Simple apparatus for polarization sensing of analytes

We describe a simple device for fluorescence sensing based on an unexpansiv e light source, a dual photocell and a Watson bridge. The emission is detec ted from two fluorescent samples, one of which changes intensity in respons e to the analyte. The emission from these two samples is observed through t wo orthogonally oriented polarizers and an analyzer polarizer. The latter p olarizer is rotated to yield equal intensities from both sides of the dual photocell, as determined by a zero voltage from the Watson bridge. Using th is device, we are able to measure fluorescein concentration to an accuracy near 2% at 1 mu M fluorescein, and pH values accurate to +/-0.02 pH units. We also use this approach with a UV hand lamp and a glucose-sensitive prote in to measure glucose concentrations near 2 mu M to an accuracy of +/-0.1 m u M. This approach requires only simple electronics, which can be battery p owered. Additionally, the method is generic, and can be applied with any fl uorescent sample that displays a change in intensity. One can imagine this approach being used to develop portable point-of-care clinical devices. (C) 2000 society of Photo-Optical Instrumentation Engineers. [S0091-3286(00)00 608-5].