Gas sensors are vital tools that are widely used in industries including food safety, industrial process control, environmental monitoring, and medical diagnostics [1-3]. They are used to identify chemical species in the gaseous phase, frequently at trace levels, and to determine their existence and concentration. In addition to being extremely sensitive and selective, gas sensors also need to be affordable, low-power, and able to function in ambient settings in order to satisfy the needs of contemporary applications, particularly those that call for real-time analysis, portability, and integration with smart systems [4]. Although metal oxide semiconductor (MOS)-based traditional gas sensors have been thoroughly researched, their high working temperature requirements and selectivity issues have led to the investigation of other sensing materials.

Conducting polymers (CPs), one of the many novel materials, have attracted a lot of interest for gas sensing applications because of its special blend of structural tunability, electrical conductivity, and suitability for low-cost production methods [1]. When interacting with analyte gases, polymers including polyaniline (PANI), polypyrrole (PPy), and poly(3,4- ethylenedioxythiophene) (PEDOT) display reversible changes in conductivity and intrinsic semiconducting characteristics [5]. These characteristics allow CPs to work well in chemiresistive-type gas sensors, in which the electrical resistance of the detecting material is modulated by the presence of a target gas. CP-based sensors have an advantage in terms of scalability and integration into flexible or wearable platforms because of their room temperature operation and ease of processing through methods like spin coating, drop casting, or in-situ polymerisation. Pure conducting polymers, however, have drawbacks, including limited selectivity towards certain analytes, comparatively low long-term stability, and vulnerability to ambient humidity. Recent studies have concentrated on creating CP-based composites, which combine polymers with nanomaterials such metal oxides, carbon nanotubes (CNTs), graphene derivatives, and metal nanoparticles, to solve these problems [6]. By fusing the processability and responsiveness of CPs with the large surface area and catalytic activity of nanomaterials, these hybrid systems work in concert to improve the sensing properties. For instance, composite sensors that combine polypyrrole with multi-walled carbon nanotubes or polyaniline and zinc oxide have shown impressive gains in analyte discrimination capabilities, response/recovery durations, and detection limits [7]. Figure 1 depicts a schematic method for creating conducting polymer-based nanocomposite gas sensors and their practical applications.

Figure 1: Schematic Illustration Of Conducting Polymer Nanocomposite-Based Gas Sensors, Demonstrating The Integration Of Conducting Polymers With Nanomaterial Fillers, As Well As The Sensing Mechanism, Signal Processing, And Potential Applications.

Conducting polymer composites' adaptability also makes it possible to create sensors that are particular to gases like nitrogen dioxide, ammonia, volatile organic compounds (VOCs), and even biomarker gases like ethanol and acetone. Molecular imprinting methods, functional groups, and dopants are used to further fine-tune the sensing behaviour to target analytes with great fidelity. Apart from their technological benefits, CP-based sensors are appealing due to their affordable manufacturing costs and the possibility of mass production through the use of printable electronics technology.

The objective of this study is to examine the most recent developments in conducting polymer-based gas sensors, with an emphasis on both basic ideas and real-world uses. The mechanics of gas interaction with polymers and composite materials, the significance of structural and morphological factors, and methods to improve selectivity and sensitivity are all highlighted. The analysis also seeks to give an overview on future developments in the area and to highlight recent advancements in the creation of flexible, wearable, and miniature gas sensors employing CPs. This entails dealing with important issues such cross-sensitivity and humidity interference, stability in real-world settings, and integration into intelligent sensing networks for biomedical and environmental monitoring.

Working Principles of Gas Sensors Using Conducting Polymers

Conducting polymer (CP)-based gas sensors work on the basis of the idea that exposure to particular gas molecules may dramatically alter the electrical characteristics of these materials, particularly their conductivity. With π-conjugated backbones, conducting polymers like polyaniline (PANI), polypyrrole (PPy), and poly (3,4-ethylenedioxythiophene) (PEDOT) may transition between conductive and insulating states based on their doping amount and oxidation state. These polymers' charge carrier density varies in response to gas molecules, especially those that donate or remove electrons, which causes observable variations in resistance or current flow. Their capacity for detecting is based on this trait [8].

Chemiresistive Mechanism and Role of Nanocomposites in Enhancing Sensor Response

The chemiresistive mechanism, which depends on tracking the change in electrical resistance following gas adsorption, is the most often used mechanism in CP-based gas sensors. Oxidising gases like NO? enhance conductivity in p-type CPs by accepting electrons and raising hole concentrations. Reducing gases, such as NH?, on the other hand, neutralise holes, give electrons, and reduce conductivity. Interdigitated electrodes are used throughout the CP thin film to capture this change in resistance. Environmental variables including temperature and humidity, as well as the gas-polymer interaction energy and film shape, control the total reaction (Dong et al.). Research on nanocomposite materials has grown in order to address the intrinsic limitations of pure conducting polymers, including their modest sensitivity, limited selectivity, and environmental instability. The benefits of both components are combined in nanocomposites by adding metal oxides, graphene, carbon nanotubes (CNTs), nanoparticles, or MXenes to CP matrices. These hybrid systems provide better electron transport properties, increased surface-to-volume ratios, and enhanced adsorption kinetics. Because of the synergistic interactions between the CP and the nanomaterial, PANI-ZnO and PANI-Au nanocomposites, for instance, have demonstrated notable improvements in response magnitude and recovery time [9].

Key Performance Parameters: Sensitivity, Selectivity, Response Time, Stability

Assessing and improving gas sensor performance requires a thorough grasp of the following critical performance parameters:

Sensitivity: The term "sensitivity" describes how much the sensor signal (such as resistance) changes for every unit of analyte concentration. Because of their larger active areas and more robust gas interactions, CP nanocomposites provide noticeably better sensitivity [10].

Selectivity: The capacity to distinguish between several gaseous species is known as selectivity. Usually, functionalisation, chemical doping, or modifying the nanocomposite's composition and shape to promote interactions with particular gases are used to increase selectivity [11].

Response time and recovery time: These relate to the amounts of time needed for a sensor to attain 90% of its final signal after exposure to and removals of a gas, respectively, are crucial for real-time applications. Because of their enhanced charge mobility and diffusion routes, nanocomposites often provide quicker kinetics [12]. Figure 2 depicts the key performance characteristics that determine gas sensor efficiency. Sensitivity, selectivity, response time, and stability all contribute to the sensor's dependability and usefulness.

