Amperometric detection of glucose based on immobilizing glucose oxidase on g-C3N4 nanosheets

Coreactant-free strong Ru(bpy)32+ ECL at ionic liquid modified electrode and its application in sensitive detection of glucose based on resonance energy transfer

In this work, we have realized the strong anodic ECL emission of Ru(bpy)32+ at ionic liquid (N-butylpyridinium tetrafluoroborate) modified electrode without additional coreactant. Methylene blue (MB) could accept the energy of Ru(bpy)32+ ECL to construct resonance energy transfer (ECL-RET) system, leading to the decrease of ECL signal. In the presence of glucose oxidase, hydrogen peroxide generated from the oxidation process of glucose could oxidize MB and block the ECL-RET route, resulting in the recovery of ECL signal. As a consequence, the designed sensor showed outstanding performance for "signal-on" detection of glucose in the concentration range of 10 μM to 1 mM, and the detection limit was determined as 1.75 μM. Importantly, this study revealed new roles of ILs in the fabrication of coreactant-free ECL sensing, which might open up a promising route for the potential design and implement in clinical analysis.

Current advancements and prospects of enzymatic and non-enzymatic electrochemical glucose sensors

This review discusses the most current developments and future perspectives in enzymatic and non-enzymatic glucose sensors, which have notably evolved over the preceding quadrennial period. Furthermore, a thorough exploration encompassed the sensor's intricate fabrication processes, the diverse range of materials employed, the underlying principles of detection, and an in-depth assessment of the sensors' efficacy in detecting glucose levels within essential bodily fluids such as human blood serums, urine, saliva, and interstitial fluids. It is worth noting that the accurate quantification of glucose concentrations within human blood has been effectively achieved by utilizing classical enzymatic sensors harmoniously integrated with optical and electrochemical transduction mechanisms. Monitoring glucose levels in various mediums has attracted exceptional attention from industrial to academic researchers for diabetes management, food quality control, clinical medicine, and bioprocess inspection. There has been an enormous demand for the creation of novel glucose sensors over the past ten years. Research has primarily concentrated on succeeding biocompatible and enhanced sensing abilities related to the present technologies, offering innovative avenues for more effective glucose sensors. Recent developments in wearable optical and electrochemical sensors with low cost, high stability, point-of-care testing, and online tracking of glucose concentration levels in biological fluids can aid in managing and controlling diabetes globally. New nanomaterials and biomolecules that can be used in electrochemical sensor systems to identify glucose concentration levels are developed thanks to advances in nanoscience and nanotechnology. Both enzymatic and non-enzymatic glucose electrochemical sensors have garnered much interest recently and have made significant strides in detecting glucose levels. In this review, we summarise several categories of non-enzymatic glucose sensor materials, including composites, non-precious transition metals and their metal oxides, hydroxides, precious metals and their alloys, carbon-based materials, conducting polymers, metal-organic framework (MOF)-based electrocatalysts, and wearable device-based glucose sensors deeply.

Co-Immobilization of Lactase and Glucose Isomerase on the Novel g-C3N4/CF Composite Carrier for Lactulose Production

The g-C₃N₄/CF composite carrier was prepared by ultrasound-assisted maceration and high-temperature calcination. The enzyme immobilization using the g-C₃N₄/CF as the novel carrier to immobilize lactase and glucose isomerase was enhanced for lactulose production. The carbon fiber (CF) was mixed with melamine powder in the mass ratio of 1:8. The g-C₃N₄/CF composite carrier was obtained by calcination at 550 °C for 3 h. After the analysis of characteristics, the g-C₃N₄/CF was successfully composited with the carbon nitride and CF, displaying the improvement of co-immobilization efficiency with the positive effects on the stability of the enzyme. The immobilization efficiency of the co-immobilized enzyme was 37% by the novel carrier of g-C₃N₄/CF, with the enzyme activity of 13.89 U g^-1 at 60 °C. The relative activities of co-immobilized enzymes maintained much more steadily at the wider pH and higher temperature than those of the free dual enzymes, respectively. In the multi-batches of lactulose production, the relative conversion rates in enzymes co-immobilized by the composite carrier were higher than that of the free enzymes during the first four batches, as well as maintaining about a 90% relative conversation rate after the sixth batch. This study provides a novel method for the application of g-C₃N₄/CF in the field of immobilizing enzymes for the production of lactulose.

