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The polyporous SnO 2 -ZnO composites were synthesized by a water-bath method. The 3D center-hollow architecture and polyporous surface were also confirmed by field-emission scanning electron microscope (FE-SEM) and the Brunauer-Emmett-Teller (BET) specific surface area. Meanwhile, structural properties of SnO 2 -ZnO have been investigated by trans-mission electron microscopy (TEM) in 1 mol% SnO 2 -ZnO. The results of photoelectric gas-sensing demonstrated that the 1 mol% SnO 2 -ZnO gas-sensor exhibits not only an excellent response to formaldehyde (HCHO) but also superior sensitivity to low HCHO concentration. The response of 1 mol% SnO 2 -ZnO for the 1 ppm HCHO has reached 30% at room temperature (25 °C), and a detection limit of 0.1 ppm HCHO was achieved. The behavior of photogenerated charge is discussed in detail by means of the surface photovotage (SPV) and the transient photovoltage (TPV) techniques. It was found that the as-prepared 1 mol% SnO 2 -ZnO composites showed excellent separation and transfer efficiency of photogenerated charges carriers. What's more, the TPV spectrum analysis provides convincing evidence that the addition of excess SnO 2 is unfavorable to the transfer of electrons so as to reduce the sensitivity of SnO 2 -ZnO for target gas. This result offers a new window to explain the effect of SnO 2 concentration on the gas sensing characteristics, and provide more information on the fabricating composite materials for gas sensors. [ABSTRACT FROM AUTHOR]

A novel ratiometric electrochemiluminescence (ECL) biosensor was developed for sensitive detection of glucose in combination of graphitic-phase carbon nitride-supported Au nanocomposites (Au-g-C 3 N 4 ) and luminol as cathodic and anodic ECL emitters, respectively, only with dissolved oxygen in aqueous solution. Glucose oxidase-immobilized Au-g-C 3 N 4 nanocomposites (GOx/Au-g-C 3 N 4 ) were modified on a glassy carbon electrode to construct a sensing platform in the presence of luminol. Before glucose was added, the g-C 3 N 4 nanosheets could give a strong cathodic ECL emission with dissolved oxygen as a coreactant in aqueous solution. In the presence of glucose, hydrogen peroxide was in situ generated from dissolved oxygen, catalyzed by GOx and further by Au nanoparticles, and was then converted to reactive oxygen species, which led to an anodic ECL emission from luminol, concomitant with a decrease in the cathodic ECL emission from the g-C 3 N 4 nanosheets. The ratiometric ECL responses were closely related to the competitive consumption of dissolved oxygen by the g-C 3 N 4 nanosheets and luminol (by means of the GOx-immobilized Au nanoparticles). The constructed ratiometric ECL biosensor showed high sensitivity and selectivity for the detection of glucose, with a wide concentration range of 0.1–8000 μM and a low detection limit of 0.05 μM (S/N = 3). Furthermore, this constructed ratiometric ECL sensing platform was successfully applied to detect glucose in real samples independent of interference from other biomolecules. This proposed strategy opens an alternative avenue for ECL signal transduction and shows a promising application in clinical diagnostics. [ABSTRACT FROM AUTHOR]

In this paper, we developed a simple one-pot method, employing inexpensive chicken egg white (EW) as a reducing/capping reagent, for microwave-assisted synthesis of water-soluble and well-dispersed chicken egg white-protected gold nanoclusters (EW@AuNCs) with far-red/near-infrared (FR/NIR) emission. The resultant AuNCs showed strong emission at 667 nm with a quantum yield of 7.23%. The excellent photostability, large Stokes shift (>350 nm), microsecond-scale lifetime and strong emission endowed EW@AuNCs potential as a sensing probe. The photoluminescence of EW@AuNCs could be quenched upon addition of either Hg 2+ or Cu 2+ ion. After ethylenediamine (En) was used as a masking agent, the EW@AuNCs offered highly selective for determination of Hg 2+ ion. Also, the resultant EW@AuNCs probe exhibited ultra-high sensitivity toward Hg 2+ ion with a detection limit as low as 20 pM, which is 500 times lower than the limit value (10 nM) defined by the U.S. Environmental Protection Agency in drinkable water. The proposed AuNCs probe for Hg 2+ ion has a linear range of 0.0446–5.90 nM and good repeatable response to 2.0 nM Hg 2+ with a relative standard deviation of 2.8% ( n = 5). Additionally, the applicability of the sensing system was also verified by analysis of Hg 2+ ion in tap water and pond water samples. [ABSTRACT FROM AUTHOR]

