Highly Sensitive Detection of Proteins Based on Metal-Enhanced Fluorescence with Novel Silver Nanostructures

We present a highly sensitive metal enhanced fluorescence (MEF) method based on a novel silver nanostructure fabricated with Cy5-functionalized silver nanoparticles (AgNPs) and AgNO3. The analytical performance has been demonstrated by microarray detection of streptavidin (SA) and human IgE. The fluorescence intensity can be enhanced substantially with the combined use of AgNPs and fluorescence enhanced solution (FES). Aptamers have been used for the preparation of Tag-C, which demonstrate IgE detection from 0.5 ng/mL to 16 ng/mL, and the limit of detection is determined to be 0.25 ng/mL. SEM images show nanogaps exist in the aggregated silver nanoparticles and the nanogaps allow for the trap of fluorophores in the nanostructures that emit brighter light upon excitation. The silver nanostructures formed by Tags and FES proved to be an excellent platform for MEF of fluorophores whose excitation and emission occurred between 436 nm and 1000 nm. Finite-difference time-domain (FDTD) simulation has been carried out to confirm the enhanced electromagnetic field inside silver nanostructures, leading to strong overlap/resonance coupling and eventual fluorescence enhancement.