Room-Temperature QCM Sensor Based on GO@WO₃ Nanocomposites for Ammonia Detection

Abstract

The detection of ammonia (NH₃) at room temperature is of significant importance for environmental monitoring, industrial safety and early disease diagnosis. In this work, a novel room-temperature ammonia sensor was developed by combining graphene oxide with WO₃ quantum dots. The as-fabricated sensor exhibited excellent comprehensive sensing performance, including high sensitivity, rapid response, outstanding selectivity, and reliable long-term stability. Specifically, when exposed to 10 ppm NH₃, the sensor based on 1.5% GO@WO₃ nanocomposites achieved a frequency shift of 578 Hz, which was 6.4 times that of the pure WO₃ QDs sensor. The theoretical limit of detection (LOD) of the sensor was calculated to be 60 ppb, enabling ppb-level NH₃ detection. In addition, the sensor demonstrated good long-term stability over a two-week period. The enhanced performance of the GO@WO₃ nanocomposite sensor is attributed to the formation of an ohmic contact between GO and WO₃, which eliminates charge transfer barriers, promotes oxygen adsorption, and amplifies the sensing signal. This work provides a simple, efficient, and practical solution for room-temperature NH₃ detection, offering significant advantages over traditional single-component sensors.

1. Introduction

Ammonia (NH₃) is a highly toxic, corrosive, and flammable gas that plays a critical role in industrial production [1,2]. In industrial processes such as fertilizer synthesis, chemical manufacturing, and food processing, NH₃ leakage not only causes severe environmental pollution but also poses great threats to the safety of production equipment and on-site operators [3]. Meanwhile, NH₃ is also an important biomarker for several human diseases [4]. Abnormal concentrations of NH₃ in exhaled breath are closely associated with chronic kidney disease, liver failure and gastrointestinal disorders [5,6,7]. Consequently, its sensitive and rapid detection is essential for early disease diagnosis. Therefore, the development of high-performance NH₃ sensors with high sensitivity, fast response, and stable operation at room temperature is urgently needed to meet the practical demands of industrial safety monitoring and clinical disease diagnosis.

In recent years, among various types of gas sensors, quartz crystal microbalance (QCM) sensors have attracted extensive attention in gas detection due to their unique advantages. Compared with traditional resistor gas sensors that require high operating temperatures, QCM sensors operate at room temperature, which effectively reduces energy consumption and avoids the problem of poor stability caused by high temperatures [8]. Additionally, QCM sensors possess high detection accuracy, simple structure, low manufacturing cost, and real-time response characteristics, enabling them to realize trace-level gas detection and be widely applied in environmental monitoring and industrial safety [9,10,11]. These inherent advantages make QCM sensors an ideal platform for room-temperature NH₃ detection.

On the other hand, the performance of QCM gas sensors is contingent on the sensitive material on the surface of the devices. Therefore, the development and modification of sensitive materials are pivotal to enhancing the gas sensor performance. Tungsten trioxide (WO₃), as a typical n-type metal oxide semiconductor, has been widely used as a gas-sensitive material due to its excellent chemical stability and high gas adsorption capacity [12,13]. The efficacy of low-dimensional WO₃ structures, including quantum dots (QDs) [3], nanosheets [14], nanofibers [15], and nanorods [13], in gas detection has been demonstrated. Due to the large surface-to-volume ratio, good solution dispersibility, and tunable bandgap of quantum dots (QDs), their integration with QCM devices holds promise for the development of stable room-temperature gas sensors. However, pure WO3 is subject to inherent limitations, including a narrow detection range and poor selectivity. This complicates the balance of sensitivity, response speed, and stability in practical applications. To address these shortcomings, researchers have focused on low-dimensional material composites. Graphene oxide (GO) is a two-dimensional (2D) carbon nanomaterial with unique structures and properties, including a large specific surface area, abundant functional groups, and high electrical conductivity [16,17]. According to the literature, the overall performance of sensors can be enhanced through the formation of heterojunctions between low-dimensional nanomaterials and 2D graphene oxide (GO), such as SnO₂/GO [18], TiO₂/GO [19], MoO₂/GO [20], ZnO/GO [21], In₂O₃/GO [22] and WO₃/GO [14]. Therefore, the combination of 0D WO₃ QDs with 2D GO nanosheets to form a 0D/2D nanocomposite structure has the potential to integrate the advantages of both materials, thereby effectively overcoming the performance limitations of single WO₃ and improving the gas-sensing performance of QCM sensors.

