add functional groups, bioreceptors, or a thin selective layer such as metal-organic frameworks to the surface (MOFs). Graphene’s moisture absorption and ultra-thinness also contribute to its poor long-term stability. In certain cases, a coating of stable thin layer materials may be all that is needed. The inherent characteristics of graphene may be readily  influenced by these material integrations, device construction, and processing stages when using graphene for functional devices in various applications. After addressing the most pressing issues, graphene-based technologies may go ahead with more confidence and success.Non-enzymatic sensors have sparked a lot of attention as an interesting substitute to overcome the inherent limits of sensors (enzymatic), and they are predicted to solve the stability problem as well as the difficult procedure for the mass production of sensors (enzymatic). As a result, each year sees an increase in the number of publications. Over the last ten years, rapid advances in nanotechnology and nanomaterials have fuelled the complexity and variety of this study field. The most notable result is significant advancement in applications  of enzyme-free systems using electrodes having nanoporous characteristics . It was Sensors, especially wearable and implanted sensors, are key components of health monitoring systems and the interface to the human body because they can detect and analyse numerous analytes or signals with high sensitivity and specificity. Since graphene layers have a large specific surface area and an atomic thickness that allows complete carbon atoms to come into direct contact with analytes, graphene-based sensors offer higher sensitivity than silicon-based sensors. Graphene’s outstanding electrical conductivity and optical transparency also make it a perfect material for seeing bio-tissue in clear images with no distortions in visual appearance. Furthermore, due to graphene’s superior performance in biosensors, such as wide potential window, ease of functionalization, its large specific surface area, and high rate for transference of electron, receptors such as deoxyribonucleic acid, antibodies and enzymes can be efficiently immobilised on its surface. In this review, we have discussed most current graphene-based sensors, also including non-invasive and invasive health monitoring, along with their unique structures, sensing methodologies, and technological advances. Moreover, we included a comprehensive discussion about the methods for synthesis of graphene that is cost efficient, highly dependable, and scalable, as well as producing high yields and quality products. The properties of graphene such as mechanical, electrical and thermal properties are explained in detail. Graphene and its derivatives are known for their improved properties, and these have been synthesised to date due to the requirement of decreasing manufacturing costs, boosting product yield, obtaining superior final product stability, and enhancing sensing capabilities. However, the detailed knowledge about different analytes present in sweat along with the properties of a good sweat sensor is very important, and an elaborate discussion was made in separate sections. Graphene-based sensors have received a lot of attention recently, but there are still a number of scientific and technical obstacles that need to be overcome before any practical applications can be developed. Graphene and its derivatives must first be thoroughly tested for their effects on human health, including their biocompatibility and biological toxicity, as well as their influence on the environment. The future holds great opportunities for the development of efficient and advanced graphene-based sensors for the detection of analytes in sweat.


Tunable temperature alarm sensorswere prepared using multilayergraphene and nitrocellulose (NC) to reliably monitor early high temperaturerisks. The graphene/NC alarm sensor keeps in a state of electricalinsulation, however, turns electrically conductive at high temperatures,such as encountering a flame attack. Its response time is limitedto only a few seconds because of a quick chemical reaction of NC.The 90% graphene/NC (wt % ratio 1:9) composite alarm sensor stablyremains insulated at an ambient temperature of 200 °C, resultingin a satisfactory responsive temperature (232 °C), instant responsetime (4.4 s), and sustained working time in the flame below the ignitiontemperature of most combustibles. Furthermore, the response temperatureand time of the alarm sensor can be tuned by graphene/NC ratios toreduce the fire risk of various combustible materials in differentfire-prone scenarios and thus has promising applications in both indoorand outdoor environments. The sensor has also proven to work in theform of paint, wallpaper, and other composites due to its superiorflame retardancy property, as well as under extreme conditions . Drivingthe development of fire safety strategies, especially preventativemethods such as early fire detection that helps to avert severe damagebefore it occurs is, therefore essential in ensuring the welfare oflives and property. Among various existing devices, smoke detectorsand infrared heat detectors are the primary fire sensors that arewidely utilized indoors.2 However, as bothof them are activated by smoke, which is only emitted after the flamingcombustion has already begun, the response time of these traditionaldetectors usually exceeds 100 s.3 The delayedresponse of these detectors makes it almost impossible to providetimely and effective warning signals to reduce losses of life andproperty. To this end, developing an early-warning fire detectionsystem with a faster response time is of critical importance. A severefire accident usually initiates with the induction of a temperatureincrease in some combustible material by an external heat source,leading to its endothermic pyrolysis.4 Thiscauses the vaporization of decomposition products and thus generatesa further rapid increase of temperature, triggering the fire as aresult. Consequently, an early-warning fire detector with an improvedresponse speed would facilitate safety, but only if it also complieswith the following requirements: it must provide warning signals forabnormally high ambient temperatures, and it must maintain