Most reported trimethylamine (TMA) sensors have to operate at high temperature, which will consume energy highly. To detect TMA at low temperature, it is necessary to modify the existing materials or develop new materials. In this paper, the sensor based on MoO 3 /Bi 2 Mo 3 O 12 hollow microspheres can work at low operating temperature of 170 °C, which were prepared via a simple solvothermal route. The phase and morphology of the product were characterized by an X-ray diffraction meter, a scanning electron microscope and a transmission electron microscope. The surface chemistry of the MoO 3 /Bi 2 Mo 3 O 12 sensor was studied with an X-ray photoelectron spectroscope to investigate the TMA sensing mechanism. The MoO 3 /Bi 2 Mo 3 O 12 sensor (S = 25.8) had a higher response to 50 ppm TMA than those of MoO 3 hollow spheres (S = 10.8) and Bi 2 Mo 3 O 12 sensors (S = 4.8) at 170 °C. In contrast to the pure MoO 3 and Bi 2 Mo 3 O 12 sensors, the MoO 3 /Bi 2 Mo 3 O 12 sensor exhibited an obviously enhanced gas-sensing property for TMA, which might be due to the heterostructure formed between MoO 3 and Bi 2 Mo 3 O 12 and the hollow morphology. It is the first time for MoO 3 /Bi 2 Mo 3 O 12 to apply in gas sensors, which might take an important step in the application of MoO 3 /Bi 2 Mo 3 O 12 or Bi 2 Mo 3 O 12 in the field of gas sensing. KEYWORDS: MoO 3 /Bi 2 Mo 3 O 12 hollow microspheres, heterostructure, low temperature, TMA sensing property, gas-sensing mechanism

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Compared with single-component metal oxides, multicomponent metal oxides show good gas sensing performance in the field of gas sensing, but they still need to be further improved in terms of rapid response. In this paper, a two-dimensional flaky WO3/Bi2W2O9 composite material with a thickness of about 32.3 nm was synthesized by a simple solvothermal method. The composite has good sensing performance and selectivity toward H2S. When the operating temperature is as low as 92 °C, the response to 100 ppm H2S reaches 84.18, and the response time is 2 s, which is extremely fast due to the open system of the two-dimensional nanosheet. A combination of gas chromatography–mass spectrometry (GC–MS) and X-ray photoelectron spectroscopy (XPS) is used to analyze the changes of H2S and the surface chemistry of WO3/Bi2W2O9 composite materials; the sensing mechanism of H2S was studied by a Kelvin probe and UV diffuse reflection. Compared with the pure phase WO3 and Bi2W2O9, good gas sensing properties of the WO3/Bi2W2O9 composite may be due to its unique heterostructure. This is the first application of WO3/Bi2W2O9 in the field of gas sensing and is of great significance for the rapid detection of H2S at low temperatures for multicomponent metal oxides.

The gas sensing performance of metal oxides is limited by the lack of conductivity and sensing activity. Inducing the release of more electrons and activating more chemisorbed oxygen ions to participate in the gas sensing reaction can effectively overcome this limitation. The development of a PbMoO 4 /MoO 3 heterostructure prepared by the addition of Pb 2+ ions with MoO 3 nanorods is reported for highly sensitive and selective trimethylamine (TMA) detection. The response of the PbMoO 4 /MoO 3 sensor (33.2) to 10 ppm TMA is improved 3-fold compared to the MoO 3 sensor (10.7), and the working temperature is reduced from 170 to 133 °C. The enhanced gas sensing performance and mechanism of PbMoO 4 /MoO 3 were demonstrated using the energy band diagram and X-ray photoelectron spectroscopy (XPS) analysis. It is mainly attributed to the following promotion: (1) the induction of Pb 2+ ions increases the electron density around the Mo element, enabling the decorated MoO 3 to release electrons easily; (2) the formed PbMoO 4 /MoO 3 heterojunction endows a high degree of electron transfer at the interface; (3) the formation of the potential barrier causes the device resistance to decrease significantly upon TMA exposure. Finally, the practicability of the sensor was verified by detecting TMA released from Carassius auratus and shrimp to reflect their freshness.

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Although the traditional enzyme-linked immunosorbent assay (ELISA) has been widely applied in pathogen detection and clinical diagnostics, it always suffers from complex procedures, a long incubation time, unsatisfying sensitivity, and a single signal readout. Here, we developed a simple, rapid, and ultrasensitive platform for dual-mode pathogen detection based on a multifunctional nanoprobe integrated with a capillary ELISA (CLISA) platform. The novel capture antibodies-modified capillaries can act as a swab to combine in situ trace sampling and detection procedures, eliminating the dissociation between sampling and detection in traditional ELISA assays. With excellent photothermal and peroxidase-like activity, the Fe3O4@MoS2 nanoprobe with a unique p–n heterojunction was chosen as an enzyme substitute and amplified signal tag to label the detection antibody for further sandwich immune sensing. As the analyte concentration increased, the Fe3O4@MoS2 probe could generate dual-mode signals, including remarkable color changes from the chromogenic substrate oxidation as well as photothermal enhancement. Moreover, to avoid false negative results, the excellent magnetic capability of the Fe3O4@MoS2 probe can be used to pre-enrich the trace analytes, amplifying the detection signal and enhancing the immunoassay’s sensitivity. Under optimal conditions, specific and rapid detection of SARS-CoV-2 has been realized successfully based on this integrated nanoprobe-enhanced CLISA platform. The detection limits were 5.41 pg·mL–1 for the photothermal assay and 150 pg·mL–1 for the visual colorimetric assay. More importantly, the simple, affordable, and portable platform can also be expanded to rapidly detect other targets such as Staphylococcus aureus and Salmonella typhimurium in practical samples, making it a universal and attractive tool for multiple pathogen analysis and clinical testing in the post COVID-19 era.