Water‐soluble luminescent copper nanoclusters as a fluorescent quenching probe for the detection of rutin and quercetin based on the inner filter effect

In the present study, we proposed a simple, sensitive and selective fluorescence method for the detection of rutin (Rut) and quercetin (Que) based on the inner filter effect (IFE) utilizing water‐ soluble cysteine‐stabilized copper nanoclusters (Cys‐CuNCs) as a fluorescent probe. The Cys‐CuNCs were successfully synthesized and characterized using UV–visible absorption, emission, Fourier‐transform infrared (FT‐IR) spectroscopy, fluorescence lifetime, high resolution transmission electron microscopy (HR‐TEM) and zeta potential measurements. Cys‐CuNCs exhibited bluish‐green luminescence under UV light with characteristic emission maxima at 486 nm. Cys‐CuNCs was successfully exploited as fluorescent probes for the detection of Rut/Que. The addition of increasing concentrations of Rut/Que led to a gradual decrease in the emission intensity of Cys‐CuNCs. The decrease in Cys‐CuNC emission intensities were attributed to the strong IFE and static quenching mechanism. The calculated limit of detection values for Rut and Que were as low as 0.021 μM and 0.035 μM, respectively. The Cys‐CuNCs sensing probe exhibited excellent selectivity in the presence of other potential interfering compounds. Furthermore, the present method was successfully applied to the analysis of both Rut and Que in biological samples. Copper nitrate and l‐cysteine were added to 7.5 ml of water under the vigorous stirring at room temperature. After a few minutes, the NaOH was added into drop wise the reaction mixture and stirred vigorously for another 2.5 h. Finally, the Cys‐CuNCs was formed. Upon the addition of increasing concentrations of Rut/Que, the emission intensity of Cys‐CuNCs decreased gradually. The decrease in Cys‐CuNCs emission intensities are attributed to the strong inner filter effect and static quenching mechanism.