Recent advances in 2D-material-based wearable VOC and humidity sensors

1 Introduction

The escalation of toxic gases and harmful environmental pollutants, such as oxides of carbon (CO2, CO), NOx, NH3, SO2, H2S, hydrocarbons, and volatile organic compounds (VOCs), has driven demand for sensitive, selective, and reliable sensors (Jalal et al., 2018). Due to high volatility and toxicity, these VOCs have a severe health impact, such as respiratory disorders, neurological issues, and even carcinogenic problems (Liu et al., 2021). Similarly, humidity, known as the concentration of water vapour, has a crucial impact on health and the environment by nurturing microbial growth and respiratory difficulties at high levels, or drying out airways at low levels, as well as affecting ambient contaminant persistence and indoor air quality (Guarnieri et al., 2023). Relative humidity also impacts the stability of pharmaceutical products and electronic products in industry, requiring crucial observation to prevent contamination, corrosion, or operational failures (Kok et al., 2025). Therefore, these rising challenges caused by VOCs and humidity highlight the urgent need for advanced detection technologies. Developing sensing platforms capable of detecting analytes under different environmental conditions remains a fundamental challenge. Several previous reviews have covered 2D materials for gas sensing, but they largely focus on either VOC detection or humidity sensing in isolation, with limited attention to wearable form factors. Moreover, existing reviews often lack critical quantitative comparison of sensor performance, mechanistic discussion of sensing principles, and analysis of the interference between VOC and humidity signals—a critical issue for real-world wearable applications.

The rapid advancement of wearable technologies has made flexible sensors essential for air quality monitoring, industrial safety, and personalized health diagnostics (Atkare et al., 2024; Kalita et al., 2024). With the rise of advanced 2D materials like graphene, MXene, and transition metal dichalcogenides (TMDs), known for their high surface area, mechanical flexibility, and tunable band gaps, there is an opportunity to develop highly sensitive, low-power sensors integrated on flexible substrates with IoT. The outstanding surface properties of these 2D materials enable strong surface interactions with gas and water molecules, resulting in enhanced sensitivity even at low concentrations. Furthermore, the defects, edge sites, and various functional groups present in the 2D materials also contribute to the adsorption-based charge-transfer process, which is crucial to the sensing mechanism (Joshi et al., 2025). Furthermore, the heterostructures based on 2D materials have shown synergistic effects, including better adsorption sites, improved charge transfer, and faster response/recovery times.

In this mini review, the focus is on the very recent developments in 2D material-based wearable sensors for VOCs as well as humidity detection. To the best of our knowledge, no mini review has comprehensively and critically examined both VOC and humidity sensors together in the context of wearable platforms, while also addressing their cross-sensitivity and providing quantitative performance benchmarks. This mini review fills this gap by: (i) providing a balanced and critical analysis of recent advances in 2D-material-based wearable sensors for both VOCs and humidity; (ii) offering a dedicated discussion of sensing mechanisms; (iii) presenting a comprehensive quantitative comparison table of sensor performance parameters; (iv) explicitly addressing the challenge of humidity interference in VOC sensing; and (v) outlining forward-looking perspectives on key challenges. Accordingly, this mini review focuses on the very recent developments in 2D material-based wearable sensors for VOCs as well as humidity detection. The discussion covers material design, defect engineering and hybrid structure formation to enhance the sensing performance. The article finally discusses the current challenges and future perspectives towards low-cost, multifunctional, and high-performance sensing platforms for the development of next-generation wearable and environmental monitoring technologies.

2 Fundamentals of 2D-material-based wearable sensing

2.1 Wearable platforms and substrates

The performance and practicality of wearable VOC and humidity sensors using 2D materials depend significantly on the substrate platform supporting the sensing layer. Choosing suitable flexible or stretchable substrates is crucial to ensuring mechanical stability, biocompatibility, durability, and reliable performance under continuous deformation. Polymers, textiles, and paper are common substrates designed for specific wearable environments.

