Fluorescence spectral detection of cysteine based on the different medium-coated gold nanorods-Rhodamine 6G probe: From quenching to enhancement

Au nanoparticles-based fluorescence quenching has been widely used for many analytes due to its high sensitivity and rapid response. However, the effects of different coating agents of Au nanorods on the assays performance remain unclear. For the first time, we demonstrated that the coating agents play a significant role in Au nanorods-based fluorescence quenching and recovery on Rhodamine 6G (R6G). Polystyrenesulfonate (PSS)-coated Au nanorods could almost totally quench the fluorescence intensity of R6G, whereas cetyltrimethyl ammonium bromide (CTAB)-coated Au nanorods and bare Au nanorods only have little effect on the fluorescence of R6G. The addition of cysteine to PSS-coated Au nanorods-R6G makes the fluorescence recover gradually, even greater than the original fluorescence intensity of R6G. Thus the PSS-coated Au nanorods-R6G could be served as a fluorescent probe to detect cysteine. The fluorescence intensity change of PSS-coated Au nanorods-R6G probe is linear with logarithm of Cys concentration over the range from 0.01 to 2.5 μg/mL. The results provide theoretical guidance for further improving Au nanorods-based fluorescence quenching and detection of protein molecules by the fluorescence off-on mechanism.