Multifunctional nanomaterials for smart wearable diabetic healthcare devices

Wearable diabetic healthcare devices have attracted great attention for real-time continuous glucose monitoring (CGM) using biofluids such as tears, sweat, saliva, and interstitial fluid via noninvasive ways. In response to the escalating global demand for CGM, these devices enable proactive management and intervention of diabetic patients with incorporated drug delivery systems (DDSs). In this context, multifunctional nanomaterials can trigger the development of innovative sensing and management platforms to facilitate real-time selective glucose monitoring with remarkable sensitivity, on-demand drug delivery, and wireless power and data transmission. The seamless integration into wearable devices ensures patient's compliance. This comprehensive review evaluates the multifaceted roles of these materials in wearable diabetic healthcare devices, comparing their glucose sensing capabilities with conventionally available glucometers and CGM devices, and finally outlines the merits, limitations, and prospects of these devices. This review would serve as a valuable resource, elucidating the intricate functions of nanomaterials for the successful development of advanced wearable devices in diabetes management.

Integrating microneedles and sensing strategies for diagnostic and monitoring applications: The state of the art

Microneedles (MNs) offer minimally-invasive access to interstitial fluid (ISF) - a potent alternative to blood in terms of monitoring physiological analytes. This property is particularly advantageous for the painless detection and monitoring of drugs and biomolecules. However, the complexity of the skin environment, coupled with the inherent nature of the analytes being detected and the inherent physical properties of MNs, pose challenges when conducting physiological monitoring using this fluid. In this review, we discuss different sensing mechanisms and highlight advancements in monitoring different targets, with a particular focus on drug monitoring. We further list the current challenges facing the field and conclude by discussing aspects of MN design which serve to enhance their performance when monitoring different classes of analytes.

Photonic Nanochains for Continuous Glucose Monitoring in Physiological Environment

Diabetes is a common disease that seriously endangers human health. Continuous glucose monitoring (CGM) is important for the prevention and treatment of diabetes. Glucose-sensing photonic nanochains (PNCs) have the advantages of naked-eye colorimetric readouts, short response time and noninvasive detection of diabetes, showing immense potential in CGM systems. However, the developed PNCs cannot disperse in physiological environment at the pH of 7.4 because of their poor hydrophilicity. In this study, we report a new kind of PNCs that can continuously and reversibly detect the concentration of glucose (Cg) in physiological environment at the pH of 7.4. Polyacrylic acid (PAA) added to the preparation of PNCs forms hydrogen bonds with polyvinylpyrrolidone (PVP) in Fe3O4@PVP colloidal nanoparticles and the hydrophilic monomer N-2-hydroxyethyl acrylamide (HEAAm), which increases the content of PHEAAm in the polymer shell of prepared PNCs. Moreover, 4-(2-acrylamidoethylcarbamoyl)-3-fluorophenylboronic acid (AFPBA), with a relatively low pKa value, is used as the glucose-sensing monomer to further improve the hydrophilicity and glucose-sensing performances of PNCs. The obtained Fe3O4@(PVP-PAA)@poly(AFPBA-co-HEAAm) PNCs disperse in artificial serum and change color from yellow-green to red when Cg increases from 3.9 mM to 11.4 mM, showing application potential for straightforward CGM.

Fluorescent Enzymatic Sensor Based Glucose Oxidase Modified Bovine Serum Albumin-Gold Nanoclusters for Detection of Glucose

An enzymatic fluorescent probe is developed for the selective detection of glucose. In this work, a Bovine Serum Albumin stabilized gold nanocluster (BSA-AuNCs) was synthesized by microwave assisted method, and it is modified with glucose oxidase, thereby a fluorescent enzymatic sensor (BSA-AuNCs@GoX) was designed for the sensitive detection of glucose with a limit of detection of 0.03 mM. The red fluorescence exhibited by the probe is quenched by the production of H2O2 on addition of glucose via. a static quenching mechanism from UV visible absorption and Fluorescence lifetime results. The developed probe exhibits good selectivity and sensitivity with other coexisting molecular species such as glycine, creatinine, methionine, histidine, uric acid, albumin, and ions such as sodium, potassium, calcium, magnesium, zinc etc. that appear in the body fluid. The practical applicability was studied in paper strip and extended its reproducibility in biological matrixes such as human serum and urine and found a good recovery percentage of 94-101 %. By this way, we have fabricated an effective fluorescent enzymatic "turn-off" sensing probe for the detection of glucose.

Recent Insights into Glucose-Responsive Concanavalin A-Based Smart Hydrogels for Controlled Insulin Delivery

Many efforts are continuously undertaken to develop glucose-sensitive biomaterials able of controlling glucose levels in the body and self-regulating insulin delivery. Hydrogels that swell or shrink as a function of the environmental free glucose content are suitable systems for monitoring blood glucose, delivering insulin doses adapted to the glucose concentration. In this context, the development of sensors based on reversible binding to glucose molecules represents a continuous challenge. Concanavalin A (Con A) is a bioactive protein isolated from sword bean plants (Canavalia ensiformis) and contains four sugar-binding sites. The high affinity for reversibly and specifically binding glucose and mannose makes Con A as a suitable natural receptor for the development of smart glucose-responsive materials. During the last few years, Con A was used to develop smart materials, such as hydrogels, microgels, nanoparticles and films, for producing glucose biosensors or drug delivery devices. This review is focused on Con A-based materials suitable in the diagnosis and therapeutics of diabetes. A brief outlook on glucose-derived theranostics of cancer is also presented.

Swellable colorimetric microneedles for glucose detection based on glucose oxidase-like gold nanoparticles

BACKGROUND

Regular blood glucose monitoring is very important for diabetic patients. The composition of skin interstitial fluid (ISF) is similar to that of blood, which can be used for daily blood sugar detection and disease care. However, most methods of ISF extraction have complicated steps, may cause skin damage, and can only extract a limited amount of ISF, resulting in low detection efficiency. Therefore, it is very necessary to develop a detection method that can not only extract a large amount of ISF safely, efficiently, and conveniently, but also realize rapid detection of glucose level in ISF.