structuralstability during a flame attack.Therewere approximately 167 000 fires in the UK from 2017to 2018.5 high mechanical properties,6 and structural stability under high temperatures. Researchers tookadvantage of the electrical insulating features of GO that would bereduced and thus turn conductive in a high temperature environmentand produced a series of temperature sensors. These sensors demonstratea lower thermal response temperature and faster response behaviorwhen compared to traditional fire detection methods which theoreticallyreduce the response time from 100 to 2–6 s.11 Chen et al.8 prepareda fire alarm using fire-resistant inorganic paper as a coating materialbased on ultralong hydroxyapatite nanowires and GO. It was arrangedwith an electrical connection between the composite paper, an alarmlamp, and an alarm buzzer to achieve an instant response time (lessthan 2 s) under a relatively high experimental temperature. Similarmorphology designs have also been successfully utilized by other researchers,who employed different materials in conjunction with GO. Endeavoringto enable fire prevention through detecting high environmental temperatures,that are, meanwhile, below the ignition temperature of combustibles,Wu et al.9 prepared hierarchical coatingson GO and silicone. These coatings were applied to different combustiblesubstrates to facilitate the exhibition of distinct temperature-responsiveelectrical resistance changes, creating a highly effective early-warningsensor. However, the authors did not define the accurate responsetemperature or time of their sensors, which is relevant and necessaryinformation for safety and sensor design as the GO/silicone compositeis coated directly onto a combustible material. Other researchersgrafted silane on GO to manufacture flexible flame-retardant paper.12 Similar to the work of Yu et al.,13 the insulating silane–GO paper couldbe thermally reduced to form a conductive network in a high-temperatureenvironment . Xu et al.11 synthesized rectangle-shaped GO wide-ribbon(GOWR) sheets from carbon nanofoams and fabricated the GOWR-wrappedmelamine–formaldehyde sponge through dip-coat processing. However,such a sponge only started to respond at around 450 °C, whichwas much higher than the desired response temperature.Existing research indicatedthat graphene and graphene oxide (GO)can be used as effective materials for fire alarm sensors due to theirhigh electron mobility, superior thermal conductivity,16 and superior thermalconductivity, have introduced graphene as the optimal candidate fortemperature sensor applications at the micron-scale or even at thenanoscale.18 Given the method for preparinggraphene with liquid-phase exfoliation,23 various polymers have been proven to be effectivein producing uniform graphene dispersion as a dispersant, which contributesa simple strategy to manufacture graphene/polymer composites effectively.Nitrocellulose (NC), one kind of chemically modified cellulose, hasrecently been proven to be a graphene-dispersing polymer that effectivelydisperses graphene in organic solvents. NC, due to its unique characteristicsin instantaneous pyrolysis and oxygen-free combustion, provides aninspiration for its potential in the design of a temperature-sensitiveearly-warning sensor. So far as we know, no substantial research hasreported any use of graphene and NC in temperature alarm sensors.This study innovatively presents a graphene/NC early-warning firesensor that efficiently responds to temperature changes and avoidssevere damage. Although the graphene/NC membrane remains electricallyinsulated normally, it turns conductive at high temperatures and thereforecan be used in sensors of an alarm system. Furthermore, the responsetemperature and sensitivity of these sensors can be tuned by adjustingthe ratio of graphene and NC to react in different fire-prone scenarios(each 1% increase in NC content leads to a ∼1.8 °C increasein the response temperature). Meanwhile, the tunable temperature sensorhas proven to withstand extreme conditions such as underwater or vacuumenvironment as thermal degradation of NC can take place in oxygen-freeenvironments. The flame retardancy test indicates the sensor’ssuperior and stable function when employed on a solid surface . All types of graphene/NC sensors with variousNC content provided continuous danger alarm even when the sampleswere removed from a flame or specific temperature environment, demonstratingeffective and stable fire warning for detecting high fire risk ofcombustible materials for applications in various scenarios.24It isworth noting that the aforementioned studies focused onlyon utilizing the mechanism of GO reduction to achieve transformationof the conductive state, not on other graphene-like materials. Herein,the electrical conductivity of graphene and the insulation of nitrocelluloseare integrated to prepare a new fire alarm sensor. The excellent properties,such as high electron mobility22.1n-butyl acetate (ACS Reagent grade) were purchased fromSigma-Aldrich. Natural graphite flakes  were purchased from Alfa Aesar. Sodium chloride  was purchased from Sigma-Aldrich and used to induce the flocculationof graphene.Collodion solution (4–8%NC in ethanol/diethyl ether), ethyl acetate, acetone, and 2.2–1 aqueous salt solution to inducethe flocculation of graphene and NC. After that, the sediment washarvested and left to dry at 70 °C in an oven. Once the organicsolvent was completely evaporated, the graphene/NC flocculation wasrinsed with deionized water several times until the surplus sodiumchloride was removed. The resulting solid was dried and stored inbottles prior to subsequent use.Graphenewas manufactured from natural graphite flakes by the liquid exfoliationmethod. First, the as-received collodion solution was poured intoa Petri dish and evaporated in a fume hood overnight until no changein weight was observed. Dried NC (10 g) was cut into small piecesand added into a 1000 mL mixed solution in a ratio of 1:4 ethyl acetateand acetone with natural graphite flakes (100 g). With a water-coolingsystem, the mixture was operated in a high shear mixer (SilversonL4RT) for 2.5 h at 6000 rpm and produced a graphene/NC solution thatwas then centrifuged at 3000 rpm for 30 min (three times) to removethe large graphite flakes. The