A new protein A assay based on Raman reporter labeled immunogold nanoparticles.

A unique, sensitive, highly specific, and photobleaching-resistant immunoassay system utilizing gold nanoparticles and surface-enhanced Raman scattering (SERS) is described. This new system, featuring a capability of bifunctional analysis, is manufactured by chemisorption of antibody immunoglobulin G (IgG) on gold nanoparticles (AuNP), followed by coupling the Raman-active reporter molecule, 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB) to the surface of IgG-AuNP. The adsorbed DTNB molecules exhibit strong Raman signals via both electromagnetic and chemical enhancement. The narrow spectral widths and high photostability assure the system to be an excellent detection label. This SERS-based immunoassay is applied to the detection of protein A, which is a specific surface antigen of Staphylococcus aureus. A working curve is obtained by plotting the intensity of the SERS signal of symmetric NO(2) stretching of DTNB at 1,333 cm(-1) versus the concentration of the analyte (antigen). A dynamic range of two to three orders of magnitude and a detection limit of 1 pg/mL of protein A are achieved.

A filter-like AuNPs@MS SERS substrate for Staphylococcus aureus detection.

An accurate, highly sensitive and rapid identification assay of cells is extremely important in areas such as medical diagnosis, biological research, and environmental monitoring. Laboratory examinations of clinical isolates require time-consuming and complex processes to identify the colony count, with approximately 10(6)-10(8) cells needed for the characterization of strains. In the present study, a highly sensitive SERS filter-like substrate is prepared with AuNPs embedded in mesoporous silica (denoted as AuNPs@MS) synthesized by a simple one-spot method, and an example of its use for the filtration and concentration of analytes from aqueous samples is reported. In an application for Staphylococcus aureus SERS discrimination, the results show that the target cells can be concentrated on the filter-like AuNPs@MS substrates within a few seconds, with much better reproducibility with regard to the SERS spectra that are obtained. The experimental findings suggest that the AuNPs@MS substrate supports much higher intensity with more distinguishable peaks compared to Au/Cr-coated substrate, and the reproducibility is also significantly improved. The substrates investigated in this study generated 900 times more SERS signals at a concentration of 10(6)CFU/mL in the detection of S. aureus on mesoporous silica (Au wt%=0) when using AuNPs@MS with 16 wt% AuNPs. The limitation of this filter-like SERS substrate can be applicable for small volume samples (few to hundred microliter).