Vanadium Oxide‐Doped Laser‐Induced Graphene Multi‐Parameter Sensor to Decouple Soil Nitrogen Loss and Temperature

Monitoring nitrogen utilization efficiency and soil temperature in agricultural systems for timely intervention is essential for crop health with reduced environmental pollution. Herein, this work presents a high‐performance multi‐parameter sensor based on vanadium oxide (VOX)‐doped laser‐induced graphene (LIG) foam to completely decouple nitrogen oxides (NOX) and temperature. The highly porous 3D VOX‐doped LIG foam composite is readily obtained by laser scribing vanadium sulfide (V5S8)‐doped block copolymer and phenolic resin self‐assembled films. The heterojunction formed at the LIG/VOX interface provides the sensor with enhanced response to NOX and an ultralow limit of detection of 3 ppb (theoretical estimate of 451 ppt) at room temperature. The sensor also exhibits a wide detection range, fast response/recovery, good selectivity, and stability over 16 days. Meanwhile, the sensor can accurately detect temperature over a wide linear range of 10–110 °C. The encapsulation of the sensor with a soft membrane further allows for temperature sensing without being affected by NOX. The unencapsulated sensor operated at elevated temperature removes the influences of relative humidity and temperature variations for accurate NOX measurements. The capability to decouple nitrogen loss and soil temperature paves the way for the development of future multimodal decoupled electronics for precision agriculture and health monitoring.

fertilization in smart or precision agriculture. [9,10] Despite their paramount importance in agriculture, gas-temperature sensors with decoupled sensing mechanisms especially those prepared by low-cost and scalable fabrication methods are rarely reported. [11] Sensors and sensing systems based on low-cost manufacturing approaches [12,13,14] start to gain momentum in health monitoring and precision medicine due to their capability to collect big data from a large population and the potential to be integrated with artificial intelligence. Recent advances in gas sensors have explored various types of nanomaterials, including transition metal dichalcogenides (TMDs), metal-organic frameworks (MOFs), metal oxides, black phosphorus, as well as transition metal carbides and carbonitrides (MXene). [15][16][17][18] The synthesis strategies of these nanomaterials often involve solution phase reaction, hydrothermal reaction, chemical vapor deposition, and electrodeposition. [19] These nanomaterials prepared by relatively complex and costly methods also need to be integrated on high-resolution interdigitated electrodes that are fabricated with photolithography in chemiresistor gas sensors. [20][21][22] Meanwhile, separately integrated heaters are commonly used to elevate the temperature for expedited gas adsorption/desorption toward real-time detection. As an alternative, the gas sensing platform based on 3D porous laser-induced graphene (LIG) by low-cost laser direct writing [23] can eliminate the need for separate heaters and high-resolution interdigitated electrodes due to large specific surface area and self-heating. [24] The LIG has also been explored directly as a gas sensor and in many other sensors/devices. [23,[25][26][27] However, it is challenging to control the porous structure of the LIG foam when using common carbon-containing materials during laser processes. Efforts to address this issue lead to the exploitation of self-assembled block copolymer during direct laser writing [28,29] in preparing for the LIG with hierarchically porous structures. [30] Vanadium oxide (VO X ) as a transition metal oxide exhibits excellent properties, including n-type conductivity good chemical and thermal stability, and excellent thermoelectric properties. [31,32] VO X and its composites also show excellent performance in physically adsorbing and chemically interacting with several gases, including nitrogen dioxide, ammonia, hydrogen, and methane, among others. [33][34][35][36] However, the application of VO X and its composites is limited by complex synthesis methods, including spray pyrolysis, [37] hydrothermal, [38] sol-gel method, [39] electrospinning, [40] chemical vapor deposition, [41] and precipitation. [42] The recent report that directly synthesizes VO X with laser [43] provides inspiration and opportunities to directly laser write the VO X /LIG foam composites. Doping metal complexes in graphene is also found to improve the gas adsorption and detection sensitivity of resulting gas sensors. [44,45] In this study, we report the one-step laser direct