In order to achieve high-precision detection of low-concentration NH₃, a high-performance room-temperature QCM NH₃ sensor based on GO@WO₃ nanocomposites was proposed. The unique quantum-scale structure of WO₃ and the hierarchical interface between GO and WO₃ endow the sensor with exceptional adsorption capacity and charge transport efficiency. By rationally optimizing the GO/WO₃ mass ratio and constructing a uniform heterojunction film, the sensor achieves significantly improved sensitivity, faster response, and better stability compared with pure WO₃ QDs. The detailed sensing mechanism involving charge transfer and oxygen adsorption behavior is systematically revealed in such a QCM-based NH₃ sensing system. This study provides a simple and effective strategy for the preparation of high-performance room-temperature NH₃ sensors and lays a foundation for their practical applications in industrial safety and environmental monitoring.

2. Materials and Methods

2.1. Chemicals

All reagents are of analytical grade and thus require no further purification before use. The graphene oxide (GO, 99%) was purchased from Macklin Biochemical Technology Co., Ltd. (Shanghai, China). Tungsten chloride (WCl₆, 99%), oleic acid (OA), ethanol (99%) and oleyl amine (OLA) were supplied by Shanghai Aladdin Biochemical Technology Co., Ltd. (Shanghai, China). The quartz crystal microbalance (QCM) devices with a center frequency of 8 MHz were provided by Shenzhen Jingyuanxing Electronics Co., Ltd. in Shenzhen, China.

2.2. Preparation of WO₃ Quantum Dots and GO@WO₃ Nanocomposites

The WO₃ quantum dots were synthesized via the solvothermal method, as previously described in our research [3]. As demonstrated in Figure 1a, 2 mmol of tungsten chloride (WCl₆) was dissolved in 20 mL of oleic acid (OA) and 2.5 mL of oleyl amine (OLA) at room temperature under magnetic stirring to form a homogeneous precursor solution for the WO₃ quantum dots. Then, 10 mL of ethanol and GO, with a mass percentage of 0.5% (2.3 mg) relative to WO₃, were added to the solution. The resulting solution was subsequently added to a Teflon-lined stainless steel autoclave and then subjected to a reaction at a temperature of 180 °C for 3 h. After cooling to room temperature, the obtained 0.5 wt% GO@WO₃ nanocomposite products were collected by centrifugation at 6000 rpm for 10 min and finally dispersed in a toluene solution at a concentration of 20 mg/mL.

To optimize the sensing performance, a series of GO@WO₃ nanocomposites with different GO mass percentages (0.5 wt%, 1 wt%, 1.5 wt%, and 2 wt%) were fabricated following the identical procedure, alongside the pure WO₃ quantum dots as a control sample.

2.3. Characterization

The size, microstructure, and surface morphology of the WO₃ quantum dots, GO, and GO@WO₃ nanocomposites were investigated using field emission scanning electron microscopy (FE-SEM, Supra 55 Sapphire, Zeiss, Seoul, Republic of Korea) and high-resolution transmission electron microscopy (HR-TEM, FEI Tecnai G2 F20, Thermo Fisher Scientific, Hillsboro, OR, USA). The as-fabricated GO@WO₃ QCM devices were directly used for FE-SEM testing without sputter coating, as the composite film has excellent intrinsic conductivity, with the QCM chip serving as the substrate. All samples were analyzed for crystalline phases using X-ray diffraction (XRD, MAXima XRD-7000, Shimadzu, Kyoto, Japan) in the 2θ range of 5–80°. The chemical states of the GO@WO₃ nanocomposite films were studied using an X-ray photoelectron spectrometer (XPS, Escalab 250Xi, Thermo Fisher, Loughborough, UK) and a Fourier transform infrared spectrum (FTIR, Vertex 70, Bruker, Ettlingen, Germany). For the FTIR measurements, the sample was prepared as a thin film spin-coated on a glass substrate, and no KBr pellets were used during the test.

2.4. Preparation of Sensors and Gas Sensing Measurement

The QCM device was subjected to sequential ultrasonic cleaning processes involving acetone, alcohol, and deionized water. Subsequently, 20 μL of GO@WO₃ nanocomposites was deposited onto the QCM device by means of spin coating at a rate of 1500 rpm for 90 s, as illustrated in Figure 1a. The mass of the sensitive material deposited on the QCM device was calculated using the Sauerbrey equation (see Equation (S1)) [23], as outlined in Table S1.

