Search

Abstract The accurate quantification of hydrogen peroxide (H 2 O 2) and glucose is essential significance in clinical diagnosis. Herein a selective and sensitive ratiometric fluorescent nanosensor was developed for the determination of H 2 O 2 and glucose by integrating peroxidase–like catalytic and fluorescent bifunctional properties of glutathione protected gold nanoclusters (GSH–AuNCs). The GSH–AuNCs exhibit inherent peroxidase–like activity and accelerate the decomposition of H 2 O 2 into hydroxyl radicals. The produced hydroxyl radicals oxidize terephthalic acid (TA), a typical non–fluorescent substrate of peroxidase, to a highly fluorescent product hydroxyterephthalate (TAOH). Upon excitation with single–wavelength at 315 nm, dual–emission fluorescence peaks were recorded at 430 and 600 nm simultaneously. The fluorescence signal of TAOH at 430 nm continuously increased with increasing the concentration of H 2 O 2 while the fluorescence signal of GSH–AuNCs at 600 nm remained unchangeable. Based upon on these facts, a ratiometric fluorescent nanosensor was fabricated for H 2 O 2 assay with TAOH as response unit and GSH–AuNCs as reference, respectively. By converting glucose into H 2 O 2 with catalytic oxidation of glucose oxidase (GOx), this nanosensor was further exploited for glucose assay. Under the optimum conditions, the detection limits of 10 nmol/L H 2 O 2 and 20 nmol/L glucose were acquired. The relative standard deviations were less than 5% for both H 2 O 2 and glucose (5.0 μmol/L solution, n = 11). The practicability of the nanosensor was verified by the determination of glucose in human serum samples. This nanosensor can be easily expanded as a general platform for the detection of other substances involving H 2 O 2 produced or consumed. Graphical abstract fx1 Highlights • Intrinsic peroxidase–like activity of GSH–AuNCs was demonstrated in fluorescent system. • A ratiometric fluorescent nanosensor was constructed with catalytic and fluorescent bifunctional properties of GSH–AuNCs. • Quantitative analysis of glucose in human serum samples was demonstrated. • The nanosensor can be easily adapted to measure other physiological substances with appropriate oxidases. [ABSTRACT FROM AUTHOR]

Abstract Tyrosinase is the key enzyme in the treatment of vitiligo. Development of rapid, simple, and visual methods for screening bioactive compounds with tyrosinase activity from natural compounds is interesting for new drug discovery. Herein, a novel visual ratiometric fluorescent assay for screening tyrosinase activators and/or inhibitors based on silicon nanoparticles (Si NPs) was explored. Inspired by the changes in both of the solution color and the fluorescence emission due to the sensing between Si NPs and dopamine (DA), we employed tyramine as the model substrate, which can transfer into DA by tyrosinase. It was found that the tyrosinase-incubated tyramine solution exhibited pale yellow under nature light or yellow fluorescence under UV light in the presence of Si NPs, where the color/fluorescence intensity were directly related to the concentration of tyrosinase. The established method showed good detection selectivity, and the LOD for tyrosinase was 0.14 U mL−1. Eventually, this assay was successfully applied to screen tyrosinase activators or inhibitors from a natural product-like library, and a tyrosinase activator with EC 50 of 2.62 μM, more potent than the commonly used tyrosinase activator 8-MOP, was discovered. Graphical abstract fx1 Highlights • The ratiometric fluorescent assay exhibited good selectivity, adequate sensitivity, and excellent tolerance to sample matrix. • The ratiometric fluorescent assay simultaneously realized visualization and quantitative analysis of tyrosinase activity. • A compound with potent tyrosinase activation (EC 50 = 2.62 μM) was found. [ABSTRACT FROM AUTHOR]

A palygorskite (Pal)-based ratiometric fluorescent nanoprobe is designed in order to establish a real time, on-site visual, and highly sensitive detection method for tetracyclines (TCs). The nanoprobe comprises the green emissive dye molecules embedded in the natural Pal, which serve as the internal reference signal. The potential red-emissive seed-europium (Eu 3+ ) ions are covalently bound on the surface of modified Pal, and they can act as the specific recognition element. The emission intensity of Eu 3+ ions significantly increases upon TC addition. The nanoprobe fluorescence changes from green to yellow, orange, or red, thereby accomplishing the visual ratiometric fluorescent detection. This nanoprobe exhibits a high sensitivity with a detection limit of 7.1 nM and an excellent selectivity in monitoring the levels of TCs in milk samples. In addition, this nanoprobe is useful for quantitative determination of TCs, and it is not affected with intensity fluctuations due to instrumental or environmental factors. The nanoprobe-immobilized test paper realizes real-time TCs analysis by using a smartphone with an easy-to-access color-scanning APP as the detection platform. Moreover, the reported construction of visual ratiometric detection system follows the sustainable development idea, that is, from nature, for nature, and into the nature. [ABSTRACT FROM AUTHOR]

A novel compound 1 based on phenanthro[9,10-d]imidazole platform has been unveiled as an effective ratiometric fluorescent probe for selective and rapid detection of NaCN. The sensing behavior was demonstrated by UV-vis, fluorescence experiments and NMR studies. This sensory system exhibited prominent visual emission color change toward CN − over other testing anions in CH 3 CN-PBS buffer (v/v, 3:1, pH 7.2) solution, with a 1:1 binding stoichiometry. Detection limit of the new cyanide-sensing probe 1 was 1.8 × 10 −9 mol L −1 , which was much lower than the World Health Organization (WHO) recommended level drinking water. The experimental results revealed that the formation of anionic species from the deprotonation of imidazole moiety by the CN − ion was responsible for the spectral changes. Calculations of the transition energies also verified such process. The spectral responses of probe could be switched back and forth alternatively by adding CN − and H + anions into the CH 3 CN-PBS buffer (v/v, 3:1, pH 7.2) solution, which indicated that compound 1 was stable and could be used in reversible manner. [ABSTRACT FROM AUTHOR]

Zinc is essential for normal growth and development, and hence selective recognition and detection for zinc has been a significant area of research. Here 4′-(4-methoxyphenyl)-2,2′:6′,2″-terpyridine is described for the ratiometric fluorescence quantification of zinc ion with high selectivity. The fluorescence of 4′-(4-methoxyphenyl)-2,2′:6′,2″-terpyridine at 406 nm was quenched in the presence of zinc, and a new emission band appeared at 452 nm. The ratiometric method for the determination of zinc ion was based on the dual fluorescence measurements at 406 and 452 nm. This fluorescence response is caused by the formation of a 1:1 complex between 4′-(4-methoxyphenyl)-2,2′:6′,2″-terpyridine and the zinc(II) ion. The analytical figures of merit for the protocol were obtained. The linear dynamic range extended for zinc concentrations from 3.0 to 40.0 µmol/L with a limit of detection of 0.28 µmol/L. Zinc was determined in water with satisfactory results. [ABSTRACT FROM PUBLISHER]