Hydrogels and Their Role in Biosensing Applications

Carrier-based immobilization of Aerococcus viridansl-lactate oxidase

l-Lactate oxidase has important applications in biosensing and finds increased use in biocatalysis. The enzyme has been characterized well, yet its immobilization has not been explored in depth. Here, we studied immobilization of Aerococcus viridansl-lactate oxidase on porous carriers of variable matrix material (polymethacrylate, polyurethane, agarose) and surface functional group (amine, Ni2+-loaded nitrilotriacetic acid (NiNTA), epoxide). Carrier activity (Ac) and immobilized enzyme effectiveness (ɳ) were evaluated in dependence of protein loading. Results show that efficient immobilization (Ac: up to 1450 U/g carrier; ɳ: up to 65%) requires a hydrophilic carrier (agarose) equipped with amine groups. The value of ɳ declines sharply as Ac increases, probably due to transition into diffusional regime. Untagged l-lactate oxidase binds to NiNTA carrier similarly as N-terminally His-tagged enzyme. Lixiviation studies reveal quasi-irreversible enzyme adsorption on NiNTA carrier while partial release of activity (≤ 25%) is shown from amine carrier. The desorbed enzyme exhibits the same specific activity as the original l-lactate oxidase. Collectively, our study identifies basic requirements of l-lactate oxidase immobilization on solid carrier and highlights the role of ionic interactions in enzyme-surface adsorption.

ROS-Responsive 4D Printable Acrylic Thioether-Based Hydrogels for Smart Drug Release

Reactive oxygen species (ROS) play a key role in several biological functions like regulating cell survival and signaling; however, their effect can range from beneficial to nondesirable oxidative stress when they are overproduced causing inflammation or cancer diseases. Thus, the design of tailor-made ROS-responsive polymers offers the possibility of engineering hydrogels for target therapies. In this work, we developed thioether-based ROS-responsive difunctional monomers from ethylene glycol/thioether acrylate (EGnSA) with different lengths of the EGn chain (n = 1, 2, 3) by the thiol-Michael addition click reaction. The presence of acrylate groups allowed their photopolymerization by UV light, while the thioether groups conferred ROS-responsive properties. As a result, smart PEGnSA hydrogels were obtained, which could be processed by four-dimensional (4D) printing. The mechanical properties of the hydrogels were determined by rheology, pointing out a decrease of the elastic modulus (G') with the length of the EG segment. To enhance the stability of the hydrogels after swelling, the EGnSA monomers were copolymerized with a polar monomer, 2-hydroxyethyl acrylate (HEA), leading to P[(EGnSA)x-co-HEAy] with improved compatibility in aqueous media, making it a less brittle material. Swelling properties of the hydrogels increased in the presence of hydrogen peroxide, a kind of ROS, reaching values of ≈130% for P[(EG3SA)7-co-HEA93] which confirms the stimuli-responsive properties. Then, the P[(EG3SA)x-co-HEAy] hydrogels were employed as matrixes for the encapsulation of a chemotherapeutic drug, 5-fluorouracil (5FU), which showed sustained release over time modulated by the presence of H2O2. Finally, the effect of the 5-FU release from P[(EG3SA)x-co-HEAy] hydrogels was tested in vitro with melanoma cancer cells B16F10, pointing out B16F10 growth inhibition values in the range of 40-60% modulated by the EG3SA percentage and the presence or absence of ROS agents, thus confirming their excellent ROS-responsive properties for the treatment of localized pathologies.

Influence of conductive carbon and MnCo2O4 on morphological and electrical properties of hydrogels for electrochemical energy conversion

In this work, a strategy for one-stage synthesis of polymer composites based on PNIPAAm hydrogel was presented. Both conductive particles in the form of conductive carbon black (cCB) and MnCo2O4 (MCO) spinel particles were suspended in the three-dimensional structure of the hydrogel. The MCO particles in the resulting hydrogel composite acted as an electrocatalyst in the oxygen evolution reaction. Morphological studies confirmed that the added particles were incorporated and, in the case of a higher concentration of cCB particles, also bound to the surface of the structure of the hydrogel matrix. The produced composite materials were tested in terms of their electrical properties, showing that an increase in the concentration of conductive particles in the hydrogel structure translates into a lowering of the impedance modulus and an increase in the double-layer capacitance of the electrode. This, in turn, resulted in a higher catalytic activity of the electrode in the oxygen evolution reaction. The use of a hydrogel as a matrix to suspend the catalyst particles, and thus increase their availability through the electrolyte, seems to be an interesting and promising application approach.

Hydrogels for Chemical Sensing and Biosensing

The development and synthesis of hydrogels for chemical and biosensing are of great value. Hydrogels can be tailored to its own physical structure, chemical properties, biocompatibility, and sensitivity to external stimuli when being used in a specific environment. Herein, hydrogels and their applications in chemical and biosensing are mainly covered. In particular, it is focused on the manner in which hydrogels serve as sensing materials to a specific analyte. Different types of responsive hydrogels are hence introduced and summarized. Researchers can modify different chemical groups on the skeleton of the hydrogels, which make them as good chemical and biosensing materials. Hydrogels have great application potential for chemical and biosensing in the biomedical field and some emerging fields, such as wearable devices.

Hydrogel Breakthroughs in Biomedicine: Recent Advances and Implications

OBJECTIVE

The objective of this review is to present a succinct summary of the latest advancements in the utilization of hydrogels for diverse biomedical applications, with a particular focus on their revolutionary impact in augmenting the delivery of drugs, tissue engineering, along with diagnostic methodologies.

METHODS

Using a meticulous examination of current literary works, this review systematically scrutinizes the nascent patterns in applying hydrogels for biomedical progress, condensing crucial discoveries to offer a comprehensive outlook on their ever-changing importance.

RESULTS

The analysis presents compelling evidence regarding the growing importance of hydrogels in biomedicine. It highlights their potential to significantly enhance drug delivery accuracy, redefine tissue engineering strategies, and advance diagnostic techniques. This substantiates their position as a fundamental element in the progress of modern medicine.

CONCLUSION

In summary, the constantly evolving advancement of hydrogel applications in biomedicine calls for ongoing investigation and resources, given their diverse contributions that can revolutionize therapeutic approaches and diagnostic methods, thereby paving the way for improved patient well-being.

Wearing the Lab: Advances and Challenges in Skin-Interfaced Systems for Continuous Biochemical Sensing

Continuous, on-demand, and, most importantly, contextual data regarding individual biomarker concentrations exemplify the holy grail for personalized health and performance monitoring. This is well-illustrated for continuous glucose monitoring, which has drastically improved outcomes and quality of life for diabetic patients over the past 2 decades. Recent advances in wearable biosensing technologies (biorecognition elements, transduction mechanisms, materials, and integration schemes) have begun to make monitoring of other clinically relevant analytes a reality via minimally invasive skin-interfaced devices. However, several challenges concerning sensitivity, specificity, calibration, sensor longevity, and overall device lifetime must be addressed before these systems can be made commercially viable. In this chapter, a logical framework for developing a wearable skin-interfaced device for a desired application is proposed with careful consideration of the feasibility of monitoring certain analytes in sweat and interstitial fluid and the current development of the tools available to do so. Specifically, we focus on recent advancements in the engineering of biorecognition elements, the development of more robust signal transduction mechanisms, and novel integration schemes that allow for continuous quantitative analysis. Furthermore, we highlight the most compelling and promising prospects in the field of wearable biosensing and the challenges that remain in translating these technologies into useful products for disease management and for optimizing human performance.