The sensor response was measured using a static sensing system (18 L volume), as illustrated in Figure 1b. The graded concentrations of the target gas were achieved by introducing varied volumes of ammonia (initial concentration: 2%) into the measurement chamber. The operating conditions were established at a room temperature of 24 ± 1 °C and a relative humidity (RH) of 60 ± 1%. The sensor response time and recovery time were defined as the time required to reach 90% of the maximum frequency shift upon exposure to the target gas, and the time required to return to 10% of the frequency shift upon exposure to air, respectively.

3. Results

3.1. Characterization of Sensitive Materials

The field emission scanning electron microscopy (FE-SEM) morphologies of GO, WO₃, and GO@WO₃ nanocomposite films were observed. As illustrated in Figure 2a,b, the images of the WO₃ film reveal a dense and continuous film structure, which facilitates a stable acquisition of QCM signals. Figure 2c,d indicate that the GO sheets exhibit a typical two-dimensional structure, with the presence of wrinkles providing a substantial number of active sites and spatial configurations for subsequent composite formation. It is worth noting that the GO@WO₃ nanocomposite effectively formed a fluffy, porous, three-dimensional network structure (see Figure 2e,f). This unique porous structure of GO@WO₃ nanocomposites provides favorable conditions for enhancing the gas-sensing performance of the QCM sensors. The interconnected porous sensitive film creates a large number of active adsorption sites for target gas molecules, and optimizes the gas diffusion pathways, enabling the gas molecules to efficiently transfer mass to the QCM device [24]. Recent studies have verified that nanocomposites with porous structures enhanced the QCM sensing performance [25,26,27]. The EDS elemental mapping (Figure 2g) results reveal that W, O, and C all exhibit clear and highly uniform distribution patterns, thus confirming the successful formation of the GO@WO₃ nanocomposite. Furthermore, the absence of discernible component segregation or substantial agglomeration in the mapping verifies the structural uniformity of the sensing layer, which is critical for ensuring a consistent and stable gas-sensing response of the QCM sensor.

Figure 3a shows the XRD patterns of pure WO₃, GO, and GO@WO₃ nanocomposite samples at different weight ratios. The diffraction peaks at 23.6°, 33.6°, and 48.4° for pure WO₃ correspond to the (200), (220), and (400) planes, respectively (PDF#46-1096), confirming the high purity and excellent crystallinity of the synthesized WO₃. In the XRD pattern of GO, a characteristic peak emerges at 10.4°, corresponding to the [001] plane [28]. All the GO@WO₃ nanocomposite samples exhibited the primary diffraction peak of WO₃, with no characteristic diffraction peaks of the GO. This phenomenon can be attributed to the low concentration and uniform distribution of GO within the composite materials [29].

The characterization of the functional groups in GO, pure WO₃ and the GO@WO₃ nanocomposites was achieved through the utilization of Fourier transform infrared (FTIR) spectroscopy (see Figure 3b). In the FTIR spectrum of GO, the peaks located at 1732 cm⁻¹ and 1625 cm⁻¹ correspond to the C=O bond of carbonyl C=C, respectively [30]. The broad band at approximately 3430 cm⁻¹ is attributed to the –OH stretching mode of physically adsorbed water molecules [17]. For the GO@WO₃ nanocomposites, the characteristic peaks at 1073, 1065, and 1634 cm⁻¹ correspond to the C-O-C, C-O, and C=C stretching vibrations of GO, respectively [17,28]. In the spectrum of pure WO₃, the peaks at 748 and 817 cm⁻¹ originate from the O–W–O stretching vibrations, while the bands at 2853 and 2923 cm⁻¹ are attributed to the aliphatic C–H stretching vibrations of oleic acid (OA) and oleyl amine (OLA) ligands. In comparison with pure WO₃, the FTIR spectrum of the GO/WO₃ nanocomposites retains the characteristic peaks of both WO₃ and GO, while the intensity of the C-H stretching bands (2853–2923 cm⁻¹) is significantly weakened. This result indicates that the majority of surface-capped OA and OLA ligands have been removed [23], which is beneficial for the material as it can expose more active sites and facilitate contact with target gas molecules, thereby improving the gas-sensing performance.

