Functional gold nanoparticle coated surfaces for CA 125 cancer biomarker detection

Abstract

Here we describe the detailed characterization of gold nanoparticle (Au Np) functionalized surfaces as a biosensing platform by studying a model streptavidin (SA)-biotin interaction. Conjugation of SA on Au Np immobilized on silicon (Si) and quartz surfaces and its interaction with biotin were characterized by X-ray photoelectron spectroscopy (XPS), UV-Vis spectroscopy, circular dichromism (CD) spectroscopy, and contact angle measurements. The immobilization method and atomic concentrations of Si 2p, Au 4f, S 2p, C 1s, N 1s, and O 1s of the resulting SA-biotin modified Si surface were determined by XPS. The CD spectrum and confocal microscopy imaging confirmed that step-by-step modification and bioconjugation can be monitored successfully. Such detailed and well-defined step-by-step characterization provides good information about the surface properties of biosensor platforms. In addition, the LSPR sensing ability of the Au Np based platforms was studied by using a model SA-biotin system. A 20 nm spectral red shift was detected when 150 nM SA was immobilized on to the Au Nps surface using the direct incubation/binding method on to the dry surface instead of the flow-injection method. The same platforms were also used to detect the CA 125 antibody-antigen system. Large spectral red shifts are very promising in terms of using these surfaces as LSPR biosensors.