Nitrogen-doped carbon quantum dots as a "turn off-on" fluorescence sensor based on the redox reaction mechanism for the sensitive detection of dopamine and alpha lipoic acid

A simple and reliable fluorescence sensing strategy, which depends on the strong fluorescence emission of nitrogen-doped carbon quantum dots (N-CQDs) and efficient catalytic oxidation of tyrosinase (Tyr), was demonstrated for the sensitive detection of dopamine (DA) and alpha lipoic acid (ALA). Under optimized conditions, the fluorescence intensity of N-CQDs was easily quenched by dopamine oxidation product dopaquinone with the addition of Tyr. When ALA was introduced into the sensing system, ALA could inhibit and reduce the oxidation process of DA, resulting in the fluorescence recovery of N-CQDs. This sensing platform showed a sensitive relationship to the DA and ALA concentrations within certain ranges of 0.05-15 and 0.5-55 mu M, and low detection limits of 0.035 and 0.39 mu M, respectively. Given the above mechanisms, the proposed biosensor was utilized for the detection of DA and ALA in real samples with satisfactory results. Moreover, we successfully measured ALA through spectrometry, which is expected to provide valuable information in medical and disease diagnosis.