supernatant was collected and thenadded with a 40 g L2.3n-butyl acetate at a concentration of 10 or 30 mg mL–1. Additional NC was added into the suspension to gain different ratiosof NC in the composite. With the abovementioned methods and the originalsuspension, the first fabricated composite where NC content was 60%was marked G@NC60. Extra NC was added to the original suspension toproduce different NC content composites such as G@NC75 and G@NC90.Altogether, three types of samples, where NC content was 60, 75, and90%, respectively, were produced and employed in the current study.The solution was then drop-casted onto a pre-cleaned blank glass slide(7.5 cm long and 2.5 cm wide) and evaporated under ambient conditions,leaving a coating membrane of graphene/NC. The thickness of thesefilms can be controlled by the amount of solution added to the substrate.Two edges of the membrane were connected to copper wires as externalelectrodes for further tests of resistance change.Thegraphene/NC mixture was then dispersed directly in 2.4–1. Ramanspectra of various samples before and after thermal treatment wereacquired from 200 to 4000 cm–1 using a RenishawSystem 1000 Raman spectrometer at ×50 objective, with an incidentpower of 2.3 mW. AFM images of graphene sheets were recorded witha Bruker Dimension Icon in peak-force mode. The spectral resolutionof system was within 1.5 cm–1 at 514 nm. TGA dataof various samples were generated using the TA Instruments Q500 inan air or nitrogen atmosphere at a heating rate of 10 °C min–1 from room temperature to 800 °C. Scanning electronmicroscopy (SEM) images were collected by a scanning electron microscope(Carl Zeiss AG-ULTRA 55). Tensile tests were performed using an Instronsingle column table frames model 3344 (100 N load cell) at a speedof 1.0 mm min–1 at room temperature following theASTM standard 882, and the sample thickness was measured by SEM.To investigatethe chemical changes of the graphene films after the thermal treatment,thermogravimetric analysis (TGA), Raman spectroscopy, atomic forcemicroscopy (AFM) analysis, and Fourier transform infrared (FTIR) spectroscopywere employed. The samples utilized for all the abovementioned characterizationmethods were divided into two types: (i) pre-annealing G@NC filmsand (ii) G@NC samples after thermal treatment at 260 °C. FTIRdata were obtained using an FTIR spectrometer  between 400 and 4000 cm–1. A custom-made LabVIEW programcontrolled the heating rate of the oven, and the sensor data was acquiredfrom a multimeter (Gw Instek GDM-8342) simultaneously between roomtemperature and 260 °C. Other response time tests were performedon various specimens which were instantly placed in the same ovenas stated above, and before testing, the environment temperature inthe oven was set as 100, 200, 300, and 400 °C, respectively.A vertical flame test was also performed to investigate the responsetime of sensors with various NC content in a simulated real fire scene.The fire from an alcohol burner was applied on the sensor samplesconnected with the multimeter and flash alarm. The additional testsare conducted to evaluate the operating state of the alarm sensorunderwater. The response time was recorded using a camera, and thedata reported in this work were the averages of three experiments.Electrical resistance variation of alarm sensors with different NCcontent was monitored utilizing the two-electrode method, and twoopposite edges of the samples were affixed to copper wires as electrodeswith the help of a copper sheet. The response temperature tests wereperformed using an oven (Carbolite LHT 4/30) that allows wires topass through when heating up to measure the temperature and resistancerelationship at various heating rates such as 2.5 °C, 5 °C,and 7.5 °C min33.1–1, which is not high enough to cast a uniform film.Though graphene is dispersed in the solution, the non-spherical graphenesheets are difficult to flow on the surface of a substrate. As thesolvent used in the mixed solution, ethyl acetate and acetone enjoystrong volatility resulting in graphene and NC particles moving slowlytoward the liquid-coated outer layer by evaporation during the evaporationof the organic solvent. The drop-cast composite membrane sufferedfrom the influence of the coffee ring effect when using the relativelylow concentration of graphene/NC solution because graphene particleshave a large amplitude fluctuation on the air–liquid interfacelayer. As the organic solvent decreases during evaporation, the flowof graphene particles might cause clogging. Therefore, it is necessaryto increase the concentration and viscosity of the graphene dispersionto fabricate a uniform and smooth composite membrane.We employed a facile and time-savingmethod, liquid exfoliation, to prepare the graphene from graphite. 2 carbon atoms arranged in a planar two-dimensionalstructure. The electron distribution has π-orbitals on two sidesof the graphene plane which represent electron densities availableto the molecule. The graphene sheets are negatively charged with asuperb store of electrons. As an electrolyte, sodium chloride is ionizedin water, and the cations (positively charged sodium ions) can coagulatethe negatively charged graphene sheets. Additionally, flocculatedgraphene sheets are coagulated into a solid porous structure witha certain mechanical strength due to the presence of NC. Concentrationof the re-dispersed graphene/NC dispersion is adjustable whereas withits highest concentration can reach 60–70 mg mL–1 (NC included), yet is limited by the viscosity of the whole dispersion.Sodium chloride solution was added here to the dispersion to induceflocculation of the graphene/NC composite. Graphene flakes or particlesconsist of sp3.2–1. As shown in TGA was carried out in an air or nitrogenatmosphere from 30 to 800 °C at a temperature ramp of 10 °CminIn comparison with the pristine NC completely degraded at ∼200°C, the graphene/NC composite demonstrated a downward trend incurve after the first weight drop peak at a similar temperature. Thisdifference indicates that the interaction of graphene and NC altersthe decomposition characteristics of the polymer and prevents or delaysthe complete thermal degradation of NC in the composite at ∼200°C because pristine NC should remain only as gases after thethermal decomposition