Complementary Surface-Enhanced Resonance Raman Spectroscopic Biodetection of Mixed Protein Solutions by Chitosan- and Silica-Coated Plasmon-Tuned Silver Nanoparticles

Abstract

Silver nanoparticles with identical plasmonic properties but different surface functionalities are synthesized and tested as chemically selective surface-enhanced resonance Raman (SERR) amplifiers in a two-component protein solution. The surface plasmon resonances of the particles are tuned to 413 nm to match the molecular resonance of protein heme cofactors. Biocompatible functionalization of the nanoparticles with a thin film of chitosan yields selective SERR enhancement of the anionic protein cytochrome <i>b</i>₅, whereas functionalization with SiO₂ amplifies only the spectra of the cationic protein cytochrome <i>c</i>. As a result, subsequent addition of the two differently functionalized particles yields complementary information on the same mixed protein sample solution. Finally, the applicability of chitosan-coated Ag nanoparticles for protein separation was tested by in situ resonance Raman spectroscopy