Advances in chitosan-based hydrogels for pharmaceutical and biomedical applications: A comprehensive review

The treatment of diseases, such as cancer, is one of the most significant issues correlated with human beings health. Hydrogels (HGs) prepared from biocompatible and biodegradable materials, especially biopolymers, have been effectively employed for the sort of pharmaceutical and biomedical applications, including drug delivery systems, biosensors, and tissue engineering. Chitosan (CS), one of the most abundant bio-polysaccharide derived from chitin, is an efficient biomaterial in the prognosis, diagnosis, and treatment of diseases. CS-based HGs possess some potential advantages, like high values of bioactive encapsulation, efficient drug delivery to a target site, sustained drug release, good biocompatibility and biodegradability, high serum stability, non-immunogenicity, etc., which made them practical and useful for pharmaceutical and biomedical applications. In this review, we summarize recent achievements and advances associated with CS-based HGs for drug delivery, regenerative medicine, disease detection and therapy.

Hydrogel-Based Sensors for Human-Machine Interaction

In the past decades, remarkable progress has been made in the field of human-machine interaction. The need for accurate sensing devices with satisfactory user experiences has propelled the development of flexible, stretchable, biocompatible, and imperceptible hydrogel-based interfaces. These innovative interfaces facilitate direct interactions between humans and machines while receiving detected input signals from sensors and giving output commands to controllers, thus motivating accurate real-time responsiveness. This Perspective discusses the sensing mechanisms for the two categories of hydrogel-based sensors and summarizes the recent progress in the development of different representations of human-machine interactions, including intelligent identification, information secrecy, interactive control, and virtual reality and augmented reality technologies. The advantages of hydrogel-based systems over conventionally used rigid electrical components are explicitly discussed. The conclusion provides a perspective on current challenges and outlines a future roadmap for the realization of state-of-the-art hydrogel-based smart systems.

Biofluid-Activated Biofuel Cells, Batteries, and Supercapacitors: A Comprehensive Review

Recent developments in wearable and implanted devices have resulted in numerous, unprecedented capabilities that generate increasingly detailed information about a user's health or provide targeted therapy. However, options for powering such systems remain limited to conventional batteries which are large and have toxic components and as such are not suitable for close integration with the human body. This work provides an in-depth overview of biofluid-activated electrochemical energy devices, an emerging class of energy sources judiciously designed for biomedical applications. These unconventional energy devices are composed of biocompatible materials that harness the inherent chemistries of various biofluids to produce useable electrical energy. This work covers examples of such biofluid-activated energy devices in the form of biofuel cells, batteries, and supercapacitors. Advances in materials, design engineering, and biotechnology that form the basis for high-performance, biofluid-activated energy devices are discussed. Innovations in hybrid manufacturing and heterogeneous integration of device components to maximize power output are also included. Finally, key challenges and future scopes of this nascent field are provided.

Portable visual and electrochemical detection of hydrogen peroxide release from living cells based on dual-functional Pt-Ni hydrogels

It is important to monitor the intra-/extracellular concentration of hydrogen peroxide (H2O2) in biological processes. However, miniaturized devices that enable portable and accurate H2O2 measurement are still in their infancy because of the difficulty of developing facile sensing strategies and highly integrated sensing devices. In this work, portable H2O2 sensors based on Pt-Ni hydrogels with excellent peroxidase-like and electrocatalytic activities are demonstrated. Thus, simple and sensitive H2O2 sensing is achieved through both colorimetric and electrochemical strategies. The as-fabricated H2O2 sensing chips exhibit favorable performance, with low detection limits (0.030 μM & 0.15 μM), wide linearity ranges (0.10 μM-10.0 mM & 0.50 μM-5.0 mM), outstanding long-term stability (up to 60 days), and excellent selectivity. With the aid of an M5stack development board, portable visual and electrochemical H2O2 sensors are successfully constructed without complicated and expensive equipment or professional operators. When applied to the detection of H2O2 released from HeLa cells, the results obtained by the developed sensors are in good agreement with those from an ultraviolet‒visible spectrophotometer (UV‒vis) (1.97 μM vs. 2.08 μM) and electrochemical station (1.77 μM vs. 1.84 μM).

Physically and Chemically Cross-Linked Poly(vinyl alcohol)/Humic Acid Hydrogels for Agricultural Applications

The preparation method of hydrogels has a significant effect on their structural and physicochemical properties. In this report, physically and chemically cross-linked poly(vinyl alcohol) (PVA) networks containing humic acid (HA) were alternatively prepared by autoclaving (AC) and through glutaraldehyde (GA) addition, respectively, for agricultural purposes. PVA/HA hydrogels were comparatively characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, mechanical assays, scanning electron microscopy, swelling kinetics measurements, and water retention tests in soil. AC hydrogels showed a more homogeneous porous microstructure, higher swelling levels, and a better capacity to preserve the humidity of soil than those obtained by adding GA. Both PVA/HA hydrogels exhibited no phytotoxicity on cultivation trials of Sorghum sp., but the plant growth was promoted with the GA-cross-linked network as compared to the effect of the AC sample. The release behavior of urea was modified according to the preparation method of the PVA/HA hydrogels. After 3 days of sustained urea release, 91% of the fertilizer was delivered from the AC hydrogel, whereas a lower amount of 56% was released for the GA-cross-linked hydrogel. Beyond the advantages of applying PVA/HA hydrogels in the agricultural field, an appropriate method of preparing these materials endows them with specific properties according to the requirements of the target crop.

Affinity Peptide-Tethered Suspension Hydrogel Sensor for Selective and Sensitive Detection of Influenza Virus

Influenza viruses are known to cause pandemic flu outbreaks through both inter-human and animal-to-human transmissions. Therefore, the rapid and accurate detection of such pathogenic viruses is crucial for effective pandemic control. Here, we introduce a novel sensor based on affinity peptide-immobilized hydrogel microspheres for the selective detection of influenza A virus (IAV) H3N2. To enhance the binding affinity performance, we identified novel affinity peptides using phage display and further optimized their design. The functional hydrogel microspheres were constructed using the drop microfluidic technique, employing a structure composed of natural (chitosan) and synthetic (poly(ethylene glycol) diacrylate and PEG 6 kDa) polymers with the activation of azadibenzocyclooctyne for the subsequent click chemistry reaction. The binding peptide-immobilized hydrogel microsphere (BP-Hyd) was characterized by field emission scanning electron microscopy, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy and exhibited selective detection capability for the IAV H3N2. To capture the detected IAV H3N2, a Cy3-labeled IAV hemagglutinin antibody was utilized. By incorporating the affinity peptide with hydrogel microspheres, we achieved quantitative and selective detection of IAV H3N2 with a detection limit of 1.887 PFU mL-1. Furthermore, the developed suspension sensor exhibited excellent reproducibility and showed reusability potential. Our results revealed that the BP-Hyd-based fluorescence sensor platform could be feasibly employed to detect other pathogens because the virus-binding peptides can be easily replaced with other peptides through phage display, enabling selective and sensitive binding to different targets.

