LIQUID CRYSTAL INTERFACES EXPERIMENTS SIMULATIONS AND BIOSENSORS (original) (raw)

Improving Liquid-Crystal-Based Biosensing in Aqueous Phases

ACS Applied Materials & Interfaces, 2012

Liquid crystal (LC)-based biological sensors permit the study of aqueous biological samples without the need for the labeling of biological species with fluorescent dyes (which can be laborious and change the properties of the biological sample under study). To date, studies of LCbased biosensors have explored only a narrow range of the liquid crystal/alignment layer combinations essential to their operation. Here we report a study of the role of LC elastic constants and the surface anchoring energy in determining the sensitivity of LC-based biosensors. By investigating a mixture of rod-shape and bent-shape mesogens, and three different alignment layers, we were able to widen the useful detection range of a LC-based sensor by providing an almost linear mapping of effective birefringence with concentration between 0.05 and 1mM of an anionic surfactant (model target analyte). These studies pave the way for optimization of LCbased biosensors and reveal the importance of the choice of both the LC material and the alignment layer in determining sensor properties.

Applications of liquid crystals in biosensing

Soft Matter, 2021

Recent investigations on the design and application of liquid crystal-based biosensors have been reviewed, according to the phenomenon that orientations of liquid crystals can be directly influenced by interactions between biomolecules and liquid crystal molecules. With the ability to detect external stimuli with high sensitivity, liquid crystal biosensors can help realize a new biosensing era.

Chemical and biological sensing using liquid crystals

Liquid Crystals Reviews, 2013

The liquid crystalline state of matter arises from orientation-dependent, non-covalent interaction between molecules within condensed phases. Because the balance of intermolecular forces that underlies formation of liquid crystals is delicate, this state of matter can, in general, be easily perturbed by external stimuli (such as an electric field in a display). In this review, we present an overview of recent efforts that have focused on exploiting the responsiveness of liquid crystals as the basis of chemical and biological sensors. In this application of liquid crystals, the challenge is to design liquid crystalline systems that undergo changes in organization when perturbed by targeted chemical and biological species of interest. The approaches described below revolve around the design of interfaces that selectively bind targeted species, thus leading to surfacedriven changes in the organization of the liquid crystals. Because liquid crystals possess anisotropic optical and dielectric properties, a range of different methods can be used to read out the changes in organization of liquid crystals that are caused by targeted chemical and biological species. This review focuses on principles for liquid crystal-based sensors that provide an optical output.

Areas of opportunity related to design of chemical and biological sensors based on liquid crystals

Liquid Crystals Today

The societal impact of liquid crystals (LCs) in electrooptical displays arrived after decades of research involving molecular-level design of LCs and their alignment layers, and elucidation of LC electrooptical phenomena at device scales. The anisotropic optical, mechanical and dielectric properties of LCs used in displays also make LCs remarkable amplifiers of their interactions with chemical and biological species, thus opening up the possibility that LCs may play an influential role in a data-driven society that depends on information coming from sensors. In this article, we describe ongoing efforts to design LC systems tailored for chemical and biological sensing, efforts that mirror the challenges and opportunities in LC design and alignment tackled several decades ago during development of LC electrooptical displays. Now, however, traditional design approaches based on structure-property relationships are being supplemented by data-driven methods such as machine learning. Recent studies also show that computational chemistry can greatly increase the rate of discovery of chemically responsive LC systems. Additionally, nonequilibrium states of LCs are being revealed to be useful for design of biological sensors and more complex autonomous systems that integrate self-regulated actuation along with sensing. These topics and others are addressed in this article with the aim of highlighting approaches and goals for future research that will realise the full potential of LC-based sensors.

Nematic liquid crystal interfaces for chemical and biological detection

Emerging Liquid Crystal Technologies VI, 2011

Nematic liquid crystals (NLCs) have traditionally been used in displays and other electro-optical applications where the orientation of NLC is manipulated by using an external electric field to display the information. In recent years, there have been significant advances in unconventional applications of NLCs in photonics, sensors, and diagnostics. In this paper, the application of NLCs for detection of vapor phase chemicals and biological entities is presented. When NLCs are in contact with another medium (solid, liquid or air) the delicate interplay between the properties of medium and NLCs determines the nature of the alignment assumed by NLCs at the interface. Interfaces functionalized with select chemical or biological entities promote alignment of NLCs in predetermined orientations (perpendicular or parallel to that interface) that are primarily dictated by local interactions at the interface. When these interfaces are exposed to target analytes, the interactions at the interfaces are perturbed and the NLC films undergo orientational transitions from perpendicular to parallel alignment, or vice versa. The orientational transition can be detected by viewing the film of NLCs between crossed polarizers (optical signal) or by measuring the differential capacitance associated with the change in alignment of NLCs (electrical signal). By engineering surfaces with different interfacial properties, sensors based on this principle have been demonstrated to selectively detect a wide variety of chemical and biological analytes that have relevance in industrial hygiene, environmental monitoring, homeland security, diagnostics, and biomedical applications.