as shown in the formula above. Meanwhile, anothermass loss in air observed at ∼620 °C is consistent withthe characteristics of graphene decomposition between 550 and 650°C. Compared to the TGA curve shown in A small and sharp peak associated with NC at∼198 °Con the TGA curve for G@NC was found to exist but difficult to observe.As decomposition of NC is not typically carried out under mild conditions,it inevitably generated an obvious gas recoil at the instant momentof deflagration. In contrast, the slight mass gain was not observedin the pristine NC TGA curve, which might be explained by the presenceof graphene that imposed restrictions on the escape of decompositionresidue through physical or chemical interactions of NC and graphene.When the graphene/NC composite was heated to 198 °C, it is mostlikely that NC deflagration gas was trapped between the graphene sheetsand released gradually from the film. Meanwhile, compared to graphene/NCcomposite, pristine NC film did not reflect any mass loss peak whichwas attributed to the absence of the sturdy graphene network membraneto catch the gas released by the instant combustion of NC. When instantaneouslyreleased gases were trapped by graphene, reactive force of the gasrecoil caused the instantaneous mass increase.–1 (D-band)and 1583 cm–1 (G band) analogously. The defect densityin graphene is characterized by the relationship between the defect-relatedpeak (D peak) and the main characteristic peak causedby in-plane vibration of carbon atoms (G peak). Ingeneral, both the ratio of peak height (D/G) and peak area (ID/IG) can estimate the quality of graphene.As D/G and ID/IG ratios increasedafter thermal treatment at 260 °C. Lower ratio generally signifiesthe fewer defects in graphene, which can be attributed to the highsp2-content amorphous carbon produced by the decompositionof NC as mentioned in TGA section before. Meanwhile, compared to theheated samples, the graphene/NC composite, before receiving thermaltreatment, demonstrated an additional peak in the band around 1090cm–1, which is roughly consistent with the typicalNC Raman spectrum peak. In addition, both two types of samples havea defect-induced D′ shoulder peak at around1620 cm–1. Regarding the number of graphene layers,it is apparent that graphene prepared with the current method hasmore than four layers as the G′ peak is smallerthan the G peak. However, the layer number dependson the choice of solution and machine for liquid-phase exfoliation.Raman spectroscopyhas become an ideal analytical technique fordetecting the evolution of defects and quantifying the disorder ofgraphene due to its high structural selectivity and high spectraland spatial resolution. Raman spectra of the graphene/NC compositeafter and before thermal treatment exhibited several prominent peaksinvolving two typical bands at 1351 cm–1 related to nitrate functionality are not measurable. This observationis consistent with the previous literature indicating the characteristicof NC denitration and decomposition at around 200 °C.25 Moreover, several prominent peaks in the rangeof 1300–1600 cm–1, indicating the covalentbonding character as shown in the shaded area in –1, which disappeared after annealingdue to the increase of the resulting molecular symmetry leading toa decline in the vibration intensity, are consistent with the skeletalC–C modes of high sp2-content amorphous carbon.26Although Raman spectroscopy provides an effective analysis of graphene,using FTIR spectroscopy was also necessary to investigate chemicalproperties of graphene/NC composites before and after thermal treatment.Generally, the first stage of NC decomposition is the denitrationprocess. In the annealed graphene/NC composite samples, as NC wasdecomposed, the peaks related to nitrate functional groups lose intensity.Therefore, for thermal treatment below 300 °C, although NC wasnot completely decomposed, the peaks at 1651 and 1267 cm3.3–1 whereas the 10 mg mL–1 sample failed to form a continuous smooth surface due to an inadequatecontent of NC. After thermal treatment, as shown in –1 has been clearly observed, which efficientlyavoided the flake-to-flake overlap. Regarding the drop-cast film of10 mg mL–1 solution, graphene flakes were furtherapart in space, resulting in a sparse network structure that negativelyaffected the efficiency of charge transfer. Therefore, a high concentrationof graphene/NC dispersion  iscrucial for excellent electrical conductivity as well as for the rateof resistance variation, which is of great implication for fire alarmpreparations.Themicrostructure of the composite membrane is expected to impact itsperformance characteristics. Theoretically, a dense, close-connectedgraphene network can exhibit excellent mechanical and electrical performance.The microstructures of the films drop-cast before and after thermaltreatment with different samples of graphene/NC solution are comparedto evaluate the influence of concentrations. Before thermal treatment,as Supporting Information) evidentlyproves that the nitro group disappeared after thermal treatment.The cross sections of the filmdistinctly presented the influenceof NC on the electrical conductivity and basic working mechanism ofthe alarm sensor before and after thermal treatment. Wrapping thegraphene flakes tightly before thermal treatment see 3e and th3.4Supporting Information). Mechanicalproperties of the graphene/NC composite films depend not only on fibrilmodulus but also on orientation and degree of interaction betweenNC and graphene within the film. 3.5The mechanism of temperature response, as shownin 2-content amorphouscarbon according to the peaks shown in FTIR spectroscopy results.In comparison with the pristine NC completely degraded at ∼200°C, the graphene/NC composite demonstrated a downward trend inthe curve after the first weight drop peak at a similar temperature.This difference indicates that the interaction of graphene and NCalters the decomposition characteristics of the polymer and preventsor delays the complete thermal degradation of NC in the compositeat ∼200 °C because pristine NC should remain only as gasesafter the thermal decomposition. This is also the reason why the responsetemperature of the graphene/NC alarm sensor is called “Tunable”.In addition, temperature changes strongly influence the