The new approach helps to minimize background environmental effects , leading to an insignificant error in the output change in frequency of the order of 0.46% when operated in light versus dark conditions. The uncertainty in readings due to background light was analyzed, and the error in the resistance was found to be of the order of 1.34 Ω, which confirms the high stability and selectivity of the proposed sensor under different background effects. Furthermore, the evolution of the graphene’s lattice defect density due to radiation was observed using Raman spectroscopy and SEM, indicating a lattice defect density of up to 1.780 × 1011/cm2 at 1 kGy gamma radiation, confirming the increase in the graphene resistance and proving the graphene’s sensitivity. In contrast, the graphene’s defect density in response to beta radiation was 0.683 × 1011/cm2 at 3 kGy beta radiation, which is significantly lower than the gamma effects. This can be attributed to the lower p-doping effect caused by beta irradiation in ambient conditions, compared with that caused by gamma irradiation. Morphological analysis was used to verify the evolution of the microstructural defects caused by ionizing irradiation. The proposed sensor monitors the low-to-medium cumulative range of ionizing radiations ranging from 0 to 1 kGy for gamma radiation and 0 to 9 kGy for beta radiation, with high resolution and selectivity, filling the research gap in the study of graphene-based radiation sensors at low-to-medium ionizing radiation doses. This range is essential for the pharmaceutical and food industries, as it spans the minimum range for affecting human health, causing cancer and DNA damage.This paper proposes a new graphene gamma- and beta-radiation sensor with a backend RF ring oscillator transducer employed to convert the change in the graphene resistivity due to ionizing irradiation into a frequency output. The sensor consists of a CVD monolayer of graphene grown on a copper substrate, with an RF ring oscillator readout circuit in which the percentage change in frequency is captured versus the change in radiation dose. The novel integration of the RF oscillator transducer with the graphene monolayer results in high average sensitivity to gamma irradiation up to 3.82 kΩ/kGy, which corresponds to a percentage change in frequency of 7.86% kGy Radiation sensors are widely used to monitor radioactive activities continuously in multiple applications such as biomedical diagnostics, pharmaceutical applications, border security, agriculture, environmental applications, astrophysics, and nuclear power plants ,2. ThereBeta irradiation results from particle ejection from a radioactive nucleus in one of two forms: negatively charged electrons  or positively charged electrons . Beta radiation can travel long distances in the air and penetrate the body by up to 3.8 cm, causing mainly skin cancer ,5,6. On Conventional radiation detectors, e.g., gas-filled detectors and scintillators, have several limitations . Gas-filSolid-state detectors have gained much attention recently due to their simplicity, low cost, and high sensitivity . In addiHowever, 2D materials such as graphene are emerging as promising materials for solid-state radiation sensors, due to their distinctive electronic properties such as ultra-high electron mobility at room temperature and a bandgap structure that can be easily tailored via external stimuli and doping. Thus, graphene can effectively be used as a radiation sensor by detecting the change in bandgap structure and resistivity due to lattice defects induced by graphene–radiation interactions ,20. FurtAlong these lines, recent research has used graphene in detecting a wide range of radiation dosages from 1 to 20 kGy via physical changes in bandgap characteristics. Gamma-radiation-induced p-doping in graphene affects the graphene’s crystal structure and band properties by breaking the zero-gap property and introducing new vacancies into the lattice structure, affecting electron mobility and thus increasing resistivity and changing the electronic properties of the 2D material ,22. In oSimilarly, integrating monolayer graphene as a radiation-sensing material was reported by Patil et al. . They usJain et al.  introduc11 defects/cm2 after a radiation dose of 20 kGy. Neither study tested graphene’s sensitivity for smaller irradiation doses below 1 kGy or eliminated the background-light photon cross-sensitivity.The studies mentioned above were mainly aimed at detecting higher doses of ionization energy using different techniques such as monitoring changes in energy and flux, which affect the resistance of graphene, or monitoring changes in drain current in parallel with gate voltage. It was also observed that the defect density could reach around 0.5 × 10The sensor’s backend readout circuit should be designed to inhibit noise, increase the S/N ratio, enhance the signal quality, and increase sensitivity and selectivity by suppressing any background environmental effects  that may affect the sensor’s reliability. This is particularly important for small-range radiation detectors due to the small changes in resistivity and possible interference from ambient light.Radiofrequency (RF) oscillators can transform changes in resistance or capacitance into readable frequency signals . LC-tankThus, in this work, we propose a monolayer graphene radiation sensor capable of detecting ionizing radiations at low (below 1 kGy) ranges with high sensitivity and resolution. Two identical sensors are connected to a backend RF ring oscillator circuit to minimize the ambient background effects, such as light photons. Incident irradiations cause an accumulated graphene lattice defect density, leading to changes in the bandgap structure and decreasing the electron mobility, leading to increased resistivity, which can be detected as the percentage change in oscillating frequency in the RF ring oscillator readout circuit. Thus, in this paper, we introduce the criteria for transforming the change in graphene resistivity caused by cumulative ionizing radiation into a change in oscillating frequency detected via the oscillating frequency of a backend RF ring oscillator circuit, with no need to monitor gate voltages and drain currents.The working principle is based on the induced lattice defects in graphene in response to ionizing radiation. These defects eventually shift the graphene towards a non-crystalline phase , in paraThe benefits of this approach are the high electron mobility of monolayer graphene and the high sensitivity and selectivity towards ionizing radiation. The proposed backend ring oscillator circuit suppresses environmental background effects  by integrating two graphene sensors, as shown in The device consists of two graphene sensors, as shown in The circuit shown in CVD-grown graphene on a 50-micron copper foil substrate was used in this study as the sensing material and was purchased from 2D Semiconductors , where procedures were used to allow graphene layer growth over the whole copper foil surface area without its being affected by the vacancy point defect concentration. The growth of the graphene monolayer required multiple processes, to achieve the required structure with all of the properties needed for our radiation-sensor device.Copper foil was first heated to elevated temperatures of around 1035 °C, then annealed while ensuring a constant flow of hydrogen gas, before starting a 3 h growth in a constant flow of a gaseous mixture of hydrogen and methane at the above-mentioned temperature. Finally rapid cooling was achieved by opening the furnace. Post-growth processes are usually used, such as cutting and storing in a humid environment for two days to allow oxidation of the copper layer and to weaken any van der Waals forces to ease the detachment of the graphene layer if transfer to another substrate is required. However, in our case, the graphene/Cu interaction was needed .2 rectangular wafers. Then, these wafers were attached to a fabricated elastic substrate to ensure protection while handling the samples during irradiation. The elastic base consisted of a paper rectangle covered with Kapton tape on both sides, with a surface area of around 25 cm2. The wafer was attached to the elastic base using an acrylonitrile AKFIX® binder, to fix the sample without slipping. This binder is used in multiple sensor applications such as strain gauges, eliminating any slipping effect with reliable adhesion. A drop of around 0.1 cm3 of the binder was added onto the substrate. The wafer was fixed carefully over the adhesive drop to avoid any of the binder getting onto the sample and damaging the graphene layer.Samples of graphene/Cu were mechanically cut into 30 mm3 each were added onto two copper wires, each located at one end of the wafer, as shown in An electrically conductive silver paste connected the Cu wiring to the graphene surface. The silver paste consisted of 3 main components: the conductive silver particles, representing around 60 wt%, an auxiliary agent, and a solvent for the other two components. Two drops of the pre-cured paste of around 0.15 cmGamma irradiation was applied to the graphene sensors while they were disassembled from the backend circuit. Gamma irradiation was applied using a Co-60 source to achieve cumulative irradiation by subjecting the graphene to the source for specific periods. Similar gamma irradiation was applied to the 2 graphene-based sensors to be subsequently connected to the backend ring oscillator circuit after the irradiation process for monitoring the induced signal via the transducer. Gamma irradiation was applied between 0 to 1 kGy, followed by RF ring oscillator characterization. The irradiation test was repeated with beta radiation for different samples using an electron beam source; the oscillating frequency was recorded using an oscilloscope for a cumulative beta-radiation dose ranging between 0 and 9 kGy.Raman spectroscopy was used as a primary material characterization technique to detect the effects on the graphene lattice that could evolve due to ionizing irradiation, such as the changes in the Dirac point caused by any deformed crystal that will affect the electron mobility through the graphene layer. A dispersive Raman spectrometer produced by Bruker  with a 20 mW, 532 nm laser source was used to characterize the irradiated samples, using a 50 × 1000 µm aperture.