Fluorescence Enhancement of IgG-FITC Based on Surface Plasmon Resonance of Ag@SiO₂ Nanoparticles as Application of Biomarker

Abstract

Ag@SiO₂ nanoparticles with the core-shell structure have been prepared, of which the silver core was about 50 nm and the thickness of silica shell was approximately 10 nm. In slightly alkaline aqueous solution (pH = 8), through electrostatic force between cationic polymer PDDA (i.e., poly-diallyldimethylammonium chloride) and the obtained Ag@SiO₂ nanoparticles, PDDA molecules were fixed on the surface of Ag@SiO₂ nanoparticles. The prepared Ag@SiO₂/PDDA nanoparticles have both rich positive surface charges and rich micro-holes of silica shell. Based on micro-hole adsorption, the small molecule FITC (i.e., fluorescein isothiocyanate) marking on IgG (i.e., immunoglobulin) was adsorbed into the rich microholes of silica shell; at the same time, the negatively charge macromolecule IgG marked by FITC was firmly fixed on the rich positive charges surface of Ag@SiO₂/PDDA nanoparticles by electrostatic interaction. And then, Ag@SiO₂/PDDA/IgG-FITC fluorescent nanoparticles with the SPR fluorescence enhancement were prepared. The shell-type SiO₂/PDDA/IgG-FITC nanoparticles were obtained by dissolving the silver core in the prepared core-shell Ag@SiO₂/PDDA/IgG-FITC nanoparticles by using H₂O₂. Compared with the shell-type nanoparticles, the fluorescence intensity of Ag@SiO₂/PDDA/IgG-FITC was enhanced 1.7 times. The prepared Ag@SiO₂/PDDA/IgG-FITC nanoparticles have both SPR-based fluorescence enhancement ability and the surface distributing IgG–based obvious advantages including good biocompatibility and easy marking with other biomolecules.

Keywords:

• Fluorescence enhancement
• IgG-FITC
• Nanoparticles
• Surface plasmon resonance

Acknowledgments

Z.-Y. Hu and J.-H. Tang contributed equally to this work.

This research was supported by grants from the National Natural Science Foundation of China (Grant no. 81001686), The Project Funded of the Priority Academic Program Development of Jiangsu Higher Education Institutions, and Jiangsu Province Projects of Innovative Research of university graduate students in 2011 (Grant no. CX2211-0113).