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.
Highlights
Since Abbott’s group demonstrated the use of a single-compound nematic liquid crystal (LC) known as 5CB in the detection of biomolecules [1], Liquid crystal (LC)-based biosensors have received much attention [2,3,4]
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
We show that cholesteric LC (CLC) can be used as a novel sensing element in the design of an alternative LC-based biosensing device
Summary
Since Abbott’s group demonstrated the use of a single-compound nematic liquid crystal (LC) known as 5CB in the detection of biomolecules [1], LC-based biosensors have received much attention [2,3,4]. A simple and unique CLC-based biosensor was developed by exploiting the highly sensitive interface between CLC molecules and vertical alignment layers consisting of N,Ndimethyl-n-octadecyl-3-aminopropyltrimethoxysilyl chloride (DMOAP) to detect various concentrations of bovine serum albumin (BSA), a common protein standard. When the biomolecules are adsorbed on the DMOAP-coated surface, the vertical anchoring strength of the CLCs is weakened, allowing CLC molecules to transfer to the P structure and, in turn, giving rise to the major-transmission mode. The transition of the CLC structure from major reflection to major transmission caused by increasing amount of biomolecules renders the color-indicating properties of CLCs. Quantitation of the BSA concentration with a lower limit of ~1 fg/ml can be achieved by measuring the surface-induced ordering transition of CLCs through transmission spectroscopy. This study unambiguously demonstrates that CLCs are advantageous in the development of highly sensitive, color-indicating and quantitative biosensing technique
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