−1. The G peak was located at a wavelength of 1582.7 cm−1, with an Unirradiated graphene demonstrated sharp graphene peaks that appeared to be clear and clean, as shown in the Raman analyses in  results .The morphology of the graphene monolayer was examined and studied using field-emission scanning electron microscopy  after each irradiation process, using magnifications that ranged between X250 to X1500, with an electron high-tension value of 4 kV and a working distance of 4.9 mm.An experiment was conducted on our sensor assembly in order to determine the impact of light photons on the oscillating output frequency generated by the RF ring oscillator circuit under different light conditions, where cumulative gamma-radiation doses ranging from 0.8 kGy to 1 kGy were applied to the two graphene sensors and oscillating frequency readings were recorded from the oscilloscope under three different environmental conditions: (i) with the two graphene films subjected to light, (ii) with one graphene film subjected to light and the other kept in darkness, and (iii) with both graphene films kept in darkness.As shown in The results showed an average % error of 0.451% in the case of two graphene sensors in darkness and 0.457% in the case of one graphene sensor in light and the other in darkness, proving the ability of the RF ring oscillator backend circuit used to eliminate the background effects, thus proving it has high selectivity with respect to ambient light photons.Furthermore, uncertainty calculations regarding the ambient light effect were performed using the % error calculations by taking the derivative of Equation (2): The uncertainty in As shown in −1, the G-band at 1582.7 cm−1, and finally the 2D band at 2671.11 cm−1. It was observed from the Raman spectra in Intrinsic  Raman bands or peaks for graphene were first analyzed, for the D-band at 1350 cmOf particular interest in this study were the intensities and the Raman shifts of the G-band and comparing these with other doses to detect the changes in electronic properties such as the bandgap. As shown in As observed from It was also observed that the broadness of the 2D peak increased with increasing cumulative radiation dose, resembling the layering effect caused by cracking and stacking of monolayer graphene into multiple layers .Raman spectroscopy was repeated in the same way for beta irradiation, as shown in adiation .A scanning electron microscope (SEM) was employed to verify the evolution of microstructural defects caused by gamma and beta irradiation observed in the Raman analysis. Wrinkles could be observed as light-grey lines inside the domain and are outlined by blue circles in the zoomed-in After each cumulative dose, the irradiated graphene sensors were subsequently connected to the backend circuit to measure the percentage change in the oscillating frequency. Cumulative gamma irradiation was applied between 0.05 Gy and 1 kGy. As shown in g per Gy of 0.12 kΩ/kGy and % change in frequency per kGy of 0.29%, showing that the sensor was 27.1 times less sensitive than for gamma radiation. This is suggested to be due to the effect of the beta irradiation taking place in an ambient environment, without applying a vacuum, allowing further adsorption of the ozone which is usually located in the electron beam and hence causing a p-doping effect to occur but with lower density than for gamma irradiation, causing a lower change in resistance than for gamma radiation [Furthermore, the RF ring oscillator circuit was used to characterize the beta-irradiated (cumulative radiation dose ranging between 0 and 9 kGy) graphene sensors. adiation .The proposed monolayer graphene ionizing radiation sensor platform was tested for cumulative irradiation with two different ionizing radiation types , with irradiation ranges of 0–1 kGy for gamma and 0–9 kGy for beta radiation, filling the research gap of sensing in the low-to-medium range of radiation doses (below 1 kGy). Raman spectroscopy and morphological characterizations showed that cumulative irradiation increases the defect density and allows for p-doping, which changes the bandgap properties of graphene, decreasing the mobility of electrons and thus increasing the resistance. The irradiated graphene sensors were further characterized morphologically using an SEM analysis, which further verified the effect of ionizing irradiation on the evolution of defects. The SEM analysis also further verified the more negligible effects of beta irradiation compared to gamma irradiation and the sensor’s linearity limits at ~1 kGy due to the excessive microstructural damage beyond this point. The RF ring oscillator backend circuit transforms the change in frequency into a change in oscillating frequency, to amplify the readout signal for more accurate readings. The circuit was tested for suppression of background light effects, and it was found that the % error due to light reached 0.457%, causing uncertainty in the change in resistance calculation of 1.344 Ω. The irradiation testing results showed a higher sensitivity to cumulative gamma irradiation (3.82 kΩ/Gy) than to beta irradiation (0.12 kΩ/Gy). This can be attributed to the fact that the induced graphene lattice defects and the p-doping due to gamma irradiation were higher than those due to beta irradiation. Due to its low cost, small size, and low power consumption, the proposed sensor is suitable for wireless sensor networks in various applications such as food, agriculture, pharmaceutical, or border security applications.


However, their accommodative response showed a significant difference between subjects gazing at an object at 0.4 m and 2.285 m and those gazing at it at 0.4 m and through a DMS. Conclusion: In this experiment, the results of the children’s accommodative response measured at 2.285 m or through a DMS are very similar. The viewing distance can be extended by a DMS, resulting in accommodative relaxation. This result may have potential applications in myopia control. Purpose: This study first proposed the application of a double-mirror system (DMS) to extend viewing distance and investigate the accommodative response of schoolchildren under a DMS. Method: Fifty-seven subjects aged between 7 and 12 years old were recruited in this study, and the experiment was divided into two stages. The first stage consisted of a case history inquiry, a refraction state, and a visual function examination. In the second stage, the subjects gazed at an object at distances of 0.4 m, 2.285 m, and through a DMS, respectively, and their accommodative responses were measured using an open-field autorefractor. Results: There was no significant difference in the schoolchildren’s accommodative response between subjects gazing at an object at 2.285 m (0.14 ± 0.35 D,  Myopia is one of the most prevalent diseases in the world today. According to a study by Brien A. Holden and others, 2.620 billion people may have had myopia in 2020, with a myopia rate of 34.0% in the global population; by 2050, the global myopia population may be as high as 4.758 billion, representing a myopia rate of nearly half of the global population (49.8%) . Post hoc tests with Bonferroni correction show that the accommodative microfluctuations of the schoolchildren at 0.4 m were significantly greater than at 2.285 m (p < 0.001) and through the double-mirror system (p < 0.001). However, there was no significant difference in the schoolchildren’s accommodative microfluctuations when they gazed at the object at 2.285 m or through a DMS (p > 0.05), as shown in The root-mean-square values of the accommodative microfluctuations (AMFs) were 1.22 ± 0.26 D, 0.37 ± 0.23 D, and 0.35 ± 0.24 D, which correspond to the subjects gazing at the object at 0.4 m, 2.285 m, and through a DMS, respectively . The oneIn order to further understand the changes in the accommodative microfluctuations at different viewing distances of 0.4 m, 2.285 m, and through a DMS, this study randomly selected one male and one female subject from each of the lower, middle, and higher grades to conduct an analysis of the accommodative response in 20 s. The results show that the accommodative microfluctuations were stable at the viewing distance of 2.285 m and through a DMS; on the contrary, the accommodative microfluctuation was unstable at the viewing distance of 0.4 m, as shown in There is much evidence suggesting that accommodation is a key factor in the development of myopia, although its exact mechanism is yet to be determined ,25,26. RWhile the accommodative responses for the subjects gazing at the object both at a distance of 2.285 m and through a DMS were similar, there was no statistically significant difference, which means that a viewing distance of 2.285 m can be achieved through a DMS, resulting in accommodative relaxation. The accommodative microfluctuations in schoolchildren at 0.4 m were significantly greater than at 2.285 m and in the double-mirror system. As a greater accommodative response is needed at the near distance of 0.4 m, unstable AMFs may be generated. The accommodative microfluctuations for the schoolchildren gazing at the object at 2.285 m and through DMS were very close, at 0.37D and 0.35D, respectively. The stability of AMFs when gazing at an image through a DMS was consistent with the results when gazing at the same object at 2.285 m.This study investigated accommodative response at different viewing distances and through a DMS. To avoid a convergence effect, which affects the accommodative response, we allowed the subjects to perform monocular fixation; therefore, there are some limitations in this study. The results show that accommodative relaxation and microfluctuation stability can be achieved by a double-mirror system.This study measured the accommodative response and microfluctuations in schoolchildren at different viewing distances of 0.4 m, 2.285 m, and through a DMS. The accommodative responses were 1.34 ± 0.43 D, 0.36 ± 0.30 D, and 0.37 ± 0.31 D; the accommodative microfluctuations were 1.22 ± 0.26 D, 0.37 ± 0.23 D, and 0.35 ± 0.24 D, which correspond to viewing distances of 0.4 m, 2.285 m, and through a DMS. The values of the accommodative responses and microfluctuations for the near-viewing distance of 0.4 m were larger than 0.97 D and 0.87 D, as well as those through a DMS. This result shows that the accommodative response can indeed reduce and stabilize microfluctuations through a DMS. In addition, the values of the accommodative response and microfluctuations for both the viewing distance of 2.285 m and through a DMS are similar, and the viewing distance can be extended through a DMS; in addition, the magnification is set to 3.386 times. The simple optical design of a double-mirror system (DMS) have potential for reducing the lag in accommodation and hyperopia defocus, and could result in slowing the development of myopia.


