Functional Three-Dimensional Porous Conductive Polymer Hydrogels for Sensitive Electrochemiluminescence in Situ Detection of H2O2 Released from Live Cells

Multi-MXene assisted large-scale manufacturing of electrochemical biosensors based on enzyme-nanoflower enhanced electrodes for the detection of H2O2 secreted from live cancer cells

In situ monitoring of H2O2 in cellular microenvironments plays a critical role in the early diagnosis and pretreatment of cancer, but is limited by the lack of efficient and low-cost strategies for the large-scale preparation of real-time biosensors. Herein, a universal strategy for MXene-based composite inks combined with a scalable screen-printing process is validated in large-scale manufacturing of electrochemical biosensors for in situ detection of H2O2 secreted from live cells. Compositing biocompatible carboxymethyl cellulose (CMCS) with excellent conductive MXene, a water-based ink electrode (MXene/CMCS) with tunable viscosity is efficiently printed with desirable printing accuracy. Subsequently, the MXene/CMCS@HRP electrochemical biosensor exhibits stable electrochemical performance through HRP nanoflower modification, showing rapid electron transport and high electrocatalytic capacity, and demonstrating a low limit of detection (0.29 μM) with a wide linear detection range (0.5 μM-3 mM), superior sensitivity (56.45 μA mM-1 cm-2), long-term stability and high anti-interference ability. Moreover, this electrochemical biosensor is effectively employed for in situ detection of H2O2 secreted from HeLa cells, revealing good biocompatibility and outstanding biosensing capability. This proposed strategy not only extends the possibility of low-cost biomedical devices, but also provides a promising approach for early diagnosis and treatment of cancer.

Photocatalytic degradation of methyl blue dye with H2O2 sensing

A condensation polymer (urea-formaldehyde resin) passivated ZnO nanoparticles were used as an efficient photocatalyst for methyl blue degradation in the presence of H2O2 involving a Fenton-like reaction. The formation of OH˙ radicals were attributed to the pivotal factor for the degradation process. The method was easy and recyclable. The dose of photocatalyst, initial dye concentration, pH variation, variations of the composition of the photocatalyst, and the effect of scavengers were gauged. The degraded product was highly fluorescent and fluorometric detection of H2O2 was achieved along with a colorimetric recognition pathway. No other dye could be degraded under similar experimental conditions, implying the novel utility of methyl blue for environmental remediation.

Visual Gustation via Regulable Elastic Photonic Crystals

The unique structural sensitivity of photonic crystals (PCs) endows them with stretchable or elastic tunability for light propagation and spontaneous emission modulation. Hydrogel PCs have been demonstrated to have biocompatibility and flexibility for potential human health detection and environmental security monitoring. However, current elastic PCs still possess a fixed elastic modulus and uncontrollable structural colors based on a tunable elastic modulus, posing considerable challenges for in situ detection, particularly in wearable or portable sensing devices. In this work, we introduced a novel chemo-mechanical transduction mechanism embedded within a photonic crystal nanomatrix, leading to the creation of structural colors and giving rise to a visual gustation sensing experience. By utilizing the captivating structural colors generated by the hydrogel PC, we employ abundant optical information to identify various analytes. The finite element analysis proved the electric field distribution in the PC matrix during stretch operations. The elastic-optical behaviors with various chemical cosolvents, including cations, anions, saccharides, or organic acids, were investigated. The mechanism of the Hofmeister effect regulating the elasticity of hydrogels was demonstrated with the network nanostructure of the hydrogels. The hydrogel PC matrix demonstrates remarkable capability in efficiently distinguishing a wide range of cations, anions, saccharides, and organic acids across various concentrations, mixtures, and even real food samples, such as tastes and soups. Through comprehensive research, a precise relationship between the structural colors and the elastic modulus of hydrogel PCs has been established, contributing to the biomatching elastic-optics platform for wearable devices, a dynamic environment, and clinical or health monitoring auxiliary.

Modular coupling MOF nanozyme with natural enzyme on hollow fiber membrane for rapid and reusable detection of H2O2 and glucose

A novel strategy based on gradient porous hollow fiber membrane (GPF) is proposed for the modular assembly of enzyme-nanozyme cascade systems. The porous structure of GPF provided sufficient specific surface area, while the gradient structure effectively minimized the leaching of enzymes and nanozymes. To enhance stability, we prepared and immobilized metal-organic framework (MOF) nanozymes, resulting in the fabrication of GPF-MOF with excellent stability and reusability for colorimetric H2O2 detection. To improve specificity and expand the detection range, micro-crosslinked natural enzymes were modularly assembled, using glucose oxidase as the model enzyme. The assembled system, GPF-mGOx@MOF, achieved a low detection limit of 0.009 mM and a linear range of 0.2 to 11 mM. The sensor retained 87.2% and 80.7% of initial activity after being stored for 49 days and 9 recycles, respectively. Additionally, the reliability of the biosensor was validated through glucose determination of human blood and urine samples, yielding comparable results to a commercial glucose meter.

