Multifunctional Nanoprobe-Amplified Enzyme-Linked Immunosorbent Assay on Capillary: A Universal Platform for Simple, Rapid, and Ultrasensitive Dual-Mode Pathogen Detection.

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.

Quantitative Time-Resolved Visualization of Catalytic Degradation Reactions of Environmental Pollutants by Integrating Single-Drop Microextraction and Fluorescence Sensing.

Current methods for evaluating catalytic degradation reactions of environmental pollutants primarily rely on chromatography that often suffers from intermittent analysis, a long turnaround period, and complex sample pretreatment. Herein, we propose a quantitative time-resolved visualization method to evaluate the progress of catalytic degradation reactions by integrating sample pretreatment [single-drop microextraction, (SDME)], fluorescence sensing, and a smartphone detection platform. The dechlorination reaction of chlorobenzene derivatives was first investigated to validate the feasibility of this approach, in which SDME plays a critical role in direct sample pretreatment, and inorganic CsPbBr3 perovskite encapsulated in a metal-organic framework (MOF-5) was utilized as the fluorescent chromogenic agent (FLCA) in SDME to realize fast in situ colorimetric detection via the color switching from green (CsPbBr3) to blue (chlorine lead bromide, inorganic CsPbCl3 perovskite). The smartphone, which can calculate the B/G value of FLCA, serves as a data output window for quantitative time-resolved visualization. Further, a [Eu(PMA)]n (PMA= pyromellitic acid) fluorescent probe was constructed to use as an FLCA for the in situ evaluation of cinnamaldehyde and p-nitrophenol catalytic reduction. This approach not only minimizes the utilization of organic solvents and achieves quantitively efficient time-resolved visualization but also provides a feasible method for in situ monitoring of the progress of catalytic degradation reactions.

In Situ Growth of Conductive Metal-Organic Framework onto Cu2O for Highly Selective and Humidity-Independent Hydrogen Sulfide Detection in Food Quality Assessment.

The sensitivity of chemiresistive gas sensors based on metal oxide semiconductors (MOSs) has been inherently affected by ambient humidity because their reactive oxygen species are easily hydroxylated by water molecules, which significantly reduces the accuracy of the gas sensors in food quality assessment. Although conventional metal organic frameworks (MOFs) can serve as coatings for MOSs for humidity-independent gas detection, they have to operate at high working temperatures due to their low or nonconductivity, resulting in high power consumption, significant manufacturing inconvenience, and short-term stability due to the oxidation of MOFs. Here, the conductive and thickness-controlled CuHHTP (HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene)-coated Cu2O are developed by combining in situ etching and layer-by-layer liquid-phase growth method, which achieves humidity-independent detection of H2S at room temperature. The response to H2S only decreases by 2.6% below 75% relative humidity (RH), showing a 9.6-fold improvement than the bare Cu2O sensor, which is ascribed to the fact that the CuHHTP layer hinders the adsorption of water molecules. Finally, a portable alarm system is developed to monitor food quality by tracking released H2S. Compared with gas chromatography method, their relative error is within 9.4%, indicating a great potential for food quality assessment.

MoO3 Nanorods Decorated by PbMoO4 Nanoparticles for Enhanced Trimethylamine Sensing Performances at Low Working Temperature.

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 PbMoO4/MoO3 heterostructure prepared by the addition of Pb2+ ions with MoO3 nanorods is reported for highly sensitive and selective trimethylamine (TMA) detection. The response of the PbMoO4/MoO3 sensor (33.2) to 10 ppm TMA is improved 3-fold compared to the MoO3 sensor (10.7), and the working temperature is reduced from 170 to 133 °C. The enhanced gas sensing performance and mechanism of PbMoO4/MoO3 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 Pb2+ ions increases the electron density around the Mo element, enabling the decorated MoO3 to release electrons easily; (2) the formed PbMoO4/MoO3 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.

Rapid detection of H2S gas driven by the catalysis of flower-like α-Bi2Mo3O12 and its visual performance: A combined experimental and theoretical study.