Specifically, the ever-increasing demand of humidity sensors in applications ranging from agriculture to healthcare equipment (to cater the current demand of COVID-19 ventilation systems), calls for a selection of suitable humidity sensing material. (2) Methods: In the present study, the TPPNi macromolecule has been synthesized by using a microwave-assisted synthesis process. The layer structure of the fabricated humidity sensor (Al/TPPNi/Al) consists of pair of planar 120 nm thin aluminum (Al) electrodes  and ~160 nm facile spin-coated solution-processable organic TPPNi as an active layer between the ~40 µm electrode gap. (3) Results: Electrical properties (capacitance and impedance) of sensors were found to be substantially sensitive not only on relative humidity but also on the frequency of the input bias signal. The proposed sensor exhibits multimode (capacitive and conductometric) operation with significantly higher sensitivity ~146.17 pF/%RH at 500 Hz and 48.23 kΩ/%RH at 1 kHz. (4) Conclusions: The developed Al/TPPNi/Al surface type humidity sensor’s much-improved detecting properties along with reasonable dynamic range and response time suggest that it could be effective for continuous humidity monitoring in multi environmental applications. Effective and reliable humidity monitoring is of prime significance in an increasing number of industrial sectors such as in the chemical, electronics, pharmaceutical, agricultural, and HVAC  sectors ,2,3. ParA capacitive type sensor, for instance, consists of a pair of metallic electrodes separated by a dielectric material, whereas a conductometric type sensor consists of electrodes separated by a semi-conductive channel. As the relative humidity (%RH) of the environment increases, the dielectric constant of the capacitive sensor and conductivity of the conductometric sensor show a gradual increase corresponding to the increase in %RH . The selRecently, conducting polymers based robust and ultra-sensitive sensors of biologically active compounds have been developed for their potential applications in biomedical diagnostics, the food and beverage industry, and environmental analysis ,13. SimiIn the present study, we report a facile realization of surface type humidity sensor (Al/TPPNi/Al) based on 5,10,15,20-tetraphenylporphyrinatonickel(II). The fabricated sensor has been operated at multiple frequencies of input bias and its electrical response (capacitance and impedance) has been examined at varied ambient humidity levels. The purpose of the current research effort is to realize enhanced humidity sensing performance of the sensor compared to those already reported in the literature. The TPPNi macromolecule has been synthesized in two successive stages. The condensation of benzaldehyde and pyrrole yielded 5,10,15,20-tetraphenylporphyrin (TPP) in the first stage . The detIn the second step, porphyrin  and nickel acetate  after dissolving in a mixture of chloroform and methanol (10:1) have been adsorbed over silica gel. After drying, silica gel was microwave irradiated (250 W) for 15 minutes at 111 °C. The reaction mixture was then applied to the top of a silica column after cooling and eluted with a chloroform and n-hexane (1:4) combination. To obtain pure 5,10,15,20-tetraphenylporphyrinatonickel(II) in a good yield of 91%, the fast-moving band was collected, and the solvent was evaporated in vacuo (II). The chromatographic separation of compound and their purification depends chiefly upon the interaction between the solute in the mobile phase and the stationary phase. The exact conditions for the purification of any compound over the solid stationary phase by using a liquid mobile phase is determined by hit and trial method. Once the ratio of the solvents is determined, column chromatography process is performed with the same mobile and stationary phases. Reasonably, each compound has its own physical and chemical properties that eventually determine its distribution between the mobile and stationary phases during the chromatographic separation. In the case of TPP, the best separation on thin layer chromatography (TLC) plate was observed when the ratio of chloroform and n-hexane was (2:1), whereas in the case of TPPNi the aforementioned ratio was (1:4).3/h) and a diffusion pump  . Both pumps have been used to evacuate the chamber of the system to 5 × 10−4 mbarr (0.05 Pa). Shadow mask has been used to pattern spacing of ~40 µm between the pair of aluminum contact pads which have been defined to allow electrical connections of the humidity sensor. In order to deposit the active sensing layer of TPPNi, a 20 mg/mL TPPNi solution was prepared and stirred overnight by magnetic stirring. The solution was later passed through Polytetrafluoroethylene (PTFE) membrane filters of 0.45 µm pore size to filter it. Later, a 150 µL solution of TPPNi in chloroform was spin-coated to deposit a dielectric thin film covering the gap between the aluminum electrical contact pads. By this process, an average thickness ~160 nm of TPPNi thin film as a sensing layer has been observed by the Dektak profilometer. The cross-sectional schematic description of the Al/TPPNi/Al planar humidity sensor is given in The humidity sensor has been fabricated in a surface-type configuration on a glass substrate using TPPNi as an active sensing layer. Regular soda lime microscopic glass slides (dimensions ~25 mm × 25 mm × 1 mm) have been used to function as the substrate for the fabrication of the device. The glass slides have been cleaned in two phases, at first using gentle rub via lint-free wipe and a cotton swab in soap-water. Later on, it was cleaned with a conventional cleaning procedure using Elmasonic E 30H ultrasonic cleaner  for 10 min each with acetone, ethanol, and DI water followed by blown dried in a dust-free environment with a dry air stream. Through a shadow mask approach, an aluminum thin film with an average thickness of 120 nm was deposited on this glass substrate by a custom-designed physical vapor deposition (PVD) system at a rate of 0.2 nm/s. The PVD system is equipped with a single-stage rotary vane pump ,  generated at 30 kV and 30 mA with a scan rate of 2° min−1 for 2θ values between 10° and 80°.Physical Characterization: The UV-vis spectrum of the active thin film has been analyzed by the Jasco V-770 spectrophotometer. Nova NanoSEM 450 Field-Emission Scanning Electron Microscope  and Agilent Technologies 5500 Atomic Force Microscope (AFM)  were used to analyze the surface morphology of the active sensing layer. The structural properties of the active sensing layer have been investigated by studying X-ray Diffraction (XRD) pattern by using Shimadzu 7000 Diffractometer  functioning with Cu KαElectrical Characterization: The experimental setup used for sensor testing is a laboratory assembled  chamber. The humidity within the chamber has been controlled by dry and humid-air flow, routed through inlet and outlet regulatory valves. The reference levels  inside the controlled environmental chamber have been effectively monitored by Pro’s Kit MT 4014 commercial Thermo-hygrometer  with a resolution of ~0.1% RH and ~0.1 °C).rms) was kept constant at 1.0 V. It is noteworthy that the high precision APPLENT AT2816B LCR Meter provides simultaneous measurement of both capacitance and impedance at all test frequencies, in a single cycle of experiment wherein the step input changes the range of 45% to 85% relative humidity is of course identical. It is also pertinent to mention that humidity is a relative function of temperature. At different temperatures, the humidity saturation value of the same space is different, and hence the relative humidity value is also different. All the experiments in the present study have been performed at 25 ± 0.5 °C. The general layout of the testing setup constructed for the calibration of humidity sensors is shown in The proposed Al/TPPNi/Al sensor was characterized for its electrical characteristics (by exposing it to various humidity levels) with a high quality (measurement accuracy 0.1%) APPLENT AT2816B LCR Meter . Furthermore, the electrical response of the sensor was recorded at four distinct frequencies of the input signal , while the applied bias  in solution as well as solid-state, as shown in 0) to the second-lowest singlet state (S2). On the other hand, the broadband at 500–575 nm with peak absorption at 525 nm is due to π–π* electron transition from the ground state (S0) to the lowest excited singlet state (S1). Quite interestingly, albeit the absorption spectra of TPPNi solution (in chloroform) and thin film (prepared by spin coating its solution in chloroform on pre-cleaned glass substrates) are somewhat similar; however, there is a significant difference in the shape of the Soret band of both spectra. Specifically, in the solution state, TPPNi macromolecule exhibited a narrow Soret band; whereas, the Soret band has become substantially broader in the solid-state spectrum. In addition, the characteristic Soret band peak has been observed to be redshifted significantly. The observed results may be due to the aggregates formation in thin film, that ultimately results in an increased π–π interaction, as reported by some other studies [Porphyrins have two electronic transitions in the visible domain of the electromagnetic spectrum: a Soret band at 350–500 nm and Q-bands around 500–700 nm with typically one order of magnitude lower intensity . The UV– studies ,27,28. Structural study of TPPNi: The crystalline structure of the TPPNi semiconducting layer has been analyzed by X-ray Diffraction (XRD) pattern, which displays diffraction intensity as a function of 2θ (as shown in Surface morphology of TPPNi thin film: field emission scanning electron microscopy (FESEM) has been used to characterize the surface morphology of a pristine TPPNi thin film. The FESEM micrographs a,b depicThe microporous structure of the active thin film is envisaged to be vital for superior humidity sensing ability since it allows a stronger interaction between the analyte (water molecules) and the sensing layer. Hence, we believe that TPPNi is an ideal template for humidity sensing by virtue of bulk porosity and essential void spaces (between microstructures), which may assist the efficient humidity circulation through the bulk. Further, the irregular-shaped sub-micron particles embedded on the pyramid-shaped structures are also believed to provide a larger specific area for improved humidity adsorption.To supplement the aforementioned experimental results, the morphology of the pristine TPPNi thin film has also been studied via atomic force microscope (AFM). Admittedly, the 2-D topographic AFM scan a is signA), inter-electrodes gap (d) and the dielectric permittivity constant (rε) of the TPPNi dielectric material influence the capacitance of the fabricated device  [C” is the capacitance of the fabricated device and “ε0” represents the dielectric permittivity of air.Humidity sensing performance study of TPPNi Generally, humidity influences a wide variety of physical, chemical and biological processes, and these effects can later be exploited to estimate variation in varied humidity levels . When option (1) .