Polymeric substrates such as polydimethylsiloxane (PDMS), polyethylene terephthalate (PET), polyimide (PI), and thermoplastic polyurethane (TPU) are widely used due to their elasticity, optical transparency, lightweight nature, and chemical stability (Hassan et al., 2022). Their low glass transition temperatures enable conformal contact with human skin, allowing real-time physiological monitoring. However, their low biodegradability raises concerns regarding their disposal and environmental effects.

Textile-based substrates offer breathability, comfort, and compatibility with daily wear. Conductive coatings or printed 2D materials can be incorporated directly into woven or knitted fabrics via methods such as dip-coating, spray deposition, or screen printing. The intrinsic roughness and porosity of textile fibers enhance surface area, improving analyte adsorption and sensor sensitivity.

Similarly, paper substrates, fabricated from cellulose-based materials, provide a biodegradable and low-cost alternative for disposable wearables. Their porous structure provides vapour diffusion and fast moisture transport, crucial for humidity detection. Furthermore, paper-based electronics can be easily fabricated using printing techniques, leading to disposable point-of-care wearable devices. However, challenges related to mechanical durability and environmental sensitivity must be addressed for long-term applications. Notably, while textile substrates offer excellent breathability and comfort for daily wear, the majority of 2D-material-based VOC and humidity sensors reviewed in this manuscript have been demonstrated on polymer or paper substrates. The integration of 2D materials into textile-based wearable sensors for VOC and humidity detection remains an emerging area requiring further investigation.

2.2 Sensing mechanisms

Understanding the underlying transduction principles is essential for the rational design of high-performance wearable sensors. Most 2D-material-based chemiresistive sensors operate on charge transfer between the analyte molecule and the sensing layer. When VOC molecules or water vapor adsorb onto graphene, MXene, or TMDs, they act as electron donors or acceptors depending on their molecular orbital energies relative to the Fermi level of the 2D material (Joshi et al., 2025). For instance, NH₃ donated electrons to p-type materials like graphene or WS₂, reducing hole concentration and increasing resistance, while NO₂ withdrew electrons, decreasing resistance (Shi et al., 2023).

Surface functional groups and defect sites play a crucial role in adsorption. Hydroxyl (-OH), carboxyl (-COOH), and epoxy (C-O-C) groups on graphene oxide act as preferential binding sites for polar VOCs and water molecules via hydrogen bonding (He et al., 2025; Lahkar et al., 2025). Defect sites such as vacancies and edge sites serve as high-energy binding locations, and intentional defect engineering amplifies sensitivity (Li et al., 2024). In Polyaniline (PANI)-based hybrids, a reversible protonation/deprotonation mechanism dominates: insulating emeraldine base PANI converts to conductive emeraldine salt upon protonation, with hybridization with 2D materials providing parallel conduction pathways for enhanced sensitivity (Feng et al., 2024; Kashyap et al., 2024; Santos-Ceballos et al., 2024; Wu et al., 2022). Heterostructures such as WS₂/MoS₂ or MXene/reduced graphene oxide (rGO) create internal built-in electric fields at the junction; gas adsorption modulates the depletion region width, amplifying the resistance change beyond individual materials (Shi et al., 2023; Yu et al., 2024). Finally, while most wearable sensors use chemiresistive readout (DC resistance change) for simplicity and low power, impedance-based sensors measure AC complex impedance to decouple bulk and interfacial contributions, offering greater robustness against humidity interference (Ke et al., 2025; Liu et al., 2021; Xiang et al., 2024; Xie et al., 2023).

2.3 Addressing humidity interference in VOC sensing

A major challenge for wearable VOC sensors is the unavoidable presence of ambient water vapor, which competes for adsorption sites, screens charge transfer signals, and introduces ionic conduction artifacts (Joshi et al., 2025). The sensors reviewed in this manuscript use several strategies to mitigate this interference. Hydrophobic surface functionalization has been effective; (Li et al., 2022); used hydrocarbon-terminated MXene to reduce water adsorption while maintaining ethanol sensitivity, and (Pang et al., 2025) employed oleylamine-functionalized graphene oxide to achieve stable NH₃ sensing up to 95% RH. Composite design with hydrophobic 2D materials also helps; (Kashyap et al., 2024); reported that WS₂ in WS₂-PANI hybrids partially suppresses humidity response compared to pure PANI. Differential dual-signal readout offers another route; (Chen et al., 2023); combined resistive and visual signals to achieve 99% RH tolerance for NH₃ detection (Wu et al., 2022). systematically demonstrated a stable NH₃ response across 20%–100% RH in their PP/G/PANI mask sensor (Figure 1B). Despite these promising approaches, many VOC sensors in the literature, including some cited in this review, either lack quantitative humidity testing or show significant performance degradation under humid conditions. Future studies should routinely report sensor response under variable RH and develop standardized protocols for humidity-independent VOC sensing.

