A comprehensive review of glucose biosensors based on nanostructured metal-oxides

Recent trends and prospective developments in metal oxide composites-based electrochemical nonenzymatic glucose sensors

Diabetes mellitus is among the fastest-growing chronic diseases worldwide, with its prevalence increasing at an alarming rate across various populations. Recent advancements notably impact the swift development of nonenzymatic glucose sensors within the fields of nanotechnology and materials science. This review comprehensively examines the relationship between nanostructure design and sensor performance, emphasizing the importance of controlling nanomaterial dimensions to enhance selectivity, specificity, sensitivity, and stability. We discuss various electrode materials' unique nanostructures and highlight innovative fabrication methods that improve glucose detection in alkaline media. This review briefly summarizes the direct oxidation of glucose by metallic redox centers, explaining the underlying mechanisms using the chemisorption model combined with the incipient hydrous oxide/adatom mediator (IHOAM) model. It then highlights recent advances in nonenzymatic glucose sensors based on transition metal oxides (such as CuO, NiO, Co3O4, IrO2, Rh2O3, Fe2O3, MnO2, TiO2, ZnO, and intermixed metal oxides). Additionally, we discuss the advantages and challenges associated with selectivity in nonenzymatic glucose sensing, while proposing practical strategies for optimization. Finally, this review aims to promote further progress in the design and synthesis of nanostructured materials by offering an extensive analysis of current research and future perspectives.

New cobalt hydroxycarbonate-based material for highly sensitive enzyme-free glucose sensors

Health monitoring with glucose sensors is essential for preventing various diseases and maintaining overall well-being. Among the numerous analytical methods used to measure glucose levels, electrochemical enzyme-free methods show high practical potential. Developing new materials for highly sensitive and stable enzyme-free sensors is of significant importance. This study presents hydroxycarbonates as a new class of materials for creating enzyme-free glucose sensors and demonstrates, for the first time, that nanostructured cobalt hydroxycarbonate is a promising candidate for effective sensor applications. Prepared using a simple one-step hydrothermal method, this material exhibited a sensitivity of 1950 µA cm-2 mM-1 with a detection limit (LOD) of approximately 30 µM and a linear range up to 3 mM glucose. In addition, the sensitivity of the sensor synthesized in a 0.1 M cobalt nitrate solution was found to increase by more than 3 times up to 6745 µA cm-2 mM-1 when only 2 mol% of zinc nitrate was added to the growth solution containing cobalt nitrate and urea during synthesis. This adjustment also significantly affects the lattice vibration spectrum and material morphology, reducing the average nanoparticle size from 30 nm to 7-8 nm. The sensors demonstrated high long-term stability when stored under normal conditions. These results highlight the significant potential of the new sensor material for the quantitative detection of glucose.

Glucose Sensing Using Pristine and Co-Doped Hematite Fiber-Optic Sensors: Experimental and DFT Analysis

Glucose monitoring plays a crucial role in managing diabetes, one of the most prevalent diseases worldwide. The development of fast-responsive, cost-effective, and biocompatible glucose sensors is essential for improving patient care. This study investigates the glucose sensing performance of pristine and Co-doped hematite synthesized via the hydrothermal method and integrated into fiber-optic evanescent wave probes. Structural and optical characterizations confirmed the enhanced properties of the Co-doped hematite. The Co-doped sensor exhibited reasonable sensitivity and a significantly improved limit of detection (LoD) of 3.99 mM compared to 6.12 mM for the pristine hematite. Density functional theory calculations further revealed an increase in glucose adsorption energy from -0.24 eV for the pristine surface to -1.28 eV for the Co-doped surface. Charge density difference and projected density of states analyses showed enhanced charge transfer and orbital delocalization upon doping, consistent with the experimentally observed improvement in LoD. These findings position Co-doped hematite as a promising candidate for noninvasive, nonenzymatic glucose detection and underscore the value of integrating experimental and theoretical approaches in biosensing technologies.

Enhancing Nonenzymatic Glucose Detection Through Cobalt-Substituted Hafnia

Engineered defect chemistry in ultrathin (≈5 nm) hafnia through substitutional cobalt (HCO) is investigated for selective glucose sensing. Thin films of HCO, grown using chemical solution deposition (CSD)-traditionally used to grow thick films-on silicon, show significant glucose sensing activity and undergo monoclinic to orthorhombic phase transformation. The presence of multivalent cobalt in hafnia, with oxygen vacancies in proximity, selectively oxidizes glucose with minimal interference from ascorbic acid, dopamine, and uric acid. Theoretical investigations reveal that these oxygen vacancies create a shallow donor level that significantly enhances electrocatalytic activity by promoting charge transfer to the conduction band. This results in considerable selectivity, repeatability, and reproducibility in sensing characteristics. These findings highlight the technological importance of using CSD for thin films, paving the way for ultrathin CSD-processed HCOs as potential candidates for selective glucose sensing applications.

Advancements in Breathomics: Special Focus on Electrochemical Sensing and AI for Chronic Disease Diagnosis and Monitoring

This Review examines the potential of breathomics in enhancing disease monitoring and diagnostic precision when integrated with artificial intelligence (AI) and electrochemical sensing techniques. It discusses breathomics' potential for early and noninvasive disease diagnosis with a focus on chronic kidney disease (CKD), chronic obstructive pulmonary disease (COPD), and lung cancer, which have been well studied in the context of VOC association with diseases. The noninvasive nature of exhaled breath analysis can be advantageous compared to traditional diagnostic methods for CKD, which often rely on blood and urine testing. VOC analysis can enhance spirometry and imaging methods used in COPD diagnosis, providing a more comprehensive picture of the disease's progression. Breathomics could also provide a less intrusive and potentially earlier diagnostic approach for lung cancer, which is now dependent on imaging and biopsy. The combination of breathomics, electrochemical sensing, and AI could lead to more personalized and successful treatment plans for chronic illnesses using AI algorithms to decipher complicated VOC patterns. This Review assesses the viability and effectiveness of combining breathomics with electrochemical sensors and artificial intelligence by synthesizing recent research findings and technological developments.