writing method to directly synthesize VO X -doped 3D porous LIG foam nanocomposites by laser scribing the block copolymers (BCPs) doped with V 5 S 8 precursor. Different from common carbon-containing materials (e.g., polyimide, polyamide-imide, poly(ether sulfone), polyphenylene sulfide) with only one monomer, the Pluronic F127-resols with a tunable mass ratio of Pluronic F127 copolymer to resols mixture in ethanol can leverage a bottom-up self-assembly process to control the resulting mesostructures and pore size distribution. The Pluronic F127-resols film can easily modulate the porous structure by the mass ratio of BCP to resins, whereas VO X particles can be anchored on the porous LIG without aggregation. [46] The VO X /LIG gas sensor shows excellent selectivity for NO X due to the lowest unoccupied molecular orbital (LUMO) of NO X lower than that of other gases resulting in more electrons transferred from the VO X / LIG. [47] Meanwhile, the adsorption energy of VO X /LIG to NO 2 gas molecules is greater than that of other interfering gases. The heterojunction formed at the VO X /LIG interface significantly enhances the sensing performance of the multi-parameter sensor, allowing for the detection of the ultra-low concentration of 3 ppb NO 2 and a wide range of soil temperature with high sensitivity. The sensor encapsulated by a soft membrane can block the permeation of the gas molecules to respond only to temperature variations. The accurately measured temperature can, in turn, allow the dual-modal sensor to determine the NO X emission from the soil. The proof-of-the-concept demonstration to decouple NO X emission and temperature variations from the soil presented in this work can be leveraged to design and apply multimodal devices with decoupled sensing mechanisms for precision agriculture in all weather conditions. Integrating the sensor with data processing and wireless transmission modules further results in a remote environmental monitoring system to wirelessly detect NO X and temperatures for human health monitoring and precision agriculture.

Device Structure and Characterization
The VO X -doped LIG sensor can be facilely obtained by laser scribing the carbon-containing material such as Pluronic F127-resols doped with a VO X precursor such as V 5 S 8 (Figure 1a, Figure S1, Supporting Information). In brief, spin coating the V 5 S 8 -doped Pluronic F127-resols solution on a Si substrate at different speeds forms a thin film with different thicknesses (Figures S2 and S3a, Supporting Information). After drying the thermosetting phenolic resin, applying the CO 2 laser in a programmed pattern on the resulting thin film creates the VO X -doped LIG sensor, which can be scalable for massive production ( Figure S3b, Supporting Information). At a scanning rate of 12.7 µm s -1 , V 5 S 8 in the thin film is instantaneously oxidized to VO X , providing uniform doping of VO X in the 3D LIG foam. The sensor capable of decoupling the NO X and temperature ( Figure 1b) allows for NO X and temperature monitoring in the soil (Figure 1c).
The porous-structured LIG (Figure 2a) doped with the laserinduced V 5 S 8 and VO X particles (Figure 2b, red box) can be observed in the scanning electron microscope (SEM) image. Several different peaks in the C 1s and V 2p of X-ray photoelectron spectrum (XPS) spectra indicate the successful formation of graphene and VO X in the laser process ( Figure S4, Supporting Information). The two V 2p peaks at the binding energy values of 517.60 and 525 eV in the spectrum correspond to V 2p 3/2 and V 2p 1/2 , respectively ( Figure 2c). The observed binding energy values with a spin-orbit splitting of 7.4 eV are in good agreement with the V 5 + oxidation state. [37,48,49] The Raman spectra confirm the presence of few-layered graphene in VO Xdoped LIG (Figure 2d) by exhibiting three prominent peaks: the D (≈1338 cm -1 ), G (≈1524 cm -1 ), and 2D (≈2673 cm -1 ). [48] The enlarged Raman spectrum shows peaks at 142, 193, 281, 404, 695, and 991 cm -1 to confirm the formation of VO X . [50,51] The combination of LIG and VO X in VO X -doped LIG abnormally shifts the peaks compared with the previously reported VO X [51] . The X-ray diffraction (XRD) patterns of VO X -doped LIG show peaks at 24.  [52,53] The spectra confirm the presence of VO X , although it is difficult to distinguish from V 5 S 8 due to the overlap in the bands. [54,55] The distinct distributions of C, O, S, and V elements in the Energy-dispersive spectroscopy (EDS) spectrum in the sensing area demonstrate that V 5 S 8 is partially transformed to VO X during laser processing (Figure 2f).