Regarding IoT integration, while several cited works demonstrate pathways toward smart sensing, including neural network-accelerated data processing (Wang et al., 2025a), machine learning-based VOC discrimination (Tran et al., 2024), and touch-free sensing platforms (Sun et al., 2025). Explicit wireless data transmission via Bluetooth or NFC remains experimentally limited in the 2D-material-based VOC and humidity sensing literature. This represents an important direction for future wearable sensor development.

3 2D materials for wearable VOC sensing

Wearable VOC sensors fabricated from 2D materials have emerged as a potential candidate for the requirement, as they can convert changes in their properties during chemical adsorption into measurable signals at room temperature. The following sections discuss specific sensor examples organized by material type. For a detailed discussion of the underlying transduction principles—including charge transfer, surface functionalization, protonation in PANI hybrids, heterostructure effects, and the distinction between chemiresistive and impedance-based readout—the reader is directed to Section 2.2. To enable meaningful comparison, the performance metrics discussed below, sensitivity, limit of detection (LOD), and response/recovery times, are summarized quantitatively in Table 1. Where available, numerical values are provided to facilitate direct material-to-material comparison.

TABLE 1. Performance comparison of 2D-material-based wearable VOC and humidity sensors is discussed in this review.

Note: Parameters denoted by “–” indicate that the corresponding values were not reported explicitly in the original references).

Graphene and its derivatives, graphene oxide (GO) and reduced graphene oxide (rGO), have been utilized extensively in flexible and wearable sensors owing to their excellent physicochemical and electrical properties. For instance, Laser irradiation of graphene and its derivatives is a powerful tool for developing flexible sensors. The laser irradiation created a porous, hydrophilic structure developed on the surgical mask, which has enhanced the material’s adsorption capacity towards VOCs (Chen et al., 2023). Wang et al., 2024b. developed a wearable NH₃ sensor using vertical graphene nanosheets on a polyimide substrate, enhanced by a physics-informed neural network for faster response times (Wang et al., 2025b). Operating at room temperature, this sensor provides a safe, non-invasive diagnostic tool with high selectivity for trace-level NH₃. In another report, Liu et al. have demonstrated exfoliated graphene mixed with conductive carbon black as a sensing material, dip-coated on filter paper, for the detection of VOCs (methanol, ethanol, etc.), as well as relative humidity (Liu et al., 2021). The wearable and flexible sensor to monitor the air is environmentally friendly due to the use of a paper substrate, which is biodegradable, ensuring easy disposal via ultrasonic treatment without producing hazardous residues. Similarly, Xiang et al. developed a flexible sensor using AgNW, carbon black, and expanded graphite on an eco-friendly cellulose substrate for VOC and humidity detection (Xiang et al., 2024). This sensor shows high selectivity for methanol and ethanol and is also fully decomposable by burning, ensuring zero electronic waste.

