Sensing of cocaine using polarized optical microscopy by exploiting the conformational changes of an aptamer at the water/liquid crystal interface
Liquid crystals (LCs) have the ability to transduce and amplify a molecular stimulus into optical signals due to their elastic and birefringence properties. An aptamer-based LC sensor for cocaine is described here. 3-Morpholinopropanesulfonic acid with amphipathic structure was used to establish recognition sites at a water/LC interface for the detection of cocaine. The cocaine-binding aptamer is formed at the interface. The conformation of the aptamer undergoes a change on binding cocaine, and this triggers the LCs anchoring transition from homeotropic to planar. Binding can also be detected by polarized optical microscopy. The fluorescence spectroscopy and circular dichroism results are used to prove that the conformation of aptamer changed from a hairpin structure to a special three-way junction structure on binding of cocaine at the interface. The assay works in the 1 nM to 10 μM cocaine concentration range and is specific.
KeywordsLiquid crystal biosensor Conformation transition Optical images Anchoring transition Optical signal Fluorescence spectra Circular dichroism Average grayscale value Urine
This study was financially supported by the National Natural Science Foundation of China (21675045 and 21874037) and the International Scientific and Technological Cooperation Projects of China (2012DFR40480).
Compliance with ethical standards
The author(s) declare that they have no competing interests.