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The demand for glucose-sensing devices has increased along with the increasing diabetic population. Here, we aimed to construct a system with a glucose oxidase (GOx)-integrated Cu-nanoflower (Cu-NF) as the underlying electrode. This novel system was successfully developed by creating a cross-linked GOx within a Cu-NF matrix, forming a c-GOx@Cu-NF-coated film on a carbon screen-printed electrode (CSPE). A comparison of the stabilities of the cross-linking methods demonstrated enhanced durability, with an activity level of >88 % maintained after approximately 35 days of storage in room temperature buffer. Regarding the ability of the c-GOx@Cu-NF modified CSPE to detect glucose via electrochemical methods, the redox potential gap (ΔE) and peak current increased in the presence of GOx. In comparison to that of glucose, the sensitivity of c-GOx@Cu-NF was approximately 8 times greater than that of GOx@Cu-NF, with a detection limit of 0.649 μM and a linear range of 5-500 μM. It sustained an average relative activity of 80 % over 20 days. After 10 cycles of repeated use, the activity remained above 75 %. In terms of evaluating the electrode's specificity for glucose, the detection rate for individual similar substances was approximately 1 %. The introduction of a crosslinking strategy to Cu-NF, leading to enhanced mechanical stability and conductivity, improved the detection capability. Furthermore, this approach led to increased long-term storage stability and reusability, allowing for specific glucose detection. To our knowledge, this report represents the first demonstration of a c-GOx@Cu-NF system for integrating electrochemical biosensing devices into digital healthcare pathways, offering enhanced sensing accuracy and mechanical stability., Competing Interests: Declaration of competing interest The authors declare no competing financial interest., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Herein, a comparative study between novel water-soluble phthalocyanine-based biosensors was performed for the application of glucose sensing. For this purpose, two different copper (II) and manganese (III) phthalocyanines and their water-soluble derivatives were synthesized, and then their role as a supporting material for enzyme immobilization was evaluated by comparing their sensor performances. Two different phthalocyanine (AP-OH 2 -MnQ (MnPc) and AP-OH 2 -CuQ (CuPc)) were tested using electrochemical biosensor with immobilized glucose oxidase (GOx). To the best of our knowledge, the related water-soluble phthalocyanine-based glucose biosensors were attempted for the first time, and the developed approach resulted in improved biosensor characteristics. The constructed biosensors GE/MnPc/GOx and GE/CuPc/GOx showed good linearity between 0.003-1.0 mM and 0.05-0.4 mM, respectively. The limit of detection was estimated at 0.0026 mM for the GE/MnPc/GOx and 0.019 mM for the GE/CuPc/GOx. K M app and sensitivity values were also calculated as 0.026 mM and 175.043 µAmM -1 cm -2 for the GE/MnPc/GOx biosensor and 0.178 mM and 117.478 µAmM -1 for the GE/CuPc/GOx biosensor. Moreover, the fabricated biosensors were successfully tested to detect glucose levels in beverages with high recovery results. The present study shows that the proposed water-soluble phthalocyanines could be a good alternative for quick and cheap glucose sensing with improved analytical characteristics.-2 for the GE/CuPc/GOx biosensor. Moreover, the fabricated biosensors were successfully tested to detect glucose levels in beverages with high recovery results. The present study shows that the proposed water-soluble phthalocyanines could be a good alternative for quick and cheap glucose sensing with improved analytical characteristics., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Nowadays, biosensors are gaining increasing interest in foods' and beverages' quality control, owing to their economic production, enhanced sensitivity, specificity, and faster analysis. In particular, colorimetric biosensors can be combined with color recognition applications on smartphones for the detection of analytes, rendering the whole procedure more applicable in everyday life. Herein, chitosan (CS) films were prepared with the deep eutectic solvent (DES) choline chloride/urea/glycerol (ChCl:U:Gly). Glucose oxidase (GOx), a widely utilized enzyme in quality control, was immobilized within CS films through glutaraldehyde (GA), leading to the formation of CS/GOx films. The optimized GOx concentration and DES content were determined for the films. Moreover, the effect of the pH and temperature of the glucose oxidation reaction on the enzymatic activity of GOx was studied. The structure, stability, and specificity of the CS/GOx films as well as the Km values of free and immobilized GOx were also determined. Finally, the analytical performance of the films was studied by using both a spectrophotometer and a color recognition application on a smartphone. The results demonstrated that the films were highly accurate, specific to glucose, and stable when stored at 4 °C for 4 weeks and when reused 10 times, without evident activity loss. Furthermore, the films displayed a good linear response range (0.1-0.8 mM) and a good limit of detection (LOD, 33 μM), thus being appropriate for the estimation of glucose concentration in real samples through a smartphone application.

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 H 2 O 2 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., (© 2024 Wiley-VCH GmbH.)

Fluorescent copper nanoparticles (CuNPs) was synthesized by one-step chemical reduction method using ascorbic acid (AA) and copper sulfate (CuSO 4 ⋅5H 2 O) as raw materials, which had good water solubility and fluorescence properties. A green, simple and safe CuNPs@Fe 2+ fluorescence probe was developed for the detection of hydrogen peroxide and glucose using Fe 2+ as a bridge. The prepared CuNPs could obtain the maximum fluorescence emission wavelength at 440 nm when the excitation wavelength was 360 nm. The average particle size of CuNPs was 10 nm, which had good photobleach resistance, stability and salt tolerance. The fluorescence intensity was quenched due to electron transfer (ET) process when hydrogen peroxide was added to CuNPs@Fe 2+ system. This result was mainly because Fenton reaction occured between hydrogen peroxide and Fe 2+ , producing hydroxyl free radicals (OH) and Fe 3+ . Since glucose could be catalyzed by specific glucose oxidase (GOX) to produce H 2 O 2 and corresponding oxidation products, the quantitative analysis of glucose was realized when glucose oxidase was introduced into the CuNPs@Fe 2+ sensor system. Therefore, a novel CuNPs@Fe 2+ fluorescent probe sensor study was constructed to further achieve quantitative detection of H 2 O 2 and glucose. Under the optimized experimental conditions, the linear ranges for H 2 O 2 and glucose were 28.219-171.562 μM and 1.237-75.771 μM, respectively. And the detection limits for H 2 O 2 and glucose were 7.169 μM and 0.540 μM, respectively. In addition, the mechanism of fluorescence probe quenching caused by the interaction between H 2 O 2 and CuNPs@Fe 2+ was also discussed. The proposed sensing system had been applied successfully to the detection of glucose in human serum samples., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier B.V.)

Glucose oxidase (GOD) is widely used in the pharmaceutical industry, fermentation products and glucose biosensors for its essential role in catalyzing the conversion of glucose to gluconic acid and hydrogen peroxide (H 2 O 2 ). As H 2 O 2 is the by-product and will have a toxic effect on glucose oxidase, so introducing another enzyme that could consume H 2 O 2 to form an enzymatic cascade reaction is a practical solution. However, this decision will lead to extra expenses and complex condition optimization such as the specific mass ratio, temperature and pH to improve the activity, stability and recyclability. Herein, we describe a mild and versatile strategy by anchoring GOD on carboxyl-activated MOF (Cu-TCPP(Fe)) through DNA-directed immobilization (DDI) technology. Robust MOF nanosheets were utilized as not only the carrier for the immobilization of GOD, but also a peroxidase-like catalyst for the decomposition of H 2 O 2 to reduce its harmful impacts. In this work, the immobilized GOD retained 55.78% of its initial activity after being used for 7 times. More than 60% of the immobilized enzyme's catalytic activity was still maintained after 96 h of being stored at 50 ℃. This study provides a new idea for preparing immobilized enzymes with enhanced stability, fast diffusion and high activity, which can be used in fields such as biocatalysis and biotechnology., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier Inc.)

