Modulating an in situ fluorogenic reaction for the label-free ratiometric detection of biothiols

Using a simple fluorogenic reaction and the inner filter effect, a label-free ratiometric method for biothiol detection is developed. The reaction between dopamine and resorcinol can generate azamonardine with strong fluorescence. Since the absorption spectrum of azamonardine overlaps with the excitation spectrum of the mercaptopropionic acid-stabilized CdTe quantum dots (MPA-CdTe QDs), the emission of QDs can be quenched via the inner filter effect in the presence of azamonardine. Biothiols can inhibit the above fluorogenic reaction, resulting in the weakening of the fluorescence of azamonardine and the recovery of the emission of MPA-CdTe QDs. The fluorescence intensity ratio of azamonardine to MPA-CdTe QDs can be used to detect biothiols. This approach exhibited a linear trend to the biothiol concentrations in the range of 2 μM to 12 μM, with a limit of detection of 0.6 μM (S/N = 3). This ratiometric analysis strategy was further applied to detect biothiols in human serum samples, showing their great application potentials in real biological samples. The constructed method is simple, easy to prepare, and low-cost.