Enhancing the Electrochemiluminescence of Porphyrin via Crystalline Networks of Metal-Organic Frameworks for Sensitive Detection of Cardiac Troponin I

Porphyrins easily aggregate due to unfavorable π-π accumulation, causing luminescent quenching in the aqueous phase and subsequently reducing luminescent efficiency. It is a feasible way to immobilize porphyrin molecules through metal-organic framework materials (MOFs). In this study, 5,10,15,20-tetrakis (4-carboxyphenyl) porphyrin (TCPP) was introduced into the metal-organic skeleton (PCN-224) as a ligand. The result showed that the electrochemiluminescence (ECL) and photoluminescence (PL) efficiency of the MOF skeleton was 8.2 and 6.5 times higher than TCPP, respectively. Impressively, the periodic distribution of porphyrin molecules in the MOF framework can overcome the bottleneck of porphyrin aggregation, resulting in the organic ligand TCPP participating in the electron transfer reaction. Herein, based on the PCN-224, a sandwich-type ECL immunosensor was constructed for the determination of cardiac troponin I (cTnI). It provided sensitive detection of cTnI in the range of 1 fg/mL to 10 ng/mL with a detection limit of 0.34 fg/mL. This work not only innovatively exploited a disaggregation ECL (DIECL) strategy via the crystalline framework of MOF to enhance the PL and ECL efficiency of porphyrin but also provided a promising ECL platform for the ultrasensitive monitoring of cTnI.

A novel point-of-care diagnostic prototype system for the simultaneous electrochemiluminescent sensing of multiple traumatic brain injury biomarkers

Traumatic brain injuries (TBI) are typically acquired when a sudden violent event causes damage to the brain tissue. A high percentage (70-85%) of all TBI patients are suffering from mild TBI (mTBI), which is often difficult to detect and diagnose with standard imaging tools (MRI, CT scan) due to the absence of significant lesions and specific symptoms. Recent studies suggest that a screening test based on the measurement of a protein biomarker panel directly from a patient's blood can facilitate mTBI diagnosis. Herein, we report a novel prototype system designed as a precursor of a future hand-held point-of-care (POC) diagnostic device for the simultaneous multi-biomarker sensing, employing a microarray-type spatially resolved electrochemiluminescence immunoassay (SR-ECLIA). The small tabletop prototype consists of a screen-printed electrode compartment to conduct multi-analyte ECL sandwich assays, a potentiostat module and a light collection module, all integrated into a compact 3D-printed housing (18.2 × 16.5 × 5.0 cm), as well as an sCMOS detector. Based on this design concept, further miniaturization, system integration, performance optimization and clinical evaluation shall pave the way towards the development of a portable instrument for use at the site of accident and healthcare. To demonstrate the system's feasibility, current performance and efficiency, the simultaneous detection of three mTBI biomarkers (GFAP, h-FABP, S100β) in 50% serum was achieved in the upper pg mL-1 range. The proposed device is amenable to the detection of other biomarker panels and thus could open new medical diagnostic avenues for sensitive multi-analyte measurements with low-volume biological sample requirements.

Upconversion nanoparticles anchored MnO2 nanosheets for luminescence "turn on" detecting hydrogen peroxide

The sensitively and reliably detecting hydrogen peroxide (H₂O₂) is of significant for biology and environment protection fields. Herein, we reported a high sensitive H₂O₂ nanoprobe based on upconversion nanoparticles (UCNPs) anchored MnO₂ nanosheets. In which, DNA modified NaYF₄@NaYF₄:Yb,Tm core-shell nanoparticles were anchored onto the MnO₂ nanosheets surface via π-π stacking. Owing to the luminescence resonance energy transfer, the blue luminescence of UCNPs was effectively quenched by MnO₂ nanosheets, then the luminescence could be restored by adding H₂O₂ for reducing MnO₂ to Mn²⁺, and achieving a H₂O₂ concentration-dependent luminescence change, the detection limit could reach to 0.23 nM (S/N = 3). The proposed method could detect H₂O₂ in serum, lake water and real samples. Thus, a desired upconversion luminescence sensing strategy for detection H₂O₂ in life and environmental analysis was successfully constructed. It may be provide a potential tool in disease diagnosis and environmental monitoring fields.

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.

Conductive and self-healing hydrogel for flexible electrochemiluminescence sensor

A flexible electrochemiluminescence (ECL) hydrogel sensor exhibiting good self-healing was constructed. A transparent self-healing oxidized sodium alginate/hydrazide polyethylene glycol (OSA/PEG-DH) hydrogel was prepared by crosslinking dynamic covalent acylhydrazone bond. The introduction of 4-amino-DL-phenylalanine, a catalyst with good biocompatibility, allows rapid gelation and self-healing of hydrogel under mild conditions. Using the hydrogel as the sensing substrate, the ionic liquid (IL) 2-hydroxy-N,N,N-trimethylethanaminium chloride and the luminescent reagent N-(aminobutyl)-N-(ethylisoluminol) (ABEI) were simultaneously immobilized in the OSA/PEG-DH hydrogel to obtain the ABEI/IL/OSA/PEG-DH hydrogel. The ABEI/IL/OSA/PEG-DH hydrogel can be directly used as a semi-solid electrolyte for constructing a flexible ECL hydrogel sensor for the detection of H₂O₂, which acted as a coreactant of ABEI. The prepared flexible ECL sensor showed good self-healing performance, can restore ECL signal intensity within 20 min after physical damage, and showed high accuracy in the analysis of complex serum samples. This research shed new light on the development of flexible ECL sensor for bioanalytical applications.