Thickness Effect of F127-Resols Hybrid Film on the Gas Sensing Performance
The film thickness modulates the laser-induced gas sensing area and gas permeation through the thickness, affecting the sensor performance. The LIG gas sensor with either a small or large thickness has a low response and signal-to-noise ratio (SNR) in the gas response curve to 1 ppm NO 2 at room temperature (Figure 3a, Figures S5 and S6, Supporting Information). On the other hand, with the increase of film thickness, the conductivity increases but gas permeability decreases [56] to give a reduced gas response. The LIG gas sensor with a larger thickness can provide abundant gas adsorption sites and continuous gas diffusion pathways, facilitating gas analyte-induced charge carrier generation for enhanced gas-sensing properties. [57] However, as the film thickness exceeds 35 µm, some structures in the resulting LIG become poor quality with uneven 3D microstructures, leading to unstable sensing performance. [58] Therefore, the optimal film thickness of 35 µm is selected in the following studies.
Compared with pure LIG gas sensors, the VO X -doped LIG gas sensors provide a higher response, e.g., over a two-fold increase from 1.2% to 2.8% when exposed to 1 ppm NO 2 ( Figure 3b). The response/recovery time of 217/650 s to 1 ppm NO 2 at room temperature is also relatively rapid ( Figure 3c). As the recovery time of 300 s is sufficient to capture the characteristics of the gas sensor, this value is selected in the following  studies unless specified otherwise. As the concentration is gradually increased from 1 to 5 ppm, the continuous response curve to NO 2 shows an increase from 2.5% to 5.5% (Figure 3d), indicating a good dynamic response/recovery at room temperature. The response and recovery time also increases with the increasing gas concentration from 1 to 5 ppm ( Figure S7, Supporting Information). The incomplete recovery comes from the short time set for rapid testing. The cycling stability of the VO Xdoped LIG sensor is confirmed by exposure to 0.5 ppm NO 2 at room temperature ( Figure 3e). The consistent response and recovery of the sensor over five cycles indicate the good steadystate response of the sensor. To provide a more accurate estimation of the theoretical limit of detection (LOD), the gas sensor is exposed to NO 2 with a progressively increased concentration from 300 to 700 ppb with a step size of 100 ppb, which gives a continuous response curve from 0.9%, 1.2%, 1.5%, 1.8%, to 2.1% ( Figure 3f). The linear fit of the sensor response to the NO 2 gas concentration from 300 to 700 ppb yields a slope of 2.929 ppm -1 with a correlation coefficient (R 2 ) of 0.997 ( Figure 3g). The linear fit of the gas sensor response to the lower concentration (3 ppb, 5 ppb, 7 ppb, 9 ppb, to 11 ppb) gives a slope of 8.4 × 10 -5 /ppb, which further leads to the determination of the theoretical LOD, defined as 3 × RMS noise /slope, [59] as 451 ppt ( Figure S8, Supporting Information). As it is challenging to use the static gas test setup to measure the gas concentration below 1 ppb (additionally spiked gas in the ambient environment), testing of the sensor to 3 ppb NO 2 still shows a response of 0.3‰ with a signal-to-noise ratio (SNR) of 26.85 ( Figure 3h). The VO X -doped LIG gas sensor only gives a small response of 0.2%, 0.06%, 0.062%, 0.12%, 0.22%, and 0.09% to 1 ppm SO 2 , 100 ppm CO 2 , 10 ppm NH 3 , 100 ppm acetone, 100 ppm methanol, and 100 ppm ethanol, respectively ( Figure 3i and Figure  S9, Supporting Information). In comparison, the significantly higher response of the sensor to NO X (e.g., 2.7%/1.1% to 1 ppm NO 2 /NO) highlights the excellent selectivity. The exposure of the chemiresistive VO X /LIG gas sensor to oxidizing NO X gas results in the extraction of the electrons in the valence band of the LIG to the adsorbed NO X and from VO X to LIG. [47] The lowest unoccupied molecular orbital (LUMO) determines the number of transferred electrons. As the LUMO of NO X gas molecules is lower than that of other gases, [60] more electrons are transferred from the LIG to give a larger response and high selectivity to NO X . As a result, the VO X -doped LIG gas sensor with an ultralow LOD and a high selectivity outperforms the other NO X gas sensors based on different nanomaterials (Table S1, Supporting Information).