Sulfated Polyglycerol-Modified Hydrogels for Binding HSV-1 and RSV

Heparan sulfate (HS) is a highly sulfated polysaccharide on the surface of mammalian cells and in the extracellular matrix and has been found to be important for virus binding and infection. In this work, we designed synthetic hydrogels with viral binding and deactivation activities through the postfunctionalization of an HS-mimicking polyelectrolyte and alkyl chains. Three polyglycerol-based hydrogels were prepared as substrates and postfunctionalized by sulfated linear polyglycerol (lPGS) via thiol-ene click reaction. The viral binding properties were studied using herpes simplex virus type 1 (HSV-1) and respiratory syncytial virus (RSV). The effect of hydrogel types and molecular weight (Mw) of conjugated lPGS on viral binding properties was also assessed, and promising binding activities were observed in all lPGS-functionalized samples. Further coupling of 11 carbons long alkyl chains to the hydrogel revealed virucidal properties caused by destruction of the viral envelope, as shown by atomic force microscopy (AFM) imaging.

Advanced Self-Powered Biofuel Cells with Capacitor and Nanogenerator for Biomarker Sensing

Self-powered biofuel cells (BFCs) have evolved for highly sensitive detection of biomarkers such as noncodon micro ribonucleic acids (miRNAs) in the presence of interfering substrates. Self-charging supercapacitive BFCs for in vivo and in vitro cellular microenvironments represent the most prevalent sensing mechanism for diagnosis. Therefore, self-powered biosensing (SPB) with a capacitor and contact separation with a triboelectric nanogenerator (TENG) offers electrochemical and colorimetric dual-mode detection via improved electrical signal intensity. In this review, we discuss three major components: stretchable self-powered BFC design, miRNA sensing, and impedance spectroscopy. A specific focus is given to 1) assembling of sensors for biomarkers, 2) electrical output signal intensification, and 3) role of supercapacitors and nanogenerators in SPBs. We outline the key features of stretchable SPBs and the sequence of miRNA sensing by SPBs. We have emphasized the need of a supercapacitor and nanogenerator for SPBs in the context of advanced assembly of the sensing unit. Finally, we outline the role of impedance spectroscopy in the detection and estimation of biomarkers. We highlight key challenges in SPBs for biomarker sensing, which needs improved sensing accuracy, integration strategies of electrochemical biosensing for in vitro and in vivo microenvironments, and the impact of miRNA sensing on cancer diagnostics. This article attempts a specific focus on the accuracy and limitations of sensing unit for miRNA biomarkers and associated tool for boosting electrical signal intensity for a potential big step further.

Space-Confined Electrochemical Aptasensing with Conductive Hydrogels for Enhanced Applicability to Aflatoxin B1 Detection

Aflatoxin B1 (AFB1) contamination has received considerable attention for the serious harm it causes and its wide distribution. Hence, its efficient monitoring is of great importance. Herein, a space-confined electrochemical aptasensor for AFB1 detection is developed using a conductive hydrogel. Plasmonic gold nanoparticles (AuNPs) and methylene blue-embedded double-stranded DNA (MB-dsDNA) were integrated into the conductive Au-hydrogel by ultraviolet (UV) polymerization. Specific recognition of AFB1 by the aptamer released MB from MB-dsDNA in the matrix. The free DNA migrated to the outer layer due to electrostatic repulsion during the Au-hydrogel formation. The electrochemical aptasensor based on this Au-hydrogel offered a twofold enlarged oxidation current of MB (IMB) compared with that recorded in the homogeneous solution for AFB1 detection. Upon light illumination, this IMB was further enlarged by the local surface plasmon resonance (LSPR) of the AuNPs. Ultimately, the Au-hydrogel-based electrochemical aptasensor provided a detection limit of 0.0008 ng mL-1 and a linear range of 0.001-1000 ng mL-1 under illumination for AFB1 detection. The Au-hydrogel allowed for space-confined aptasensing, favorable conductivity, and LSPR enhancement for better sensitivity. It significantly enhanced the applicability of the electrochemical aptasensor by avoiding complicated electrode fabrication and signal loss in a bulk homogeneous solution.

Smart G-quadruplex hydrogels: From preparations to comprehensive applications

In recent years, the accelerated development of G-quadruplexes and hydrogels has driven the development of intelligent biomaterials. Based on the excellent biocompatibility and special biological functions of G-quadruplexes, and the hydrophilicity, high-water retention, high water content, flexibility and excellent biodegradability of hydrogels, G-quadruplex hydrogels are widely used in various fields by combining the dual advantages of G-quadruplexes and hydrogels. Here, we provide a systematic and comprehensive classification of G-quadruplex hydrogels in terms of preparation strategies and applications. This paper reveals how G-quadruplex hydrogels skillfully utilize the special biological functions of G-quadruplexes and the skeleton structure of hydrogels, and expounds its applications in the fields of biomedicine, biocatalysis, biosensing and biomaterials. In addition, we deeply analyze the challenges in preparation, applications, stability and safety of G-quadruplex hydrogels, as well as potential future development directions.

Perspectives on recent advancements in energy harvesting, sensing and bio-medical applications of piezoelectric gels

The development of next-generation bioelectronics, as well as the powering of consumer and medical devices, require power sources that are soft, flexible, extensible, and even biocompatible. Traditional energy storage devices (typically, batteries and supercapacitors) are rigid, unrecyclable, offer short-lifetime, contain hazardous chemicals and possess poor biocompatibility, hindering their utilization in wearable electronics. Therefore, there is a genuine unmet need for a new generation of innovative energy-harvesting materials that are soft, flexible, bio-compatible, and bio-degradable. Piezoelectric gels or PiezoGels are a smart crystalline form of gels with polar ordered structures that belongs to the broader family of piezoelectric material, which generate electricity in response to mechanical stress or deformation. Given that PiezoGels are structurally similar to hydrogels, they offer several advantages including intrinsic chirality, crystallinity, degree of ordered structures, mechanical flexibility, biocompatibility, and biodegradability, emphasizing their potential applications ranging from power generation to bio-medical applications. Herein, we describe recent examples of new functional PiezoGel materials employed for energy harvesting, sensing, and wound dressing applications. First, this review focuses on the principles of piezoelectric generators (PEGs) and the advantages of using hydrogels as PiezoGels in energy and biomedical applications. Next, we provide a detailed discussion on the preparation, functionalization, and fabrication of PiezoGel-PEGs (P-PEGs) for the applications of energy harvesting, sensing and wound healing/dressing. Finally, this review concludes with a discussion of the current challenges and future directions of P-PEGs.