Metal oxide semiconductor (MOSs) are attractive materials for the development of H2S gas sensors. However, detecting H2S with short response and recovery times while also lowering the limit of detection to sub-ppb levels remains a significant challenge. We therefore developed flower-like α-Bi2Mo3O12 microspheres for H2S gas detection that provide fast response and recovery times (3 and 22 s, respectively, for 100 ppm H2S), while also reducing the limit of detection to 1 ppb. The sensor performs well in terms of sensitivity, reproducibility, long-term stability, including humidity stability. X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations revealed that H2S dissociates readily on the reduced α-Bi2Mo3O12 surface and that Mo plays a catalytic role, accelerating the rate of H2S decomposition and enabling a fast response. Moreover, test strips containing α-Bi2Mo3O12 were also prepared, which enabled the naked eye detection of ppm-level H2S gas at room temperature; a light-yellow to orange to brown color change occurs when exposed to H2S, due to its conversion into stable sulfides. This work expands the application of α-Bi2Mo3O12 to H2S gas sensing, and provides a strategy for the use of MOSs as sensor materials for the detection of other gases.

Controllable construction of ZnFe2O4-based micro-nano heterostructure for the rapid detection and degradation of VOCs.

Micro-nano heterogeneous oxides have received extensive attention due to their distinctive physicochemical properties. However, it is a challenge to prepare the hierarchical multicomponent metal oxide nanomaterials with abundant heterogeneous interfaces in a controllable way. In this work, the effective construction of the heterogeneous structure of the material is achieved by regulating the ratio of metal salts under thermal solvent condition. Three-dimensional spheres (ZnFe2O4) constructed by zero-dimensional ultra-small nanoparticles, in particular three-dimensional hollow sea urchin spheres (ZnO/ZnFe2O4) constructed by one-dimensional nanorods and three-dimensional hydrangeas (α-Fe2O3/ZnFe2O4) assembled by two-dimensional nanosheets were obtained. The two composite materials contain a large number of heterojunctions, which enhances the sensitivity of material to volatile organic compounds gas. Among them, the α-Fe2O3/ZnFe2O4 composite shows the best sensing performance for VOCs. For example, its response to 100 ppm acetone reaches 142 at 170 °C with the response time shortened to 3 s and the detection limit falling to 10 ppb. Meanwhile, the composite material presents a degradation rate of more than 90% for VOCs at a flow rate of 20 mL/min at 170 °C. In addition, the sensing and sensitivity mechanism of the composite material are studied in detail by combining GC-MS, XPS with UV diffuse reflectance tests.

Cu2O induced Au nanochains for highly sensitive dual-mode detection of hydrogen sulfide.

Colorimetric and chemoresistive gas sensing methods have aroused great interest in H2S monitoring due to their unique merits of naked-eye readout, and highly sensitive and rapid detection. However, combining these two methods for gas detection, especially utilizing one material as their common sensing material is a grand challenge because they are inconsistent in sensing mechanism. Taking advantage of the strong chemical affinity of Cu2O for H2S and the excellent performance of localized surface plasmon resonance (LSPR) of Au nanoparticles (NPs) in the visible regions and its ability as a noble metal to enhance gas sensing property, the Cu2O-Au nanochains (NCs) were prepared for dual-mode detection of H2S gas. The Cu2O-Au chemoresistive gas sensor shows a 5-fold higher response than Cu2O sensor at room temperature with a low detection limit of 10 ppb. Such good performance is attributed to the spillover effect and catalytic activity of Au NPs, and the enhanced H2S adsorption after Au loading as revealed by density functional theory calculation. Test strips containing Cu2O-Au produced for gaseous H2S detection show superior color gradient changes (blue, yellow, and brown). Finally, the practicability of the method was validated by real-time monitoring H2S released from cell culture.

Novel Two-Dimensional WO3/Bi2W2O9 Nanocomposites for Rapid H2S Detection at Low Temperatures.

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.

Enhanced Gas-Sensing Properties for Trimethylamine at Low Temperature Based on MoO3/Bi2Mo3O12 Hollow Microspheres.

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 MoO3/Bi2Mo3O12 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 MoO3/Bi2Mo3O12 sensor was studied with an X-ray photoelectron spectroscope to investigate the TMA sensing mechanism. The MoO3/Bi2Mo3O12 sensor ( S = 25.8) had a higher response to 50 ppm TMA than those of MoO3 hollow spheres ( S = 10.8) and Bi2Mo3O12 sensors ( S = 4.8) at 170 °C. In contrast to the pure MoO3 and Bi2Mo3O12 sensors, the MoO3/Bi2Mo3O12 sensor exhibited an obviously enhanced gas-sensing property for TMA, which might be due to the heterostructure formed between MoO3 and Bi2Mo3O12 and the hollow morphology. It is the first time for MoO3/Bi2Mo3O12 to apply in gas sensors, which might take an important step in the application of MoO3/Bi2Mo3O12 or Bi2Mo3O12 in the field of gas sensing.