2D materials possess great potential to serve as gas-sensing materials due to their large, specific surface areas and strong surface activities. Among this family, transition metal chalcogenide materials exhibit different properties and are promising candidates for a wide range of applications, including sensors, photodetectors, energy conversion, and energy storage. Herein, a high-shear mixing method has been used to produce multilayered MoS₂ nanosheet dispersions. MoS₂ thin films were manufactured by vacuum-assisted filtration. The structural morphology of MoS₂ was studied using ς-potential, UV–visible, scanning electron microscopy (SEM), atomic force microscopy (AFM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Raman spectroscopy (RS). The spectroscopic and microscopic analyses confirm the formation of a high-crystalline MoS₂ thin film with good inter-sheet connectivity and relative thickness uniformity. The thickness of the MoS₂ layer is measured to be approximately 250 nm, with a nanosheet size of 120 nm ± 40 nm and a number of layers between 6 and 9 layers. Moreover, the electrical characteristics clearly showed that the MoS₂ thin film exhibits good conductivity and a linear I–V curve response, indicating good ohmic contact between the MoS₂ film and the electrodes. As an example of applicability, we fabricated chemiresistive sensor devices with a MoS₂ film as a sensing layer. The performance of the MoS₂-chemiresistive sensor for NO₂ was assessed by being exposed to different concentrations of NO₂ (1 ppm to 10 ppm). This sensor shows a sensibility to low concentrations of 1 ppm, with a response time of 114 s and a recovery time of 420 s. The effect of thin-film thickness and operating temperatures on sensor response was studied. The results show that thinner film exhibits a higher response to NO₂; the response decreases as the working temperature increases.

The detection of the spread of toxic gas molecules in the air at low concentration in the field requires a robust miniaturized system combined with an analytical technique that is portable and able to detect and identify the molecules, as is the case with surface enhanced Raman scattering (SERS). This work aims to address capability gaps faced by first responders in real-time detection, identification and monitoring of neurotoxic gases by developing robust, reliable and reusable SERS microfluidic chips. Thus, the key performance attributes of a portable SERS detection system that must be addressed in detail are its limit of detection, response time and reusability. To this purpose, we integrate a 3D plasmonic architecture based on closely packed mesoporous silica (MCM48) nanospheres decorated with Au nanoparticle arrays, denoted as MCM48@Au, into a Si microfluidic chip designed and used for preconcentration and label-free detection of gases at a trace concentration level. The SERS performance of the plasmonic platform is thoroughly analyzed using DMMP as a model neurotoxic simulant over a 1 cm² SERS active area and over a range of concentrations from 100 ppbV to 2.5 ppmV. The preconcentration-based SERS signal amplification by the mesoporous silica moieties is evaluated against dense silica counterparts, denoted as Stöber@Au. To assess the potential for applications in the field, the microfluidic SERS chip has been interrogated with a portable Raman spectrometer, evaluated with temporal and spatial resolution and subjected to several gas detection/regeneration cycles. The reusable SERS chip shows exceptional performance for the label-free monitoring of 2.5 ppmV gaseous DMMP.

Single-walled carbon nanotubes (SWCNTs) are promising candidates for gas sensing applications, providing an efficient solution to the device miniaturization challenge and allowing low power consumption. SWCNT gas sensors are mainly based on field-effect transistors (SWCNT-FETs) where the modification of the current flowing through the nanotube is used for gas detection. A major limitation of these SWCNT-FETs lies in the difficulty to measure their transfer curves, since the flowing current typically varies between 10⁻¹² and 10⁻³ A. Thus, voluminous and energy consuming systems are necessary, severely limiting the miniaturization and low energy consumption. Here, we propose an inverter device that combines two SWCNT-FETs which brings a concrete solution to these limitations and simplifies data processing. In this innovative sensing configuration, the gas detection is based on the variation of an electric potential in the volt range instead of a current intensity variation in the microampere range. In this study, the proof of concept is performed using NO₂ gas but can be easily extended to a wide range of gases.

Superconducting nanowire single photon detectors (SNSPDs) made with thin NbN films can reach high performances. While sputtering has been the deposition method of choice, here, we show that ammonia-molecular beam epitaxy (NH3-MBE) can produce pertinent epitaxial cubic NbN thin films on silicon substrates using an AlN buffer. Despite granular morphology and a high density of grain boundaries as well as the presence of rotational twins, Tc = 12.7 K for a 5.6 nm thick film and saturation of internal detection efficiency up to 850 nm are achieved. Morphology and stoichiometry as well as strain have a strong impact on the detector properties, highlighting the importance of a precise control of the growth parameters. These results pave the way for high fabrication yield of SNSPDs on large-scale silicon wafers using epitaxial NbN thin films grown by MBE.