Advances in electrochemiluminescence luminophores based on small organic molecules for biosensing

Electrochemiluminescence (ECL) has several advantages, such as a near-zero background signal, high sensitivity, wide dynamic range, simplicity, and is widely used for sensing, imaging, and single cell analysis. ECL luminophores are the key factors in the performance of various applications. Among various luminophores, small organic luminophores exhibit many intriguing features including good biocompatibility, facile modification, well-defined molecular structure, and sustainable raw materials, making small organic luminophores attractive for the use in the ECL field. Although many great achievements have been made in the synthesis of new small organic luminophores, solving various challenges, and expanding new applications, there are almost no comprehensive reviews on small organic ECL luminophores. In this review, we briefly introduce the advantages and emission mechanisms of small organic ECL luminophores, summarize the main types, molecular characteristics, and ECL properties of most existing small organic ECL luminophores, and present the important applications and design principles in sensors, imaging, single cell analysis, sterilization, and other fields. Finally, the challenges and outlook of organic ECL luminophores to be popularized in biosensing applications are also discussed.

An enhanced chemiluminescence hybrids of luminol by sulfonated polyaniline decorated copper-based metal organic frame composite applicable to the measurement of hydrogen peroxide in a wide pH range

Here, sulfonated polyaniline (SPAN) was decorated on the surface of copper-based metal organic frame (HKUST-1) and the composite was functionalized by luminol to construct a chemiluminescence (CL) hybrids (SPAN/HKUST-1@Luminol). The as-prepared SPAN/HKUST-1@Luminol demonstrated a great dispersion and stability performance in aqueous solution. Moreover, the resultant SPAN/HKUST-1@Luminol hybrids exhibited extremely strong CL properties, and the CL quantum yield was 136 times higher than that of luminol. In particular, it exhibited outstanding CL activity not only under alkaline conditions, but also under neutral conditions. The sensitive response of the hybrid to hydrogen peroxide was used to construct CL methods for the detection of hydrogen peroxide at a wide range of pH, with the detection limit of 60 nM at a neutral condition and 25 pM at alkaline condition. Due to strong and stable signal of the SPAN/HKUST-1@Luminol, the CL method provides a viable tool for determination of H₂O₂ in biological systems and enabled the monitoring of stimulated production of H₂O₂ released by living cells.

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.

Emerging single-atom iron catalysts for advanced catalytic systems

Due to the elusive structure-function relationship, traditional nanocatalysts always yield limited catalytic activity and selectivity, making them practically difficult to replace natural enzymes in wide industrial and biomedical applications. Accordingly, single-atom catalysts (SACs), defined as catalysts containing atomically dispersed active sites on a support material, strikingly show the highest atomic utilization and drastically boosted catalytic performances to functionally mimic or even outperform natural enzymes. The molecular characteristics of SACs (e.g., unique metal-support interactions and precisely located metal sites), especially single-atom iron catalysts (Fe-SACs) that have a similar catalytic structure to the catalytically active center of metalloprotease, enable the accurate identification of active centers in catalytic reactions, which afford ample opportunity for unraveling the structure-function relationship of Fe-SACs. In this review, we present an overview of the recent advances of support materials for anchoring an atomic dispersion of Fe. Subsequently, we highlight the structural designability of support materials as two sides of the same coin. Moreover, the applications described herein illustrate the utility of Fe-SACs in a broad scope of industrially and biologically important reactions. Finally, we present an outlook of the major challenges and opportunities remaining for the successful combination of single Fe atoms and catalysts.

In Situ Imaging of Endogenous Hydrogen Peroxide Efflux from Living Cells via Bipolar Gold Nanoelectrode Array and Electrochemiluminescence Technology

The integration of a closed bipolar electrode (c-BPE) array and electrochemiluminescence (ECL) detection received a boost in applications in the detection of cell adhesion and disease-related biomarkers. This work proposed a gold nanorod array based c-BPE-ECL system to realize an in situ image of endogenous hydrogen peroxide (H₂O₂) efflux from living cells and parallel analysis of endogenous H₂O₂ released from multiple cells by converting electrochemical signals into optical signals. The gold nanorod array with high density was prepared by a repeating chronopotentiometry procedure with anodic aluminum oxide (AAO) membrane as a template. The c-BPE array was fabricated by assembling poly(dimethylsiloxane) (PDMS) chips on both sides of the gold nanorod array. When an appropriate driving potential is applied, H₂O₂ generated from living cells at the sensing pole was reduced on the gold nanorod, triggering the oxidation of the ECL reagent at the reporting pole, which allowed the detection of H₂O₂ released from living cells. Under phorbol myristate acetate (PMA) stimulation, H₂O₂ released from living HeLa, HepG2, MCF-7, and LO2 cells was determined to be 47, 32.4, 25.7, and 6.3 μM, respectively. This indicated that the amount of H₂O₂ released from PMA-stimulated cancer cells was significantly higher than that from the stimulated normal cells. This work presented a new approach for in situ imaging of H₂O₂ released from living cells and could also be used to detect other electrochemically active or non-electrochemically active molecules through simple cell surface modification, which may have potential applications in cell apoptosis study and disease diagnosis.

