A compact long-wavelength fluorescence detection system and its application to flow injection immunoassay

A compact and robust long-wavelength fluorescence detection system (LWFDS) has been constructed using a pulsed diode laser as the light source and a photodiode detector. The detection limits for naphthofluorescein (NF) and the cyanine dyes Cy5 and Cy5.5 at pH 8.8, determined using the LWFDS, were 1.0 × 10-10, 2.3 × 10-12 and 6.2 × 10-11M, respectively. These values compared favourably with data from a commercial research grade fluorescence spectrometer. The LWFDS instrument was used as the detector for a competitive heterogeneous flow injection immunoassay for α-interferon with Cy5 as the label. A calibration graph usable over the range 0.5-10 μg ml-1 α-interferon was obtained. The instrument demonstrated its potential for rapid ( <200s per sample) multi-analyte assays and for field monitoring.