Effects of Operating Temperature from Self-Heating on the Gas Sensing Performance
As the temperature is often used to modulate the gas sensing performance, [61][62][63] self-heating of the LIG is explored to modulate the temperature by changing the applied voltage during the resistance measurements (Figure 4a) with the infrared thermal images shown in Figure S10   to 88/406 s, but the response is also reduced from 2.5% to 1.3% (to 1 ppm NO 2 ) (Figure 4b, Figure S11, Supporting Information). The accelerated response/recovery at elevated temperature results from the promoted electron transfer (crossing the potential barrier), but the accelerated desorption rate of gas molecules also results in a smaller response. [64] This temperature-dependent behavior is consistent with the results of room-temperature NO X gas sensors in the previous literature reports. [65][66][67][68] As the relative humidity (RH) level can vary in a large range in greenhouse and soil environments, it is essential to analyze its influence on the gas sensing performance. [69,70] Because of the adsorption competition between NO 2 and water molecules on the sensor surface in the high RH range, [71] the response of the sensor to 1 ppm NO 2 decreases from 1.92% to 0.54% as the RH level is increased from 50% to 80% at room temperature ( Figure S12, Supporting Information). However, the influence of RH on the NO 2 response can be drastically reduced when the sensor is operated at elevated temperatures [68] (e.g., a response of 1.43/1.41/1.4/1.31% in the RH of 50/60/70/80% at 50°C) ( Figure 4c, Figure S13, Supporting Information). The elevated temperature in the sensing area creates thermal radiation to drive the water molecules away from the region. [  b) The comparison in the response between the gas sensors based on LIG and VO X -doped LIG to 1 ppm NO 2 . c) Typical response curve of the gas sensor to determine the response/recovery time. d) Dynamic response test in the presence of NO 2 from 1 to 5 ppm at room temperature. e) Repeatability test to 0.5 ppm NO 2 for five consecutive cycles. f) Dynamic response test to NO 2 from 300 to 700 ppb at room temperature and g) its linear fit to the calibration curve (error bars from three samples). h) Experimental demonstration of the ultralow limit of detection to 3 ppb NO 2 at room temperature. i) Selectivity test to NO X over a wide range of other gaseous molecules. (Note: results are obtained from the gas sensor based on VO X -doped LIG unless specified otherwise). strategies such as superhydrophobic coating can be further explored to minimize the effects of humidity. [73][74][75] The sensor is also highly stable over time, as evidenced by the almost unchanged response to 1 ppm NO 2 for 16 days (Figure 4d), demonstrating a high potential for practical applications.

Gas-Sensing Mechanisms and Theoretical Calculations
The gas sensing mechanism of the chemoresistive VO X -doped LIG relies on the direct charge transfer between the absorbed O 2 and NO X gas molecules and the sensing material. The large density of oxygen vacancy defects and dangling bonds in both LIG and VO X allow easy adsorption of oxygen molecules onto the composite structure at room temperature. The NO X adsorbed on the VO X /LIG surface continuously extracts electrons and extends the hole (main carriers) accumulation zone on the VO X /LIG surface to lower the resistance, resulting in negative values in the relative changes as in the previous literature reports. [76] In the VO X -doped LIG sensor, the work functions of LIG and VO X are ≈ 4.7 (W G ) and 6.8 eV (W M ), respectively. Due to the difference in work function, the majority of charge carriers (holes and electrons) in the p-type LIG [77,78] and n-type VO X [79] migrate across the heterojunction established at the interface forming a depletion layer by energy band bending (Figure 5a). Heterojunction systems have been recognized to explain the enhanced gas sensing characteristics of ZnO/rGO, [80] ZnO/NiO, [81] CuO/ZnO, [82] CoO/SnO 2 , [83] PdO-ZnO, [84] ZnFe 2 O 4 -ZnO [85] in previous papers. The exposure of VO X -doped LIG to NO 2 traps electrons from the conduction band and further bends the energy band (Figure 5b) to decrease the resistance. Compared with pure LIG, the VO Xdoped LIG shows enhanced carrier transfer, leading to higher conductivity [86] as shown in the linear I-V curves ( Figure S14, Supporting Information). Small changes in charge carrier concentration can also lead to great enhancement in the sensor response. [78] The decoration of VO X also decreases the initial concentration of electrons in LIG, providing a larger change in NO 2 gas adsorption and response per electron. [87] The difference in the structure and electronic properties between pristine LIG and VO X -doped LIG can be revealed by the density functional theory (DFT) calculations. [88,89] Compared to pristine LIG, the VO X -doped LIG with heterostructures ( Figure 5c) exhibits enhanced electronic levels near the Fermi level to elevate electron transfer (Figure 5d) due to the VO X