Two-Dimensional and Three-Dimensional Ultrathin Multilayer Hydrogels through Layer-by-Layer Assembly

Stimuli-responsive multilayer hydrogels have opened new opportunities to design hierarchically organized networks with properties controlled at the nanoscale. These multilayer materials integrate structural, morphological, and compositional versatility provided by alternating layer-by-layer polymer deposition with the capability for dramatic and reversible changes in volumes upon environmental triggers, a characteristic of chemically cross-linked responsive networks. Despite their intriguing potential, there has been limited knowledge about the structure-property relationships of multilayer hydrogels, partly because of the challenges in regulating network structural organization and the limited set of the instrumental pool to resolve structure and properties at nanometer spatial resolution. This Feature Article highlights our recent studies on advancing assembly technologies, fundamentals, and applications of multilayer hydrogels. The fundamental relationships among synthetic strategies, chemical compositions, and hydrogel architectures are discussed, and their impacts on stimuli-induced volume changes, morphology, and mechanical responses are presented. We present an overview of our studies on thin multilayer hydrogel coatings, focusing on controlling and quantifying the degree of layer intermixing, which are crucial issues in the design of hydrogels with predictable properties. We also uncover the behavior of stratified "multicompartment" hydrogels in response to changes in pH and temperature. We summarize the mechanical responses of free-standing multilayer hydrogels, including planar thin coatings and films with closed geometries such as hollow microcapsules and nonhollow hydrogel microparticles with spherical and nonspherical shapes. Finally, we will showcase potential applications of pH- and temperature-sensitive multilayer hydrogels in sensing and drug delivery. The knowledge about multilayer hydrogels can advance the rational design of polymer networks with predictable and well-tunable properties, contributing to modern polymer science and broadening hydrogel applications.

Copper-based metal-organic frameworks for biomedical applications

Metal-organic frameworks (MOFs) are a class of important porous, crystalline materials composed of metal ions (clusters) and organic ligands. Owing to the unique redox chemistry, photochemical and electrical property, and catalytic activity of Cu^2+/+, copper-based MOFs (Cu-MOFs) have been recently and extensively explored in various biomedical fields. In this review, we first make a brief introduction to the synthesis of Cu-MOFs and their composites, and highlight the recent synthetic strategies of two most studied representatives, three-dimensional HKUST-1 and two-dimensional Cu-TCPP. The recent advances of Cu-MOFs in the applications of cancer treatment, bacterial inhibition, biosensing, biocatalysis, and wound healing are summarized and discussed. Furthermore, we propose a prospect of the future development of Cu-MOFs in biomedical fields and beyond.

Bioinspired Hydrogen Peroxide-Activated Nanochannels and Their Applications in Cancer Cell Analysis

Bioinspired nanochannels that manipulate ion transport have shown great potential for understanding complex physiological processes. Herein, inspired by the gating function of the biological ion channels, we designed and constructed artificial hydrogen peroxide (H₂O₂)-activated nanochannels by decorating the inner pore surface with 4-(phenoxymethyl) benzeneboronic acid pinacol ester (PBAE). Benefiting from the specific hydrolysis reaction between H₂O₂ and PBAE in the confined nanochannels, the functionalized artificial nanochannels exhibited a highly selective and sensitive response toward H₂O₂. The system could switch between open/closed states in the presence/absence of H₂O₂ by the ionic current test. Meanwhile, comsol simulations were carried out to evidence the mechanism of hydrogen peroxide triggered regulation of ion transport by the nanochannels. It was found that the surface charge density of the nanochannels changed along with the addition of H₂O₂. Furthermore, based on the sensing strategy, the PBAE-functionalized nanochannel membrane was applied in the detection of H₂O₂ in the tumor microenvironment, which achieved highly selective distinguishing of cancerous cells from normal cells. This work provides a versatile method to construct bioinspired nanochannel-based platforms for detecting small reactive molecules and offers prospects for the application of disease diagnosis and prognosis.

Single-atom Nanozymes for Biomedical Applications： Recent Advances and Challenges

Nanozymes have received extensive attention in the fields of sensing and detection, medical therapy, industry, and agriculture thanks to the combination of the catalytic properties of natural enzymes and the physicochemical properties of nanomaterials, coupled with superior stability and ease of preparation. Despite the promise of nanozymes, conventional nanozymes are constrained by their oversized size and low catalytic capacity in sophisticated practical application environments. single-atom nanozymes (SAzymes) were characterized as nanozymes with high catalytic efficiency by uniformly distributed single atoms as catalysis sites, thus effectively addressing the defects of conventional nanozymes. This paper reviews the activity improvement scheme and catalytic mechanism of SAzymes and highlights the latest research progress of SAzymes in the fields of biomedical sensing and therapy. Eventually, the challenges and future directions of SAzymes are discussed in this paper.

Self-enhanced luminol-based electrochemiluminescent hydrogels: An ultrasensitive biosensing platform for fusion gene analysis coupled with target-initiated DNAzyme motor

BCR/ABL fusion gene has been discovered as an important and reliable biomarker for early diagnosis of chronic myeloid leukemia (CML). Herein, a novel and switching electrochemiluminescence (ECL) biosensor was developed for ultrasensitive determination of the fusion gene based on the self-enhanced polyethyleneimine-luminol (PEI-Lum) hydrogels coupled with target-initiated DNAzyme motor. The facilely prepared PEI-Lum hydrogels could not only immobilize enormous luminol but shorten the distance of binary system, thus facilitating the mass and electron transfer efficiency of the sensing interface, so that the enhanced ECL signal was achieved. Moreover, the engineering DNA motor was powered by Mg²⁺-dependent DNAzyme for isothermal DNA signal amplification. As a result, the fabricated ECL biosensor enabled highly sensitive detection of BCR/ABL fusion gene with a broad linear range from 10.0 fM to 10.0 nM and a low detection limit of 3.75 fM (S/N = 3). Significantly, the developed biosensing method provides a potential tool for nucleic acid analysis in clinical diagnosis and a new avenue to design high-efficient ECL nanomaterials.