In recent years, non-invasive detection of VOCs in exhaled human breath for disease detection has emerged as a potential diagnostic tool in the medical field. Wu et al. coated graphene/PANI (PP/G/PANI) on disposable polypropylene masks, enabling NH₃ detection (250% at 50 ppm, 100 ppb LOD) and volatile sulfur compounds via enhanced surface area and PANI protonation/deprotonation (Wu et al., 2022). Figure 1A,B shows the schematic of the synthesis, the sensing chamber setup, and the sensing response of the fabricated sensor. Importantly, Wu et al., 2022) systematically evaluated the humidity dependence of this sensor, demonstrating stable NH₃ response across 20%–100% relative humidity (RH) (Figure 1B), which is critical for practical mask-integrated breath monitoring. Pang et al. developed a flexible OFET-based wearable NH₃ sensor using oleylamine-functionalized graphene oxide (OA-GO) blended with DPP-polymer and SEBS elastomer, achieving 67.01%/ppm sensitivity, 9.19 ppb LOD, and stability up to 95% RH for non-invasive kidney disease diagnosis via skin-adherable breath monitoring, where the hydrophobic oleylamine chains effectively suppress water adsorption, minimizing humidity-induced signal drift (Pang et al., 2025). Similarly, Chen et al., 2024. fabricated a dual-signal (resistive/visual) sensor with PAN/PANI/rGO and PAN/BCG nanofiber films on porous PAN substrates, offering 70 s response time, 99% RH tolerance, and mask integration for CKD detection above 2 ppm exhaled NH₃ (Chen et al., 2023). Santos-Ceballos et al. used electrochemical deposition for PANI@LIG nanocomposites, yielding excellent RT sensitivity/selectivity (2.38 ppb LOD) through reversible PANI protonation, ideal for wearable platforms (Santos-Ceballos et al., 2024). These graphene/PANI hybrids excel in humidity-tolerant, breath-based NH₃ sensing for kidney biomarkers. Similarly. Bi et al. developed a multifunctional rGO/PPy composite fabric that detects ammonia in breath for non-invasive renal disease diagnosis (Bi et al., 2021). This versatile material also functions as a wearable Joule heater, enabling a dual-action system for both disease detection and responsive therapy. Similarly, in TMD-based materials, Shi et al. have developed a multifunctional WS₂/MoS₂ heterostructure on a conductive foam to simultaneously monitor NO₂ breath biomarkers, occlusal force, and maxillofacial movements for the non-invasive diagnosis of oral diseases (Shi et al., 2023). MXene-based materials have also been explored for health monitoring in recent years. Li et al. developed a room-temperature wearable volatile organic compound sensor using termination-modified Ti₃C₂T_x MXene, which uses hydrocarbon groups to reduce humidity interference and significantly amplify ethanol sensitivity for real-time breath alcohol monitoring (Li et al., 2022). Taromsari et al. fabricated a 3D, vertically aligned MXene and PEDOT: PSS aerogel via a novel directional freeze-casting method, creating a mechanically robust, wide-range chemoresistive sensor for human breath analysis and VOC detection (Mohseni Taromsari et al., 2025). Similarly, composites with MXene have also been explored for breath acetone detection to monitor the metabolic activity in human health (Li et al., 2023; Zhou et al., 2025). Figure 1 [C] shows the Schematic and sensing responses of acetone detection in human exhaled breath by flower-like Ti₃C₂T_x anchored with MoS₂ quantum dots (F−Ti₃C₂T_x/MoS₂) coated facial mask.

