Abstract
In this study, a novel liquid crystal (LC) biosensor was developed for the highly sensitive and selective detection of Cd2+ based on Cd2+ inducing the bending of PS-oligo. This strategy makes use of the DNA conformational change to enhance the disruption of orientation of LC leading to an amplified optical signal. DNA containing-SH was bound on the glass slide of the LC cell modified with the DMOAP/APTES. The DMOAP can effectively induce the homeotropic alignment of LC. In the presence of Cd2+, Cd2+ can induce DNA to bend and become a 2 nm spherical structure, which can greatly disrupt the orientational arrangement of LC, resulting in the correspond changes of the optical image of LC cell birefringent under the polarizing microscope. When the Cd2+ concentration is low to 0.1 nM, the optical signal of LC biosensor has an obvious change. But in the absence of Cd2+, there is no orientational response of LC and the optical image under the polarizing microscope is still a uniform dark background. Thus, this LC sensing method has a sensitive and clear distinction between positive and negative results and offers a highly sensitive detection of Cd2+ with a low detection limit down to 0.1 nM.
Highlights
Cadmium (Cd) is a heavy metal environmental toxicant which is widely present in air, soil, water and food
To improve the signal-to-background contrast, we studied the background signal affected by the self-assembling modification of dimethyl-N-octadecyl-3-aminopropyltrimethoxysilyl chloride (DMOAP)/APTES mixture with different volume ratio
When the volume ratio of DMOAP/APTES is further increased to 1:10 or 1:5, the image shows a uniform dark background and appears a cross diffraction spots under the cone light mode while the bright spots in the optical images disappeare completely (Figure 2(d) and Figure 2(e)), which proves that liquid crystal (LC) molecules are uniform homeotropic alignment
Summary
Cadmium (Cd) is a heavy metal environmental toxicant which is widely present in air, soil, water and food. Wu [17] group successfully developed a high-sensitivity LC biosensor for Hg2+ with detection limit 0.1 nM using T-T mismatch aptamers as Hg2+ recognition molecules and LC (Liquid Crystal, LC) molecules as signal transducer and signal amplification molecules. This sensor made skillfully the high selectivity of aptamers to combine with high sensitivity of LC molecules, which had some advantages such as simple manufacture, no optical aids and visible results observed directly by naked eyes. Combining the DNA specificity and the advantages of LC biosensors, we exploit a high specificity and sensitivity LC biosensing technique using DNA as specific recognition for Cd2+ detection
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