In this work, a novel "turn-on" fluorescence sensor for the detection of H 2 O 2 and glucose was developed based on green fluorescent carbon dots (CDs). The CDs was newly prepared by a facile one-pot hydrothermal method with Eosin Y and branched polyethylenimine as precursors. Interestingly, in the presence of H 2 O 2 and HRP, the fluorescence of the CDs enhanced significantly with a red-shift emission due to their "aggregation". Meanwhile, the oxidation of glucose catalyzed by glucose oxidase could generate H 2 O 2 . Thus, a simple sensing system based on the CDs as fluorescent probes was constructed for H 2 O 2 and glucose determination, avoiding the fluorescence quenching and subsequent recovery process in conventional turn-on strategy. The method showed good selectivity and sensitivity for glucose sensing with the detection limit of 0.12 μM. The method was further applied to glucose detection in real samples. The obtained results demonstrated the simplicity, selectivity and practicality of the method. This work expands the carbon nanomaterials with fluorescence emission enhancement properties. It provides a new and direct "turn-on" strategy for H 2 O 2 and glucose detection, which could be a simple and effective tool for screening biological substances involved in H 2 O 2 -generation reaction., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Diabetes is a chronic disease caused by a decrease in insulin level or insulin resistance. Diabetes also has detrimental effects on the brain, which can lead to the injury of the blood-brain barrier and influence the glucose transport. In this study, we use in vivo electrochemical measurement to explore the glucose variation in the brain of early diabetic mice. The glucose level in mice brain is measured using a carbon fiber microelectrode modified with the osmium-derivatized polymer and glucose oxidase. The electrode shows an excellent electrochemical performance, antibiofouling ability, and high stability, which can work stably in the mice brain for 2 h. By monitoring the glucose level in the brain of normal and diabetic mice after injection of concentrated glucose solution into the abdominal cavity, it is found that the variation of cerebral glucose decreases by ∼2 fold for diabetic mice. It is proposed that diabetes can downregulate the activity of glucose transporter in the brain and finally inhibit the brain glucose uptake.

In recent years, two-dimensional nanosheet metal-organic frameworks (2D MOFs) have been widely considered as promising carriers for enzyme immobilization owing to their large surface area, designable and tunable structures, and other properties that enhance enzyme loading and modulate interactions with enzymes. In this study, a series of ultrathin 2D M-TCPP (M = Co, Ni, Zn, Cu) nanosheets were synthesized employing a surfactant-assisted bottom-up approach, and the effect of solvent ratio on the morphology and properties of 2D MOFs was explored. After systematic characterization, Cu-based 2D MOFs with large specific surface areas and excellent water stability was selected as the carrier for the co-immobilization of glucose oxidase (GOx) and horseradish peroxidase (HRP). The effects of adsorption and covalent immobilization strategies on bis-enzyme loading and enzyme activity, as well as their applications in rapid glucose detection, were systematically investigated. The results showed that A-CTGH and C-CTGH owned enzyme loadings of 187.9 and 249.1 mg/g, respectively, and exhibited superior enzymatic activity when exposed to harsh environments compared to free enzymes. In addition, the covalently immobilized biocatalyst based on GOx demonstrated a more sensitive glucose detection performance, including a wide linear range from 5.0 to 16 μM with a detection limit of 0.6 μM., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier B.V.)

Manipulation and control of cell chemotaxis remain an underexplored territory despite vast potential in various fields, such as cytotherapeutics, sensors, and even cell robots. Herein is achieved the chemical control over chemotactic movement and direction of Jurkat T cells, as a representative model, by the construction of cell-in-catalytic-coat structures in single-cell nanoencapsulation. Armed with the catalytic power of glucose oxidase (GOx) in the artificial coat, the nanobiohybrid cytostructures, denoted as Jurkat [Lipo_GOx] , exhibit controllable, redirected chemotactic movement in response to d-glucose gradients, in the opposite direction to the positive-chemotaxis direction of naïve, uncoated Jurkat cells in the same gradients. The chemically endowed, reaction-based fugetaxis of Jurkat [Lipo_GOx] operates orthogonally and complementarily to the endogenous, binding/recognition-based chemotaxis that remains intact after the formation of a GOx coat. For instance, the chemotactic velocity of Jurkat [Lipo_GOx] can be adjusted by varying the combination of d-glucose and natural chemokines (CXCL12 and CCL19) in the gradient. This work offers an innovative chemical tool for bioaugmenting living cells at the single-cell level through the use of catalytic cell-in-coat structures., (© 2023 Wiley-VCH GmbH.)

Enzyme immobilization on metal-organic frameworks (MOFs) has interested researchers in recent decades due to the outstanding characteristics of MOFs. However, despite some enzyme@MOF composites exhibiting better tolerance, stability and catalysis than free enzymes, boosting the catalytic performance of stimuli-responsive polymer-grafted MOFs composites remains a challenging task. Herein, a glucose oxidase (GOx)-horseradish peroxidase (HRP)@MOF (UiO-66-NH 2 , U)@polymer composite with tunable catalytic ability was constructed by modification with thermo-responsive poly( N -isopropylacrylamide) (PN) via a surface-selective post-synthetic protocol. Temperature increases changed the PN-based soft armour from a "stretch" to a "coil" conformation on the MOF surface, resulting in the confinement effect and boosting the catalytic performance of the GOx-HRP@U@PN composites. Compared with its maximum catalytic reaction rate at 25 °C, the proposed composites showed 18-fold improvement in catalytic performance at 37 °C. Additionally, a colourimetric method for serum glucose analysis was developed using a GOx-HRP-based catalytic cascade reaction with a linear range from 0.1 to 2.0 mM and a low detection limit of 0.03 mM. Remarkably, the surface PN-shell-based soft armour proved to be the key factor for enhancing the catalytic performance of the as-designed composites. The co-immobilization of GOx-HRP onto the thermo-responsive U@PN surface provides a new approach for the development of highly sensitive colourimetric glucose sensing protocols.

Antibacterial dynamic therapy (ADT) triggered by reactive oxygen species (ROS) is promising for diabetic infectious disease treatment. However, the limited local O 2 /H 2 O 2 production and post-treatment inflammation remain long-standing issues. To address these challenges, a novel H 2 -evolving bio-heterojunction enzyme (Bio-HJzyme) consisting of graphite-phase carbon nitride/copper sulfide (CN/Cu 2-x S) heterojunction and glucose oxidase (GOx) is created. The Bio-HJzyme offers glutathione peroxidase (GPx), peroxidase (POD), and catalase (CAT) mimetic activities; provides anti-pathogen properties via programmed light activation; and effectively promotes diabetic wound healing. Specifically, its GPx-mimetic activity and the presence of GOx significantly enhance the yield of H 2 O 2 , which can be catalyzed through POD-mimetic activity to produce highly germicidal •OH. The H 2 O 2 can also be catalyzed to H 2 O and O 2 , assisted by the CAT-mimetic activity. The catalyzed products can then be catalyzed into germicidal •OH and •O 2 - under NIR light irradiation, giving enhanced ADT. Further, CN can split water to form H 2 under solar light, which dramatically suppresses the inflammation caused by excessive ROS. In vivo evaluation confirms that Bio-HJzyme promotes the regeneration of diabetic infectious skin through killing bacteria, enhancing angiogenesis, promoting wound bed epithelialization, and reinforcing anti-inflammatory responses; hence, providing a revolutionary approach for diabetic wounds healing., (© 2023 The Authors. Advanced Science published by Wiley-VCH GmbH.)