Similarly, heterostructure formation of PANI with TMDs has also been explored for wearable health monitoring in recent years (Feng et al., 2024; Zhao et al., 2026). These wearable sensors show promising results in developing real-time monitoring of human health via exhaled breath. Moreover, there are very recent reports on PANI composites with TMDs with highly sensitive wearable NH₃ sensors at room temperature (Kashyap et al., 2024; Tian et al., 2023; Wang et al., 2024a). Figure 1 [D] shows the sensing responses of the WS₂-PANI flexible sensor towards NH₃ at room temperature (Kashyap et al., 2024). In the WS₂-PANI system, the hydrophobic nature of WS₂ partially mitigates humidity interference compared to pure PANI-based sensors, though quantitative humidity-dependent studies remain limited. Recently, metal-organic framework (MOF)-based composite sensors have attracted considerable attention owing to their porous structure, which provides abundant surface area for interaction with gas molecules. Although MOFs are not 2D materials themselves, their composites with graphene combine the high porosity and molecular selectivity of MOFs with the electrical conductivity and mechanical flexibility of 2D materials—a synergy particularly valuable for wearable VOC sensing. Kim et al. developed a highly sensitive and transparent ethanol sensor by depositing a Ni-based metal-organic framework (MOF) directly onto a highly conductive graphene layer (Kim et al., 2024). In this composite, graphene serves as the conductive channel and flexible transparent substrate, while the MOF layer provides selective ethanol adsorption sites through its porous structure. This flexible device achieves a low detection limit of 1 ppm with ultra-fast response times, demonstrating remarkable stability over 100,000 bending cycles for next-generation wearable electronics. In a similar composite structure, Tran and coworkers created a flexible chemiresistive sensor combining a zeolitic imidazolate framework (ZIF-8) MOF with laser-scribed graphene to non-invasively detect lung cancer biomarkers in exhaled breath at room temperature (Tran et al., 2024). Here, laser-scribed graphene provides the conductive network and mechanical flexibility for wearable integration, while the MOF contributes a selective “gas cage” sieving effect that discriminates between different VOCs based on molecular size. By leveraging the MOF’s selective “gas cage” sieving effect and a machine learning algorithm, the sensor successfully discriminates between various volatile organic compounds with 96.5% accuracy for point-of-care diagnostics. Metal and metal oxide incorporation into the 2D materials has been explored extensively for VOC detection in recent years. Recently, Sun et al. developed a flexible, wearable electrochemical sensor using Pt-CNTs/rGO composite electrocatalysts for real-time and trace methanol gas detection (Sun et al., 2023). By utilizing an optimal 1:2 ratio of carbon nanotubes to reduced graphene oxide, the sensor achieves high sensitivity, rapid response times, and excellent stability. Across the VOC sensors reviewed above, humidity interference remains a recurring challenge. Several strategies have proven effective: hydrophobic surface functionalization (Li et al., 2022; Pang et al., 2025), differential dual-signal readout (Chen et al., 2023), and composite design with hydrophobic 2D materials (Kashyap et al., 2024). However, many of the cited works either did not report humidity-dependent performance or tested only under dry conditions. Future wearable VOC sensors should systematically evaluate cross-sensitivity to ambient humidity—a gap this review highlights for the research community. To provide a quantitative overview and enable direct comparison of reported sensing performances, Table 1 summarizes the key parameters of the 2D-material-based wearable VOC and humidity sensors discussed in this review.

Quantitative comparison of the VOC sensors in Table 1 reveals several clear trends. For NH₃ detection, sensitivity ranges from 67.01%/ppm (Pang et al., 2025) to 250% at 50 ppm (Wu et al., 2022), while LOD varies from 9.19 ppb to 2.38 ppb. Graphene/PANI hybrids offer the best balance of sensitivity and humidity tolerance, whereas OFET-based OA-GO sensors provide superior LOD at the cost of fabrication complexity. MXene-based sensors excel at detecting ethanol and acetone due to their tunable surface terminations but exhibit greater baseline drift in humid conditions than graphene-based alternatives. Notably, response and recovery times are rarely reported for VOC sensors—a significant gap, as real-time wearable applications require rapid kinetics. This stands in contrast to the humidity sensing field, where response times are routinely reported.

4 2D materials for wearable humidity sensing

The humidity sensing mechanisms described in Section 2.2, particularly the role of surface hydroxyl groups and ionic conduction, are directly applicable to the following examples. In recent years, significant progress has been made in wearable health-monitoring technologies, especially in real-time, continuous assessment of physiological parameters. Among these, humidity-based human respiratory monitoring has attracted significant attention, as it provides crucial information on pulmonary and cardiovascular health (Pandey et al., 2026).

To date, many materials have been explored for developing wearable humidity sensors, including polymers, metal oxides, and 2D materials. Among these, 2D materials have emerged as potential sensing materials in wearable humidity sensors. Owing to their exceptional mechanical, electrical, chemical, and optical properties, they have found their applications in various fields, including humidity sensing (Shaukat et al., 2024).

