title: Cetyltrimethylammonium bromide-modified spherical and cube-like gold nanoparticles as extrinsic Raman labels in surface-enhanced Raman spectroscopy based heterogeneous immunoassays.
abstract: This paper reports on the characterization and preliminary comparison of gold nanoparticles of differing surface modification and shape when used as extrinsic Raman labels (ERLs) in high-sensitivity heterogeneous immunoassays based on surface enhanced Raman scattering (SERS). ERLs are gold nanoparticles coated with an adlayer of an intrinsically strong Raman scatterer, followed by a coating of a molecular recognition element (e.g., antibody). Three types of ERLs, all with a nominal size of approximately 30 nm, were fabricated by using spherical citrate-capped gold nanoparticles (sp-cit-Au NPs), spherical CTAB-capped gold nanoparticles (sp-CTAB-Au NPs), or cube-like CTAB-capped gold nanoparticles (cu-CTAB-Au NPs) as cores. The performance of these particles was assessed via a sandwich immunoassay for human IgG in phosphate buffered saline. The ERLs fabricated with sp-CTAB-Au NPs as cores proved to be more than 50 times more sensitive than those with sp-cit-Au NPs as cores; the same comparison showed that the ERLs with cu-CTAB-Au NPs as cores were close to 200 times more sensitive. Coupled with small differences in levels of nonspecific adsorption, these sensitivities translated to a limit of detection (LOD) of 94, 2.3, and 0.28 ng/mL, respectively, for the detection of human IgG in the case of sp-cit-Au NPs, sp-CTAB-Au NPs, and cu-CTAB-Au NPs. The LOD of the cu-CTAB-Au NPs is therefore approximately 340 times below that for the sp-cit-Au NPs. Potential applications of these labels to bioassays are briefly discussed.
authors.affiliation: Department of Chemistry, University of Utah, Salt Lake City, Utah 84112-0850, USA.
authors.forename: Radha
authors.initials: R
authors.lastname: Narayanan
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Lipert
authors.forename: Marc D
authors.initials: MD
authors.lastname: Porter
mesh_terms: D000077286:Cetrimonium; D002593:Cetrimonium Compounds / Q000737:chemistry*; D006046:Gold / Q000737:chemistry*; D007118:Immunoassay / Q000379:methods*; D053768:Metal Nanoparticles; D046529:Microscopy, Electron, Transmission; D013056:Spectrophotometry, Ultraviolet; D013059:Spectrum Analysis, Raman / Q000379:methods*; D013499:Surface Properties
chemical_list: D002593:Cetrimonium Compounds; D006046:Gold; D000077286:Cetrimonium