The microstructural characteristics of pure WO₃ QDs, GO, and GO@WO₃ nanocomposites were investigated by high-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED). As shown in Figure 4a,b, pure WO₃ QDs exhibit a uniform nanoparticle morphology with particle sizes of 5–10 nm. Figure 4b displays a lattice fringe spacing of 0.37 nm, corresponding to the (200) crystal plane of WO₃. The corresponding SAED pattern (Figure 4c) reveals the (200), (220), (400), and (420) crystal planes of WO₃, indicating the polycrystalline nature and good crystallinity of WO₃ QDs, which corroborates the results from the HRTEM and XRD. GO exhibits typical wrinkled layered morphology (see Figure 4d), and the inserted SAED pattern displays diffuse annular features, indicating that GO possesses a disordered layered structure. As illustrated in Figure 4e, the distribution of WO₃ QDs on the surface of the GO sheets is consistent and uniform. The 0.37 nm lattice fringes of the WO₃ (200) crystal plane are clearly observable. Figure 4f displays the characteristic diffraction ring of WO₃ QDs and the weak diffraction ring of the GO crystal plane, thus confirming the successful formation of nanocomposites of GO and WO₃ QDs.

The surface valence bond states of the WO₃ QDs and 1.5 wt% GO@WO₃ nanocomposites were analyzed by XPS, as illustrated in Figure 5. The W 4f spectrum (Figure 5a) displays two characteristic peaks at 37.76 eV and 35.63 eV, corresponding to W 4f_5/2 and W 4f_7/2, respectively, which are consistent with the typical valence state of W⁶⁺ in WO₃ [31]. An additional satellite peak at 41.29 eV is assigned to the WO₃ loss feature, further confirming the formation of stoichiometric WO₃ [32]. The O 1s spectrum (Figure 5b) can be deconvoluted into three components: chemisorbed oxygen (O_C, 531.81 eV), oxygen vacancies (O_V, 530.63 eV), and lattice oxygen (O_L, 530.01 eV). The presence of O_V indicates the presence of oxygen vacancy defects in the WO₃ QDs, which are advantageous for gas adsorption [33]. The C 1s spectrum (Figure 5c) displays a solitary, predominant peak at 284.80 eV, which is ascribed to adventitious carbon originating from the surrounding environment. The W 4f spectrum (Figure 5d) exhibits the characteristic doublet of W 4f_5/2 (37.93 eV) and W 4f_7/2 (35.79 eV), with a slight shift to higher binding energy compared to pure WO₃ QDs. This shift is indicative of a strong electronic interaction between WO₃ QDs and GO sheets at the heterojunction interface [34]. The O 1s spectrum (Figure 5e) is composed of O_C (531.85 eV), O_V (530.65 eV), and O_L (530.11 eV), with an enhanced O_V ratio, suggesting that the introduction of GO further promotes the formation of O_V in the composite. The increase in O_V indicates that the GO@WO₃ nanocomposites contain more defect sites compared to the pure WO₃, which is conducive to gas adsorption and sensor response [35]. Furthermore, the detection of C-C (284.79 eV), C-O (285.77 eV) and C=O (288.34 eV) in the GO@WO₃ nanocomposites confirms the successful incorporation of GO (see Figure 5f).

3.2. Sensing Performance of Sensors

Figure 6a depicts the real-time frequency response behaviors of THE QCM sensors based on pure WO₃ QDs and GO@WO₃ nanocomposites (0.5–2 wt%) under exposure to target gas concentrations ranging from 0.2 ppm to 60 ppm. A pronounced downward frequency shift is observed for all samples upon the introduction of NH₃ gas, which is attributable to the mass loading effect. The adsorption of NH₃ molecules onto the sensing layer increases the effective mass of the QCM sensors, resulting in a reduction in resonant frequency. Notably, the incorporation of GO markedly enhances the sensing performance relative to the pure WO₃ QDs (see Figure 6b). Of all the nanocomposites, the 1.5 wt% GO@WO₃ sensor has the highest sensitivity. It achieves a frequency shift of −1170 Hz at 60 ppm, which is 3.5 times greater than that of the pure WO₃ QD sensor (−334 Hz). Even at a concentration of 0.2 ppm, this composite sensor still generates a discernible frequency deviation, demonstrating its capability for low-concentration detection. The improved sensing performance is due to the combined effects of GO and WO₃ QDs. The large surface area of GO provides many adsorption sites for gas molecules, and its high electrical conductivity promotes interfacial charge transfer. These factors together increase the sensitivity of the QCM sensor. At low concentrations (<10 ppm), the frequency shift increases nearly linearly with gas concentration, indicating the efficient adsorption of gas molecules onto the sensing surface. As the concentration rises beyond 10 ppm, the frequency shift increment rate slows down markedly (Figure 6b). This suggests that the active adsorption sites on the material surface are gradually becoming occupied, which leads to saturation. This saturation behavior arises from the equilibrium between gas adsorption and desorption on the sensing layer. At high concentrations, the adsorption sites become fully occupied, so further increases in gas concentration can no longer induce a proportional increase in frequency shift, resulting in a plateau-like response trend.