Imprinted Hydrogel Nanoparticles for Protein Biosensing: A Review

Over the past decade, molecular imprinting (MI) technology has made tremendous progress, and the advancements in nanotechnology have been the major driving force behind the improvement of MI technology. The preparation of nanoscale imprinted materials, i.e., molecularly imprinted polymer nanoparticles (MIP NPs, also commonly called nanoMIPs), opened new horizons in terms of practical applications, including in the field of sensors. Currently, hydrogels are very promising for applications in bioanalytical assays and sensors due to their high biocompatibility and possibility to tune chemical composition, size (microgels, nanogels, etc.), and format (nanostructures, MIP film, fibers, etc.) to prepare optimized analyte-responsive imprinted materials. This review aims to highlight the recent progress on the use of hydrogel MIP NPs for biosensing purposes over the past decade, mainly focusing on their incorporation on sensing devices for detection of a fundamental class of biomolecules, the peptides and proteins. The review begins by directing its focus on the ability of MIPs to replace biological antibodies in (bio)analytical assays and highlight their great potential to face the current demands of chemical sensing in several fields, such as disease diagnosis, food safety, environmental monitoring, among others. After that, we address the general advantages of nanosized MIPs over macro/micro-MIP materials, such as higher affinity toward target analytes and improved binding kinetics. Then, we provide a general overview on hydrogel properties and their great advantages for applications in the field of Sensors, followed by a brief description on current popular routes for synthesis of imprinted hydrogel nanospheres targeting large biomolecules, namely precipitation polymerization and solid-phase synthesis, along with fruitful combination with epitope imprinting as reliable approaches for developing optimized protein-imprinted materials. In the second part of the review, we have provided the state of the art on the application of MIP nanogels for screening macromolecules with sensors having different transduction modes (optical, electrochemical, thermal, etc.) and design formats for single use, reusable, continuous monitoring, and even multiple analyte detection in specialized laboratories or in situ using mobile technology. Finally, we explore aspects about the development of this technology and its applications and discuss areas of future growth.

Unraveling the New Perspectives on Antimicrobial Hydrogels: State-of-the-Art and Translational Applications

The growing impact of infections and the rapid emergence of antibiotic resistance represent a public health concern worldwide. The exponential development in the field of biomaterials and its multiple applications can offer a solution to the problems that derive from these situations. In this sense, antimicrobial hydrogels represent a promising opportunity with multiple translational expectations in the medical management of infectious diseases due to their unique physicochemical and biological properties as well as for drug delivery in specific areas. Hydrogels are three-dimensional cross-linked networks of hydrophilic polymers that can absorb and retain large amounts of water or biological fluids. Moreover, antimicrobial hydrogels (AMH) present good biocompatibility, low toxicity, availability, viscoelasticity, biodegradability, and antimicrobial properties. In the present review, we collect and discuss the most promising strategies in the development of AMH, which are divided into hydrogels with inherent antimicrobial activity and antimicrobial agent-loaded hydrogels based on their composition. Then, we present an overview of the main translational applications: wound healing, tissue engineering and regeneration, drug delivery systems, contact lenses, 3D printing, biosensing, and water purification.

Hydrogel-Based Biosensors for Effective Therapeutics

Nanotechnology and polymer engineering are navigating toward new developments to control and overcome complex problems. In the last few decades, polymer engineering has received researchers' attention and similarly, polymeric network-engineered structures have been vastly studied. Prior to therapeutic application, early and rapid detection analyses are critical. Therefore, developing hydrogel-based sensors to manage the acute expression of diseases and malignancies to devise therapeutic approaches demands advanced nanoengineering. However, nano-therapeutics have emerged as an alternative approach to tackling strenuous diseases. Similarly, sensing applications for multiple kinds of analytes in water-based environments and other media are gaining wide interest. It has also been observed that these functional roles can be used as alternative approaches to the detection of a wide range of biomolecules and pathogenic proteins. Moreover, hydrogels have emerged as a three-dimensional (3D) polymeric network that consists of hydrophilic natural or synthetic polymers with multidimensional dynamics. The resemblance of hydrogels to tissue structure makes them more unique to study inquisitively. Preceding studies have shown a vast spectrum of synthetic and natural polymer applications in the field of biotechnology and molecular diagnostics. This review explores recent studies on synthetic and natural polymers engineered hydrogel-based biosensors and their applications in multipurpose diagnostics and therapeutics. We review the latest studies on hydrogel-engineered biosensors, exclusively DNA-based and DNA hydrogel-fabricated biosensors.

Hydrogel-Based Bioelectronics and Their Applications in Health Monitoring

Flexible bioelectronics exhibit promising potential for health monitoring, owing to their soft and stretchable nature. However, the simultaneous improvement of mechanical properties, biocompatibility, and signal-to-noise ratio of these devices for health monitoring poses a significant challenge. Hydrogels, with their loose three-dimensional network structure that encapsulates massive amounts of water, are a potential solution. Through the incorporation of polymers or conductive fillers into the hydrogel and special preparation methods, hydrogels can achieve a unification of excellent properties such as mechanical properties, self-healing, adhesion, and biocompatibility, making them a hot material for health monitoring bioelectronics. Currently, hydrogel-based bioelectronics can be used to fabricate flexible bioelectronics for motion, bioelectric, and biomolecular acquisition for human health monitoring and further clinical applications. This review focuses on materials, devices, and applications for hydrogel-based bioelectronics. The main material properties and research advances of hydrogels for health monitoring bioelectronics are summarized firstly. Then, we provide a focused discussion on hydrogel-based bioelectronics for health monitoring, which are classified as skin-attachable, implantable, or semi-implantable depending on the depth of penetration and the location of the device. Finally, future challenges and opportunities of hydrogel-based bioelectronics for health monitoring are envisioned.

Smartphone-Based Chemiluminescence Glucose Biosensor Employing a Peroxidase-Mimicking, Guanosine-Based Self-Assembled Hydrogel

Chemiluminescence is widely used for hydrogen peroxide detection, mainly exploiting the highly sensitive peroxidase-luminol-H₂O₂ system. Hydrogen peroxide plays an important role in several physiological and pathological processes and is produced by oxidases, thus providing a straightforward way to quantify these enzymes and their substrates. Recently, biomolecular self-assembled materials obtained by guanosine and its derivatives and displaying peroxidase enzyme-like catalytic activity have received great interest for hydrogen peroxide biosensing. These soft materials are highly biocompatible and can incorporate foreign substances while preserving a benign environment for biosensing events. In this work, a self-assembled guanosine-derived hydrogel containing a chemiluminescent reagent (luminol) and a catalytic cofactor (hemin) was used as a H₂O₂-responsive material displaying peroxidase-like activity. Once loaded with glucose oxidase, the hydrogel provided increased enzyme stability and catalytic activity even in alkaline and oxidizing conditions. By exploiting 3D printing technology, a smartphone-based portable chemiluminescence biosensor for glucose was developed. The biosensor allowed the accurate measurement of glucose in serum, including both hypo- and hyperglycemic samples, with a limit of detection of 120 µmol L^-1. This approach could be applied for other oxidases, thus enabling the development of bioassays to quantify biomarkers of clinical interest at the point of care.