Chemiluminescence is widely used for hydrogen peroxide detection, mainly exploiting the highly sensitive peroxidase-luminol-H 2 O 2 system. Hydrogen peroxide plays an important role in several physiological and pathological processes and is produced by oxidases, thus providing a straightforward way to quantify these enzymes and their substrates. Recently, biomolecular self-assembled materials obtained by guanosine and its derivatives and displaying peroxidase enzyme-like catalytic activity have received great interest for hydrogen peroxide biosensing. These soft materials are highly biocompatible and can incorporate foreign substances while preserving a benign environment for biosensing events. In this work, a self-assembled guanosine-derived hydrogel containing a chemiluminescent reagent (luminol) and a catalytic cofactor (hemin) was used as a H 2 O 2 -responsive material displaying peroxidase-like activity. Once loaded with glucose oxidase, the hydrogel provided increased enzyme stability and catalytic activity even in alkaline and oxidizing conditions. By exploiting 3D printing technology, a smartphone-based portable chemiluminescence biosensor for glucose was developed. The biosensor allowed the accurate measurement of glucose in serum, including both hypo- and hyperglycemic samples, with a limit of detection of 120 µmol L -1 . This approach could be applied for other oxidases, thus enabling the development of bioassays to quantify biomarkers of clinical interest at the point of care.

The simple and accurate monitoring of blood glucose level is of great significance for the prevention and control of diabetes. In this work, a magnetic nanozyme was fabricated based on loading nitrogen-doped carbon dots (N-CDs) on mesoporous Fe 3 O 4 nanoparticles for the colorimetric detection of glucose in human serum. Mesoporous Fe 3 O 4 nanoparticles were easily synthesized using a solvothermal method, and N-CDs were then prepared in situ and loaded on the Fe 3 O 4 nanoparticles, leading to a magnetic N-CDs/Fe 3 O 4 nanocomposite. The N-CDs/Fe 3 O 4 nanocomposite exhibited good peroxidase-like activity and could catalyze the oxidation of the colorless enzyme substrate 3,3',5,5'-tetramethylbenzidine (TMB) to blue TMB oxide (ox-TMB) in the presence of hydrogen peroxide (H 2 O 2 ). When the N-CDs/Fe 3 O 4 nanozyme was combined with glucose oxidase (Gox), Gox catalyzed the oxidization of glucose, producing H 2 O 2 and leading to the oxidation of TMB under the catalysis of the N-CDs/Fe 3 O 4 nanozyme. Based on this mechanism, a colorimetric sensor was constructed for the sensitive detection of glucose. The linear range for glucose detection was from 1 to 180 μM, and the limit of detection (LOD) was 0.56 μM. The recovered nanozyme through magnetic separation showed good reusability. The visual detection of glucose was also realized by preparing an integrated agarose hydrogel containing the N-CDs/Fe 3 O 4 nanozyme, glucose oxidase, and TMB. The colorimetric detection platform has an enormous potential for the convenient detection of metabolites.

The inclusion of online, in situ biosensors in microfluidic cell cultures is important to monitor and characterize a physiologically mimicking environment. This work presents the performance of second-generation electrochemical enzymatic biosensors to detect glucose in cell culture media. Glutaraldehyde and ethylene glycol diglycidyl ether (EGDGE) were tested as cross-linkers to immobilize glucose oxidase and an osmium-modified redox polymer on the surface of carbon electrodes. Tests employing screen printed electrodes showed adequate performance in a Roswell Park Memorial Institute (RPMI-1640) media spiked with fetal bovine serum (FBS). Comparable first-generation sensors were shown to be heavily affected by complex biological media. This difference is explained in terms of the respective charge transfer mechanisms. Under the tested conditions, electron hopping between Os redox centers was less vulnerable than H 2 O 2 diffusion to biofouling by the substances present in the cell culture matrix. By employing pencil leads as electrodes, the incorporation of these electrodes in a polydimethylsiloxane (PDMS) microfluidic channel was achieved simply and at a low cost. Under flow conditions, electrodes fabricated using EGDGE presented the best performance with a limit of detection of 0.5 mM, a linear range up to 10 mM, and a sensitivity of 4.69 μA mM -1 cm -2 .

A disposable paper-based glucose biosensor with direct electron transfer (DET) of glucose oxidase (GOX) was developed through simple covalent immobilization of GOX on a carbon electrode surface using zero-length cross-linkers. This glucose biosensor exhibited a high electron transfer rate (ks, 3.363 s -1 ) as well as good affinity (km, 0.03 mM) for GOX while keeping innate enzymatic activities. Furthermore, the DET-based glucose detection was accomplished by employing both square wave voltammetry and chronoamperometric techniques, and it achieved a glucose detection range from 5.4 mg/dL to 900 mg/dL, which is wider than most commercially available glucometers. This low-cost DET glucose biosensor showed remarkable selectivity, and the use of the negative operating potential avoided interference from other common electroactive compounds. It has great potential to monitor different stages of diabetes from hypoglycemic to hyperglycemic states, especially for self-monitoring of blood glucose.

In this study, we developed a glucose fiber sensor incorporating heterodyne interferometry to measure the phase difference produced by the chemical reaction between glucose and glucose oxidase (GOx). Both theoretical and experimental results showed that the amount of phase variation is inversely proportional to glucose concentration. The proposed method provided a linear measurement range of the glucose concentration from 10 mg/dL to 550 mg/dL. The experimental results indicated that the sensitivity is proportional to the length of the enzymatic glucose sensor, and the optimum resolution can be obtained at a sensor length of 3 cm. The optimum resolution of the proposed method is better than 0.6 mg/dL. Moreover, the proposed sensor demonstrates good repeatability and reliability. The average relative standard deviation (RSD) is better than 10% and satisfied the minimum requirement for point-of-care devices.

A highly sensitive, biocompatible, and scalable phosphorescent oxygen sensor formulation is designed and evaluated for use in continuous metabolite sensors for biological systems. Ethyl cellulose (EC) and polystyrene (PS) nanoparticles (NPs) stabilized with Pluronic F68 (PF 68), Polydimethylsiloxane-b-polyethyleneglycol methyl ether (PDMS-PEG), sodium dodecylsulfate (SDS), and cetyltimethylammonium bromide (CTAB) were prepared and studied. The resulting NPs with eight different surfactant−polymer matrix combinations were evaluated for physical properties, oxygen sensitivity, effect of changes in dispersion matrix, and cytotoxicity. The EC NPs exhibited a narrower size distribution and 40% higher sensitivity than PS, with Stern−Volmer constants (Ksv) 0.041−0.052 µM−1 for EC, compared to 0.029−0.034 µM−1 for PS. Notably, ethyl cellulose NPs protected with PF68 were selected as the preferred formulation, as they were not cytotoxic towards 3T3 fibroblasts and exhibited a wide phosphorescence lifetime response of >211.1 µs over 258−0 µM and ~100 µs over 2.58−0 µM oxygen, with a limit of detection (LoD) of oxygen in aqueous phase of 0.0016 µM. The EC-PF68 NPs were then efficiently encapsulated in alginate microparticles along with glucose oxidase (GOx) and catalase (CAT) to form phosphorescent nanoparticles-in-microparticle (NIMs) glucose sensing microdomains. The fabricated glucose sensors showed a sensitivity of 0.40 µs dL mg−1 with a dynamic phosphorescence lifetime range of 46.6−197.1 µs over 0−150 mg dL−1 glucose, with a glucose LoD of 18.3 mg dL−1 and maximum distinguishable concentration of 111.1 mg dL−1. Similarly, lactate sensors were prepared with NIMs microdomains containing lactate oxidase (LOx) and found to have a detection range of 0−14 mg dL−1 with LoD of 1.8 mg dL−1 and maximum concentration of 13.7 mg dL−1 with lactate sensitivity of 10.7 µs dL mg−1. Owing to its versatility, the proposed NIMs-based design can be extended to a wide range of metabolites and different oxygen-sensing dyes with different excitation wavelengths based on specific application.

