A highly sensitive dual-readout assay based on gold nanoclusters for folic acid detection

We describe a sensitive fluorometric and colorimetric dual-readout probe for folic acid (FA). It is based on the use of the gold nanoclusters (AuNCs) and cysteamine-modified gold nanoparticles (cyst-AuNPs). The bovine serum albumin stabilized AuNCs exhibit strong fluorescence emission at 652 nm. Upon addition of cyst-AuNPs, the fluorescence intensity of the AuNCs showed dramatic decrease due to the surface plasmon enhanced energy transfer process. This is due to an FA-induced aggregation of the cyst-AuNPs which shifts the absorption peaks from 530 to 670 nm. Thus, the surface plasmon enhanced energy transfer between cyst-AuNPs and AuNCs is weakened and the fluorescence intensity of AuNCs is recovered. The fluorescence intensity of the AuNCs/cyst-AuNPs system is proportional to the concentration of FA in the range from 0.11 to 2.27 mu mol L-1. The dual-readout probe reported here was successfully applied to the determination of FA in spiked serum samples and folic acid tablets.