An integrated liquid crystal sensing device assisted by the surfactant-embedded smart hydrogel

Construction of Liquid Crystal-Based Sensors Using Enzyme-Linked Dual-Functional Nucleic Acid on Magnetic Beads

The development of liquid crystal (LC)-based sensors with superior performances such as high portability, excellent stability, great convenience, and remarkable sensitivity is highly demanded. This work proposes a new strategy for constructing the LC-based sensor using enzyme-linked dual-functional nucleic acid (d-FNA) on magnetic beads (MBs). The detection of kanamycin (KA) is demonstrated as a model. Acetylcholinesterase (AChE) is assembled onto the KA aptamer-modified MBs with a d-FNA strand that consists of an AChE aptamer and the complementary sequence of a KA aptamer. As the specific recognition of KA by its aptamer triggers the release of AChE from the MBs, the myristoylcholine (Myr) solution after incubation with the MBs causes the black image of the LCs due to the formation of the Myr monolayer at the aqueous/LC interface. Otherwise, in the absence of KA, AChE is still decorated on the MBs and causes the hydrolysis of Myr. Therefore, a bright image of LCs is obtained. The detection of KA is successfully achieved with a lower detection limit of 48.1 pg/mL. In addition, a thin polydimethylsiloxane (PDMS) layer-coated glass and a portable optical device are used to improve the stability and portability of the LC-based sensor to advance potential commercial applications. Furthermore, the detection of KA in milk with a portable device is demonstrated, showing the potential of the proposed enzyme-linked LC-based sensor.

Morphology and Enzyme-Mimicking Activity of Copper Nanoassemblies Regulated by Peptide: Mechanism, Ultrasensitive Assaying of Trypsin, and Screening of Trypsin Inhibitors

To regulate nanostructure synthesis is of crucial importance for developing various applications, including catalysis, bioanalysis, and optical devices. Herein, the morphology and peroxidase (POD)-mimicking activity of peptide-templated copper nanoassemblies (Cu NAs) are regulable with peptide types. The Cu NAs templated with peptide containing single cysteine are uniform nanoclusters with strong POD-like activity. However, the Cu NAs templated with peptide containing two cysteines are fusiform-like with very weak POD-like activity. Unexpectedly, the POD-like activity of Cu NAs templated with peptide containing two cysteines with lysine between the cysteines is significantly enhanced when trypsin is incubated, which is unchanged for the Cu NAs templated with peptide containing two cysteines without lysine between the cysteines. The remarkably enhanced POD-mimicking activity originates from trypsin specifically shearing the peptide bond on the lysine, thereby allowing the aggregated Cu NAs to unravel into individual nanoclusters. Therefore, a robust colorimetric sensing platform was constructed for sensitive and selective detection of trypsin, which showed a linear concentration range of 3-1000 nM and a detection limit of 0.82 nM (S/N = 3). More interestingly, featured by trypsin inhibitor restraining trypsin activity, it enabled us to screen trypsin inhibitors as well. Subsequently, the developed assay was applied to detect trypsin in serum samples with good accuracy and reproducibility. Thus, this strategy shows great potential application in the clinic for diagnosis of trypsin-indicating diseases as well as the screening of trypsin inhibitor-based anti-cancer drugs.

Molecular Visual Sensing, Boolean Logic Computing, and Data Security Using a Droplet-Based Superwetting Paradigm

Inspired by information processing and logic operations of life, many artificial biochemical systems have been designed for applications in molecular information processing. However, encoding the binary synergism between matter, energy, and information in a superwetting system remains challenging. Herein, a superwetting paradigm was proposed for multifunctional applications including molecular visual sensing and data security on a superhydrophobic surface. A Triton X-100-encapsulated gelatin (TeG) hydrogel was prepared and selectively decomposed by trypsin, releasing the surfactant to decrease the surface tension of a droplet. Integrating the droplet with the superhydrophobic surface, the superwetting behavior was utilized for visual detection and information encoding. Interestingly, the proposed TeG hydrogel can function as an artificial gelneuron for molecular-level logic computing, where the combination of matters (superhydrophobic surface, trypsin, and leupeptin) acts as inputs to interact with energy (liquid surface tension and solid surface energy) and information (binary character), resulting in superwettability transitions (droplet surface tension, contact angle, rolling angle, and bounce) as outputs. Impressively, the TeG gelneuron can be further developed as molecular-level double cryptographic steganography to encode, encrypt, and hide specific information (including the maze escape route and content of the classical literature) due to its programmability, stimuli responsive ability, and droplet concealment. This study will encourage the development of advanced molecular paradigms and their applications, such as superwetting visual sensing, molecular computing, interaction, and data security.