decoration. [90][91][92] Deformation charge density elucidates large charge transfer between VO X and LIG and the adsorption of NO 2 on the sensor surface (Figure 5e). The adsorption energy E ad of gas molecules on the sensor surface can be calculated as: [93] E where E VO /LIG X and E VO /LIG gas + X are the total energy of the system before and after the adsorption of gas molecules and E gas is the energy of the isolated gas molecule. The larger negative values of E ad correspond to the stronger interaction between the sensor surface and the gas molecule. The adsorption energy of -1.434 eV of NO 2 on VO X -doped LIG is almost 7 times of -0.219 eV on pristine LIG, indicating improved interaction between NO 2 and VO X -doped LIG. [89] Meanwhile, the adsorption energies of other gas molecules (e.g., NH 3 , SO 2 , CO 2 , and acetone) on VO X -doped LIG are lower in magnitude than that of NO 2 (Figure 5f), which supports the highly selective detection of NO 2 over interfering gas molecules.

The Temperature Sensing Performance of the Multi-Parameter Sensor
Due to the high electron mobility, superior thermal conductivity, and structural stability at high temperatures of LIG, [68,94] the multi-parameter sensor shows a sensitive response with high repeatability (Figure 6a) over a wide temperature range from 30 to 110°C (Figure 6b). The fitting of the linear calibration curve gives a negative temperature coefficient and a sensitivity of 4.52 × 10 -4° C -1 (R 2 = 0.97) (Figure 6c). Further increased linearity (R 2 = 0.99) is observed in the temperature range from 30 to 50°C (relevant for soil, human body, and infant formula temperatures) ( Figure S15, Supporting Information). The sensor also exhibits a low limit of detection of 0.2°C (Figure 6d  monitor both subtle and large temperature changes in practical applications. The proof-of-the-concept demonstrations include the detection of formula milk temperature in the bottle for the infant (Figure 6g) or simulated fever (Figure 6h), with a response time of 60 s that is much shorter than that (>6 min) [95] of most commercial mercurial thermometers. The above results confirm that the VO X -doped LIG temperature sensor exhibits high sensitivity, wide detection range, fast response, and good reliability, which is suitable for dynamic temperature detection with favorable performance over the previously reported literature studies (Table S2, Supporting Information).

Application of the VO X -Doped LIG Multi-Parameter Sensor for Soil Monitoring
The VO X -doped LIG sensor shows excellent sensing performance to both NO X gas and temperature, so it is imperative for the sensor to decouple gas and temperature when the two stimuli are simultaneously present in large-scale soil monitoring (Figure 7). Therefore, the polydimethylsiloxane (PDMS) membrane that is impermeable to gas is introduced as an encapsulation layer to break the symmetry in gas and temperature response (Figure 7a). The VO X -doped LIG sensor encapsulated with a 10 µm-thick PDMS membrane exhibits a significantly diminished response to NO 2 at room temperature (RH of 80%) (Figure 7b, Figure S16, Supporting Information). Meanwhile, the rapid heat transport in the 10 µm thick PDMS membrane has minimal effect on the temperature sensing, resulting in a negligible difference with the unencapsulated sensor (Figure 7c, Figure S17, Supporting Information). The encapsulated sensor can also be combined with the unencapsulated sensor operated at elevated temperature from self-heating to completely decouple the temperature and NO X gas (Figure 7d, Figure S18, Supporting Information). The temperature can be accurately captured by the encapsulated sensor, whereas the NO X gas can be determined by the self-heated sensor as it removes the influence from the temperature changes, with no interference between the two input signals. In the proof-of-the-concept demonstration, the encapsulated sensor does not show any response to the NO 2 gas from 1 to 3 ppm (at room temperature), which is captured by Adv. Mater. 2023, 35, 2210322   Figure 7. Demonstration of the VO X -doped LIG sensor to decouple gas and temperature. a) Schematic of the encapsulated sensor to block the permeation of the gas molecules. b) Response of the VO X -doped LIG sensor with and without the encapsulation membrane to 1 ppm NO 2 . c) Response of VO X -doped LIG sensors with varying encapsulation thicknesses to the temperature of 30, 40, and 50 °C. d) Application of the encapsulated VO X -doped LIG sensor and the unencapsulated one operated at 50 °C from self-heating to completely decouple NO 2 gas and temperature. The top illustrations show the changes in gas concentration and temperature. the self-heated sensor operated at 50°C (blue shaded region in Figure 7d). Similarly, the progressively increased temperature from 22 to 50°C and then decreased back to 22°C (to 3 ppm NO 2 ) does not cause any response in the self-heated sensor. Meanwhile, the temperature change is accurately detected by the encapsulated sensor (yellow shaded region in Figure 7d).
