Polarization-based sensing with a self-referenced sample

We describe a new method of fluorescence sensing based on fluorescence polarization. The sensor consists of two compartments, both of which contain the sensing fluorophore. One side of the sensor contains a constant concentration of analyte, an the other contains the unknown concentration. Emission from both sides is observed through polarizers, with the polarization from the sample being rotated 90° from that of the reference. Changes in the fluorescence intensity of the sample result in changes in the measured polarization for the combined emission. We show that this approach can be used to measure glucose and calcium using fluorophores which show analyte-dependent intensity changes, and no change in the spectral shape. Only a single fluorophore is required, this being the sensing fluorophore in both sides of the sensor. We also show that polarization sensing of glucose and calcium can be performed with visual detection of the polarization. In this case the only electronic component is the light source. These simple schemes can be used with a variety of analytes. The only requirement is a change in fluorescence intensity in response to the analyte.