Applications of Gelatin in Biosensors: Recent Trends and Progress

Gelatin is a natural protein from animal tissue with excellent biocompatibility, biodegradability, biosafety, low cost, and sol-gel property. By taking advantage of these properties, gelatin is considered to be an ideal component for the fabrication of biosensors. In recent years, biosensors with gelatin have been widely used for detecting various analytes, such as glucose, hydrogen peroxide, urea, amino acids, and pesticides, in the fields of medical diagnosis, food testing, and environmental monitoring. This perspective is an overview of the most recent trends and progress in the development of gelatin-based biosensors, which are classified by the function of gelatin as a matrix for immobilized biorecognition materials or as a biorecognition material for detecting target analytes.

Liquid Crystal Biosensors: Principles, Structure and Applications

Liquid crystals (LCs) have been widely used as sensitive elements to construct LC biosensors based on the principle that specific bonding events between biomolecules can affect the orientation of LC molecules. On the basis of the sensing interface of LC molecules, LC biosensors can be classified into three types: LC-solid interface sensing platforms, LC-aqueous interface sensing platforms, and LC-droplet interface sensing platforms. In addition, as a signal amplification method, the combination of LCs and whispering gallery mode (WGM) optical microcavities can provide higher detection sensitivity due to the extremely high quality factor and the small mode volume of the WGM optical microcavity, which enhances the interaction between the light field and biotargets. In this review, we present an overview of the basic principles, the structure, and the applications of LC biosensors. We discuss the important properties of LC and the principle of LC biosensors. The different geometries of LCs in the biosensing systems as well as their applications in the biological detection are then described. The fabrication and the application of the LC-based WGM microcavity optofluidic sensor in the biological detection are also introduced. Finally, challenges and potential research opportunities in the development of LC-based biosensors are discussed.

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.

An effective formaldehyde gas sensor based on oxygen-rich three-dimensional graphene

Three-dimensional (3D) graphene with a high specific surface area and excellent electrical conductivity holds extraordinary potential for molecular gas sensing. Gas molecules adsorbed onto graphene serve as electron donors, leading to an increase in conductivity. However, several challenges remain for 3D graphene-based gas sensors, such as slow response and long recovery time. Therefore, research interest remains in the promotion of the sensitivity of molecular gas detection. In this study, we fabricate oxygen plasma-treated 3D graphene for the high-performance gas sensing of formaldehyde. We synthesize large-area, high-quality, 3D graphene over Ni foam by chemical vapor deposition and obtain freestanding 3D graphene foam after Ni etching. We compare three types of strategies-non-treatment, oxygen plasma, and etching in HNO₃solution-for the posttreatment of 3D graphene. Eventually, the strategy for oxygen plasma-treated 3D graphene exceeds expectations, which may highlight the general gas sensing based on chemiresistors.

An Overview on Recent Progress of the Hydrogels: From Material Resources, Properties to Functional Applications

Hydrogels, as the most typical elastomer materials with three-dimensional network structures, have attracted wide attention owing to their outstanding features in fields of sensitive stimulus response, low surface friction coefficient, good flexibility and bio-compatibility. Because of numerous fresh polymer materials (or polymerization monomers), hydrogels with various structure diversities and excellent properties are emerging, and the development of hydrogels is very vigorous over the past decade. This review focuses on state-of-the-art advances, systematically reviews the recent progress on construction of novel hydrogels utilized several kinds of typical polymerization monomers, and explores the main chemical and physical cross-linking methods to develop the diversity of hydrogels. Following the aspects mentioned above, the classification and emerging applications of hydrogels, such as pH response, ionic response, electrical response, thermal response, biomolecular response, and gas response, are extensively summarized. Finally, we have done this review with the promises and challenges for the future evolution of hydrogels and their biological applications. cross-linking methods; functional applications; hydrogels; material resources This article is protected by copyright. All rights reserved.