(1)C=ε0rε, A, or d  or electrode separation (d) are pretty uncommon). The dielectric permittivity of vacuum is exactly 1, and that of notable gases is within 1% of unity [Interestingly for efficient detection of chemical analytes/gas molecules via capacitive-sensing mechanism, the molecules of interest must induce a remarkable change either in of unity . Reasonaof unity .rε) and polarizability (dα) as given in Equation (2) [dN and dα represent number density of molecules and polarizability in sensing layer in dry condition.dN and dα represent number density of molecules and polarizability in sensing layer in wet/humid condition. Here dryε and wetε are the relative dielectric constants for the desiccated and humid active sensing layer, respectively, and “n” is the dielectric morphology related factor. Generally, the dielectric permittivity of desiccated organic semiconductor layer is ~5 which is considerably smaller than that of water ~80 [Dielectric permittivity of the active humidity sensing layer is triggered by polarization in the TPPNi layer (humid and desiccated). Typically, there are four mechanisms i.e., dipolar, ionic, space charge, or electronic, which may contribute towards polarizability of the active layer . The Clation (2) , where, acitance .(3)CSC0ater ~80 . Naturalater ~80 .The capacitance variation in the 39–58%RH range is not noticeable, as seen in °C–80 °C), the capacitance of the fabricated sensor exhibited an upsurge in its value. Specifically, the capacitance increase has been observed to be ~1.3 times of the initial value when the temperature was gradually increased from 55 °C–80 °C.For the ageing process, the sensor has been placed in ambient environment at room temperature for two months. The sensor has later been tested again under different %RH levels for two round tests. During the test, the sensor showed good stability, consistency and repeatability. Specifically, the sensor showed an average of ~3.42% decrease in capacitive response at 500 Hz after the ageing process. The capacitance of the fabricated humidity sensor has also shown reasonably good stability with the changes in temperature until ~55 °C. However, with further increase in the temperature from  is depicted in 3O)+ as charge carriers, as described in chemical Equation (4). Therefore, the conductivity of the semiconductor thin film at higher %RH is now dictated by the ionic conduction [+) to its neighboring water molecule, and the chain reaction continues. The effective proton hopping between neighboring molecules in physiosorbed H2O molecules layers considerably reduces the electrical impedance of the TPPNi sensing layer [The operating mechanism of impedance-type sensors may be described with the help of the Grothus mechanism. At low %RH range, primarily immobile chemisorbed water molecules layer is formed on the surface of TPPNi thin film, and the conduction of the active layer at this stage is mainly by virtue of intrinsic electrons only . Furthernduction . In bulkng layer .(4)H2O+When analyzing the sensor’s performance, the response time or the recovery/reset time is a critical parameter of interest. It is computed during the humidification/desiccation cycle of the humidity sensor’s dynamic curve . The senFabrication and characterization of TPPNi thin films for their use as surface type humidity sensors have been studied for the TPPNi synthesized by microwave-assisted method. An optical study is enabled to visualize the reason for broadening in Soret band absorption spectra and observed redshift in the peak absorption values for solid-state TPPNi in comparison with solution state TPPNi. The observed “halo” pattern in XRD structural characterization has clearly demonstrated that the fabricated thin films possess amorphous, glassy, or disordered structures. Furthermore, FESEM investigation has confirmed that TPPNi thin films comprise essentially of micro-pyramidal shaped structures, which is foresighted to be useful to increase the specific area for humidity absorption. The surface morphological study has also shown that the interior volume of the active sensing layers has fine pores/voids, which are speculated to be the main admittance sites for humidity and facilitates the adsorption kinetics of water inside the active sensing film. By registering AC capacitance and impedance, the feasibility of the recommended active layer for humidity sensing to differentiate between varying %RH levels has been demonstrated. With an increase of %RH level from 39 to 85 percent, the amount of capacitance and the impedance value has changed 54.36 times at 500 Hz and 28.32 times at 1 kHz. This incremental variation of capacitance is expected due to the high difference in dielectric permittivity constants of water and TPPNi thin film. The pronounced conductivity at the high order of humidity levels may be the source of the drop in the value of sensor’s impedance at raised %RH levels. The sensitivity of the fabricated devices towards ambient humidity has been measured to be 146.17 pF/%RH and 48.23 kΩ/%RH for capacitance and Impedance measured at 500 Hz and 1 kHz, respectively. The observed increase in the sensitivity compared to previously published noteworthy humidity sensors can be correlated to prominent high surface roughness in TPPNi thin films, which causes the high surface-to-volume ratio. In comparison with published set of humidity sensors, it has been shown that TPPNi semiconductor-based humidity sensor can effectively function quasi linearly in dual (capacitive as well as conductometric) mode for ambient relative humidity monitoring with superior sensitivity with a compromise in response recovery/reset time.


The data provided by the atomistic simulations were then used in the Finite Element Method (FEM) simulations to evaluate the effective thermal conductivity of polymer nanocomposites at the continuum level. We explored the effects of nanofiller type, volume content, geometry aspect ratio and thickness on the nanocomposite effective thermal conductivity. As a very interesting finding, we found that borophene nanosheets, despite having almost two orders of magnitude lower thermal conductivity than graphene, can yield very close enhancement in the effective thermal conductivity in comparison with graphene, particularly for low volume content and small aspect ratios and thicknesses. We conclude that, for the polymer-based nanocomposites, significant improvement in the thermal conductivity can be reached by improving the bonding between the fillers and polymer, or in other words, by enhancing the thermal conductance at the interface. By taking into account the high electrical conductivity of borophene, our results suggest borophene nanosheets as promising nanofillers to simultaneously enhance the polymers’ thermal and electrical conductivity.Graphene and borophene are highly attractive two-dimensional materials with outstanding physical properties. In this study we employed combined atomistic continuum multi-scale modeling to explore the effective thermal conductivity of polymer nanocomposites made of polydimethylsiloxane (PDMS) polymer as the matrix and graphene and borophene as nanofillers. PDMS is a versatile polymer due to its chemical inertia, flexibility and a wide range of properties that can be tuned during synthesis. We first conducted classical Molecular Dynamics (MD) simulations to calculate the thermal conductance at the interfaces between graphene and PDMS and between borophene and PDMS. Acquired results confirm that the interfacial thermal conductance between nanosheets and polymer increases from the single-layer to multilayered nanosheets and finally converges, in the case of graphene, to about 30 MWm Such remarkable improvement was attributed to the creation of a tight percolation network of graphene platelets; in percolation theory, above the percolation threshold the thermal conductivity boosts, determining a bi-linear trend [−1 K−1 for neat SR to 0.3 W m−1 K−1 for the composite. The comparison between the work of Zhao [Thermal management is a design issue in several fields, such as electronics and electrified vehicles. In fact, inappropriate thermal management may result in the sudden or local rise of hot spots, which not only can substantially shorten a device’s life but can also lead to hazardous operating conditions. In recent years, the development of flexible devices, such as wearable technologies, have presented new challenges in thermal management, as traditional solutions are often less effective. After graphene was successfully isolated in 2004 ,2, two-d−1 K−1 . Within −1 K−1 ,7 monola−1 K−1  and was −1 K−1 , borophe−1 K−1 . The mos−1 K−1 ,12, boro−1 K−1 . Moreove−1 K−1  found thar trend ,16. The ar trend  were obtar trend  adopted  of Zhao  and Tian of Zhao  points o of Zhao  reviewed of Zhao  or the eIn the present work, our objective is to explore the effectiveness of borophene as a novel and highly important nanomaterial for the enhancement of polymers’ thermal conductivity. For the sake of comparison, we compare the same structures made of graphene, representing one of the most well-performing and deeply studied materials of the last decade. For this goal we performed combined atomistic continuum multi-scale modeling. This approach follows a two-stage procedure. First, we conduced classical molecular dynamics simulations to calculate the interfacial thermal conductance  that ri2 C, sp3 C and B. The equilibrium distance and potential energy well depth were calculated by applying Lorentz-Berthelot mixing rules [3)2-O- units, Si-methyl terminated, for a total of 507 atoms. To trigger proper interactions between PDMS chains and the layered materials, PDMS molecules were packed in a larger simulation box, with PBC set in all coordinates. This system was made of 30 PDMS chains  made by a modified Markov process [3. To reach a densely packed PDMS, the system was first equilibrated using Nosé-Hoover thermostat (NVT) at 300 K and then was heated up to 500 K to allow the rearrangement of atomic position. The system was then cooled down to 300 K with the Nosé-Hoover barostat and thermostat (NPT). The final density of the polymer volume was set to 0.97 ± 0.05 g cm−3, to fit the typical literature values [From the multi-scale modeling point of view, in order to investigate the effective thermal conductivity of nanocomposites, one needs to know the thermal conductivity of the polymer and nanosheets as well as the thermal conductance between these two phases. In this section, we first explain the conduced classical Molecular Dynamics (MD) simulations to evaluate the thermal conductance between nanosheets and PDMS. Taking the values for the thermal conductivity of pristine nanosheets from the literature, we will then discuss the continuum FEM simulations. To perform the MD simulations, the Large-scale Atomic-Molecular Massively Parallel Simulator (LAMMPS) ,23 packang rules  from Uning rules . The pree values . After oEffective thermal conductivities of PDMS-based nanocomposites were obtained using FEM with ABAQUS-Standard software, along with Python subroutines for the modeling of nanocomposite samples. We evaluated the effective thermal conductivity by solving a steady-state heat transfer problem, in which load is applied by heat fluxes. The computational details are the same as those in our earlier study . In thesIt should be first noted that there are several reports that state that, within layered 2D materials, the interfacial thermal conductance between nanosheets and substrate can be affected by the thickness or number of layers . The afo2, which means a contact area of twice the aforementioned value form with PDMS polymer in the thermal conductance calculations. The height of the systems varied from 84.6 to 105 Å, depending on layer stacking. Each layer of graphene, 3.4 Å thick, was made of 1760 carbon atoms, bringing the total amount of atoms, including the PDMS, from 32,180 individual atoms for single layer graphene to 40,980 atoms for the six-layer model. Similarly, for the borophene models, the contact area is about 4289 Å2. In this case, 1260 atoms are included in each layer of borophene, bringing the total amount of atoms in the final models from 31,680 for the single layer borophene to 37,980 atoms for six-layer borophene. The height varied with borophene layer thickness; therefore, the size of composite systems along the stacking directions varied from 92 Å for the monolayer to 112 Å for the six layers of borophene. The slight difference in cell topology between graphene and borophene models is due to the lattice differences of the crystalline materials.To determine the interfacial thermal conductance values for PDMS–borophene and PDMS–graphene interfaces, the asymptotic value of convergence occurring around six layers ,35 was cpM and filler fM, the heat capacity of polymer pCp, filler fCp, and the interfacial area A, the interfacial thermal conductance across the interface To calculate the thermal conductance between PDMS polymer and the layers of graphene and borophene platelets, the thermal equilibration method ,38,39,40tion (1) ,39.