The influence of surface ligand chemistry for the synthesis of blue fluorescent gold nanoclusters for the detection of serotonin in biofluids

Gold nanoclusters have been widely applied for the sensing of biomolecules, biomarkers and drugs. Herein, a simple method for the fabrication of gold nanoclusters (Au NCs) is put forward by using two ligands, namely 6-thioguanine (6-TG) and tryptophan (Trp). First, blue emitting 6-TG-Au NCs have been synthesized and then the surface of the 6-TG-Au NCs was modified with Trp. This surface modification results in the enhancement of the fluorescence intensity with a red shift in the emission peak confirming the formation of 6-TG-Trp-Au NCs. The as-synthesized 6-TG-Trp-Au NCs work as a fluorescent sensor for the sensitive recognition of biomarker serotonin. The 6-TG-Trp-Au NCs exhibit a strong emission peak at 473 nm when excited at 380 nm. The 6-TG-Trp-Au NC-based method shows a fluorescence turn-off mechanism toward serotonin with a linear range of 0.041-1.25 μM and limit of detection of 5.58 nM. Moreover, 6-TG-Trp-Au NCs show a quick response for the development of a cost-effective analytical strategy for a serotonin assay in biofluids. Fluorescence detection of serotonin using 6-TG-Trp-Au NCs as a fluorescent sensor.