Plasmon-enhanced Fluorescence Imaging With Silicon-based Silver Chips For Protein And Nucleic Acid Assay

Fluorescence immunoassay has the advantages of high sensitivity, quantification, rapid analysis and minimal damage to sample. However, the quantum yield of frequently-used fluorescent dye, especially in the near infrared wave band, is relatively low, which limits its practical application to a certain extent. Therefore, it is an important practical problem to improve the fluorescence intensity in fluorescence immunoassay technology. Metal enhanced fluorescence shows great potential for improving the sensitivity of fluorescence determination, which has been widely used in protein and nucleic acid detection for biosensor and bioassay applications. In comparison with the traditional glass-supported metal nanoparticles(MNPs), the introduction of a silicon substrate has shown to provide higher surface enhanced Raman scattering(SERS) effect due to the coupling between the MNPs and the semiconducting silicon substrate. In this work we further investigated the fluorescence-enhanced effect of the silicon-supported silver-island(Ag@Si) plasmonic chips, especially their practical applications in improving the traditional immunoassay items including the biotin-streptavidin based protein assay and the protein-/nucleic acid-labeled cell and tissue samples. The protein assay test shows a wavelength-dependent enhancement effect of the Ag@Si chip, with an enhancement factor ranging from 1.2(at 532 nm) to 57(at 800 nm). Moreover, for the traditional protein- and nucleic acid-labeled cell/tissue samples, the Ag@Si chip provides a fluorescence-enhancement factor of 3.0-4.1(at 800 nm) and a significant improvement in the signal/background ratio for the microscopy images. Such a good accommodation of the fluorescence-enhanced effect for the traditional immunoassay samples indicates broad applications of the Ag@Si chip in not only biological but also clinic fields.