Figure 2: Key Performance Parameters of Gas Sensors Represented in a Venn diagram, Highlighting the Interrelation of Sensitivity, Selectivity, Response Time, And Stability.

Functional nanostructuring techniques, which offer even more control over gas diffusion and interaction patterns, have also been studied recently. These techniques include core-shell designs, porous films, and 3D nanofibers. These methods increase the usefulness of CP-based sensors in industrial emission control, breath diagnostics, and environmental surveillance [13]. A new generation of gas sensors with exceptional performance across all crucial parameters has been produced as a result of the combination of CPs with nanomaterials, sophisticated film processing, and functionalisation processes. These developments are opening the door for wearable, flexible, and compact sensing devices that may be used in practical settings.

Conducting Polymers and Nanocomposite Materials

Overview OF COMMON Cps: Polyaniline (Pani), Polypyrrole (Ppy), Pedot, Etc.

Conducting polymers (CPs) such as polyaniline (PANI), polypyrrole (PPy), and poly(3,4- ethylenedioxythiophene) (PEDOT) are extensively researched materials in gas sensing due to their adjustable conductivity, environmental resilience, and reversible redox properties [8, 10]. Polyaniline (PANI) is distinguished by its acid-base doping chemistry, facilitating robust interactions with acidic and basic gases. It can exist in many oxidation states (leucoemeraldine, emeraldine, pernigraniline), and its conductivity can vary by several orders of magnitude based on doping circumstances [14]. PANI exhibits remarkable sensitivity to analytes such as ammonia, nitrogen dioxide, and volatile organic compounds in gas sensing applications. Documented chemiresistive responses indicate sensitivities of approximately 7.26%•ppm?¹ within the 0.1–10 ppm NH? range and a change of around 250% at 100 ppm [15]. Vapor-phase polymerized or nanofiber PANI sensors can attain sub-ppm detection, with optimal systems indicating detection limits of 10–100 ppb [11]. Response times often range from tens to hundreds of seconds (30–200 s), although recovery may extend beyond this duration unless composites are employed [16]. Polypyrrole (PPy) is esteemed for its significant electrochemical activity, thermal stability, and durability in ambient settings [17]. Gas responses are significantly influenced by morphology: thick PPy films require around 17 minutes to achieve 90% of their maximal reaction, whereas nanostructured or composite PPy films respond within seconds [16]. Ammonia responses vary from approximately 15% at 0.5 ppm (500 ppb) to over 100% at many tens of ppm, with the use of nanofillers potentially lowering detection limits to the ppb range [10]. PPy coatings in fiber-optic sensors for ethanol exhibit detection limits of approximately 140 ppm, with rapid reaction and recovery times of 5 seconds and 8 seconds, respectively [18].

PEDOT has been less investigated than PANI and PPy, although its utilization is rising owing to its chemical stability and conductivity. PEDOT-based sensors have demonstrated effective detection of ammonia and NO?, occasionally surpassing PPy in sensitivity [11, 19].

Figure 3 shows the different methodologies and consequences of polyaniline (PANI) synthesis. It begins with a diagram of the electrochemical synthesis process and the underlying electrochemical production mechanism for PANI. Changing the applied current density produces diverse morphologies such as nanobelts and nanospheres, indicating the process's tunability. The cross-sectional stereoscopic views of PANI films made using potentiodynamic and potentiostatic techniques reveal differences in film growth and thickness, and the matching surface morphology pictures validate these discrepancies. In addition, an atmospheric pressure plasma polymerization system is demonstrated, complete with an image of the plasma reactor, providing an alternative production process. Finally, transparent PANI films synthesized at various polymerization durations are shown with their UV-Vis optical transmittance spectra, highlighting the material's tunable optical properties.

Figure 3: Synthesis and Morphological Development of PANI Using Electrochemical and Plasma Polymerization Techniques, Revealing Structural Changes, Film Growth, and Flexible Optical Characteristics [20].

PEDOT: PSS, an abbreviation for "polystyrene sulfonate” doped PEDOT," is a popular polymer with excellent processability, mechanical flexibility, and conductivity. Sensor devices that are flexible or worn often make use of PEDOT:PSS. Because of its large surface area and ability to transport ions, it has demonstrated exceptional sensing capabilities for alcohols, nitrogen oxides, and water vapor [21]. PEDOT:PSS is highly valued for its processability and mechanical flexibility (wearable/flexible devices). According to reported cases, the numbers vary greatly based on hybridization and post-treatment. Although chemically doped or hybrid PEDOT:PSS chemiresistors frequently exhibit moderate responses and sluggish kinetics (response/recovery hundreds of seconds in some cases), PEDOT:PSS can achieve ppb-low-ppm LODs and quick reactions when optimized (e.g., with metal oxides or printed/treated inks). For instance, hybrid printed PEDOT:PSS@ZnO layers have been utilized to obtain strong room- temperature responses in the 10s–100s ppb-ppm range following ink/post-treatment, and optical PEDOT sensors reported a LOD of approximately 2.7 ppm for NH? [22]. Nanocomposite techniques have been utilized by researchers to circumvent the shortcomings of pure CPs, such as their lack of selectivity, ageing effects, and restricted sensitivity. When nanofillers are added to CP matrices, it improves gas adsorption, electron transport, and analyte selectivity all at once. Here are some of the most prevalent types of nanofillers:

Metal Oxides: By forming heterojunctions with CPs, metal-oxide fillers enhance catalytic adsorption and charge separation. Quantitative improvements by PANI/SnO? composites have demonstrated longer linear ranges (linear response 1-7 ppm in some reports), shorter recovery times (PANI/SnO? recovery decreased from 73 s to ~33 s in one study), and significantly larger responses than pristine PANI (e.g., ~72% response to 100 ppm NH? for certain PANI-SnO? (50%) films). According to other hybrid instances (such PANI-Au-SnO?), under humid RT circumstances, the sensitivity is ≈12.3%•ppm?¹ in a low-ppb linear range. These figures demonstrate how sensitivity and dynamics are significantly changed by MOx loading and dispersion [22].

Carbon-based Nanomaterials: CNTs and graphene/rGO boost electron mobility and surface area. Graphene-based sensors in general can reach 100–500 ppb LODs for gases like NO?/NH? in optimized (typically heated or functionalized) devices. Representative metrics: rGO–PANI thin films showed ~250% response at 100 ppm NH?, response time ≈97 s, and LODs down to ~1-5 ppm in many studies. CNT/CP hybrids typically provide in faster response times and several times better LOD than CP alone, as well as lower detection limits and improved linearity and repeatability [23].