Tuning the Ratio of Pt(0)/Pt(II) in Well-Defined Pt Clusters Enables Enhanced Electrocatalytic Reduction/Oxidation of Hydrogen Peroxide for Sensitive Biosensing

Rational design and construction of advanced sensing platforms for sensitive detection of H₂O₂ released from living cells is one of the challenges in the field of physiology and pathology. Noble metal clusters are a kind of nanomaterials with well-defined chemical composition and special atomic structures, which have been widely explored in catalysis, biosensing, and therapy. Compared with noble metal nanoparticles, noble metal clusters exhibit great potential in electrochemical biosensing due to their high atom utilization efficiency and abundant reactive active sites. Herein, Pt nanoclusters anchored on hollow carbon spheres (Pt_NCS/HCS) were successfully prepared for sensitive detection of H₂O₂. By tuning the ratio of Pt(0)/Pt(II) at different annealing temperatures, the optimized Pt_NCS/HCS-550 showed higher H₂O₂ reduction and oxidation catalytic activities than other control samples. Density functional theory calculations revealed that H₂O₂^*can be better activated and dissociated in the Pt_0II model featured with the co-existence of Pt(0)/Pt(II) and the key intermediates OOH*/OH* have a stronger interaction with the Pt_0II model. As a concept application, the electrochemical biosensing platform was successfully applied to sensitive detection of H₂O₂ released from the cells.

A Smartphone Optical Device for Point-of-Care Testing of Glucose and Cholesterol Using Ag NPs/UiO-66-NH2-Based Ratiometric Fluorescent Probe

Point-of-care testing (POCT) with the advantages of simplicity, rapidity, portability, and low-cost is of great importance to improve healthcare, especially in resource-limited settings and home healthcare settings. Moreover, it is a great challenge to quantitative POCT of multiplexed biomarkers within a single accessible assay but provides enhanced diagnostic accuracy and improved diagnostic efficiency. Herein, a smartphone optical device has been designed for POCT of glucose and cholesterol in metabolic syndrome patients using a ratiometric fluorescent sensor. The sensing system of Ag NPs/UiO-66-NH₂ and o-phenylenediamine presents a dual-emission response to H₂O₂ (the main product of glucose and cholesterol catalyzed by glucose oxidase and cholesterol oxidase) on account of the inner filter effect, resulting in an increase in the response of the fluorescence intensity ratio (F_555 nm/F_425 nm) accompanied by a distinguishable color transition from blue to yellow green. After compositing probes with a flexible substrate, the obtained test strip can be integrated with a smartphone-based portable platform to read RGB values for accurate testing of glucose and cholesterol with both detection limits of 10 μmol L^-1, which are hundreds of times lower than their concentrations in human serum. With the advantages of low-cost, ease of operation, and broad adaptability, this smartphone optical device holds great potential for portable detection of numerous targets in personalized healthcare and clinical diagnosis.

Long-term cell culture and electrically in situ monitoring of living cells based on a polyaniline hydrogel sensor

Accurate, in situ and long-term electrically monitoring of cell development plays an important role in cell study, which brings in challenges in terms of biocompatibility, processability, and sensing capability of electrochemical sensors. Based on biocompatible conductive polyaniline (PAni) hydrogels, we constructed a flexible sensor with flexible carbon cloth for electrical analysis of living cells. The carbon fiber substrate modified with conductive PAni hydrogels was selected as the electrode to promote the current collection of the sensor. The three dimensional nanostructured mesoporous matrix of PAni hydrogels is favorable for in situ generation of catalytic Pt nanoparticles and cell growth. With these hierarchically nanostructured features, the hydrogel electrochemical sensor was endowed with high sensitivity and selectivity in the detection of H₂O₂ (with a low detection limit of 1.6 μM in 0.01 M PBS and a wide linear range from 10 μM to 10 mM), and good biocompatibility for cell growth as long as 5 days. The accurate detection of H₂O₂ released from cells enabled us to differentiate the physiological states of cells and imitate the different stimuli-responsive behavior, which can provide real-time information on cell biological events. With outstanding biocompatibility, operability and repeatability, this strategy can be expanded to the fields of other biosensor fabrication and cell-related biomarker monitoring, which exhibits a broad application potential in bioanalysis catering to new generation sensors.

Gel-Based Luminescent Conductive Materials and Their Applications in Biosensors and Bioelectronics

The gel is an ideal platform for fabricating materials for bio-related applications due to its good biocompatibility, adjustable mechanical strength, and flexible and diversified functionalization. In recent decades, gel-based luminescent conductive materials that possess additional luminescence and conductivity simultaneously advanced applications in biosensors and bioelectronics. Herein, a comprehensive overview of gel-based luminescent conductive materials is summarized in this review. Gel-based luminescent conductive materials are firstly outlined, highlighting their fabrication methods, network structures, and functions. Then, their applications in biosensors and bioelectronics fields are illustrated. Finally, challenges and future perspectives of this emerging field are discussed with the hope of inspire additional ideas.

