Multiplexed lateral flow immunoassays using high photostability gap-enhanced Raman nanotags: Highly sensitive, rapid, efficient and portable point-of-care tests.

Sensitive and multiplexed point-of-care tests (POCTs) with accurate quantitative ability are urgently needed for early diagnostic of infectious diseases and myocardial injury. In this study, we developed a unique surface-enhanced Raman scattering-based lateral flow immunoassay (LFIA) for the simultaneous detection of multiplexed biomarkers through the integration of ultrahigh photostability gap-enhanced Raman tags (GERTs), Raman comprehensive full-spectrum analysis, and customized portable Raman detectors. Our results demonstrated that the detection limit for quantitative analysis of cardiac troponin I (cTnI) using GERTs was approximately 0.65 pg mL-1; this value was at least one order of magnitude more sensitive than conventional fluorescent LFIAs, and the use of these GERTs is expected to address the dilemma of the low sensitivity of LFIAs and their inability to quickly diagnose patients with critical myocardial infarction onsite. In addition, we successfully achieved specific detection of the recombinant SARS-CoV-2 spike protein (RSSP), influenza A virus (FluA) and influenza B virus (FluB) on a single test (T) line simultaneously using three kinds of GERTs. Compared with traditional colloidal gold, the detection sensitivity was improved by 2-3 orders of magnitude. Notably, this highly sensitive LFIA method had a short detection time of only 15 min when a more practical and affordable small portable Raman detector was used and could be used to facilitate the development of rapid, ultrasensitive and quantitative POCTs in analytical chemistry and clinical applications.