Background: Blood gas analyzers employing glucose-oxidase biosensors under-recover glucose when pO 2 is low. The manufacturer of the GEM®Premier™ series of analyzers introduced an algorithm to detect specimens at risk of low pO 2 interference. We investigated the reliability of this algorithm., Methods: Whole blood specimens were tested by GEM®Premier™ 4000 (GEM 4000) and 5000 (GEM 5000). Specimens with an incalculable ("incalc") error code for glucose result or that had a glucose ≥ 20 mmol/L were retested on a second analyzer of the same type within 5 min over the course of 30 months in 5 hospitals in Calgary, Alberta. Discordant retests were defined as either: 1) paired numeric results with a difference >10 %, or 2) an "incalc" code that yielded a numeric result upon retesting. Glucose recovery in relation to pO 2 level was assessed by comparing specimens experimentally depleted of pO 2 between GEM 5000 and a laboratory analyzer (Siemens Vista®)., Results: Of 1,776 glucose tests repeated on the GEM 5000 or 1,544 on GEM 4000, 10% were discordant. GEM 5000 produced twice as many discordant numeric retests versus the GEM 4000 [5.9% (98/1,651) vs 2.7% (38/1,391)]. The majority of "incalc" error codes repeated with a numeric glucose result on both GEM analyzers [(79.7% (122/153) vs 75.2% (94/125)]. Among specimens experimentally depleted of pO 2, the GEM 5000 under-recovered glucose by up to 30% compared to the Siemens Vista and were not flagged by an "incalc" code., Conclusions: The algorithm in the GEM®Premier TM series of analyzers that flags specimens at risk for glucose under-recovery due to low pO 2 does not reliably detect specimens at risk for glucose under-recovery., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 The Canadian Society of Clinical Chemists. Published by Elsevier Inc. All rights reserved.)

Aberrant cerebral glucose metabolism is related to many brain diseases, especially brain tumor. However, it remains challenging to measure the dynamic changes in cerebral glucose. Here, we developed a near-infrared (NIR) optical transducer to sensitively monitor the glucose variations in cerebrospinal fluid in vivo. The transducer consists of an oxygen-sensitive nanoparticle combined with glucose oxidase (GOx), yielding highly sensitive NIR phosphorescence in response to blood glucose change. We demonstrated long-term continuous glucose monitoring by using the NIR transducer. After subcutaneous implantation, the glucose transducer provides a strong luminescence signal that can continuously monitor blood glucose fluctuations for weeks. By using the NIR emission of the transducer, we further observed abnormal dynamic changes in cerebrospinal fluid glucose and quantitatively assessed cerebral glucose uptake rates in transgenic mice bearing brain tumors. This study provides a promising method for the diagnosis of various metabolic diseases with altered glucose metabolism.

It is generally accepted that glucose oxidase (GOx) shows unique specificity in β-d-glucose catalysis. However, it has been found that GOx can catalyze diverse monosaccharides. Therefore, the sensing accuracy for glucose biosensors using GOx as probes will be largely compromised by the presence of other monosaccharides. Herein, multifunctional bi-nanospheres (Fe 3 O 4 @Au NCs), which show both peroxidase-like and catalase-like catalytic activities in different working conditions, are successfully constructed and served as desirable platform with huge surface area for the immobilization of large amount of GOx probes. In acidic environment, hydroxyl radicals could be generated via the cascaded catalysis of β-d-glucose by Fe 3 O 4 @Au-GOx, and then employed to initiate the polymerization of boric acid derivative to prepare molecularly imprinted polymers (MIPs) on the surface of GOx using β-d-glucose as template. Then, the molecularly imprinted GOx are immobilized on the surface of highly oriented pyrolytic graphite (HOPG) electrode and an electrochemical biosensor (Fe 3 O 4 @Au-GOx-HOPG) for glucose sensing is successfully obtained. Interestingly, the as-prepared biosensors could selectively detect glucose in the range of 10.0 μM - 5.0 mM with a LOD = 5.0 μM with the help of MIPs, which is comparable or better than other glucose sensors reported recently., (Copyright © 2022. Published by Elsevier B.V.)

In recent years, many efforts have been made to develop rapid, sensitive and user-friendly glucose biosensors for monitoring blood glucose concentration in patients. In this study, the electrochemical glucose biosensors based on graphite rod (GR) electrode electrochemically modified with dendritic gold nanostructures (DGNs) and glucose oxidase (GOx) were developed. Phenazine methosulfate was used as a soluble redox mediator. Three GOx immobilization methods: adsorption on DGNs and cross-linking with glutaraldehyde (GA) vapour (GA-GOx/DGNs/GR), covalent immobilization on DGNs modified with 11-mercaptoundecanoic acid self-assembled monolayer (SAM) (GOx-SAM/DGNs/GR) and covalent immobilization on SAM with additional cross-linking with GA vapour (GA-GOx-SAM/DGNs/GR), were used. It was determined that GA significantly improved the stability of the enzyme layer. The difference of maximal current generated during the enzymatic reaction (Δ I max ) equal to 272.06 ± 8.69 µA was obtained using a biosensor based on GA-GOx/DGNs/GR electrodes. However, the highest Δ I max equal to 384.20 ± 16.06 µA was obtained using GA-GOx-SAM/DGNs/GR electrode. Δ I max for biosensors based on the GA-GOx-SAM/DGNs/GR electrode was 1.41 times higher than for the GA-GOx/DGNs/GR, whereas the linear dynamic range from 0.1 to 10 mM was the same using all three GOx immobilization methods. The limit of detection using GA-GOx-SAM/DGNs/GR and GA-GOx/DGNs/GR electrodes was 0.019 and 0.022 mM, respectively. The ability to detect glucose in the serum by developed biosensors was evaluated.

Whey protein isolate (WPI) was modified by a ternary system containing horseradish peroxidase, glucose oxidase and d-glucose through the one- and two-step protocols, yielding two respective crosslinked products MWPI-1 and MWPI-2 with the enhanced relative dityrosine contents (127.4 and 101.0). Compared with WPI, both MWPI-1 and MWPI-2 had much ordered secondary structure, increased disulfide-bond contents, average particle sizes, surface hydrophobicity, oil-binding capacity, emulsification and thermal stability, but reduced free sulfhydryl groups contents and in vitro digestibility. Moreover, both MWPI-1 and MWPI-2 in dispersions showed higher apparent viscosity, larger viscoelastic moduli than WPI, together with the lower gelling temperatures (67.1 °C and 70.1 °C versus 73.6 °C). Overall, MWPI-1 with a higher crosslinking extent consistently exhibited more remarkable property alteration. It is concluded that the ternary system is an effective approach when aiming to modify secondary structure especially these properties of WPI, such as aggregation, emulsification, gelation, rheology and thermal stability., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Redox enzymes are capable of harvesting electrical energy from biofuels in high catalytic activity and under mild condition. However, it is difficult to achieve efficient electron transfer and deep oxidation of biofuels simultaneously in a single-enzyme catalytic system. Herein, we report a hybrid catalyst cascade consisting of an organic oxidation catalyst, 2,2,6,6-tetramethyl-1-piperidine N-oxyl (TEMPO), and an enzyme, glucose oxidase (GOx), for electrochemical oxidation of glucose. It is found that TEMPO is capable of mediating electron transfer between the redox center of GOx and the electrode surface. While glucose can be oxidized into glucuronic acid under neutral conditions. Thus, combining GOx and TEMPO, we are able to achieve 4e - electrooxidation of glucose using the hybrid enzymatic and organic cascade (HEOC) system. When coupled with an air-breathing Pt cathode, the resulting glucose/air biofuel cell using the proposed HEOC anode exhibits a maximum power density of 38.1 μW cm -2 with a short-circuit current of 651.4 μA cm -2 , which can be attributed to the enhanced energetic efficiency, enabling TEMPO a promising catalyst for glucose oxidation in bioelectronics applications., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021. Published by Elsevier B.V.)