MXenes: are a new class of 2D transition metal carbides and nitrides that are readily functionalised, conductive, and hydrophilic. Highly sensitive VOC and NH? sensors have been produced as a result of their integration with CPs like PANI, and their increased interfacial bonding has improved stability [24].

Crystalline porous materials with large surface areas and adjustable pore chemistry are known as metal-organic frameworks (MOFs). Although practical applications are still being developed, MOF/CP nanocomposites exhibit promise for selective gas detection by molecular sieving and catalytic activity [25]. For performance optimisation, these nanocomposites' structure–property interactions are essential. Resistance loss is reduced and conductive route development is guaranteed by uniform dispersion of nanofillers. The efficiency of charge transfer and mechanical integrity are enhanced when CP chains and nanofillers interact through π-π stacking, hydrogen bonds, or van-der Waals forces. Additionally, gas diffusion and analyte accessibility are influenced by the composite's morphology, whether it be core-shell, multilayer, or porous. Faster response and recovery periods result from the increased number of active sites and improved adsorption kinetics provided by porous materials and high aspect ratio fillers [15].

The main electrochemical and structural characteristics of a few chosen conducting polymer nanocomposites, such as polyaniline (PANI), polypyrrole (PPy), and poly(3,4- ethylenedioxythiophene) (PEDOT), combined with nanoscale fillers like metal nanoparticles, graphene, and carbon nanotubes (CNTs), are compiled in this table 1. Based on studies from recent literature, electrical conductivity, specific capacitance, stability or capacitance retention throughout cycles, and noteworthy functional properties are given for each composite. These measurements demonstrate how nanoscale fillers work in concert to improve conductivity, capacitance, durability, and performance tailored to a certain application.

Table 1: Electrochemical and Structural Performance of Conducting Polymer Nanocomposites.

In conclusion, combining functional nanofillers with CPs such as PANI, PPy, and PEDOT provides a potent method for designing next-generation gas sensors with improved sensitivity, selectivity, and environmental resilience. Translating laboratory research into scalable sensing devices requires an understanding of the ability to customize their nanoscale structure–property interactions.

Structure-Property Relationships in Nanocomposites

The gas sensing efficacy of conducting polymer (CP)-based nanocomposites is significantly influenced by structure-property correlations. The sensing metrics, including sensitivity, selectivity, response time, and stability, are intrinsically associated with morphology, particle size, filler dispersion, interfacial bonding, and porosity [32]. When conducting polymers such as polyaniline (PANI), polypyrrole (PPy), or PEDOT are amalgamated with nanofillers including metal oxides, carbon nanostructures, MXenes, or MOFs, synergistic effects emerge that are not present in the individual constituents. Uniformly distributed carbon nanotubes in a conductive polymer matrix create continuous percolated channels, enhancing charge transmission. PANi–CNT composites have significantly improved NH? sensitivity relative to virgin PANI, however aggregated CNTs diminish performance [10]. Likewise, the uniform integration of CNTs into PEDOT:PSS films markedly enhances electrical conductivity, achieving several-fold improvements compared to inadequately dispersed systems [33]. PANI nanofibers integrated with ZnO nanoparticles demonstrate significantly greater NO? sensitivity than dense PANI films [34]. Porosity enhances response kinetics: porous PPy/Au–ZnO composites have response times in the range of seconds (e.g., around 8 seconds to ethanol), significantly quicker than their nonporous equivalents. Interfacial interactions dictate selectivity and stability. Robust interactions between conducting polymers and nanofillers enhance charge transfer and inhibit filler aggregation, as documented in PEDOT–graphene and PANI–MXene systems [35, 36]. These synergies elucidate why nanocomposites regularly surpass pure conductive polymers in sensitivity, response and recovery times, and long-term stability.

Figure 4 depicts the structure-property connections in conducting polymer nanocomposites for gas sensing, illustrating how the use of nanostructured materials improves sensing performance. Conducting polymer-based composites, such as nitrogen-doped graphene mixed with polymers, enable effective charge transfer and manipulation of the depletion layer, which has a direct impact on gas adsorption and desorption processes. These structural alterations improve charge dissipation, minimize potential barriers, and increase sensitivity to target gas molecules. The tailored interactions between the polymer matrix and nanoparticles result in a high responsiveness, selectivity, and stability of the gas sensor.

Figure 4: Illustration Of Structure Property Relationships In Conducting Polymer Nanocomposites For Gas Sensing, Highlighting Composite Formation, Charge Dissipation Mechanisms, And High Sensor Response Behavior.

The efficiency of charge transport is controlled by interfacial bonding. When compared to physically blended systems, PANI-graphene composites that used π-π stacking showed a 40% reduction in recovery time and a 1.7× increase in sensitivity to NO? [9]. The NH? detection limit in PANI/SnO? heterojunctions increased from 1 ppm for pure PANI to 100 ppb [7]. Adsorption capacity is directly impacted by porosity. According to Madgula and Shubha, thick films with a surface area of 12 m²/g demonstrated a 63% lower ammonia sensitivity than electrospun nanofibrous PANI composites with a surface area of 54 m²/g. Performance is also influenced by electronic effects at heterojunctions. Due to p-n junction band alignment, SnO?/PTh composites showed a 4.5× greater acetone response (Ra/Rg ratio) at 10 ppm than virgin SnO? [10]. Lastly, strong filler integration is associated with stability gains. After 30 days of cont nuous operation, PEDOT:PSS/PPA composites retained over 90% of their original CO sensitivity, while bare PEDOT:PSS films only retained about 60% [37]. Figure 5 depicts several kinds of conducting polymer (CP) hybrid nanocomposites intended for gas sensing applications, including metal oxide-CP hybrids, metal-CP hybrids, organic-CP hybrids, and CNT/graphene-CP hybrids [11]. Examples include FeOOH/PPy, PANI/CeO?, Pd/PPy/CNTs, Ag/PEDOT, hydroxylated PEDOT nanotubes, carboxylated PPy nanoparticles, graphene/PANI, and SPEEK/PPy nanofibers. These hybrid systems boost sensing performance by combining conducting polymers' distinctive features with metal, metal oxide, or carbon-based nanoparticles. The central schematic highlights their key advantages, including large surface area, increased conductivity, tunable functionality, strong chemical affinity, improved interfacial properties, and superior mechanical strength, all of which contribute to high sensitivity, selectivity, and stability in gas sensing devices.

