Label-Free Liquid Crystal Biosensor Based on Specific Oligonucleotide Probes for Heavy Metal Ions

Abstract

In this study, to enhance the capability of metal ions disturbing the orientation of liquid crystals (LCs), we designed a new label-free LC biosensor for the highly selective and sensitive detection of heavy metal ions. This strategy makes use of the target-induced DNA conformational change to enhance the disruption of target molecules for the orientation of LC leading to an amplified optical signal. The Hg(2+) ion, which possesses a unique property to bind specifically to two DNA thymine (T) bases, is used as a model heavy metal ion. In the presence of Hg(2+), the specific oligonucleotide probes form a conformational reorganization of the oligonucleotide probes from hairpin structure to duplex-like complexes. The duplex-like complexes are then bound on the triethoxysilylbutyraldehyde/N,N-dimethyl-N-octadecyl (3-aminopropyl) trimethoxysilyl chloride (TEA/DMOAP)-coated substrate modified with capture probes, which can greatly distort the orientational profile of LC, making the optical image of LC cell birefringent as a result. The optical signal of LC sensor has a visible change at the Hg(2+) concentration of low to 0.1 nM, showing good detection sensitivity. The cost-effective LC sensing method can translate the concentration signal of heavy metal ions in solution into the presence of DNA duplexes and is expected to be a sensitive detection platform for heavy metal ions and other small molecule monitors.

Label-free immunodetection of the cancer biomarker CA125 using high-Δn liquid crystals

“…9,11,12 However, 5CB has seemingly been the only choice and little attention has been paid to the selection of LCs or to how the birefringence (i.e., optical anisotropy) Δn is correlated with the sensitivity in this type of label-free immunodetection. [13][14][15][16] In this work, we demonstrate that, in the detection of biomolecules, higher sensitivity can be well achieved through a more significant phase retardation using an LC mixture of larger birefringence material designated HDN (Δn ¼ 0.333) instead of the commonly applied nematogen 5CB (Δn ¼ 0.179).…”

“…[10][11][12][13][14][15][16] It is known that biomolecules immobilized or adsorbed on solid surfaces may trigger the reorientation of LC molecules, and the effect depends on the concentration of biomolecules. 10 When the reorientation of LCs occurs, 17 optical responses can be observed under a polarized optical microscope, whose two polarizers are placed after the light source and before the eyepiece or camera through the light passage.…”

Optical birefringence of liquid crystals for label-free optical biosensing diagnosis

“…In addition, this technique can measure the induced birefringence quantitatively without a spectrophotometer. 16 However, it should be noted that the technique presented cannot afford to provide the relevant optical images of LCs in real time, unlike that of Yang et al 17 The detection technique presented is a modified version of that reported in Nguyen et al 18 for quantitative measurement of optical birefringence. Unlike the reported optical technique that used the combined effects of optical intensity and birefringence in Nguyen et al 18 we can, however, extract only the birefringence information in this work to estimate LCs' orientations subject to the properties of interface where biological molecules are immobilized.…”

“…Recently, our group has reported optical birefringenceassisted sensing platform for label-free optical biosensing with the aid of a plasmonic sensing head, where combined effects of optical intensity and birefringence were measured for quantitative diagnosis of analytes with the minimum resolvable refractive index of approximately 10 -6 RIU. 17 In this paper, we present an optical sensing system with an optical cell that contains LCs of 4-cyano-4′-pentylbiphenyl (5CB) for a quantitative optical biosensing without a spectrophotometer or a retardation compensator. The key elements that make the detection system relatively compact include a rotatable half-wave plate (λ/2), a polarizing beam splitter, and a balanced detector (BD) that replaces a photodetector in a conventional system.…”

Applications of metal ions and liquid crystals for multiplex detection of DNA

“…For example, Abbott's group reported LC sensors for detecting peptides, lipids and other chemical compounds [2][3][4][5][6][7]. Other groups also developed a series of LC sensors for the detection of DNA, proteins and small molecules including thiol, amines and metal ions [8][9][10][11]. An interesting observation arising from these studies is that when a thin layer of LC is in contact with a liquid or a solid interface, the orientation of LC becomes very sensitive to ionic species (proton, electrolytes, and metal ions) present at the interface [12][13][14].…”