RESULTS

Here, we developed a gold nanoparticle (AuNP)-based swellable colorimetric MN patch with minimally invasive sampling function and real-time ISF glucose analysis ability. The MN patch could quickly absorb a large amount of skin ISF, and 60.2 mg of ISF was extracted within 10 min in vitro. It was divided into two layers: the tip layer was embedded with AuNPs with glucose oxidase (GOx)-like activity, which catalyzed the oxidation of glucose extracted from ISF and produced hydrogen peroxide (H2O2); horseradish peroxidase (HRP) encapsulated in the backing layer catalyzed the oxidation of 3, 3', 5, 5'-tetramethylbenzidine (TMB) by H2O2 to produce oxTMB, which led to a visible color shift in the backing layer. The ISF glucose level was judged by naked eyes and further quantified by color analysis with Image J software. As a result, the colorimetric MN patch successfully identified the normal blood sugar and hyperglycemia state in vivo.

SIGNIFICANCE

The colorimetric MN patch combined in-situ colorimetric sensing based on AuNP nanozyme with MN patch, which detected glucose level without blood drawing, increasing patients' compliance and reducing detection steps and time. Compared with the detection methods based on natural nanozymes, our method had better stability and sensitivity to complex environments (extreme pH and high temperature, etc.) in actual detection.

A Small Highly Sensitive Glucose Sensor Based on a Glucose Oxidase-Modified U-Shaped Microfiber

Diabetes patients need to monitor blood glucose all year round. In this article, a novel scheme is proposed for blood glucose detection. The proposed sensor is based on a U-shaped microfiber prepared using hydrogen-oxygen flame-heating technology, and then 3-aminopropyltriethoxysilane (APTES) and glucose oxidase (GOD) are successively coated on the surface of the U-shaped microfiber via a coating technique. The glucose reacts with the GOD of the sensor surface to produce gluconic acid, which changes the effective refractive index and then shifts the interference wavelength. The structure and morphology of the sensor were characterized via scanning electron microscope (SEM) and confocal laser microscopy (CLM). The experimental results show that the sensitivity of the sensor is as high as 5.73 nm/(mg/mL). Compared with the glucose sensor composed of the same material, the sensitivity of the sensor increased by 329%. The proposed sensor has a broad application prospect in blood glucose detection of diabetic patients due to the advantages of miniaturization, high sensitivity, and good stability.

Glucose Oxidase Loading in Ordered Porous Aluminosilicates: Exploring the Potential of Surface Modification for Electrochemical Glucose Sensing

Enzymatic electrochemical sensors have become the leading glucose detection technology due to their rapid response, affordability, portability, selectivity, and sensitivity. However, the performance of these sensors is highly dependent on the surface properties of the electrode material used to store glucose oxidase and its ability to retain enzymatic activity under variable environmental conditions. Mesoporous thin films have recently attracted considerable attention as promising candidates for enzyme storage and activity preservation due to their well-defined nanoarchitecture and tunable surface properties. Herein, we systematically compare pathways for the immobilization of glucose oxidase (GOx) and their effectiveness in electrochemical glucose sensing, following modification protocols that lead to the electrostatic attraction (amino functionalization), covalent bonding (aldehyde functionalization), and electrostatic repulsion (oxygen plasma treatment) of the ordered porous aluminosilicate-coated electrodes. By direct comparison using a quartz crystal microbalance, we demonstrate that glucose oxidase can be loaded in a nanoarchitecture with a pore size of ∼50 nm and pore interconnections of ∼35 nm using the native aluminosilicate surface, as well as after amino or aldehyde surface modification, while oxygen plasma exposure of the native surface inhibits glucose oxidase loading. Despite a variety of routes for enzyme loading, quantitative electrochemical glucose sensing between 0 and 20 mM was only possible when the porous surface was functionalized with amino groups, which we relate to the role of surface chemistry in accessing the underlying substrate. Our results highlight the impact of rational surface modification on electrochemical biosensing performance and demonstrate the potential of tailoring porous nanoarchitecture surfaces for biosensing applications.

Paper-based colorimetric sensors for point-of-care testing

By eliminating the need for sample transportation and centralized laboratory analysis, point-of-care testing (POCT) enables on-the-spot testing, with results available within minutes, leading to improved patient management and overall healthcare efficiency. Motivated by the rapid development of POCT, paper-based colorimetric sensing, a powerful analytical technique that exploits the changes in color or absorbance of a chemical species to detect and quantify analytes of interest, has garnered increasing attention. In this review, we strive to provide a bird's eye view of the development landscape of paper-based colorimetric sensors that harness the unique properties of paper to create low-cost, easy-to-use, and disposable analytical devices, thematically covering both fundamental aspects and categorized applications. In the end, we authors summarized the review with the remaining challenges and emerging opportunities. Hopefully, this review will ignite new research endeavors in the realm of paper-based colorimetric sensors.

Pyridine-Regulated Lamellar Nickel-Based Metal-Organic Framework (Ni-MOF) for Nonenzymatic Electrochemical Glucose Sensor

2D metal-organic frameworks (MOFs) are considered as promising electrochemical sensing materials and have attracted a lot of attention in recent years. Compared with bulk MOFs, the construction of 2D MOFs can increase the exposure of active sites by obtaining a larger surface area ratio. Herein, a facile one-pot hydrothermal synthesis of pyridine-regulated lamellar Ni-MOFs with ultrathin and well-defined 2D morphology is described. Compared with the bulk structure, the 2D lamellar Ni-MOF has higher surface area and active site density, showing better electrochemical glucose sensing performance. The 2D lamellar Ni-MOF exhibits a fast amperometric response of less than 3 s and a high sensitivity of 907.54 µA mm-1 cm-2 toward glucose with a wide linear range of 0.5-2665.5 µm. Furthermore, the 2D lamellar Ni-MOF also possesses excellent stability and reproducibility, and can be used to detect glucose with high accuracy and reliability in different environments.

Sugar Detection in Aqueous Solution Using an SMS Fiber Device

We report on the fabrication and testing of a fiber optics sensor based on multimodal interference effects, which aims at the detection of different types of sweeteners dissolved in water. The device, which has a simple structure, commonly known as the SMS configuration, is built by splicing a segment of commercial-grade, coreless multimode fiber (NC-MMF) between two standard single-mode fibers (SMFs). In this configuration, the evanescent field traveling outside the core of the NC-MMF allows the sensing of the refractive index of the surrounding media, making it possible to detect different levels of sugar concentration. The optical sensor was tested with aqueous solutions of glucose, fructose, and sucrose in the concentration range from 0 wt% to 20 wt% at room temperature. The proposed device exhibits a linear response with a sensitivity of 0.1835 nm/wt% for sucrose, 0.1687 nm/wt% for fructose, and 0.1694 nm/wt% for glucose, respectively, with a sensing resolution of around 0.5 wt%. Finally, we show that, despite having similar concentration behavior, some degree of discrimination between the different sugars can be achieved by assessing their thermo-optical response.