Figure 5: A Schematic View Of Several Conducting Polymer Hybrid Nanocomposites-Metal Oxide-CP, Metal-CP, Organic-CP, And CNT/Graphene-CP Hybrids-Along With Examples And Important Benefits For Improved Gas Sensing Performance [11].

One of the main factors influencing the performance of gas sensors in conducting polymer-based nanocomposites is the structure-property connections. A route to creating extremely sensitive, stable, and selective gas sensing devices is provided by optimizing shape, dispersion, porosity, interfacial bonding, and electrical alignment. Real-time, wearable, and flexible sensor systems for environmental and biological applications are constantly being advanced by developments in nanocomposite engineering.

Ammonia (NH?) Sensors

The sensitivity and overall efficacy of conducting polymer (CP) nanocomposite ammonia sensors are markedly enhanced by the incorporation of nanostructured fillers, like metal oxides or carbon nanotubes. In PANI/SnO? composites, SnO? nanoparticles offer numerous adsorption sites and enhance electron transport, resulting in superior NH? reactions compared to unmodified PANI. Reports indicate that PANI–SnO? nanostructures may detect ammonia concentrations as low as 10 ppm with improved sensitivity and accelerated kinetics, surpassing the performance of pure PANI films [19, 38].

The addition of nanotubes in polythiophene (PTh)/MWCNT composites significantly enhances NH? sensing capabilities. In comparison to pristine PTh, composites exhibit reduced detection limits (as low as 0.1–0.5 ppm) and significantly enhanced sensitivity, attributed to π–π interactions between CNTs and the polymer backbone that improve charge mobility [39-41]. These composites demonstrate a more rapid reaction and recovery than pure PTh, rendering them exceptionally appropriate for room-temperature NH? detection. Figure 6 shows the design, performance, and sensing mechanism for PANI-based nanocomposite NH? sensors [42]. Fig. 6 (a) and (d) demonstrate the fabrication of PANI/Sr?Ge?O?? and PANI/CoO? films by hydrothermal growth, layer-by-layer assembly, and in situ polymerization methods. The dynamic response curves in (b) and (f) show that nanocomposites are substantially more sensitive and recover quicker than pure PANI, with steady responses lasting hundreds of cycles (c). Selectivity study in (e) supports the composites' high preference for NH? over other interfering gases. The hypothesized process in (g) proposes that NH? adsorption drives dedoping and charge transfer between PANI and metal oxide nanostructures, resulting in observable resistance changes and increased sensing performance.

Figure 6: PANI-Based Nanocomposite NH? Sensors' Synthesis Pathways, Sensing Capabilities, Stability, Selectivity, and Suggested Procedure [42].

Another area in which nanocomposites perform better than pure CPs is response and recovery times. At ammonia concentrations ranging from 5 to 100 ppm, the majority of CP- based nanocomposites react in 30 to 60 seconds. The high binding of NH? molecules to the polymer backbone causes pure conducting polymers, especially polypyrrole (PPy), to recover slowly or not at all. In contrast, MWCNT–PPy composites recover completely in less than three minutes thanks to the nanotubes' changed surface energy and decreased binding strength [43]. For cyclic sensing in real-world applications, where sensors must rapidly reset for repeated readings, faster desorption is essential. One significant benefit of CP-based nanocomposites is their ability to function well at room temperature, in contrast to many metal oxide sensors that need higher temperatures. They are still more susceptible to humidity interference, though, which can reduce sensitivity by more than 15% in situations with high relative humidity. This is demonstrated in pure PPy films, where ammonia and water vapour compete for adsorption sites, degrading performance [15]. The categorization of conducting polymers and their composites for ammonia (NH?) gas sensing is compiled in Table 2. It shows the essential performance metrics (sensitivity, response/recovery time, and operating temperature), their sensing systems, and pertinent research references. According to the comparison, composites including nanomaterials (such as MWCNTs, graphene oxide, and Au–ZnO hybrids) greatly improve sensitivity, response speed, and recovery behavior, even if virgin polymers like PANI and PPy offer high sensitivity at ambient temperature. BBL and other emerging n-type polymers are renowned for their reversible and stable NH? sensing capabilities.

Table 2: Ammonia (NH?) Gas Sensing Classification of Conducting Polymers and Their Composites Including Important Sensing Properties.

The optimization of these materials for certain applications is demonstrated by application- specific designs. For instance, in food rotting settings, a PANI/WO? composite with 10% WO? loading can detect ammonia as low as 5 ppm with a quick 30-second response time, which is sufficient for real-time monitoring in packing or storage environments [50]. The large response magnitude (≥80% at 50 ppm) seen in MWCNT–PPy composites makes them extremely competitive for environmental or industrial leak detection, where speed and complete recovery are crucial.

Nitrogen Dioxide (NO₂) Sensors

Nanocomposites based on conducting polymers (CPs) for nitrogen dioxide (NO?) detection utilize the elevated surface area and catalytic characteristics of inorganic fillers in conjunction with the inherent sensitivity of CPs at room temperature. Among these, PPy/metal oxide hybrids have been extensively investigated. Polypyrrole, when combined with tungsten oxide (WO?), creates p-n junctions at the polymer–oxide interface, which markedly enhances NO? response relative to pristine PPy by improving charge separation and adsorption efficiency [51, 52]. PEDOT:PSS/TiO? nanofiber composites demonstrate superior NO? sensing capabilities. The nanofibrous structure offers an extensive interfacial surface and numerous adsorption sites, leading to enhanced sensitivity and accelerated reactions, even at low ppm concentrations [19, 53]. Likewise, SnO?/reduced graphene oxide (rGO)/PEDOT nanocomposites exhibit improved NO? detection owing to their conductive networks and synergistic electron-transfer pathways. These characteristics facilitate expedited recovery and enhanced sensitivity compared to either CPs or metal oxides independently, rendering them promising materials for pollution monitoring [54, 55]. Pure PANI with 5-10 µm porous particles that provide a large surface area is seen in Figure 7(a). A porous network with additional adsorption sites is created in the polyaniline (PANI)/black phosphorus (BP) composites (Fig. 7b) by weaving PANI particles (~3-5 µm) with BP sheets (5-20 µm wide, a few nm thick) [56]. The EDS maps and composite spectra of C, Cl, N, and P are shown in Figure 7(c-g).

Figure 7: SEM Photographs of PANI and PANI/BP Composite, As Well As the Composite's Elemental Mapping (C, Cl, N, and P) and EDS Spectrum [56].

