AVS 50th International Symposium
    Nanometer Structures Friday Sessions
       Session NS+BI-FrM

Paper NS+BI-FrM6
Real-Time, Label Free Biosensing using Immobilized Gold Nanoparticles: Influence of Nanoparticle Size on Sensor Performance

Friday, November 7, 2003, 10:00 am, Room 317

Session: Nanotechnology and Biology
Presenter: N. Nath, Duke University
Authors: N. Nath, Duke University
A. Chilkoti, Duke University
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We recently demonstrated a label-free optical sensor to quantify biomolecular interactions in real-time that exploits the surface plasmon resonance effect exhibited by noble metal nanoparticles (nanoSPR). The sensor monitors changes in the extinction spectrum of a monolayer of gold nanoparticles on glass as a function of biomolecular binding. We have previously shown that 13 nm diameter gold nanoparticles can monitor the binding of streptavidin to biotin with a detection limit of 16nM. The performance of the biosensor is controlled by the size, shape and dielectric constant of the metal nanostuctures, and their interparticle spacing. As a first towards optimization of the nanoSPR sensor, we investigated the size of gold nanoparticles on sensor performance. Monodisperse gold nanoparticles were chemically synthesized with diameters ranging from 12 nm to 50 nm. The extinction spectrum of the monolayers of gold nanoparticles of all sizes exhibited both a red shift as well as an increase in the extinction at peak wavelength as a function of bulk solution refractive index. However, sensitivity, defined as change in extinction per unit change in bulk refractive index, increases with an increase in particle size and reaches a maximum value of 1.42 for a particle size of 39 nm. Second, the sensing volume of the immobilized gold nanoparticles, defined as the distance from the surface within which a bulk refractive index change will result in a change in the optical signal, increases with particle size and peaks for 39 nm diameter nanoparticles. Based on these results, an optimized sensor was fabricated using 39 nm gold nanoparticles, and its detection limit for biotin-streptavidin binding was found to be ~1 nM. NanoSPR on a chip is attractive for biosensing because of simple solution based assembly and ability to measure extinction spectrum using widely available UV-vis spectrophotometers.