Surface modification of alignment layer by ultraviolet irradiation to dramatically improve the detection limit of liquid-crystal-based immunoassay for the cancer biomarker CA125

Liquid crystal-assisted optical biosensor for early-stage diagnosis of mammary glands using HER-2

Breast cancer (BC) is one of the most commonly diagnosed cancers and the second leading cause of cancer mortality among women around the world. The purpose of this study is to present a non-labeled liquid crystal (LC) biosensor, based on the inherent feature of nematic LCs, for the evaluation of BC using the human epidermal growth factor receptor-2 (HER-2) biomarker. The mechanism of this sensing is supported by surface modification with dimethyloctadecyl [3-(trimethoxysilyl) propyl] ammonium chloride (DMOAP) encouraging the long alkyl chains that induce a homeotropic orientation of the LC molecules at the interface. To enhance the binding efficacy of more HER-2 antibody (Ab) on LC aligning agents, a simple ultraviolet radiation-assisted method was also used to increase functional groups on the DMOAP coated slides, thereby improving binding affinity and efficiency onto HER-2 Abs. The designed biosensor makes use of the specific binding of HER-2 protein to HER-2 Ab and disruption of the orientation of LCs. This orientation change leads to a transition of the optical appearance from dark to birefringent, enabling the detection of HER-2. This novel biosensor exhibits a linear optical response to HER-2 concentration in the wide dynamic range of 10^-6-10² ng/mL, with an ultra-low detection limit of 1 fg/mL. As a proof of concept, the designed LC biosensor was successfully investigated for the quantification of HER-2 protein in patients suffering from BC. Owing to the sensitivity, selectivity, and label-free detection, this biosensor may amplify the application of LC-based biosensors for the detection of most types of cancers.

A liquid-crystal aptasensing platform for label-free detection of a single circulating tumor cell

Circulating tumor cells (CTCs), which are shed from a primary site into the bloodstream and lead to distal metastases, are pivotal as a prognostic marker for evaluating the treatment response of cancer patients. One of the major challenges of detecting CTCs is their scarcity in blood. We report herein a label-free liquid crystal (LC) cytosensor by adopting an aptamer against epithelial cell adhesion molecule (EpCAM) to capture EpCAM-positive cancer cells. The optical and dielectric signals transduced from the interaction between LC and different numbers of captured breast cancer cells were investigated. A limit of detection (LOD) of 5 CTCs was resulted from the optical biosensing approach relying on texture observation and image analysis of the optical signal in polarizing micrographs. The LOD was further lowered to a single CTC in the dielectric approach by studying the real- and imaginary-part dielectric constants of LC at 1 kHz and 30 Hz as well as the relaxation frequency. The LC-based EpCAM-specific dielectric cytosensor was successfully applied to single-cell CTC detection in cancer cell-spiked human serum and whole blood. This platform demonstrates the potential of LC-based biosensing technologies in cellular-level detection and quantitation, which is crucial to the early diagnosis of cancer metastasis and progression.

State-of-the-Art Development in Liquid Crystal Biochemical Sensors

As an emerging stimuli-responsive material, liquid crystal (LC) has attracted great attentions beyond display applications, especially in the area of biochemical sensors. Its high sensitivity and fast response to various biological or chemical analytes make it possible to fabricate a simple, real-time, label-free, and cost-effective LC-based detection platform. Advancements have been achieved in the development of LC-based sensors, both in fundamental research and practical applications. This paper briefly reviews the state-of-the-art research on LC sensors in the biochemical field, from basic properties of LC material to the detection mechanisms of LC sensors that are categorized into LC-solid, LC–aqueous, and LC droplet platforms. In addition, various analytes detected by LCs are presented as a proof of the application value, including metal ions, nucleic acids, proteins, glucose, and some toxic chemical substances. Furthermore, a machine-learning-assisted LC sensing platform is realized to provide a foundation for device intelligence and automatization. It is believed that a portable, convenient, and user-friendly LC-based biochemical sensing device will be achieved in the future.