Facile Synthesis of MXene-Ti3C2/Co Nanosheet Hydrogel Sensor with the Assistance of a Smartphone for On-Site Monitoring of Glucose in Beverages

A one-step cobaltous chloride (CoCl₂) molten salt method was employed to prepare multilayer MXene-Ti₃C₂/Co materials with further ultrasonic treatment to acquire single-layer MXene-Ti₃C_2/Co nanosheets (NSs). MXene-Ti₃C₂/Co NSs were characterized, and their enzyme-like activities were investigated. Under the catalysis of MXene-Ti₃C₂/Co NSs, 3,3',5,5'-tetramethylbenzidine (TMB) could be oxidized by H₂O₂, with the color changing from colorless to blue. The affinity of MXene-Ti₃C₂/Co NSs to H₂O₂ and TMB was better than that of nanozymes reported in previous studies. The MXene-Ti₃C₂/Co NSs were used for the colorimetric determination of H₂O₂/glucose, with limits of detection (LODs) of 0.033 mM and 1.7 μM, respectively. MXene-Ti₃C₂/Co NSs embedded in sodium alginate (SA) hydrogel were used to construct a sensor platform. The digital pictures combined with a smartphone-installed app (color recognizer) could be used to analyze RGB values for colorimetric detection of glucose in beverages. This point-of-care testing platform has the advantages of cost-effectiveness and good transferability, with the potential to realize quick, intelligent and on-site detection.

Continuous Glucose Monitoring Enabled by Fluorescent Nanodiamond Boronic Hydrogel

Continuous monitoring of glucose allows diabetic patients to better maintain blood glucose level by altering insulin dosage or diet according to prevailing glucose values and thus to prevent potential hyperglycemia and hypoglycemia. However, current continuous glucose monitoring (CGM) relies mostly on enzyme electrodes or micro-dialysis probes, which suffer from insufficient stability, susceptibility to corrosion of electrodes, weak or inconsistent correlation, and inevitable interference. A fluorescence-based glucose sensor in the skin will likely be more stable, have improved sensitivity, and can resolve the issues of electrochemical interference from the tissue. This study develops a fluorescent nanodiamond boronic hydrogel system in porous microneedles for CGM. Fluorescent nanodiamond is one of the most photostable fluorophores with superior biocompatibility. When surface functionalized, the fluorescent nanodiamond can integrate with boronic polymer and form a hydrogel, which can produce fluorescent signals in response to environmental glucose concentration. In this proof-of-concept study, the strategy for building a miniatured device with fluorescent nanodiamond hydrogel is developed. The device demonstrates remarkable long-term photo and signal stability in vivo with both small and large animal models. This study presents a new strategy of fluorescence based CGM toward treatment and control of diabetes.

Medical micro- and nanomotors in the body

Attributed to the miniaturized body size and active mobility, micro- and nanomotors (MNMs) have demonstrated tremendous potential for medical applications. However, from bench to bedside, massive efforts are needed to address critical issues, such as cost-effective fabrication, on-demand integration of multiple functions, biocompatibility, biodegradability, controlled propulsion and in vivo navigation. Herein, we summarize the advances of biomedical MNMs reported in the past two decades, with particular emphasis on the design, fabrication, propulsion, navigation, and the abilities of biological barriers penetration, biosensing, diagnosis, minimally invasive surgery and targeted cargo delivery. Future perspectives and challenges are discussed as well. This review can lay the foundation for the future direction of medical MNMs, pushing one step forward on the road to achieving practical theranostics using MNMs.

Carbon Nanotube Fiber-Based Flexible Microelectrode for Electrochemical Glucose Sensors

Electrochemical sensors are gaining significant demand for real-time monitoring of health-related parameters such as temperature, heart rate, and blood glucose level. A fiber-like microelectrode composed of copper oxide-modified carbon nanotubes (CuO@CNTFs) has been developed as a flexible and wearable glucose sensor with remarkable catalytic activity. The unidimensional structure of CNT fibers displayed efficient conductivity with enhanced mechanical strength, which makes these fibers far superior as compared to other fibrous-like materials. Copper oxide (CuO) nanoparticles were deposited over the surface of CNT fibers by a binder-free facile electrodeposition approach followed by thermal treatment that enhanced the performance of non-enzymatic glucose sensors. Scanning electron microscopy and energy-dispersive X-ray analysis confirmed the successful deposition of CuO nanoparticles over the fiber surface. Amperometric and voltammetric studies of fiber-based microelectrodes (CuO@CNTFs) toward glucose sensing showed an excellent sensitivity of ∼3000 μA/mM cm², a low detection limit of 1.4 μM, and a wide linear range of up to 13 mM. The superior performance of the microelectrode is attributed to the synergistic effect of the electrocatalytic activity of CuO nanoparticles and the excellent conductivity of CNT fibers. A lower charge transfer resistance value obtained via electrochemical impedance spectroscopy (EIS) also demonstrated the superior electrode performance. This work demonstrates a facile approach for developing CNT fiber-based microelectrodes as a promising solution for flexible and disposable non-enzymatic glucose sensors.

Bioinspired Colloidal Photonic Composites: Fabrications and Emerging Applications

Organisms in nature have evolved unique structural colors and stimuli-responsive functions for camouflage, warning, and communication over millions of years, which are essential to their survival in harsh conditions. Inspired by these characteristics, colloidal photonic composites (CPCs) composed of colloidal photonic crystals embedded in the polymeric matrix are artificially prepared and show great promise in applications. This review focuses on the summary of building blocks, i.e., colloidal particles and polymeric matrices, and constructive strategies from the perspective of designing CPCs with robust performance and specific functionality. Furthermore, their state-of-the-art applications are also discussed, including colorful coatings, anti-counterfeiting, and regulation of photoluminescence, especially in the field of visualized sensing. Finally, current challenges and potential for future developments in this field are discussed. The purpose of this review is not only to clarify the design principle for artificial CPCs but also to serve as a roadmap for the exploration of next-generation photonic materials.

