Aptamer-based colorimetric probe for cocaine.

Complex of an anti-cocaine aptamer and the dye diethylthiotricarbocyanine behaves as a colorimetric sensor with attenuation in absorbance at 760 nm for cocaine in the concentration range of 2-600 muM. 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 followed with the unaided eye as displaced dye precipitates and supernatant decolorizes.