Graphene oxide (GO) has attracted considerable attention in wearable humidity and respiratory sensing owing to its excellent hydrophilicity, flexibility, and ease of fabrication. Wang et al. developed a GO-coated non-woven fabric sensor for respiratory monitoring, where bovine serum albumin pretreatment improved GO adhesion and enhanced humidity sensitivity (Wang et al., 2020). Likewise, Lahkar et al. reported a flexible paper-based GO humidity sensor employing hand-drawn interdigitated electrodes to monitor different breathing patterns and apnea-like conditions (Figure 2A) (Lahkar et al., 2025). To overcome the inherent limitations of GO, such as moderate sensitivity and slower response/recovery characteristics, He et al. developed a plasma-treated GO sensor integrated with laser-induced graphene electrodes on PDMS, achieving enhanced sensitivity, rapid response/recovery times (15 s/9 s), and stable performance over 60 days (He et al., 2025).

The progression from GO to reduced graphene oxide (rGO) and its composites represents a clear trend: rGO offers higher electrical conductivity, while composites with hygroscopic materials compensate for rGO’s reduced hydrophilicity. Paeng et al. developed a copper nanoparticle/graphene nanoplatelet composite on polyimide Figure 2B (Paeng et al., 2024), as shown in Figure 2 [B]. Zhao et al. reported an rGO/cellulose acetate composite where hydroxyl-rich cellulose acetate improved moisture adsorption (Zhao et al., 2025). Ke et al. synthesized an rGO/MoS₂ composite, achieving a response time of 0.65 s over 11%–95% RH, highlighting the advantage of heterostructured rGO with TMDs (Ke et al., 2025). The response time of 0.65 s achieved by (Ke et al., 2025) is the fastest among all humidity sensors reviewed here, outperforming MXene-based sensors (12 s, (Liu et al., 2024),) and plasma-treated GO (15 s, (He et al., 2025)) by more than an order of magnitude.

In addition to graphene-based materials, MXene-based humidity sensors have demonstrated significant potential for wearable health monitoring owing to their high electrical conductivity, hydrophilic surface terminations, and excellent mechanical flexibility. Xing et al. developed an MXene/MWCNT electronic fabric integrated into a mask for real-time respiration monitoring during different physical activities (Xing et al., 2022), while Liu et al. reported an MXene/TPU composite humidity sensor exhibiting a rapid response time of 12 s and low hysteresis of 7% (Liu et al., 2024). The response/recovery, hysteresis, and reproducibility of the MXene/TPU humidity sensor are shown in Figure 2C. Furthermore, Yu et al. fabricated an MXene/rGO composite humidity sensor with fast response/recovery and minimal hysteresis, and Wang et al. developed a highly responsive MXene/SWCNT-based sensor for respiratory monitoring (Yu et al., 2024; Wang et al., 2024a). More recently, Zhang et al. and Sun et al. demonstrated paper-based and MXene/silk composite humidity sensors, respectively, enhancing porosity and interconnected electron transport pathways significantly improved sensing performance and sensitivity (Zhang et al., 2024; Sun et al., 2025).

Several very recent reports have pushed MXene-based humidity sensing to new performance levels. Wang et al. (2025a) developed a Ti₃C₂T_x MXene-based integrated pressure-humidity sensor using MXene as the sole sensitive material, achieving a rapid humidity response of 3.46 s and recovery of 1.50 s with high sensitivity of 0.67% (%RH)⁻¹ over 11.5%–98.1% RH (Wang et al., 2025b). Li et al. (2025) engineered MXene/GO heterostructures for capacitive humidity sensing, exploiting synergistic interactions between MXene’s polar surface terminations and GO’s water transport properties to achieve an ultrahigh sensitivity (S = 1.24 × 10⁶% ΔC/C₀), a 228-fold improvement over pristine MXene, with response/recovery times of 17 s and 7 s (Li et al., 2025). Zhang et al. (2025) reported a bacterial cellulose/MXene/GO composite film where BC constructs a network structure preventing MXene stacking while GO enhances hygroscopicity, achieving 217% responsivity over 11%–98% RH (Zhang et al., 2025). Most recently, Zhu et al. (2025) demonstrated a paper-based MXene@GO sensor with self-assembling 3D configuration through Ti─O─C bonding, achieving response/recovery times of 36.3 s/21.4 s for wearable medical monitoring (Zhu et al., 2025).

Comparing MXene-based and graphene-based sensors, MXenes generally offer faster response times due to their metallic conductivity and abundant hydrophilic terminations. However, MXenes are more prone to oxidation over time, a limitation less severe for graphene-based sensors.