thermal motionin graphene, and the increase in temperature can reduce resistivity.For graphene prepared by liquid-phase exfoliation in this study, multilayergraphene (MLG) has a negative temperature coefficient of resistance(TCR) value due to no electric field intensity existing in the interlayers,which will be discussed later.27 However,the characteristic that graphene resistance decreases with temperaturehas no effect on the working principle of the sensor alarm.The interaction betweengraphene and NC is crucial for studying the detailed mechanism oftemperature response. The bonding between graphene and NC after annealingis likely to be regarded as the covalent bonding character such asskeletal C–C modes of high sp28 Unlike the traditional fire alarm, the graphene/NC temperature alarmsensor meets all the requirements of efficient fire detection: (i)extraordinary rapid response and steady performance, (ii) structuralstability during flame attack, and (iii) early warning signal forabnormally high environmental temperature.An efficient alarm sensor for early-fire warning has to offer analarm signal at high environmental temperature with extremely fastresponse time and maintain structural stability throughout the flameattack. Although most polymeric materials ignite around 300–500°C, the majority of commercial temperature-sensitive fire alarmsonly respond between 60 and 80 °C which is much lower than theignition temperature. This may be explained by the fact that the flametemperature of the combustible materials is much higher than the averagetemperature at each point in the burning space. When a fire breaksout in a compartment, the rise of the hot air flowing results in theformation of a higher temperature layer of hot air above the compartmentwhereas the fire temperature commonly refers to the temperature ofthese hot air layers. In most cases, however, the indoor fire alarmis installed on the ceiling of the compartment, leaving it less functionalas its fire response temperature is much lower than the environmentaltemperature around combustible materials. Prior to detecting the extensivefire and sending the alarm signals, commercial temperature-sensitivefire alarms are not able to initiate early-fire warning in the earlystage of fire as in the growth phase (the first stage) of the idealizedfire temperature curve shown by Milan et al.–1). It should be noted thatbecause the graphene/NC alarm sensors were originally non-conductivebefore being heated, the initial resistance (R0) was set as the maximum measuring range (5.1 × 107 Ω) of the multimeter. As depicted in –1 was indicated as 155, 161, and 167 °Cas shown in –1 heating rate resulting in an increase of ∼6 °C in responsetemperature. Similar trends were also observed in G@NC75 as well asG@NC90 . Considering that the ignitiontemperatures of most combustible polymeric materials range from 300to 500 °C, which is similar to the inner and outer flame temperatureof the alcohol lamp, this test environment can effectively simulatethe applications of the graphene/NC alarm sensor in flame rapid detectionand early warning sensors. Response time is one of the most critical characters in a firewarning device. To evaluate the response time of graphene/NC alarmsensors more accurately and to investigate the impact of ambient temperatureon alarm response quantitatively, direct flame attack and differentenvironmental temperatures of 100, 200, 300, and 400 °C in theoven were employed in this study. To simulate the actual working conditionsduring a flame attack, the alarm sensors with different NC contents were set under the same testing setup as shown in 2 V–1 s–1, respectively.29 TCR of graphene is not identically zero no matterif it is single-layer graphene or MLG. Suspended single-layer graphenehas a small TCR because the dominant electron–electron scatteringis dependent on temperature negligibly.30 However, the MLG utilized in this study has a larger TCR  because no electric field intensity can affect the carriermobility in the interlayer channels.27 Testingunder different environmental temperatures was conducted to observethe TCR of the alarm sensor with various NC content. TCR here is calculatedusing the following equation: –1 within the temperature range of 200–220 °C,indicating that the main pyrolysis process of NC occurs in this temperatureinterval which is similar to the observed results from pure NC TGAtests. The TCR of G@NC60 and G@NC75 decreases to ∼ −2%°C–1 within the temperature range of 240–260°C, which means that the decomposition process of NC and residueapproached to finish in this range. Moreover, the resistance variationof G@NC90 in the range of 220–240 °C is similar to thatof low NC content in the range of 200–220 °C, whereasthe TCR of the same sensor is relatively stable at different heatingrates. This phenomenon may indicate that there is a significant differencebetween the initial temperature at the beginning of pyrolysis of alarmsensors with high NC content and low NC content, but not between thewhole NC thermal decomposition process. However, it still does nothave a huge impact on the sensing mechanism of this temperature alarmsensor.The relationship between temperature and resistance of the graphene/NCalarm sensors is further investigated for standardizing by TCR. Underideal conditions, the theoretical and practical electrical conductivityof graphene is ∼185 000 and 200 000 cmSupporting Information). First, the p-value achieved by two-wayANOVA without replication of NC contents and heating rates is 2.33× 10–5 and 3.60 × 10–3, respectively, indicating that the association between these twofactors and the response temperature was statistically significant.Moreover, the influence of NC content was relatively more effective.Obviously, the goodness of fit is higher than 0.98 at any heatingrate, resulting in a reliable fitting degree and hypothesis accuracy.Therefore, the average value of estimated coefficients (1.8) can affirmthe trend where each 1% increase in NC content leads to ∼1.8°C increase in the response temperature. In addition, the two-wayANOVA with replication method was adopted to analyze the originalresponse time data. The p-value has proven that the effects on responsetime from NC contents and environment temperature are also statisticallysignificant when considering