Optical Multisensor Array with Functionalized Photonic Droplets by an Interpenetrating Polymer Network for Human Blood Analysis

Photonic Interpenetrating Polymer Network Fibers Comprising Intertwined Solid-State Cholesteric Liquid Crystal and Polyelectrolyte Networks for Sensor Applications

Uniform-sized photonic interpenetrating polymer network (IPN) fibers comprising intertwined solid-state cholesteric liquid crystal (CLCsolid) and anionic poly(acrylic acid) (PAA) or cationic poly(2-dimethylaminoethyl methacrylate) (PDMAEMA) networks (photonic IPNPAA or IPNPDMAEMA fibers) were developed for sensor applications. IPNPAA or IPNPDMAEMA fibers with a perfect photonic structure were fabricated inside Teflon tube templates without any treatments for realizing a planar orientation in those fibers. The dominant wavelength of the photonic color from a photograph taken with a cellular phone was used to measure the photonic color change. Photonic IPNPAA fibers treated with KOH (IPNKOH fibers) were used for sensing humidity and divalent metal ions. The linear ranges for relative humidity and Ca2+ detection were 21-92% and 0.5-3.5 mM, and their limits of detection (LODs) were 7.86% and 0.07 mM, respectively. The photonic IPNPAA (or IPNPDMAEMA) fiber immobilized with urease (IPNPAA-urease) (or glucose oxidase (IPNPDMAEMA-GOx)) was used for urea (or glucose) biosensor application. The photonic IPNPAA-urease (or IPNPDMAEMA-GOx) fiber was red-shifted in response to urea (or glucose) in the linear range of 10-60 mM (or 2-16 mM) with an LOD of 2.54 mM (or 0.76 mM). These photonic IPN fibers are promising because of their easy fabrication and miniaturization, battery-free device, cost-effectiveness, and visual detection without using sophisticated analytical instruments. The developed photonic IPN fibers provide new possibilities for the widespread use of photonic sensors in cutting-edge wearable technology and beyond.

Biomedical applications of stimuli-responsive "smart" interpenetrating polymer network hydrogels

In recent years, owing to the ongoing advancements in polymer materials, hydrogels have found increasing applications in the biomedical domain, notably in the realm of stimuli-responsive "smart" hydrogels. Nonetheless, conventional single-network stimuli-responsive "smart" hydrogels frequently exhibit deficiencies, including low mechanical strength, limited biocompatibility, and extended response times. In response, researchers have addressed these challenges by introducing a second network to create stimuli-responsive "smart" Interpenetrating Polymer Network (IPN) hydrogels. The mechanical strength of the material can be significantly improved due to the topological entanglement and physical interactions within the interpenetrating structure. Simultaneously, combining different network structures enhances the biocompatibility and stimulus responsiveness of the gel, endowing it with unique properties such as cell adhesion, conductivity, hemostasis/antioxidation, and color-changing capabilities. This article primarily aims to elucidate the stimulus-inducing factors in stimuli-responsive "smart" IPN hydrogels, the impact of the gels on cell behaviors and their biomedical application range. Additionally, we also offer an in-depth exposition of their categorization, mechanisms, performance characteristics, and related aspects. This review furnishes a comprehensive assessment and outlook for the advancement of stimuli-responsive "smart" IPN hydrogels within the biomedical arena. We believe that, as the biomedical field increasingly demands novel materials featuring improved mechanical properties, robust biocompatibility, and heightened stimulus responsiveness, stimuli-responsive "smart" IPN hydrogels will hold substantial promise for wide-ranging applications in this domain.

Solid-State Cholesteric Liquid Crystals as an Emerging Platform for the Development of Optical Photonic Sensors

Over the past decade, solid-state cholesteric liquid crystals (CLCsolid ) have emerged as a promising photonic material, heralding new opportunities for the advancement of optical photonic biosensors and actuators. The periodic helical structure of CLCsolid s gives rise to their distinctive capability of selectively reflecting incident radiation, rendering them highly promising contenders for a wide spectrum of photonic applications. Extensive research is conducted on utilizing CLCsolid 's optical characteristics to create optical sensors for bioassays, diagnostics, and environmental monitoring. This review provides an overview of emerging technologies in the field of interpenetrating polymeric network-CLCsolid (IPN) and CLCsolid -based optical sensors, including their structural designs, processing, essential materials, working principles, and fabrication methodologies. The review concludes with a forward-looking perspective, addressing current challenges and potential trajectories for future research.

Complex-Shape Solid-State Photonic Droplets Prepared via Phase Separation and Microfluidics

Complex-shape solid-state cholesteric liquid crystal (CLCsolid) droplets were prepared via solvent removal, phase separation, and photopolymerization of uniformly sized reactive CLC (rCLC)/fluorocarbon oil (FCO)/dichloromethane (solvent) droplets produced via a microfluidic method. The interfacial energies between rCLC and FCO, rCLC and water, and FCO and water of a rCLC/FCO droplet in an aqueous solution were precisely controlled through the specified surfactants. The shape of the rCLC/FCO droplet was strongly dependent on the balances among these interfacial energies, enabling the preparation of complex-shape droplets through the controlled concentration of the used surfactants. The complex-shape rCLC/FCO droplets showed photonic patterns consisting of a central reflection from a convex surface, cross-communication from a convex surface between adjacent particles, a photonic reflection band from the outer upward-facing concave surface, and total internal reflection from the inner upward-facing surface. Complex-shape CLCsolid particles obtained after photopolymerization and extraction of a nonreactive chiral dopant and FCO showed photonic patterns similar to those before photopolymerization without much deterioration of the photonic structure. These complex patterns make CLCsolid and rCLC/FCO droplets promising anticounterfeiting materials.