Beyond MXenes, transition metal dichalcogenides (TMDs) have also emerged as promising materials for wearable humidity sensing due to their layered structures, high surface-to-volume ratios, and abundant active adsorption sites. Xie et al. developed a flexible MoOx nanoparticle-based humidity sensor capable of detecting near-zero humidity with rapid response, enabling non-contact respiration monitoring and human–machine interaction to minimize cross-infections as shown in Figure 2D (Xie et al., 2023). Similarly, Kim et al. fabricated a MoS₂-based humidity sensor using CVD and hydrothermal synthesis for respiratory monitoring, while Li et al. enhanced humidity sensitivity through oxygen plasma-treated MoS₂ integrated with nitrogen-doped laser-induced graphene for detecting abnormal breathing patterns (Kim et al., 2023; Li et al., 2024). Furthermore, Li and Yu reported a flower-shaped MoSe₂–SnS₂ humidity sensor exhibiting fast response/recovery characteristics and extremely low hysteresis of 1%, highlighting the growing potential of TMD-based wearable humidity sensors (Li and Yu, 2025). Additionally, a 2025 study demonstrated 2H-WSe₂-based electroconductive coatings on cotton textiles for humidity detection within 30%–90% RH, showing good repeatability and sensitivity for wearable e-textile applications (Trovato et al., 2025).

In summary, the humidity sensors reviewed here show a clear performance hierarchy: MXene/GO heterostructures currently offer the highest sensitivity (1.24 × 10⁶%); GO-Lys composites provide the fastest response (0.17 s); MXene-based sensors offer fast response (3–12 s) but face oxidation concerns; rGO composites provide a balanced trade-off; and TMD-based sensors excel in specialized applications such as textile integration and near-zero humidity detection. Notably absent from most studies is a systematic comparison under identical testing conditions. Future work should prioritize direct comparative studies and standardized evaluation protocols.

5 Outlook and future directions

Recent advances in 2D-material-based wearable VOC and humidity sensors have demonstrated significant potential for real-time healthcare and environmental monitoring. However, several critical challenges must be addressed before these sensors can transition from laboratory prototypes to practical wearable devices. Selectivity remains a major hurdle, as most 2D materials respond broadly to multiple analytes; future efforts should focus on surface functionalization with selective receptors and the development of sensor arrays (electronic noses) combined with pattern recognition algorithms to discriminate between different VOCs and minimize cross-sensitivity, particularly from humidity. Power consumption is another key consideration; while chemiresistive sensors operate at low power (microwatts to milliwatts), integrating energy-harvesting technologies such as triboelectric or piezoelectric nanogenerators could enable self-powered wearable systems. Biocompatibility and skin safety require systematic evaluation, especially for MXenes, which may degrade into potentially toxic byproducts under oxidative conditions; encapsulation with biocompatible polymers and long-term dermal irritation studies are needed. While laboratory demonstrations frequently achieve high performance, the technology readiness and practical commercialization of these sensors currently remain at Technology Readiness Levels (TRL) 3–4. Transitioning these early-stage prototypes into market-ready commercial products requires overcoming critical manufacturing bottlenecks. Furthermore, achieving higher technology-readiness levels will depend on moving beyond isolated sensor elements to fully integrated IoT systems with wireless data transmission, backed by rigorous clinical validation and standardized testing protocols to ensure long-term stability in real-world environments. Scalable and cost-effective fabrication methods, including inkjet printing, screen printing, and roll-to-roll processing, are essential for commercial translation, with laser-induced graphene offering a promising route. Finally, the field urgently needs standardized testing protocols (defined RH levels, analyte concentrations, flow rates, and mechanical deformation conditions) and rigorous clinical validation in human cohorts to establish diagnostic accuracy and clinical utility. Addressing these challenges will accelerate the deployment of next-generation wearable sensing technologies for personalized healthcare and environmental monitoring.

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Footnotes

Edited by: Arnab Hazra, Birla Institute of Technology and Science, India

Reviewed by: Preethi S, Sathyabama University, India