Recent progress on nanomaterial-based electrochemical sensors for glucose detection in human body fluids

In the modern age, half of the population is facing various chronic illnesses due to glucose maintenance in the body, major causes of fatality and inefficiency. The early identification of glucose plays a crucial role in medical treatment and the food industry, particularly in diabetes diagnosis. In the past few years, non-enzymatic electrochemical glucose sensors have received a lot of interest for their ability to identify glucose levels accurately. Electrochemical biosensors are developing as a propitious solution for personalized health monitoring due to their accuracy, specificity, and affordability. This review article provides an observation of a variety of non-enzymatic glucose sensor resources, such as carbon nanomaterials, noble metals gold and silver, transition metal and their oxides, and porous material composites. Moreover, basic knowledge of the reaction mechanism of enzymatic and nonenzymatic glucose sensors are outlined and recent advancements in glucose sensors applications to various human body biofluids such as sweat, tears, urine, saliva, and blood are presented. Finally, this review summarizes electrochemical sensors for glucose detection in human body fluids, the challenges they faced, and their solutions.

Carbon dots: synthesis, sensing mechanisms, and potential applications as promising materials for glucose sensors

The disruption of glucose (Glu) metabolism in the human body can lead to conditions such as diabetes and hyperglycemia. Therefore, accurately determining Glu levels is crucial for clinical diagnosis and other applications. Carbon dots (CDs) are a novel category of carbon nanomaterials that exhibit outstanding optical properties, excellent biocompatibility, high water solubility, low production costs, and straightforward synthesis. Recently, researchers have developed various carbon dot sensors for fast and real-time Glu monitoring. In this context, we provide a comprehensive introduction to Glu and CDs for the first time. We categorize the synthetic methods for CDs and the sensing mechanisms, further classifying the applications of carbon dot probes into single-probe sensing, ratiometric sensing, and visual detection. Finally, we discuss the future development needs for CD-based Glu sensors. This review aims to offer insights into advancing Glu sensors and modern medical treatments.

Chemosensitive Properties of Electrochemically Synthesized Poly-3-Thienylboronic Acid: Conductometric Detection of Glucose and Other Diol-Containing Compounds under Electrical Affinity Control

Due to the presence of the boronic acid moieties, poly-3-thienylboronic acid has an affinity for saccharides and other diol-containing compounds. Thin films of this novel chemosensitive polymer were synthesized electrochemically on the gold surface. The adhesion of the polymer was enhanced by the deposition of a monomolecular layer of thiophenol. The technology was used to fabricate conductometric sensors for glucose and other diol-containing compounds. Simultaneous two- and four-electrode conductivity measurements were performed. The chemical sensitivity to sorbitol, fructose, glucose, and ethylene glycol was studied at different pH and electrode potentials, and the corresponding binding constants were obtained. Depending on the electrode potential, the reciprocal values of the binding constants of glucose to poly-3-thienylboronic acid at neutral pH are in the range of 0.2 mM-1.0 mM. The affinity for glucose has been studied in buffer solutions and in solutions containing the major components of human blood. It was shown that the presence of human serum albumin increases the affinity of poly-3-thienylboronic acid for diol-containing compounds.

Recent Development on Sensing Strategies for Small Molecules Detections

Sensors play a critical role in the detection and monitoring of various substances present in our environment, providing us with valuable information about the world around us. Within the field of sensor development, one area that holds particular importance is the detection of small molecules. Small molecules encompass a wide range of organic or inorganic compounds with low molecular weight, typically below 900 Daltons including gases, volatile organic compounds, solvents, pesticides, drugs, biomarkers, toxins, and pollutants. The accurate and efficient detection of these small molecules has attracted significant interest from the scientific community due to its relevance in diverse fields such as environmental pollutants monitoring, medical diagnostics, industrial optimization, healthcare remedies, food safety, ecosystems, and aquatic and terrestrial life preservation. To meet the demand for precise and efficient monitoring of small molecules, this summary aims to provide an overview of recent advancements in sensing and quantification strategies for various organic small molecules including Hydrazine, Glucose, Morpholine, Ethanol amine, Nitrosamine, Oxygen, Nitro-aromatics, Phospholipids, Carbohydrates, Antibiotics, Pesticides, Drugs, Adenosine Triphosphate, Aromatic Amine, Glutathione, Hydrogen Peroxide, Acetone, Methyl Parathion, and Thiophenol. The focus is on understanding the receptor sensing mechanism, along with the electrical, optical, and electrochemical response. Additionally, the variations in UV-visible spectral properties of the ligands upon treatment with the receptor, fluorescence and absorption titration analysis for limit of detection (LOD) determination, and bioimaging analysis are discussed wherever applicable. It is anticipated that the information gathered from this literature survey will be helpful for the perusal of innovation regarding sensing strategies.

Chiral silver nanoparticles with surface-anchored L(D)-Cys exhibit dissimilar biological characteristics in vitro but not in vivo

This work investigated the influence of surface chirality on cellular internalization, cytotoxicity, and tissue distribution of silver nanoparticles (AgNPs). D-cysteine and L-cysteine are chiral forms of the amino acid cysteine. These enantiomers exhibit distinct spatial arrangements, with D-cysteine having a different configuration from L-cysteine. This structural dissimilarity can lead to variations in how these forms interact with biological systems, potentially impacting their cytotoxic responses. Four distinct types of AgNPs were synthesized, each possessing a unique surface coating: pristine AgNPs (pAgNPs), L-cysteine coated AgNPs (AgNPs@L-Cys), D-cysteine coated AgNPs (AgNPs@D-Cys), and racemic AgNPs coated with both L-Cys and D-Cys (AgNPs@L/D-Cys). We found chiral-dependent cytotoxicity of AgNPs on J774A.1 cells. Specifically, AgNPs@L-Cys exhibited the highest toxicity, and AgNPs@D-Cys exhibited the lowest toxicity. Meanwhile, the cellular uptake of the AgNPs correlated nicely with their cytotoxicity, with AgNPs@L-Cys being internalized to the greatest extent while AgNPs@D-Cys displays the least internalization. Scavenger receptors and clathrin predominantly mediate the cellular internalization of these AgNPs. Strikingly, the dissimilar cellular internalization and cytotoxicity of AgNPs with different chirality were eliminated upon protein corona coverage. Notably, following intravenous injection in mice, these four types of AgNPs showed similar patterns among various organs due to the inevitable protein adsorption in the bloodstream. These findings underscored the pivotal role of surface chirality in governing the biological interactions and toxicity of AgNPs.

