A highly sensitive caffeic acid fluorescent probe for detecting laccase in grape juice and mushrooms

Laccase is a kind of copper-containing polyphenol oxidase obtained with similar properties from different sources, and its catalytic reaction requires only oxygen and releases only water. The most widely used method for laccase detection is spectrophotometric assay with limited sensitivity. Herein, we report a highly sensitive fluorescence method for detecting the activity of laccase. The reported probe shows high selectivity, reliable accuracy and a good linear relationship toward different concentrations of laccase. Upon reaction, a new absorption peak appears around 420 nm accompanied by a significant fluorescence increase at 470 nm, which was consistent with the conjugation extension after the polyphenol structure was oxidized to quinone. The effects of different inhibitors and metal ions on the activity of laccase were assessed and the probe was compared with a commercial laccase detection kit and it showed higher sensitivity. Furthermore, this method was successfully used for the determination of laccase in grape musts with different degrees of fermentation as well as in three kinds of mushroom extracts.