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

Abstract

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.

Holographic metasurface gas sensors for instantaneous visual alarms

“…In addition, previous works demonstrated the induced retardation change to be dependent on how much gas molecules diffuse into the LCs and disrupt the molecular ordering of LCs. Therefore, one can engineer the gas sensitivity of LC cells by tuning the molecular properties of LCs (e.g., diffusion coefficient, intermolecular interaction, and elasticity) that can be precisely and readily controlled via external stimuli, such as temperature, pressure, electric/magnetic fields, dopants, and chemical biding ( 6 – 11 , 33 – 36 , 51 – 57 ). A wide pool of LC phases having different internal ordering (and thus different physical/chemical characteristics) can be used.…”

Applications of Microfluidics in Liquid Crystal-Based Biosensors

“…In addition, using machine learning techniques for data analysis may provide another future direction to enhance the selectivity of LC-based microfluidic sensors. Compared with the adoption of naked eyes to distinguish the differences in the optical appearance of LCs, the machine learning techniques can uncover valuable information underlying the microscopy images of LCs, providing a more accurate detection result [13,[110][111][112]. To date, the LC-based biosensors are still studied in laboratories using a polarized optical microscope to observe the detection results, and real breakthroughs are still expected to develop a portable, easy-to-use LC-based sensing device for commercial applications.…”

Quantitative volatile organic compound sensing with liquid crystal core fibers

“… 6 , 7 , 8 Better selectivity may be provided from specific chemical interactions between a target VOC and a dye or other responsive material, which reports the VOC presence through a change in appearance. 9 , 10 , 11 An interesting class of such optically VOC-responsive materials is given by liquid crystals (LCs), 12 , 13 which despite their liquid nature exhibit long-range orientational order along a direction called the “director.” 14 This gives them properties normally seen only in crystalline solids, such as birefringence and, in case of chiral LCs, structural color. 15 LCs have been shown to signal exposure to toluene, 16 , 17 , 18 , 19 , 20 acetone, 19 , 21 NO 2 , 22 CO 2 , 23 , 24 , O 2 , 24 amines, 25 cyclohexane and acetic acid, 26 chloroform and ethanol, 27 , 28 isopropanol, 29 tetrahydrofuran, methanol, tetrachloroethylene, 27 pyridine, hexane, and benzene 21 and to VOCs mimicking the nerve gas sarin.…”