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In this work, a novel fluorescent method for the detection of dopamine (DA) was developed based on a fluorescent nanocomposite (Pdots@AMP-Cu) with polyphenol oxidase activity. Pdots@AMP-Cu was first prepared by the composite of fluorescent polymer dots and coordination nanostructures of adenosine monophosphate (AMP) and Cu2+. The Pdots@AMP-Cu exhibited obvious red fluorescence emission (668 nm), as well as polyphenol oxidase activity by catalyzing the substrate 2,4-DP and 4-AP, and resulted in obvious changes of the solution color from colorless to red. A novel detection method for DA was then developed based on Pdots@AMP-Cu. It is observed that DA can be oxidized by Pdots@AMP-Cu to form eumelanin, and at the same time, the fluorescence of Pdots@AMP-Cu is efficiently quenched by eumelanin due to electron transfer. A good linear relationship was observed between the fluorescent intensity and DA concentration from 10 to 400 μM, and the limit of detection for DA was 4 μM. Moreover, the proposed method exhibited high selectivity toward common amino acids, ascorbic acid, uric acid, etc. And it could also be utilized for DA sensing in human serum samples with satisfactory recoveries. [ABSTRACT FROM AUTHOR]

Wild edible mushrooms can accumulate significantly elevated levels of mercury from the surrounding environment, which could be harmful to consumers' health. Speciation analysis of mercury in wild edible mushrooms aids in understanding the human exposure to these toxic compounds. In this study, we developed a high-performance liquid chromatography hyphenated to inductively coupled plasma mass spectrometry (HPLC-ICP-MS) method for the simultaneous determination of inorganic mercury (Hg(II)), methylmercury (MeHg), ethylmercury (EtHg), and phenylmercury (PhHg) in wild edible mushrooms. A rapid separation of four target mercury species was achieved within 11 min by a C8 column without utilizing high proportion of organic phase in HPLC. The parameters affecting the extraction efficiency of mercury in samples have been investigated. The proposed method showed good linearity within 0–50 μg/L with the detection and quantification limits of 0.6–4.5 μg/kg (S/N = 3), and 2.0–15 μg/kg (S/N = 10), respectively. This proposed method was successfully applied to the mercury speciation analysis in 7 varieties (95 samples) of wild edible mushrooms. The results indicated that in most mushroom samples, mercury mainly occurred as inorganic mercury. But there were two Tricholoma matsutakes, one contained 0.14 mg/kg of methylmercury, another contained 1.05 mg/kg of phenylmercury, which were higher than the maximum allowable content of total mercury in edible mushrooms in China. [ABSTRACT FROM AUTHOR]

Monitoring and imaging glutathione (GSH) in living systems is an essential tool to determine the key roles of GSH in biological pathways, but most fluorescent sensors can only be used in vitro because of their potential biotoxicity. Here, a peptide-based fluorescent sensor, FP, has been successfully designed and synthesized based on the biocompatibility of the peptide backbone and low toxicity. The design strategy of FP contains a specific spatial structure of the peptide sequence which selectively binds to Cu2+, triggering fluorescence quenching. Interestingly, the fluorescence of FP can be fully restored by GSH, due to the strong binding between Cu2+ and the GSH sulfhydryl groups. Finally, the sensor is highly sensitive and selective for imaging GSH both in vitro and in vivo with low toxicity. Thus, FP with its strong "on-off-on" fluorescence changes is a powerful way to image GSH both in cells and zebrafish larvae to study the GSH pathway. [ABSTRACT FROM AUTHOR]

A novel carboxyl Fe3O4 magnetic nanoparticle-based solid-phase extraction combined with high-performance liquid chromatography was developed for the analysis of oxytetracycline, tetracycline, demeclocycline, metacycline, chlortetracycline, and doxycycline in water samples. Driven by the electrostatic interaction and the strong chelation between tetracyclines and iron ions, tetracyclines in samples were adsorbed onto the adsorbents. The adsorbed analytes were subsequently eluted with oxalic acid and separated with a C18 column under gradient condition with a mobile phase consisting of methanol, acetonitrile, and oxalic acid at a flow rate of 0.5 mL/min. The detection was performed at variable ultraviolet wavelengths. Under optimized conditions, the developed method gave an enrichment factor of 33.3, linearity ranges of 5.00-1000 μg/L, detection limits of (2.86-5.19) × 10-2 μg/L, quantification limits of (9.54-17.3) × 10-2 μg/L, recoveries of 76.2-98.0%, and intra- and inter-day RSDs of 0.132-15.5% and 2.28-14.5% for these tetracyclines. The established method was successfully applied for the determination of these six tetracyclines in tap water, river water, pond water, and lake water samples.ᅟ [ABSTRACT FROM AUTHOR]

