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A plasmonic hot electron transfer-induced multicolor chromogenic system is described for label-free visual colorimetric determination of silver(I). The chromogenic system consists of plasmonic MoO 3-x nanosheets with oxygen vacancies and Ag(I). Under white light-emitting diode (LED) excitation, energetic hot hole-electron pairs are formed on the surface of the blue MoO 3-x nanosheets. The resulting hot electrons are transferred to Ag(I) upon which it becomes reduced. This results in the generation of yellow silver nanoparticles. Simultaneously, the hot holes lead to the oxidation of the MoO 3-x nanosheets to yield colorless MoO 3 nanosheets. Similarly, energetic hot hole-electron pairs can also be generated on the surface of AgNPs under white LED irradiation, which contributes to the reduction of Ag(I) and the oxidation of MoO 3-x . Overall, a colorful transition from blue to green and finally to yellow can be observed. This multicolor chromogenic system was applied to the colorimetric determination of Ag(I) in the 33–200 μM concentration range and a 0.66 μM limit of detection, at analytical wavelengths of 430 and 760 nm. The method also is amenable to semi-quantitative visual determination of Ag(I). Graphical abstract Schematic representation of plasmonic hot electron transfer-induced multicolor MoO 3-x -based chromogenic system for visual and colorimetric determination of silver(I).

There is great interest in detection of the level of 2,4,6-trinitrotoluene (TNT) explosive due to its importance in public security and environmental protection fields. The conventional chemical sensors do not simultaneously realize simple, rapid, sensitive, selective, and direct detection of TNT in different medium without sample pretreatment. Here we present a modified wood-based chemical sensor for visual colorimetric detection of TNT in water, air, and soil. The natural wood undergoes a delignified process, which is further functionalized by 3-aminopropyltriethoxysilane (APTES). When TNT solutions are introduced, the wood-based sensor shows a colorimetric transition from light yellow to brown for naked-eye readout because of the generation of Meisenheimer complex between APTES and TNT. The photographs are collected by smartphone camera, and the RGB components are extracted to calculate the adjusted intensity for qualitative detection of TNT. This visual colorimetric sensor for TNT solution displays a linearity in the range of 0.01–5 mM with a limit of detection of 3 μM. In addition, by taking advantage of its inherent mesostructure, the wood-based sensor can be employed for visual detection of TNT vapor as well. Furthermore, it is also able to directly detect TNT in wet soil samples based on capillary action, in which TNT carried by water transports upward along the wood microchannel, triggering the generation of Meisenheimer complex.

Colla corii asini (CCA) made from donkey-hide has been widely used as a traditional animal-based Chinese medicine. Chondroitin sulfate (CS), dermatan sulfate (DS) and hyaluronic acid (HA) are structurally complex classes of glycosaminoglycans (GAGs) that have been implicated in a wide range of biological activities. However, their possible structural characteristics in CCA are not clear. In this study, GAG fractions containing CS/DS and HA were isolated from CCA and their disaccharide compositions were analyzed by high sensitivity liquid chromatography-ion trap/time-of-flight mass spectrometry (LC-MS-ITTOF). The result showed that CS/DS/HA disaccharides were detected in the three lower salt fractions from anion-exchange chromatography. The sulfation patterns and densities of CS/DS chains in these fractions differed greatly, while HA chains varied in their chain lengths. The quantitative analysis first revealed that the amount of GAGs in CCA varied significantly in total and in each fraction. This novel structural information could help clarify the possible involvement of these polysaccharides in the biological activities of CCA.

We report a molybdenum oxide (MoO3) nanomaterial-based three-input logic gate that uses Sn2+, NO2−, and H+ ions as inputs. Under acidic conditions, Sn2+ is able to reduce MoO3 nanosheets, generating oxygen-vacancy-rich MoO3−x nanomaterials along with strong localized surface plasmon resonance (LSPR) and an intense blue solution as the output signal. When NO2− is introduced, the redox reaction between the MoO3 nanosheets and Sn2+ is strongly inhibited because the NO2− consumes both H+ and Sn2+. The three-input logic gate was employed for the visual colorimetric detection of Sn2+ and NO2− under different input states. The colorimetric assay’s limit of detection for Sn2+ and the lowest concentration of NO2− detectable by the assay were found to be 27.5 nM and 0.1 μM, respectively. The assay permits the visual detection of Sn2+ and NO2− down to concentrations as low as 2 μM and 25 μM, respectively. The applicability of the logic-gate-based colorimetric assay was demonstrated by using it to detect Sn2+ and NO2− in several water sources.

The authors report on a fast chemiluminescence (CL) assay for the food additive sodium tripolyphosphate (STPP). It is based on the use of gold nanoflowers (AuNFs) bifunctionalized with luminol and chitosan that act as a CL probe and a molecular recognitions systems because chitosan can bind STPP. In the absence of STPP, the luminol-chitosan-AuNF CL system is triggered by addition of H 2 O 2 and Co(II) ions. However, on addition of STPP, modified AuNFs bind STPP and aggregate. This suppresses CL. Under optimized conditions, the system responds to STPP in the 0.7 to 700 μM concentration range, and the limit of concentration is as low as 0.5 μM. This is lower than that of other analytical techniques for STPP. The method was applied to the determination of STPP in (spiked) ham samples, and recoveries ranged from 98% to 107% with a relative standard deviation of <5.0%. Graphical abstract A fast chemiluminescent strategy is described for the detection of sodium tripolyphosphate (STPP). The method is based on the luminol-chitosan bifunctionalized gold nanoflower (AuNF)-H 2 O 2 -Co 2+ system. It can be completed within 7 min and is capable of detecting STPP in real samples such as commercial ham.

