Fluorescence detection of dopamine based on the polyphenol oxidase-mimicking enzyme

In this work, a novel fluorescent method for the detection of dopamine (DA) was developed based on a fluorescent nanocomposite (Pdots@AMP-Cu) with polyphenol oxidase activity. Pdots@AMP-Cu was first prepared by the composite of fluorescent polymer dots and coordination nanostructures of adenosine monophosphate (AMP) and Cu²⁺. The Pdots@AMP-Cu exhibited obvious red fluorescence emission (668 nm), as well as polyphenol oxidase activity by catalyzing the substrate 2,4-DP and 4-AP, and resulted in obvious changes of the solution color from colorless to red. A novel detection method for DA was then developed based on Pdots@AMP-Cu. It is observed that DA can be oxidized by Pdots@AMP-Cu to form eumelanin, and at the same time, the fluorescence of Pdots@AMP-Cu is efficiently quenched by eumelanin due to electron transfer. A good linear relationship was observed between the fluorescent intensity and DA concentration from 10 to 400 μM, and the limit of detection for DA was 4 μM. Moreover, the proposed method exhibited high selectivity toward common amino acids, ascorbic acid, uric acid, etc. And it could also be utilized for DA sensing in human serum samples with satisfactory recoveries. Graphical abstract.