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

Abstract

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.

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

“…To eliminate the costly and time-consuming p cedure of labeling, a number of label-free approaches aimed at enhancing the optical s nal and thereby improving detection sensitivity at the LC-solid interface of a sandwich LC cell were proposed, which include the use of a highly birefringent LC [38,39] and L photopolymer composite [12], adjustment of the direction of linearly polarized light fo dye-doped LC [16], modification of the alignment layer by ultraviolet light irradiation [ and application of a weak electric field to orient LC molecules in a pre-tilted state [4 Because of the similar working principles between the LC film and LC cell in biodetecti at the LC-glass interface, most of the previously reported signal amplification approach for sandwiched cells would be applicable to the LC film. We have demonstrated that s nal amplification can be achieved with both spin-coated film and sandwiched cell of LC-photopolymer composite [12,31]. In addition, the intensity of the optical response Signal amplification mediated by labeling with gold nanoparticles has been reported in several LC-based biosensors [33][34][35][36][37].…”

“…Because of the similar working principles between the LC film and LC cell in biodetection at the LC-glass interface, most of the previously reported signal amplification approaches for sandwiched cells would be applicable to the LC film. We have demonstrated that signal amplification can be achieved with both spin-coated film and sandwiched cell of an LC-photopolymer composite [12,31]. In addition, the intensity of the optical response to BSA was enhanced when a 3.4 µm-thick E7 film was spin-coated on DMOAP slides modified with ultraviolet light or when the high-birefringence LC HDN was used instead of E7 to form the sensing LC film, resulting in an improvement in LOD from 10 −8 to 10 −9 g/mL BSA (data not shown).…”

“…A wide variety of LC-based biosensing technologies were demonstrated at the LC-solid or LC-aqueous interface for different types of biological analytes, with strategies to improve sensing performance summarized in several review papers [3][4][5][6][7][8][9]. While conventional optical texture observation mainly permits qualitative analysis of the optical signal, attention has been paid to developing quantitative biosensing techniques by exploiting the dielectric and electro-optical characteristics of nematic LCs [10][11][12], Bragg reflection of chiral LCs [13][14][15], and selective absorption features of a dye-LC as well as a dye-doped LC [16,17].…”

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

“…The characteristic birefringence in LCs enables such interactions to be observed through the change in optical appearance under a polarizing optical microscope (POM) [4][5][6][7][8]. In addition to textural observation, other unique properties of LCs, particularly dielectric anisotropy and electro-optical response, are utilized to establish novel LC-based biosensors for quantitative and signal amplification purposes [5,[9][10][11][12]. For biodetection at the LC-glass interface, dimethyloctadecyl [3-(trimethoxysilyl)propyl] ammonium chloride (DMOAP), a silane coupling reagent, is commonly used to maintain the vertical alignment of LC molecules through its long alkyl chain.…”

“…Using bovine serum albumin (BSA) as the model protein and pristine nematic LCs such as the eutectic mixture E7 as the sensing mesogenic media, the limit of detection (LOD) for LC-based biosensors was reported to be within the order of magnitude of 10 −5 -g/mL BSA [11]. Several strategies have been developed in order to improve the LOD of LC-based detection at the LC-glass interface.…”