Ultra-Sensitive and Stable Multiplexed Biosensors Array in Fully Printed and Integrated Platforms for Reliable Perspiration Analysis

Electrochemical biosensors have emerged as one of the promising tools for tracking human body physiological dynamics via non-invasive perspiration analysis. However, it remains a key challenge to integrate multiplexed sensors in a highly controllable and reproducible manner to achieve long-term reliable biosensing, especially on flexible platforms. Herein, a fully inkjet printed and integrated multiplexed biosensing patch with remarkably high stability and sensitivity is reported for the first time. These desirable characteristics are enabled by the unique interpenetrating interface design and precise control over active materials mass loading, owing to the optimized ink formulations and droplet-assisted printing processes. The sensors deliver sensitivities of 313.28 µA mm-1 cm-2 for glucose and 0.87 µA mm-1 cm-2 for alcohol sensing with minimal drift over 30 h, which are among the best in the literature. The integrated patch can be used for reliable and wireless diet monitoring or medical intervention via epidermal analysis and would inspire the advances of wearable devices for intelligent healthcare applications.

Revolutionizing Glucose Monitoring: Enzyme-Free 2D-MoS2 Nanostructures for Ultra-Sensitive Glucose Sensors with Real-Time Health-Monitoring Capabilities

The growing requirement for real-time monitoring of health factors such as heart rate, temperature, and blood glucose levels has resulted in an increase in demand for electrochemical sensors. This study focuses on enzyme-free glucose sensors based on 2D-MoS2 nanostructures explored by simple hydrothermal route. The 2D-MoS2 nanostructures were characterized by powder X-ray diffraction, energy-dispersive X-ray spectroscopy, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and XPS techniques and were immobilized at GCE to obtain MoS2-GCE interface. The fabricated interface was characterized by electrochemical impedance spectroscopy which shows less charge transfer resistance and demonstrated superior electrocatalytic properties of the modified surface. The sensing interface was applied for the detection of glucose using amperometry. The MoS2-GCE-sensing interface responded effectively as a nonenzymatic glucose sensor (NEGS) over a linearity range of 0.01-0.20 μM with a very low detection limit of 22.08 ng mL-1. This study demonstrates an easy method for developing a MoS2-GCE interface, providing a potential option for the construction of flexible and disposable nonenzymatic glucose sensors (NEGS). Moreover, the fabricated MoS2-GCE electrode precisely detected glucose molecules in real blood serum and urine samples of diabetic and nondiabetic persons. These findings suggest that 2D-MoS2 nanostructured materials show considerable promise as a possible option for hyperglycemia detection and therapy. Furthermore, the development of NEGS might create new prospects in the glucometer industry.

Metal oxide nanomaterials based electrochemical and optical biosensors for biomedical applications: Recent advances and future prospectives

The amalgamation of nanostructures with modern electrochemical and optical techniques gave rise to interesting devices, so-called biosensors. A biosensor is an analytical tool that incorporates various biomolecules with an appropriate physicochemical transducer. Over the past few years, metal oxide nanomaterials (MONMs) have significantly stimulated biosensing research due to their desired functionalities, versatile chemical stability, and low cost along with their unique optical, catalytic, electrical, and adsorption properties that provide an attractive platform for linking the biomolecules, for example, antibodies, nucleic acids, enzymes, and receptor proteins as sensing elements with the transducer for the detection of signals or signal amplifications. The signals to be measured are in direct proportionate to the concentration of the bioanalyte. Because of their simplicity, cost-effectiveness, portability, quick analysis, higher sensitivity, and selectivity against a broad range of biosamples, MONMs-based electrochemical and optical biosensing platforms are exhaustively explored as powerful early-diagnosis tools for point of care applications. Herein, we made a bibliometric analysis of past twenty years (2004-2023) on the application of MONMs as electrochemical and optical biosensing units using Web of Science database and the results of which clearly reveal the increasing number of publications since 2004. Geographical area distribution analysis of these publications shows that China tops the list followed by the United States of America and India. In this review, we first describe the electrochemical and optical properties of MONMs that are crucial for the creation of extremely stable, specific, and sensitive sensors with desirable characteristics. Then, the biomedical applications of MONMs-based bare and hybrid electrochemical and optical biosensing frameworks are highlighted in the light of recent literature. Finally, current limitations and future challenges in the field of biosensing technology are addressed.

Preparation of nickel foam modified by multiwalled hollow spheres of NiCo2O4 as a promising non-enzymatic glucose sensor

Nickel foam modified by hollow sphere NiCo2O4 particles was successfully prepared via a hydrothermal method using nanosphere SiO2 particles as the hard template for the hollow structure. Characterisation using SEM-EDX and TEM confirmed the structure as multiwalled hollow spheres with an average size of 270 nm, while characterisation using SEM, XRD, and XPS confirmed that the NiCo2O4 particles were attached on the surface of the nickel foam. BET analysis showed that the surface area of the synthesized NiCo2O4@Ni foam was nearly three times higher compared to that of the unmodified Ni foam. Investigation of the NiCo2O4-modified nickel foam as an electrode for the detection of glucose in sodium hydroxide solution showed high linearity of the anodic currents (R2 = 0.99) in the concentration range of 0-2.5 μM with sensitivity of 0.060 mA μM-1 and an estimated limit of detection of 0.060 μM. Excellent stability of the current response was also obtained with a relative standard deviation of 1.51% (n = 10). Furthermore, the developed sensor demonstrates strong applicability for glucose detection in real samples of human blood plasma, making it highly suitable for practical use. The results indicate that the material is promising for the further development of nickel-based sensors.

High performance nonenzymatic electrochemical sensors via thermally grown Cu native oxides (CuNOx) towards sweat glucose monitoring

Diabetes, which is the seventh leading cause of death globally, necessitates real-time blood glucose monitoring, a process that is often invasive. A promising alternative is sweat glucose monitoring, which typically uses transition metals and their oxide nanomaterials as sensors. Despite their excellent surface-to-volume ratio, these materials have some drawbacks, including poor conductivity, structural collapse, and aggregation. As a result, selecting highly electroconductive materials and optimizing their nanostructures is critical. In this work, we developed a high-performance, low-cost, nonenzymatic sensor for sweat glucose detection, using the thermally grown native oxide of copper (CuNOx). By heating Cu foil at 160, 250, and 280 °C, we grew a native oxide layer of approximately 140 nm cupric oxide (CuO), which is excellent for glucose electrocatalysis. Using cyclic voltammetry, we found that our CuNOx sensors prepared at 280 °C exhibited a sensitivity of 1795 μA mM-1 cm-2, a linear range up to the desired limit of 1.00 mM for sweat glucose with excellent linearity (R2 = 0.9844), and a lower limit of detection of 135.39 μM. For glucose sensing, the redox couple Cu(II)/Cu(III) oxidizes glucose to gluconolactone and subsequently to gluconic acid, producing an oxidation current in an alkaline environment. Our sensors showed excellent repeatability and stability (remaining stable for over a year) with a relative standard deviation (RSD) of 2.48% and 4.17%, respectively, for 1 mM glucose. The selectivity, when tested with common interferants found in human sweat and blood, showed an RSD of 4.32%. We hope that the electrocatalytic efficacy of the thermally grown CuNOx sensors for glucose sensing can introduce new avenues in the fabrication of sweat glucose sensors.