the integrated data .The response temperature of graphene/NC alarm sensorsis tunableby different NC contents within limits. To investigate the relationshipbetween various NC contents and response temperature under differentheating rates, the obtained response temperature data were analyzedutilizing linear fitting, as presented in Figure S6 . It follows then that the alarm sensor canwork stably in other types of extreme environments (outdoor) in theform of paint or wallpaper sending high-temperature alarm signalsto protect people’s lives. The excellent adhesion, mechanicalrobustness, and high flexibility of the graphene/NC film are alsoindispensable for high-performance alarm sensors in the form of wallpaper.It is well known that NC is one of the most versatile adhesives asa standard household cement. Comparison tests were carried out byother authors between annealed graphene/ethyl cellulose (EC) and graphene/NCfilms to investigate the adhesion and mechanical properties of graphene/NCfilms using ultrasonic treatment in water. Compared to the distinctdelamination and breakage of graphene/EC film that occurred within10 s in the ultrasonic bath, the graphene/NC film had negligible delaminationand disintegration for over 1 min. However, the film on polyimidesalso showed even better performance in this test (up to 10 min), indicatingthis difference is based on adhesion at the interface between filmsand substrates. Furthermore, the peeling test was adopted to testthe adhesion performance of the graphene/NC film on a glass slide.A piece of scotch tape was applied to the surface of graphene/NC filmand then peeled at a consistent speed. The graphene/NC film showedexcellent adhesion with glass because no evidence showed that visibleresidue was left on the tape. Compared to similar tests conductedon graphene/EC, which exhibits a noticeable change in graphene pattern.On the other hand, uncertainty and variation of the substrate mayalso affect the operating performance of the graphene/NC alarm sensorwhen it is utilized as wallpaper. However, according to previous studies,different substrates do not significantly affect the TCR of graphene.27 The substrate effect is lessened with the increasingthickness of graphene/NC film resulting in a stable electrical conductivityof graphene in annealed composites. Meanwhile, the evidence of thepersistent alarm signal test and long-term stability test  ensure thestability and flame retardancy of graphene as a wallpaper. For instance,G@NC75 film without a carrier burnt in 1.5 s, whereas it took another0.5 s to burn up thoroughly when carried with the polyimide tape.However, G@NC75 with glass slide maintained its initial shape evenwith small bubble formation on the surface and did not catch firein 10 s. Obviously, the flame retardancy of G@NC was superior whenemployed as wallpaper or coating materials. All types of graphene/NCalarm sensors maintained continuous danger alarm even after the sampleswere removed from a flame or specific temperature environment, demonstratingeffective and stable fire warning that can be applied in various scenariosto detect high fire risk of combustible materials.Because theNC thermal decomposition reacts in instances and requires only heat(where oxygen is an indispensable factor), the alarm sensor is ableto work stably in an oxygen-free or vacuum environment. The TGA resultshave proved that the graphene/NC composite reflects the same workingprocess in a nitrogen environment as in normal ones. The extra testswere conducted to evaluate the operating state of the alarm sensorunderwater. The testing setup and electrical resistance change curveare illustrated in 4In summary, we report a fixed temperature firealarm prepared usingNC and MLG to reliably monitor early-fire risk of combustible materials.The graphene/NC alarm sensor remains in a state of electrical insulationthough instantly turning conductive at high temperatures. Once encounteringa flame attack, NC decomposes rapidly at high temperature and inducesa distinct transition in its electrical resistance, causing the transformationprocess of the alarm sensor from being electrically insulated to anelectron conductive state. Consequently, the LED alarm lamp connectedto the graphene/NC sensor provides an ultrafast alarm response andearly-fire warning signals under flame attacks or abnormal ambienthigh temperatures. The response temperature and time of graphene/NCalarm sensor keep similar upward tendencies as the embedded NC contentincreases. For example, the G@NC90 alarm remained stably insulatedat an ambient temperature of 200 °C, resulting in a satisfactoryresponsive temperature (232 °C), instant response time (4.4 s),and sustained working time in the flame below the ignition temperatureof most combustibles (400 °C). Furthermore, the response temperatureand time of graphene/NC alarm sensor can be tuned by graphene/NC ratiosto reduce fire risk of various combustible materials in differentfire-prone scenarios and thus has promising applications in both indoorand outdoor environments. As the research results show, alarm sensorswith lower NC contents (60 and 75%) reflected lower response temperature(161 and 208 °C) and faster response time, up to 1.6 and 1.9s, respectively. Moreover, the graphene/NC composite film can be processedinto various shapes due to its relatively high mechanical strengthand flexibility. This developed fire alarm also broadens the applicationsof chemical-modified cellulose and graphene composites in temperature-inducedresistance transition sensors with smart responsive behaviors, whichprovides a promising concept for its applications concerning publicsafety in terms of fire risk at high fire risk examinations.


