US Patent 7381531 Displacement assay for detection of small molecules

Complex of an anti-cocaine aptamer and the dye diethylthiotricarbocyanine behaves as a calorimetric sensor with attenuation in absorbance at 760 nm for cocaine in the concentration range of 2-5000 μM. Mechanistic studies indicate an intermolecular displacement of the dye as the mechanism of action of the sensor. As the dye is insoluble in buffer, cocaine binding can be detected as displaced dye precipitates and supernatant decolorizes.