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Bilirubin is a key biomarker in the diagnosis of jaundice. Herein, we proposed a simple and convenient quantitative method for the fluorescent detection of bilirubin. We developed a copper nanoclusters coated by zinc-based metal-organic frameworks (Cu NCs@MOF). The prepared Cu NCs@MOF exhibited bright blue fluorescence excited with ultra-violet light and well stability at various environments. More importantly, Cu NCs@MOF was used for bilirubin detection based on the emerging red fluorescence emission peak induced by bilirubin. Furthermore, Cu NCs@MOF were made into test strip for the visual detection of bilirubin by the fluorescence color variation. [ABSTRACT FROM AUTHOR]

In this paper, bovine serum albumin served as the initial materials for preparing a kind of cyan-emitting fluorescent protein nanoparticles (BSA NPs). The BSA NPs were further adopted as a template to synthesize protein nanoparticles-stabilized silver nanoclusters (BSA NPs@Ag NCs) that offered two well-separated fluorescence emission peaks respectively at 470 nm and 670 nm. Dopamine could specifically induce the fluorescence enhancement at 470 nm and the fluorescence quenching at 670 nm of BSA NPs@Ag NCs. Moreover, cupric ions could cause the fluorescence quenching at 670 nm of BSA NPs@Ag NCs just with a negligible impact on the fluorescence intensity at 470 nm. The BSA NPs@Ag NCs can serve as a ratiometric probe for detection of dopamine and cupric ions. [ABSTRACT FROM AUTHOR]

In this paper, we prepared fluorescence-tunable water-soluble CdS quantum dots (QDs) with hexametaphosphate as stabilizers by a simple route. The prepared CdS QDs were utilized to detect calcium ion (Ca 2+ ) based on an obvious fluorescence enhancement of CdS QDs induced by Ca 2+ . The results demonstrated there was an excellent linear relationship between the fluorescence intensity of hexametaphosphate-capped CdS QDs and Ca 2+ concentration in the range from 10 μmol/L to 400 μ mol/L and the detection limit for Ca 2+ was 4 μmol/L. Furthermore, fluoride ions (F − ) can react with Ca 2+ to generate the insoluble calcium fluoride that would inhibit the Ca 2+ -induced fluorescence enhancement of CdS QDs. Therefore, the designed Ca 2+ -induced fluorescence enhancement system was also able to effectively detect fluoride. [ABSTRACT FROM AUTHOR]

A facile chemical synthetic route was developed to prepare near-infrared fluorescent trypsin-stabilized Ag nanoclusters (Try-Ag NCs). The fluorescence emission wavelength of the produced Try-Ag NCs is tunable by simple adjusting pH value of the synthesis system, and the Try-Ag NCs offer a symmetric fluorescent excitation and emission peak. The fluorescence of Try-Ag NCs remains constant in the presence of various ions and molecules, and it can be effectively quenched by 1,4-dihydronicotinamide adenine dinucleotide (NADH) instead of its oxidized forms nicotinamide adenine dinucleotide (NAD + ). This property enables the Try-Ag NCs to be a novel analytical platform to monitor biological reaction involved with NADH. In this work, the Try-Ag NCs was also applied to analyze ethanol based on the generation of NADH which was the product of NAD + and ethanol in the catalysis of alcohol dehydrogenase. And the proposed platform allowed ethanol to be determined in the range from 10 to 300 μmol/L with 5 μmol/L detection limit. [ABSTRACT FROM AUTHOR]

Abstract: Water-soluble CuInS2 quantum dots (QDs) were directly synthesized in an aqueous solution with mercaptopropionic acid (MPA) as stablizers, and were functionalized using tryptophan molecules to form tryptophan-functionalized CuInS2 QDs (W-CuInS2 QDs) that had a strong fluorescence emission around 689nm. The fluorescence of W-CuInS2 QDs could be quenched by Cu2+ and then the addition of pyrophosphate (PPi) could effectively turn on the quenched fluorescence due to the strong interaction between Cu2+ and PPi. The alkaline phosphatase (ALP) could catalyze the hydrolysis of PPi that would disassemble the complex of PPi–Cu2+–PPi. Therefore, the recovered fluorescence could be quenched again by the addition of ALP. In this paper, we developed a novel near-infrared fluorescence probe for the simple and convenient assay of ALP. [Copyright &y& Elsevier]