Quantitative Biosensing Based on a Liquid Crystal Marginally Aligned by the PVA/DMOAP Composite for Optical Signal Amplification

The working principle for a liquid crystal (LC)-based biosensor relies on the disturbance in the orderly aligned LC molecules induced by analytes at the LC-aqueous or LC-solid interface to produce optical signals that can be typically observed under a polarizing optical microscope (POM). Our previous studies demonstrate that such optical response can be enhanced by imposing a weak electric field on LCs so that they are readily tilted from the homeotropic alignment in response to lower concentrations of analytes at the LC-glass interface. In this study, an alternative approach toward signal amplification is proposed by taking advantage of the marginally tilted alignment configuration without applying an electric field. The surface of glass substrates was modified with a binary aligning agent of poly(vinyl alcohol) (PVA) and dimethyloctadecyl[3-(trimethoxysilyl)propyl] ammonium chloride (DMOAP), in which the amount of PVA was fine-tuned so that the interfacing LC molecules were slightly tilted but remained virtually homeotropically aligned to yield no light leakage under the POM in the absence of an analyte. Two nematic LCs, E7 and 5CB, were each sandwiched between two parallel glass substrates coated with the PVA/DMOAP composite for the detection of bovine serum albumin (BSA), a model protein, and cortisol, a small-molecule steroid hormone. Through image analysis of the optical appearance of E7 observed under the POM, a limit of detection (LOD) of 2.5 × 10−8 μg/mL for BSA and that of 3 × 10−6 μg/mL for cortisol were deduced. Both values are significantly lower than that obtained with only DMOAP as the alignment layers, which correspond to signal amplification of more than six orders of magnitude. The new approach for signal amplification reported in this work enables analytes of a wide range of molecular weights to be detected with high sensitivity.

Technological Advancements in Bio‐recognition using Liquid Crystals: Techniques, Applications, and Performance

The application of liquid crystal (LC) materials has undergone a modern-day renaissance from its classical use in electronics industry as display devices to new-fangled techniques for optically detecting biological and chemical analytes. This review article deals with the emergence of LC materials as invaluable material for their use as label-free sensing elements in the development of optical, electro-optical and electrochemical biosensors. The property of LC molecules to change their orientation on perturbation by any external stimuli or on interaction with bioanalytes or chemical species has been utilized by many researches for the fabrication of high sensitive LC-biosensors. In this review article we categorized LC-biosensor based on biomolecular reaction mechanism viz. enzymatic, nucleotides and immunoreaction in conjunction with operating principle at different LC interface namely LC-solid, LC-aqueous and LC-droplets. Based on bimolecular reaction mechanism, the application of LC has been delineated with recent progress made in designing of LC-interface for the detection of bio and chemical analytes of proteins, virus, bacteria, clinically relevant compounds, heavy metal ions and environmental pollutants. The review briefly describes the experimental set-ups, sensitivity, specificity, limit of detection and linear range of various viable and conspicuous LC-based biosensor platforms with associated advantages and disadvantages therein.

A Single-Substrate Biosensor with Spin-Coated Liquid Crystal Film for Simple, Sensitive and Label-Free Protein Detection

A liquid crystal (LC)-based single-substrate biosensor was developed by spin-coating an LC thin film on a dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride (DMOAP)-decorated glass slide. Compared with the conventional sandwiched cell configuration, the simplified procedure for the preparation of an LC film allows the film thickness to be precisely controlled by adjusting the spin rate, thus eliminating personal errors involved in LC cell assembly. The limit of detection (LOD) for bovine serum albumin (BSA) was lowered from 10-5 g/mL with a 4.2-μm-thick sandwiched cell of the commercial LC E7 to 10-7 g/mL with a 4.2-μm-thick spin-coated E7 film and further to 10-8 g/mL by reducing the E7 film thickness to 3.4 μm. Moreover, by exploiting the LC film of the highly birefringent nematic LC HDN in the immunodetection of the cancer biomarker CA125, an LOD comparable to that determined with a sandwiched HDN cell was achieved at 10-8 g/mL CA125 using a capture antibody concentration an order of magnitude lower than that in the LC cell. Our results suggest that employing spin-coated LC film instead of conventional sandwiched LC cell provides a more reliable, reproducible, and cost-effective single-substrate platform, allowing simple fabrication of an LC-based biosensor for sensitive and label-free protein detection and immunoassay.

