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.

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.

Au nanoparticles (AuNPs) have good absorption properties in the visible region, while upconversion nanoparticles (UCNPs) have an emission at 547 nm upon excitation with a 980 nm laser, which could avoid most interfering signals of biomolecules in serum. In this paper, we developed an aptasensor for platelet-derived growth factor (PDGF-BB) detection in 30% blood serum based on fluorescence resonance energy transfer between AuNPs and UCNPs. With the proposed aptasensor, PDGF-BB in 30% blood serum was detected. Two consecutive linear ranges allow a wide determination of PDGF-BB concentrations with a low detection limit of 10 nM (S/N ¼ 3). Importantly, the fluorescence biosensor can directly detect PDGF-BB in blood serum of lymphoma patient. This detection approach can also exhibit good stability and selectivity.

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