Development of highly sensitive SERS-based assay platforms for sexual hormones and high-risk pathogens

Abstract

Surface-enhanced Raman scattering (SERS) is a powerful and ultrasensitive vibrational spectroscopic technique to analyze molecules near or on the surface of noble metal. SERS has been applied in a wide range of analysis, especially for biochemical analysis, since its first discovery in 1970s. The classic application is the direct measurement of various molecules that adsorbed on the surface of SERS substrate. The SERS signals can be detected at the SERS active sites due to electromagnetic and chemical enhancements, which are known as “hot spots”. This enhancement can greatly enhance the signals, especially at low concentration. In addition, SERS can avoid the photobleaching. In this work, SERS is used as an ultrasensitive detection technique in SERS-based immunoassay and SERS-based lateral flow assay. Owing to the ultrahigh sensitivity and multiplex detection capability, immunoassays using SERS have gained increasing attention in the numerous applications such as clinical diagnosis, environmental detection and other biochemical sensors. Based on the principle, various SERS-based platforms have been developed for ultrasensitive biochemical and chemical analysis. In chapter 2, we demonstrated a novel SERS-based competitive immunoassay technique for highly sensitive quantification of hormone estradiol (17β-estradiol, E2), which plays an important role in sexual development and serves as an important diagnostic biomarker of various clinical conditions. Particularly, the serum E2 concentration is very low (<10 pg/mL) in prepubertal girls. Accordingly, many efforts to develop a sensitive method of detection and quantification of E2 in human serum have been made. Nonetheless, current clinical detection methods are insufficient for accurate assessment of E2 at low concentrations (<10 pg/mL). Thus, there is an urgent need for new technologies with efficient and sensitive detection of E2 for use in routine clinical diagnostics. In this study, we introduce a new E2 assay technique using a surface-enhanced Raman scattering (SERS)-based detection method. The SERS-based assay was performed with 30 blood samples to assess its clinical feasibility, and the results were compared with data obtained using the ARCHITECT chemiluminescence immunoassay. Whereas the commercial assay system was unable to quantify serum levels of E2 lower than 10 pg/mL, the limit of detection of E2 using the novel SERS-based assay described in this study was 0.65 pg/mL. Thus, the proposed SERS-based assay has a strong potential to be a valuable tool in the early diagnosis of precocious puberty due to its excellent analytical sensitivity. In chapter 3, we reported a new SERS-based LFA for the rapid and highly sensitive detection of five pathogens for preparedness of bioterrorism, including BoN A, Y. pestis, F. tularensis, B. anthracis and V. virus. Recently, microbiological culture and colony counting, polymerase chain reaction (PCR), immunoassay or conventional lateral flow assay has been developed for the detection of pathogens including toxin, bacteria and virus. However, these methods cannot meet the requirement of rapid and highly sensitive detection because they need a long sample preparation time and also has limited detection sensitivity. With this new assay technique, highly sensitive detection and accurate quantitative analysis could be achieved through measuring the SERS signals of Raman reporter labeled AuNPs that accumulated in the test line of SERS-based LFA strip. This method needs a short assay time (15 min) and small volume of pathogens sample (40 μL) with high sensitivity. The LODs of BoN A, Y. pestis, F. tularensis, B. anthracis and V. virus could reach 18.5 pg/mL, 43.4 CFU/mL, 45.8 CFU/mL, 357 CFU/mL and 2.49×103 PFU/mL, respevtively, which were more sensitive than that of commercial rapid kits. We believe that the proposed SERS-based LFA has a strong potential to be a valuable tool in the early detection of specific pathogens due to its excellent analytical sensitivity.