Colorimetric and fluorometric dual-signal determination of dopamine by the use of Cu-Mn-O microcrystals and C-dots

Transition metal oxides are potent catalytic materials owing to the high electron transport efficiency and high catalytic activity properties, thus they are widely used as mimic enzyme material. In this work, Cu-Mn-O catalytic material was prepared by hydrothermal synthesis of Cu doped dumbbell MnCO3 microcrystals as precursor and calcination of the precursor. The morphology and structure were characterized by TEM, SEM, XRD and XPS. With the oxidase activity, the Cu-Mn-O material can catalyze the oxidation of colorless substrate 3,3', 5,5'-tetramethylbenzidine (TMB) to generate the blue product of oxTMB. The absorption of oxTMB overlaps with the emission of the C-dots due to the fluorescence inner filter effect, leading to the reduction of the fluorescence emission intensity from the carbon quantum dots. Moreover, dopamine can inhibit the activity of Cu-Mn-O catalytic material, leading to the fading of the blue color of the oxTMB, and the fluorescence from carbon quantum dots is restored, thus achieving the goal of colorimetric and fluorescence dual-signal determination for dopamine. The linear range of the colorimetric method is 0-75 mu M with the limit of detection (LOD) of 0.5 mu M, while the linear range for the fluorescence method is 0-100 mu M with the LOD of 0.125 mu M. The Cu-Mn-O material has high potential in biomedical analysis of dopamine.