An accurate measurement of sweat glucose is a promising alternative to invasive finger prick blood test, and may provide effective self-monitoring of blood glucose with good patient compliance. Herein, an interrelated catalytic enzyme system has been developed, termed as CataFlower, which is composed of nanoflower MoS 2 (peroxidase) decorated with GOx (glucose oxidase) and MnO 2 (oxygen generator), and exhibits synergistic oxidative capability for sensitively monitoring sweat glucose. CataFlower can not only generate oxygen in situ to maximize GOx activity, but promote peroxidase-triggered H 2 O 2 oxidation of methylene blue, resulting in sensitive colorimetric detection of glucose. We identify that CataFlower can precisely detect glucose with a detection limit of 10 μM, allowing for measuring glucose levels in different biological samples, such as blood and urine. Particularly, CataFlower is capable of monitoring dynamic changes in sweat glucose with high sensitivity and accuracy during exercise. Therefore, CataFlower provides a stepping stone to eliminate invasive blood tests, significantly improving the diagnosis and management of diabetes mellitus., (Copyright © 2021 Elsevier B.V. All rights reserved.)

A chemiluminescence (CL) sensor was constructed for the one-step determination of glucose. Glucose oxidase (GOx) was successfully encapsulated into Zn-doped zeolitic imidazolate framework-67 (Zn-ZIF-67) via a simple one-pot strategy. The as-prepared GOx@Zn-ZIF-67 nanocomposite can trigger cascade reactions of glucose oxidation to generate H 2 O 2 and H 2 O 2 -mediated luminol reaction to give an intense CL emission. The sensor responds linearly to glucose in the 20.0-400.0 μmol·L -1 range with a limit of detection (LOD) of 4.7 μmol·L -1 . Eleven replicated measurements of 200.0 μmol·L -1 glucose solution gives a relative standard deviation (RSD) of 1.7%. The sensor exhibits good selectivity and stability and was successfully applied to the determination of glucose in real human serum samples. Schematic representation of one-step determination of serum glucose with GOx@Zn-ZIF-67 nanocomposite triggering cascade reactions between luminol and glucose., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.)

The assessment of blood glucose levels is necessary for the diagnosis and management of diabetes. The accurate quantification of serum or plasma glucose relies on enzymatic and nonenzymatic methods utilizing electrochemical biosensors. Current research efforts are focused on enhancing the non-invasive detection of glucose in sweat with accuracy, high sensitivity, and stability. In this work, nanostructured mesoporous carbon coupled with glucose oxidase (GO x ) increased the direct electron transfer to the electrode surface. A mixed alloy of CuNi nanoparticle-coated mesoporous carbon (CuNi-MC) was synthesized using a hydrothermal process followed by annealing at 700 °C under the flow of argon gas. The prepared catalyst's crystal structure and morphology were explored using X-ray diffraction and high-resolution transmission electron microscopy. The electrocatalytic activity of the as-prepared catalyst was investigated using cyclic voltammetry (CV) and amperometry. The findings show an excellent response time of 4 s and linear range detection from 0.005 to 0.45 mM with a high electrode sensitivity of 11.7 ± 0.061 mA mM cm -2 in a selective medium.

Metformin is a clinically-approved anti-diabetic drug with emerging antitumor potential, but its antitumor activity is highly susceptible to local glucose abundance. Herein, we construct a nanotherapeutic platform based on biocompatible constituents to sensitize tumor cells for metformin therapy via cooperative glucose starvation. The nanoplatform was synthesized through the spontaneous biomineralization of glucose oxidase (GOx) and metformin in amorphous calcium phosphate nanosubstrate, which was further modified with polyethylene glycol and cRGD ligands. This biomineralized nanosystem could efficiently deliver the therapeutic payloads to tumor cells in a targeted and bioresponsive manner. Here GOx could catalyze the oxidation of glucose into gluconic acid and H 2 O 2 , thus depleting the glucose in tumor intracellular compartment while accelerating the release of the entrapped therapeutic payloads. The selective glucose deprivation would not only disrupt tumor energy metabolism, but also upregulate the PP2A regulatory subunit B56δ and sensitize tumor cells to the metformin-induced CIP2A inhibition, leading to efficient apoptosis induction via PP2A-GSK3β-MCL-1 axis with negligible side effects. This study may offer new avenues for targeted tumor therapy in the clinical context., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

This work focuses on the synthesis of novel modified core-shell CdTe/CdS quantum dots (QDs) and develops as a fluorescence sensor for glucose determination. The (E)-2,2'-(4,4'-dioxo-2,2'-dithioxo-2H,2'H-[5,5'-bithiazolylidene]-3,3'(4H,4'H)-diyl)bis(3- mercaptopropanoic acid) (DTM) as a new derivative of thiazolidine was synthesized and characterized and used to surface-modification of CdTe/CdS QDs. DTM-capped CdTe/CdS QDs used to immobilization of glucose oxidase (GOD). The intensity fluorescence emission of the CdSe/CdS-DTM/GOD is highly sensitive to the concentration of H 2 O 2 as a byproduct of the catalytic oxidation of glucose. The experimental results showed that the quenched fluorescence was proportional to the glucose concentration within the range of 10 nM-0.32 μM under optimized experimental conditions. The limit of detection of this system was found to be 4.3 nM. Compared with most of the existing methods, this newly developed system possesses many advantages, including simplicity, low cost, and good sensitivity., (© 2021. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

The electrochemical biosensor devices based on enzymes for monitoring biochemical substances are still considered attractive. We investigated the immobilization of glucose oxidase (GOx) on a new composite nanomaterial poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT:PSS)/titanium carbide,(Ti 3 C 2 )/graphene quantum dots(GQD) modified screen-printed carbon electrode (SPCE) for glucose sensing. The characterization and electrochemical behavior of PEDOT:PSS/Ti 3 C 2 /GQD towards the electrocatalytic oxidation of GOx was analyzed by FTIR, XPS, SEM, cyclic voltammetry (CV), and differential pulse voltammetry (DPV). This composite nanomaterial was found to tend to increase the electrochemical behavior and led to a higher peak current of 100.17 µA compared to 82.01 µA and 95.04 µA for PEDOT:PSS and PEDOT:PSS/Ti 3 C 2 alone. Moreover, the detection results demonstrated that the fabricated biosensor had a linear voltammetry response in the glucose concentration range 0-500 µM with a relatively sensitivity of 21.64 µAmM -1 cm -2 and a detection limit of 65 µM (S/N = 3), with good stability and selectivity. This finding could be useful as applicable guidance for the modification screen printed carbon (SPCE) electrodes focused on composite PEDOT:PSS/Ti 3 C 2 /GQD for efficient detection using an enzyme-based biosensor.

In this study, ratiometric fluorescent glucose and lactate biosensors were developed using a ratiometric fluorescent oxygen-sensing membrane immobilized with glucose oxidase (GOD) or lactate oxidase (LOX). Herein, the ratiometric fluorescent oxygen-sensing membrane was fabricated with the ratio of two emission wavelengths of platinum meso-tetra (pentafluorophenyl) porphyrin (PtP) doped in polystyrene particles and coumarin 6 (C6) captured into silica particles. The operation mechanism of the sensing membranes was based on (i) the fluorescence quenching effect of the PtP dye by oxygen molecules, and (ii) the consumption of oxygen levels in the glucose or lactate oxidation reactions under the catalysis of GOD or LOX. The ratiometric fluorescent glucose-sensing membrane showed high sensitivity to glucose in the range of 0.1-2 mM, with a limit of detection (LOD) of 0.031 mM, whereas the ratiometric fluorescent lactate-sensing membrane showed the linear detection range of 0.1-0.8 mM, with an LOD of 0.06 mM. These sensing membranes also showed good selectivity, fast reversibility, and stability over long-term use. They were applied to detect glucose and lactate in artificial human serum, and they provided reliable measurement results.