State-of-the-Art Insights and Potential Applications of Cellulose-Based Hydrogels in Food Packaging: Advances towards Sustainable Trends

Leveraging sustainable packaging resources in the circular economy framework has gained significant attention in recent years as a means of minimizing waste and mitigating the negative environmental impact of packaging materials. In line with this progression, bio-based hydrogels are being explored for their potential application in a variety of fields including food packaging. Hydrogels are three-dimensional, hydrophilic networks composed of a variety of polymeric materials linked by chemical (covalent bonds) or physical (non-covalent interactions) cross-linking. The unique hydrophilic nature of hydrogels provides a promising solution for food packaging systems, specifically in regulating moisture levels and serving as carriers for bioactive substances, which can greatly affect the shelf life of food products. In essence, the synthesis of cellulose-based hydrogels (CBHs) from cellulose and its derivatives has resulted in hydrogels with several appealing features such as flexibility, water absorption, swelling capacity, biocompatibility, biodegradability, stimuli sensitivity, and cost-effectiveness. Therefore, this review provides an overview of the most recent trends and applications of CBHs in the food packaging sector including CBH sources, processing methods, and crosslinking methods for developing hydrogels through physical, chemical, and polymerization. Finally, the recent advancements in CBHs, which are being utilized as hydrogel films, coatings, and indicators for food packaging applications, are discussed in detail. These developments have great potential in creating sustainable packaging systems.

Stimuli-bioresponsive hydrogels as new generation materials for implantable, wearable, and disposable biosensors for medical diagnostics: Principles, opportunities, and challenges

Hydrogels are excellent water-swollen polymeric materials for use in wearable, implantable, and disposable biosensors. Hydrogels have unique properties such as low cost, ease of preparation, transparency, rapid response to external conditions, biocompatibility and self-adhesion to the skin, flexibility, and strain sensitivity, making them ideal for use in biosensor platforms. This review provides a detailed overview of advanced applications of stimuli-responsive hydrogels in biosensor platforms, from hydrogel synthesis and functionalization for bioreceptor immobilization to several important diagnostic applications. Emphasis is placed on recent advances in the fabrication of ultrasensitive fluorescent and electrically conductive hydrogels and their applications in wearable, implantable, and disposable biosensors for quantitative measurements. Design, modification, and assembly techniques of fluorescent, ionically conductive, and electrically conductive hydrogels to improve performance will be addressed. The advantages and performance improvements of immobilizing bioreceptors (e.g., antibodies, enzymes, and aptamers), and incorporating fluorescent and electrically conductive nanomaterials are described, as are their limitations. Potential applications of hydrogels in implantable, wearable, disposable portable biosensors for quantitative detection of the various bioanalytes (ions, molecules, drugs, proteins, and biomarkers) are discussed. Finally, the global market for hydrogel-based biosensors and future challenges and prospects are discussed in detail.

Recent Progress in Biomedical Sensors Based on Conducting Polymer Hydrogels

Biosensors are increasingly taking a more active role in health science. The current needs for the constant monitoring of biomedical signals, as well as the growing spending on public health, make it necessary to search for materials with a combination of properties such as biocompatibility, electroactivity, resorption, and high selectivity to certain bioanalytes. Conducting polymer hydrogels seem to be a very promising materials, since they present many of the necessary properties to be used as biosensors. Furthermore, their properties can be shaped and enhanced by designing conductive polymer hydrogel-based composites with more specific functionalities depending on the end application. This work will review the recent state of the art of different biological hydrogels for biosensor applications, discuss the properties of the different components alone and in combination, and reveal their high potential as candidate materials in the fabrication of all-organic diagnostic, wearable, and implantable sensor devices.

An Electrochemical o-Phthalaldehyde Sensor Using a Modified Disposable Screen-Printed Electrode with Polyacrylate Hydrogel for Concentration Verification of Clinical Disinfectant

The study proposes an o-phthalaldehyde (OPA) sensor for rapid and reliable detection of OPA in healthcare disinfection practices, based on a hydrogel-modified screen-printed carbon electrode strip. The hydrogel film, which contains glycine and N-acetylcysteine, reacts with OPA to produce a reductive isoindole derivative. The derivative is then oxidized for OPA determination using cyclic voltammetry. The proposed sensor achieves an optimal detection time of 20-30 s and requires only a small analyte volume of 5 µL. It exhibits good precision (10%) and sensitivity (3.3 μA/cm² mM) in a phosphate-buffered solution (pH 7.6), with excellent linearity (R² > 0.97) and precision (<3%) in the detection range (0.2-0.6%) required for clinical OPA solutions. Moreover, the sensor demonstrates good concentration verification of Cidex-OPA disinfection in healthcare institutes, with high sensitivity (18.28 μA/cm² mM) and precision around the minimum effective concentration (0.3%). Overall, the proposed sensor offers a promising and practical solution for accurate and reliable OPA detection in clinical disinfection practices.

Carbon Dot-Doped Hydrogel Sensor Array for Multiplexed Colorimetric Detection of Wound Healing

Effective wound care and treatment require a quick and comprehensive assessment of healing status. Here, we develop a carbon dot-doped hydrogel sensor array in polydimethylsiloxane (PDMS) for simultaneous colorimetric detections of five wound biomarkers and/or wound condition indicators (pH, glucose, urea, uric acid, and total protein), leading to the holistic assessment of inflammation and infection. A biogenic carbon dot synthesized using an amino acid and a polymer precursor is doped in an agarose hydrogel matrix for constructing enzymatic sensors (glucose, urea, and uric acid) and dye-based sensors (pH and total protein). The encapsulated enzymes in such a matrix exhibit improved enzyme kinetics and stability compared to those in pure hydrogels. Such a matrix also provides stable colorimetric responses for all five sensors. The sensor array exhibits high accuracy (recovery rates of 91.5-113.1%) and clinically relevant detection ranges for all five wound markers. The sensor array is established for simulated wound fluids and validated with rat wound fluids from perturbed wound models. Distinct color patterns are obtained that can clearly distinguish healing vs nonhealing wounds visually and quantitatively. This hydrogel sensor array shows great potential for on-site wound sensing due to its long-term stability, lightweight, and flexibility.

1H NMR and EPR Spectroscopies Investigation of Alginate Cross-Linking by Divalent Ions

Alginate is a natural polymer widely applied in materials science, medicine, and biotechnology. Its ability to bind metal ions in order to form insoluble gels has been comprehensively used to create capsules for cell technology, drug delivery, biomedical materials, etc. To modify and predict the properties of cross-linked alginate, knowledge about the mechanism of alginate binding with metal ions and the properties of its gels is necessary. This article presents the results obtained by proton Nuclear Magnetic Resonance Spectroscopy for alginate containing calcium and strontium (alkaline earth metal diamagnetic) ions and by Electron Paramagnetic Resonance Spectroscopy for alginate with copper (Cu) and manganese (Mn) (transition metal paramagnetic) ions. It was found that in the case of calcium (Ca) and Mn ions, their concentration does not affect their distribution in the alginate structure and the cross-linking density. In the case of strontium (Sr) and Cu ions, their number affects the number of binding sites and, accordingly, the cross-linking density. Thus, the cross-linking of alginate depends mainly on the characteristics of specific cations, while the nature of the bond (ionic or coordination type) is less important.

