S.P. Mulvaney, D.A. Kidwell, J.N. Lanese, R.P. Lopez, M.E. Sumera, E. Wei
US Naval Research Laboratory,
Keywords: lateral-flow immunoassays (LFIs or LFIAs), point-of-care, diagnostic technology, catalytic amplification, nanozyme
Summary:Lateral-flow immunoassays (LFIs or LFIAs) are a widely used point-of-care technology. They are most familiar as home-pregnancy tests, but are also employed for testing for a wide variety of diseases, biomarkers, and even small molecules Visually-read, LFIAs typical use colloidal gold or colored latex as the reporter elements for the recognition binding event. While simple to perform and easy to read, the sensitivity of LFIAs is ultimately limited by the extinction coefficients of the reporter elements as enough material must be localized to be visually observed. We have substituted specially-prepared, colloidal palladium for the colorimetric labels and use the palladium nanoparticles as a chemical catalyst to produce an easily-observable, stable, blue dye that localizes at the capture line. We term our test system cLFIA™ for catalytic LFIAs. Importantly, the catalyst is heat stable, functions at room temperature, under physical conditions, and results in multiple orders of magnitude increase in sensitivity with less than five additional minutes of development. Although blue is an optimum color for most biological assays, the dye chemistry is derived from color photography and hair dying products so that different colors can be produced, spanning the visual spectrum. The catalytic chemistry requires that three chemicals react with the palladium nanoparticle label, and we have designed the assay to incorporate all chemical elements onto the cLFIA™ test strip thereby requiring no additional steps to be performed by the user. The all-in-one nature of our cLFIA™ test strip design and the nature of the palladium conjugates we utilize sets this technology apart from other approaches using metal nanoparticles to amplify the signal of LFIAs. The preparation and characterization of the catalyst, the basis for the dye chemistry, and their facile use in cLFIA™ assays will be described.