Nonenzymatic Hydrogen Peroxide Detection Using Surface-Enhanced Raman Scattering of Gold-Silver Core-Shell-Assembled Silica Nanostructures

Hydrogen peroxide (H₂O₂) plays important roles in cellular signaling and in industry. Thus, the accurate detection of H₂O₂ is critical for its application. Unfortunately, the direct detection of H₂O₂ by surface-enhanced Raman spectroscopy (SERS) is not possible because of its low Raman cross section. Therefore, the detection of H₂O₂ via the presence of an intermediary such as 3,3,5,5-tetramethylbenzidine (TMB) has recently been developed. In this study, the peroxidase-mimicking activity of gold–silver core–shell-assembled silica nanostructures (SiO₂@Au@Ag alloy NPs) in the presence of TMB was investigated using SERS for detecting H₂O₂. In the presence of H₂O₂, the SiO₂@Au@Ag alloy catalyzed the conversion of TMB to oxidized TMB, which was absorbed onto the surface of the SiO₂@Au@Ag alloy. The SERS characteristics of the alloy in the TMB–H₂O₂ mixture were investigated. The evaluation of the SERS band to determine the H₂O₂ level utilized the SERS intensity of oxidized TMB bands. Moreover, the optimal conditions for H₂O₂ detection using SiO₂@Au@Ag alloy included incubating 20 µg/mL SiO₂@Au@Ag alloy NPs with 0.8 mM TMB for 15 min and measuring the Raman signal at 400 µg/mL SiO₂@Au@Ag alloy NPs.

Au-Fe3O4 nanoagent coated cell membrane for targeted delivery and enhanced chem/photo therapy

Here, we propose a cancer cell membrane (CM) coated Au-Fe₃O₄ complex (AFTP@CM), loaded with tannic acid and phorbol 12-myristate 13-acetate for targeted drug delivery and enhanced chem/photo therapy.

Crumpled Graphene/Poly (azure I) Modified Electrode for Non-enzymatic Detection of Hydrogen Peroxide Secreted from Tumor Cells

Hydrogen peroxide (H₂O₂), an important representatives of reactive oxygen species, its aberrant expression is related to many diseases, including cancers. Therefore, it is very significant to design a reliable method for the real-time detection of endogenous H₂O₂. Herein, we describe preparing a poly (azure I)/crumpled graphene (cGN) modified electrode by an electro-polymerization method. The results showed that this electrode presented obvious electrocatalytic effect on the reduction of H₂O₂. Amperometric method was employed to monitor H₂O₂, and the amperometric response exhibited a good linear relationship with its concentration in the range of 8.0 × 10^-6 - 1.25 × 10^-3 mol/L; the detection limit reached to 6.7 × 10^-7 mol/L (S/N = 3). Furthermore, this modified also displayed good selectivity, long-term stability and a high anti-interference ability. Excitingly, the established method could be successfully used to detect H₂O₂ in human serum samples, and measured H₂O₂ secreted from living MCF-7 cells. It could have potential use in cancer diagnosis.

Pentamethinium Salts Nanocomposite for Electrochemical Detection of Heparin

This study presents a simple route to heparin detection and develops a voltammetric approach using supramolecular principles and nanomaterials. Nanocomposites, including gold nanoparticles (AuNPs) and γ-substituted pentamethinium salts (PMS) deposited on a glass carbon (GC) electrode surface (GC/AuNPs/PMS) and covered by a plasticized poly(vinyl chloride) (PVC) membrane, are proposed for heparin detection. The conductivity of the nonconducting PVC-plasticized membrane is guaranteed by AuNPs, and the selectivity is provided by the interaction between γ-substituted PMS and anionic analytes. In order to extend the linear range, it is necessary to apply a solvent compatible with PVC-plasticized membrane, namely tetrahydrofuran. The proposed voltammetric sensor showed a concentration dependence from 1.72 up to 45.02 IU mL⁻¹ heparin and was used for heparin detection in saline and biological samples with recovery of 95.1–100.9%.

A three-dimensional hydrogel-modified indium tin oxide electrode with enhanced performance for in situ electrochemical detection of extracellular H2O2

Two different electrochemical sensors (Hemin-G4/Au/GCE and Hemin-G4/Au/ITO) were developed and applied to explore the electrocatalytic capacity of H₂O₂ reduction. Due to the excellent catalytic activity of Hemin-G4 and high conductivity of gold nanoparticles, both electrodes show excellent electrochemical performances towards H₂O₂ with a low LOD (0.67 μM for Hemin-G4/Au/GCE and 0.65 μM for Hemin-G4/Au/ITO), rapid response (<4 s), and high selectivity and sensitivity (314.33 μA mM^-1 cm^-2 for Hemin-G4/Au/GCE and 322.22 μA mM^-1 cm^-2 for Hemin-G4/Au/ITO). The two electrodes allow sensitive capture of H₂O₂ produced by A549 cells. Compared with the conventional method of detection in cell suspensions, an ITO electrode with a large specific surface area and good biocompatibility can provide a promising platform for cell adhesion, so as to realize real-time and in situ detection of extracellular H₂O₂. The experimental results show that A549 cells can adhere to the surface of the Hemin-G4/Au/ITO electrode and grow well. This is benefitted from the three-dimensional structure of the Hemin-G4/Au hydrogel, which provides a suitable microenvironment for cell adhesion and growth. Furthermore, the in situ detection shows a faster response time than that of in-solution detection. This is because the H₂O₂ generated by the cells can be directly captured by the ITO electrode, which avoids diffusion from the solution to the electrode. These results indicate that the self-supporting hydrogel modified ITO electrode has great application prospects in basic biomedical research and continuous dynamic surveillance of diseases.

Mesoporous TiO2-based architectures as promising sensing materials towards next-generation biosensing applications

In the past two decades, mesoporous TiO2 has emerged as a promising material for biosensing applications. In particular, mesoporous TiO2 materials with uniform, well-organized pores and high surface areas typically exhibit superior biosensing performance, which includes high sensitivity, broad linear response, low detection limit, good reproducibility, and high specificity. Therefore, the development of biosensors based on mesoporous TiO2 has significantly intensified in recent years. In this review, the expansion and advancement of mesoporous TiO2-based biosensors for glucose detection, hydrogen peroxide detection, alpha-fetoprotein detection, immobilization of enzymes, proteins, and bacteria, cholesterol detection, pancreatic cancer detection, detection of DNA damage, kanamycin detection, hypoxanthine detection, and dichlorvos detection are summarized. Finally, the future perspective and research outlook on the utilization of mesoporous TiO2-based biosensors for the practical diagnosis of diseases and detection of hazardous substances are also given.

