Catalytic lateral flow immunoassays (cLFIA™): Amplified signal in a self-contained assay format

Abstract

Lateral-flow immunoassays (LFIAs) are a widely used point-of-care technology because they are simple to perform and easy to read. LFIAs typically use colloidal gold or colored latex beads, however the sensitivity of LFIAs is ultimately limited by the label's extinction coefficients as enough material must be localized to be observed. Greater sensitivity requires visualization of fewer labels and herein we substitute palladium nanoparticles as a catalyst to produce a stable, blue indamine dye that precipitates at the capture line. We term our system cLFIA™ for catalytic LFIAs. The catalytic chemistry requires that three chemicals react with the palladium, and we have incorporate all three elements onto the cLFIA™ in the chemistry release fiber (CRF). With the CRF, cLFIA™ strips operate exactly as traditional LFIA strips, requiring no additional steps from the user, however the resulting lines are blue not red and provide much greater sensitivity. The all-in-one nature of cLFIA™ assays and the nature of the Pd conjugates we utilize sets this technology apart from other approaches that enhance LFIA sensitivity. We demonstrate that 2 nm Pd nanoparticles have a 40× catalytic advantage over 50 nm Pd-coated nanoparticles for our dye system. Our dye system is more robust than common peroxidase dyes (TMB), providing 8× signal and at a fast rate. Lastly, we demonstrate that the cLFIA™ approach is 1000× more sensitivity for detection of human chorionic gonadotropin than commercial pregnancy assays. The preparation of the palladium catalyst, the dye chemistry, and their facile use in cLFIA™ assays are described.