(1)Δ−1K−1 for PDMS [−1K−1 for graphene [−1K−1 for borophene [T(t), decays exponentially. By conducting a fitting to the temperature difference, the interfacial thermal conductance was evaluated using Equation (1).The heat capacity values adopted in this work are literature values: 1.46 J gfor PDMS , 0.71 J graphene  and 1.02−2 K−1 for the six- and seven-layer graphene–PDMS systems, in agreement with the literature [−2 K−1, which is 10% more than that of the graphene–PDMS interface. This result shows that the buckled structure of borophene could enhance the heat transfer at the interface with the polymer even better than graphene.In terature ,35. In t−1 K−1 [−1 K−1 [effk = LqΔT−1, where L is the size of RVE, q is the applied heat flux and ΔT is the established temperature difference between the two ends of the model.The values of thermal conductance calculated by MD simulations were implemented within a continuum model to calculate the effective lattice thermal conductivity of macroscopic samples using the finite element approach. In this work, the thermal conductivity of multilayer graphene and borophene is taken from the literature and assumed to be 2000 Wm−1 K−1 ,43 and 7 [−1 K−1 , respect−1 K−1), demonstrating enhancement due to the presence of fillers with higher thermal conductivity. The volume fraction of the filler, as known from the literature, was confirmed as the typical parameter to tune in order to improve heat transfer in composite materials; 4% of filler about doubled the TC compared to 1%. As expected, by increasing the volume fraction and aspect ratio, the effective thermal conductivity of PDMS nanocomposites increased monotonically. By increasing the aspect ratio, the fillers allowed more direct heat transfer along the composite. As known from the literature [We first studied the effects of volume fraction and aspect ratio on the effective thermal conductivity of nanocomposites, and the obtained results are shown in terature , short p−2 K−1 and 33 MWm−2 K−1, respectively. Acquired results confirm that the interfacial thermal conductance between nanosheets and polymer increases from the single-layer to the multilayered nanofillers and finally converges, in accordance with the adopted technique. These estimated converged values were then employed to define contact thermal conductance in the finite element modeling of nanocomposites’ representative volume elements. Taking into account the high electrical conductivity of borophene, our results therefore suggest borophene nanosheets as promising candidates for the improvement of polymers’ thermal and electrical conductivity. As a very interesting finding, we showed that borophene nanosheets, despite having almost two orders of magnitude lower thermal conductivity than graphene, yield very close enhancement in the effective thermal conductivity in comparison with graphene, particularly for low content and small aspect ratio and thickness. This finding confirms that, for polymer-based composites, thermal resistance between the fillers and matrix can dominate the heat transport. Thus, significant improvement in the thermal conductivity can be reached by improving the bonding between the fillers and polymer, or in other words, by enhancing the thermal conductance at the interface, for example, by chemical functionalization. Additionally, the possibility of manufacturing an effective percolation network through the exploitation of flake-to-flake junctions represents the most efficient and challenging route to improve the thermal conductivity of nanocomposites. The future development of theoretical models capable of managing flake-to-flake thermal conductance and chemical functionalization will reduce the gap between the experimental and the computational approaches, driving a more accurate generation of predictive studies.In this study, a combined atomistic continuum multi-scale modeling approach was developed to explore the effective lattice thermal conductivity of polymer nanocomposites made of PDMS and graphene or borophene nanofillers. This approach includes an initial step where classical molecular dynamics simulations were employed to investigate the interfacial thermal conductance between graphene–polymer and borophene–polymer interfaces. In a following step, the estimated interfacial thermal conductances were used within the finite element method to evaluate the effective thermal conductivity of polymer nanocomposites in the continuum. In particular, we examined the effects of nanofiller type—borophene or graphene—and their volume content, geometrical aspect ratio and thickness. Based on the Molecular Dynamics calculations, the interfacial thermal conductance between the PDMS polymer and graphene or borophene were predicted to be 30 MWm


Shorter corridors have a visible but relatively small affinity. This study provides some empirical evidence of how the corridor configuration influences the turn taking of people and provides a theoretical reference for adding a guiding function to the spatial arrangement in underground malls.In retail space, wayfinding difficulties can cause problems, such as loss of time, stress, or discomfort, negatively affecting the shopping experience of consumers and even their patronage intentions. Although studies have reported that space configuration may facilitate navigation, there has been a lack of detailed discussion, particularly in underground malls, where people often encounter wayfinding issues. In this study, a series of exit-finding tasks in virtual malls were simulated to determine if it was practical to encourage turn taking by changing the corridor width, length, height, or angle. The results showed that people have a right-turn preference during exit finding. Moreover, exit-finders mostly prefer taking the upward pathway  Traffic congestion and ground space limitations highlight the need for more urban underground spaces . In someRetailers in malls, or otherwise trying to improve wayfinding, face an interesting dilemma. The retailers want customers to stay longer in the mall to encourage impulse purchases, but exit-finding difficulties negatively influence the shopping experience of the customers and even degrade the reputation of the store . ThroughEnvironmental psychological studies have revealed the navigational function of spatial information , as theyThis study examined whether it was practical to encourage turn taking by changing the corridor width, length, height, or angle using virtual roaming technology to simulate specific turns when walking through the corridors. Four spatial configuration attributes  were extracted from a literature review and combined into pairs to obtain 11 different T-type intersections. Subsequently, the 3D Studio Max (3Dmax) and Unreal Engine 4 (UE4) were used to produce virtual malls that included all the intersections, followed by a simulated series of exit-finding tasks of 124 college students. Finally, the route choice of the participants and their time spent in the decision area were combined to measure the wayfinding performance during turn taking.Unlike navigation, wayfinding is a daily life process that may be as simple as moving from room to room or as complicated as escaping from a building . Clear dThe addition of signs, including the posted maps, is considered an effective method to resolve wayfinding problems in existing environments. Designers are keen to post arrows, swords, pictograms, and even maps on ceilings or walls at various decision points.Balancing signage simplicity and regularity is considered problematic cf., . Calori Focusing on these limitations in signage strategy, designers have attempted other ways to assist in wayfinding. For example, researchers conducting a study on hotel corridor design found that most participants selected directions with better lighting when lost because of their need for security . TiffereEnvironmental psychology-related studies have suggested that that thoughts and feelings of people are shaped by the spaces they inhabit . In an iThe corridor width is associated with privacy because it restricts the social distance among occupants. The corridor length influences the curiosity and desire of the pathfinders to explore, with longer corridors promising more information gain than alternative ones . In a trA higher spatial position usually indicates safer conditions or higher social status, the same way that a podium functions in a classroom or a lecture hall . In an oSmooth curves at intersection corners usually facilitate safe and quick turns. In an outdoor environment, building intersections usually have cut or rounded corners because pedestrians or drivers need sufficient sight distance to decide whether it is safe to turn. The corner curvature at junctions was suggested to be calculated according to the sight triangle principle, which depends on the reflection time and moving speed of the people . In an oAs suggested above, several studies have used the route choice frequency to evaluate the wayfinding performance  technology branch, through intelligent hardware and open-source game engine platforms, such as UE4 or Unity 3D . Unlike Based on a literature review , the four corridor configurations, i.e., width, length, height, and angle, were combined to generate 11 different intersections, and 3Dmax and UE4 were used to produce virtual underground malls that included all the intersections. With reference to the International Building Code , which i2/minute (service level-A) to avoid retail crowding based on the level of service standard developed by To simulate a realistic wayfinding environment as much as possible and improve the probability of wayfinding information being recognized in a complex social environment , some evAlthough the nonspatial cues in virtual malls have been controlled to avoid any effective wayfinding information besides the four spatial configurations, individuals may have an innate directional bias when facing a two-directional path. This type of directional clue (left or right) was suggested as a variable that affects the route choices of the participants . TherefoTo examine if the participants in this study have a directional bias, experiment 1 was first conducted in the control condition environment . At intersection b, the length of the left corridor was reduced from 22 to 11 m. At intersection c, an arc with a 3 m radius was added to the corner of the left corridor. For intersection d, stairs were set on the left side corridor.Taking intersection The side with different features remained the same during the experiment . Otherwise, a comparison between the test results would be meaningless because the spatial and directional clues influence the results