The VO X -doped LIG sensor capable of decoupling NO X and temperature can be applied to accurately monitor the soil temperature and NO X emission for future precision agriculture. The encapsulated sensor on the soil surface can accurately monitor the soil temperature without being affected by the NO X gas emission (Figure 8a). By heating the soil sample in the oven to simulate overheating, the soil temperature cycled from 35°C (suitable for crop growth) to 40°C (unfavorable to crop growth) and then back to 35°C and room temperature is accurately captured by our sensor (Figure 8b). Meanwhile, the sensor without encapsulation but operated at an elevated temperature such as 50°C from self-heating can be used to detect NO X volatilized from the soil at the specified temperature after applying urea (Figure 8c). In the representative demonstration, the NO X gas emission from the soil sample (23 cm × 19 cm × 4 cm) fertilized with 5 g urea can be detected at a much larger response than the un-fertilized control sample after three days (Figure 8d), which is consistent with previous literature reports. [7,96] Although the sensor operated at room temperature is largely influenced by the RH (50-60% in the soil environment) to give a positive response ( Figure S19, Supporting Information), the sensor operated at 50°C from self-heating largely eliminates the humidity effect to allow for accurate gas detection. As a result, the positive response is reduced to only 0.2‰ in unfertilized soils (RH of 50-60%) to demonstrate a very weak influence of humidity. The decoupled measurements of NO X and tempera-ture from the multi-parameter sensor can provide accurate, real-time monitoring of the crop growth environment for smart or precision agriculture.

Remote Environmental Monitoring System
The VO X /LIG sensor can be integrated with data processing and wireless transmission modules to yield a remote environmental monitoring system for human health monitoring and precision agriculture (Figure 9). The signal measured by the VO X /LIG sensor and processed by a low pass filter to remove the noise is first digitized using a 16-bit delta-sigma modulator and then wirelessly transmitted to the smartphone via a Bluetooth module (Figure 9a). When the real-time monitored NO 2 in the local environment around the human subject exceeds the safety threshold, the system automatically triggers a red light and sends an alert to the smartphone for timely protection (Figure 9b and Video S1, Supporting Information). Additionally, the integrated wireless monitoring system can also be used to wirelessly monitor NO X concentration after fertilization and soil temperature in the greenhouse for promoting plant growth in smart agriculture (Figure 9c and Videos S2 and S3, Supporting Information).

Discussion
In summary, this work reports the design, fabrication, and application of VO X -doped LIG nanocomposites to decouple NO X and temperature for soil environment monitoring. Created from a single-step laser scribing of V 5 S 8 -doped block copolymer and phenolic resin self-assembled films, the VO Xdoped LIG exhibits an ultra-low detection limit to NO X and high sensitivity/precision over a wide temperature range. Introducing a soft membrane as an encapsulation layer on the sensor blocks the permeation of the gas molecules to provide accurate temperature measurements, which further helps decouple the NO X gas from temperature. Additionally, the influence of the RH in the ambient environment can be effectively removed by operating the sensor at elevated temperatures from self-heating. The unencapsulated sensor operated at elevated temperatures also allows accurate measurements of the NO X gas without being affected by environmental temperature variations. Therefore, the combination of the encapsulated VO X -doped LIG sensor and the unencapsulated sensor operated at elevated temperatures can completely decouple temperature and NO X without interference. The proof-of-the-concept demonstration of the multi-parameter decoupled sensors is showcased to detect nitrogen loss and soil temperature for smart agriculture. The design strategies and demonstrations from this work can also be leveraged to help create the next-generation multi-parameter stretchable sensors with decoupling sensing mechanisms.