Carbon Dot-Based Hydrogels: Preparations, Properties, and Applications

Hydrogels have extremely high moisture content, which makes it very soft and excellently biocompatible. They have become an important soft material and have a wide range of applications in various fields such as biomedicine, bionic smart material, and electrochemistry. Carbon dot (CD)-based hydrogels are based on carbon dots (CDs) and auxiliary substances, forming a gel material with comprehensive properties of individual components. CDs embedding in hydrogels could not only solve their aggregation-caused quenching (ACQ) effect, but also manipulate the properties of hydrogels and even bring some novel properties, achieving a win-win situation. In this review, the preparation methods, formation mechanism, and properties of CD-based hydrogels, and their applications in biomedicine, sensing, adsorption, energy storage, and catalysis -are summarized. Finally, a brief discussion on future research directions of CD-based hydrogels will be given.

Fabrication of bFGF/polydopamine-loaded PEEK implants for improving soft tissue integration by upregulating Wnt/β-catenin signaling

The difficulties associated with polyetheretherketone (PEEK) implants and soft tissue integration for craniomaxillofacial bone repair have led to a series of complications that limit the clinical benefits. In this study, 3D printed multi-stage microporous PEEK implants coated with bFGF via polydopamine were fabricated to enhance PEEK implant-soft tissue integration. Multistage microporous PEEK scaffolds prepared by sulfonation of concentrated sulfuric acid were coated with polydopamine, and then used as templates for electrophoretic deposition of bFGF bioactive factors. Achieving polydopamine and bFGF sustained release, the composite PEEK scaffolds possessed good mechanical properties, hydrophilicity, protein adhesion properties. The in vitro results indicated that bFGF/polydopamine-loaded PEEK exhibited good biocompatibility to rabbit embryonic fibroblasts (REF) by promoting cell proliferation, adhesion, and migration. Ribonucleic acid sequencing (RNA-seq) revealed that bFGF/polydopamine-loaded PEEK implants significantly upregulated the expression of genes and proteins associated with soft tissue integration and activated Wnt/β-catenin signaling in biological processes, but related expression of genes and proteins was significantly downregulated when the Wnt/β-catenin signaling was inhibited. Furthermore, in vivo bFGF/polydopamine-loaded PEEK implants exhibited excellent performance in improving the growth and adhesion of the surrounding soft tissue. In summary, bFGF/polydopamine-loaded PEEK implants possess soft tissue integration properties by activating the Wnt/β-catenin signaling, which have a potential translational clinical application in the future.

Recent Development of Functional Chitosan-Based Hydrogels for Pharmaceutical and Biomedical Applications

Chitosan is a promising naturally derived polysaccharide to be used in hydrogel forms for pharmaceutical and biomedical applications. The multifunctional chitosan-based hydrogels have attractive properties such as the ability to encapsulate, carry, and release the drug, biocompatibility, biodegradability, and non-immunogenicity. In this review, the advanced functions of the chitosan-based hydrogels are summarized, with emphasis on fabrications and resultant properties reported in literature from the recent decade. The recent progress in the applications of drug delivery, tissue engineering, disease treatments, and biosensors are reviewed. Current challenges and future development direction of the chitosan-based hydrogels for pharmaceutical and biomedical applications are prospected.

Fluorescent Nanocomposite Hydrogels Based on Conjugated Polymer Nanoparticles as Platforms for Alkaline Phosphatase Detection

This work describes the development and characterization of fluorescent nanocomposite hydrogels, with high swelling and absorption capacity, and prepared using a green protocol. These fluorescent materials are obtained by incorporating, for the first time, polyfluorenes-based nanoparticles with different emission bands-poly[9,9-dioctylfluorenyl-2,7-diyl] (PFO) and poly[(9,9-di-n-octylfluorenyl-2,7-diyl)-alt-(1,4-benzo-{2,1,3}-thiadiazole)] (F8BT)-into a three-dimensional polymeric network based on polyacrylamide. To this end, two strategies were explored: incorporation of the nanoparticles during the polymerization process (in situ) and embedment after the hydrogel formation (ex situ). The results show that the combination of PFO nanoparticles introduced by the ex situ method provided materials with good storage stability, homogeneity and reproducibility properties, allowing their preservation in the form of xerogel. The fluorescent nanocomposite hydrogels have been tested as a transportable and user-friendly sensing platform. In particular, the ability of these materials to specifically detect the enzyme alkaline phosphatase (ALP) has been evaluated as a proof-of-concept. The sensor was able to quantify the presence of the enzyme in an aqueous sample with a response time of 10 min and LOD of 21 nM. Given these results, we consider that this device shows great potential for quantifying physiological ALP levels as well as enzyme activity in environmental samples.

Applications of Stimuli-Responsive Hydrogels in Bone and Cartilage Regeneration

Bone and cartilage regeneration is an area of tremendous interest and need in health care. Tissue engineering is a potential strategy for repairing and regenerating bone and cartilage defects. Hydrogels are among the most attractive biomaterials in bone and cartilage tissue engineering, mainly due to their moderate biocompatibility, hydrophilicity, and 3D network structure. Stimuli-responsive hydrogels have been a hot topic in recent decades. They can respond to external or internal stimulation and are used in the controlled delivery of drugs and tissue engineering. This review summarizes current progress in the use of stimuli-responsive hydrogels in bone and cartilage regeneration. The challenges, disadvantages, and future applications of stimuli-responsive hydrogels are briefly described.

Growth Control of Metal-Organic Framework Films on Marine Biological Carbon and Their Potential-Dependent Dopamine Sensing

Ever-evolving advancements in films have fueled many of the developments in the field of electrochemical sensors. For biosensor application platforms, the fabrication of metal-organic framework (MOF) films on microscopically structured substrates is of tremendous importance. However, fabrication of MOF film-based electrodes always exhibits unsatisfactory performance, and the mechanisms of the fabrication and sensing application of the corresponding composites also need to be explored. Here, we report the fabrication of conformal MIL-53 (Fe) films on carbonized natural seaweed with the assistance of an oxide nanomembrane and a potential-dependent electrochemical dopamine (DA) sensor. The geometry and structure of the composite can be conveniently tuned by the experimental parameters, while the sensing performance is significantly influenced by the applied potential. The obtained sensor demonstrates ultrahigh sensitivity, a wide linear range, a low limit of detection, and a good distinction between DA and ascorbic acid at an optimized potential of 0.3 V. The underneath mechanism is investigated in detail with the help of theoretical calculations. This work bridges the natural material and MOF films and is promising for future biosensing applications.