alternately.t, the configurations on the left and right sides were changed simultaneously, and intersections e–j were obtained to compare each side with different features at intersections a–d in pairs, thereby obtaining spatial validity ranking information on turn-taking.Experiment 3 was conducted under experimental condition 2 , with vat-tests and F-tests), and a 0.5 effect size, a 0.05 α value, and a 95% confidence level were achieved. To properly implement the one-sample and paired t-tests, this study used a convenience sample comprising 124 college students, aged 18–32 years  from Pusan National University in Korea . To improve the smoothness of the virtual experiments, the participants were required to have VR gaming experience when recruited. All the participants were recruited via campus e-mails and posts on the college bulletin board, and the wayfinding simulation experiments were conducted in the department laboratory. The study was approved and conducted in accordance with the standards of the Institutional Review Board of the university, and all participants completed an informed consent form before the study. Shopping vouchers were provided as an incentive for participation.G-Power 3.1.9.2.2 was used to obtain good statistical significance  cf., . SpecifiWhen pathfinders faced a bidirectional path decision, their left- or right-turn preference should be complementary in theory . Simply t is the time spent in the decision area, then the wayfinding performance p can be expressed as follows (1):Considering the inverse relationship between the time spent and wayfinding performance , if t isa = -0.045 and b = 1.1577 were obtained , 120 cases  remained after removing the outliers and technical errors. The time that the participants spent in the decision-making area ranged from 3.5 to 14.6 s. Hence, the two extreme points “i”  and “ii”  were substituted into formula (1), and obtained . The wayBased on the literature in Section “Spatial Configuration and Wayfinding”, five hypotheses were formulated to explore the relationship between the corridor configuration attributes  and turn taking of the exit-finders:t, the exit-finders prefer to turn right.H0: At intersection a, the exit-finders prefer to turn right (wider path).H1: At intersection b, the exit-finders prefer to turn right (longer path).H2: At intersection c, the exit-finders prefer to turn left (path with a curved corner).H3: At intersection d, the exit-finders prefer to turn left (path with steps on the floor).H4: At intersection t-test was conducted to verify the tendency of the participants to turn right after the control condition experiment (experiment 1). A paired sample t-test was performed after experiment 2 to determine if the configuration of the intersection, rather than the innate left- or right-turn preference of the participants, affected their turn taking. A paired sample t-test was conducted after experiment 3 to compare each side with different features at intersections a–d in pairs, thereby obtaining spatial validity ranking information on turn taking.A one-sample t was calculated using formula (1). The results in t, with the same corridor configuration attributes, the exit-finders exhibited a mean right-turn performance of 62.22% (>50%). This suggests that the participants may have preferred to turn right while attempting to find an exit; those who turned right spent less time in the decision area than those who turned left.When the participants finished the wayfinding task under the control condition (experiment 1), the right-turn performance of all 120 participants at intersection t-test confirmed that at intersection t, the participants exhibited an apparent right-turn tendency while looking for an exit (p = 0.05). Therefore, H0 was supported.The one-sample a–d was computed. To illustrate , which increased the right-turn performance of the participants  from 62.22% (at control condition intersection t) to 72.99%. Such an increase in the right-turn performance indicated that broader corridors increased the original preference of exit-finders for right turns. At least three factors may have contributed to an increase in right turn performance: (1) the number of participants who turned right increased; (2) the number of participants who turned right did not change, but the participants who turned right spent less time at intersection a than at intersection t; (3) both the number of participants who turned right and their time spent did not change, but the participants who turned left were more hesitant and took longer to make a decision.After experiment 2, the right-turn performance of the 120 participants at intersections lustrate , for intb, when the length of the left corridor was reduced from 22 to 11 m, the right-turn performance of the exit-finders decreased from 62.22 to 23.47% (<50%). This means that a shorter corridor disrupted their original preference for turning right and increased their likelihood of turning left. While some maze design studies have found that people prefer longer or deeper corridors when finding exits , the stairs on the left side of intersection d were set. As a result, the average right-turn performance of the exit-finders was reduced further to 13.76%, as they finally chose to turn left despite their original right-turn preference.At intersection t-test results of all the experimental conditions (a–d) and control conditions exhibited significant differences (p = 0.05). This finding supported H1, H3, and H4 but not H2.The e–j  At intersection f, their right-turn performance was 67.86%. (3) At intersection g, the participants preferred to turn right, with a mean performance of 85.24%, which indicated that people might prefer a taller corridor to a wider configuration. (4) At intersection h, the participants chose to turn right with a mean performance of 72.87%. This indicated that exit-finders were more likely to choose a smoother corridor to a shorter configuration. (5) At intersection i, the participants preferred to turn right, with a mean performance of 85.15%, suggesting that people were more inclined toward a taller corridor over a shorter configuration. (6) At intersection j, the participants chose to turn left with a mean performance of 76.26%.After experiment 3, the right-turn performance of each participant was calculated separately at intersections e–j : (1) At t-test between the experimental condition intersections (e–j) and control condition intersection t indicated that the right-turn performance of the participants at intersections e and f was similar, suggesting that they had difficulty choosing between shorter and wider corridors, and between wider and smoother corridors. Nevertheless, further research is warranted because some participants stated that they hardly noticed the width discrepancy in the two routes despite their 2-m difference.The results of the paired sample Overall, this study addressed two issues to improve wayfinding at T-type intersections in underground malls: whether the turn taking of exit-finders was influenced by adjustments in corridor configurations, i.e., width, length, height, or angle, and how much these spatial configuration attributes influenced the turn-taking decisions of the exit-finders and enhanced the practicality of the study.via random sampling. On the other hand, according to b, which is a departure from previous views. This is because e and f. Although exit-finders are more inclined to turn right than left at intersections e and f , and with specific subjects (students). To enhance the external validity of our findings, future replications are needed using different participants , different countries and cultures, different settings .If the exit paths in underground shopping malls simultaneously fulfill the features of being “wider,” “shorter,” “taller,” and “smoother,” they will be considered “more attractive.” In other words, people will find these exits more natural and efficient. In practice, however, it is difficult for the corridor configurations of underground malls to fulfill all four requirements due to the constraints of the built environment or other factors. Therefore, mall managers need to make optimal choices according to their judgment.Based on these results, this paper provides the following suggestions. First, creating visible spatial differences in a vertical direction, such as setting steps, slopes, or other exit path facilities, is important for guiding people toward exits. Steps or slopes need to be near decision points within the sight of people. The usability of stairs should also be considered, for example, whether they have gentle slopes and handrails to facilitate passage for the elderly or disabled individuals. In cases where the existing environment does not allow steps to be added, other architectural methods, such as the addition of vaulted ceilings or atrium spaces that introduce natural light, may be employed to remind people that they can go up from here. Second, visually shorter corridors also have an apparent guiding function associated with the time cost. Generally, setting exits relatively close to intersections helps improve wayfinding performance. If building structure restrictions require an exit to be located far from a decision area, an autowalk could be installed, or some horizontal or vertical structures could be added, such as beams or pillars, to divide the passage into segments, which can reduce the stress caused by long distances. Third, the width of an exit corridor should be increased to help pathfinders find exits more efficiently and prevent accidents, such as stampedes, during an emergency. If the width of a corridor is fixed and cannot be changed, the path space can be expanded by adding a curved corner at the intersection, and reflective metals or panels can be used for corridor decoration. Finally, setting a specific arc at the intersection corner also helps guide people toward an exit, as curved wall corners can help improve the sight of the pathfinders, thereby improving their perception of safety and confidence when turning.Although these recommendations are not fully applicable to aboveground buildings, they may have specific reference value for improving the spatial layouts of hospitals, schools, and nursing homes. For example, at T-type intersections, if the exit follows a higher, shorter, wider, or smoother direction according to the spatial preferences of the exit-finders, the opposite direction will inevitably be “unpopular” or “unreachable” but will increase spatial privacy. A corridor in a direction opposite to the exit is appropriate when organizing spaces, such as lounges, reading rooms, and other areas requiring privacy and silence. In contrast, a corridor in the direction of an exit is more appropriate for planning relatively popular spaces, such as entertainment and conference rooms, thereby ensuring that crowds can evacuate in the event of a wayfinding problem.The original contributions presented in the study are included in the article/The studies involving human participants were reviewed and approved by Pusan National University Institutional Review Board, PNU IRB. The patients/participants provided their written informed consent to participate in this study.SZ and SP have made substantial contributions to the conception or design of the work; or the acquisition, analysis, or interpretation of data for the work. SZ have drafted the work or revised it critically for important intellectual content. Both authors have approved the final version to be published, we agree to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.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.