Optical Biosensor Based on Graphene and Its Derivatives for Detecting Biomolecules

Graphene and its derivatives show great potential for biosensing due to their extraordinary optical, electrical and physical properties. In particular, graphene and its derivatives have excellent optical properties such as broadband and tunable absorption, fluorescence bursts, and strong polarization-related effects. Optical biosensors based on graphene and its derivatives make nondestructive detection of biomolecules possible. The focus of this paper is to review the preparation of graphene and its derivatives, as well as recent advances in optical biosensors based on graphene and its derivatives. The working principle of face plasmon resonance (SPR), surface-enhanced Raman spectroscopy (SERS), fluorescence resonance energy transfer (FRET) and colorimetric sensors are summarized, and the advantages and disadvantages of graphene and its derivatives applicable to various types of sensors are analyzed, and the methods of surface functionalization of graphene and its derivatives are introduced; these optical biosensors can be used for the detection of a range of biomolecules such as single cells, cellular secretions, proteins, nucleic acids, and antigen-antibodies; these new high-performance optical sensors are capable of detecting changes in surface structure and biomolecular interactions with the advantages of ultra-fast detection, high sensitivity, label-free, specific recognition, and the ability to respond in real-time. Problems in the current stage of application are discussed, as well as future prospects for graphene and its biosensors. Achieving the applicability, reusability and low cost of novel optical biosensors for a variety of complex environments and achieving scale-up production, which still faces serious challenges.

Nanozyme-based colorimetric biosensor with a systemic quantification algorithm for noninvasive glucose monitoring

Diabetes mellitus accompanies an abnormally high glucose level in the bloodstream. Early diagnosis and proper glycemic management of blood glucose are essential to prevent further progression and complications. Biosensor-based colorimetric detection has progressed and shown potential in portable and inexpensive daily assessment of glucose levels because of its simplicity, low-cost, and convenient operation without sophisticated instrumentation. Colorimetric glucose biosensors commonly use natural enzymes that recognize glucose and chromophores that detect enzymatic reaction products. However, many natural enzymes have inherent defects, limiting their extensive application. Recently, nanozyme-based colorimetric detection has drawn attention due to its merits including high sensitivity, stability under strict reaction conditions, flexible structural design with low-cost materials, and adjustable catalytic activities. This review discusses various nanozyme materials, colorimetric analytic methods and mechanisms, recent machine learning based analytic methods, quantification systems, applications and future directions for monitoring and managing diabetes.

Facile preparation of Fe3O4@Pt nanoparticles as peroxidase mimics for sensitive glucose detection by a paper-based colorimetric assay

A simple strategy to rapidly detect glucose was developed by utilizing core (Fe₃O₄)-shell (Pt) magnetic nanoparticles (Fe₃O₄@Pt NPs) as a nanoenzyme and a paper-based colorimetric sensor. In the presence of H₂O₂, Fe₃O₄@Pt NPs catalyze the redox reaction of 3,3',5,5'-tetramethylbenzidine (TMB) and generate a colour change from colourless to blue. On this basis, a colorimetric glucose sensing method assisted by glucose oxidase (GOx) was developed. Under the optimal conditions, the detection limits of the proposed assay for H₂O₂ and glucose were 0.36 µM and 1.27 µM, respectively. Furthermore, the fabricated colorimetric method was successfully applied to analyze glucose concentrations by using a paper device as a measuring platform without a spectrometer. In addition, this method exhibited satisfactory recovery for glucose detection in human serum samples and urine samples, which satisfied the requirements for normal detection of real samples. This study provides a good candidate for health monitoring of glucose and also expands the applications of nanoenzymes and paper-based colorimetric assays in point-of-care testing.

In Vitro Evaluation of Miniaturized Amperometric Enzyme Sensor Based on the Direct Electron Transfer Principle for Continuous Glucose Monitoring

BACKGROUND

The bacterial derived flavin adenine dinucleotide (FAD)-dependent glucose dehydrogenase (FADGDH) is the most promising enzyme for the third-generation principle-based enzyme sensor for continuous glucose monitoring (CGM). Due to the ability of the enzyme to transfer electrons directly to the electrode, recognized as direct electron transfer (DET)-type FADGDH, although no investigation has been reported about DET-type FADGDH employed on a miniaturized integrated electrode.

METHODS

The miniaturized integrated electrode was formed by sputtering gold (Au) onto a flexible film with 0.1 mm in thickness and divided into 3 parts. After an insulation layer was laminated, 3 openings for a working electrode, a counter electrode and a reference electrode were formed by dry etching. A reagent mix containing 1.2 × 10^-4 Unit of DET-type FADGDH and carbon particles was deposited. The long-term stability of sensor was evaluated by continuous operation, and its performance was also evaluated in the presence of acetaminophen and the change in oxygen partial pressure (pO₂) level.

RESULTS

The amperometric response of the sensor showed a linear response to glucose concentration up to 500 mg/dL without significant change of the response over an 11-day continuous measurement. Moreover, the effect of acetaminophen and pO₂ on the response were negligible.

CONCLUSIONS

These results indicate the superb potential of the DET-type FADGDH-based sensor with the combination of a miniaturized integrated electrode. Thus, the described miniaturized DET-type glucose sensor for CGM will be a promising tool for effective glycemic control. This will be further investigated using an in vivo study.

Microsensor in Microbioreactors: Full Bioprocess Characterization in a Novel Capillary-Wave Microbioreactor

Microbioreactors (MBRs) with a volume below 1 mL are promising alternatives to established cultivation platforms such as shake flasks, lab-scale bioreactors and microtiter plates. Their main advantages are simple automatization and parallelization and the saving of expensive media components and test substances. These advantages are particularly pronounced in small-scale MBRs with a volume below 10 µL. However, most described small-scale MBRs are lacking in process information from integrated sensors due to limited space and sensor technology. Therefore, a novel capillary-wave microbioreactor (cwMBR) with a volume of only 7 µL has the potential to close this gap, as it combines a small volume with integrated sensors for biomass, pH, dissolved oxygen (DO) and glucose concentration. In the cwMBR, pH and DO are measured by established luminescent optical sensors on the bottom of the cwMBR. The novel glucose sensor is based on a modified oxygen sensor, which measures the oxygen uptake of glucose oxidase (GOx) in the presence of glucose up to a concentration of 15 mM. Furthermore, absorbance measurement allows biomass determination. The optical sensors enabled the characterization of an Escherichia coli batch cultivation over 8 h in the cwMBR as proof of concept for further bioprocesses. Hence, the cwMBR with integrated optical sensors has the potential for a wide range of microscale bioprocesses, including cell-based assays, screening applications and process development.