Based on a novel signal amplification strategy by catalytic hairpin assembly and displacement of G-quadruplex DNA, an enzyme-free, non-label fluorescent aptasensing approach was established for sensitive detection of four tetracycline veterinary drugs in milk. The network consisted of a pair of partially complementary DNA hairpins (HP1 and HP2). The DNA aptamer of four tetracycline veterinary drugs was located at the sticky end of the HP1. The ring region of HP1 rich in G and C could form a stable G-quadruplex structure, which could emit specific fluorescence signal after binding with the fluorescent dye and N-methylmesoporphyrin IX (NMM). When presented in the system, the target analytes would be repeatedly used to trigger a recycling procedure between the hairpins, generating numerous HP1-HP2 duplex complexes and displacing G-quadruplex DNA. Thus, the sensitive detection of target analytes was achieved in a wide linear range (0-1000 μg/L) with the detection limit of 4.6 μg/L. Moreover, this proposed method showed high discrimination efficiency towards target analytes against other common mismatched veterinary drugs, and could be successfully applied to the analysis of milk samples.Schematic of target analyte detection based on catalytic hairpin assembly reaction and displacement of G-quadruplex [ABSTRACT FROM AUTHOR]

A fluorescence turn-on assay for alkaline phosphatase (ALP) activity is developed through the controlled release of polyethyleneimine-capped copper nanoclusters (PEI-capped CuNCs) from the MnO nanosheets. In an aqueous solution, the positively charged PEI-capped CuNCs could be adsorbed onto the surface of the negatively charged MnO nanosheets. Such adsorption through favorable electrostatic interactions could efficiently quench the nanocluster fluorescence emission via resonance energy transfer from the PEI-capped CuNCs to the MnO nanosheets. 2-Phospho- l-ascorbic acid (AAP) could be hydrolyzed to l-ascorbic acid (AA) in the presence of ALP. AA could reduce MnO into Mn and trigger the disintegration of the MnO nanosheets. As a result, the CuNCs were released and the quenched fluorescence was recovered efficiently. The detection strategy is simple, inexpensive, sensitive, selective, with low toxicity, and has better biocompatibility. The newly fabricated biosensor for ALP activity will potentially make it a robust candidate for numerous biological and biomedical applications. [ABSTRACT FROM AUTHOR]

A label-free fluorescence turn-on strategy for alkaline phosphatase (ALP) detection was established based on its enzymatic catalyzed hydrolysis of polyphosphoric acid (PPA, an anionic polymer) that had been utilized for aggregation with our homemade positively charged perylene derivative (Probe-1) via noncovalent interactions. The disaggregation caused turn-on fluorescence signal which was recovered by the released Proble-1 molecules whose original strong fluorescence in an aqueous buffer solution had been quenched due to their previous aggregation induced by PPA. Such method presents its great advantages of free labeling, convenience and simplicity, cost effectiveness, high selectivity, and high sensitivity, with a detection limit of 0.5 mU/mL of ALP. [ABSTRACT FROM AUTHOR]

The manganese-tetrasulfonatophthalocyanine (MnTSPc) catalyzed luminol–hydrogen peroxide chemiluminescence (CL) systems can be quenched in the presence of proteins. A highly sensitive CL quenching method has been developed for the determination of proteins. Under optimum conditions, the linear ranges of the calibration curves were 0.1–20 µg/mL for human serum albumin (HSA), 0.2–20 µg/mL for human γ-IgG, and 0.5–50 µg/mL for the bovine serum albumin (BSA) with the corresponding detection limits were 1.9 ng/mL, 2.7 ng/mL, and 3.4 ng/mL. The method has been applied to the analysis of total proteins in human serum samples and the results were in good agreement with clinical data provided. [ABSTRACT FROM AUTHOR]