Rhodamine-assisted fluorescent detection for lysozyme based on the inner filter effect of gold nanoparticles

This work proposed a rapid, sensitive and low-cost fluorescent assay to achieve lysozyme detection in the presence of gold nanoparticles (AuNPs) and rhodamine 6G (R6G). When R6G and AuNPs aqueous solutions were mixed, fluorescence of R6G was quenched via the inner filter effect (IFE). Whereas, upon addition of lysozyme into AuNPs solution, lysozyme with positive charge bound to the negatively-charged AuNPs, leading to the aggregation of AuNPs. After that, R6G as a fluorescence indicator was introduced into the above-mentioned mixture. In this case, weakened IFE occurred between AuNPs and R6G. It is found that the fluorescent intensity of R6G enhanced as the concentration of lysozyme increased. The optimum concentrations of R6G and AuNPs were studied by fluorescence spectrophotometer. Based on the above, lysozyme could be detected and its detection limit is about 1 ng/mL. Quantitative evaluation of lysozyme could be performed within a concentration range of 0.1–10 μg/mL. This strategy was also applied to monitor lysozyme in urine samples with a pleased result. It provides a great promise for the diagnosis and prognosis by fluorescence for lysozyme-related diseases.