Fe–L1. We designed Fe–L1 to “break-apart” upon HO-1-catalyzed porphyrin degradation,perturbing the efficient FRET mechanism from a coumarin donor to aporphyrin acceptor fluorophore. Analysis of HO-1 activity using Escherichia coli lysates overexpressing hHO-1 found thata 6-fold increase in emission intensity at 383 nmwas observed following incubation with NADPH. The identities of thedegradation products following catabolism were confirmed by MALDI-MSand LC–MS, showing that porphyrin catabolism was regioselectiveat the α-position. Finally, through the analysis of Fe–L2, we have shown that close structural analoguesof heme are required to maintain HO-1 activity. It is anticipatedthat this work will act as a foundation to design and develop newprobes for HO-1 activity in the future, moving toward applicationsof live fluorescent imaging.Heme oxygenase-1(HO-1) is a vital enzyme in humans that primarilyregulates free heme concentrations. The overexpression of HO-1 iscommonly associated with cardiovascular and neurodegenerative diseasesincluding atherosclerosis and ischemic stroke. Currently, there areno known chemical probes to detect HO-1 activity, limiting its potentialas an early diagnostic/prognostic marker in these serious diseases.Reported here are the design, synthesis, and photophysical and biologicalcharacterization of a coumarin–porphyrin FRET break-apart probeto detect HO-1 activity,  HMOX1 and HMOX2 genes, respectively. The primary roleof HO is to prevent the accumulation of cytotoxic “free”heme (Fe-PPIX),2 which has the potential to actas a Fenton catalyst in vivo, leading to the generationof reactive oxygen species.  Heme catabolism is a three-step reaction that requires molecularoxygen, NADPH, and cytochrome p450 reductase  and ferrous iron (Fe2+). Biliverdin is further convertedto bilirubin by biliverdin reductase (BVR) in the cytosol.5 Both isoforms catalyze heme degradation.6 However, HO-1 is the only isoform that is inducedby cellular stress stimuli in the body and has a defensive role ina number of diseases including atherosclerosis8 andsome cancers.11Heme oxygenase (HO)is an important homeostatic microsomal enzymein vascular biology and cell signaling. There are two active mammalianisoforms, namely HO-1 and HO-2, encoded by the eductase 1.3,4 Dur2+ is chelated by ferritin, where it issafely stored out of Fenton activity, and a number of studies havedemonstrated that CO is an essential intracellular signaling molecule,activating the KATP ion channel12 and suppressing endothelial cell apoptosis.14 Finally, bilirubin has also been proven to display antioxidant properties.15 Individuals with bilirubin concentrations abovebasal levels, in genetic disorders such as Gilbert syndrome, are significantlyless likely to develop cardiovascular disease over their lifetime.16Each of the byproducts of heme degradation is known to becytoprotective.For example, Fe18 and coronary artery disease.19 In atherosclerosis,HO-1 is induced during intraplaque hemorrhage (IPH), a rupture ofthe vulnerable plaque coating the artery walls. IPH is an atheroaccelerant,releasing cholesterol-enriched membrane lipids and hemoglobin intothe plaque interior.20 In turn, IPH leadsto the development of more advanced vulnerable plaques and can furtherlead to the development of blood clots, restricting the blood flowto the heart and the brain.HO-1 plays a protective role in atherosclerosis,a leading causeof death in the western world. Defined by the gradual buildup of plaqueon the artery walls, atherosclerosis has no symptoms in its mild formbut, dangerously, over time can lead to the onset of ischemic stroke23 Its high sensitivity and spatial resolution allowfor the detection of a variety of biological targets.25 Fluorescence resonance energy transfer (FRET) is a distance-dependentdipolar interaction between two fluorophores that can unlock detailedinformation on the nanometer scale.26 Theprocess is characterized by a nonradiative energy transfer from adonor fluorophore to an acceptor, providing there is a good spectraloverlap between the donor emission and acceptor absorbance spectrumand they are close enough in space.Fluorescence imaging is a powerful,noninvasive imaging modalityused in cell biology.26 labile pools of biologically relevant metal ions,28 peroxynitrate anions,29 and “free”heme.32 The biosensing of enzyme activity by ratiometric“break-apart” probes has enabled enzyme activity tobe detected in real-time.35 Many of these probes are peptide-based,sensing cutting enzymes such as caspase-3,36 and recently, an alternative method has been developed enablinga “labeling after recognition” strategy to be utilizedeffectively.37Over the years, FRET probeshave been designed to detect numerousbiological processes including protein folding,There are no knownchemical probes to detect HO-1 enzyme activity.Current enzyme assays are long and cumbersome processes, and mostdo not allow real-time kinetic measurements. The development of afluorescent chemical probe to detect HO-1 will, therefore, significantlymove the field forward. Such an advancement will enable the detectionof IPH and potentially plaque instability, often the portent of plaquerupture and severe associated conditions.38 In contrast, Liuand co-workers developed a Zn–coumarin–porphyrin FRETprobe based on 5-(4-hydroxyphenyl)-10,15,20-triphenyl porphyrin (HP-TPP)and monitored the binding properties to DNA.39Recently, coumarin-porphyrindiads have gained an increasing interest,displaying a high FRET efficiency between the coumarin donor and theporphyrin acceptor fluorophores. In 2011, Lin and co-workers reporteda ratiometric coumarin–porphyrin probe for biologically relevantthiols. For example, cysteine cleaved the disulfide bond linking thetwo fluorophores, resulting in a 60-fold increase in the coumarinemission intensity.Fe–L1 (Fe–L1 is basedon the structure of dimethyldeuteroheme (Fe–DMD), a symmetricalanalogue of Fe–PPIX, known to display an activity toward HO-1.40 The “turn-on” fluorescent probewas designed to exploit the regioselective α-cleavage of Fe-PPIXobserved during HO-1 catabolism. In this process, the α-carbonatom linking the coumarin donor and porphyrin acceptor fluorophoresis lost during porphyrin decyclization and the FRET process is switchedoff, resulting in an increase in the fluorescence emission intensityof the coumarin donor fluorophore . Additionally, 7-hydroxymethylcoumarinderivatives are also known to be fairly photostable,42 including compound 1 , a characteristic that will importantly maximize the observed increasein fluorescence following enzymatic probe cleavage.Here, we report the design, synthesis, photophysical, andbiologicalcharacterization of a “turn-on” coumarin–porphyrinFRET probe for HO-1, namely Fe–L1 2.Compleorophore 2A. A 7-hFe–L1 α-cleavage is expected to be analogous to thatof α-meso phenylheme—where regioselectivedecyclizationoccurs at the α-carbon atom to form benzoic acid and biliverdin.44 HO-1 catabolism of α-meso phenylheme occursvia a slightly different pathway from that of Fe-PPIX oxy)ethoxy)benzoic acid (1)is likely to be responsible for the fluorescence “turn-on”following porphyrin catabolism (The mechanism of  Fe-PPIX 1 and wittabolism 2A.Fe–L1 and Fe–L2 toward HO-1 catabolism.An E. coli lysate system overexpressing human HO-1(hHO-1) was selected to act as a proof-of-concept model. Complex Fe–L2 is based on the structureof HP-TPP, and the subsequent Zn-complex has been previously synthesizedby Liu and co-workers.39 In our study,the Fe complex was of greater interest, however, as Zn-porphyrinssuch as zinc protoporphyrin (ZnPP) are known to inhibit hHO-1 activity.45 As the structure of Fe–L2 differs significantly from biologicallyrelevant Fe-PPIX, it will provide an additional insight into the structuralrequirements to maintain HO-1 activity. It was expected that unlike Fe–L1, Fe–L2 would not act as a substrate for HO-1 andwould be used as a control  of the propionic acid residues.50 Such reactivity has been summarized in an excellent review by Sengeand Sitte.51 However, it still remainsa major challenge to functionalize the α-meso-position of PPIX selectively, as each of the four inequivalent meso-positions have an almost identical reactivity leadingto a mixture of species that are difficult to separate.53Over the years, numerous analoguesof protoporphyrinIX (PPIX) have been synthesized for applications from photosensitizersin photodynamic therapy (PT)meso-position of PPIX, we designed a porphyrin probe basedon Fe–DMD, Fe–L1 , first reportedby Lash and co-workers in 1994.54 Condensationof 2 with 4-hydroxybenzaldehydein dichloromethane and trifluoracetic acid formed 3 inmoderate yield following purification by column chromatography. Subsequentbenzyl ester hydrogenation and MacDonald-type condensation55 with diformyl dipyrromethene 5(6. Alkylation of 6 with 7 was achieved in DMF at room temperatureover 5 d with potassium carbonate as the base in a procedure adaptedfrom Wang and Liu.39 Complexation of 8 with FeCl2·4H2O in chloroform/methanol(3:1) and methyl ester hydrolysis under basic conditions gave riseto the formation of complex Fe–L1. Ester hydrolysis after metal complexation was found to bemuch more effective. Complexation of the free-acid porphyrin was difficultto achieve, due in part to its poorer solubility in organic solventsand purification difficulties via column chromatography. No demetalationwas observed during the ester hydrolysis of Fe–L1–DME, with only thedesired product present in the MALDI-MS.The synthetic route toward methene 5 producedFe–L2 was synthesizedas a control to Fe–L1 forthe biological characterization assays. The synthesis of Fe–L2 is based on an alkylation reaction of HP–TPP 9 with coumarin 7 under conditions identicalto those reported for the alkylation of 6 (Scheme S1).Complex Fe–L1 is predicted to produce coumarin 1 as a byproduct accompanyingbiliverdin and Fe2+. In order to confirm the identity ofthe coumarin-based degradation product formed during porphyrin catabolism, 1 was synthesized in a two-step procedure from ethyl 4-hydroxybenzoate(Scheme S2). Coumarin methyl ester 12 was also synthesized and fully characterized to assistthe mass spectrometry analysis of the E. coli lysates.HO-1 catabolism of 59 chemical probes,and organic light-emitting devices (OLEDs).60 The photophysical properties of the two coumarin–porphyrinligands and their subsequent Fe2+ complexes in this studywere recorded in aqueous solutions of PBS buffer at pH 7.4 in orderto mimic physiological conditions (Supporting Information (Table S1). It was foundin both PBS buffer and chloroform that all coumarin–porphyrindiads display excellent FRET efficiencies, estimated at greater 95%. Such a high efficiency supports the literature precedent of anefficient intramolecular energy transfer between coumarin donor andporphyrin acceptor fluorophores.39The photophysical properties of porphyrin compounds havebeen studied in great detail due to their widespread application asphotosensitizers for photodynamic therapy,nditions 1. For coormation S1. It waFe–L1 and Fe–L2 in PBSbuffer and chloroform are shown in the Supporting Information . In PBS buffer, Fe–L1 displayed a broad Soret band centered at401 nm and a broad Q-band stretching from 541 to 680 nm assigned toS0 → S2 and S0 → S1 transitions, respectively. The absorbance at 320 nm was assignedto the coumarin moiety. Biologically relevant