Label-Free Direct Detection of 4MU by Plasmon Enhanced Fluorescence Sensing Based on Ag@SiO₂ NPs

As the primary active ingredient in Compound Dantong Capsules (CDC), 4MU is commonly used to treat cholecystitis, cholangitis, post-gallbladder syndrome, and related symptoms. Current analytical techniques for detecting 4MU content face critical limitations, including insufficient selectivity, complex procedures and high costs. An urgent need exists for a simple, economical, and selective method for label-free direct detection of 4MU. Herein, a label-free fluorescence sensing system based on plasmon enhanced fluorescence (PEF) was developed employing Ag@SiO₂ nanoparticles (Ag@SiO₂NPs). Compared to pure 4MU solution, the 4MU-Ag@SiO₂ system exhibited significantly enhanced fluorescence intensity, achieving a maximum enhancement factor of 31.296 ± 0.864. Capitalizing on the PEF effect, the concentration of 4MU was effectively determined within the range of 12.5 nM to 50 µM, while reducing the limit of detection (LOD) from 1.03 nM to the remarkably low value of 0.16 nM. The method was also successfully applied to detect 4MU in Chinese patent medicine CDC samples, demonstrating strong correlation and reliability. The proposed fluorescence sensing system combines the advantages of being label-free, highly specific, stable and cost-effective by enhancing detection performance through the PEF effect, it offers significant potential for practical fluorescence detection applications in various fields.