Advances in nanostructured material-based non-enzymatic electrochemical glucose sensors

Non-enzymatic electrochemical sensors that use functional materials to directly catalyze glucose have shown great promise in diabetes management, food control, and bioprocess inspection owing to the advantages of high sensitivity, long-term stability, and low cost. Recently, in order to produce enhanced electrochemical behavior, significant efforts have been devoted to the preparation of functional materials with regular nanostructure, as it provides high specific surface area and well-defined strong active sites for electrochemical sensing. However, the structure-performance correlation in this field has not been reviewed thoroughly in the literature. This review aims to present a comprehensive report on advanced zero- to three-dimensional nanostructures based on the geometric feature and to discuss in depth their structural effects on enzyme-free electrochemical detection of glucose. It starts by illustrating the sensing principles of nanostructured materials, followed by a detailed discussion on the structural effects related to the features of each dimension. The structure-performance correlation is explored by comparing the performance derived from diverse dimensional architectures, which is beneficial for the better design of regular nanostructure to achieve efficient enzyme-free sensing of glucose. Finally, future directions of non-enzymatic electrochemical glucose sensors to solve emerging challenges and further improve the sensing performance are also proposed.

New Au/chitosan nanocomposite modified carbon paste sensor for voltammetric detection of nicotine

A profoundly touchy voltammetric sensor for detection of nicotine (NIC) in urine and tobacco specimens has been developed in light of the boosted electrochemical response of NIC at gold and chitosan nanocomposite modified carbon paste electrode (ACMCPE). Material characterization techniques Scanning Electron Microscope and Energy Dispersive X-ray (SEM & EDX) were utilized to describe the ACMCPE surface material. The impedance spectroscopy technique (EIS), cyclic voltammetry (CV), chronoamperometry (CA), and differential pulse voltammetry (DPV) were employed to explore the electrochemical sensing of NIC at ACMCPE. The created sensor exhibits an exceptional electrochemical sensitivity to NIC in a universal Britton-Robinson (B-R) buffer solution with a pH range of 2.0 to 8.0. The sensor shows a linear response over NIC concentration ranges of 4.0-320.0 µM, with the detection limit (LOD) of 7.6 µM. The prepared sensor has been shown to be exceptionally viable in detecting NIC with amazing selectivity and reproducibility. We suggest it as a trustworthy and useful electrochemical sensor for NIC location.

Non-enzymatic amperometric glucose sensing on CuO/mesoporous TiO2 modified glassy carbon electrode

The present study illustrates the fabrication of a glucose sensing electrode based upon binary composite of copper oxide and mesoporous titanium dioxide on glassy carbon (CuO/TiO2/GCE). The X-ray diffraction, scanning electron microscopy and energy dispersive X-ray analysis evidently showed the phase pure monoclinic CuO nanoparticles and anatase TiO2. N2 adsorption-desorption analysis verified the mesoporosity in TiO2 with specific surface area greater than 105 m2 g-1. Electrochemical impedance spectroscopic analysis proved the remarkable decrease in the charge transfer resistance and facilitation of electron transfer process on the fabricated electrode. The optimum weight ratio of CuO to TiO2 was 1 : 1, and the optimum potential was 0.6 V vs. saturated calomel electrode. The chronoamperometric measurements displayed a detection limit of 1.9 μM, and sensitivities of 186.67 μA mM-1 cm-2 and 90.53 μA mM-1 cm-2 in two linear ranges of 0.05 to 5.2 mM and 5.2 to 20 mM, respectively. The amperometric analysis further showed good reproducibility, high specificity and outstanding stability of the modified electrode.

Road Map of Semiconductor Metal-Oxide-Based Sensors: A Review

Identifying disease biomarkers and detecting hazardous, explosive, flammable, and polluting gases and chemicals with extremely sensitive and selective sensor devices remains a challenging and time-consuming research challenge. Due to their exceptional characteristics, semiconducting metal oxides (SMOxs) have received a lot of attention in terms of the development of various types of sensors in recent years. The key performance indicators of SMOx-based sensors are their sensitivity, selectivity, recovery time, and steady response over time. SMOx-based sensors are discussed in this review based on their different properties. Surface properties of the functional material, such as its (nano)structure, morphology, and crystallinity, greatly influence sensor performance. A few examples of the complicated and poorly understood processes involved in SMOx sensing systems are adsorption and chemisorption, charge transfers, and oxygen migration. The future prospects of SMOx-based gas sensors, chemical sensors, and biological sensors are also discussed.

Development of nanozyme based sensors as diagnostic tools in clinic applications: a review

Since 1970, many artificial enzymes that imitate the activity and structure of natural enzymes have been discovered. Nanozymes are a group of nanomaterials with enzyme-mimetic properties capable of catalyzing natural enzyme processes. Nanozymes have attracted great interest in biomedicine due to their excellent stability, rapid reactivity, and affordable cost. The enzyme-mimetic activities of nanozymes may be modulated by numerous parameters, including the oxidative state of metal ions, pH, hydrogen peroxide (H2O2) level, and glutathione (GSH) concentration, indicating the tremendous potential for biological applications. This article delivers a comprehensive overview of the advances in the knowledge of nanozymes and the creation of unique and multifunctional nanozymes, and their biological applications. In addition, a future perspective of employing the as-designed nanozymes in biomedical and diagnostic applications is provided, and we also discuss the barriers and constraints for their further therapeutic use.