Charge transfer between PANI (Ef = 4.4 eV, Eg ≈ 2.8 eV) and BP occurs during the gas sensitization of PANI/BP composites, resulting in Fermi-level equilibration. Electrons liberated from chemisorbed oxygen decrease hole concentration upon NO? adsorption, increasing resistance (Fig. 8a-c).

Figure 8: Schematic of NO? Adsorption on PANI/BP and Band Diagrams of PANI, BP, and Their Composite [56].

To enhance NO? detection, graphene oxide (GO) has also been combined with conductive polymers such as polyaniline (PANI). When exposed to NO?, a PANI/GO thin-film sensor showed a quick, reversible resistance change, improving both response magnitude and stability in comparison to pure PANI. To maximize performance, morphological adjustment of the composite film such as optimizing GO content is essential [57]. Further improvement in NO? sensing has been demonstrated by more intricate multi-component systems such as PANI/Ag?O/GO. While GO preserves the conductivity and mechanical integrity of the sensing film, the addition of AgO nanoparticles offers catalytic activity, speeding up the rates of NO? adsorption and desorption [58]. At room temperature, ordered ultrathin CP films can attain significant NO? sensitivity, but they frequently struggle with humidity interference. Incorporating metal oxides or carbon-based nanomaterials to stabilise the sensor response helps to partially overcome this problem [59]. The latest advancements in conducting polymers (CPs) and their composites for NO? gas detection from 2020 to 2025 are compiled in Table 3. The categorization emphasizes a range of systems, such as printed flexible composites, ionic liquid– metal–organic framework (IL-MOF) polymer hybrids, hybrid composites with reduced graphene oxide (rGO) and MXenes, and pure polymers (e.g., PANI and PPy nanofibers). The majority of CP-based composites function well at room temperature, exhibiting moderate to good recovery and quick reaction times (less than 30 s). Sensitivity is further increased by hybridization with MOFs and 2D materials (rGO, MXene), occasionally attaining ultra-high levels with reversible sensing. Additionally, trends highlight printable and flexible electronics, showing promise for wearable and portable applications. Although it is less frequent, high-temperature operation may be found in porous polymer/metal oxide composites, which exhibit optimal sensitivity at temperatures between 200 and 250 °C. High sensitivity, adaptability, and room-temperature operation are the general trends for CP-based NO? sensors, making them appropriate for next- generation environmental and health monitoring.

Table 3: Conducting Polymers and Their Composites for NO? Gas Sensing: Classification and Performance Comparison.

Hydrogen Sulfide (H?S) Sensors

In order to achieve high sensitivity, quick response, and selective detection even at sub- ppm levels, hydrogen sulphide (H?S) sensors based on conducting polymer (CP) nanocomposites take advantage of the room-temperature activity of polymers with the high surface area and catalytic capabilities of inorganic fillers. A noteworthy example is the electrochemically polymerised PANI/f-SWCNT thin-film sensor, which exhibits significantly greater conductivity and sensitivity than pure PANI sheets. Functionalised single-walled carbon nanotubes speed up the adsorption–desorption kinetics of H?S by increasing the active surface area and facilitating charge transfer [67]. Likewise, PANI–metal salt composites have been demonstrated to enhance low-concentration detection, where metal salts serve as gas interaction catalytic sites, improving response stability and amplitude [68]. Hybrid systems, such PANI/SnCl? composites, have demonstrated ultra-sensitive detection capabilities, achieving sub-ppm detection limits at room temperature. This makes them appropriate for environmental monitoring in situations with low safety thresholds [69]. By combining the gas-reactive polypyrrole backbone, the conductive network of reduced graphene oxide, and the semiconducting response of cadmium sulphide, CdS@PPy/rGO nanocomposites exhibit even greater selectivity and sensitivity. This architecture is perfect for long-term air quality monitoring since it responds to H2S strongly, reversibly, and recovers quickly [70]. Utilising their quick (<30 s) reaction to low concentrations, which is essential for tracking perishable goods, PANI/WO? nanocomposite films have been utilised in application-specific settings for food deterioration detection via H?S sensing [50]. As evidenced by the development of other sophisticated structures for dual H?S and H?O? sensing, such as BaInSbSe?/graphene-PPy composites, CP nanocomposites can be customised for multi- gas detection in industrial settings [71].

Figure 9 illustrates the use of a multidimensional CuO/CeO? nanostructure-based high- response H?S chemiresistive gas sensor in a portable warning system that operates in real time [72]. The offshore oil extraction platform serves as a reminder of the usefulness of H2S monitoring in dangerous industrial settings. The portable sensing device combined with CuO/CeO? material for on-site detection is depicted in the expanded schematic. The interaction of H?S with CuO to create CuS and H?O is the sensing process, which is shown in the upper right corner. CeO? improves electron transport and oxygen storage/release, increasing sensitivity and selectivity. With a quick reaction time of around 39 seconds, the dynamic response curve (bottom left) at 180 °C shows a steep resistance decline following exposure to 100 ppm H?S. This is followed by recovery upon gas removal, which is facilitated by heating at 220 °C. The exceptional sensitivity of the CuO/CeO? sensor to H?S (~2010) in comparison to other gases including NO?, CO, NH?, ethanol, acetone, and methanol is confirmed by the selectivity bar graph (bottom right) at 200 °C. Overall, the figure demonstrates the CuO/CeO? sensors' exceptional sensitivity, selectivity, and usefulness in real-time H?S warning systems.

Figure 9: An Illustration Of A Multidimensional Cuo/Ceo? Nanostructure Based High Response H?S Chemiresistive Gas Sensor. The H?S Detecting Mechanism, Dynamic Resistance Response At 100ppm H?S, And Exceptional Selectivity Against Other Interfering Gases Are All Demonstrated In The Figure, Which Also Shows How It Is Used In A Portable Real-Time Alert Device For Offshore Oil Sites [72].

Overall, CP nanocomposite H?S sensors demonstrate that π-conjugated polymers combined with semiconductors, catalytic oxides, or nanostructured carbon materials produce significant improvements in detection limit (often sub-ppm), response time (<1 min), and long- term stability, along with the added advantage of room-temperature operation.

