In situ Metal-Enhanced Fluorescence of gold nanoclusters for enzymatic biosensors

A fluorescent enzymatic biosensor based on the in-situ observation of the MEF (Metal- Enhanced Fluorescence) effect has been developed for the first time. It has been demonstrated that during the enzymatic reaction of cadaverine with Diamine Oxidase (DAO) (used as proof of concept) in the presence of Au (III), the product can reduce the gold precursor to form AuNPs. When the reaction takes place in the presence of silica-coated gold nanoclusters (AuNCs@Si), an increase in the fluorescence signal is observed, which can also be related to the concentration of cadaverine. To understand the mechanism, the interaction between the AuNCs@Si and the enzymatic reaction, as well as their interaction with Au (III), has been studied. Under optimal conditions, the method shows a linear response range up to 250 μM Cadaverine, a limit of quantification of 52 μM and a limit of detection of 16 μM, which is about two orders of magnitude lower than the method without MEF (DAO/cadaverine/Au (III). It has been applied to the determination of cadaverine in spiked oily fish with a recovery of 95 ± 8 % (n = 3) and no significant differences (P = 0.05) were observed compared to a reference method. This MEF effect was also observed for the enzymatic determination of both xanthine with xanthine oxidase and tyramine with tyramine oxidase.