Significant quantum yield enhancement for near infrared fluorescence dyes by silica templated silver nanorods

Abstract

Silver's inherent optical properties of low absorption cross section, over a broad wavelength range, makes it an attractive material for use in biosensing. We report herein a unique silica template method to synthesize cetrimonium bromide free silver nanorods (AgNRs). The application of AgNRs in metal enhanced fluorescence (MEF) was explored by immobilizing visible/near-infrared (NIR) fluorescent dyes on AgNR assembled substrates exhibiting broadband optical properties. Theoretical modeling was performed to analyze the nanoscale “chaotic nature” of the AgNR substrates, showing that the plasmon band shifts and broadening were attributed to the resonance coupling between assembled nanorods with different conformations. The quantum yield (QY) of NIR dye Alex Fluor 790 was increased dramatically from 4% to 84%, with total fluorescence enhancement up to two orders of magnitudes. In addition, AgNR substrates can also amplify fluorescence emissions from high quantum yield dyes, nearly 10-fold for Alexa Fluor 647 (QY:33%) and threefold for Alexa Fluor 488 (QY:92%). The AgNR demonstrates the capability of dramatically enhancing NIR dye's QY, holding great potential for building up an ultra-sensitive fluorescence bioassay platform for early diagnosis of diseases.