Novel Copper-Zinc-Manganese Ternary Metal Oxide Nanocomposite as Heterogeneous Catalyst for Glucose Sensor and Antibacterial Activity

A novel copper-zinc-manganese trimetal oxide nanocomposite was synthesized by the simple co-precipitation method for sensing glucose and methylene blue degradation. The absorption maximum was found by ultraviolet–visible spectroscopy (UV-Vis) analysis, and the bandgap was 4.32 eV. The formation of a bond between metal and oxygen was confirmed by Fourier Transform Infrared Spectroscopy (FT-IR) analysis. The average crystallite size was calculated as 17.31 nm by X-ray powder diffraction (XRD) analysis. The morphology was observed as spherical by scanning electron microscope (SEM) and high-resolution transmission electron microscopy (HR-TEM) analysis. The elemental composition was determined by Energy Dispersive X-ray Analysis (EDAX) analysis. The oxidation state of the metals present in the nanocomposites was confirmed by the X-ray photoelectron spectroscopy (XPS) analysis. The hydrodynamic diameter and zeta potential of the nanocomposite were 218 nm and −46.8 eV, respectively. The thermal stability of the nanocomposite was analyzed by thermogravimetry-differential scanning calorimetry (TG-DSC) analysis. The synthesized nanocomposite was evaluated for the electrochemical glucose sensor. The nanocomposite shows 87.47% of degradation ability against methylene blue dye at a 50 µM concentration. The trimetal oxide nanocomposite shows potent activity against Escherichia coli. In addition to that, the prepared nanocomposite shows strong antioxidant application where scavenging activity was observed to be 76.58 ± 0.30, 76.89 ± 0.44, 81.41 ± 30, 82.58 ± 0.32, and 84.36 ± 0.09 % at 31, 62, 125, 250, and 500 µg/mL, respectively. The results confirm the antioxidant potency of nanoparticles (NPs) was concentration dependent.

Fabrication of Enzyme-Free and Rapid Electrochemical Detection of Glucose Sensor Based on ZnO Rod and Ru Doped Carbon Nitride Modified Gold Transducer

Over 3 in 4 adults with diabetes live in low- and middle-income counties and health expenditure also increased 316% over the last 15 years. In this regard, we fabricate low cost, reusable and rapid detection of diabetes sensor based on zinc oxide rod inserted ruthenium-doped carbon nitride (ZnO-g-Ru-C₃N₄) modified sensor device. Developed sensor device physically and electrochemically characterized using X-ray diffraction (XRD), fourier-transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), chronoamperometry (CA) and differential pulse voltammetry (DPV). Sensing device as an effective enzyme-free glucose detection with high sensitivity (346 μA/mM/cm²) over the applied lower potential of +0.26 V (vs. Ag/AgCl), fast response (3 s) and broad linear range of (2-28) mM, coupled with a lower limit of detection (3.5 nM). The biosensing device gives better anti-interference ability with justifiable reproducibility, reusability (single electrode re-use 26 times in physiological buffer and 3 times in serum) and stability. Moreover, the real-time applicability of the sensor device was evaluated in human blood, serum and urine samples.

Copper Cobalt Sulfide Structures Derived from MOF Precursors with Enhanced Electrochemical Glucose Sensing Properties

Nonenzymatic electrochemical detection of glucose is popular because of its low price, simple operation, high sensitivity, and good reproducibility. Co-Cu MOFs precursors were synthesized via the solvothermal way at first, and a series of porous spindle-like Cu-Co sulfide microparticles were obtained by secondary solvothermal sulfurization, which maintained the morphology of the MOFs precursors. Electrochemical studies exhibit that the as-synthesized Cu-Co sulfides own excellent nonenzymatic glucose detection performances. Compared with CuS, Co (II) ion-doped CuS can improve the conductivity and electrocatalytic activity of the materials. At a potential of 0.55 V, the as-prepared Co-CuS-2 modified electrode exhibits distinguished performance for glucose detection with wide linear ranges of 0.001–3.66 mM and high sensitivity of 1475.97 µA·mM⁻¹·cm⁻², which was much higher than that of CuS- and Co-CuS-1-modified electrodes. The constructed sulfide sensors derived from MOF precursors exhibit a low detection limit and excellent anti-interference ability for glucose detection.

Carbon dots and Methylene blue facilitated photometric quantification of Hemoglobin

Early detection and monitoring of any abnormality of Hemoglobin (Hb) concentration in whole blood samples are important as this may be related to anemia, leukemia, dengue, etc. To facilitate quantitative detection and to monitor the hemoglobin level in the blood, we attempt to develop a low-cost, portable point of care (POC) device based on the spectrophotometric principle. Optical sensitivities of carbon quantum dots (CDs) are found to be highly responsive, while there is a selective reaction between Hb and reduced form of Methylene Blue (MB_red). The interaction of Hb, MB_red, and CDs is delineated using UV-Visible (UV-Vis) spectroscopy. CDs have a characteristic UV-Vis peak at ∼ 347 nm, and it shows a gradual increase in intensity with a slight red shift (∼355 nm) on the progressive increase in Hb concentration. Simultaneously, the colorless MB_red is oxidized to its blue oxidized form MB_ox and its characteristic peak starts reappearing at ∼ 663 nm. These responses are exploited to quantify Hb concentration with a limit of detection (LOD) as low as ∼ 2 g dL^-1 in a developed POC device, and the results are validated with the clinical data obtained from a local hospital with reasonably good agreement. This photometric detection approach can be adopted for other quantitative biosensors.

