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

Abstract

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.

Label-free protein sensing by employing blue phase liquid crystal

“…Although the data are somewhat scattered, the coefficient of determination r 2 for the linear fit is still greater than 0.92 in each case. When BSA was immobilized on a DMOAP-coated glass surface, we observed that the detection limit of BPLC-based protein assay, 10 −9 g/ml (15 pM) BSA, was similar to that based on voltage-dependent capacitance measurement of HDN, but was three orders of magnitude higher than that of the CLC-based protein assay (10 −12 g/ml), as described in our previous work [12,17]. Other studies on LC-based BSA detection demonstrated that biosensing with 5CB on a glass surface functionalized with gold nanoparticles resulted in a detection limit of 0.5 μg/ml (7.5 nM) BSA based on optical texture observation [26].…”

“…A LC cell, with a thin layer of the mixture sandwiched between two glass slides, was prepared as described in our previous study [12]. Glass slides were washed successively with detergent and deionized water accompanied by ultrasonication at room temperature.…”

“…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]. We also established a colorindicating protein biosensor facilitated by vertically aligned CLCs [12]. A real-time detector based on lyotropic chromonic liquid crystals, a different category of LCs as opposed to nematic ones, was developed to monitor microbial immunocomplexes [13].…”

“…In addition, the anchoring energy of LCs is measured in an attempt to quantitate the concentration of antibodies specifically bound to peptide ligands [16]. By exploiting the Bragg reflection of CLC and transmission spectroscopy, the concentration of BSA can be correlated with the minimum transmittance or bandwidth of incident light [12]. Through the measurement of capacitance properties of LCs under an externally applied electric field, we observed that BSA quantitation can also be achieved by measuring the voltage-dependent capacitance of nematic LC cells containing immobilized BSA [17].…”

“…Traditional protein assays are easy to perform with an absorption spectrometer, but the concentration range of linearity is usually limited to an order of magnitude. In LCbased protein assays, linearity may be expanded to three to four orders of magnitude according to our previous reports [12,17]. By controlling the temperature within the ranges of the BP and smectic A (SmA) phase existence, we analyzed the transmission spectra of BPLC interfaced with BSA at various concentrations along with complementary optical texture observations.…”