Polyethylenimine-capped silver nanoclusters as a fluorescence probe for highly sensitive detection of folic acid through a two-step electron-transfer process.

A highly sensitive folic acid (FA) detection method based on the fluorescence quenching of polyethylenimine-capped silver nanoclusters (PEI-AgNCs) was put forward. In the sensing system, FA and PEI-AgNCs were brought into close proximity to each other by electrostatic interaction, and a two-step electron-transfer process, in which the electron was transferred from FA to AgNCs through PEI molecule, led to fluorescence quenching. The fluorescence quenching efficiency of PEI-AgNCs was linearly related to the concentration of FA over the range from 0.1 nM to 2.75 μM. Good linear correlation (R(2) = 0.9981) and a detection limit of 0.032 nM were obtained under optimum conditions. Moreover, the proposed method was used for the determination of FA in real samples with satisfactory results, and those coexistent substances could not cause any significant decrease in the fluorescence intensity of AgNCs. Therefore, the proposed research system is of practical significance and application prospects.