Highly fluorescent water-soluble PTCA incorporated silver nano-cluster for sensing of dopamine

In the present work, we designed a novel nanocluster (PTCA/Capt-AgNC) with a remarkably enhanced fluorescence, photostability and water solubility. This green fluorescent nanocluster with dimension of ~ 2–4 nm was characterized by UV–Vis, Fourier transformed infrared, Raman, photoluminescence (PL) spectroscopies; X-ray diffraction (XRD), high resolution transmission electron microscopy and selected area electron diffraction techniques. It was observed that the incorporation of a tiny amount of 3,4,9,10-perylene tetracarboxylic acid (PTCA) into captopril (Capt) protected silver nanocluster (Capt-AgNCs) resulted in the increase of PLQY by several orders of magnitude compared to PTCA and Capt-AgNCs. The PL studies indicated that the material has high photoluminescence quantum yield (PLQY ~ 0.25) in comparison to the previously reported Capt-AgNCs. Fluorescence intensity of PTCA/Capt-AgNCs was quenched upon addition of various concentrations of dopamine. Selectivity in fluorescence quenching was evaluated with structurally similar bio-molecules such as l-cysteine and urea. Time resolved fluorescence spectroscopy revealed that the average fluorescence lifetime of the nanocluster was reduced strikingly upon addition of dopamine in comparison to that with l-cysteine and urea which clearly indicated the selectivity and sensitivity. Density functional theory calculations were performed to investigate the PL enhancement and quenching mechanisms. We believe that strategy reported in the present study could be adopted for designing highly efficient biosensors.