Self-healing mechanism and bioelectrochemical interface properties of core-shell guanosine-borate hydrogels

The self-healing mechanism and bioelectrochemical interface properties of supramolecular gels have been rarely explored. In this context, we propose a constitutive "fibril-reorganization" model to reveal the self-healing mechanism of a series of core-shell structured guanosine-borate (GB) hydrogels and emphasize that interfibrillar interactions at the supramolecular polymer scale (G-quadruplex nanowires) drive the self-healing process of GB hydrogels. Structure-electrochemical sensing performance studies reveal that GB hydrogel nanofibers with relatively strong biomolecular affinity such as -SH modified GB hydrogel (GB-SH) show a high sensitivity of response and low limit of detection for tumour marker alpha-fetoprotein sensing (AFP; 0.076 pg mL^-1). Guanosine/ferroceneboronic acid (GB-Fc) hydrogel nanofibers with superior conductivity and redox activity display the widest linear detection range for AFP (0.0005-100 ng mL^-1). Structure-property correlations of GB hydrogels provide useful insight for the future design of advanced self-healing materials and electrochemical biosensors.

Fe-MOGs-based enzyme mimetic and its mediated electrochemiluminescence for in situ detection of H2O2 released from Hela cells

Enzyme mimetics have attracted wide interest due to their inherent enzyme-like activity and unique physicochemical properties, as well as promising applications in disease diagnosis, treatment and monitoring. Inspired by the attributes of nonheme iron enzymes, synthetic models were designed to mimic their capability and investigate the catalytic mechanisms. Herein, metal-organic gels (Fe-MOGs) with horseradish peroxidase (HRP) like Fe-N_X structure were successfully synthesized though the coordination between iron and 1,10-phenanthroline-2,9-dicarboxylic acid (PDA) and exhibited excellent peroxidase-like activity. Its structure-activity relationship and the in-situ electrochemiluminescence (ECL) detection of H₂O₂ secreted by Hela cells were further investigated. The highly dispersed Fe-N_X active sites inside Fe-MOGs were able to catalyze the decomposition of H₂O₂ into large amounts of reactive oxygen species (ROS) via a Fenton-like reaction under a low overpotential. Due to the accumulation of ROS free radicals, the luminol ECL emission was significantly amplified. A proof-of-concept biosensor was constructed with a detection limit as low as 2.2 nM and a wide linear range from 0.01 to 40 μM. As a novel metal organic gels based enzyme mimetic, Fe-MOGs show great promises in early cancer detection and pathological process monitoring.

Synthesis of Au–Cu Alloy Nanoparticles as Peroxidase Mimetics for H2O2 and Glucose Colorimetric Detection

The detection of hydrogen peroxide (H2O2) is essential in many research fields, including medical diagnosis, food safety, and environmental monitoring. In this context, Au-based bimetallic alloy nanomaterials have attracted increasing attention as an alternative to enzymes due to their superior catalytic activity. In this study, we report a coreduction synthesis of gold–copper (Au–Cu) alloy nanoparticles in aqueous phase. By controlling the amount of Au and Cu precursors, the Au/Cu molar ratio of the nanoparticles can be tuned from 1/0.1 to 1/2. The synthesized Au–Cu alloy nanoparticles show good peroxidase-like catalytic activity and high selectivity for the H2O2-mediated oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB, colorless) to TMB oxide (blue). The Au–Cu nanoparticles with an Au/Cu molar ratio of 1/2 exhibit high catalytic activity in the H2O2 colorimetric detection, with a limit of detection of 0.141 μM in the linear range of 1–10 μM and a correlation coefficient R2 = 0.991. Furthermore, the Au–Cu alloy nanoparticles can also efficiently detect glucose in the presence of glucose oxidase (GOx), and the detection limit is as low as 0.26 μM.

Electrochemical enantioselective sensor for effective recognition of tryptophan isomers based on chiral polyaniline twisted nanoribbon

Effective enantioselective recognition with chiral nanomaterials remains a challenge in the field of chemistry and biology. In this paper, a pair of left- and right-handed polyaniline (defined as S-PANI and R-PANI) were synthesized by chemical oxidation of aniline to form a specially twisted nanoribbon, which was induced by enantiomeric camphorsulfonic acid. Both S-PANI and R-PANI were used to construct electrochemical chiral sensors for the discrimination of tryptophan isomers (D- and L-Trp). Owing to the formation of efficient chiral nanospace with special nanoribbon morphology and enormous amounts of oxygen-containing functional groups of S-PANI or R-PANI, the high enantioselectivity was obtained with the recognition efficiency of 4.90 (D-Trp) on S-PANI and 4.20 (L-Trp) on R-PANI, respectively. The obtained chiral electrodes were also used for the determination of the enantiomeric excess (ee) for Trp, and a good linear relationship between peak currents and ee% of Trp was obtained. Furthermore, the strategy we proposed has tremendous potential in enantiomer recognition field.