Water-soluble CuInS quantum dots (QDs) stabilized with 3-mercaptopropionic acid were synthesized in aqueous solution and then coated with bovine serum albumin. The resulting particles display fluorescence with a peak at 680 nm that is effectively quenched by 1, 4-dihydro-nicotinamide adenine dinucleotide (NADH), but not by 1, 4-nicotinamide adenine dinucleotide (NAD). The enzyme lactate dehydrogenase catalyzes the reduction of pyruvate and dehydrogenation of lactic acid using NAD or NADH as a cosubstrate. The new QDs were applied to monitor the course of lactate dehydrogenase-catalyzed reaction of pyruvate by detecting NADH via its quenching effect. This resulted in a convenient and selective detection scheme for pyruvate. The detection limit is as low as 25 nM. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

A novel sensing strategy for sequence-specific recognition of Staphylococcus aureus (S. aureus) DNA was designed based on the DNA hybridization between dye-labeled single-stranded DNA (ssDNA) and the complementary target DNA. Graphene oxide (GO) can adsorb FITC-labeled probes and quench the fluorescence efficiently via Förster resonance energy transfer (FRET). However, the formation of double-stranded DNA (dsDNA) will alter the conformation of ssDNA and disturb the interaction between GO and ssDNA. Thus the dsDNA–GO mixture exhibits a stronger fluorescence emission than that of the ssDNA–GO mixture, and the relative fluorescence intensity ΔI/I0 (ΔI = Ia−Iq) is related to the concentration of ssDNA (S. aureus DNA). Here we illustrate a “post-mixing” strategy in which the fluorescent dye-labeled DNA was allowed to hybridize with S. aureus DNA prior to the addition of GO. In this experiment, the competition between ssDNA–GO adsorption and the dsDNA formation was avoided and the incubation time was shortened to 20 min. Under the optimum conditions, the relative fluorescence intensity ΔI/I0 was proportional to the concentration of S. aureus DNA in the range 0.0125–3.125 nmol L−1, with a detection limit of 0.00625 nmol L−1 and good sequence selectivity. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The dual-emission carbon dots were directly prepared by carbonizing glutathione in the water/formamide mixture. • The carbon dots exhibited dual emission peaks at 470 nm and 655 nm with excitation of 400 nm. • Fe3+ can be detected based on the fluorescence quenching at 655 nm of DCDs in acidic environments. • Zn2+ can be detected based on the fluorescence quenching at 470 nm of DCDs in alkaline environments. Abstract Herein, we developed a facile route for the preparation of dual-emission carbon dots (DCDs) by carbonizing glutathione in the water/formamide mixture. The synthesized DCDs displayed dual emission band respectively at 470 nm and 655 nm under the single-wavelength excitation at 400 nm, which can be used for the detection iron ions (Fe3+) and zinc ions (Zn2+) in different pH environments. An obvious fluorescence quenching around 655 nm was detected with the addition of Fe3+ in acidic environments, and a linear range of 2.5–30 μmol·L−1 and a detection limit of 0.8 μmol L−1 for Fe3+ were achieved. Moreover, another fluorescence quenching at 470 nm was also observed with the addition of Zn2+ in alkaline environments, and a linear range of 2.5–50 μmol L−1 and a detection limit of 1.2 μmol L−1 for Zn2+ were achieved. The prepared DCDs was used as a ratiometric fluorescent probe for determination of Fe3+ and Zn2+ ions in serum samples. [ABSTRACT FROM AUTHOR]