A biosensing membrane base on ferulic acid and glucose oxidase is synthesized onto a carbon paste electrode by electropolymerization via cyclic voltammetry in aqueous media at neutral pH at a single step. The developed biosensors exhibit a linear response from 0.082 to 34 mM glucose concentration, with a coefficient of determination R 2 equal to 0.997. The biosensors display a sensitivity of 1.1 μAmM -1 cm -2 , a detection limit of 0.025 mM, and 0.082 mM as glucose quantification limit. The studies reveal stable, repeatable, and reproducible biosensors response. The results indicate that the novel poly-ferulic acid membrane synthesized by electropolymerization is a promising method for glucose oxidase immobilization towards the development of glucose biosensors. The developed glucose biosensors exhibit a broader linear glucose response than other polymer-based glucose biosensors.

Glucose starvation has emerged as a therapeutic strategy to inhibit tumor growth by regulating glucose metabolism. However, the rapid proliferation of cancer cells could induce the hypoxic tumor microenvironment (TME) which limits the therapeutic efficacy of glucose starvation by vascular isomerization. Herein, we developed a "dual-lock" supramolecular nanomedicine system for synergistic cancer therapy by integrating glucose oxidase (GOx) induced starvation and hypoxia-activated gene therapy. The host-guest interactions (that mediate nano-assembly formation) and hypoxia-activatable promoters act as two locks to keep glucose oxidase (GOx) and a therapeutic plasmid (RTP801::p53) inside supramolecular gold nanovesicles (Au NVs). Upon initial dissociation of the host-guest interactions and hence Au NVs by cancer-specific reactive oxygen species (ROS), GOx is released to consume glucose and oxygen, generate H2O2 and induce the hypoxic TME, which act as the two keys for triggering burst payload release and promoter activation, thus allowing synergistic starvation and gene therapy of cancer. This "dual-lock" supramolecular nanomedicine exhibited integrated therapeutic effects in vitro and in vivo for tumor suppression.

A "closed-loop" insulin delivery system that can mimic the dynamic and glucose-responsive insulin secretion as islet β-cells is desirable for the therapy of type 1 and advanced type 2 diabetes mellitus (T1DM and T2DM). Herein, we introduced a kind of "core-shell"-structured glucose-responsive nanoplatform to achieve intravenous "smart" insulin delivery. A finely controlled one-pot biomimetic mineralization method was utilized to coencapsulate insulin, glucose oxidase (GOx), and catalase (CAT) into the ZIF-8 nanoparticles (NPs) to construct the "inner core", where an efficient enzyme cascade system (GOx/CAT group) served as an optimized glucose-responsive module that could rapidly catalyze glucose to yield gluconic acid to lower the local pH and effectively consume the harmful byproduct hydrogen peroxide (H 2 O 2 ), inducing the collapse of pH-sensitive ZIF-8 NPs to release insulin. The erythrocyte membrane, a sort of natural biological derived lipid bilayer membrane which has intrinsic biocompatibility, was enveloped onto the surface of the "inner core" as the "outer shell" to protect them from elimination by the immune system, thus making the NPs intravenously injectable and could stably maintain a long-term existence in blood circulation. The in vitro and in vivo results indicate that our well-designed nanoplatform possesses an excellent glucose-responsive property and can maintain the blood glucose levels of the streptozocin (STZ)-induced type 1 diabetic mice at the normoglycemic state for up to 24 h after being intravenously administrated, confirming an intravenous insulin delivery strategy to overcome the deficits of conventional daily multiple subcutaneous insulin administration and offering a potential candidate for long-term T1DM treatment.

Chiral carbon dots (CDs) integrated the advantages of achiral CDs and the unique chiral property, which expand the prospect of the biological applications of CDs. However, the structure control and the origin of chirality for chiral CDs remain unclear. Herein, chiral CDs were obtained by thermal polymerization of chiral amino acids and citric acid, and their handedness of chirality could be controlled by adjusting the reaction temperature, which leads to different kinds of surface modifications. With aliphatic amino acids as a chiral source, all of the CDs that reacted at different temperatures (90-200 °C) have the same handedness of the chiral source. But with aromatic amino acids as a chiral source, CDs with maintained or inversed handedness compared with the chiral source could be obtained by adjusting the reaction temperature. Below a temperature of 120 °C, the chiral source was modified with CDs by esterification and transferred the handedness of chirality; at high temperatures (above 150 °C), which mainly connected by amidation accompanying with the formation of rigid structure generated by the π conjugation between the aromatic nucleus of chiral source and the carbon core of CDs, caused the inversing of the chiral signal. Further, we investigated the chiral effects of CDs on the glucose oxidase activity for a highly sensitive electrochemical biosensor.

Impaired glucose metabolism in diabetes causes severe acute and long-term complications, making real-time detection of blood glucose indispensable for diabetic patients. Existing continuous glucose monitoring systems are unsuitable for long-term clinical glycemic management due to poor long-term stability. Polymer dot (Pdot) glucose transducers are implantable optical nanosensors that exhibit excellent brightness, sensitivity, selectivity, and biocompatibility. Here, it is shown that hydrogen peroxide-a product of glucose oxidation in Pdot glucose sensors-degrades sensor performance via photobleaching, reduces glucose oxidase activity, and generates cytotoxicity. By adding catalase to a glucose oxidase-based Pdot sensor to create an enzymatic cascade, the hydrogen peroxide product of glucose oxidation is rapidly decomposed by catalase, preventing its accumulation and improving the sensor's photostability, enzymatic activity, and biocompatibility. Thus, a next-generation Pdot glucose transducer with a multienzyme reaction system (Pdot-GOx/CAT) that provides excellent sensing characteristics as well as greater detection system stability is presented. Pdot glucose transducers that incorporate this enzymatic cascade to eliminate hydrogen peroxide will possess greater long-term stability for improved continuous glucose monitoring in diabetic patients., (© 2020 Wiley-VCH GmbH.)

Biofuel cells allow for constructing sensors that leverage the specificity of enzymes without the need for an external power source. In this work, we design a self-powered glucose sensor based on a biofuel cell. The redox enzymes glucose dehydrogenase (NAD-GDH), glucose oxidase (GOx), and horseradish peroxidase (HRP) were immobilized as biocatalysts on the electrodes, which were previously engineered using carbon nanostructures, including multi-wall carbon nanotubes (MWCNTs) and reduced graphene oxide (rGO). Additional polymers were also introduced to improve biocatalyst immobilization. The reported design offers three main advantages: (i) by using glucose as the substrate for the both anode and cathode, a more compact and robust design is enabled, (ii) the system operates under air-saturating conditions, with no need for gas purge, and (iii) the combination of carbon nanostructures and a multi-enzyme cascade maximizes the sensitivity of the biosensor. Our design allows the reliable detection of glucose in the range of 0.1-7.0 mM, which is perfectly suited for common biofluids and industrial food samples.