A Sensitive and Selective Colorimetric Method Based on the Acetylcholinesterase-like Activity of Zeolitic Imidazolate Framework-8 and Its Applications

In this study, a simple colorimetric method was established to detect copper ion (Cu²⁺), sulfathiazole (ST), and glucose based on the acetylcholinesterase (AChE)-like activity of zeolitic imidazolate framework-8 (ZIF-8). The AChE-like activity of ZIF-8 can hydrolyze acetylthiocholine chloride (ATCh) to thiocholine (TCh), which will further react with 5,5′-dithiobis (2-nitrobenzoic acid) (DTNB) to generate 2-nitro-5-thiobenzoic acid (TNB) that has a maximum absorption peak at 405 nm. The effects of different reaction conditions (buffer pH, the volume of ZIF-8, reaction temperature and time, and ATCh concentration) were investigated. Under the optimized conditions, the value of the Michaelis-Menten constant (K_m) is measured to be 0.83 mM, which shows a high affinity toward the substrate (ATCh). Meanwhile, the ZIF-8 has good storage stability, which can maintain more than 80.0% of its initial activity after 30 days of storage at room temperature, and the relative standard deviation (RSD) of batch-to-batch (n = 3) is 5.1%. The linear dependences are obtained based on the AChE-like activity of ZIF-8 for the detection of Cu²⁺, ST, and glucose in the ranges of 0.021–1.34 and 5.38–689.66 µM, 43.10–517.24 µM, and 0.0054–1.40 mM, respectively. The limit of detections (LODs) are calculated to be 20.00 nM, 9.25 µM, and 5.24 µM, respectively. Moreover, the sample spiked recoveries of Cu²⁺ in lake water, ST in milk, and glucose in strawberry samples were measured, and the results are in the range of 98.4–115.4% with the RSD (n = 3) lower than 3.3%. In addition, the method shows high selectivity in the real sample analysis.

Two-Dimensional Graphitic Carbon Nitride (g-C3N4) Nanosheets and Their Derivatives for Diagnosis and Detection Applications

The early diagnosis of certain fatal diseases is vital for preventing severe consequences and contributes to a more effective treatment. Despite numerous conventional methods to realize this goal, employing nanobiosensors is a novel approach that provides a fast and precise detection. Recently, nanomaterials have been widely applied as biosensors with distinctive features. Graphite phase carbon nitride (g-C₃N₄) is a two-dimensional (2D) carbon-based nanostructure that has received attention in biosensing. Biocompatibility, biodegradability, semiconductivity, high photoluminescence yield, low-cost synthesis, easy production process, antimicrobial activity, and high stability are prominent properties that have rendered g-C₃N₄ a promising candidate to be used in electrochemical, optical, and other kinds of biosensors. This review presents the g-C₃N₄ unique features, synthesis methods, and g-C₃N₄-based nanomaterials. In addition, recent relevant studies on using g-C₃N₄ in biosensors in regard to improving treatment pathways are reviewed.

Immobilization of glucose oxidase on bioinspired polyphenol coatings as a high-throughput glucose assay platform

Glucose oxidase (GOx) is an enzyme with important industrial and biochemical applications, particularly in glucose detection. Here we leveraged the oxidative self-polymerization phenomenon of simple polyphenols (pyrogallol or catechol) in the presence of polyethylenimine (PEI) to form adhesive coatings that enabled GOx immobilization on conventional multi-well plates. Immobilization was verified and optimized by directly measuring GOx activity inside the coated wells. Our results showed that incorporating PEI in polyphenol coatings enhanced their enzyme immobilization efficiency, with pyrogallol (PG)-based coatings displaying the greatest enzyme activity. The immobilized enzyme maintained similar affinity to glucose compared to the free enzyme. GOx-immobilized PG/PEI-coated wells exhibited intermediate recycling ability but excellent resistance to urea as a denaturing agent compared to the free enzyme. GOx-immobilized 96-well plates allowed the construction of a linear glucose calibration curve upon adding glucose standards, with a detection limit of 0.4–112.6 mg dL⁻¹, which was comparable to commercially available enzymatic glucose assay kits. The assay platform was also capable of effectively detecting glucose in rat plasma samples. Our findings present a simple enzyme immobilization technique that can be used to construct a glucose assay platform in a convenient multi-well format for high-throughput glucose quantification.

Glucose oxidase was immobilized on conventional multi-well plates via bioinspired polyphenol chemistry for convenient colorimetric quantitation of glucose.