Volatile Organic Compounds (VOC) Sensors

The intrinsic chemical sensitivity of π-conjugated polymers and the high surface area, catalytic, or conductive properties of nanoscale fillers are used by conducting polymer (CP) nanocomposites-based volatile organic compound (VOC) sensors to provide quick, accurate, and room-temperature detection. Conjugated polymers are mixed with nanoparticles to enhance charge transfer and increase adsorption sites in CP/nanoparticle nanocomposites for real-time VOC monitoring, one of the earlier innovations. With quick reaction times of just a few seconds, these instruments are capable of detecting a variety of volatile organic compounds (VOCs), such as ethanol, acetone, and toluene [73]. Also conducting polymer–carbon black nanocomposites have been optimised by molecular dynamics to connect structural features with VOC adsorption behaviour, exhibiting variable selectivity depending on the parameters of the polymer-VOC interaction [74].

Particularly efficient fillers include carbon nanomaterials like single-walled carbon nanotubes (SWNTs) and reduced graphene oxide (rGO). P3HT/rGO composites, for instance, exhibit notable enhancements in mobility and sensing current in organic field-effect transistor (OFET) VOC sensors, resulting in quicker and more powerful reactions to target gases [75]. Similarly, the combination of the gas-permeable matrix of the polymer and the SWNT conductive network allows PEDOT:PSS-coated SWNT sensors to detect saturated VOC vapours with good repeatability [76]. By utilizing ZnO's potent gas adsorption and PANI's conductive response, metal oxide polymer nanocomposites like PANI/ZnO have been created for broad-class VOC detection. This allows for quantifiable resistance changes across a variety of VOC types, which makes them appropriate for environmental monitoring applications. Furthermore, sensitivity and recovery durations have been demonstrated to be greatly impacted by morphological management, such as nanofiber or nanoparticle dispersion; optimized nanocomposite structures exhibit sub-ppm detection limits and brief (<30 s) recovery cycles [77].

Carbon Monoxide (CO) and Carbon Dioxide (CO?) Sensors

Conducting polymer (CP) nanocomposites-based carbon monoxide (CO) and carbon dioxide (CO?) sensors combine the catalytic and high surface area qualities of inorganic fillers with the gas sensitivity of π-conjugated polymers to provide room temperature operation, enhanced selectivity, and quicker reaction times. Early research using ultrathin CP nanocomposite films showed detectable conductivity changes in response to CO exposure; performance was enhanced by controlling the thickness at the nanoscale to promote diffusion and interaction [78]. With resistance variations proportionate to CO concentration throughout a broad detection range, PEDOT:PSS/PPA nanocomposites have more recently demonstrated good CO sensitivity and reproducibility [37]. Because graphene oxide's high surface area and PEDOT's conductivity work in concert, PEDOT/GO composites have improved performance even further, allowing for ultrafast detection with high signal-to-noise ratios and quick recovery [79].

Polypyrrole (PPy) is a common matrix for CO? detection because of its sensitivity to acidic gases. Although the addition of oxide nanoparticles can increase selectivity, chemically synthesised PPy sensors react with detectable resistance changes [80]. PANI/polystyrene blends have shown mechanical robustness and a stable CO? response with good reversibility [81]. When SnO? nanoparticles are added to PANI, CO? adsorption and charge transfer are improved, and response magnitude and recovery speed are further increased by UV irradiation [82]. Through p-n heterojunction effects, BiO?-loaded PPy nanocomposites have also been utilised to increase CO? stability and sensitivity [83].

Hydrogen (H?) Sensors

Conducting polymer (CP) nanocomposites-based hydrogen (H?) sensors combine the high surface area, catalytic, and electronic features of nanofillers with the room-temperature operation and chemical tunability of polymers to provide quick, sensitive, and selective detection. The graphene/polyaniline (PANI) nanocomposite is one extensively researched formulation that shows enhanced H? sensitivity because of graphene's strong electron mobility and huge surface area. Low detection limits and quick reaction times are made possible by the hybrid material's improved charge transfer and quicker adsorption–desorption dynamics when compared to pristine PANI [84]. With nanotube networks functioning as conductive bridges that promote quicker electron transit, MWCNT/PANI nanocomposite films also exhibit enhanced response magnitude and stability [85]. Table 4 shows the classification of conducting polymers and composites used for hydrogen (H?) gas sensing (2020-2025). The table compares several polymer systems, including their sensing processes, sensitivity limitations, response/recovery characteristics, and operating temperatures, emphasizing the impact of nanostructuring and hybridization (e.g., with CNTs, rGO, MOFs, and metal oxides) on performance. Recent research highlight the adaptability of polyaniline (PANI)-based composites, the impact of 2D materials and porous frameworks on adsorption and charge transfer, and the development of flexible/wearable polymer-based sensors for next-generation H? detection applications.

Table 4: Classification of Conducting Polymers and Composites Used For Hydrogen (H?) Gas Sensing (2020-2025).

Another important group is metal oxide–polymer composites. Because p–n junctions occur between the polymer and oxide, PANI/SnO? nanocomposites have been reported to detect H? at room temperature with greater sensitivity and faster recovery than pure PANI [93]. In a similar vein, TiO?-doped PANI composites made via oxidative polymerisation exhibit increase selectivity for hydrogen over other gases and larger response amplitudes [94]. Nanostructuring works especially well for improving performance. Because of the combination catalytic action of silver and the huge reactive surface area of nanofibers, electrospun Ag–SnO?/PANI nanofibers have low detection limits, high responsiveness, and a lower operating temperature [95].

Recent Advances and Emerging Trends in CP Based Gas Sensors

Conducting polymers (CPs) and inorganic nanoparticles are being integrated to improve sensor performance at room temperature and low working temperatures, according to a thorough analysis of current developments in CP-based nanocomposites for gas sensing. In order to achieve high sensitivity, selectivity, and quick response times, these hybrid nanocomposites combine inorganic nanostructures like metal oxides, metal-organic frameworks (MOFs), and transition metal dichalcogenides with the special electrical, chemical, and structural characteristics of CPs, such as polyaniline (PANI), polypyrrole (PPy), and other derivatives [96], [7] and [97].

In order to create well-dispersed, nanostructured materials with large surface areas, one popular tactic is the synthesis of nanocomposites using hydrothermal, wet chemical, or organic polymer-assisted exfoliation techniques. For example, reduced graphene oxide (rGO)/CoO? nanocomposites were prepared by Meng et al. [98] using a one-step hydrothermal procedure, and at low temperatures, they showed remarkable sensitivity to xylene. Similarly, using a one-pot wet chemical method created rGO-ZnO nanocomposites that demonstrated quick and accurate ammonia detection at ambient temperature [99]. These investigations highlight how crucial controlled synthesis methods are for customizing nanocomposite structures for the best gas sensing results. To maximize synergistic effects, CP integration with metal oxides has been thoroughly investigated. In order to enable room-temperature hydrogen sensing, Pippara et al.[100] created a hybrid film consisting of SnO? nanosheets doped with Pd and inserted within polyaniline. The conductive polymer matrix and SnO?'s semiconducting characteristics work together to improve charge transfer processes, which raises sensitivity and response times. The relevance of polypyrrole-based hybrid nanocomposites in chemiresistive gas sensors was also thoroughly reviewed by Das et al. [96], who emphasized the materials high sensitivity, stability, and ease of production.

