Sunlight and ultrasound-assisted synthesis of photoluminescent silver nanoclusters: A unique 'Knock out' sensor for thiophilic metal ions

We demonstrate the fine tuning of sunlight and ultrasound in green synthesis of photoluminescent silver nanoclusters (AgNCs) having quantum dot (QD) character for the first time. The use of hazardous additives (e.g. reducing agents, organic solvents, etc.) is minimized. The role of sunlight (which ruptures the S-S linkage) and ultrasound (which produces free radicals) in controlling various synthetic parameter as well as properties are carefully monitored and scientifically explained. The synthesized materials have the capabilities in sensing thiophilic metals ions (Hg2+, Pb2+, Cd2+, Zn2+) up to nanomolar (nM) and milimolar (mM) ranges by photoluminescence (PL) spectroscopy and PL microscopy respectively. The sensing of metal ions is based on fluorescence quenching. Hard soft acid base principle (HSAB) plays a major role to recognise the synthesized material as,a unique 'knock out' sensor. The HR-MS and HR-TEM show that the silver nanocluster is made of 2-6 silver atoms having diameter in the range of 2-3 nm respectively. The synthesized materials may be a good candidate for bio-labelling, bio-sensing and cell imaging. (C) 2016 Elsevier B.V. All rights reserved.