Liquid Crystal Microdroplets Research Articles

Translational and rotational drives of micro-droplets of nematic liquid crystal with chiral dopant

The translational and rotational control of liquid crystal micro-droplets by electric fields has been explored for the future use in MEMS and lab-on-a-chip devices. The liquid crystal droplets are generated by the phase transition process of a liquid crystalline material, 4-n-4’-pentylcyanobiphenyl (5CB), from the isotropic to the nematic phase, and are thus suspended in the isotropic phase of 5CB. The addition of a chiral dopant to 5CB induces the symmetry breaking of the molecular orientation configuration within the droplet, leading to the formation of helical molecular orientation configurations. The helical configuration of the molecular orientation field is the key to enabling the translational and rotational drives of the droplet. Under electric fields, the translational drive of the droplets occurs in a direction perpendicular to both the electric field and the helical axis, and the rotational drive of the droplets occurs to align the helical axis perpendicular to the electric field. Finally, we propose the method for 2D and 3D manipulation of the droplets by combining the translational and rotational drives.

Rotation of liquid crystal microdroplets in the intensity minima of an optical vortex beam.

An optical vortex is characterized by its donut-shaped intensity distribution and helical phase structure. In this study, we demonstrate that an optical vortex beam, generated by a spatial light modulator, can trap, circulate, and rotate liquid crystal microdroplets of various sizes at different positions within the beam. Our findings indicate that larger microdroplets are trapped at intensity minima without altering their internal liquid crystal orientation, which is fluid by nature, and the rotation of microdroplets were observed. This rotation, a rare phenomenon, occurs without damaging or altering the inner liquid crystal molecules, offering an advantage over traditional circularly polarized optical trapping, which can generally alter inner molecular arrangements of liquid crystal. This report details the relationship between trapped particle size, trapping position, and rotation angle of liquid crystal microdroplets within an optical vortex beam.

A Wearable Thin-Film Hydrogel Laser for Functional Sensing on Skin.

Flexible photonics offers the possibility of realizing wearable sensors by bridging the advantages of flexible materials and photonic sensing elements. Recently, optical resonators have emerged as a tool to improve their oversensitivity by integrating with flexible photonic sensors. However, direct monitoring of multiple psychological information on human skin remains challenging due to the subtle biological signals and complex tissue interface. To tackle the current challenges, here, we developed a functional thin film laser formed by encapsulating liquid crystal droplet lasers in a flexible hydrogel for monitoring metabolites in human sweat (lactate, glucose, and urea). The three-dimensional cross-linked hydrophilic polymer serves as the adhesive layer to allow small molecules to penetrate from human tissue to generate strong light--matter interactions on the interface of whispering gallery modes resonators. Both the hydrogel and cholesteric liquid crystal microdroplets were modified specifically to achieve high sensitivity and selectivity. As a proof of concept, wavelength-multiplexed sensing and a prototype were demonstrated on human skin to detect human metabolites from perspiration. These results present a significant advance in the fabrication and potential guidance for wearable and functional microlasers in healthcare.

High-κ elastomer with dispersed ferroelectric nematic liquid crystal microdroplets

An emergent liquid ferroelectric material is dispersed into polydimethylsiloxane as microdroplets, realizing a stretchable and ferroelectric high-κ elastomer.

Compact fiber sensor for rapid trypsin detection based on the whispering gallery mode with a liquid crystal microdroplet

Trypsin, a protease produced in the pancreas, plays a crucial role in various medical conditions, including acute pancreatitis, cystic fibrosis, and malnutrition, where abnormal trypsin levels are often implicated. Consequently, trypsin detection has emerged as a valuable diagnostic tool in clinical medicine. In this study, we introduced an integrated fiber sensor that capitalizes on the amplification and transduction capabilities of liquid crystals, coupled with the high sensitivity of the whispering gallery mode, to achieve precise trypsin detection. This innovative approach offers consecutive measurement and rapid response times, typically under 200 s, and remarkably low sample consumption, as little as 3 nL, potential for detection in capillary blood sampling. Furthermore, when subjected to validation tests for trypsin detection in human serum, our method demonstrated excellent consistency and reliability, with recovery ratios falling within the range of 97–112%. Beyond trypsin, this method's adaptability and versatility make it a universal technique with potential applications in the field of biosensing and biochemistry.

Computational Analysis on the Performance of Elongated Liquid Crystal Biosensors.