Enhanced Performance of Bioelectrodes Made with Amination-Modified Glucose Oxidase Immobilized on Carboxyl-Functionalized Ordered Mesoporous Carbon

This research reveals the improved performance of bioelectrodes made with amination-modified glucose oxidase (GOx-NH2) and carboxyl-functionalized mesoporous carbon (OMC-COOH). Results showed that when applied with 10 mM EDC amination, the functional groups of NH2 were successfully added to GOx, according to the analysis of 1H-NMR, elemental composition, and FTIR spectra. Moreover, after the aminated modification, increased enzyme immobilization (124.01 ± 1.49 mg GOx-NH2/g OMC-COOH; 2.77-fold increase) and enzyme activity (1.17-fold increase) were achieved, compared with those of non-modified GOx. Electrochemical analysis showed that aminated modification enhanced the peak current intensity of Nafion/GOx-NH2/OMC-COOH (1.32-fold increase), with increases in the charge transfer coefficient α (0.54), the apparent electron transfer rate constant ks (2.54 s-1), and the surface coverage Γ (2.91 × 10-9 mol·cm-2). Results showed that GOx-NH2/OMC-COOH exhibited impressive electro-activity and a favorable anodic reaction.

Dual-mode glucose nanosensor as an activatable theranostic platform for cancer cell recognition and cascades-enhanced synergetic therapy

Integration of disease diagnosis and therapy is crucial in precise medicine, while the "always on" mode often hinders its clinical applications. Herein, inspired by cascaded catalysis, an integrated dual-mode glucose nanosensor as an activable theranostic platform is developed, which is further exploited for cancer cell recognition and enhanced synergistic therapy of lymph cancer. This nanosensor is prepared through the in-situ growth of silver nanoparticles (AgNPs) with the synergetic reduction of tannic acid (TA) and graphene quantum dots (GQDs), which are further decorated with glucose oxidase (GOx). A cascaded catalytic reaction is triggered by glucose, in which GOx catalyzes the oxidation of glucose into gluconic acid and hydrogen peroxide (H₂O₂), and hydroxyl radical (•OH) is further produced with the catalysis of GQDs nanozyme with peroxidase-like activity, resulting in the degradation of AgNPs@GQDs-GOx with the release of Ag⁺. Accordingly, a "turn-off" colorimetric and "turn-on" fluorescence dual-mode glucose nanosensor is fabricated, which is readily applied for cancer cell recognition via fluorescence imaging based on the high glucose level in tumor microenvironment. Moreover, the degradation of AgNPs@GQDs-GOx in response to glucose facilitates the cascades-enhanced synergistic therapy of lymph cancer with the combination of starving-like therapy, metal ion therapy and TA-induce apoptosis. This study highlights a glucose-activated theranostic nanoplatform, which provides a great opportunity for cancer-related biosensing, bioimaging and biomedical applications.

Nickel sulfide-incorporated sulfur-doped graphitic carbon nitride nanohybrid interface for non-enzymatic electrochemical sensing of glucose

A nickel sulfide-incorporated sulfur-doped graphitic carbon nitride (NiS/S-g-C₃N₄) nanohybrid was utilized as an interface material for the non-enzymatic sensing of glucose in an alkaline medium (0.1 M NaOH). The precursors used in the preparation of NiS/S-g-C₃N₄ hybrid were thiourea and nickel nitrate hexahydrate as the sulfur and nickel sources, respectively. The HRTEM results reveal that NiS nanoparticles incorporated on the S-g-C₃N₄ nanosheet surface could enhance the electrocatalytic activity and electrical conductivity. The prepared NiS/S-g-C₃N₄ crystalline nature, surface functionalities, graphitic nature, thermal stability and surface composition were investigated using XRD, FT-IR, Raman spectroscopy, TGA and XPS analyses. The NiS/S-g-C₃N₄ modified electrode was used for the non-enzymatic sensing of glucose at an applied potential of 0.55 V vs. Ag/AgCl with a detection limit of 1.5 μM (S/N = 3), sensitivity of 80 μA mM^-1 cm^-2 and the response time of the fabricated sensor was close to 5 s. Different inorganic ions and organic substances did not interfere during glucose sensing. The NiS/S-g-C₃N₄ nanohybrid material could be extended for a real sample analysis and open the way for diverse opportunities in the electrochemical sensing of glucose.

Electrochemical Sensors Based on Carbon Nanomaterial Used in Diagnosing Metabolic Disease

Metabolic diseases have become common diseases with the improvement of living standards because of changed dietary habits and living habits, which seriously affect health. Currently, related biomarkers have been widely used as important indicators for clinical diagnosis, treatment, and prognosis of metabolic diseases. Among all detection methods for biomarkers of metabolic diseases, electrochemical sensor technology has the advantages of simplicity, real-time analysis, and low cost. Carbon nanomaterials were preeminent materials for fabricating electrochemical sensors in order to enhance the performance. In this paper, we summarize the research progress in the past 3 years of electrochemical sensors based on carbon nanomaterials in detecting markers of metabolic diseases, which include carbon nanotubes, graphene, carbon quantum dots, fullerene, and carbon nitride. Additionally, we discuss the future prospects for this field.