Microfluidic Construction of Responsive Photonic Microcapsules of Cholesteric Liquid Crystal for Colorimetric Temperature Microsensors

Abstract

It plays a critical role in various physiological activities and pathological states of organisms, including gene expression, cell division and inflammatory responses. [2] Monitoring the temperature on the micro/nano-scale is of major fundamental interest for a wide range of disciplines, ranging from biological processes, [3] chemical reactions, [4] micro/nano-electronics, [5] and micro/ nano-fluidics. [6] Currently, temperature microsensors are mainly thermocouples, [7] thermistors [8] and luminescence thermometers. [9] Thermocouples and thermistors are realized based on electrical properties with great stability and reliability; however, their structural features and uncertain material cytotoxicity may cause damage to cells. [7,8] Luminescence thermometer with small size and high sensitivity is an excellent candidate for measuring temperature. However, the fabrication of such systems depends on special chemical reagents and miscellaneous steps, leading to poor biocompatibility. [9c] Therefore, it is still a challenge to fabricate a temperature sensor with good stability and biocompatibility.Colorimetric temperature microsensors hold advantages of simple usage and direct read. In the class of colorimetric materials, cholesteric liquid crystal (CLC) possesses the advantages of quick response, and reversible and adjustable color range, [10] which have shown great potential for As alternatives to electronic devices, optically active structures from responsive nanomaterials offer great opportunity for building up smart functional sensors. This work reports on the construction and application of photonic microcapsules (PMCs) for colorimetric temperature microsensors, enabling miniaturization for injectable local micro-area sensing and integration for large-area sensing. Monodispersed PMCs are produced by in situ photopolymerization of hydrogel shells of cholesteric liquid crystal (CLC)-in-waterin-oil double emulsion droplets prepared using microfluidic devices, with controllable physical structures and chemical compositions. Constructed PMCs exhibit thermal responsive structural color according to the selective Bragg reflection of CLC's periodical helical structures within the microdroplet's spherical confinement. CLC mixtures with phase transition temperature of 56.0 and 37.8 °C have been prepared and employed to construct PMCs exhibiting obviously visible and quantifiable optical response in 52-56 and 33-38 °C, respectively. The PMCs have been successfully applied for monitoring the living cell extracellular temperature via co-incubation with cell suspension, and for sensing human forehead temperature via a flexible device from assembled PMCs. These PMCs can be flexibly applied in either micro-environment or large-area surface, enabling wide applications for a precision temperature monitoring of biological activities (e.g., cells or organs), optoelectronic devices working conditions (e.g., temperature indicators under extreme conditions), etc.

Liquid Crystal Materials for Biomedical Applications

“…In that case, the cholesteric LCs could be viewed as 1D photonic crystals with photonic bandgaps, and their visual colors can be modulated by temperature, concentration, external field, etc. [57][58][59][60][61] In addition to the nematic, smectic, columnar, and cholesteric phases, there are other LC phases such as the blue phase and the twisted grain boundary phase. These LC phases are not discussed in this review, and more details about them could be found in other review articles.…”

Progress in Fabrication and Applications of Cholesteric Liquid Crystal Microcapsules

“…Qin et al [106] prepared microcapsules by mixing two core materials, one is E7 and the other is fluorescent dye, through the microfluidic method, and the obtained CLCMCs displayed structural colors under white light and fluorescent color under UV irradiation (λ = 388 nm) (Figure 7A), respectively. Xie et al [107] prepared CLCMCs with a shell-core structure using poly(ethylene glycol)diacrylate (PEGDA) and CLC mixtures (Figure 7B). By adjusting the composition of the CLC mixture, the core material exhibited a phase-transition temperature of 37.8 °C, so that the prepared CLCMCs were able to sense temperature changes in the range of 33-38 °C.…”

“…Recently, flexible monitoring devices for cellular temperature based on CLCMCs detecting forehead temperature have been developed. [107] Placing the flexible CLCMC film patches on the forehead, and when the forehead temperature was higher than 38 °C, all four regions filled with CLCMCs became transparent, showing the substrate color and could be read directly with the naked eye (Figure 10A). In addition, owing to their small size, they can be used as temperature sensors for specific localized microenvironments to sense and display slight temperature changes.…”

Twisted Optical Micro/Nanofibers Enabled Detection of Subtle Temperature Variation

“…The ability to detect subtle temperature variation is of profound importance for its applications in proximity sensing, , tumor monitoring, , and microfluidics. , Recently, various temperature sensors have been developed based on resistance, capacitance, thermal-sensitive upconversion nanoparticles (UCNPs), Mach–Zehnder interferometer (MZI), , and Fabry–Perot (FP) resonator. , Among them, sensors based on optical principles have made remarkable development due to their advantages such as high sensitivity, fast response, and immunity to electromagnetic interference. − For example, Guo et al demonstrated a flexible temperature sensor fabricated by incorporating temperature-sensitive UCNPs in stretchable polymer-based optical fibers, achieving a sensitivity of 1.8%/°C . Yuan et al proposed a ring-core fiber-based MZI fiber temperature sensor, achieving a sensitivity of 72 pm/°C .…”

“…The ability to detect subtle temperature variation is of profound importance for its applications in proximity sensing, 1,2 tumor monitoring, 3,4 and microfluidics. 5,6 Recently, various temperature sensors have been developed based on resistance, 7 capacitance, 8 thermal-sensitive upconversion nanoparticles (UCNPs), 9 Mach−Zehnder interferometer (MZI), 10,11 and Fabry−Perot (FP) resonator. 12,13 Among them, sensors based on optical principles have made remarkable development due to their advantages such as high sensitivity, fast response, and immunity to electromagnetic interference.…”