We report on the fabrication of a microneedle-based electrochemical biosensor for use in transdermal biosensing, which includes a screen-printed electrode containing a Prussian blue-gold nanohybrid as the working electrode. The Prussian blue gold nanohybrid is made from polyethylenime (PEI)- mediated simultaneous synthesis of Prussian blue (PBNP) and gold nanoparticles (AuNP), which forms a PBNP-AuNP nanohybrid with a remarkable change in the Prussian blue character. PEI-protected polycrystalline PBNPs can be synthesized in acidic media from the single precursor potassium ferricyanide [K 3 Fe(CN) 6 ] at 60°C. Since PEI also enables the controlled formation of gold nanoparticles (AuNPs) in the presence of formaldehyde, nanohybrids containing PBNPs and AuNPs may be prepared. Two different methods of PEI mediated synthesis of AuNP in the presence of PBNP were considered. In Method 1, AuNP and PBNP were made independently and mixed together in an appropriate ratio. In Method 2, PBNPs were made first, followed by PEI- and formaldehyde-mediated reduction of gold cations in the presence of PBNP. PBNP-AuNPs display a remarkable change in Prussian blue behavior such that the absorption maxima of PBNP-AuNPs made through Method 1 tend to increase at 670 nm as a function of gold concentration as compared with the control; the reverse was observed when PBNP-AuNPs were made through Method 2. As made PBNPs and PBNP-AuNPs made through Method 1 display excellent catalytic activity toward both reduction and oxidation of hydrogen peroxide based on peroxidase mimetic activity. In addition, the as-synthesized PBNPs displayed superparamagnetic behavior that can be manipulated in the presence of AuNPs. The results from peroxidase mimetic activity, chemiluminescence, cyclic voltammetry, and amperometry showed suitable analytical performance of the as-made PBNP-AuNP nanohybrid for biomedical applications., (© 2020 Wiley Periodicals LLC.)

Background and Aims: Blood glucose measurement is central to the diagnosis and management of patients with diabetes. Considering that a clinician relies heavily on blood (or rarely other body fluid) glucose values for decision making, an understanding of the basic aspects of glucose measurement in body fluids is necessary., Methods: A literature search was conducted in PubMed for articles in English on measurement of glucose in body fluids., Results: Glucose can be measured in several body fluids, namely blood, interstitial fluid, urine, cerebrospinal fluid, pleural fluid and ascitic fluid in appropriate clinical settings. For blood glucose measurement, the present-day enzymatic methods have replaced the older reducing and condensation methods on account of their better accuracy. It is important to consider preanalytical factors such as sample collection, storage and transport when analyzing a laboratory blood glucose report. The measurement of glucose in interstitial fluid using continuous glucose monitoring system (CGMS) enables better understanding of glucose trends and fluctuations. The CGMS data should be reported using standard metrics which include parameters such as mean 24-h glucose, glycemic variability and time-in, below and above range. The measurement of glucose in urine sample is rarely ever used these days and should be reserved for exceptional circumstances., Conclusion: This review provides a detailed account of various aspects of glucose measurement including their evolution, pitfalls, and their utility in current clinical practice., Competing Interests: Declaration of competing interest The authors declare no conflicts of interest., (Copyright © 2020 Diabetes India. Published by Elsevier Ltd. All rights reserved.)

In the context of an integrated Lab-on-PCB wearable patch extracting interstitial fluid from the patient via integrated microneedles, the requirements from the integrated biosensing part are quite special compared to static glucose electrochemical biosensors. Hence, in this study, a fully PCB-integrated enzymatic glucose quantification Lab-on-Chip device is presented and evaluated considering these special requirements for such a patch implementation: a) range and limit of detection compatible with interstitial fluid glucose levels of diabetic patients and b) effect of sample flow rate on the biosensing platform performance. This work employs a chronoamperometric approach for glucose detection based on covalently immobilized glucose oxidase on PCB-integrated electrodes. The chronoamperometric measurements show that this platform exhibits μM range sensitivity, high specificity, and good reproducibility, and the assay can detect glucose from 10 μM to 9 mM with a lower limit of detection of 10 μM. The demonstrated detection range under continuous flow proved compatible with interstitial fluid glucose levels of diabetic patients. The sample-to-answer time of our Lab-on-PCB device is less than 1 min (sample delivery of few seconds and 20 s for electrochemical measurement), employing sample volumes of 50 μL in this instance. Increased flow rates substantially improve the platform sensitivity (1.1 μA/mM @0 μL/min to 6.2 μA/mM @10 μL/min), with the measured current increasing exponentially to the flow rate, as opposed to the theoretically expected much lower dependence. This work demonstrates the feasibility of Lab-on-PCB patches in terms of biosensing performance, paving the way for the first cost-effective, painless diabetes management microsystem., (Copyright © 2020 Elsevier B.V. All rights reserved.)

The monosaccharide 1,5-anhydroglucitol (1,5-AG) is a known indicator of glucose levels. Conventional 1,5-AG quantification methods with enzyme-based sensors using pyranose oxidase (PROD) require elimination of interference from the sample (a laborious and time-consuming process), as PROD cannot distinguish 1,5-AG from other sugars. We developed a one-step paper-based sensor for detecting 1,5-AG using glucose oxidase, catalase, and mutarotase that eliminates excess glucose, which interferes with 1,5-AG detection. This sensor consists of two compartments for the quantification of glucose and 1,5-AG and reflects the concentration of these targets after reaction with water or spiked human urine. The limit of detection of the sensor was 0.9 mg dL-1 for glucose and 3.2 μg mL-1 for 1,5-AG.

Organic semiconductors and conducting polymers are the most promising next-generation conducting materials for electrochemical biosensors as the greener and cheaper alternative for electrodes based on transition metals or their oxides. Therefore, polycarbazole as the organic semiconducting polymer was electrochemically synthesized and deposited on working electrode. Structure and semiconducting properties of polycarbazole have theoretically and experimentally been analyzed and proved. For these electrochemical systems, a maximal sensitivity of 14 μA·cm -2 ·mM -1 , a wide linear range of detection up to 5 mM, and a minimal limit of detection of around 0.2 mM were achieved. Moreover, Michaelis's constant of these sensors depends not only on the enzyme but on the material of electrode and applied potential. The electrocatalytic mechanism and performance of the non- and enzymatic sensors based on this material as a conducting layer have been discussed by estimating pseudocapacitive and faradaic currents and by adding glucose as an analyte at the different applied potentials. In this work, the attention was focused on the electrochemical origin and mechanism involved in the non- and enzymatic oxidation and reduction of glucose.

Herein, a novel electrochemical glucose biosensor based on glucose oxidase (GOx) immobilized on a surface containing platinum nanoparticles (PtNPs) electrodeposited on poly(Azure A) (PAA) previously electropolymerized on activated screen-printed carbon electrodes (GOx-PtNPs-PAA-aSPCEs) is reported. The resulting electrochemical biosensor was validated towards glucose oxidation in real samples and further electrochemical measurement associated with the generated H 2 O 2 . The electrochemical biosensor showed an excellent sensitivity (42.7 μA mM -1 cm -2 ), limit of detection (7.6 μM), linear range (20 μM-2.3 mM), and good selectivity towards glucose determination. Furthermore, and most importantly, the detection of glucose was performed at a low potential (0.2 V vs. Ag). The high performance of the electrochemical biosensor was explained through surface exploration using field emission SEM, XPS, and impedance measurements. The electrochemical biosensor was successfully applied to glucose quantification in several real samples (commercial juices and a plant cell culture medium), exhibiting a high accuracy when compared with a classical spectrophotometric method. This electrochemical biosensor can be easily prepared and opens up a good alternative in the development of new sensitive glucose sensors.