Label-Free Detection and Spectrometrically Quantitative Analysis of the Cancer Biomarker CA125 Based on Lyotropic Chromonic Liquid Crystal

Compared with thermotropic liquid crystals (LCs), the biosensing potential of lyotropic chromonic liquid crystals (LCLCs), which are more biocompatible because of their hydrophilic nature, has scarcely been investigated. In this study, the nematic phase, a mesophase shared by both thermotropic LCs and LCLCs, of disodium cromoglycate (DSCG) was employed as the sensing mesogen in the LCLC-based biosensor. The biosensing platform was constructed so that the LCLC was homogeneously aligned by the planar anchoring strength of polyimide, but was disrupted in the presence of proteins such as bovine serum albumin (BSA) or the cancer biomarker CA125 captured by the anti-CA125 antibody, with the level of disturbance (and the optical signal thus produced) predominated by the amount of the analyte. The concentration- and wavelength-dependent optical response was analyzed by transmission spectrometry in the visible light spectrum with parallel or crossed polarizers. The concentration of CA125 can be quantified with spectrometrically derived parameters in a linear calibration curve. The limit of detection for both BSA and CA125 of the LCLC-based biosensor was superior or comparable to that of thermotropic LC-based biosensing techniques. Our results provide, to the best of our knowledge, the first evidence that LCLCs can be applied in spectrometrically quantitative biosensing.

Development of liquid crystal biosensor for the detection of amyloid beta-42 levels associated with Alzheimer's disease

This study represents the development of a biosensor which is based on the liquid crystal (LC) orientation as a function of the peptide concentration to detect an amyloid-beta-42 (Aβ42) antibody-antigen binding events. The Aβ42 peptide binds to the Aβ42 antibody forming an immunocomplex which is immobilized on the Dimethyloctadecyl[3-(trimethoxysilyl)propyl] ammonium chloride (DMOAP) coated surface. The disturbed orientation of LCs as a result of the binding of the formed immunocomplex was observed using the polarized optical microscope (POM) as a function of decreasing Aβ42 peptide concentration from 1000 to 1 pg/ml. The concentration, as low as 1 pg/ml of Aβ42 peptide was able to be successfully detected in our system. Apolipoprotein E4 (ApoE4), that specifically bound to the Aβ42 peptide, was added into the system and a remarkable change in reflection spectra of samples was observed with increasing Aβ42 peptide concentration. The concentration of ApoE4 protein was detected in the range of 0.1-30 nM by this system due to the interaction between the two proteins.

Signal Amplification in an Optical and Dielectric Biosensor Employing Liquid Crystal-Photopolymer Composite as the Sensing Medium

An optical and dielectric biosensor based on a liquid crystal (LC)-photopolymer composite was established in this study for the detection and quantitation of bovine serum albumin (BSA). When the nematic LC E7 was doped with 4-wt.% NOA65, a photo-curable prepolymer, and photopolymerized by UV irradiation at 20 mW/cm² for 300 s, the limit of detection determined by image analysis of the LC optical texture and dielectric spectroscopic measurements was 3400 and 88 pg/mL for BSA, respectively, which were lower than those detected with E7 alone (10 μg/mL BSA). The photopolymerized NOA65, but not the prepolymer prior to UV exposure, contributed to the enhanced optical signal, and UV irradiation of pristine E7 in the absence of NOA65 had no effect on the optical texture. The effective tilt angle θ, calculated from the real-part dielectric constant ε', decreased with increasing BSA concentration, providing strong evidence for the correlation of photopolymerized NOA65 to the intensified disruption in the vertically oriented LC molecules to enhance the optical and dielectric signals of BSA. The optical and dielectric anisotropy of LCs and the photo-curable dopant facilitate novel quantitative and signal amplification approaches to potential development of LC-based biosensors.