MOF-derived metal oxide nanocomposites have also demonstrated encouraging outcomes. An In?O?/ZnO nanocomposite that resembled a fern and was made from MIL- 68/ZIF-8 was described by Liu et al. [101] as having exceptional triethylamine sensing properties including high responsiveness and ultralow operating temperature. The mesoporous structure made from MOFs improves sensing capability by facilitating gas diffusion and offering a large number of active sites. Similar to this, Zhan et al.[102] showed that core-shell SnO?/ZIF- 8 nanospheres greatly enhanced NO? detection, highlighting the significance of nanostructure engineering in composites based on CP.

Optimising gas sensing properties requires careful consideration of surface modification and nanostructure morphology. Using a one-step hydrothermal process, Li et al. [103] created ZnO/Zn?SnO? nanocomposites with a homogenous hexagonal lamellar structure that demonstrated improved formaldehyde sensing. The enhanced sensitivity was a result of the accessible active sites and large surface area. Furthermore, Yuan et al. [104] produced high- performance 2-butanone sensors that functioned at ambient temperature by introducing flaws into Fe-doped CoO? nanocomposites and surface-decorating them with Ag nanoparticles. Better gas adsorption and charge transfer are made possible by these changes, which are essential for high-performance sensing. The benefits of CP-inorganic nanocomposites in gas sensing applications have been emphasized in recent reviews. Conducting polymer-inorganic nanocomposites were examined by Yan et al. [7], who emphasized their easily functionalized nature and tunable electrical characteristics. In a similar vein, Shinde et al. [105] examined GO- based nanocomposites and highlighted their low production costs, excellent sensitivity, and selectivity. Because of its larger surface area and better charge transport channels, GO combined with CPs or metal oxides improves sensing performance overall. In order to optimise active sites and promote quick gas diffusion, ternary and dual-mesoporous nanocomposites have also been investigated. Dual-mesoporous transition metal oxide/noble metal nanocomposites were created by Ma et al. [106], who showed that they may be used to detect biomarkers such 3-hydroxy-2- butanone in real time. Superior sensing properties result from the regulated mesoporous design, which guarantees excellent dispersion of active nanoparticles and accessible paths for gas molecules.

One major area of focus is still the synthesis of nanocomposites with specific surface functions and nanostructures. In order to demonstrate the adaptability of CP-based nanocomposites in sensing a variety of gases, Kuang et al. [107] used hydrothermal techniques to create Ti?C?Tx-TiO? nanocomposites that could detect volatile organic molecules at room temperature. Likewise, Zhang et al. [108] produced MOFs-based In?O?/ZnO/Ti?C?TX MXene ternary nanocomposites, which demonstrated outstanding ethanol sensing at ambient temperature, underscoring the significance of mixing several nanomaterials to produce high- performance sensors.

The substantial potential of CP-based nanocomposites in gas sensing applications is highlighted by the existing literature, to sum up. Conducting polymers and inorganic nanostructures-particularly metal oxides and MOFs work in concert to improve operational stability, sensitivity, and selectivity under ambient circumstances. The development of high- performance gas sensors has been greatly aided by developments in surface modification, nanostructure control, and synthesis methods. To further increase sensor performance, future research approaches are probably going to concentrate on understanding the basic principles driving gas interactions, investigating new CP-inorganic pairings, and optimising nanostructure topologies [96], [7], and [105].

The design architecture of the devices as well as the fabrication methods utilised to create nanocomposites have a significant impact on the functionality and performance of conducting polymer (CP)-based gas sensors. Recent advances (2020–2025) have refined synthetic strategies and integrated these materials into flexible and miniaturised devices, leading to quantitative improvements in gas detection, including lower detection limits, faster response/recovery times, and improved long-term stability.

Synthesis Techniques for Nanocomposites

In situ polymerization is one of the best fabrication techniques because it allows nanofillers to be intimately blended into the polymer matrix, guaranteeing even dispersion and robust interfacial contact. In a recent work, for instance, SnO?/PTh nanocomposites made by in situ polymerization demonstrated a response time of less than 15 seconds and a 70% greater response to NH? at 50 ppm than pure polythiophene [10].

Electrospinning: This process is now widely used to create one-dimensional nanostructures with large surface areas and porosity. Electrospun PANI/CNT nanofibers outperformed bulk films by a factor of ~2× in kinetics and ~3× in sensitivity, exhibiting a limit of detection (LOD) for NH? as low as 0.9 ppm, a response time of 10–20 s, and a recovery time < 60 s [15]. These improvements result from the nanofiber network's higher surface-to-volume ratio and open porosity.

Vapor-phase polymerization (VPP): Combining vapor-phase polymerization (VPP) with methods like as drop casting or electrospinning allows for uniform coating of high-aspect-ratio nanofillers and fine morphological control, which enhances mechanical stability and conductivity. Using VPP, Pan et al. (2024) created PANI/MXene composites that had >90% response retention over 30 days, a detection limit of ~200 ppb, and a 10-fold increase in sensitivity to NO? (10–100 ppb range) [5].

Sensor Architectures: Chemiresistors, Fets, and Optical Sensors

Chemiresistors prevail in contemporary CP-based gas sensor systems owing to their simplicity in manufacture and signal acquisition. These devices are generally fabricated with interdigitated electrodes and a sensor layer applied via drop-casting or spin-coating, demonstrating excellent linearity and reproducibility. Hooshmand et al. (2023) documented a PANI-ZnO chemiresistor exhibiting a response of around 85% to 10 ppm NH?, with selectivity ratios surpassing 3× in comparison to interfering gases such as ethanol and acetone [109]. Semiconducting CPs like P3HT and PEDOT have been used more recently in the development of field-effect transistors (FETs). P3HT-based FET gas sensors were demonstrated by Cheng et al. [110] to exhibit a 60% threshold voltage shift in response to 5 ppm NO? and two orders of magnitude modulation of on/off current. These characteristics offer intrinsic amplification and enhanced selectivity in comparison to chemiresistors. Although they are less prevalent, optical sensors that use CP nanocomposites provide multi-modal detection. PEDOT-based thin films, for example, have been investigated for optical transduction and have demonstrated sub-minute response times and absorbance shifts of 10-20% upon exposure to 50 ppm VOCs.

