A novel fluorescent biosensor for adrenaline detection and tyrosinase inhibitor screening.

In this work, a novel simple fluorescent biosensor for the highly sensitive and selective detection of adrenaline was established. Firstly, water-soluble CuInS2 quantum dots (QDs) capped by L-Cys were synthesized via a hydrothermal synthesis method. Then, the positively charged adrenaline was assembled on the surface of CuInS2 QDs due to the electrostatic interactions and hydrogen bonding, which led to the formation of adrenaline-CuInS2 QD (Adr-CuInS2 QD) electrostatic complexes. Tyrosinase (TYR) can catalyze adrenaline to generate H2O2, and additionally oxidize the adrenaline to adrenaline quinone. Both the H2O2 and the adrenaline quinone can quench the fluorescence of the CuInS2 QDs through the electron transfer (ET) process. Thus, the determination of adrenaline could be facilely achieved by taking advantage of the fluorescence "turn off" feature of CuInS2 QDs. Under the optimum conditions, the fluorescence quenching ratio If/If0 (If and If0 were the fluorescence intensity of Adr-CuInS2 QDs in the presence and absence of TYR, respectively) was proportional to the logarithm of adrenaline concentration in the range of 1 × 10-8-1 × 10-4 mol L-1 with the detection limit of 3.6 nmol L-1. The feasibility of the proposed biosensor in real sample assay was also studied and satisfactory results were obtained. Significantly, the proposed fluorescent biosensor can also be utilized to screen TYR inhibitors. Graphical abstract Schematic illustration of the fluorescent biosensor for adrenaline detection (A) and tyrosinase inhibitor screening (B).