Lighting up Plasmonic Nanostar Colloids for Metal-Enhanced Fluorescence under Two-Photon Near-Infrared Excitation

Abstract

Literature reports detail the theory for strong electric-field enhancements sustained and localized on gold nanostars (NSs). The enhanced fields are expected to alter the fluorescence of nearby fluorophores. However, there are very few literature reports on experimental evidence for enhanced fluorescence from dyes bound to gold NSs. Furthermore, the literature lacks experimental studies on metal-enhanced fluorescence under near-infrared (NIR) two-photon excitation. In our work, a nanoassembly was made with a NS at the core, then coated with avidin followed by biotinylated-DNA-linkers that hybridized to different Cy3-labeled DNA strands. We will discuss experimental results on physical insights including: (1) how the nanoassembly synthesis conditions and dye orientation affected the fluorescence enhancement and (2) how the NSs affected the organic fluorophore’s photostability—both under NIR two-photon excitation. We observed enhancement factors ranging from 1.2 to 3.5 depending on the nanoassembly synthesis conditions. A biotin displacement experiment supported the fluorescence enhancement results. Our work contributes new knowledge and empirical insights that will enable advances in the field of colloidal dye NS-based applications.