Label-Free, Smartphone-Based, and Sensitive Nano-Structural Liquid Crystal Aligned by Ceramic Silicon Compound-Constructed DMOAP-Based Biosensor for the Detection of Urine Albumin

INTRODUCTION

The sensitive interfacial interaction of liquid crystals (LC) holds potential for precision biosensors. In the past, the developments of LC biosensors were limited by the complicated manufacturing process, which hinders commercialization and wider applications of such devices. In this report, we demonstrate the first nano-structural polymeric stabilized-cholesteric LC (PSCLC) thin films to be a new label-free biosensing technology.

METHODS

The transmission spectra of PSCLC devices were measured by the fiber-optic spectrometer with high-resolution. In addition, a smartphone was set on the stage, and the camera of smartphone was placed and aligned with a set of lenses embedded in the designed stage. To decrease the chromatic and spherical aberrations, an achromatic lens set composition, consisting of both dual-convex lens and concave-plane lens, was applied for measuring and imaging the PSCLC texture. The average and the estimated standard deviation (SD) were used to present quantitative experimental results. The test BSA was immobilized and fulfilled by the ceramic silicon-constructed DMOAP-coated glass in aqueous BSA solutions at 1 mg/mL, 1 µg/mL, and 1 ng/mL.

RESULTS

The fabrication process of PSCLC is much simplified compared to previous LC biosensors. The color of PSCLC biosensor altered with the BSA concentration, making detection result easy to read. The detection limit of 1 ng/mL is achieved for label-free PSCLC biosensor. The PSCLC biosensor was able to successfully detect due to the albumin concentration's alteration, with a linear range of 1 ng/mL-2 mg/mL. Thus, the label-free-proposed design-integrated nanoscale PSCLCs smartphone-based biosensor could successfully detect BSA in a preclinical urine sample.

CONCLUSION

Finally, we propose a design to integrate the PSCLC biosensor with a smartphone. The PSCLC owns potential for high performance, low cost for detecting various disease biomarkers in home use. Owing to its great potential for high performance and low cost, the PSCLC biosensors can be used as a label-free point-of-care for detecting various disease biomarkers for patients in care homes.

Color-Indicating, Label-Free, Dye-Doped Liquid Crystal Organic-Polymer-Based-Bioinspired Sensor for Biomolecule Immunodetection

The highly sensitive interfacial effects between liquid crystal (LC) and alignment layers make LC-bioinspired sensors an important technology. However, LC-bioinspired sensors are limited by quantification requiring a polarized microscope and expensive equipment, which makes it difficult to commercialize LC-bioinspired sensors. In this report, we first demonstrate that dye-doped LC (DDLC) chips coated with vertically aligned layers can be employed as a new LC-bioinspired sensing technology. The DDLC-bioinspired sensor was tested by detecting bovine serum albumin (BSA) and immunocomplexes of BSA pairs. The intensities of the dye color of the DDLC-bioinspired sensor can be changed with the concentrations of biomolecules and immunocomplexes. A detection limit of 0.5 µg/mL was shown for the color-indicating DDLC-bioinspired sensors. We also designed a new method to use the quantitative DDLC-bioinspired sensor with a smart-phone for potential of home test. The novel DDLC-bioinspired sensor is cheap, label-free, and easy to use, furthering the technology for home and field-based disease-related detection.

Liquid crystal-photopolymer composite films for label-free single-substrate protein quantitation and immunoassay