Glucose biosensors based on Michael addition crosslinked poly(ethylene glycol) hydrogels with chemo-optical sensing microdomains

Continuous glucose monitoring (CGM) devices have the potential to lead to better disease management and improved outcomes in patients with diabetes. Chemo-optical glucose sensors offer a promising, accurate, long-term alternative to the current CGMs that require frequent calibration and replacement. Recently, we have proposed glucose sensor designs using phosphorescence lifetime-based measurement of chemo-optical glucose sensing microdomains embedded within alginate hydrogels. Due to the poor long-term stability of calcium-crosslinked alginate, we propose poly(ethylene glycol) (PEG) hydrogels synthesized via thiol-Michael addition chemistry as an alternative hydrogel carrier. The objective of this study was to evaluate the suitability of Michael addition crosslinked PEG hydrogels compared to calcium crosslinked alginate hydrogels for encapsulating glucose-sensing microdomains. PEG hydrogels crosslinked via thiol-vinyl sulfone addition achieved gelation in under 5 minutes, resulting in an even distribution of sensing microdomains. The shear storage modulus of the PEG hydrogels was tunable from 2.2 ± 0.1 kPa to 9.5 ± 1.8 kPa, which was comparable to the alginate hydrogels (10.5 ± 0.8 kPa), and the inclusion of microdomains did not significantly impact stiffness. The high water content of PEG hydrogels resulted in high glucose permeability that closely corresponded to the glucose permeability of alginate (D = 0.09 and 0.12 cm² s^-1, respectively; p = 0.47), but the PEG hydrogels exhibited superior stability. Both PEG and alginate-embedded sensors exhibited a sensing range up to ∼200 mg dL^-1 glucose. The lower limits of detection (LOD) for PEG and alginate-based glucose sensors were 19.8 and 20.6 mg dL^-1 with a difference of just 4.2% variation. The small difference between PEG and alginate embedded sensors indicates that their sensing properties are primarily determined by the glucose sensing microdomains rather than the hydrogel matrix. Overall, the results of this study indicate that Michael addition-crosslinked PEG hydrogels are a promising platform for encapsulation of chemo-optical glucose sensing microdomains.

Biosensors in Food and Healthcare Industries: Bio-Coatings Based on Biogenic Nanoparticles and Biopolymers

Biosensors use biological materials, such as enzymes, antibodies, or DNA, to detect specific analytes. These devices have numerous applications in the health and food industries, such as disease diagnosis, food safety monitoring, and environmental monitoring. However, the production of biosensors can result in the generation of chemical waste, which is an environmental concern for the developed world. To address this issue, researchers have been exploring eco-friendly alternatives for immobilising biomolecules on biosensors. One solution uses bio-coatings derived from nanoparticles synthesised via green chemistry and biopolymers. These materials offer several advantages over traditional chemical coatings, such as improved sensitivity, stability, and biocompatibility. In conclusion, the use of bio-coatings derived from green-chemistry synthesised nanoparticles and biopolymers is a promising solution to the problem of chemical waste generated from the production of biosensors. This review provides an overview of these materials and their applications in the health and food industries, highlighting their potential to improve the performance and sustainability of biosensors.

Past, present and future of biomedical applications of dextran-based hydrogels: A review

This review extensively surveys the biomedical applications of hydrogels containing dextran. Dextran has gained much attention as a biomaterial due to its distinctive properties such as biocompatibility, non-toxicity, water solubility and biodegradability. It has emerged as a critical constituent of hydrogels for biomedical applications including drug delivery devices, tissue engineering scaffolds and biosensor materials. The benefits, challenges and potential prospects of dextran-based hydrogels as biomaterials are highlighted in this review.

Nanomaterial-based biohybrid hydrogel in bioelectronics

Despite the broadly applicable potential in the bioelectronics, organic/inorganic material-based bioelectronics have some limitations such as hard stiffness and low biocompatibility. To overcome these limitations, hydrogels capable of bridging the interface and connecting biological materials and electronics have been investigated for development of hydrogel bioelectronics. Although hydrogel bioelectronics have shown unique properties including flexibility and biocompatibility, there are still limitations in developing novel hydrogel bioelectronics using only hydrogels such as their low electrical conductivity and structural stability. As an alternative solution to address these issues, studies on the development of biohybrid hydrogels that incorporating nanomaterials into the hydrogels have been conducted for bioelectronic applications. Nanomaterials complement the shortcomings of hydrogels for bioelectronic applications, and provide new functionality in biohybrid hydrogel bioelectronics. In this review, we provide the recent studies on biohybrid hydrogels and their bioelectronic applications. Firstly, representative nanomaterials and hydrogels constituting biohybrid hydrogels are provided, and next, applications of biohybrid hydrogels in bioelectronics categorized in flexible/wearable bioelectronic devices, tissue engineering, and biorobotics are discussed with recent studies. In conclusion, we strongly believe that this review provides the latest knowledge and strategies on hydrogel bioelectronics through the combination of nanomaterials and hydrogels, and direction of future hydrogel bioelectronics.

Recent Implementations of Hydrogel-Based Microbial Electrochemical Technologies (METs) in Sensing Applications

Hydrogel materials have been used extensively in microbial electrochemical technology (MET) and sensor development due to their high biocompatibility and low toxicity. With an increasing demand for sensors across different sectors, it is crucial to understand the current state within the sectors of hydrogel METs and sensors. Surprisingly, a systematic review examining the application of hydrogel-based METs to sensor technologies has not yet been conducted. This review aimed to identify the current research progress surrounding the incorporation of hydrogels within METs and sensors development, with a specific focus on microbial fuel cells (MFCs) and microbial electrolysis cells (MECs). The manufacturing process/cost, operational performance, analysis accuracy and stability of typical hydrogel materials in METs and sensors were summarised and analysed. The current challenges facing the technology as well as potential direction for future research were also discussed. This review will substantially promote the understanding of hydrogel materials used in METs and benefit the development of electrochemical biosensors using hydrogel-based METs.

Advances in the Translation of Electrochemical Hydrogel-Based Sensors

Novel biomaterials for bio- and chemical sensing applications have gained considerable traction in the diagnostic community with rising trends of using biocompatible and lowly cytotoxic material. Hydrogel-based electrochemical sensors have become a promising candidate for their swellable, nano-/microporous, and aqueous 3D structures capable of immobilizing catalytic enzymes, electroactive species, whole cells, and complex tissue models, while maintaining tunable mechanical properties in wearable and implantable applications. With advances in highly controllable fabrication and processability of these novel biomaterials, the possibility of bio-nanocomposite hydrogel-based electrochemical sensing presents a paradigm shift in the development of biocompatible, "smart," and sensitive health monitoring point-of-care devices. Here, recent advances in electrochemical hydrogels for the detection of biomarkers in vitro, in situ, and in vivo are briefly reviewed to demonstrate their applicability in ideal conditions, in complex cellular environments, and in live animal models, respectively, to provide a comprehensive assessment of whether these biomaterials are ready for point-of-care translation and biointegration. Sensors based on conductive and nonconductive polymers are presented, with highlights of nano-/microstructured electrodes that provide enhanced sensitivity and selectivity in biocompatible matrices. An outlook on current challenges that shall be addressed for the realization of truly continuous real-time sensing platforms is also presented.