Recent Progress in Diboronic-Acid-Based Glucose Sensors

Non-enzymatic sensors with the capability of long-term stability and low cost are promising in glucose monitoring applications. Boronic acid (BA) derivatives offer a reversible and covalent binding mechanism for glucose recognition, which enables continuous glucose monitoring and responsive insulin release. To improve selectivity to glucose, a diboronic acid (DBA) structure design has been explored and has become a hot research topic for real-time glucose sensing in recent decades. This paper reviews the glucose recognition mechanism of boronic acids and discusses different glucose sensing strategies based on DBA-derivatives-based sensors reported in the past 10 years. The tunable pK_a, electron-withdrawing properties, and modifiable group of phenylboronic acids were explored to develop various sensing strategies, including optical, electrochemical, and other methods. However, compared to the numerous monoboronic acid molecules and methods developed for glucose monitoring, the diversity of DBA molecules and applied sensing strategies remains limited. The challenges and opportunities are also highlighted for the future of glucose sensing strategies, which need to consider practicability, advanced medical equipment fitment, patient compliance, as well as better selectivity and tolerance to interferences.

Applications of trimetallic nanomaterials as Non-Enzymatic glucose sensors

OBJECTIVE

This article critically reviews recent research on the use of trimetallic nanomaterials for the fabrication of non-enzymatic glucose sensors (NEGS), also known as fourth-generation glucose sensors (FGGS).

SIGNIFICANCE

Diabetes is a prevalent chronic disease worldwide, and glucose monitoring is crucial for its management. However, conventional enzymatic glucose sensors suffer from several technological drawbacks, and there is a need to develop new-generation glucose sensors that can overcome these limitations. NEGS, particularly those composed of trimetallic nanocomposites, have demonstrated promising results in terms of improved shelf life, higher sensitivity, and simplicity of operation during glucose measurement.

METHODS

In this review, we discuss the different trimetallic nanomaterials developed and used by researchers in recent years for glucose detection, including their mechanisms of action. We also provide a brief discussion of the advantages and disadvantages of FGGS-based trimetallic nanomaterials, as well as the industrial challenges in this area of research.

RESULTS

Trimetallic nanomaterials for FGGS have shown excellent reproducibility and high stability, making them suitable for continuous glucose monitoring. The different types of trimetallic nanomaterials have varying sensing properties, and their performance can be tuned by controlling their synthesis parameters.

CONCLUSION

Trimetallic nanomaterials are a promising avenue for the development of FGGS, recent research has demonstrated their potential for glucose monitoring. However, there are still some challenges that need to be addressed before their widespread adoption, such as their long-term stability and cost-effectiveness. Further research in this area is needed to overcome these challenges and to develop commercially viable FGGS for diabetes management.

Biomaterial-mediated strategies for accurate and convenient diagnosis, and effective treatment of diabetes: advantages, current progress and future perspectives

As a kind of widespread chronic disease, diabetes potentially triggers serious complications, thereby severely threatening patients' life and health. To achieve the goal of more accurate and convenient diagnosis, and effective treatment of diabetes that what could be achieved based on traditional methods, many biomaterial-mediated strategies have been launched in recent studies, and have shown promising application potentials. In this review, we have systematically summarized the biomaterial-mediated diagnosis strategies in three parts including combined use of biomedical nanomaterials or organometallic compounds and Raman spectroscopy, utilization of gas sensors made of biomedical metal-oxides to detect glucose in exhaled gas, and detection of glucose by wearable sensors made of biomaterials with high sensitivity and conductivity, and the biomaterial-mediated treatment strategies in four parts including antidiabetic drug delivery by nanoparticles, transdermal drug delivery systems, gels and vesicles, and achieving insulin secretion by transplantation of pancreatic endocrine cells or tissue engineered islets. In particular, advantages of every strategy, current research progress, as well as the challenges and perspectives are elaborated. This review will certainly help to spark new ideas and possibilities for accurate and convenient diagnosis, and effective treatment of diabetes.

Electrochemical sensing of dual biomolecules in live cells and whole blood samples: A flexible gold wire-modified copper-organic framework-based hybrid composite

For clinical research, the precise measurement of hydrogen peroxide (H₂O₂) and glucose (Glu) is of paramount importance, due to their imbalanced concentrations in blood glucose, and reactive oxygen species (ROS) play a huge role in COVID-19 viral disease. It is critical to construct and develop a simple, rapid, flexible, long-term, and sensitive detection of H₂O₂ and glucose. In this paper, we have developed a unique morphological structure of MOF(Cu) on a single-walled carbon nanotube-modified gold wire (swnt@gw). Highly designed frameworks with nanotube composites enhance electron rate-transfer behavior while extending conductance and electroactive surface area.The composite sensing system delivers wide linear-range concentrations, low detection limit, and interference-free performance in co-existence with other biomolecules and metal ions. Endogenous quantitative tracking of H₂O₂ was performed in macrophage live-cells with the help of a strong stimulator lipopolysaccharide.The composite device was effectively utilized for the measurement of H₂O₂ and glucose in turbid samples of whole blood and milk samples without a pretreatment process. The practical results of biofluids showed favorable voltammetric results and acceptance recovery percentage levels between 97.49 and 98.88%. Finally, a flexible MOF-based hybrid system may provide a suitable detection platform in the construction of electro-biosensors and hold potential promise for clinical-sensory applications.

The Enzymatic Doped/Undoped Poly-Silicon Nanowire Sensor for Glucose Concentration Measurement

In this work, enzymatic doped/undoped poly-silicon nanowire sensors with different lengths were fabricated using a top-down technique to measure glucose concentration. The sensitivity and resolution of these sensors correlate well with the dopant property and length of nanowire. Experimental results indicate that the resolution is proportional to the nanowire length and dopant concentration. However, the sensitivity is inversely proportional to the nanowire length. The optimum resolution can be better than 0.02 mg/dL for a doped type sensor with length of 3.5 μm. Furthermore, the proposed sensor was demonstrated for 30 applications with similar current-time response and showed good repeatability.

Surface specific adsorption of glucose to ZnO

ZnO is bio-safe and hence, may be a potential candidate for direct use as a glucose sensor. This requires an understanding of the interaction of glucose with four common surfaces, (101̄0), (112̄0), (0001) and (0001̄) of ZnO. We carry out molecular dynamics (MD) simulations enhanced by umbrella sampling of a glucose molecule in a solvent over a hydrated ZnO slab. The slab is obtained by quantum mechanical optimization. We observe that hydration layers formed above the surfaces affect the approach of glucose to the surfaces. Potential of mean force (PMF) calculations show that the (101̄0) surface shows the strongest adsorption of adsorption free energy -6.81 kJ mol^-1 towards glucose. Thus, we offer a theoretical understanding on the interactions at the nano-bio junction of glucose and ZnO surfaces. Our study suggests that the (101̄0) surface may be used to fabricate a direct glucose sensor.