The high demand for pressure devices with miniaturization and a wide bearing range has encouraged researchers to explore new high-performance sensors from different approaches. In this study, a sensitive element based on graphene in-plane compression properties for realizing pressure sensing is experimentally prepared using microelectromechanical systems (MEMS) fabrication technology; it consists of a 50 µm thick, 1400 µm wide square multilayer component membrane and a graphene monolayer with a meander pattern. The prepared sample is extensively characterized and analyzed by using various techniques, including atomic force microscopy, Raman spectroscopy, infrared spectroscopy, X-ray photoelectron spectroscopy, COMSOL finite element method, and density functional theory. The sensing performance of the new pressure sensor based on the sensitive element are obtained by theoretical analysis for electromechanical measurements of the sensitive element before and after low-temperature annealing in atmosphere. Results demonstrate that atmospheric annealing at 300 °C enhances the pressure sensing sensitivity by 4 times compared to pristine graphene without annealing, which benefits from the desorption of hydroxyl groups on the graphene surface during annealing. The sensitivity is comparable and even better than that of previous sensors based on graphene in-plane properties. Our results provide new insights into realizing high-performance MEMS devices based on 2D sensitive materials. Graphene, experimentally discovered in 2004 ,2, is thThe post-treatment process can promote rearrangement of the material lattice and clean up the contaminants on the material surface, which is helpful to further improve the sensing performance of devices. The effects of different post-treatment processes on the properties of graphene have been reported. Plasma treatments on graphene surfaces can reduce polymer residue contamination but result in graphene with a defective graphitic structure . New defA graphene MEMS pressure sensor with a Wheatston bridge circuit formed from several graphene resistances integrated on a chip, with pressure sensing achieved only by the in-plane compressible properties of a graphene monolayer with exceptional properties ,30,31, iA commercial single-crystal silicon wafer was purchased. The silicon wafer was grown following the directions in [110], and its thickness was 0.5 mm. A graphene monolayer coated by polymethyl methacrylate (PMMA) was a trivial transfer graphene from ACS MATERIAL .x), was used as the structural element in this pressure-sensing device. As illustrated in P0 is the pressure inside the cavity, and P is the pressure outside the cavity. When differential pressure is applied, the membrane undergoes deflection and deforms into a concave shape.A schematic of the device is shown in x membrane after etching by O2 plasma. From the top view, only the graphene monolayer resistance has the meander pattern. The graphene resistance is above the cavity and acts as a sensitive element.The technological process for fabricating the device is shown in 2 plasma process.The devices are fabricated using standard techniques. The silicon nitride membrane was deposited on the oxide with a thickness of 200 nm for electrical isolation after the silicon wafer was thermally oxidized. Its thickness was about 100 nm. Cr (50 nm) and Au (250 nm) were evaporated onto the silicon nitride layer for the contact. The electrode patterning was acquired by photolithography and chemical etching. The devices must possess electromechanical sensing ability. To this end, 1400 μm-wide square cavities defined with photoresistance were etched 450.3 μm deep into the silicon layer at the backside of the wafer. A piece of glass was bonded with the wafer’s backside in order to seal gas in the cavities, which can form a pressure difference inside and outside of them. The graphene monolayer was transferred to the abovementioned substrate. The graphene with PMMA was rinsed in deionized water and picked up with the chip. The chip was baked for 20 min at 100 °C to allow the graphene to adhere to the silicon nitride layer and the gold electrodes. The PMMA was then dissolved by acetone and rinsed with ethyl alcohol and deionized water. The chip was then baked again for 10 min at 50 °C to dry the graphene. To image the graphene, its patterning was defined by photolithography and etched using an OIn recent years, the atomic force microscope, Raman spectrometer, infrared spectrometer, and X-ray photoelectron spectrometer have become powerful characterization and metrology tools for solid materials at the nanoscale. They are employed to detect the roughness, number of plies, and functional groups of the graphene and to verify its quality on the chip surface.−1 was used for spectral testing. The photoelectron spectrometer used was an ESCALAB 250Xi . This instrument has an energy resolution of 0.45 eV/(Ag 3d5/2) and a spatial resolution of less than 3 μm.The atomic force microscope used was a Dimension Edge . This microscope has an atomic resolution with a lateral resolution of 0.1 nm and a longitudinal resolution of 0.01 nm. The Raman spectrometer was an inVia . The spectrometer was used to test graphene with a laser wavelength of 532 nm and a laser power of 2.4 mW. The infrared spectrometer was a Frontier . Its spatial resolution was 1.56 μm. A resolution of 4 cmThe atomic force micrograph and the Raman spectrum of the graphene are shown in As shown in A COMSOL finite element method was used to analyze the strain distribution caused by the differential pressure across the cavity membrane. The simulation results were obtained through a process that included setting geometric dimensions, setting materials, selecting solid mechanical-physical fields, fine meshing, researching, and computing. The whole strain distributions on the cavity membrane were simulated when pressure differences of 0.1 and 0.5 MPa were applied to this membrane. The strain data were correspondingly extracted and analyzed when pressure differences from 0.1 MPa to 0.5 MPa were applied to the cavity membrane.c axis. Calculations were performed using a 2 × 2 k-point mesh for the supercell surface and using one mesh point along the c direction.Density functional theory (DFT) was used to calculate the difference of the charge distribution and Fermi velocity of graphene absorbing pollutants in order to illustrate the effects of annealing on the device properties. A primitive graphene cell was constructed using two carbon atoms. In our study, we considered a 6 × 6 × 1 graphene supercell consisting of 36 1 × 1 × 1 unit cells, and one pollutant, such as a hydroxide radical, was placed on the top of the carbon atom. Approximately 25 Å of vacuum was added to the graphene surface in order to separate the repeated cells along the K points in the inverted lattice space of the graphene system using the DFT