Protein Fibril-Templated Biomimetic Synthesis of Highly Fluorescent Gold Nanoclusters and Their Applications in Cysteine Sensing

[Image: see text] Biomimetic synthesis of multifunctional fluorescent gold nanoclusters (Au NCs) is of great demand because of their ever-increasing applications. In this study, we have used self-assembled bovine serum albumin (BSA) amyloid-like nanofibers as the bioinspired scaffold for the synthesis of Au NCs. The amyloid fibril stabilized gold nanocluster (Fib-Au NC) has been found to have appreciable enhancement of fluorescence emission and a large 25 nm red shift in its emission maxima when compared to its monomeric protein counterpart (BSA-Au NC). The underlying mechanism accountable for the fluorescence behavior and its spectral shift has been thoroughly investigated by a combined use of spectroscopic and microscopic techniques. We have subsequently demonstrated the use of Fib-Au NCs for cysteine (Cys) sensing both in vitro and inside live cells. Additionally, cellular uptake and postpermeation effect of Fib-Au NCs have also been ascertained by detailed flow cytometry analysis, viability assay, and real-time apoptotic gene expression profiling.