Conventional liquid crystal (LC)-based biosensing at the LC-glass interface requires the assembly of an LC cell formed by two glass substrates with an LC film sandwiched in between. As most biochemical and clinical assays are performed on a single solid substrate, the feasibility of a single-substrate biodetection platform based on a thin film of LC-photopolymer composite was explored in this study. The LC mixture, consisting of nematic LC, E7 or AY40-006, doped with a small amount (≤ 5 wt%) of a photocurable prepolymer was spin-coated on a glass substrate modified with dimethyloctadecyl[3-trimethoxysilyl)propyl] ammonium chloride (DMOAP), a vertical alignment reagent, followed by irradiation with ultraviolet (UV) light. During the photopolymerization process, the accumulated and polymerized NOA65 at the LC-glass interface weakened the anchoring strength of DMOAP, resulting in a decrease in the pretilt angle of LC and allowing the LC molecules to be more easily disturbed in the presence of biomolecules, compared with vertically aligned LC in the absence of polymerized NOA65. Incorporating NOA65 in the LC film therefore provides a means for signal amplification. When an LC-photopolymer composite film consisting of AY40-006 and 4-wt% NOA65 was exposed to UV at 15 mW/cm² for 30 s and utilized as the biosensing mesogen, the limits of detection were 1.6 × 10^-12 g/ml for the direct detection of bovine serum albumin (BSA) and 2.1 × 10^-8 g/ml for the immunoassay of the cancer biomarker CA125, significantly lower than those detected with AY40-006 alone or AY40-006/NOA65 mixture without UV irradiation. The results from this study offer a compelling implication on the biomedical application of LC-photopolymer composites in label-free and single-substrate biodetection.

Electric-field-assisted signal amplification for label-free liquid-crystal-based detection of biomolecules

The fundamental principle of liquid-crystal (LC)-based biosensing is the sensitive response of LC orientation to external stimuli. Biomolecules such as proteins or DNAs immobilized on the glass substrate of a LC cell are detected through disrupting the LC alignment and, in turn, altering the birefringence, resulting in changes in the optical texture that can be readily observed under a polarizing optical microscope. With an additional weak electric field across a sandwiched LC cell, we demonstrate in this study a novel label-free biodetection technique with amplified signal and improved detection limit. By applying the binarization analysis as the quantitative approach, the increase in the light leakage area in the optical texture of LCs with increasing amount of biomolecules can be quantitated with a bright-area-ratio (BAR)-versus-concentration curve. The reported biosensing technique exploits both the optical and electrical properties of LCs and is potentially applicable to other LC-based rapid screening and bioassays.

Label-free, color-indicating, and sensitive biosensors of cholesteric liquid crystals on a single vertically aligned substrate

Biosensors based on liquid crystal (LC) materials can be made by employing the sensitive interfacial effect between LC molecules and alignment layers on substrates. In the past, the optical texture observation method was used in the LC biosensor field. However, the method is limited by a complicated fabrication process and quantitative reproducibility of results that bv evidence that both the reliability and accuracy of LC biosensors need to be improved. In this report, we demonstrate that cholesteric LC (CLC) cells in which one substrate is coated with a vertically aligned layer can be used as a new sensing technology. The chirality of the single vertically anchored (SVA)/CLC biosensor was tested by detecting bovine serum albumin (BSA), a protein standard commonly used in the lab. The colors and corresponding spectrum of the SVA/CLC biosensor changed with the BSA concentrations. A detection limit of 1 ng/ml was observed for the SVA/CLC biosensor. The linear optical properties of the SVA/CLC biosensor produced cheap, inexpensive, and color-indicating detection of biomolecules, and may promote the technology of point-of-care devices for disease-related biomarker detection.

Quantitative analysis of liquid crystal-based immunoassay using rectangular capillaries as sensing platform

In past studies, liquid crystal (LC)-based immunoassays were accomplished by fabricating an LC cell with two pieces of glass slides after immunobinding, which makes the determination of the immunoassay not in real-time and requires trained personnel. Herein, we developed the LC-based immunoassay by using rectangular capillaries as the substrate for immunobinding. The inner surface of rectangular capillaries was decorated with a long alkyl saline, dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride (DMOAP), followed by immobilization of human serum albumin (HSA) as the probe. In this situation, the orientation of LC was homeotropic and dark LC image was observed under polarized light. When the solution containing anti-human serum albumin (anti-HSA) were dispensed into the capillary through capillary action, the specific immunobinding between HSA and anti-HSA formed an immunocomplex on the inner surface of capillary, which disrupted the original orientation of LC and led to a dark-to-bright transition of the LC images. The quantification of anti-HSA can be achieved by measuring the length of the bright LC image in the rectangular capillary. By using this immunoassay, the limit of detection (LOD) for anti-HSA is 1 μg/mL, and it did not respond to HSA and anti-human immunoglobulin G (anti-h-IgG). On the other hand, the diversity of the LC-based immunoassay can be extended for HSA detection when we immobilized anti-HSA in the capillary. Because the post-fabrication of LC cell was waived by using rectangular capillaries to develop the LC-based immunoassay, it is more convenient for users to handle and collect more reliable data. Moreover, the results of the immunoassay were visualized through naked-eye and could be recorded by a smartphone; it is more suitable for portable and point-of-care applications.