An amphiprotic paper-based electrode for glucose detection based on layered carbon nanotubes with silver and polystyrene particles

In this work, a flexible amphiprotic amino-bonded carbon nanotube-Ag nanoparticle/polystyrene (CNT-NH₂-Ag/PS) paper electrode was fabricated to measure glucose in human body fluids by a combination of vacuum filtration and high temperature baking. The front side of the fabricated paper electrode was hydrophobic and conductive, whereas its back side was hydrophilic and nonconductive. In the fabrication process, the coating sequence of CNT-NH₂, Ag and PS was critical to determine the performance of the resulting CNT-NH₂-Ag/PS electrode besides other parameters (e.g., amount of soluble starch, PS and Ag nanoparticles, type and amount of CNT-NH₂, and electrode sensing area). Based on a series of experimental observations, the possible mechanism of glucose detection on the paper electrode was proposed, in which glucose was more favorable to migrate to the hydrophilic back side of the paper and interact with the active species (e.g., O₂^-) on the electrode surface. The electrochemical results showed that the CNT-NH₂-Ag/PS paper electrode maintained stable electrochemical properties even after five cycles of use and 60 days of storage in air. The amphiprotic paper electrode demonstrated excellent sensing performance for glucose with a linear range of 1 μM to 1000 μM, a low detection limit of 0.2 μM, and a sensitivity of 31 333.0 μA mM^-1 cm^-2. The fabricated paper electrode was also successfully applied to detect different levels of glucose in complex human body fluids such as saliva, urine, and serum. These features make this type of paper electrode promising for glucose measurement.

A sensitive, fast, selective, and reusable enzyme-free glucose sensor based on monodisperse AuNi alloy nanoparticles on activated carbon support

In this study, a glucose sensor modified with activated carbon supported gold-nickel (AuNi@AC) metal nanoparticles was prepared for the early diagnosis of diabetes. Electrochemical tests were carried out by determining the optimum working conditions of the prepared glucose sensor. The characterization analyses of the designed glucose sensor were performed by Transmission Electron Microscopy (TEM), X-Ray Diffraction (XRD), X-Ray Photoelectron Spectroscopy (XPS) and Raman Spectroscopy. It was determined that the average particle size of the nanoparticles in the AuNi alloy structure was 2.03 ± 0.37 nm. The determined detection limit of the AuNi@AC nanosensor was calculated as 0.41 μM as a result of the high linear range provided up to 1.7 mM. In addition, the sensitivity of AuNi@AC nanosensor to glucose, which has a high sensitivity value of 1955 μA mM^-1 cm^-2, was determined.

An update on microneedle-based systems for diabetes

Diabetes is one of the most serious chronic diseases today. Patients with diabetes need frequent insulin injections or blood sampling to monitor blood glucose levels. The microneedles are a painless transdermal drug delivery system, which has great advantages in achieving self-management. There have been a lot of researches on microneedles used in diabetes treatment. Microneedle-based treatment of diabetes has also changed from a simple and reliable system to a complex and efficient system. This review introduces microfluidic, glucose response, and other contents based on microneedles, and some challenges in the development of microneedles.

Advances in fluorescence sensing enabled by lanthanide-doped upconversion nanophosphors

Lanthanide-doped upconversion nanoparticles (UCNPs), characterized by converting low-energy excitation to high-energy emission, have attracted considerable interest due to their inherent advantages of large anti-Stokes shifts, sharp and narrow multicolor emissions, negligible autofluorescence background interference, and excellent chemical- and photo-stability. These features make them promising luminophores for sensing applications. In this review, we give a comprehensive overview of lanthanide-doped upconversion nanophosphors including the fundamental principle for the construction of UCNPs with efficient upconversion luminescence (UCL), followed by state-of-the-art strategies for the synthesis and surface modification of UCNPs, and finally describing current advances in the sensing application of upconversion-based probes for the quantitative analysis of various analytes including pH, ions, molecules, bacteria, reactive species, temperature, and pressure. In addition, emerging sensing applications like photodetection, velocimetry, electromagnetic field, and voltage sensing are highlighted.

2D Material-Based Optical Biosensor: Status and Prospect

The combination of 2D materials and optical biosensors has become a hot research topic in recent years. Graphene, transition metal dichalcogenides, black phosphorus, MXenes, and other 2D materials (metal oxides and degenerate semiconductors) have unique optical properties and play a unique role in the detection of different biomolecules. Through the modification of 2D materials, optical biosensor has the advantages that traditional sensors (such as electrical sensing) do not have, and the sensitivity and detection limit are greatly improved. Here, optical biosensors based on different 2D materials are reviewed. First, various detection methods of biomolecules, including surface plasmon resonance (SPR), fluorescence resonance energy transfer (FRET), and evanescent wave and properties, preparation and integration strategies of 2D material, are introduced in detail. Second, various biosensors based on 2D materials are summarized. Furthermore, the applications of these optical biosensors in biological imaging, food safety, pollution prevention/control, and biological medicine are discussed. Finally, the future development of optical biosensors is prospected. It is believed that with their in-depth research in the laboratory, optical biosensors will gradually become commercialized and improve people's quality of life in many aspects.

ZnO Transducers for Photoluminescence-Based Biosensors: A Review

Zinc oxide (ZnO) is a wide bandgap semiconductor material that has been widely explored for countless applications, including in biosensing. Among its interesting properties, its remarkable photoluminescence (PL), which typically exhibits an intense signal at room temperature (RT), arises as an extremely appealing alternative transduction approach due to the high sensitivity of its surface properties, providing high sensitivity and selectivity to the sensors relying on luminescence output. Therefore, even though not widely explored, in recent years some studies have been devoted to the use of the PL features of ZnO as an optical transducer for detection and quantification of specific analytes. Hence, in the present paper, we revised the works that have been published in the last few years concerning the use of ZnO nanostructures as the transducer element in different types of PL-based biosensors, namely enzymatic and immunosensors, towards the detection of analytes relevant for health and environment, like antibiotics, glucose, bacteria, virus or even tumor biomarkers. A comprehensive discussion on the possible physical mechanisms that rule the optical sensing response is also provided, as well as a warning regarding the effect that the buffer solution may play on the sensing experiments, as it was seen that the use of phosphate-containing solutions significantly affects the stability of the ZnO nanostructures, which may conduct to misleading interpretations of the sensing results and unreliable conclusions.

