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

Abstract

Liquid crystal (LC)-based biosensing has attracted much attention in recent years. We focus on improving the detection limit of LC-based immunoassay techniques by surface modification of the surfactant alignment layer consisting of dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride (DMOAP). The cancer biomarker CA125 was detected with an array of anti-CA125 antibodies immobilized on the ultraviolet (UV)-modified DMOAP monolayer. Compared with a pristine counterpart, UV irradiation enhanced the binding affinity of the CA125 antibody and reproducibility of immunodetection in which a detection limit of 0.01 ng∕ml for the cancer biomarker CA125 was achieved. Additionally, the optical texture observed under a crossed polarized microscope was correlated with the analyte concentration. In a proof-of-concept experiment using CA125-spiked human serum as the analyte, specific binding between the CA125 antigen and the anti-CA125 antibody resulted in a distinct and concentration-dependent optical response despite the high background caused by nonspecific binding of other biomolecules in the human serum. Results from this study indicate that UVmodification of the alignment layer, as well as detection with LCs of large birefringence, contributes to the enhanced performance of the label-free LC-based immunodetection, which may be considered a promising alternative to conventional label-based methods.

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

“…Currently, LC-based biosensing is applied in the detection of enzymatic reactions, antibody-antigen immunoreactions, DNA hybridization, and the like [1,3,4]. Our previous studies established that the sensitivity of LC-based immunodetection for the cancer biomarker CA125 can be significantly enhanced by using a eutectic nematic LC with a wide nematic range (<−30-95 °C compared with 5CB having a narrow nematic range of ~24-35 °C) and large birefringence (Δn = 0.333 at 589 nm and 20 °C) [7][8][9]. Nevertheless, present techniques based on optical texture observation are limited by the non-uniformity of LC textures, which are difficult to reproduce and hard to be quantitated.…”

Label-free protein sensing by employing blue phase liquid crystal

“…To extend current technique to clinical application, BSA can be substituted for an antibody specific for a disease-related biomarker, which is then reacted with a serum sample containing the biomarker to assess the detection specificity of BPLCs, as described in our previous work on the LC-based detection of the cancer biomarker CA125 [8][9][10]. Although the process of achieving and maintaining BPs may require further simplification to enhance practical application, results from this study provide the first implications that quantitative biosensors based on BPLCs may be realized with the fast development of BP-related photonic technologies.…”

“…Moreover, TL205, a nematic LC of low cytotoxicity, served as the substrate for the imaging of human embryonic stem cells [7]. By exploiting the large birefringence of another nematic LC, HDN, we demonstrated that the increased birefringence is critical to lowering the detection limit of CA125, a cancer biomarker, in a LC-based immunoassay [8][9][10]. For biological detection with other phases of LCs, cholesteric LCs (CLCs), produced by incorporating a chiral dopant in nematic LCs, were utilized as droplets in the design of glucose and cholesterol biosensors [11].…”

Liquid Crystals: A Novel Approach for Cancer Detection and Treatment

“…The sample preparation procedure of LC-based immunological assays has multiple steps [ 79 , 80 , 81 ]. Initially, the glass slides are cleaned by immersing in detergent solution, deionized water, and finally in 99% ethanol in sequential order and in each step allowing the ultra-sonication for 15 min at room temperature.…”

“…In the final step, LC is filled through capillary mechanism. The LC cell optical texture is observed under a microscope in the transmitted light illumination by using crossed polarizers [ 79 , 80 , 81 ]. The fundamental mechanism behind this principle is a change in the optical texture of LCs, directly proportional to the number and type of biomolecules from the analyst source present in an LC aligning layer.…”