In silico study of interaction of (ZnO)12 nanocluster to glucose oxidase-FAD in absence and presence of glucose

Diabetes mellitus is one of the foremost global concerns, as it has impacted millions of lives. Therefore, there is an urgent need to develop a technology for continuous glucose monitoring in vivo. In the current study, we employed computational methods such as docking, MD simulations, and MM/GBSA, to obtain molecular insights into the interaction between (ZnO)12 nanocluster and glucose oxidase (GOx) that cannot be obtained through experiments alone. For this, theoretical modeling of the 3D cage-like (ZnO)12 nanocluster in ground state configuration was performed. Further docking of (ZnO)12 nanocluster with GOx molecule was carried out to find the nano-bio-interaction of (ZnO)12-GOx complex. To understand the whole interaction and dynamics of (ZnO)12-GOx-FAD-with and without glucose, we performed MD simulation and MM/GBSA analysis of (ZnO)12-GOx-FAD complex and glucose-(ZnO)12-GOx-FAD complex separately. The interaction was found to be stable, and the binding energy of (ZnO)12 to GOx-FAD increases in the presence of glucose by 6 kcal mol-1. This may be helpful in nano probing of the interaction of GOx with glucose. It can help in making a device like fluorescence resonance energy transfer (FRET) based nano-biosensor to monitor the glucose level in pre and post diabetic patient.Communicated by Ramaswamy H. Sarma.

Procedure to Obtain Cu2O Isolate Films, Structural, Electrical, and Morphological Characterization, and Its Use as an Electrical Isolator to Build a New Tube Furnace

Copper oxide is a widely studied compound in wastewater decontamination, hydrogen production, solar cell production, and sensor fabrication. In recent years, many architectures and structures with the potential for developing clean technologies have been synthesized. A procedure by thermal oxidation to grow electrical insolate Cu2O films on copper surfaces in an air atmosphere was developed. The results of the morphological and structural characterization of the copper oxide layers evidence the presence of Cu2O polycrystalline films. The films have polyhedral architectures of approximately 1.4 μm thickness and are electrically insulating. A novel copper resistive furnace was built using this copper oxide film which was used as an electrical insulator between the electrical resistance of the heater and the surface of the copper thermal block. The application improves the efficiency of the resistive furnace in terms of the temperature reached and the thermal coupling response time relative to the performance of conventional furnaces using ceramic insulation. Over the entire operating temperature range explored for the same power supply, the copper oxide-coated furnace achieved higher temperatures and faster response times than the traditionally coated furnace.

Cellulose microfluidic pH boosting on copper oxide non-enzymatic glucose sensor strip for neutral pH samples

A cellulose microfluidic pH boosting layer adapts a non-enzymatic copper oxide glucose sensor strip for neutral pH samples. This adaptation allows the non-enzymatic technology to realize in-situ glucose measurements. A three-electrode system is constructed to test samples in a classical electrochemical cell, and in a sensing strip to test the microfluidic system. The system consists of copper oxide as working electrode, and silver and carbon paints as reference, and counter electrodes, respectively. The fabrication of the pH-boosting layer is made with natural cellulose. Within this layer are NaOH crystals, grown by a drying processes after immersion of cellulose in a concentrated solution of NaOH. The microfluidic layer is placed on top of the sensing electrodes, and while it transports the fluid sample to the sensing electrodes, the fluid dissolves the NaOH crystals, increasing the pH of the sample. This change allows the non-enzymatic mechanism to sense the glucose concentration in the fluid. Our system shows the capability to measure glucose in samples with neutral pH and human blood with a sensitivity of 70 μA/mM cm², enough to distinguish between hypoglycemia and hyperglycemia.

Nanomaterial Gas Sensors for Biosensing Applications: A Review

BACKGROUND

Nanomaterial is one of the most used materials for various gas sensing applications to detect toxic gases, human breath, and other specific gas sensing. One of the most important applications of nanomaterial based gas sensors is biosensing applications. In this review article, the gas sensors for biosensing are discussed on the basis of crystalline structure and different categories of nanomaterial.

METHODS

In this paper, firstly, rigorous efforts have been made to find out research questions by going through a structured and systematic survey of available peer reviewed high quality articles in this field. The papers related to nanomaterial based biosensors are then reviewed qualitatively to provide substantive findings from the recent developments in this field.

RESULTS

In this mini-review article, firstly, classifications of nanomaterial gas sensors have been presented on the basis of the crystalline structure of nanomaterial and different types of nanomaterial available for biosensing applications. Further, the gas sensors based on nanomaterial for biosensing applications are collected and reviewed in terms of their performance parameters such as sensing material used, target gas component, detection ranges (ppm-ppb), response time, operating temperature and method of detection, etc. The different nanomaterials possess slightly different sensing and morphological properties due to their structure; therefore, it can be said that a nanomaterial must be selected carefully for a particular application. The 1D nanomaterials show the best selectivity and sensitivity for gases available in low concentration ranges due to their miniaturised structure compared to 2D and 3D nanomaterials. However, these 2D and 3D nanomaterials also so good sensing properties compared to bulk semiconductor materials. The polymer and nanocomposites which are also discussed in this patent article have opened the door for future research and have great potential for new generation gas sensors for detecting biomolecules.

CONCLUSION

These nanomaterials extend great properties towards sensing the application of different gases for a lower concentration of particular gas particles. Nano polymer and nanocomposites have great potential to be used as gas sensors for the detection of biomolecules.

CuO/Cu/rGO nanocomposite anodic titania nanotubes for boosted non-enzymatic glucose biosensors

Highly arranged porous anodic titania (TiO2) nanotube arrays (ATNT) were fruitfully fabricated by the anodization of Ti foil in an ammonium fluoride electrolyte.

