SERS-based immunoassay using core–shell nanotags and magnetic separation for rapid and sensitive detection of cTnI.

We developed a highly sensitive and rapid SERS immunoassay for cardiac troponin I (cTnI), a biomarker for the diagnosis of acute myocardial infarction (AMI), using core–shell SERS nanotags. Here, covering a Ag shell on the Au core bound to Raman reporter molecule (4MBA) generates a large number of "hot spots", which have a strong Raman enhancement effect, and then they bind to antibodies to form SERS immunoprobes. In the presence of cTnI, SERS tags and capture probes form sandwich structures through immune responses, and then the immune complex is enriched by a specific reaction of streptavidin on the surface of magnetic beads with biotin. Finally, the concentration of biomarkers was quantified by detecting the characteristic Raman peak intensities of the Raman-reporter molecules. With this SERS immunization platform, the detection limit of cTnI was 9.80 pg mL⁻¹. Moreover, cTnI does not cross-react with non-specific proteins and has good specificity. Furthermore, SERS immunoassay combined with the proposed magnetic beads does not require complex separation procedures and detection was rapid. More importantly, the portable Raman instrument was used in this study, which can meet the requirements of the point-of-care test and small sample size (50 μL). To summarize, it is proved again that SERS immunoassay has good potential in the early diagnosis of AMI. [ABSTRACT FROM AUTHOR]