Bilayer Actuator Film for Urea Biosensing with Dual Responsiveness: Bending Actuation and Photonic Color Change

A noninvasive sweat-based biosensor was developed for urea detection using a photonic bilayer actuator film (BAF) consisting of an interpenetrating polymer network (IPN) as the active layer and a flexible poly(ethylene terephthalate) (PET) substrate as the passive layer (IPN/PET). The active IPN layer comprises intertwined solid-state cholesteric liquid crystal and poly(acrylic acid) (PAA) networks. Urease was immobilized in the PAA network in the IPN layer of the photonic BAF. The interaction with aqueous urea altered the curvature and photonic color of the photonic urease-immobilized IPN/PET (IPNurease/PET) BAF. The curvature (and wavelength of the photonic color) of the IPNurease/PET BAF increased linearly with urea concentration (Curea) in the range of Curea = 20-65 (and 30-65) mM with a limit of detection value of 1.42 (and 1.34) mM. The developed photonic IPNurease/PET BAF exhibited high selectivity toward urea and excellent spike test results with real human sweat. This novel IPNurease/PET BAF is promising because it enables battery-free, cost-effective, and visual detection-based analysis without the use of sophisticated instruments. Furthermore, the application of this photonic IPN/PET BAF can be easily extended to other biosensors by immobilizing other receptors on the IPN.

Janus Microdroplets with Tunable Self-Recoverable and Switchable Reflective Structural Colors

Microdroplets made from chiral liquid crystals (CLCs) can display reflective structural colors. However, the small area of reflection and their isotropic shape limit their performance. Here, Janus microdroplets are synthesized through phase separation between CLCs and silicone oil. The as-synthesized Janus microdroplets show primary structural colors with ≈14 times larger area compared to their spherical counterparts at a specific orientation; the orientation and thus the colored/transparent states can be switched by applying a magnetic field. The color of the Janus microdroplets can be tuned ranging from red to violet by varying the concentration of the chiral dopant in the CLC phase. Due to the density difference between the two phases, the Janus microdroplets prefer to orientate the silicone oil side up vertically, enabling the self-recoverable structural color after distortion. The Janus microdroplets can be dispersed in aqueous media to track the configuration and speed of magnetic objects. They can also be patterned as multiplexed labels for data encryption. The magnetic field-responsive Janus CLC microdroplets presented here offer new insights to generate and switch reflective colors with high color saturation. It also paves the way for broader applications of CLCs, including anti-counterfeiting, data encryption, display, and untethered speed sensors.

State-of-the-Art Development in Liquid Crystal Biochemical Sensors

As an emerging stimuli-responsive material, liquid crystal (LC) has attracted great attentions beyond display applications, especially in the area of biochemical sensors. Its high sensitivity and fast response to various biological or chemical analytes make it possible to fabricate a simple, real-time, label-free, and cost-effective LC-based detection platform. Advancements have been achieved in the development of LC-based sensors, both in fundamental research and practical applications. This paper briefly reviews the state-of-the-art research on LC sensors in the biochemical field, from basic properties of LC material to the detection mechanisms of LC sensors that are categorized into LC-solid, LC-aqueous, and LC droplet platforms. In addition, various analytes detected by LCs are presented as a proof of the application value, including metal ions, nucleic acids, proteins, glucose, and some toxic chemical substances. Furthermore, a machine-learning-assisted LC sensing platform is realized to provide a foundation for device intelligence and automatization. It is believed that a portable, convenient, and user-friendly LC-based biochemical sensing device will be achieved in the future.

Cholesteric Liquid Crystal Photonic Hydrogel Films Immobilized with Urease Used for the Detection of Hg2+

Mercury ion is one of the most widespread heavy metal contaminants which can accumulate in the body through multiple channels, posing a detrimental impact on human health. We demonstrate a simple and low-cost method for the detection of Hg2+ assisted by a cholesteric liquid crystal photonic hydrogel (polyacrylic acid (PAA)) film with immobilized urease (CLC-PAAurease film). In the absence of Hg2+, a significant change in color and an obvious red shift in the reflected light wavelength of the prepared film were observed, since urease can hydrolyze urea to produce NH3, resulting in an increasing pH value of the microenvironment of CLC-PAAurease film. Hg2+ can inhibit the activity of urease so that the color change of the film is not obvious, corresponding to a relatively small variation of the reflected light wavelength. Therefore, Hg2+ can be quantitatively detected by measuring the displacement of the reflected light wavelength of the film. The detection limit of Hg2+ is about 10 nM. This approach has a good application prospect in the monitoring of heavy metal ions in environmental water resources.

