Fluorescence enhancement of cysteine-rich protein-templated gold nanoclusters using silver(I) ions and its sensing application for mercury(II)

Keratins are a group of cysteine-rich structural proteins found abundant in hair, wool, feathers, etc. In this work, a highly luminescent gold nanocluster (AuNCs-Ag@Keratin) was synthesized for the first time by using keratin as the template, followed by a simple modification with silver(I) ions. The prepared AuNCs-Ag@Keratin could exhibit dramatically enhanced red fluorescence (λ em  = 725 nm), which was about 5-folds higher than that of common AuNCs@Keratin. The interactions of AuNCs with silver(I) ions were systematically characterized by fluorescence measurements, fluorescence correlation spectroscopy (FCS) and X-ray photoelectron spectroscopy (XPS). It was demonstrated that the “silver effect” could not only enhance the fluorescence intensity of AuNCs, but also improved the particles’ dispersion and stability. The as-prepared AuNCs-Ag@Keratin was applied to detect Hg 2+ in a wide detection range (2.44–2500 nM) and low detection limit (2.31 nM).