Integration with Array-Based, Compact and Portable Devices

Modern gas sensing applications increasingly require real-time monitoring, mobility, and adaptability. Recent studies have focused on incorporating conducting polymer (CP) nanocomposites into flexible and miniaturized systems based on printed electronics and CMOS- compatible platforms [10, 111]. PANI/CNT (or MWCNT) composites on flexible PET have been developed for NH? sensing, with quick responses at low-ppm levels and good mechanical endurance, indicating their potential for wearable devices. Examples include a wireless flexible PANI-MWCNT/PET system and transparent flexible PANI micromesh devices that retain performance despite repeated bending (e.g., ~14% sensitivity change after 1000 bending cycles at 5 ppm NH?) [112, 113]. While specific response/recovery values vary, numerous CP-based NH? sensors report second-to-tens-of-seconds dynamics at room temperature. Examples include thin PANI sheets and electrospun/flexible architectures [114, 115]. Also CP or CNT chemiresistors with machine learning enables reliable multi-gas classification (e.g., NH?, NO?, CO, ethanol, acetone and other VOCs), with many reports achieving >90% accuracy under study conditions and sub-20-s-class responses in some systems. These capabilities have been extensively described in recent array/ML reviews and chemiresistive array demonstrations [116]. Concurrently, MEMS integration is progressing, with sub-millimeter-scale footprints and low power operation appropriate for compact/portable platforms; recent reviews highlight materials, microhotplate designs, and stability solutions for MEMS gas sensors [117]. Researchers are also looking on battery-free alternatives, such as passive RFID/NFC-coupled chemical sensors, to enable widespread and low-maintenance deployments for environmental and biological monitoring [118].

Limitations in Stability, Reproducibility and Environmental Interference

Conducting polymer (CP)-based nanocomposite sensors frequently has issues with temperature-dependent performance, humidity sensitivity, and long-term drift despite tremendous advancements. Hydrophilic polymers like PANI can swell due to environmental conditions like moisture, changing baseline resistance and reducing repeatability [90]. Variability in nanofiller dispersion and polymerization conditions makes batch-to-batch repeatability difficult; for devices that are ostensibly identical, relative standard deviations (RSD) in sensitivity have been found to range from 5 to 15% [33]. Although stability problems still exist because certain CP sensors lose over 30% of their initial response in just four weeks when exposed to ambient conditions [10].

Commercial Viability and Scalability

Cost, homogeneity, and integration issues arise when laboratory-scale fabrication is scaled up to mass production. Potential remedies include roll-to-roll deposition and screen printing, however it is difficult to preserve nanostructure integrity when scaling up [119]. Commercial feasibility and green production are hampered by the use of hazardous solvents or expensive precursors in many CP-based nanocomposites [120]. Furthermore, there are still issues with device packing and calibration for reliable large-scale performance.

Future Research Directions

Predictive maintenance, drift compensation, and automatic gas identification are made possible by the integration of artificial intelligence. For complicated gas mixes, AI-enhanced systems have demonstrated >95% classification accuracy and over 40% reduction in false- positive rates [121]. Green synthesis: Environmental impact can be reduced by using biodegradable substrates and solvent-free, aqueous-phase, or sustainable polymerization [122]. Bio-derived fillers and dopants, such as cellulose nanofibers, present promising environmentally friendly substitutes. Multipurpose sensors: Context-aware sensing and enhanced selectivity will be made possible by the creation of flexible, wearable devices that integrate temperature, humidity, and strain detection with gas sensing. Alsohybrid CP–metal oxide/MXene devices have shown negligible cross-sensitivity in the simultaneous detection of CO and VOCs [10]. In conclusion, for CP-based nanocomposite gas sensors to advance from research prototypes to practical, commercially viable devices, stability, repeatability, and environmental interference must be addressed while permitting sustainable large-scale manufacture. A promising route to the next generation of intelligent, environmentally friendly, and high-performing gas sensing platforms is the integration of AI-assisted analytics, green chemistry, and multifunctionality.

In this review, we have looked at how conducting polymer (CP)-based nanocomposites' sensing ability is fundamentally defined by structure–property interactions. Through quantitative literature data, it was demonstrated that elements including energy level alignment, interfacial bonding, porosity, customised morphology, and nanofiller dispersion significantly improved sensitivity, selectivity, and response speed. For instance, porous PPy/Au–ZnO composites decreased the ethanol response time from 27 s to just 8 s, while well-dispersed CNT/PPy systems increased NH? sensitivity from 12% to 45% at 100 ppm. Faster electron exchange for VOC detection was made possible by matching work function alignment in PANI/MXene sensors, and heterojunction designs in PANI/SnO? systems reduced NH? detection limits from 1 ppm to 100 ppb. Despite these developments, we found enduring issues: a lot of CP-based sensors continue to show large baseline drift (>50% change) under high humidity, 5–15% repeatability variance between batches, and 20–40% signal degradation within a month. Costly nanofillers (such as graphene oxide, which costs more than $200/g), hazardous solvents, and nanostructure collapse during high-throughput fabrication-which can lower sensitivity by about 25% when compared to lab-scale devices-are barriers to scalability.

Three convergent techniques will be necessary for future advancement. First, real-time, adaptive, and interference-compensated sensing will depend on AI-assisted sensing, which has already achieved >95% accuracy in gas mixture categorisation and reduced false positives by over 40%. Second, it has been demonstrated that green synthesis methods such aqueous-phase oxidative polymerisation can reduce VOC emissions by more than 90% while providing comparable sensitivities (ΔR/R? = 85% at 10 ppm NH?). Third, multipurpose sensor platforms pave the way for durable, adaptable wearable and distributed sensing network devices. For example, CP/MXene hybrids with <8% cross-sensitivity, <10 s response, and >1,000-cycle mechanical durability.

In summary, integrated, sustainable, and intelligent platforms are replacing basic materials innovation in CP-based nanocomposite gas sensors. The field is well-positioned to provide commercially viable, high-performance sensors for industrial safety, biomedical diagnostics, and environmental monitoring by concurrently developing nanostructure engineering, eco-friendly fabrication, and AI-enabled analytics.

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