Logic systems that yield two or more signal outputs in the presence of the input are scarce. A universal logic system consisting of plasmonic MoO 3-x nanodots and 3,3′-diaminobenzidine (DAB) for fabrication of visual contrary logic pairs and circuits are presented here. They do not require the use of expensive instrumentation but can be visually read. It is based on the facts that the blue dispersion of MoO 3-x nanodots turns to colorless after oxidation, while the colorless reagent DAB is oxidized by various oxidants to generate a brown color. On this basis, the complete contrary logic pairs and circuits such as YES-NOT, AND-NAND, OR-NOR, XOR-XNOR, INH-IMH, and MAJ-MIN can be fabricated. Various oxidants serve as inputs, and absorbances as outputs. A smart logic voting system with “one-vote deny” function is also described that is based on the cascade of MAJ logic circuit and INH logic gate using ascorbic acid (AA) as the superior denier. All the logic operations can visually read due to the appearance of distinct color changes. Graphical abstract Schematic presentation of the contrary logic pairs and circuits using a visually and colorimetrically detectable redox system consisting of MoO 3-x nanodots and 3,3′-diaminobenzidine.

A plasmonic hot electron transfer-induced multicolor chromogenic system is described for label-free visual colorimetric determination of silver(I). The chromogenic system consists of plasmonic MoO.sub.3-x nanosheets with oxygen vacancies and Ag(I). Under white light-emitting diode (LED) excitation, energetic hot hole-electron pairs are formed on the surface of the blue MoO.sub.3-x nanosheets. The resulting hot electrons are transferred to Ag(I) upon which it becomes reduced. This results in the generation of yellow silver nanoparticles. Simultaneously, the hot holes lead to the oxidation of the MoO.sub.3-x nanosheets to yield colorless MoO.sub.3 nanosheets. Similarly, energetic hot hole-electron pairs can also be generated on the surface of AgNPs under white LED irradiation, which contributes to the reduction of Ag(I) and the oxidation of MoO.sub.3-x. Overall, a colorful transition from blue to green and finally to yellow can be observed. This multicolor chromogenic system was applied to the colorimetric determination of Ag(I) in the 33-200 [mu]M concentration range and a 0.66 [mu]M limit of detection, at analytical wavelengths of 430 and 760 nm. The method also is amenable to semi-quantitative visual determination of Ag(I).

Colla corii asini (CCA) made from donkey-hide has been widely used as a health-care food and an ingredient of traditional Chinese medicine. Heparan sulfate (HS)/heparin is a structurally complex class of glycosaminoglycans (GAGs) that have been implicated in a wide range of biological activities. However, their presence within CCA, and their possible structural characteristics, were previously unknown. In this study, GAG fractions containing HS/heparin were isolated from CCA and their disaccharide compositions were analyzed by high sensitivity liquid chromatography-ion trap/time-of-flight mass spectrometry (LC-MS-ITTOF). This revealed that, in addition to the eight commonly seen HS disaccharides, the four rare N-unsubstituted disaccharides were also detected in significant quantities. The disaccharide compositions varied significantly between HS/heparin fractions indicating chains with differing domain structures. This novel structural information may lead to a better understanding of the biological activities (i.e. anticoagulation and antitumor action) of CCA.

Logic systems that yield two or more signal outputs in the presence of the input are scarce. A universal logic system consisting of plasmonic MoO.sub.3-x nanodots and 3,3'-diaminobenzidine (DAB) for fabrication of visual contrary logic pairs and circuits are presented here. They do not require the use of expensive instrumentation but can be visually read. It is based on the facts that the blue dispersion of MoO.sub.3-x nanodots turns to colorless after oxidation, while the colorless reagent DAB is oxidized by various oxidants to generate a brown color. On this basis, the complete contrary logic pairs and circuits such as YES-NOT, AND-NAND, OR-NOR, XOR-XNOR, INH-IMH, and MAJ-MIN can be fabricated. Various oxidants serve as inputs, and absorbances as outputs. A smart logic voting system with \"one-vote deny\" function is also described that is based on the cascade of MAJ logic circuit and INH logic gate using ascorbic acid (AA) as the superior denier. All the logic operations can visually read due to the appearance of distinct color changes.

A plasmonic hot electron transfer-induced multicolor chromogenic system is described for label-free visual colorimetric determination of silver(I). The chromogenic system consists of plasmonic MoO nanosheets with oxygen vacancies and Ag(I). Under white light-emitting diode (LED) excitation, energetic hot hole-electron pairs are formed on the surface of the blue MoO nanosheets. The resulting hot electrons are transferred to Ag(I) upon which it becomes reduced. This results in the generation of yellow silver nanoparticles. Simultaneously, the hot holes lead to the oxidation of the MoO nanosheets to yield colorless MoO nanosheets. Similarly, energetic hot hole-electron pairs can also be generated on the surface of AgNPs under white LED irradiation, which contributes to the reduction of Ag(I) and the oxidation of MoO . Overall, a colorful transition from blue to green and finally to yellow can be observed. This multicolor chromogenic system was applied to the colorimetric determination of Ag(I) in the 33-200 μM concentration range and a 0.66 μM limit of detection, at analytical wavelengths of 430 and 760 nm. The method also is amenable to semi-quantitative visual determination of Ag(I). Graphical abstractSchematic representation of plasmonic hot electron transfer-induced multicolor MoO -based chromogenic system for visual and colorimetric determination of silver(I).