analogues L1 and Fe–L1 displayed a significantly broader absorbance spectrumin aqueous media compared to that in chloroform. Such a phenomenonis typical of PPIX analogues, due to the increase in π-stacking,and is strongly dependent on pH and ionic strength.61 As such, slight fluctuations in the absorbance spectrawere observed for Fe–L1 with pH. However, very little change in the absorbance or emissionspectra were observed for the expected break-apart product (1) from pH 6–10 .Theabsorbance spectra of L1,analoguesof HP–TPP, L2 and Fe–L2, displayed sharper absorbancespectra in PBS buffer, and red-shifted Soret bands at 430 and 417nm, respectively . In both Fe-basedporphyrins, complexation of Fe2+ was confirmed by the changein the number of Q-bands in the UV–vis spectrum in chloroform–fromfour to two. A blue-shift in the Soret band was also observed in aqueousand organic media. Complex Fe–L1–DME, for example, displayed a 10 nm hypsochromicshift in PBS buffer after Fe2+ complexation , characteristic porphyrin emission spectra was observed infree base analogues L1–DME and L2. However, a rather differentemission profile was observed in each case. In PBS buffer, L1–DME displayed two mainpeaks at 638 and 675 nm with a broad shoulder at 708 nm . Such behavior is not surprising,as Fe2+ is well-known to quench fluorescence through electronand/or energy transfer processes.63 Complexationof Fe2+ also significantly quenches residual coumarin emission.Therefore, prior to porphyrin catabolism by hHO-1, no porphyrin andonly weak coumarin fluorescence was observed.Following FeFe–L1 and Fe–L2 act as substrates for HO-1, we incubated the two probes with an E. coli lysate overexpressing hHO-1. E. coli systems have been shown to support recombinant HO-1 function inthe absence of cytochrome p450 reductase (CPR), with the role of CPRlikely substituted by flavodoxin and flavodoxin reductase.64 Such systems are an ideal proof-of-concept modeldue to a high level of hHO-1 expression and have been used effectivelyby Sigala and co-workers to probe His-Heme ligation in HO catalysis.65 In mammalian systems, biliverdin is subsequentlyconverted to bilirubin by biliverdin reductase (BVR); however, E. coli BL21 does not express BVR. Therefore, the biliverdinproduct formed from Fe-L1 decyclizationis expected to accumulate.To determine whetherthe coumarin–porphyrin diads Fe–L1 and Fe–L2 were incubated at 37 °C (310 K) for 16 h with E. coli lysate fractions and 1 mM NADPH, a required substrateof HO-1 catalyzed heme degradation. Such concentrations of NADPH arehigher than physiological levels but were chosen to ensure maximumpossible reaction conversion for our novel design. In order to quantifyHO-1 activity, a control experiment was carried out where Fe–L1 and Fe–L2 were mixed with an equal volume of E. coli lysate without addition of NADPH and without incubation. UV–vis,fluorescence spectroscopy, and mass spectrometry analysis of the bacteriallysate systems were used to monitor the HO-1-catalyzed porphyrin degradationof Fe–L1 and Fe–L2.Complexes 1 was found to decrease at concentrationsabove 50 μM . However,it was determined that probe concentrations of 50 μM were toodilute to obtain accurate MS analysis. Instead, concentrations of200 μM were used for the mass spectrometry analysis.Probe concentrations of 50 μMwere chosen for the UV–visand fluorescence analysis of the lysates. Additionally, the emissionintensity of E. coli lysate system, Fe–PPIXwas incubated with the lysate and NADPH (1 mM). Significant changesin the UV–vis absorbance spectrum indicative of heme degradationwere observed following 16 h incubation after the addition of NADPH in the E. coli lysate support literature precedent suggesting thatthe propionic acid residues are essential to maintain HO-1 activity.67 In both cases, very little spectralchange was observed following incubation in the E. coli lysates with NADPH .Absorbance studies of the dimethylesters of Fe–PPIX (Fe–PPIX–DME)and Fe–L1, minimal spectral differences were reportedwhen Fe–L2 was incubatedwith hHO-1 and NADPH  would not form during porphyrin catabolism of Fe–L2. However, if any activitytoward HO-1 was displayed, the appearance of a peak in the range of650–700 nm corresponding to the formation of an open-chaintetrapyrrole would be expected.In contrast to Fe–PPIX and nd NADPH 4C. No shFe–L1 and Fe–L2 in thehHO-1 E. coli lysatewith and without incubation with NADPH (1 mM) are shown in E. coli lysate controls, likely due to NADPH. In the bacterial lysate, thecoumarin emission intensity was lower in Fe–L2 compared to Fe–L1. Such a fluorescence response was also observed inPBS buffer, where a 3.0-fold decrease in the coumarin emission wasreported for Fe–L2 vs Fe–L1 .The emission spectra of Fe–L1 displayed a 6-fold increase in fluorescence at383 nm following incubation with added NADPH versus the control . Thesignificant 6-fold “turn-on” in thefluorescence intensity in the coumarin region of the spectrum confirmsthat α-cleavage of the porphyrin is taking place, accompaniedby the perturbation of the coumarin–porphyrin FRET mechanism.A fluorescence increase following incubation with NADPH supports theUV–vis data in Fe–L1 reaction incubatedwith hHO-1 expressing E. coli lysate and NADPH, noincrease in fluorescence emission intensity versus the control experimentwas observed .Fe-DMD analogue  control 5. Such antrol .It was also envisaged that these techniques would provide additionalinformation on the regioselectivity of the α-cleavage and confirmthe chemical structure of the break-apart products.In order to further certifyand understand the porphyrin catabolism of E. coli lysateswere first acidified in H2SO4/methanol (5% v/vH2SO4) to form their subsequent methyl estersand extracted into chloroform. Such procedures have been used previouslyto good effect to form organic soluble biliverdin dimethyl esters,enabling the regioselectivity of heme analogues to be studied followingporphyrin catabolism44Prior toMS analysis, reaction samples from the Fe–L1 in E. coli lysates containing excess NADPH,there was only evidence for the formation of one biliverdin compoundwith a mass of 587 Da . Signalsfor both mono- and dimethyl esters of Fe–L1 are also present, supporting the UV–visdata .From MALDI-MS it was determinedthat porphyrin catabolism is regioselectiveat the α-position with the release of the coumarin donor fluorophore.Following incubation of f 587 Da S18. SignFe–L1,MALDI-MS of Fe–L2 reactionmixture extracts in the absence and presence of NADPH produced identicalMALDI-MS spectra .There was no evidence toward formation of any porphyrin degradationproducts following incubation with excess NADPH.In contrast to Fe–L1 and Fe–L2 with and without incubation with NADPH(1 mM) were compared to compound 12, the methyl esterof the predicted break-apart product 1. The UV detectionwas set to 320 nm, the absorbance wavelength maximum for 12 and 1 . Samplesof 12 and 1 6.12 displayed a LC retention time of 12.1min and a mass of 341 Da, suggesting that methyl ester hydrolysiswas occurring during the analysis , or for the reaction mixture extractsof Fe–L2. Such an observationsupports the UV–vis and fluorescence measurements in Compound analysis 6A,C. It and mass 6A,D. SucFe–L1, a coumarin-porphyrin FRET probe for hHO-1. We have shown usingan E. coli lysate overexpressing hHO-1 that followingincubation with excess NADPH a 6-fold “turn-on”in fluorescence at 383 nm is observed. The increase in fluorescenceis due to porphyrin α-cleavage and the perturbation of FRETfrom a coumarin donor to a porphyrin acceptor fluorophore. The identityof the coumarin break-apart product was confirmed by LC-MS to be compound 1, supporting work by Ortiz de Montellano and co-workers whodetected the formation of benzoic acid following HO-1 oxidation ofα-meso-phenylheme.43 Moreover, we have demonstrated from MALDI-MS analysis that porphyrincatabolism of Fe–L1 isregiospecific at the α-position.Herein, we report thedesign, synthesis, photophysical, and biologicalcharacterization of Fe–L2 was found to not actas a substrate for hHO-1 from UV–vis,fluorescence, and mass spectrometry analysis. Therefore, it was usedas a control in the assay experiments. The synthesis and analysisof Fe–L2 have providedan additional insight into the structural tolerance of the hHO-1 activesite. It is likely that the addition of three meso-phenyl substituents provide anadditional steric hindrance in the HO-1 binding pocket reducing itsbinding affinity and subsequent activity. It is expected that theabsence of two propionic acid residues in Fe–L2 is also responsible for the lack of metabolismby HO-1. These residues are known to have important electrostaticinteractions with positively charged side chains lysine (Lys18) andarginine (Arg183), anchoring heme analogues in the HO-1 active site.The importance of the propionic acid residues is further highlightedfrom the UV–vis spectra of Fe–PPIX–DME and Fe–L1–DME in E. coli lysates where no spectral change wasreported following addition of NADPH and incubation.HP-TPP analogue E. coli lysates, we are now investigatingthe biological characterization of Fe–L1 in mammalian cells and human derived macrophages,with promising data . Moreover,it is thought that a FRET break-apart probe of this nature could beused to identify HO-1 overexpression in real-time and as a researchtool to accelerate work on the pathophysiology of HO-1. Critically,it could be developed into a real-time imaging and detection reagentthat would allow the detection of hemorrhagic pathologies. These includecoronary intraplaque hemorrhage in cardiology, or other internal hemorrhagesin stroke or aneurysm. Since hemorrhage or HO-1 is suspected to playa role in many pathologies, the scope for development is significant.We also note that this is one of the first descriptions of the applicationof the FRET break-apart principle to a small/medium-sized moleculemetabolite. This principle could, therefore, be extended to otherinteresting medium-sized metabolites, such as lipids.To thebest of our knowledge, this is the first known chemicalprobe capable of detecting HO-1 activity. The work detailed here showsvery encouraging and promising results. Following our proof-of-conceptstudy in 2+, allowing the porphyrin to act as a fluorescent donor to a NIR acceptor.Another possible avenue to explore is to incorporate both the donorand acceptor fluorophores onto the structure of Fe-DMD. We are alsoexploring the possibility of experimenting with altering the polypyrrolestructure to red-shifted polypyrroles, such as bacteriochlorins, thatare expected to interact with some of the smaller NIR dyes. To thisend, work is currently ongoing to develop new probes with red-shiftedwavelength maxima, to improve the photophysical properties for livefluorescence imaging. It is important to note that care must alsobe taken to ensure that the chosen fluorophore(s) have a high photostabilityprior to undertaking these experiments.The structureof our probe offers flexibility in design for futuremodifications, with the possibility of developing a FRET system containinga more favorable NIR fluorophore. First, a NIR analogue could be achievedfollowing coordination of an alternative metal ion, e.g. MgThe development of suchprobes will continue to further advancethe field and could enable a range of cardiovascular and neurodegenerativedisorders to be diagnosed more effectively in the near future.