Liquid Crystals: A Novel Approach for Cancer Detection and Treatment

Liquid crystals are defined as the fourth state of matter forming between solid and liquid states. Earlier the applications of liquid crystals were confined to electronic instruments, but recent research findings suggest multiple applications of liquid crystals in biology and medicine. Here, the purpose of this review article is to discuss the potential biological impacts of liquid crystals in the diagnosis and prognosis of cancer along with the risk assessment. In this review, we also discussed the recent advances of liquid crystals in cancer biomarker detection and treatment in multiple cell line models. Cases reviewed here will demonstrate that cancer diagnostics based on the multidisciplinary technology and intriguingly utilization of liquid crystals may become an alternative to regular cancer detection methodologies. Additionally, we discussed the formidable challenges and problems in applying liquid crystal technologies. Solving these problems will require great effort and the way forward is through the multidisciplinary collaboration of physicists, biologists, chemists, material-scientists, clinicians, and engineers. The triumphant outcome of these liquid crystals and their applications in cancer research would be convenient testing for the detection of cancer and may result in treating the cancer patients non-invasively.

Label-free protein sensing by employing blue phase liquid crystal

Blue phases (BPs) are mesophases existing between the isotropic and chiral nematic phases of liquid crystals (LCs). In recent years, blue phase LCs (BPLCs) have been extensively studied in the field of LC science and display technology. However, the application of BPLCs in biosensing has not been explored. In this study, a BPLC-based biosensing technology was developed for the detection and quantitation of bovine serum albumin (BSA). The sensing platform was constructed by assembling an empty cell with two glass slides coated with homeotropic alignment layers and with immobilized BSA atop. The LC cells were heated to isotropic phase and then allowed to cool down to and maintained at distinct BP temperatures for spectral measurements and texture observations. At BSA concentrations below 10^-6 g/ml, we observed that the Bragg reflection wavelength blue-shifted with increasing concentration of BSA, suggesting that the BP is a potentially sensitive medium in the detection and quantitation of biomolecules. By using the BPLC at 37 °C and the same polymorphic material in the smectic A phase at 20 °C, two linear correlations were established for logarithmic BSA concentrations ranging from 10^-9 to 10^-6 g/ml and from 10^-6 to 10^-3 g/ml. Our results demonstrate the potential of BPLCs in biosensing and quantitative analysis of biomolecules.

Highly sensitive color-indicating and quantitative biosensor based on cholesteric liquid crystal

Liquid crystal (LC)-based biosensors employ highly sensitive interfaces between the alignment layers and LCs to detect biomolecules and their interactions. Present techniques based on optical texture observation of the homeotropic-to-planar response of nematic LCs are limited by their quantitative reproducibility of results, indicating that both the accuracy and reliability of LC-based detection require further improvements. Here we show that cholesteric LC (CLC) can be used as a novel sensing element in the design of an alternative LC-based biosensing device. The chirality of the vertically anchored (VA) CLC was exploited in the detection of bovine serum albumin (BSA), a protein standard commonly used in protein quantitation. The color appearance and the corresponding transmission spectrum of the cholesteric phase changed with the concentration of BSA, by which a detection limit of 1 fg/ml was observed. The optical response of the VA CLC interface offers a simple and inexpensive platform for highly sensitive and naked-eye color-indicating detection of biomolecules, and, thus, may facilitate the development of point-of-care devices for the detection of disease-related biomarkers.