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Highlights • PPy/Zn 2 SnO 4 nanofilm–based ammonia sensor was fabricated via layer-by-layer self-assembly. • Ultrahigh ammonia-sensing properties of PPy/Zn 2 SnO 4 nanofilm sensor were demonstrated. • The sensing mechanism for the PPy/Zn 2 SnO 4 nanofilm sensor toward ammonia was discussed. Abstract This paper demonstrates an ultra-highly sensitive ammonia gas sensor based on polypyrrole/zinc stannate (PPy/Zn 2 SnO 4) nanocomposite. The PPy/Zn 2 SnO 4 nanocomposite was synthesized by layer-by-layer alternative deposition of PPy nanospheres and Zn 2 SnO 4 hollow spheres. The as-prepared sample was characterized by X-ray diffraction (XRD), FT-IR spectrums, scanning electron microscope (SEM), energy dispersive spectrometer (EDS), X-ray photoelectron spectroscopy (XPS) and transmission electron microscope (TEM). The gas-sensing properties of the PPy/Zn 2 SnO 4 nanofilm were investigated upon exposure to ammonia gas. The result showed that the PPy/Zn 2 SnO 4 nanofilm sensor exhibited lower detection limit, higher response, faster response/recovery time, outstanding repeatability toward NH 3 gas, which was greatly superior to the pure PPy and Zn 2 SnO 4 counterparts. Such dramatically enhancement of gas-sensing properties for PPy/Zn 2 SnO 4 nanofilm is attributed to the deprotonation/protonation process of ammonia adsorption/desorption on PPy surface, special interactions at p-n heterojunction, and high surface area of PPy/Zn 2 SnO 4 nanocomposite. [ABSTRACT FROM AUTHOR]

The extraordinary properties of black phosphorus (BP) make it an attracting candidate for next-generation chemical sensors. BP is strain-sensitive due to piezoresistive effect, but the impact of strain on BP chemical sensing performance is still unknown which is critical to flexible devices. Additionally, BP sensor integration is highly desired because of the complexity of real samples, but it remains only theoretically explored. Here, we developed flexible integrated BP sensor arrays (FIBA) functionalized with ionophore, which demonstrated excellent mechanical flexibility (strain limits of 1%) and stability (bending 500 times). Small strain variation (from 0.33% to −0.16%) resulted in 175% enhancement of sensitivity due to Schottky barrier modulation. Rapid (4 s) label-free detection of 1 μg/L Hg 2+ was achieved, within the permissible limit of the guideline for drinking water quality provided by the World Health Organization (WHO). The low-cost simple-structured FIBA realized multiplexed detection of Hg 2+ , Cd 2+ , Pb 2+ , and Na + at trace concentration with excellent selectivity. FIBA also exhibited the ability of monitoring target ions in real samples (Cd 2+ in tap water and Na + in human sweat). These results demonstrate that FIBA is a promising candidate for wide range of vital signs or environment monitoring. [ABSTRACT FROM AUTHOR]

Highlights • Intrinsic MoS 2 without photon absorption exhibits ultrahigh sensitivity. • Illumination reduces the response of MoS 2 by up to 95% and changes sensing mechanism. • Integration of intrinsic MoS 2 ion sensors with outstanding selectivity was realized. Abstract Molybdenum disulfide (MoS 2) is a promising nanomaterial for chemical sensing due to its exceptional properties. However, it is extremely sensitive to illumination and converts the energy of photons absorbed into photocurrent, which has hampered efforts to explore the sensing performance and underlying transduction mechanism of intrinsic MoS 2. Here we systematically explored the sensing behavior of intrinsic MoS 2 and the impact of illumination. In dark environment, MoS 2 demonstrated record-high sensitivity reaching 1030 for pH change by 1 unit. Its photoresponsivity (1300 A/W) can be tuned by ions in electrolyte. Photon absorption not only substantially reduced the response of intrinsic MoS 2 by up to 95%, but also changed its sensing mechanism. After revealing the remarkable sensing performance of intrinsic MoS 2 , we demonstrated the possibility of the integration of MoS 2 sensors functionalized with ionophore. Multiplex trace detection of Na+, Hg2+, and Cd2+ was realized on a 1 cm×1 cm chip with tunable sensitivity by illumination. The ion sensing results demonstrated outstanding selectivity, repeatability, detection limit (50 nM), response rate (10 s), and the capability of detecting target ions in environmental water samples. Our results show the prominent advantages of intrinsic MoS 2 as a chemical sensing material. [ABSTRACT FROM AUTHOR]