Figure 6c shows the linearity analysis of the optimal 1.5 wt% GO@WO₃ sensor at low concentrations, yielding a high coefficient of determination (R² = 0.989), which confirms excellent linearity in the 0.2–10 ppm range. The theoretical limit of detection (LOD) was calculated to be 60 ppb, demonstrating the sensor’s excellent performance in detecting ammonia at room temperature. The detailed calculation procedure is provided in Equation (S2). Together, these results demonstrate that moderate GO incorporation effectively enhances the sensitivity, linearity and low-concentration detection performance of WO₃-based QCM gas sensors by providing abundant adsorption sites and facilitating interfacial charge transport.

Figure 7a illustrates the real-time dynamic frequency response of pure WO₃ and GO@WO₃ nanocomposite sensors upon exposure to 10 ppm NH₃. All samples exhibit reversible frequency shifts: the frequency decreases rapidly upon the injection of NH₃ gas and recovers gradually after the gas is removed. As shown in Figure 7b, with increasing GO content, the response time gradually shortens from 69 s (pure WO₃) to 42 s (2 wt% GO@WO₃), while the recovery time also decreases from 168 s to 105 s. Notably, the 1.5 wt% GO@WO₃ sample achieves a balanced optimization of response (43 s) and recovery (109 s) kinetics, demonstrating the best overall dynamic performance. This enhanced response speed is attributed to the high specific surface area and excellent conductivity of GO, which accelerates gas adsorption and interfacial charge transfer.

The 1.5 wt% GO@WO₃ sensor demonstrates excellent reproducibility and stability towards 10 ppm NH₃, as shown in Figure 8a. After 14 days, the frequency shift in the 1.5 wt% GO@WO₃ sensor remained at 90% of its initial response, revealing excellent long-term reliability for practical room-temperature NH₃ sensing (Figure 8b). The sensor exhibits a much larger frequency shift toward 10 ppm NH₃ compared to all other interfering gases (even at higher concentrations), demonstrating an excellent selectivity for ammonia detection (Figure 8c). Figure 8d shows the frequency response of the 1.5 wt% GO@WO₃ sensor to 10 ppm NH₃ at room temperature across 30–80% RH. Although the response shows slight attenuation with rising humidity, due to water molecules competing for the active sites in the composite, the sensor still exhibits stable, significant frequency shifts even at 80% RH. This confirms its exceptional humidity resistance in practical humid environments.

The performance of the sensor was summarized and compared with that of previously reported WO₃/carbon-based composite sensors, as shown in

Table 1. The performance comparison of gas sensors of WO₃/carbon-based sensors.

Material	Target Gas	Temperature (°C)	Gas Concentration (ppm)	LOD (ppm)	Response/Recovery Time (s)	Reference
WO3	NH3	142	1.3	-	59/47	[36]
WO3/CNTs	NO2	RT	1	-	-	[37]
1 wt%CNT/WO3 NB	NH3	RT	10	-	210/330	[38]
GO/WO3 nanorods	NH3	200	100	-	10–15	[32]
PPy–GO–WO3	NH3	RT	10	-	50/120	[30]
rGO/WO3 nanowire	NH3	300	100	0.138	-	[39]
3% rGO-CuO/WO3	Acetone	320	500	1	6/9	[40]
WO3/rGO	C2H2	150	50	1.3	52/27	[41]
WO3–N-GO 6%	NO2	200	200	-	90/205	[14]
1.5 wt% GO@WO3	NH3	RT	10	0.06	43/109	This work

. The WO₃@GO QCM sensor developed in this work exhibits outstanding overall sensing performance compared with previously reported WO₃/carbon-based composites. Operating at room temperature, our sensor achieves lower detection limits and faster responses than most WO₃ sensors modified with carbon materials. These results confirm that combining zero-dimensional WO₃ quantum dots with two-dimensional GO improves the sensor’s performance.