Nanotechnology-Enabled Biosensors: A Review of Fundamentals, Design Principles, Materials, and Applications

Biosensors are modern engineering tools that can be widely used for various technological applications. In the recent past, biosensors have been widely used in a broad application spectrum including industrial process control, the military, environmental monitoring, health care, microbiology, and food quality control. Biosensors are also used specifically for monitoring environmental pollution, detecting toxic elements' presence, the presence of bio-hazardous viruses or bacteria in organic matter, and biomolecule detection in clinical diagnostics. Moreover, deep medical applications such as well-being monitoring, chronic disease treatment, and in vitro medical examination studies such as the screening of infectious diseases for early detection. The scope for expanding the use of biosensors is very high owing to their inherent advantages such as ease of use, scalability, and simple manufacturing process. Biosensor technology is more prevalent as a large-scale, low cost, and enhanced technology in the modern medical field. Integration of nanotechnology with biosensors has shown the development path for the novel sensing mechanisms and biosensors as they enhance the performance and sensing ability of the currently used biosensors. Nanoscale dimensional integration promotes the formulation of biosensors with simple and rapid detection of molecules along with the detection of single biomolecules where they can also be evaluated and analyzed critically. Nanomaterials are used for the manufacturing of nano-biosensors and the nanomaterials commonly used include nanoparticles, nanowires, carbon nanotubes (CNTs), nanorods, and quantum dots (QDs). Nanomaterials possess various advantages such as color tunability, high detection sensitivity, a large surface area, high carrier capacity, high stability, and high thermal and electrical conductivity. The current review focuses on nanotechnology-enabled biosensors, their fundamentals, and architectural design. The review also expands the view on the materials used for fabricating biosensors and the probable applications of nanotechnology-enabled biosensors.

Progress of Enzymatic and Non-Enzymatic Electrochemical Glucose Biosensor Based on Nanomaterial-Modified Electrode

This review covers the progress of nanomaterial-modified electrodes for enzymatic and non-enzymatic glucose biosensors. Fundamental insights into glucose biosensor components and the crucial factors controlling the electrochemical performance of glucose biosensors are discussed in detail. The metal, metal oxide, and hybrid/composite nanomaterial fabrication strategies for the modification of electrodes, mechanism of detection, and significance of the nanomaterials toward the electrochemical performance of enzymatic and non-enzymatic glucose biosensors are compared and comprehensively reviewed. This review aims to provide readers with an overview and underlying concept of producing a reliable, stable, cost-effective, and excellent electrochemical performance of a glucose biosensor.

CuO Nanowires Fabricated by Thermal Oxidation of Cu Foils towards Electrochemical Detection of Glucose

In view of the various stability issues and high cost of enzymatic glucose biosensors, non-enzymatic biosensors have received great attention in recent research and development. Copper oxide (CuO) nanowires (NWs) were fabricated on Cu foil substrate using a simple thermal oxidation method. The phase and morphology of the CuO NWs could be controlled by synthesis temperature. Variation in oxidation states enables CuO NWs to form Cu (III) species, which is crucial in catalysing the eletro-oxidation of glucose. The Cu-based metal/oxide composite electrode works as a non-enzymatic biosensor that adapts to the fast, dynamic change in glucose concentration, with a low saturation concentration (~0.7 mM) and a lower detection limit of 0.1 mM, making CuO NWs an excellent sensor towards impaired fasting glucose. The simplicity, cost-effectiveness and non-toxicity features of this study might make a way for potentially scalable application in glucose biosensing.

Metallic Structures Based on Zinc Oxide Film for Enzyme Biorecognition

Two structures (Ag/ZnO/ITI/glass: #1 sample and Ag/ZnO/SiO₂/Si: #2 sample) are investigated, on the one hand, from the point of view of the formation of evanescent waves in the gratings of metal strips on the structures when the incident TEz wave in the radio frequency range is used. The simulation of the formation of evanescent waves at the edge of the Ag strips, with thicknesses in the range of micrometers, was carried out before the test in the subwavelength regime, with the help of a new improved transducer with metamaterial (MM) lenses. By simulation, a field snapshot was obtained in each sequence of geometry. The evanescent waves are emphasized in the plane XY, due to the scattering of the field on the edge of the strips. On the other hand, ZnO nanoparticles are investigated as a convenient high-efficiency biodetection material, where these structures were used as a biosensitive element to various enzymes (glucose, cholesterol, uric acid, and ascorbic acid). The obtained results demonstrate that the investigated structures based on ZnO nanostructures deposited on different supports are fast and sensitive for enzyme detection and can be successfully incorporated into a device as a biosensing element.

Copper oxide nanostructured thin films processed by SILAR for optoelectronic applications

The lack of high-functioning p-type semiconductor oxide material is one of the critical challenges that face the widespread performance of transparent and flexible electronics. Cu x O nanostructured thin films are potentially appealing materials for such applications because of their innate p-type semi-conductivity, transparency, non-toxicity, abundant availability, and low-cost fabrication. This review summarizes current research on Cu x O nanostructured thin films deposited by the SILAR technique. After a brief introduction to the advantages of Cu x O semiconductor material, diverse approaches for depositing and growing such thin films are discussed. SILAR is one of the simplest deposition techniques in terms of better flexibility of the substrate choice, the capability of large-area fabrication, budget-friendly, deposition of stable and adherent film, low processing temperature for the film fabrication as well as reproducibility. In addition, various fabrication parameters such as types of copper salts, pH of precursors, number of cycles during immersion, annealing of as-deposited films, doping by diverse dopants, and growth temperature affect the rate of fabrication with the structural, electrical, and optical properties of Cu x O nanostructured thin films, which led the technique unique to study extensively. This review will include the recent progress that has recently been made in different aspects of Cu x O processed by the SILAR. It will describe the theory, mechanism, and factors affecting SILAR-deposited Cu x O. Finally, conclusions and perspectives concerning the use of Cu x O materials in optoelectronic devices will be visualized.

Hierarchical Structures Composed of Cu(OH)2 Nanograss within Directional Microporous Cu for Glucose Sensing

Cu(OH)₂ nanomaterials are widely investigated for non-enzymatic glucose sensors due to their low-cost and excellent performance. Cu(OH)₂ nanomaterials usually grow on substrates to form sensor electrodes. Reported works mainly focus on structure adjusting of the Cu(OH)₂ nanostructures, while the optimization of substrates is still lacking. In the present work, directional porous Cu (DPC) was applied as the substrate for the growth of Cu(OH)₂ nanograss (NG), and hierarchical structures of Cu(OH)₂@DPC were prepared by alkaline oxidation. The morphology and microstructure evolution of the prepared hierarchical structures was investigated, and the non-enzymatic glucose sensing performance was evaluated. Cu(OH)₂@DPC exhibits enhanced comprehensive non-enzymatic glucose sensing performance compared to the reported ones, which may benefit from both the effective adsorption of the Cu(OH)₂ NG with a relatively high surface area and the high solute exchange of the DPC by a channel effect. This work provides new insights into the further improvement of the non-enzymatic glucose sensing performance of Cu(OH)₂ nanostructures by optimizing the substrate structure.

