LAUSR

Abstract A fluorescent and colorimetric dual-mode “light-on” assay for the detection of dopamine (DA) was developed based on Fe3+-H2O2-OPD system. In general, Fe3+ could catalyze the H2O2-mediated oxidation of colorless and nonfluorescent o-phenylenediamine (OPD), and the resultant 2,3-diaminophenazine (DAP) exhibits a visible yellow color and yellow fluorescence. However, the reaction rate is extremely slow. By comparison, the introduction of DA can trigger a typical Fenton reaction that generates hydroxyl radical (−OH) continuously, thus increasing the conversion rate of OPD to DAP. Correspondingly, both color and fluorescence of the sensing system are enhanced obviously. On the basis of this fact, a sensor with dual readout for the detection of DA was established via measuring the fluorescent and colorimetric signals of the Fe3+-H2O2-OPD system. The linear ranges were 0.05–20 mM and 0.10–18 mM, and the detection limits were calculated to be 15 and 65 nM (S/N = 3) for fluorescent and colorimetric detection, respectively. The proposed dual-readout method features with simplicity, high sensitivity, visualization and good accuracy. Moreover, the method has been successfully applied to the detection of DA in human urine with satisfactory results.