Sensing of cocaine using polarized optical microscopy by exploiting the conformational changes of an aptamer at the wate
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ORIGINAL PAPER
Sensing of cocaine using polarized optical microscopy by exploiting the conformational changes of an aptamer at the water/liquid crystal interface Shihong Wang 1 & Guannan Zhang 1 & Qianshan Chen 1 & Jun Zhou 1 & Zhaoyang Wu 1 Received: 10 May 2019 / Accepted: 19 September 2019 # Springer-Verlag GmbH Austria, part of Springer Nature 2019
Abstract 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 cocainebinding 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. Keywords Liquid crystal biosensor . Conformation transition . Optical images . Anchoring transition . Optical signal . Fluorescence spectra . Circular dichroism . Average grayscale value . Urine
Introduction Cocaine is initially used as a topical anesthetic, but at the same time, it is also one of the most dangerous and illegal drugs. The abuse of cocaine causes instantaneous and overwhelming stimulation on central nervous system and severe side effects on human, such as organ damage and human immunodeficiency [1]. Up to now, many analytical techniques for cocaine detection have been developed, such as colorimetry [2], electrochemical analysis [3, 4], fluorometry [5–7] and surfaceenhanced Raman spectroscopy (SERS) [8], and some can even be used in real sample detection, which acquires impressive results. However, these methods always tend to require Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00604-019-3855-1) contains supplementary material, which is available to authorized users. * Zhaoyang Wu [email protected] 1
State Key Laboratory of Chemo/Biosensing and Chemometrics, College of Chemistry and Chemical Engineering, Hunan University, Changsha 410082, People’s Republic of China
complicated response substrates or labeled species for the generation of signals. Thus, it is still a compelling goal to achieve real-time and sensitive detection for cocaine. Liquid crystals (LCs) are sensitive functional soft materials with unique physical properties such as surface anchoring, elasticity and birefringence. These properties make the LCs useful as the responsive substrates in the biochemical analysis field. Furthermore, there is no need for complicated laboratory instruments while the LCs a
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