Elongated ellipsoidal liquid crystal microdroplet reorientation dynamics are discussed in this paper for biosensor applications. To investigate the effect of elongated droplets on nematic liquid crystal droplet biosensors, we simulated a model of a liquid crystal droplet using ellipse geometry. Director reorientation is examined in relation to the elongated droplet shape. In addition, we examined aspect ratio as a factor affecting biosensor response time in relation to surface viscosity and anchoring energy. Finally, the findings suggest that the aspect ratio should be taken into account when designing biosensors. These results can be used to develop more effective biosensors for a variety of applications. This model then predicts the director reorientation angle, which is dependent on the anchoring energy and surface viscosity. This model further suggests that both surface viscosity and homeotropic anchoring energy play an important role when it comes to the director reorientation angle. We developed and applied a nonlinear unsteady-state mathematical model utilizing torque balance and Frank free energy according to the Leslie-Ericksen continuum theory for simulating elongated nematic liquid crystal biosensor droplets with aqueous interfaces. Using the Euler-Lagrange equation, a transient liquid crystal-aqueous interface realignment is modeled by changing the easy axis when surfactant molecules are added to the interface. The realignment at the surface of the droplet is assumed to be driven by the effect of the surfactant, which causes an anchoring transition. According to the results, the response time of the biosensor depends on the aspect ratio. Therefore, the elongation has the potential to control biosensing response time. The result of our study provides a better understanding of director reorientation in elongated liquid crystal droplets in biosensing applications through the numerical results which are presented in this paper.

Dynamic Control of Multiple Optical Patterns of Cholesteric Liquid Crystal Microdroplets by Light-Driven Molecular Motors

Dynamic Control of Multiple Optical Patterns of Cholesteric Liquid Crystal Microdroplets by Light-Driven Molecular Motors

Creating liquid crystal microdroplet arrays for multiplexed sensing by spatially-controlled molecular patterning

In this study, we presented a spatially-controlled molecular patterning technique to prepare liquid crystal (LC) microdroplet arrays on glass substrates. This technique utilizes an oxygen plasma activated PDMS stamp to remove the pre-coated dimethyloctadecyl 3-(trimethoxysilyl) propyl ammonium chloride (DMOAP) molecules from glass substrates, producing a surface with complementary patterns and specific hydrophobicity. When LC molecules are introduced onto this produced molecular pattern, a LC microdroplet array with uniform droplet size and positional order is formed. By using the LC microdroplet array doped with a Hg2+ selective ligand, the lowest detectable concentration of Hg2+ is 200-fold lower than that of conventional LC-based sensors. In addition, multiplexed detection of Hg2+, Al3+, Fe3+ and pH value in real water samples with a high recovery rate (∼100%) was demonstrated by using the LC microdroplet arrays doped with different molecular probes. Due to the specific arrangement of the LC microdroplet arrays, the collected optical signal of LC microarrays can be transformed into numerical symbols. The developed spatially controlled molecular patterning technique could be used to prepare highly uniform LC microdroplet arrays with consistent optical signals, providing a simple method to prepare the LC-based sensing platforms with improved sensing performance.

Lasing behavior of a nematic liquid crystal microdroplet depending on the irradiation position

This paper reports the random lasing and whispering gallery mode (WGM) lasing in dye-doped nematic liquid crystal (NLC) droplets. We discuss the emission behavior of the droplets in detail. Their lasing behavior depends on irradiation position and droplet diameter. Moreover, the two types of lasers likely share energy. Naturally, stopping one increases the efficiency of the other. Besides, the coexistence of the two types of lasers in an NLC droplet offers a controllable dye laser emitting two lights in different wavelength ranges.

Liquid crystal doped photopolymer micro-droplets printed by a simple and clean laser-induced forward transfer process.

We print a tunable photopolymer (photopolymer dispersed liquid crystal -PDLC), using the laser-induced direct transfer technique without absorber layer, which was a challenge for this technique given the low absorption and high viscosity of PDLC, and which had not been achieved so far to our knowledge. This makes the LIFT printing process faster and cleaner and achieves a high-quality printed droplet (aspheric profile and low roughness). A femtosecond laser was needed to reach sufficiently peak energies to induce nonlinear absorption and eject the polymer onto a substrate. Only a narrow energy window allows the material to be ejected without spattering.