Swift Janitor: Efficient Absorption of a Minor Component from the Mixtures of Immiscible Liquids by Thermoresponsive Macroscopic and Microscopic Hydrogels

Polymer hydrogels are known to be efficient absorbents of various aqueous solutions. Along with the hydrophilicity of the polymer network, the presence of specific functional groups is required for the absorption of respective solutes. Alternatively, a selective uptake can be realized without any specific attraction of solutes to the network, which is shown in this paper. By combining experimental and simulation approaches, we demonstrated that thermoresponsive poly(N-isopropylacrylamide) gels and microgels in compositionally strongly asymmetric water/1-octanol mixtures selectively uptake the minor (1-octanol) component. Initially swollen in water, the gels substitute water by the organic solvent upon the addition of its small fraction into aqueous solution. In turn, for microgels, it was shown that the single particles could absorb the amount of the organic liquid more than two times higher than their mass while preserving the colloidal stability. At the same time, the accumulation of 1-octanol in the networks "switches off" the temperature response. The mesoscopic computer simulations revealed a physical reason and molecular picture of the phenomenon. Absorption of the minor component by the gels is caused by the decrease in water/1-octanol interfacial tension due to the formation of the dense polymer layer at the interface. The simulations allowed tracking the evolution of the size and the internal structure of the single microgels with changing 1-octanol concentration.

Electrodeposition of Silver Nanoparticles on Indium-Doped Tin Oxide Using Hydrogel Electrolyte for Hydrogen Peroxide Sensing

Nanoparticles are used in various fields, including fuel cells, energy conversion devices, and sensors, because of their large surface area and excellent catalytic properties. Although various methods of synthesizing nanoparticles are available, the most popular is the solution-phase reduction of metal ions. Electrodeposition is a method of reducing metal ions in solution and is widely used because of its various advantages. In this study, Ag nanoparticles with a narrow size distribution were evenly dispersed on the surface of an electrode by applying electrodeposition in an agarose hydrogel medium instead of in solution, confirming the feasibility of Ag deposition in agarose hydrogel, even at a lower reduction potential than that in solution. These results are attributed to the electrolyte effect owing to the hydrophilic backbone of the agarose hydrogel and the gel effect, which reduces unexpected convection. H₂O₂ was detected by using the Ag nanoparticles synthesized in agarose hydrogel, and the limit of detection for H₂O₂ was found to be 4.82 µM, with a dynamic range of 1-500 µM. The nanoparticle synthesis platform proposed in this study is expected to be actively used for the synthesis of other metal/nonmetal nanoparticles.

Multi-target tyrosine kinase inhibitor nanoparticle delivery systems for cancer therapy

Multi-target Tyrosine Kinase Inhibitors (MTKIs) have drawn substantial attention in tumor therapy. MTKIs could inhibit tumor cell proliferation and induce apoptosis by blocking the activity of tyrosine kinase. However, the toxicity and drug resistance of MTKIs severely restrict their further clinical application. The nano pharmaceutical technology based on MTKIs has attracted ever-increasing attention in recent years. Researchers deliver MTKIs through various types of nanocarriers to overcome drug resistance and improve considerably therapeutic efficiency. This review intends to summarize comprehensive applications of MTKIs nanoparticles in malignant tumor treatment. Firstly, the mechanism and toxicity were introduced. Secondly, various nanocarriers for MTKIs delivery were outlined. Thirdly, the combination treatment schemes and drug resistance reversal strategies were emphasized to improve the outcomes of cancer therapy. Finally, conclusions and perspectives were summarized to guide future research.

Hydrogel-Based Biosensors

There is an increasing interest in sensing applications for a variety of analytes in aqueous environments, as conventional methods do not work reliably under humid conditions or they require complex equipment with experienced operators. Hydrogel sensors are easy to fabricate, are incredibly sensitive, and have broad dynamic ranges. Experiments on their robustness, reliability, and reusability have indicated the possible long-term applications of these systems in a variety of fields, including disease diagnosis, detection of pharmaceuticals, and in environmental testing. It is possible to produce hydrogels, which, upon sensing a specific analyte, can adsorb it onto their 3D-structure and can therefore be used to remove them from a given environment. High specificity can be obtained by using molecularly imprinted polymers. Typical detection principles involve optical methods including fluorescence and chemiluminescence, and volume changes in colloidal photonic crystals, as well as electrochemical methods. Here, we explore the current research utilizing hydrogel-based sensors in three main areas: (1) biomedical applications, (2) for detecting and quantifying pharmaceuticals of interest, and (3) detecting and quantifying environmental contaminants in aqueous environments.

Enzymes Encapsulated within Alginate Hydrogels: Bioelectrocatalysis and Electrochemiluminescence Applications

A simple procedure to incorporate enzymes (horseradish peroxidase, HRP, and lactate oxidase, LOx) within alginate hydrogels is reported with electrochemiluminescence (ECL) used to detect the enzymatic reactions with the corresponding substrates. First, HRP and LOx were successfully immobilized into CaCO3 microspheres, followed by the electrostatic layer-by-layer deposition of a nanoshell onto the microspheres, and finally by their dispersion into alginate solution. The as-prepared dispersion was drop cast onto the glassy carbon electrodes and cross-linked by the external and internal gelation methods using Ca2+ cations. The enzymes encapsulated within the alginate hydrogels were characterized using cyclic voltammetry and kinetic studies performed using ECL. The results showed that the enzymatic activity was significantly maintained as a result of the immobilization, with values of the apparent Michaelis-Menten constants estimated as 7.71 ± 0.62 and 8.41 ± 0.43 μM, for HRP and LOx, respectively. The proposed biosensors showed good stability and repeatability with an estimated limit of detection of 5.38 ± 0.05 and 0.50 ± 0.03 μM for hydrogen peroxide and lactic acid, respectively. The as-prepared enzymes encapsulated within the alginate hydrogels showed good stability up to 28 days from their preparation. The sensitivity and selectivity of the enzymes encapsulated within the alginate hydrogels were tested in real matrices (HRP, hydrogen peroxide, in contact lens solution; LOx, lactic acid in artificial sweat) showing the sensitivity of the ECL detection methods for the detection of hydrogen peroxide and lactic acid in real samples.

Mucus-Inspired Dynamic Hydrogels: Synthesis and Future Perspectives

Mucus hydrogels at biointerfaces are crucial for protecting against foreign pathogens and for the biological functions of the underlying cells. Since mucus can bind to and host both viruses and bacteria, establishing a synthetic model system that can emulate the properties and functions of native mucus and can be synthesized at large scale would revolutionize the mucus-related research that is essential for understanding the pathways of many infectious diseases. The synthesis of such biofunctional hydrogels in the laboratory is highly challenging, owing to their complex chemical compositions and the specific chemical interactions that occur throughout the gel network. In this perspective, we discuss the basic chemical structures and diverse physicochemical interactions responsible for the unique properties and functions of mucus hydrogels. We scrutinize the different approaches for preparing mucus-inspired hydrogels, with specific examples. We also discuss recent research and what it reveals about the challenges that must be addressed and the opportunities to be considered to achieve desirable de novo synthetic mucus hydrogels.