Glucose concentration is an important parameter in biomedicine since glucose is involved in many metabolic pathways in organisms. Many methods for glucose detection have been developed for use in various applications, particularly in the field of healthcare in diabetics. In this study, ratiometric fluorescent glucose-sensing membranes were fabricated based on the oxygen levels consumed in the glucose oxidation reaction under the catalysis of glucose oxidase (GOD). The oxygen concentration was measured through the fluorescence quenching effect of an oxygen-sensitive fluorescent dye like platinum meso-tetra (pentafluorophenyl) porphyrin (PtP) by oxygen molecules. Coumarin 6 (C6) was used as a reference dye in the ratiometric fluorescence measurements. The glucose-sensing membrane consisted of two layers: The first layer was the oxygen-sensing membrane containing polystyrene particles (PS) doped with PtP and C6 (e.g., PS@C6^PtP) in a sol-gel matrix of aminopropyltrimethoxysilane and glycidoxypropyltrimethoxysilane (GA). The second layer was made by immobilizing GOD onto one of three supporting polymers over the first layer. These glucose-sensing membranes were characterized in terms of their response, reversibility, interferences, and stability. They showed a wide detection range to glucose concentration in the range of 0.1 to 10 mM, but high sensitivity with a linear detection range of 0.1 to 2 mM glucose. This stable and sensitive ratiometric fluorescent glucose biosensor provides a reliable way to determine low glucose concentrations in blood serum by measuring tear glucose.

The subject of the submitted work is the proposal of electrodes for the continual measurement of the glucose concentration for the purpose of specifying further hemodynamic parameters. The proposal includes the design of the electronic measuring system, the construction of the electrodes themselves and the functionality of the entire system, verified experimentally using various electrode materials. The proposed circuit works on the basis of micro-ammeter measuring the size of the flowing electric current and the electrochemical measurement method is used for specifying the glucose concentration. The electrode system is comprised of two electrodes embedded in a silicon tube. The solution consists of the measurement with three types of materials, which are verified by using three solutions with a precisely given concentration of glucose in the form of a mixed solution and enzyme glucose oxidase. For the testing of the proposed circuit and the selection of a suitable material, the testing did not take place on measurements in whole blood. For the construction of the electrodes, the three most frequently used materials for the construction of electrodes used in clinical practice for sensing biopotentials, specifically the materials Ag/AgCl, Cu and Au, were used. The performed experiments showed that the material Ag/AgCl, which had the greatest sensitivity for the measurement even without the enzyme, was the most suitable material for the electrode. This conclusion is supported by the performed statistical analysis. On the basis of the testing, we can come to the conclusion that even if the Ag/AgCl electrode appears to be the most suitable, showing high stability, gold-plated electrodes showed stability throughout the measurement similarly to Ag/AgCl electrodes, but did not achieve the same qualities in sensitivity and readability of the measured results.

Biosensors based on Organic Electrochemical Transistors (OECTs) are developed for the selective detection of glucose and lactate. The transistor architecture provides signal amplification (gain) with respect to the simple amperometric response. The biosensors are based on a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) channel and the gate electrode is functionalised with glucose oxidase (GOx) or lactate oxidase (LOx) enzymes, which are immobilised within a Ni/Al Layered Double Hydroxide (LDH) through a one-step electrodeposition procedure. The here-designed OECT architecture allows minimising the required amount of enzyme during electrodeposition. The output signal of the biosensor is the drain current ( I ), which decreases as the analyte concentration increases. In the optimised conditions, the biosensor responds to glucose in the range of 0.1-8.0 mM with a limit of detection (LOD) of 0.02 mM. Two regimes of proportionality are observed. For concentrations lower than 1.0 mM, a linear response is obtained with a mean gain of 360, whereas for concentrations higher than 1.0 mM, d is proportional to the logarithm of glucose concentration, with a gain of 220. For lactate detection, the biosensor response is linear in the whole concentration range (0.05-8.0 mM). A LOD of 0.04 mM is reached, with a net gain equal to 400.I d is proportional to the logarithm of glucose concentration, with a gain of 220. For lactate detection, the biosensor response is linear in the whole concentration range (0.05-8.0 mM). A LOD of 0.04 mM is reached, with a net gain equal to 400., Competing Interests: The authors declare no conflict of interest.

The fabricating of metal oxide thin films onto conducting surfaces continues to grow and their potential applications as surfaces for biosensor applications is of paramount importance. The correct orientation of glucose oxidase redox enzymes yields very important biointerfaces capable of selectively detecting d-glucose as a measure of blood sugar for healthy and diabetic sick patients. The electrodeposition of redox enzymes, such as glucose oxidase enzymes, onto gold electrode surfaces pre-modified with nickel oxide was investigated in this work. The surface characterization confirmed the chemical nature, morphology and thin film composition of the modification of bare and modified gold electrodes. The electrodeposition of GOx enzyme onto nickel oxide/hydroxide thin film resulted in a surface with excellent bioelectrocatalytic properties towards the detection of d-glucose. The nickel within the nickel oxide/hydroxide thin film had a Ni(II) oxidation state. A well-defined redox peak of GOx enzyme co-factor (FAD/FADH 2 ) was observed confirming the oriented immobilization onto NiO/Ni(OH) 2 conducting surfaces. The amount of GOx enzyme deposited was determined by integrating the charge (Q = 0.368 μF) under the reduction peak and the surface coverage was found to be 1.43 × 10 -10 mol. cm -2 . A linear plot of electrocatalytic reduction currents against d-glucose concentrations was obtained up to 30.0 mM with a linear correlation coefficient (R 2 ) of 0.99. The limit of detection (LoD) using S/N = 3 was calculated to be 1.54 ± 0.03 mM. The sensitivity of the biosensors was 1.95 ± 0.13 μA.mM.cm -2 . The selectivity towards only d-glucose and not ascorbic acid and uric acid was evaluated and the Au-NiO/Ni(OH) 2 -GOx could not detect 1.0 mM of ascorbic acid and uric acid., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Carbon-based nanoelectrodes fabricated by means of pyrolysis of an alkane precursor gas purged through a glass capillary and subsequently etched with HF were modified with redox polymer/enzyme films for the detection of glucose at the single-cell level. Glucose oxidase (GOx) was immobilized and electrically wired by means of an Os-complex-modified redox polymer in a sequential dip coating process. For the synthesis of the redox polymer matrix, a poly(1-vinylimidazole-co-acrylamide)-based backbone was used that was first modified with the electron transfer mediator [Os(bpy) 2 Cl] + (bpy = 2,2'-bipyridine) followed by the conversion of the amide groups within the acrylamide monomer into hydrazide groups in a polymer-analogue reaction. The hydrazide groups react readily with bifunctional epoxide-based crosslinkers ensuring high film stability. Insertion of the nanometre-sized polymer/enzyme modified electrodes into adherently growing single NG108-15 cells resulted in a positive current response correlating with the intracellular glucose concentration. Moreover, the nanosensors showed a stable current output without significant loss in performance after intracellular measurements., Competing Interests: Declaration of Competing Interest Te authors declare no conflict of interest., (Copyright © 2020 Elsevier B.V. All rights reserved.)

In this study we have investigated the effect of glucose and glucose oxidase (GOD) on the absorption spectrum of gold nanoparticles (Au NPs) with 10-13 nm diameter, in order to improve optical methods of glucose monitoring using surface plasmon resonance of these particles. Different concentrations of glucose solution in water were prepared in the range of human saliva intensity. Two procedures are applied to study glucose effects on the particles; mixing the glucose to the nanocolloid and then adding the GOD, and reversely mixing the glucose and GOD solutions and then pouring in to the nanocolloid. Two different results were obtained that are analyzed based on optical properties. In each method, the effect of glucose and GOD on the size and Uv-vis spectrum of gold nanoparticles has been investigated. Results were interpreted by the physical concept of surface Plasmon resonance (SPR) of Au NPs. This study can open new insight about optical glucose sensing based on surface plasmon of metal nanoparticles., (Copyright © 2020 Elsevier B.V. All rights reserved.)