Fiber optic-based time-resolved fluorimetry for Immunoassays

Rare earth metal chelate fluorescent labels for immunoassays possess extremely long fluorescence lifetimes and permit the effective use of time-resolved detection. This is shown to be very important in fiber optic-based fluorimetry, which is a technique that ordinarily exhibits large signal backgrounds due to backscatter radiation. Using time-resolved detection to reject the backscatter radiation, the fiber optic-based limit of detection for Eu-2-naphthoyltrifluoroacetone is 10^-12 M; nearly three orders of magnitude lower than for the fiber optic-based measurement of the most common fluorescent label, fluorescein isothiocyanate. Commercially available Eu-chelate labeled reagents are used to demonstrate the potential utility of time-resolved fluorimetry in fiber optic-based immunoassays. Rabbit Immunoglobulin G (IgG) is covalently bonded to the distal end of quartz optical fibers prior to exposing to Eu-chelate labelled anti-rabbit IgG. The limit of detection for the assay is approximately 1 x 10^-4 mg/mL.