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A simple strategy has been designed for ratiometric fluorescence sensing of BLM on the basis of Cu2+-triggered fluorogenic reactions coupled with nanoparticle-mediated autocatalytic reactions. On one hand, Cu2+ can oxidize ascorbic acid (AA) to produce dehydroascorbic acid (DHAA), which condensates with o-phenylenediamine (OPD) to form fluorescent 3-(dihydroxyethyl) furo[3,4-b]quinoxaline-1-one (DFQ) with strong emission at 436 nm. On the other hand, Cu2+ and OPD undergo a redox reaction to form fluorescent 2,3-diaminophenazine (DAP) showing strong emission at 565 nm and copper nanoparticles (CuNPs) that further catalyze this redox reaction. A ratiometric fluorescence system comes into being due to these two well-resolved emission peaks. Ascribed to the complexation of BLM with Cu2+, larger CuNPs are obtained which weaken the autocatalytic reaction between Cu2+ and OPD. Thus, the fluorescence intensities at 565 nm belonging to DAP decrease while those at 436 nm corresponding to DFQ change slightly. With the fluorescence intensity ratio (F436/F565) as a readout, BLM can be detected selectively and sensitively with a detection limit of 50 pM. [ABSTRACT FROM AUTHOR]

As alternatives to nanozymes, some metal ions have been used in chemical/biochemical sensors owing to their facile acquisition avoiding tedious preparation and purification. Ce4+ has been reported to possess oxidase-like activity. Ascribed to its strong oxidative ability, Ce4+ can trigger the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) to its blue product oxTMB without the requirement of H2O2. When ALDS is added, the oxidation ability of Ce4+ can be reduced because of the redox reaction between Ce4+ and ALDS. The absorbance intensity ascribed to oxTMB decreases followed by the fading of the solution. On the basis of such a mechanism, a simple method is proposed for monitoring ALDS in two linear ranges of 0.1–10.0 μM and 10.0–60.0 μM. The detection limit is low to 0.05 μM. Furthermore, this method exhibits great potential for ALDS detection in real biological body fluids and pharmaceutical samples. [ABSTRACT FROM AUTHOR]

In this work, we proposed a convenient fluorescent assay for the detection of quinolones based on their inhibition towards the oxidation of o-phenylenediamine (OPD) by copper ions (Cu2+). Free Cu2+ can oxidize OPD into fluorescent 2,3-diaminophenzine followed by the formation of copper nanoparticles (CuNPs), which would further catalyze the oxidation of OPD. When quinolones were added, their strong binding affinity to Cu2+ inhibited the oxidase-like activity of Cu2+. So, the fluorescence intensity of the Cu2+–OPD system decreased obviously. The determination of quinolones can be achieved by using this fluorimetric assay without the use of complicated instruments and protocols. As demonstrated, this assay offered a highly sensitive readout for quinolones including nalidixic acid, cinoxacin, ciprofloxacin, and moxifloxacin in the linear ranges of 1.0–100 nM, 0.5–100 nM, 1.0–100 nM, and 0.1–100 nM, respectively. In addition, the developed assay was successfully applied to the direct analysis of quinolones in real amples. [ABSTRACT FROM AUTHOR]

In this work, we proposed a convenient fluorescent assay for the detection of quinolones based on their inhibition towards the oxidation of o-phenylenediamine (OPD) by copper ions (Cu2+). Free Cu2+ can oxidize OPD into fluorescent 2,3-diaminophenzine followed by the formation of copper nanoparticles (CuNPs), which would further catalyze the oxidation of OPD. When quinolones were added, their strong binding affinity to Cu2+ inhibited the oxidase-like activity of Cu2+. So, the fluorescence intensity of the Cu2+–OPD system decreased obviously. The determination of quinolones can be achieved by using this fluorimetric assay without the use of complicated instruments and protocols. As demonstrated, this assay offered a highly sensitive readout for quinolones including nalidixic acid, cinoxacin, ciprofloxacin, and moxifloxacin in the linear ranges of 1.0–100 nM, 0.5–100 nM, 1.0–100 nM, and 0.1–100 nM, respectively. In addition, the developed assay was successfully applied to the direct analysis of quinolones in real amples. [ABSTRACT FROM AUTHOR]

An efficient sensor was developed for highly sensitive and selective determination of melamine based on Ag nanoclusters (Ag NCs) capped by hyperbranched polyethyleneimine (PEI) molecules with different molecular weights. The fluorescence of the Ag NCs could be quenched by Hg2+ and recovered by melamine. The molecular weights of PEI had an appreciable effect on the sensitivity, and Ag NCs capped by PEI with a molecular weight of 600 were more sensitive; the linear range of melamine was from 0.1 to 30 μM with a detection limit 30 nM. Moreover, this Ag NCs–Hg2+ system displayed excellent selectivity over common interferences such as metal ions, amino acids, sugars and nitrogen-containing organic molecules. Benefiting from the high selectivity, good recoveries ranging from 96% to 101% were obtained in food samples, including milk, infant formula, and dog food. More importantly, Ag NC-doped agarose hydrogels were fabricated easily to construct a visual device for the detection of melamine in food samples. [ABSTRACT FROM AUTHOR]