A Concise and Systematic Review on Non-Invasive Glucose Monitoring for Potential Diabetes Management

The current standard of diabetes management depends upon the invasive blood pricking techniques. In recent times, the availability of minimally invasive continuous glucose monitoring devices have made some improvements in the life of diabetic patients however it has its own limitations which include painful insertion, excessive cost, discomfort and an active risk due to the presence of a foreign body under the skin. Due to all these factors, the non-invasive glucose monitoring has remain a subject of research for the last two decades and multiple techniques of non-invasive glucose monitoring have been proposed. These proposed techniques have the potential to be evolved into a wearable device for non-invasive diabetes management. This paper reviews research advances and major challenges of such techniques or methods in recent years and broadly classifies them into four types based on their detection principles. These four methods are: optical spectroscopy, photoacoustic spectroscopy, electromagnetic sensing and nanomaterial based sensing. The paper primarily focuses on the evolution of non-invasive technology from bench-top equipment to smart wearable devices for personalized non-invasive continuous glucose monitoring in these four methods. With the rapid evolve of wearable technology, all these four methods of non-invasive blood glucose monitoring independently or in combination of two or more have the potential to become a reality in the near future for efficient, affordable, accurate and pain-free diabetes management.

Synthesis and validation of ultrasensitive stripping voltammetric sensor based on polypyrrole@ZnO/Fe3O4 core-shell nanostructure for picomolar detection of artesunate and dopamine drugs

A stripping voltammetric sensor for ultrasensitive detection of artesunate (ART) and dopamine HCl (DA) has been successfully developed using a Ppy@ZnO/Fe₃O₄ core-shell nanocomposite ([PZM])-modified carbon paste sensor (MCPS). Fourier transform infrared spectroscopy, X-ray diffraction, field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, dynamic light scattering, Brunauer-Emmett-Teller surface area method, and high-resolution transmission electron microscopy were used to characterize the physicochemical properties of the nanomaterials. Noteworthily, the morphology of [PZM] reveals a spherical core-shell nanostructure with an increase in the average diameter range of 20-37.5 nm (specific surface area (SSA) of 28.5 m² g^-1 (0.0247 cm³ g^-1)) when compared with the average diameter range 7.5-15.7 nm (SSA of 5.43 m² g^-1 (0.0111 cm³ g^-1)) of ZnO/Fe₃O₄[ZM]. The [PZM] MCPS provided the best electroactive surface area (0.078 cm²) and the least electrocatalytic activity (R_st = 370 Ω). Furthermore, the MCPS showed low detection limits (LODs) of 0.092 pg mL^-1 (0.24 pM) and 0.0046 pg mL^-1 (0.03 pM) for ART and DA, respectively. Moreover, LODs were found to be 0.029 pg mL^-1 (0.75 pM) and 0.014 pg mL^-1 (0.09 pM) for ART mixed with 0.7 pM of DA (ART₁) and DA in the presence of 2.0 pM of ART drug (DA₁), respectively. In addition, the MCPS revealed a proper repeatability, reproducibility, and storage stability (93.5-90.48%). During the routine analysis, the [PZM] MCPS detected ART and DA concentrations in human urine, without interference.

Imprinted-Zeolite-X-Based Sensor for Non-Enzymatic Detection of Blood Glucose by Potentiometry

The development of sensors based on imprinted zeolite X to detect blood glucose through potentiometry was performed. In this study, the sensor was made of a mixture of carbon paste and imprinted zeolite X. Zeolite X was synthesized using a sol–gel-hydrothermal method at a temperature of 100 °C with basic materials of NaAlO2, NaOH, TEOS, and distilled water. The characterization results of XRD showed the presence of specific peaks, which were confirmed with standard zeolite X. Imprinted zeolite X exhibited a 20 times greater adsorption capacity size, and an adsorption efficiency 3 times greater than that of zeolite X. This is thought to be due to the presence of a molecular template within it. The IZ–carbon paste electrode showed optimum performance due to a mass ratio of carbon, paraffin, and imprinted zeolite X of 12:7:1. The electrode performance was expressed by the Nernst factor value of 30 mV/decade, the measuring range of 10−4–10−2 M, the upper detection limit of 1.38 × 10−2 M, and the lower detection limit of 1.28 × 10−4 M, so this electrode can be used for glucose analysis with a normal concentration (70–110 mg/dL or equivalent to 3.8 × 10−3–6.1 × 10−3 M), as well as the glucose concentration of people with diabetes mellitus (>200 mg/dL or about 10−2 M). This electrode showed precision values of 97.14–99.02%, accuracy values of 98.65–99.39%, and electrode response times of 10–13 s. The electrodes showed high stability for more than 5 weeks with 141 uses. The electrodes also showed high selectivity for glucose in the matrix of uric acid, urea, NaCl, and KCl. Therefore, its use as an alternative electrode for routine glucose analysis in the medical field is recommended.

Prospects of Biosensors Based on Functionalized and Nanostructured Solitary Materials: Detection of Viral Infections and Other Risks

Advances in nanotechnology over the past decade have emerged as a substitute for conventional therapies and have facilitated the development of economically viable biosensors. Next-generation biosensors can play a significant role in curbing the spread of various viruses, including HCoV-2, and controlling morbidity and mortality. Pertaining to the impact of the current pandemic, there is a need for point-of-care biosensor-based testing as a detection method to accelerate the detection process. Integrating biosensors with nanostructures could be a substitute for ultrasensitive label-free biosensors to amplify sensing and miniaturization. Notably, next-generation biosensors could expedite the detection process. An elaborate description of various types of functionalized nanomaterials and their synthetic aspects is presented. The utility of the functionalized nanostructured materials for fabricating nanobiosensors to detect several types of viral infections is described in this review. This review also discusses the choice of appropriate nanomaterials, as well as challenges and opportunities in the field of nanobiosensors.