Detection of protein molecules by surface-enhanced Raman spectroscopy-based immunoassay using 2-5 nm gold nanoparticle lables

Here we report the synthesis of 2–5 nm size gold nanoparticle labels for surface‐enhanced Raman Spectroscopy (SERS) based immunoassay to detect protein molecules. The Au nanoparticles were conjugated with fluorescein isothiocyanate (FITC) and goat anti‐h‐IgG (immunoglobin) and the resultant particles were used for the detection of h‐IgG. Commercially available nitrocellulose strip and silver enhancement method were used for SERS‐based immunoassays. The FITC acts as a Raman probe, and vibrational fingerprint of this molecule was used for the detection of h‐IgG in concentration ranging from 1 to 100 ng/µl. Our Raman probe is robust and small in size and has high water solubility with minimum steric effect during antigen–antibody binding. Copyright © 2007 John Wiley & Sons, Ltd.