Long-Term In Vivo Glucose Monitoring by Polymer-Dot Transducer in an Injectable Hydrogel Implant

Optical sensors have attracted a great deal of interest for glucose detection. However, their practical applications for continuous glucose monitoring are still constrained by operational reliability in subcutaneous tissues. Here, we show an implantable hydrogel platform embedded with luminescent polymer dots (Pdots) for sensitive and long-term glucose monitoring. We use Pdot transducer in a polyacrylamide hydrogel matrix to construct an implantable platform. The hydrogel-Pdot transducer showed bright luminescence with ratiometric response to glucose changes. The in vitro and in vivo sensitivities of the hydrogel implant were enhanced by varying the enzyme concentration and injection volume. After implantation, the hydrogel with Pdot transducer remained at the implanted site without migration for 1 month and can be removed from the subcutaneous tissue for further analysis. Our results indicate that the hydrogel-Pdot platform maintains the intrinsic sensing property with excellent stability during 1 month implantation, while fibrous capsule formation on the implant in some cases needs to be solved for long-term continuous glucose monitoring.

Surface-halogen-introduced 2D NiCo bimetallic MOFs via a modulation method for elevated electrochemical glucose sensing

A series of NiCo MOFs is prepared through a simple method by introducing pyridine as modulator and 4-halogenpyridine as surface functional group. The MOFs show excellent electrocatalytic activity and stability for the glucose oxidation reaction.

Fluorescent Sensor Array for Quantitative Determination of Saccharides

Accurate monitoring of sugar levels is essential for many fields from food industry to human health. Here, we developed FRET-based dual chromophore sensors for saccharides that form oxazolidine boronate and may be employed as a noninvasive method for monitoring of sugar levels in biological fluids, namely, urine. The saccharide-binding properties of the sensors were studied using fluorescence spectroscopy and utilized in the determination of saccharides in a high-throughput manner. Here, two fluorescent sensors were successful in the classification of nine different monosaccharides and disaccharides with 100% correct classification. Furthermore, the dual chromophore self-assembled sensors were successfully utilized for the quantitative determination of important carbohydrates such as glucose in the presence of competitive saccharides (fructose) and in complex media (urine) without sample pretreatment. The present fluorescent sensors allow for quantification of glucose in a concentration range of 0-60 mM, which matches the concentration range of frequently used urinalysis test strips.

Sonochemiluminescence Using Apertureless USB Piezoelectric Ultrasonic Transducer and Its Applications for the Detection of Hydrogen Peroxide, Glucose, and Glucose Oxidase Activity

The mesh-type USB piezoelectric ultrasonic transducer (USB-PUT) used in household humidifiers and inhalation therapy devices is very cheap, small, and energy saving. It holds great promise for sonochemistry. However, the microtapered apertures in the center of the stainless steel substrate of mesh-type USB-PUT can lead to rapid atomization of solution, leakage of solutions containing surfactants and organic solvent through the apertures, and high background emission. Herein, we design a new type of USB-PUT by replacing the meshed stainless steel substrate with an apertureless stainless steel substrate. We have found that this apertureless USB-PUT can not only induce intense sonochemiluminescence (SCL) but can also enable sensitive luminol SCL detection of hydrogen peroxide which is practically impossible using mesh-type PUT because of the strong background SCL emission. By using this apertureless device to induce SCL and using smart phone as a detector, a visual hydrogen peroxide SCL detection method with a linear range of 0.5-50 μM and a detection limit of 0.32 μM is established. Moreover, the device can achieve the detection of glucose oxidase (GOD) activity and glucose by enzymatic conversion of glucose to hydrogen peroxide. The linear range of GOD detection is 1-200U/L with a detection limit of 0.86 U/L. The linear range of glucose detection is 0.5-70 μM with a detection limit of 0.43 μM. The cheap (a few dollars) and user-friendly apertureless USB-PUT is promising for sonochemistry applications and chemical education.

Non-Enzymatic Detection of Glucose in Neutral Solution Using PBS-Treated Electrodeposited Copper-Nickel Electrodes

Transition metals have been explored extensively for non-enzymatic electrochemical detection of glucose. However, to enable glucose oxidation, the majority of reports require highly alkaline electrolytes which can be damaging to the sensors and hazardous to handle. In this work, we developed a non-enzymatic sensor for detection of glucose in near-neutral solution based on copper-nickel electrodes which are electrochemically modified in phosphate-buffered saline (PBS). Nickel and copper were deposited using chronopotentiometry, followed by a two-step annealing process in air (Step 1: at room temperature and Step 2: at 150 °C) and electrochemical stabilization in PBS. Morphology and chemical composition of the electrodes were characterized using scanning electron microscopy and energy-dispersive X-ray spectroscopy. Cyclic voltammetry was used to measure oxidation reaction of glucose in sodium sulfate (100 mM, pH 6.4). The PBS-Cu-Ni working electrodes enabled detection of glucose with a limit of detection (LOD) of 4.2 nM, a dynamic response from 5 nM to 20 mM, and sensitivity of 5.47 ± 0.45 μA cm-2/log10(mole.L-1) at an applied potential of 0.2 V. In addition to the ultralow LOD, the sensors are selective toward glucose in the presence of physiologically relevant concentrations of ascorbic acid and uric acid spiked in artificial saliva. The optimized PBS-Cu-Ni electrodes demonstrate better stability after seven days storage in ambient compared to the Cu-Ni electrodes without PBS treatment.

Review on recent progress in metal-organic framework-based materials for fabricating electrochemical glucose sensors

Diabetes is a type of disease that threatens human health, which can be diagnosed based on the level of glucose in the blood. Recently, various MOF-based materials have been developed as efficient electrochemical glucose sensors because of their tunable pore channels, large specific surface area well dispersed metallic active sites, etc. In this review, the significance of glucose detection and the advantages of MOF-based materials for this application are primarily discussed. Then, the application of MOF-based materials can be categorized into two types of glucose sensors: enzymatic biosensors and non-enzymatic sensors. Finally, insights into the current research challenges and future breakthrough possibilities regarding electrochemical glucose sensors are considered.

Practical monitoring technologies for cells and substrates in biomanufacturing

Precise control over bioreactor operation is desired for optimal productivity and product quality, and there is an increased drive to automation in biomanufacturing. All of these goals require sensors, not only of the basic parameters of temperature, pH, and dissolved oxygen, but of the biomass and substrate concentrations, which directly determine the outcome of the bioprocess. While there are many innovative sensing concepts for biomass and substrate concentrations, this review focuses on sensors that are in-line with the bioreactor, providing data continuously without the removal of sample from the system. The discussion emphasizes the requirements of industry for these sensors, including performance, ease of use, and cost. As the bioeconomy grows, advances in sensing technologies will be needed to achieve the automation of the future for a wider array of bioreactors.