Phase-Transition Microcavity Laser

Liquid-crystal microcavity lasers have attracted considerable attention because of their extraordinary tunability and sensitive response to external stimuli, and because they operate generally within a specific phase. Here, we demonstrate a liquid-crystal microcavity laser operated in the phase transition in which the reorientation of liquid-crystal molecules occurs from aligned to disordered states. A significant wavelength shift of the microlaser is observed, resulting from the dramatic changes in the refractive index of liquid-crystal microdroplets during the phase transition. This phase-transition microcavity laser is then exploited for sensitive thermal sensing, enabling a two-order-of-magnitude enhancement in sensitivity compared with the nematic-phase microlaser operated far from the transition point. Experimentally, we demonstrate an exceptional sensitivity of -40 nm/K and an ultrahigh resolution of 320 μK. The phase-transition microcavity laser features compactness, softness, and tunability, showing great potential for high-performance sensors, optical modulators, and soft matter photonics.

Autonomous Microlasers for Profiling Extracellular Vesicles from Cancer Spheroids

Self-propelled micro/nanomotors are emergent intelligent sensors for analyzing extracellular biomarkers in circulating biological fluids. Conventional luminescent motors are often masked by a highly dynamic and scattered environment, creating challenges to characterize biomarkers or subtle binding dynamics. Here we introduce a strategy to amplify subtle signals by coupling strong light-matter interactions on micromotors. A smart whispering-gallery-mode microlaser that can self-propel and analyze extracellular biomarkers is demonstrated through a liquid crystal microdroplet. Lasing spectral responses induced by cavity energy transfer were employed to reflect the abundance of protein biomarkers, generating exclusive molecular labels for cellular profiling of exosomes derived from 3D multicellular cancer spheroids. Finally, a microfluidic biosystem with different tumor-derived exosomes was employed to elaborate its sensing capability in complex environments. The proposed autonomous microlaser exhibits a promising method for both fundamental biological science and applications in drug screening, phenotyping, and organ-on-chip applications.

Compact fiber sensor for pH measurement based on the composite effect of hydrogel deformation and LC refractive index variation.

A novel, to the best of our knowledge, type of compact pH fiber sensor combined with a hydrogel based on the whispering gallery mode (WGM) is proposed and integrates a liquid crystal (LC) microdroplet in a capillary in a compact structure as small as 180 µm. In the research, the hydrogel performs both as a supporting frame and a responsive material that causes morphological deformation of the LC microdroplet with pH variation. Moreover, a new phenomenon of pH-induced LC refractive index variation is observed and applied in the pH measurement, so that the acid itself can also lead the LC microdroplet structure transition. Thus, the WGM method is applied to detect the composite effect simultaneously to improve the sensing capability. The sensitivity of the sensor in the pH range from 4.55 to 6.86 reaches 3.19 nm/pH. The response time is short, within 60 s. The simple and compact structure of the sensor reduces the cost and enhances the stability, which is of great potential for biomedical pH measurement.

Spatial Patterning of Fluorescent Liquid Crystal Ink Based on Inkjet Printing.

Fluorescent cholesteric liquid crystal materials (FCLC) with aggregation-induced emission (AIE) properties can effectively solve the contradiction between aggregation-induced quenching (ACQ) and liquid crystal self-assembly when light-emitting materials are aggregated, and they have great application value in the fields of anti-counterfeit detection and information hiding. However, generating a visually appealing design, logo, or image in the application typically requires an intricate fabrication process, such as the use of prefabricated molds and photomasks, which greatly limits the practical application of FCLC materials. Herein is reported a new method for spatially patterned liquid crystal (LC) microdroplet arrays using drop-on-demand inkjet printing technology. Through rational composition design, a spatial array composed of different liquid crystal microdroplets was established, and the array contains two entirely distinct but intact patterns at the same time, which can be reversibly switched under the irradiation of UV and natural light. This study provides a new method for the integrated preparation of different component liquid crystal materials.

Carbon Quantum Dots doped Cholesteric Liquid Crystal Films and Microdroplets for Anti-Counterfeiting

Carbon Quantum Dots doped Cholesteric Liquid Crystal Films and Microdroplets for Anti-Counterfeiting

Designing Biological Microsensors with Chiral Nematic Liquid Crystal Droplets.

