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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. [ABSTRACT FROM AUTHOR]

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.