(680f) Development and Modeling of Single Particle SERS Assays

Nanoparticles have been synthesized from a variety of organic and inorganic materials and find use in fields as diverse as electronics, drug delivery, and bioassays.  Nanoparticle synthesis and surface modification provide a simple and reproducible method of preparing nanoscale surfaces.  Bioassays for the detection of DNA, antibodies and antigens have benefitted from the application of nanoparticles and  the introduction of nanoparticles has also accelerated the use of surface enhanced Raman spectroscopy (SERS) as a bioassay detection method.  Gold surfaces provide for facile attachment of biomolecules and gold plasmonic effects in the visible wavelength region make nanoparticles ideal for surface enhanced Raman spectroscopy (SERS) bioassays.  Single particle bioassays can be developed by incorporating magnetic capture and a gold functionalized surface into a single nanoparticle.  By using methods such as the polyol process, a magnetic cobalt core can be reduced in a diol solution and a gold shell can be deposited subsequently.  This produces a particle with the magnetic characteristics of cobalt, and the light scattering and biocompatible character of gold.  Single particle assay systems can simplify the collection and reading of target analytes in bioassays by allowing the collection of surface bound analyte from solution by the application of a magnetic field and the formation of a pellet with the particles for detection.  When coupled with Raman spectroscopy, only the analyte bound with a gold particle will produce a detectable signal due to the SERS effect. 

Gold colloids can provide a large surface area per unit volume and a mobile capture surface that reduces average diffusion distances for analytes in a bioassay solution.  Brownian motion of both the analyte and capture substrate also renders the assay less mass transport limited than surface based assays.  Surface assays have benefitted from models which elucidate the important physical parameters and their interrelationships, leading to reduced assay time, improved signal generation and improved limits of detection.  To further the development and understanding colloidal assays, modeling of the colloidal system could also produce similar gains by improving understanding of the system as well as improving performance, particularly single particle bioassays using surface enhanced Raman spectroscopy (SERS) for detection.  We present the preliminary modeling of solution based colloidal assays.