In this study, C-dots were facilely synthesized via microwave irradiation using citric acid and ethylenediamine as carbon precursors. The fluorescence emissions of the C-dots could be selectively quenched by Fe3+, and the degree of quenching was linearly related to the concentrations of Fe3+ presented. This phenomenon was utilized to develop a sensitive fluorescence assay for Fe3+ detection with broad linear range (0–250, 250–1200 μmol/L) and low detection limit (1.68 μmol/L). Most importantly, the assay demonstrated high reliability towards samples in deionized water, tap water and lake water, which should find potential applications for Fe3+ monitoring in complicated environments.

In this report, red-emissive carbon dots (C‑dots) were facilely prepared from o-phenylenediamine via microwave-assisted hydrothermal treatment. The C-dots demonstrated excitation wavelength-independent emission with maximums at 621 nm that could be effectively quenched by Ag+ via static quenching. This phenomenon was exploited to establish a sensitive fluorescence assay with a low detection limit (0.37 μM) and wide linear range (0–50 μM). In addition, this assay demonstrated excellent selectivity toward Ag+, free from the interference of 16 commonly seen metal ions. Most importantly, the assay demonstrated high reliability toward samples in deionized water, mineral water, lake water, and serum, which could indicate potential applications for Ag+ monitoring in complicated natural and biological environments.