An immobilized gold nanoparticle sensor for label free optical detection of biomolecular interactions

We present a new label free optical technique to study biomolecular interactions in real time on a surface. This method monitors changes in the absorbance spectrum of a monolayer of gold on glass as a function of biomolecular binding. Gold nanoparticles with a diameter of 13 nm were chemisorbed onto an amine-terminated glass surface. The absorbance spectrum of the monolayer exhibited both a red shift as well as an increase in the absorbance at peak wavelength as a function of bulk solution refractive index. The increase in absorbance at 550 nm was employed to study the kinetics of fibrinogen adsorption on the immobilized monolayer. The results obtained with the absorbance sensor were compared with those obtained using conventional SPR. This sensor is attractive because of its simplicity: gold nanoparticles are easily prepared with high reproducibility, they can be easily immobilized on glass, and their absorbance spectrum can be easily measured using widely available UV-vis spectrophotometers. Furthermore, this technique should be easily amenable to the design of chips in an array format for application in high-throughput immunoassays and proteomics.