Hydrogel, Electrospun and Composite Materials for Bone/Cartilage and Neural Tissue Engineering

Injuries of the bone/cartilage and central nervous system are still a serious socio-economic problem. They are an effect of diversified, difficult-to-access tissue structures as well as complex regeneration mechanisms. Currently, commercially available materials partially solve this problem, but they do not fulfill all of the bone/cartilage and neural tissue engineering requirements such as mechanical properties, biochemical cues or adequate biodegradation. There are still many things to do to provide complete restoration of injured tissues. Recent reports in bone/cartilage and neural tissue engineering give high hopes in designing scaffolds for complete tissue regeneration. This review thoroughly discusses the advantages and disadvantages of currently available commercial scaffolds and sheds new light on the designing of novel polymeric scaffolds composed of hydrogels, electrospun nanofibers, or hydrogels loaded with nano-additives.

A novel liquid crystal sensing platform for highly selective UO22+ detection based on a UO22+-specific DNAzyme

A label-free and selective sensor was established for uranyl ion (UO₂²⁺) detection based on a UO₂²⁺-dependent DNAzyme and liquid crystals (LCs). In the presence of UO₂²⁺, the substrate chains can be cleaved at the rA site by the DNAzyme strands. The cleaved products released from the DNAzyme strand will hybridize with the capture probes that are fixed on the LC sensing substrate to form double strands. The formation of double strands would disturb the original orientation and induce the rearrangement of liquid crystal molecules, resulting in the polarization images changing from uniform black to bright. Attributed to the specificity of the DNAzyme and the optical signal of the LC, a highly selective and label-free method was established with a detection limit of 25 nM. This approach showed satisfactory analytical performance and offered an inspiring platform for detecting other radioactive elements.

Gelatin hydrogel/contact lens composites as rutin delivery systems for promoting corneal wound healing

Corneal wound healing is a highly regulated biological process that is of importance for reducing the risk of blinding corneal infections and inflammations. Traditional eye drop was the main approach for promoting corneal wound healing. However, its low bioavailability required a high therapeutic concentration, which can lead to ocular or even systemic side effects. To develop a safe and effective method for treating corneal injury, we fabricated rutin-encapsulated gelatin hydrogel/contact lens composites by dual crosslinking reactions including in situ free radical polymerization and carboxymethyl cellulose/N-hydroxysulfosuccinimide crosslinking. In vitro drug release results evidenced that rutin in the composites could be sustainedly released for up to 14 days. In addition, biocompatibility assay indicated nontoxicity of the composites. Finally, the effect of rutin-encapsulated composites on the healing of the corneal injury in rabbits was investigated. The injury was basically cured in corneas using rutin-encapsulated composites (healing rate, 98.3% ± 0.7%) at 48 h post-operation, while the damage was still present in corneas using the composite (healing rate, 87.0% ± 4.5%). Further proteomics analysis revealed that corneal wound healing may be promoted by the ERK/MAPK and PI3K/AKT signal pathways. These results inform a potential intervention strategy to facilitate corneal wound healing in humans.

Hydrogel-assisted paper-based lateral flow sensor for the detection of trypsin in human serum

The detection of trypsin and its inhibitor is significantly important for both clinical diagnosis and disease treatment. Herein, we demonstrate a hydrogel-assisted paper-based lateral flow sensor for the detection of trypsin and its inhibitor for the first time. The gelatin hydrogel is hydrolyzed based on the gel-to-sol transition in the presence of trypsin, which results in the release of the trapped water molecules in the gelatin hydrogel. By placing one end of a pH indicator strip onto the hydrolyzed gelatin hydrogel, water is flowing along the pH indicator strip. However, in the absence of trypsin, water cannot flow along the pH indicator strip as the water molecules are trapped in the gelatin hydrogel. The detection limit of the system reaches as low as 1.0 × 10^-6 mg/mL, and it is also applied to the quantitative detection of trypsin in human serum. In addition, the detection of a clinical drug aprotinin that is an inhibitor of trypsin is also successfully achieved. Noteworthy, only the gelatin hydrogel, pH indicator strip, and PS substrate are needed to fulfill the detection of trypsin without the need of other chemicals or reagents. Overall, we develop a particularly simple, elegant, robust, competitive, high-throughput, and low-cost approach for the rapid and label-free detection of trypsin and its inhibitor, which is very promising in the development of commercial products for sensing, diagnostic, and pharmaceutical applications. Besides, the hydrogel-assisted paper-based lateral flow sensor can also be employed to detect other analytes of interest by use of different stimuli-responsive hydrogel systems.