method.For the difference of the charge distribution, the constructed hydroxy-adsorbed graphene system was optimized to the minimum energy needed to obtain a stable system. For the charge distributions of this system, the graphene retained by removing the hydroxyl group from the system and the hydroxyl group retained by removing the graphene from the system were calculated. The charge distribution of the system was subtracted from the charge distributions of the independent graphene and hydroxyl groups. In this way, the charge changes of the adsorbed hydroxyl graphene relative to the independent, clean graphene are obtained. The Fermi velocity was obtained by calculating the energy band along the path of As shown in G = ΔR/Rε. The gauge factor for graphene was obtained by dividing the relative change in graphene resistance at each pressure by the corresponding mean strain in COMSOL simulation was performed using the details provided in R above the cavity acts as sensitive elements, but the remaining R0 is not above the cavity and remains constant. As shown in V is connected to output electrodes 2 and 4. The voltage output ΔV of the Wheatston bridge can be expressed as Equation (1), where U represents the voltage of the DC source.A new pressure sensor based on the above sensitive element is proposed and presented in −5/kPa, is greater than that of the one without annealing. From the performance comparison among the MEMS pressure sensors in The electromechanical performance of the proposed sensor can be obtained by the combination of electromechanical measurements of only the graphene monolayer resistance as a sensitive element in The pressed courses are shown in Reversible performance of the sensor can be obtained for the device in −1 is observed in the infrared spectra. The spectrum line without annealing has a more prominent bulge than that with annealing. The broad bulge of the spectrum line without annealing is most likely the result of the interaction between the major and minor groups around 1400 cm−1. The sample surface contains water molecules, because the sample was rinsed with deionized water in the process or remained in the air. The hydroxyl radicals absorbed on the graphene surface may be formed by the interaction between water molecules attached to the graphene surface and oxygen molecules in air before annealing [−1 [From the data obtained above, it can be determined that the performance of the sensor undergoing 300 °C annealing is more excellent than that of the one without annealing. The samples are contaminated frequently in the process device fabrication. The pollutants, such as hydrogen ions and hydroxide radicals, may be absorbed on the graphene surface when all types of chemical reagents are applied. nnealing . The watnnealing , which rling [−1 , so the From the above-mentioned experimental results, the sensitivity of annealed graphene is higher than that of unannealed graphene, and the difference between the two sensitivities tends to decrease with the increase in deformation. In accordance with Boltzmann’s theory, this phenomenon can be explained by the relative change in the Fermi velocities of the same material under different deformation conditions. The unannealed graphene, which has a hydroxyl group adsorbed to its surface, has a low initial Fermi velocity. The graphene surface becomes cleaner with hydroxyl desorption, and the cleaner graphene has a higher initial Fermi velocity after annealing. The difference between the initial Fermi velocities of the two graphene systems results in the different levels of sensitivity.A theoretical model using a linearized Boltzmann transport equation can accurately describe the charge carrier density and mobility in the strained graphene and the gauge factor . The chaConsidering the scattering mechanism of the defects, the dependence of the mobility on the Fermi velocity is given by Equation (3).Thus, the resistivity is approximately proportional to the inverse of the squared Fermi velocity :(4)ρe(ε)q is the basic unit of charge. The resistance of a strained graphene can be defined as Equation (5).The resistance is further expressed asTherefore, the relative change in strained graphene resistance is expressed asThe gauge factor can reflect the sensitivity of the graphene material. The gauge factor can be determined using Equation (8).K points in the inverted lattice space of the graphene system using the DFT method. Therefore, every gauge factor in The gauge factor of the graphene system under specific deformation can be obtained by calculating the Fermi velocities for the original and deformed graphene systems. The Fermi velocity to be introduced into the formula is obtained by calculating the energy band along the path of In this study, we used MEMS standard technology to propose a pressure sensor based on the in-plane compressible characteristic of monolayer graphene and thoroughly investigate its performance before and after atmospheric annealing at 300 °C. The performance metrics, including sensitivity, response speed, and linear response range, were markedly improved by atmospheric annealing. Atmospheric annealing at 300 °C enhanced the pressure-sensing sensitivity by 4 times compared with the pristine graphene without annealing, which can be proven by the differential degree of the gauge factors of graphene before and after annealing. The response speed of the annealed sensor to gas pressure was faster than that of the nonannealed sensor. The linear response range of 0–70 kPa is an improvement over those of previous sensors. Simultaneously, the research shows the effective response of the in-plane piezoresistive effect of monolayer graphene to gas pressure, and that the performance of the sensor undergoing 300 °C annealing is more excellent than the one without annealing, which benefits predominantly from the desorption of hydroxyl groups on the graphene surface during annealing. The sensitivity of graphene annealed in atmosphere at 300 °C is higher than that of the unannealed graphene under the conditions of small deformation, but it no longer has a remarkable advantage over that of unannealed graphene under the conditions of large deformation. Our results provide new insights into obtaining high performance of MEMS devices based on 2D sensitive materials.