Estrogen fluoroimmunoassay with a fluorimeter designed for low-intensity light detection

A small, highly sensitive, inexpensive fluorimeter for the detection of very low fluorescence intensities for analytical and clinical purposes is described. High sensitivity is achieved by use of an inexpensive continuous wave laser with a power of a few milliwatts. The optical arrangement of the instrument has been thoroughly designed so that the effects of Rayleigh and Raman scattering are minimized. Fluorescence is dected through optical filters with a side-on photomultiplier. Concentrations of rhodamine B in ethanol as low as 10^?11 M can be measured. To use this instrument for a fluoroimmunoassay of urinary estrogens (10^?9?10^?7 M), a purified monoclonal IgG, raised against estradiol, was labelled with RITC (rhodamine isothiocyanate) in a 1:1 molar ratio. It was possible to measure IgG-RITC concentrations between 10^?9 and 10^?10 M with good accuracy and reproducibility.