Nematic liquid crystal interfaces for chemical and biological detection

2011

Nematic liquid crystals (NLCs) have traditionally been used in displays and other electro-optical applications where the orientation of NLC is manipulated by using an external electric field to display the information. In recent years, there have been significant advances in unconventional applications of NLCs in photonics, sensors, and diagnostics. In this paper, the application of NLCs for detection of vapor phase chemicals and biological entities is presented. When NLCs are in contact with another medium (solid, liquid or air) the delicate interplay between the properties of medium and NLCs determines the nature of the alignment assumed by NLCs at the interface. Interfaces functionalized with select chemical or biological entities promote alignment of NLCs in predetermined orientations (perpendicular or parallel to that interface) that are primarily dictated by local interactions at the interface. When these interfaces are exposed to target analytes, the interactions at the interfaces are perturbed and the NLC films undergo orientational transitions from perpendicular to parallel alignment, or vice versa. The orientational transition can be detected by viewing the film of NLCs between crossed polarizers (optical signal) or by measuring the differential capacitance associated with the change in alignment of NLCs (electrical signal). By engineering surfaces with different interfacial properties, sensors based on this principle have been demonstrated to selectively detect a wide variety of chemical and biological analytes that have relevance in industrial hygiene, environmental monitoring, homeland security, diagnostics, and biomedical applications.

Liquid crystals based sensing platform-technological aspects

In bulk phase, liquid crystalline molecules are organized due to non-covalent interactions and due to delicate nature of the present forces; this organization can easily be disrupted by any small external stimuli. This delicate nature of force balance in liquid crystals organization forms the basis of Liquidcrystals based sensing scheme which has been exploited by many researchers for the optical visualization and sensing of many biological interactions as well as detection of number of analytes. In this review, we present not only an overview of the state of the art in liquid crystals based sensing scheme but also highlight its limitations. The approaches described below revolve around possibilities and limitations of key components of such sensing platform including bottom substrates, alignments layers, nature and type of liquid crystals, sensing compartments, various interfaces etc. This review also highlights potential materials to not only improve performance of the sensing scheme but also to bridge the gap between science and technology of liquid crystals based sensing scheme.

Capacitive Based Liquid Crystal Chemical and Biological Sensors

2007 IEEE Sensors, 2007

This paper demonstrates the principle of capacitive sensing in liquid crystal (LC) based sensors with potential applications to chemical and biological systems. The theory for tracking the average molecular deformation partially disorder LC film via capacitive sensing is investigated. Three capacitance measurements are required to track the average molecular orientation as well as the degree of disorder in the LC film. Sensors' outputs are digitized by involving capacitance to digital converter to be applied to computerized applications. Both the experimental and calculated capacitances of a selected sensor structure are presented.

Accurate Optical Detection of Amphiphiles at Liquid-Crystal–Water Interfaces

Liquid-crystal–based biosensors utilize the high sensitivity of liquid-crystal alignment to the presence of amphiphiles adsorbed to one of the liquid-crystal surfaces from water. They offer inexpensive, easy optical detection of biologically relevant molecules such as lipids, proteins, and cells. Present techniques use linear polarizers to analyze the alignment of the liquid crystal. The resulting images contain information not only about the liquid-crystal tilt with respect to the surface normal, the quantity which is controlled by surface adsorption, but also on the uncontrolled in-plane liquid-crystal alignment, thus making the detection largely qualitative. Here we show that detecting the liquid-crystal alignment between circular polarizers, which are only sensitive to the liquid-crystal tilt with respect to the interface normal, makes possible quantitative detection by measuring the transmitted light intensity with a spectrophotometer. Following a new procedure, not only the concentration dependence of the optical path difference but also the film thickness and the effective birefringence can be determined accurately. We also introduce a new " dynamic " mode of sensing, where (instead of the conventional " steady " mode, which detects the concentration dependence of the steady-state texture) we increase the concentration at a constant rate.

Thermotropic liquid crystal films for biosensors and beyond

We briefly review studies of liquid crystal films suspended in submillimeter size grids for biosensing applications and beyond. Due to intense recent research, the sensitivity of liquid crystal films to targeted biologically relevant agents can be increased, and the LC surface can be functionalized to be sensitive only to pre-assigned pathogens. Beyond sensor applications, we show that novel liquid crystal defect structures can be used to manipulate separation and deposition of lipids. Finally, we demonstrate that not only the nematic liquid crystal phase, but also chiral nematic (cholesteric and blue phase) and smectic liquid crystals can be used for sensing and may extend the sensitivity and/or the selection of biomaterials, which can be sensed.