Inner filter effect based selective detection of picric acid in aqueous solution using green luminescent copper nanoclusters

Designing superior probes to detect trace amounts of picric acid (PA) is of huge importance for homeland security and environmental protection. In this study, a simple and rapid fluorescent sensor was developed for the highly selective and sensitive detection of PA in aqueous solution using cysteine stabilized copper nanoclusters (Cys-CuNCs) as a probe. The synthesized Cys-CuNCs were characterized by UV-visible, fluorescence, Fourier-transform infrared spectroscopy (FT-IR), high resolution transmission electron microscopy (HR-TEM), zeta potential and fluorescence lifetime measurements. The HR-TEM image shows that the Cys-CuNCs were spherical in shape with an average diameter of 2.2 nm. The prepared Cys-CuNCs were green luminescent under UV light and show maximum emission at 494 nm, when excited at 370 nm. The emission intensity of Cys-CuNCs was significantly quenched by the addition of PA, while addition of other nitro compounds induced meagre quenching of Cys-CuNCs, suggesting the high selectivity of Cys-Cys-CuNCs. This drastic change is ascribed to the strong inner filter effect (IFE) and static quenching between PA an Cys-CuNCs. The present sensor system exhibits a good linear response to PA ranging from 2.5 to 25 mu M with a correlation coefficient of 0.9930, and the limit of detection was found to be 0.19 mu M (S/N = 3). In addition, the developed sensing method was successfully applied to determine PA in tap and lake water samples.