Fluorescence turn-off detection of spermine in biofluids using pepsin mediated synthesis of gold nanoclusters as a probe

In this work, a simple, one step and eco-friendly synthetic strategy is developed for the fabrication of gold nanoclusters (Au NCs) using pepsin as a reducing and capping agent. The pepsin-Au NCs (P-Au NCs) displayed the excitation and emission peaks at 416 and 655 nm, and exhibiting red luminescence under UV lamp at 365 nm. The fluorescence quantum yield (QY) of P-Au NCs is 7.4%. The P-Au NCs act as specific biosensor for the detection of spermine in the presence of other structural similar compounds via fluorescence turn-off mechanism. The sensing principle is based on the spermine-induced fluorescence quenching of P-Au NCs, which leads to increase the size of Au NCs. The degree of florescence quenching was linear with spermine concentration (0.0075-10 mu M), with a detection limit of 1.75 nM, which is much lower for the quantification of spermine in urine samples of cancer patients. Compared to other reported methods, the P-Au NCs-based analytical strategy provides a simple synthetic route for fluorescent Au NCs with good QY and showed high selectivity for the detection of spermine with improved accuracy and precision. This method demonstrates as a facile and cost-effective analytical strategy for sensitive and selective fluorescence turn-off assay of spermine in urine samples. (C) 2019 Elsevier B.V. All rights reserved.