Characterization: Field-emission scanning electron microscopy (FESEM) (JSM 7100F, JEOL) was used to characterize the structure and morphology. X-ray photoelectron spectroscopy (XPS) was applied by ESCALAB 250 photoelectron spectrometer (Thermo Fisher Scientific, USA). Raman scattering was performed on a laser micro Raman spectrometer (Renishaw, in Via Reflex). X-ray diffraction (XRD) was obtained by a D8 Discover X-ray diffractometer.
Sensor Fabrication and Measurement: The sensing region (width of 150 µm and length of 4.5 mm) with two square electrodes was directly created by scribing the V 5 S 8 -doped Pluronic F127-resols hybrid film with a CO 2 laser (Universal Laser, 10.6 µm, spot size of 127 µm, and power of 9 mW) ( Figure S3b, Supporting Information). The laser processing parameters were fixed (power of 3.0%, speed of 1%, and PPI of 500), unless specified otherwise. Copper tapes with silver paste on the square electrodes connected the sensor to the data acquisition system. The PDMS solution was prepared at room temperature with stirring using 2 g of prepolymer (a) and 0.1 g of crosslinking agent (b) in a mass ratio of 20:1. Then, the PDMS solution was spin-coated onto the sensing area of VO X -LIG sensor at varying speeds (i.e., 6000, 7000, 8000, and 9000 rpm) and drying in a vacuum oven at 85°C for 1 h. Target gas is first collected into an aluminum foil gas collecting bag and then injected into a closed chamber for static detection. Different concentrations of NO X were prepared by diluting and fully mixing the commercial calibration gas of 50 ppm NO X with air in the chamber (volume of 5 L). The different relative humidity values in the chamber were prepared by the saturated Figure 9. The design and demonstration of the integrated remote environment monitoring system based on the VO X /LIG sensor. a) The circuit design of the remote monitoring system for b) real-time monitoring of NO 2 in the local environment of the human subject and c) soil gas and temperature detection for smart agriculture.
salt solution method. [97] The concentration of the VOC was obtained by injecting the needed quantity of anhydrous liquid analytes into a sealed glass container using a microliter syringe. The concentration (C in ppm) of the VOC in the chamber was calculated using the following equation: where ρ, V S , and M are the density (g ml -1 ), volume (µL), and molecular weight (g mol -1 ) of the anhydrous liquid VOC, T is the testing temperature (K), and V is the volume of the glass container (L) filled with the VOC. A demonstration of the sensor performance is provided in Video S4 (Supporting Information). The real-time resistance was recorded by a SourceMeter (Keithley 2400) at a constant voltage of 0.05 V. The sensor response is defined as S = ΔR/R 0 with ΔR = R -R 0 , where R 0 is the initial resistance in air and R is the resistance in the target gas. The response (or recovery) time is the time taken for the sensor response to reach 90% of the response (or recovery) at saturation in the target gas (or air).
Computational Methods: The Vienna Ab initio Simulation Package (VASP) was employed to perform all the spin-polarized density functional theory (DFT) calculations within the generalized gradient approximation (GGA) using the Perdew-Burke-Ernzerhof (PBE) formulation. The projected augmented wave (PAW) potential was selected to describe the ionic cores and take valence electrons into account using a plane wave basis set with a kinetic energy cut-off of 520 eV. The density of k-meshs grids for Brillouin zone sampling was set as 0.04 × 2π/Å. Partial occupancies of the Kohn-Sham orbitals were allowed using the Gaussian smearing method and a width of 0.05 eV. The electronic energy was considered self-consistent when the energy change was smaller than 10 -6 eV. The geometry optimization was considered convergent when the force on each atom was smaller than 0.02 eV Å -1 .

Supporting Information
Supporting Information is available from the Wiley Online Library or from the author.