Insulin-dependent glucose consumption dynamics in 3D primary human liver cultures measured by a sensitive and specific glucose sensor with nanoliter input volume

The liver plays a central role in glucose homeostasis and hepatic insulin resistance constitutes a key feature of type 2 diabetes. However, platforms that accurately mimic human hepatic glucose disposition and allow for rapid and scalable quantification of glucose consumption dynamics are lacking. Here, we developed and optimized a colorimetric glucose assay based on the glucose oxidase-peroxidase system and demonstrate that the system can monitor glucose consumption in 3D primary human liver cell cultures over multiple days. The system was highly sensitive (limit of detection of 3.5 µM) and exceptionally accurate (R²  = 0.999) while requiring only nanoliter input volumes (250 nL), enabling longitudinal profiling of individual liver microtissues. By utilizing a novel polymer, off-stoichiometric thiol-ene (OSTE), and click-chemistry based on thiol-Michael additions, we furthermore show that the assay can be covalently bound to custom-build chips, facilitating the integration of the sensor into microfluidic devices. Using this system, we find that glucose uptake of our 3D human liver cultures closely resembles human hepatic glucose uptake in vivo as measured by euglycemic-hyperinsulinemic clamp. By comparing isogenic insulin-resistant and insulin-sensitive liver cultures we furthermore show that insulin and extracellular glucose levels account for 55% and 45% of hepatic glucose consumption, respectively. In conclusion, the presented data show that the integration of accurate and scalable nanoliter glucose sensors with physiologically relevant organotypic human liver models enables longitudinal profiling of hepatic glucose consumption dynamics that will facilitate studies into the biology and pathobiology of glycemic control, as well as antidiabetic drug screening.

MRI-Based Glucose Assay Using Magnetic Nanoparticle Sensors

Glucose sensors for NMR relaxometry and magnetic resonance imaging (MRI) can be used for the direct measurement of glucose in turbid biological specimens. Here, we proposed a magnetic glucose sensor based on superparamagnetic iron oxide (SPIO) nanoparticles conjugated to a mannopyranoside derivative and concanavalin A (ConA). The binding of mannopyranoside groups to ConA produced a nanoparticle cluster that was dissociated by competitive binding of glucose to ConA, resulting in changes in the transverse relaxation time (T2) in a glucose-dependent manner. The sensor gave rise to significant T2 changes in physiological glucose levels of 3 - 8 mM at a nanoparticle concentration of 0.5 nM. Significant T2 responses were observed within 6 min of 5 mM glucose detection. Sensor-based MRI by a benchtop 1 tesla scanner permitted a measurement of multiple samples within 8 min. These results demonstrate that the relaxometric glucose sensor could lead to high throughput direct assay of blood samples by using a compact MRI scanner for point-of-care testing.

Low dimensional materials for glucose sensing

Biosensors are essential components for effective healthcare management. Since biological processes occur on molecular scales, nanomaterials and nanosensors intrinsically provide the most appropriate landscapes for developing biosensors. Low-dimensional materials have the advantage of offering high surface areas, increased reactivity and unique physicochemical properties for efficient and selective biosensing. So far, nanomaterials and nanodevices have offered significant prospects for glucose sensing. Targeted glucose biosensing using such low-dimensional materials enables much more effective monitoring of blood glucose levels, thus providing significantly better predictive diabetes diagnostics and management. In this review, recent advances in using low dimensional materials for sensing glucose are summarized. Sensing fundamentals are discussed, as well as invasive, minimally-invasive and non-invasive sensing methods. The effects of morphological characteristics and size-dependent properties of low dimensional materials are explored for glucose sensing, and the key performance parameters such as selectivity, stability and sensitivity are also discussed. Finally, the challenges and future opportunities that low dimensional materials can offer for glucose sensing are outlined.

Dermacozine N, the First Natural Linear Pentacyclic Oxazinophenazine with UV-Vis Absorption Maxima in the Near Infrared Region, along with Dermacozines O and P Isolated from the Mariana Trench Sediment Strain Dermacoccus abyssi MT 1.1T

Three dermacozines, dermacozines N-P (1-3), were isolated from the piezotolerant Actinomycete strain Dermacoccus abyssi MT 1.1T, which was isolated from a Mariana Trench sediment in 2006. Herein, we report the elucidation of their structures using a combination of 1D/2D NMR, LC-HRESI-MSn, UV-Visible, and IR spectroscopy. Further confirmation of the structures was achieved through the analysis of data from density functional theory (DFT)-UV-Visible spectral calculations and statistical analysis such as two tailed t-test, linear regression-, and multiple linear regression analysis applied to either solely experimental or to experimental and calculated 13C-NMR chemical shift data. Dermacozine N (1) bears a novel linear pentacyclic phenoxazine framework that has never been reported as a natural product. Dermacozine O (2) is a constitutional isomer of the known dermacozine F while dermacozine P (3) is 8-benzoyl-6-carbamoylphenazine-1-carboxylic acid. Dermacozine N (1) is unique among phenoxazines due to its near infrared (NIR) absorption maxima, which would make this compound an excellent candidate for research in biosensing chemistry, photodynamic therapy (PDT), opto-electronic applications, and metabolic mapping at the cellular level. Furthermore, dermacozine N (1) possesses weak cytotoxic activity against melanoma (A2058) and hepatocellular carcinoma cells (HepG2) with IC50 values of 51 and 38 μM, respectively.

Brain neurochemical monitoring

Brain neurochemical monitoring aims to provide continuous and accurate measurements of brain biomarkers. It has enabled significant advances in neuroscience for application in clinical diagnostics, treatment, and prevention of brain diseases. Microfabricated electrochemical and optical spectroscopy sensing technologies have been developed for precise monitoring of brain neurochemicals. Here, a comprehensive review on the progress of sensing technologies developed for brain neurochemical monitoring is presented. The review provides a summary of the widely measured clinically relevant neurochemicals and commonly adopted recognition technologies. Recent advances in sampling, electrochemistry, and optical spectroscopy for brain neurochemical monitoring are highlighted and their application are discussed. Existing gaps in current technologies and future directions to design industry standard brain neurochemical sensing devices for clinical applications are addressed.