Synergetic enhancement of electrochemical H2O2 detection in a nitrogen-doped carbon encapsulated FeCo alloy architecture

The development of Earth-abundant metal-based non-enzymatic electrodes with ultralow metal loadings for the efficient detection of hydrogen peroxide (H₂O₂) is highly desirable. We report here a remarkable three-dimensional nitrogen-doped porous carbon (NPC) encapsulated Earth-abundant metal architecture, i.e., NPC encapsulating FeCo alloy nanoparticles toward highly efficient electrochemical H₂O₂ detection. Specifically, an Fe_0.06Co_0.04@NPC-950 modified electrode can show excellent electrochemical performance for non-enzymatic H₂O₂ sensing in neutral media, with a wide linear range of 0.004 to 8 mM, a high sensitivity of 794 μA mA^-1 cm^-2 and a low limit of detection (LOD) of 0.13 μM, outperforming most of the reported non-noble metal electrocatalysts. Meanwhile, the fabricated Fe_0.06Co_0.04@NPC-950 modified electrode is capable of real-time monitoring of H₂O₂ in commercial orange juice, milk and serum, revealing its application potential toward the accurate detection of H₂O₂ in real-sample analysis. This electrode also has high selectivity, long-term stability and good reproducibility. Its excellent performance is correlated with the synergetic catalysis of the FeCo alloy, nitrogen-rich NPC with a large specific surface area (SSA) and the core-shell structure protecting the active sites from corrosion. This study offers an efficient pathway for developing high-performance and Earth-abundant catalysts toward electrochemical H₂O₂ detection.

Aggregation-Induced Emission Fluorescent Gels: Current Trends and Future Perspectives

The development of fluorescent gels, if not the current focus, is at the center of recent efforts devoted to the invention of a new generation of gels. Fluorescent gels have numerous properties that are intrinsic to the gel structure, with additional light-emitting properties making them attractive for different applications. This review focuses on current studies associated with the development of fluorescent gels using aggregation-induced emission fluorophores (AIEgens) to ultimately suggest new directions for future research. Here, we discuss major drawbacks of the methodologies used frequently for the fabrication of fluorescent gels using traditional fluorophores compared to those using AIEgens. The fabrication strategies to develop AIE-based fluorescent gels, including physical mixing, soaking, self-assembly, noncovalent interactions, and permanent chemical reactions, are discussed thoroughly. New and recent findings on developing AIE-active gels are explained. Specifically, physically prepared AIE-based gels including supramolecular, ionic, and chemically prepared AIE-based gels are discussed. In addition, the intrinsic fluorescent properties of natural gels, known as clustering-triggered fluorescent gel, and new and recent relevant findings published in peer-reviewed journals are explained. This review also revealed the biomedical applications of AIE-based fluorescent hydrogels including drug delivery, biosensors, bioimaging, and tissue engineering. In conclusion, the current research situation and future directions are identified.

Use of Triangular Silver Nanoplates as Low Potential Redox Mediators for Electrochemical Sensing

Redox mediators can facilitate the electrochemical communication between targets and electrodes for material characterization and investigation. To provide an alternative to the chemical-based redox mediators, herein, we present a nanoparticle-based redox mediator, i.e., the trisodium citrates (TSC)-capped triangular silver nanoplates (Tri-Ag-NP_TSC), which demonstrates an efficient oxidative process at around 0.13 V (vs Ag/AgCl) with acceptable redox reversibility by exploiting the interaction between the carbonyl group of TSC and the Ag element of Tri-Ag-NP_TSC. The TSC of Tri-Ag-NPs can be selectively replaced by thiols and enable the obtained Tri-Ag-NP_TSC-thiol with changed electrochemical redox response, which could be utilized to determine various thiols at 0.13 V, a much lowered oxidative potential than traditional redox mediators, with a similar linear response range, response slope, and limit of detection (LOD). This work proposes a surface-engineering approach to design and develop electrochemical redox probes using Ag nanoparticles with particular morphology, indicating that the interaction between the carbonyl group and Ag nanoparticles might be extended to sensing application beyond the surface-enhanced Raman scattering.

The mechanisms of HSA@PDA/Fe nanocomposites with enhanced nanozyme activity and their application in intracellular H2O2 detection

Nanozymes have drawn increasing attention with their broad applications but most nanozymes lack enzyme-like molecular structures, resulting in weak selectivity and low activity. Bioinspired molecular assembly provides an extremely promising strategy to mimic natural enzyme processes and develop function enhanced architectures. Herein, a new bioinspired molecular assembly strategy based on human serum albumin@polydopamine/Fe nanocomposites (HSA@PDA/Fe NCs) was proposed, in which Fe(iii)/Fe(ii) were anchored on HSA supported on PDA. HSA@PDA/Fe NCs with iron as the active center and HSA@PDA as the skeleton showed excellent peroxidase-like activity, which was nearly 1000 times higher than that of free Fe(iii). This may be attributed to the phenomenon that the cycle of quinones and the hydroxyl group on the nanocomposite surface greatly accelerate the conversion of Fe(iii)/Fe(ii) in acidic microenvironments. Systematic experimental studies illustrated that its activity was mainly affected by the metal active center, followed by the polymeric ligand, while the protein framework has little effect on its activity. Meanwhile, even after freeze-thaw and thermal cycle tests, it also showed excellent catalytic stability. Besides, a colorimetric assay based on HSA@PDA/Fe NCs was developed for detection of H₂O₂in vitro and in situ detection of H₂O₂ generated from live cells. This work will facilitate the developments on theoretical analysis, rational design and practical applications of nanozymes based on bioinspired molecular assemblies.