LAUSR

Here, we report gold nanoparticle-coated starch magnetic beads (AuNP@SMBs) which were prepared by in situ synthesis of AuNPs on the surface of SMBs. Upon functionalization of the surface with specific antibody, the immuno-AuNP@SMBs were found to be effective in separating and concentrating the target pathogenic bacteria, E. coli O157:H7, from an aqueous sample as well as providing hotspot for SERS-based detection. We employed bi-functional linker protein, 4X-gold binding peptide-tagged Streptococcal protein G (4GS), to immobilize antibodies on AuNP@SMBs and AuNPs in oriented form. The linker protein also served as a Raman reporter, exhibiting a strong and unique fingerprint signal during the SERS measurement. The amplitude of SERS signal was shown to have a good correlation with the concentration of target bacteria ranging from 10^0 - 10^5 CFU/ml. The detection limit was determined to be as low as a single cell, and the background signals derived from non-target bacteria were negligible due to the excellent specificity and colloidal stability of the immuno-AuNP@SMBs and SERS tags. The highly sensitive nature of the SERS-based detection system will provide a promising means to detect the pathogenic microorganisms in food or clinical specimen.