• A ratiometric electrochemical biosensor for sensitive miRNA detection was developed. • The combination of Mg2+-dependent DNAzyme and competitive host-guest recognition enhanced detection sensitivity. • Satisfactory monitoring of miRNA in human serum samples was achieved. A novel ratiometric electrochemical biosensor was designed for sensitive miRNA-21 detection by combining Mg2+-dependent DNAzyme-cleavage cycling with competitive host-guest inclusion. The dual ferrocene-labeled hairpin DNA (2Fc-DNA)-assembled triple-helix magnetic probe (THMP) and methylene blue (MB)-immobilized reduced graphene oxide/β-cyclodextrin nanocomposites-modified glassy carbon electrode (RGO/β-CD/GCE) were served as target recognition and signal transformation units, respectively. Upon the hybridization reaction between target miRNA-21 and two auxiliary probes, the active DNAzyme was liberated from the caged structure, which bound with 2Fc-DNA to catalyze its cleavage in the presence of Mg2+, and triggered continuous cleavage reaction to obtain a large number of Fc-labeled DNA fragments. After magnetic separation, Fc-labeled DNA fragments could replace MB by the competitive host-guest recognition reaction and accumulate on the electrode surface, resulting in the gradually enhanced Fc and weakened MB signals, respectively. Under the optimal conditions, the constructed biosensor with ratiometric detection mode showed wide concentration range (10 fM−0.1 nM), low detection limit (1.8 fM), high sensitivity, and good selectivity, as well as satisfactory reproducibility and stability. And the developed sensing strategy may provide a new pathway in molecular diagnosis and bioanalysis. [ABSTRACT FROM AUTHOR]

We report a facile strategy to synthesize a novel fluorescent gold nanoclusters (NAC-AuNCs) in one step by using only the reactants of HAuCl 4 and N -acetyl- l -cysteine. The as-prepared AuNCs exhibited a fluorescence emission at 590 nm and a quantum yield of 13.6%. On the basis of metallophilic Hg 2+ –Au + interaction-induced fluorescence quenching mechanism, the fluorescent NAC-AuNCs offer highly sensitivity with a limit of detection of 0.2 nM for determination of Hg 2+ ions, which is 50 times lower than the limit value (10 nM) defined by the U.S. Environmental Protection Agency in drinkable water. The proposed fluorescent probe has a linear response range of 2.0–3200 nM Hg 2+ ions and good repeatable response to 20 nM Hg 2+ with a relative standard deviation of 3.2% ( n = 6). Also, the luminescence response of the NAC-AuNCs probe in the presence of EDTA is especially selective to Hg 2+ . The proposed method has been successfully applied for determination of Hg 2+ in various water samples, and the results agreed well with those obtained by the ICP-AES method. [ABSTRACT FROM AUTHOR]

Pesticide pollution has become a severe challenge for harming food quality and human safety. Therefore, it's urgent to develop sensitive methods to detect and analyse pesticides. Herein, we successfully developed a new turn-on fluorescent chemosensor (TPE-4P), a tetraphenyl ethylene derivative modified with four pillar[5]arenes, which could sensitively, selectively, and rapidly detect the pesticide paraquat. In our study, we took full advantage of both the host-guest strategy and aggregation-induced emission (AIE) to achieve fluorescent enhancement of the chemosensor for paraquat, in which four pillar[5]arenes as the recognition units can selectively capture paraquat. The formation of the supramolecular complexes based on the interlaced host-guest interactions effectively restricted the intramolecular single-bond rotation and skeletal vibration, resulting in the intensive fluorescent emission. The detection limit for paraquat was low enough to reach 154.1 nM, and the detection time was short enough to meet the rapid detection conditions. Moreover, the test strips loaded- TPE-4P facilitated the detection process and achieved the semi-quantitative analysis for paraquat in real spiked samples. In addition, TPE-4P could respond to paraquat in living zebrafish obviously. These results suggest that the cooperation of host-guest and AIE chemistry could become useful for the design to detect some appropriate organic molecules. [Display omitted] • A turn-on chemosensor was synthesized based on TPE and pillar[5]arene. • The sensor can rapidly, selectively, and sensitively detect pesticide paraquat through host-guest and AIE chemistry. • The sensor can be used in visual determination of paraquat in real samples and zebra fish. • The fabricated test strips can quantitatively detect paraquat. • The cooperation of host-guest and AIE chemistry is useful for the design of chemosensors. [ABSTRACT FROM AUTHOR]