A novel label-free upconversion fluorescence resonance energy transfer-nanosensor for ultrasensitive detection of protamine and heparin.

A novel label-free fluorescence nanosensor was developed for ultrasensitive detection of protamine and heparin based on fluorescence resonance energy transfer (FRET) between NaYF4:Yb,Er upconversion nanoparticles (UCNPs) and gold nanoparticles (AuNPs). The FRET system was formed by the electrostatic adsorption of AuNPs on UCNPs, and the fluorescence of UCNPs was significantly quenched. When protamine was added to the mixture of UCNPs-AuNPs, the AuNPs interacted with protamine and then desorbed from the surface of UCNPs and aggregated, resulting in the recovery of the fluorescence of UCNPs. On the addition of both protamine and heparin, the FRET system formed owing to the stronger interaction between heparin and protamine than that with AuNPs, leading to a marked fluorescence quenching of UCNPs. The concentrations of protamine and heparin were proportional to the changes of the fluorescence of UCNPs. The linear response range was obtained over the concentration ranges of 0.02 to 1.2µg/ml and 0.002 to 2.0µg/ml with low detection limits of 6.7 and 0.7ng/ml for protamine and heparin, respectively. Simultaneous measurement of protamine and heparin in human serum can be achieved, suggesting that the nanosensor can be used in a complex biological sample matrix.

Water-dispersible silicon dots as a peroxidase mimetic for the highly-sensitive colorimetric detection of glucose.

We demonstrate that photoluminescent Si-dots exhibit intrinsic peroxidase-like activity, and can catalyze the oxidization of 3,3',5,5'-tetramethylbenzidine (TMB) by H2O2, and produce a color change. This strategy can be used to detect glucose with high sensitivity and selectivity.

Gold nanoparticle coupled with fluorophore for ultrasensitive detection of protamine and heparin.

Here we report a novel label-free fluorescent sensor for ultrasensitive detection of protamine and heparin based on the high quenching ability of gold nanoparticles to the fluorescence of fluorescein. The fluorescence was significantly quenched when fluorescein molecules were attached to the surface of gold nanoparticles by electrostatic interaction. Upon addition of protamine, the fluorescein molecules were detached from the surface of the gold nanoparticles due to the stronger adsorption of protamine on the surface of AuNPs, and resulting in the recovery of the fluorescein molecules fluorescence. Heparin is able to bind with Protamine specifically. In the presence of heparin, the interaction of heparin with protamine makes the AuNPs de-aggregate and the fluorescein molecules re-attach to the AuNPs, which lead to marked fluorescence quench again. By measuring the changes in the fluorescence of the fluorescein molecules, the concentration of protamine and heparin were sequentially determined. The linear response range was obtained over the concentration range from 0 to 0.8 µg/mL and 4 to 1.6 µg/mL with the low detection limit 0.0067 µg/mL and 0.0013 µg/mL for protamine and heparin, respectively.

Green synthesis of carbon dots with down- and up-conversion fluorescent properties for sensitive detection of hypochlorite with a dual-readout assay.

High quality carbon dots (C-dots) with down- and up-conversion fluorescence have been synthesized through low-temperature carbonization using sweet pepper as the carbon source. The C-dots with a quantum yield (QY) of 19.3% exhibit superior photophysical properties, for example, narrow and symmetric emission spectra, large stock shifts, resistance to photobleaching, and excitation-dependent fluorescence behavior. The excellent C-dots serve as useful fluorescent probes for hypochlorite (ClO(-)) detection by both down- and up-conversion fluorescence. Two consecutive linear ranges allow a wide determination of ClO(-) concentrations with a low detection limit of 0.05 µmol L(-1) and 0.06 µmol L(-1) (S/N = 3) for down- and up-conversion fluorescence measurements, respectively. The proposed detection method is advantageous because it is simple, sensitive, dual-signalling model and low-cost and has potential extensive applications in environmental and biological assays.