Overview of Liquid Crystal Biosensors: From Basic Theory to Advanced Applications

Liquid crystals (LCs), as the remarkable optical materials possessing stimuli-responsive property and optical modulation property simultaneously, have been utilized to fabricate a wide variety of optical devices. Integrating the LCs and receptors together, LC biosensors aimed at detecting various biomolecules have been extensively explored. Compared with the traditional biosensing technologies, the LC biosensors are simple, visualized, and efficient. Owning to the irreplaceable superiorities, the research enthusiasm for the LC biosensors is rapidly rising. As a result, it is necessary to overview the development of the LC biosensors to guide future work. This article reviews the basic theory and advanced applications of LC biosensors. We first discuss different mesophases and geometries employed to fabricate LC biosensors, after which we introduce various detecting mechanisms involved in biomolecular detection. We then focus on diverse detection targets such as proteins, enzymes, nucleic acids, glucose, cholesterol, bile acids, and lipopolysaccharides. For each of these targets, the development history and state-of-the-art work are exhibited in detail. Finally, the current challenges and potential development directions of the LC biosensors are introduced briefly.

The Bioanalytical and Biomedical Applications of Polymer Modified Substrates

Polymers with different structures and morphology have been extensively used to construct functionalized surfaces for a wide range of applications because the physicochemical properties of polymers can be finely adjusted by their molecular weights, polydispersity and configurations, as well as the chemical structures and natures of monomers. In particular, the specific functions of polymers can be easily achieved at post-synthesis by the attachment of different kinds of active molecules such as recognition ligand, peptides, aptamers and antibodies. In this review, the recent advances in the bioanalytical and biomedical applications of polymer modified substrates were summarized with subsections on functionalization using branched polymers, polymer brushes and polymer hydrogels. The review focuses on their applications as biosensors with excellent analytical performance and/or as nonfouling surfaces with efficient antibacterial activity. Finally, we discuss the perspectives and future directions of polymer modified substrates in the development of biodevices for the diagnosis, treatment and prevention of diseases.

Ultra-low sample consumption consecutive-detection method for biochemical molecules based on a whispering gallery mode with a liquid crystal microdroplet

Ultra-low sample consumption detection has many applications in molecular biology, bioanalytical chemistry, and medical science. In this Letter, a novel, to the best of our knowledge, simple type of ultra-low sample consumption detection method based on a whispering gallery mode is proposed as a means to realize consecutive detection with a liquid crystal (LC) microdroplet for biochemical molecule detection, using deoxyribonucleic acid (DNA) as a model biomarker. The sensor consists of a 105-µm-core multimode fiber fused with a hollow capillary tube, with the LC microdroplet suspended stably in the testing solution. Its application to the detection of salmon sperm DNA yielded an adjustable measurement range of 3.75-11.25 μg/ml and a sensitivity of 0.33 nm/µg/ml. The test solution required as little as 3 nl of the sample, and the limit of detection was 1.32 µg/ml, which corresponds to the effective detection of as little as 3.96 pg of DNA. This method has great potential for application in the ultra-low sample consumption detection of biochemical molecules.

Recent Progress of Layer-by-layer Assembly, Free-Standing Film and Hydrogel Based on Polyelectrolytes

Nowadays, polyelectrolytes play an essential role in the development of new materials. Their use allows creating new properties of materials and surfaces and vary them in a wide range. Basically, modern methods are divided into three areas-the process of layer-by-layer deposition, free-standing films, and hydrogels based on polyelectrolytes. Layer-by-layer assembly of polyelectrolytes on various surfaces is a powerful technique. It allows giving surfaces new properties, for example, protect them from corrosion. Free-standing films are essential tools for the design of membranes and sensors. Hydrogels based on polyelectrolytes have recently shown their applicability in electrical and materials science. The creation of new materials and components with controlled properties can be achieved using polyelectrolytes. This review focuses on new technologies that have been developed with polyelectrolytes over the last five years.

Bottom-Up Assembled Photonic Crystals for Structure-Enabled Label-Free Sensing

Photonic crystals (PhCs) display photonic stop bands (PSBs) and at the edges of these PSBs transport light with reduced velocity, enabling the PhCs to confine and manipulate incident light with enhanced light-matter interaction. Intense research has been devoted to leveraging the optical properties of PhCs for the development of optical sensors for bioassays, diagnosis, and environmental monitoring. These applications have furthermore benefited from the inherently large surface area of PhCs, giving rise to high analyte adsorption and the wide range of options for structural variations of the PhCs leading to enhanced light-matter interaction. Here, we focus on bottom-up assembled PhCs and review the significant advances that have been made in their use as label-free sensors. We describe their potential for point-of-care devices and in the review include their structural design, constituent materials, fabrication strategy, and sensing working principles. We thereby classify them according to five sensing principles: sensing of refractive index variations, sensing by lattice spacing variations, enhanced fluorescence spectroscopy, surface-enhanced Raman spectroscopy, and configuration transitions.