3.3. Sensing Mechanism of the Sensor

Figure 9 illustrates the NH₃-sensing mechanism of the GO@WO₃ nanocomposites. In the air, ambient O₂ molecules extract free electrons from the nanocomposites to form ionized adsorbed oxygen species. The type of dominant chemisorbed oxygen species is strongly temperature-dependent: at temperatures below 100 °C, the primary species is $O_{2\left(ads\right)}^{-}$; in the intermediate range of 100–300 °C, $O_{\left(ads\right)}^{-}$ becomes the dominant form; and at temperatures exceeding 300 °C, $O_{\left(ads\right)}^{2-}$ is the stable adsorbed oxygen ion [42,43]. In this work, all the sensing measurements were taken at room temperature, thereby confirming $O_{2\left(ads\right)}^{-}$ as the primary active species for the NH₃ sensing reaction, as shown in Formula (1) [44]. Upon exposure to NH₃, these adsorbed oxygen ions react with NH₃ molecules, releasing electrons back into the nanocomposites (Formula (2)) [2,45].

$$O_{2\left(gas\right)}\to O_{2\left(ads\right)}^{-}$$

(1)

$${4NH}_3+{3O}_{2\left(ads\right)}^{-}\to {2N}_2+{6H}_{2}O+{3e}^{-}$$

(2)

The enhanced sensing performance is attributed to the formation of an ohmic contact at the WO₃/GO interface. As displayed in Figure S1, the current–voltage (I–V) curves of the GO@WO₃ composite films exhibit good linearity and symmetry within the voltage range of −15 V to +15 V, which is consistent with the characteristic behavior of ohmic contact. To elucidate the charge transfer mechanism at the GO-WO₃ heterojunction and the gas-sensing behavior, a detailed band alignment diagram is constructed, as shown in Figure 9. It should be noted that the electronic properties of GO, such as its electron mobility, vary with the degree of oxidation, which may have a slight effect on the arrangement of the interface bands [46,47]. WO₃ exhibits a bandgap of 2.7 eV, an electron affinity of 3.9 eV [15], and a work function of 5.7 eV, while GO has a work function of 5.3 eV. The work function of conductive GO (5.3 eV) is lower than that of n-type WO₃ (5.7 eV) (Figure 9a) [29]. This results in the migration of electrons from GO to WO₃ upon contact, thereby bending the energy bands to align their Fermi levels and creating an electron accumulation layer at the heterojunction (Figure 9b). This ohmic contact facilitates an unobstructed charge carrier flow across the interface, while the electron accumulation layer promotes enhanced O₂ adsorption, leading to the generation of more $O_{2\left(ads\right)}^{-}$ (Figure 9c). The formation of the GO@WO₃ heterojunction introduces a significant quantity of $O_{2\left(ads\right)}^{-}$, thereby enhancing the adsorption capacity for the NH₃ gas. As demonstrated in the Sauerbrey equation (see Equation (S1)), this direct mass change on the QCM surface is converted into a measurable frequency shift, which constitutes the gas-sensitive response of the QCM sensor. Upon exposure to NH₃, the reaction with adsorbed oxygen ions results in the release of electrons. These electrons are then transferred rapidly via an ohmic contact, leading to a reduction in the sensor’s response and recovery times (Figure 9d).

4. Conclusions

In summary, a GO@WO₃ nanocomposite sensor was fabricated for room-temperature NH₃ detection, exhibiting significantly enhanced sensing performance compared to pure WO₃. This includes high sensitivity, fast response/recovery speed, excellent selectivity against common interfering gases and long-term stability, with a theoretical limit of detection of 60 ppb for NH₃ monitoring. The enhanced performance is attributed to the heterojunction formed at the WO₃/GO interface, which introduces additional adsorbed oxygen molecules that participate in the gas-sensing reaction, thereby improving the response. Furthermore, when exposed to NH₃, the released electrons are rapidly transferred via ohmic contact, thereby enhancing the sensor’s response speed. This work demonstrates that GO@WO₃ nanocomposites have the potential to function as effective room-temperature ammonia sensors, thus providing valuable insights into the enhancement of ammonia sensor performance at room temperatures.