Liquid Crystal Droplet-Based Biosensors: Promising for Point-of-Care Testing

Abstract

The development of biosensing platforms has been impressively accelerated by advancements in liquid crystal (LC) technology. High response rate, easy operation, and good stability of the LC droplet-based biosensors are all benefits of the long-range order of LC molecules. Bioprobes emerged when LC droplets were combined with biotechnology, and these bioprobes are used extensively for disease diagnosis, food safety, and environmental monitoring. The LC droplet biosensors have high sensitivity and excellent selectivity, making them an attractive tool for the label-free, economical, and real-time detection of different targets. Portable devices work well as the accessory kits for LC droplet-based biosensors to make them easier to use by anyone for on-site monitoring of targets. Herein, we offer a review of the latest developments in the design of LC droplet-based biosensors for qualitative target monitoring and quantitative target analysis.

Keywords: LC droplets; POC; biosensing; clinical applications; enzyme sensors; single-cell monitoring.

Figure 8

(a) An optical image (left) and a schematic (right) of the microfluidic channel with dimensions. (b) Schematic illustration of radial to bipolar transition of the 5CB_PAA-biotin in an avidin aqueous solution. Reprinted with permission from ref. [121]. Copyright 2015 Elsevier. (c) Schematic illustration of generating a vector beam driven by molecular interaction. (d) Comparison of laser mode with conventional spectra interrogation. (e) Schematic illustration of topological transformation in laser mode pattern. (f) Illustration of the developed encoding rule. Reprinted with permission from ref. [126]. Copyright 2021 John Wiley and Sons.

Figure 11

Schematic diagram of the experimental principle. The POM images of the 5CB_SADrop and their corresponding configurations in the aqueous solutions of (a) CTAB, (b) CTAB and AFB1 aptamer, and (c) CTAB, AFB1 aptamer, and AFB1, respectively. The dark cross appearance and the four-leaf clover appearance correspond to the radial and escape-radial configurations of LC droplets, respectively. Reprinted with permission from ref. [172]. Copyright 2022 Elsevier. (d) Schematic illustration of orientation states for LCs: the absence and presence of DDVP in ALP solution on the SMP doped-5CB droplet patterns. Reprinted with permission from ref. [178]. Copyright 2018 Elsevier.

Figure 1

Schematic illustration of the procedure used to prepare LC droplets of predetermined sizes within polymeric multilayer shells. Reprinted with permission from ref. [55] Copyright 2009 American Chemical Society.

Figure 2

(a) Schematic of the capillary microfluidic device combining co-flow and flow-focusing geometries. Photographic images of the microfluidic capillary devices were used in the (b) absence and (c) presence of fluids. Reprinted with permission from ref. [67]. Copyright 2016 Royal Society of Chemistry.

Figure 3

Polarized light microscopy images of surface-anchored LC droplet patterns in a different solution. Reprinted with permission from ref. [73]. Copyright 2014 John Wiley and Sons. The scale bar is 20 µm.

Figure 4

Schematic illustration of (a) the microchip to generate monodisperse 5CB droplets, (b) flow-focusing element, and (c) entrapment of the 5CB droplets in the microstructure. (d) Photograph of the microchip. (e) The POM and (f) bright-field images of the 5CB droplets. Reprinted with permission from ref. [74]. Copyright 2020 Elsevier. The scale bar is 50 µm. (g) Schematic illustration of the director configuration transition of PVA/SC₁₂S-stabilized CLC droplets from homeotropic to planar, triggered by surfactant–bile acid interactions at the surface of the dispersed CLC droplets. Reprinted with permission from ref. [86]. Copyright 2021 Royal Society of Chemistry.

Figure 5

Schematic illustrations of poly(L-lysine)-coated LC droplets for sensitive detection of DNA and their applications in controlled release of drug molecules. Reprinted with permission from ref. [94]. Copyright 2017 American Chemical Society.

Figure 6

Schematic illustration of lipid-protein interactions that control the reorientation at the LC droplet interface. Reprinted with permission from ref. [109]. Copyright 2021 American Chemical Society.

Figure 7

(a) Schematic illustration of slide cover glass immobilized LC microdroplets for sensitive detection of an IgG antigen. Reprinted with permission from ref. [117]. Copyright 2017 American Chemical Society. (b) Schematic illustration of using a LC droplet sensing platform to detect CES and its inhibitors Reprinted with permission from ref. [118]. Copyright 2022 MDPI. The scale bar is 100 µm.

Figure 9

(a) Schematic illustration of LC droplet-based chemical sensors. Reprinted with permission from ref. [136]. Copyright 2013 John Wiley and Sons. (b) Schematic illustration of immobilized P-E7_PBA droplets on cells cultured in a microfluidic channel. NH₃ released from the cell results in a radial-to-bipolar change of the E7_PBA encapsulated in the polymeric microcapsule. Reprinted with permission from ref. [138]. Copyright 2019 John Wiley and Sons. (c) Schematic illustration of LCEM-HRP immobilized on the cell membrane and its reversible transfiguration. Reprinted with permission from ref. [139]. Copyright 2020 John Wiley and Sons.

Figure 10

Schematic illustration of the mechanism for the detection of Salmonella enterica using chiral nematic (N*) complex emulsions. Changes in the reflected light are produced through changes in the interfacial activity of boronic acid polymeric surfactants induced by a competitive binding/unbinding of IgG antibodies at the LC/W interface. Reprinted with permission from ref. [152]. Copyright 2021 American Chemical Society.

Figure 12

(a) Schematic illustration of the structural transition of stearic acid-doped 5CB microdroplet from planar anchoring to homeotropic anchoring. Reprinted with permission from ref. [41]. Copyright 2019 Elsevier. (b) Several tens of micrometer-sized photonic solid-state cholesteric LC (CLCsolid) balls have been functionalized with a weak anionic polyelectrolyte of poly(acrylic acid) in the form of an interpenetrating polymer network (IPN). Reprinted with permission from ref. [194]. Copyright 2020 Elsevier.

Figure 13

(a) Schematic illustration of essential steps for emulsification of (i) two-phase system, (ii) formation of an aqueous dispersion of MG stabilized LC droplets, (iii) response of LC droplets to SDS, and (iv) on-demand emulsion breaking. Reconfiguration of high-chirality LC droplets in the presence of DLPC amphiphiles. Reprinted with permission from ref. [201]. Copyright 2019 Royal Society of Chemistry. (b) Reflection mode POM images of reconfiguration dynamics in 30 µm high-chirality droplets in the presence of 0.5 mM DLPC. (c) Schematic of the planar to homeotropic ordering transition. (d) Bright-field and fluorescent image of adsorbed labeled DLPC amphiphiles on the chiral droplet’s interface. Reprinted with permission from ref. [202]. Copyright 2022 MDPI. The scale bar is 20 µm.