Biosensing using liquid crystals has a tremendous potential by coupling the high degree of sensitivity of their alignment to their surroundings with clear optical feedback. Many existing set-ups use birefringence of nematic liquid crystals, which severely limits straightforward and frugal implementation into a sensing platform due to the sophisticated optical set-ups required. In this work, we instead utilize chiral nematic liquid crystal microdroplets, which show strongly reflected structural color, as sensing platforms for surface active agents. We systematically quantify the optical response of closely related biological amphiphiles and find unique optical signatures for each species. We detect signatures across a wide range of concentrations (from micromolar to millimolar), with fast response times (from seconds to minutes). The striking optical response is a function of the adsorption of surfactants in a nonhomogeneous manner and the topology of the chiral nematic liquid crystal orientation at the interface requiring a scattering, multidomain structure. We show that the surface interactions, in particular, the surface packing density, to be a function of both headgroup and tail and thus unique to each surfactant species. We show lab-on-a-chip capability of our method by drying droplets in high-density two-dimensional arrays and simply hydrating the chip to detect dissolved analytes. Finally, we show proof-of-principle in vivo biosensing in the healthy as well as inflamed intestinal tracts of live zebrafish larvae, demonstrating CLC droplets show a clear optical response specifically when exposed to the gut environment rich in amphiphiles. Our unique approach shows clear potential in developing on-site detection platforms and detecting biological amphiphiles in living organisms.

Optical Manipulation of a Liquid Crystal (LC) Microdroplet by Optical Force

AbstractLiquid crystal (LC) is a particular type of molecule that exhibits directional properties. Its optical birefringence property offers potential non‐contact optical manipulation by optical forces. The optical manipulation of LC in the form of microdroplets shows various potential applications such as biosensors and microactuators. This review discusses the basic concept of LC, the optical manipulation of LC, and its potential applications as LC‐based sensors and microactuators in the form of microdroplets.

Multifunctional Laser Imaging of Cancer Cell Secretion with Hybrid Liquid Crystal Resonators (Laser Photonics Rev. 16(8)/2022)

Laser Emission Imaging In article number 2100734, Yu-Cheng Chen and colleagues have developed a label-free laser emission microscope for imaging secreted molecules associated with the cell–cell environment. Liquid crystal microdroplets are designed as signal amplifiers to report subtle molecular functions in a hybrid Fabry–Pérot microcavity. By integrating resonators with a galvo-scanning system, dynamic information of cell physiological processes could be recorded through different lasing wavelengths for a wide range of cellular applications.

Bio-derived chlorophyll dye doped cholesteric liquid crystal films and microdroplets for advanced anti-counterfeiting security labels

Herein, we have shown security codes based on an advanced anti-counterfeiting material that are difficult to duplicate and are substantially distinct from the present technology. The anti-counterfeiting material can be made by dispersing green synthesized chlorophyll from spinach leaves into cholesteric liquid crystal (Red, Green and Blue reflections). The resultant anti-counterfeiting material reflects color in daylight (Red/Green/ Blue) due to the reflection property of CLCs and magenta color in UV light due to the fluorescence property of chlorophyll. Furthermore, we have shown that anti-counterfeiting material confined to spherical microdroplets produced by glass capillary microfluidic approach exhibit dual-mode display and security ink properties under daylight and ultraviolet light, including authenticate/non-authenticate QR codes, implying their potential applications in anti-counterfeiting technologies for the protection of valuable objects. These color variations are easily detectable in real time and may be used to create anti-counterfeiting patterns with color changesin both reflection and fluorescence modes. Because of the easy technique, we believe this can give a new platform for numerous security and color-based applications that is more cost-effective and environmentally friendly than traditional approaches.

Multifunctional Laser Imaging of Cancer Cell Secretion with Hybrid Liquid Crystal Resonators

AbstractLaser emission imaging is an emerging technology, which offers immense potential for revealing biological behavior with enhanced light‐matter interactions and signal contrast. State‐of‐the‐art lasers mostly provide physical information of cells, without being able to perform various biochemical functions or biological information of cell. Here this need is addressed by introducing hybrid liquid crystal microlaser resonators, an approach for label‐free laser emission imaging of secreted molecules associated with various types of cell–environment interaction. Liquid crystal microdroplets are designed as signal amplifiers to report subtle molecular events sandwiched in a Fabry–Pérot microcavity. Through the integration with a galvometer scanner, dynamic information of cell physiological processes is recorded through different lasing wavelengths. The capability of detecting small molecule, redox oxygen species, to larger molecules such as overexpressed proteins is demonstrated by using pancreatic cancer cell line. The capability of monitoring cell responses to anticancer drug is also illustrated. The proposed concept can be extended to multiplexed biolasers for investigating cell signaling, cell–cell interactions, and drug screening.