Enzyme-based Glucose Biosensors Research Articles

Nonenzymatic Glucose Biosensors: Latest Advances and Perspectives

Over the sixty years since glucose biosensor was introduced, development of glucose biosensor had experienced three generations. Considering the increasing demand of glucose biosensor, research and development has been carried out for more promising nonenzymatic glucose biosensor. Compared to the traditional enzyme-based glucose biosensor, nonenzymatic sensor is more capable to continuous glucose detection and has higher stability. Additionally, nonenzymatic glucose biosensor has a lower fabrication cost, which can be beneficial to the wide range of patients with the need for constant checking for blood glucose concentration. This paper introduces two proposed nonenzymatic glucose detection models: activated chemisorption and incipient hydrous oxide adatom mediator. As the developing trend of glucose biosensors is toward wearable and continuous glucose monitoring, two wearable sensors and working principles are introduced. This paper describes the application progress of different types of materials in enzyme-free blood glucose sensors, puts forward the existing problems in the application of enzyme-free blood glucose sensors, and looks forward to its future application prospects.

Partially Oxidized Carbon Nanomaterials with Ni/NiO Heterostructures as Durable Glucose Sensors.

Conventional enzyme-based glucose biosensors have limited extensive applications in daily life because glucose oxidase is easily inactivated and is expensive. In this paper, we propose a strategy to prepare a new type of cost-effective, efficient, and robust nonenzymatic Ni-CNT-O for electrochemical glucose sensing. It is first followed by the pyrolysis of Ni-ABDC nanostrips using melamine to grow carbon nanotubes (CNTs) to give an intermediate product of Ni-CNT, which is further accompanied by partial oxidation to enable the facile formation of hierarchical carbon nanomaterials with improved hydrophilicity. A series of physicochemical characterizations have fully proved that Ni-CNT-O is a carbon-coated heterostructure of Ni and NiO nanoparticles embedded into coordination polymer-derived porous carbons. The obtained Ni-CNT-O exhibits a better electrocatalytic activity for glucose oxidation stemming from the synergistic effect of a metal element and a metal oxide than unoxidized Ni-CNT, which also shows high performance with a wide linear range from 1 to 3000 μM. It also offers a high sensitivity of 79.4 μA mM-1 cm-2, a low detection limit of 500 nM (S/N = 3), and a satisfactory long-term durability. Finally, this glucose sensor exhibits good reproducibility, high selectivity, as well as satisfactory results by comparing the current response of simulated serum within egg albumen.

Graphene Quantum Dots Electrochemistry and Sensitive Electrocatalytic Glucose Sensor Development.

Graphene quantum dots (GQDs), derived from functionalized graphene precursors are graphene sheets a few nanometers in the lateral dimension having a several-layer thickness. They are zero-dimensional materials with quantum confinement and edge site effects. Intense research interest in GQDs is attributed to their unique physicochemical phenomena arising from the sp2-bonded carbon nanocore surrounded with edged plane functional moieties. In this work, GQDs are synthesized by both solvothermal and hydrothermal techniques, with the optimal size of 5 nm determined using high-resolution transmission electron microscopy, with additional UV-Vis absorption and fluorescence spectroscopy, revealing electronic band signatures in the blue-violet region. Their potential in fundamental (direct electron transfer) and applied (enzyme-based glucose biosensor) electrochemistry has been practically realized. Glucose oxidase (GOx) was immobilized on glassy carbon (GC) electrodes modified with GQDs and functionalized graphene (graphene oxide and reduced form). The cyclic voltammetry, differential pulse voltammetry, and electrochemical impedance spectroscopy are used for characterizing the direct electron transfer kinetics and electrocatalytical biosensing. The well-defined quasi-reversible redox peaks were observed under various electrochemical environment and conditions (pH, concentration, scan rate) to determine the diffusion coefficient (D) and first-order electron transfer rate (kET). The cyclic voltammetry curves showed homogeneous ion transport behavior for GQD and other graphene-based samples with D ranging between 8.45 × 10−9 m2 s−1 and 3 × 10−8 m2 s−1 following the order of GO < rGO < GQD < GQD (with FcMeOH as redox probe) < GOx/rGO < GOx/GO < HRP/GQDs < GOx/GQDs. The developed GOx-GQDs biosensor responds efficiently and linearly to the presence of glucose over concentrations ranging between 10 μM and 3 mM with a limit of detection of 1.35 μM and sensitivity of 0.00769 μA μM−1·cm−2 as compared with rGO (0.025 μA μM−1 cm−2, 4.16 μM) and GO (0.064 μA μM−1 cm−2, 4.82 μM) nanosheets. The relatively high performance and stability of GQDs is attributed to a sufficiently large surface-to-volume ratio, excellent biocompatibility, abundant hydrophilic edges, and a partially hydrophobic plane that favors GOx adsorption on the electrode surface and versatile architectures to ensure rapid charge transfer and electron/ion conduction (<10 ms). We also carried out similar studies with other enzymatic protein biomolecules on electrode surfaces prepared from GQD precursors for electrochemical comparison, thus opening up potential sensing applications in medicine as well as bio-nanotechnology.

Intramolecular Electron Transfer through Poly-Ferrocenyl Glucose Oxidase Conjugates to Carbon Electrodes: 1. Sensor Sensitivity, Selectivity and Longevity

Enzyme-based amperometric biosensors measure target analyte concentrations through the transduction of enzymatically generated electrons into a detectable current at an electrode surface. To achieve efficient electron transfer, many such systems rely on the use of diffusive electron mediators or intricate, nanostructured electrode materials, which can limit applicability. Herein, we report on the development and characterization of enzyme-based glucose biosensors operating using a combination of intramolecular electron transfer and electron self-exchange through ferrocene-containing redox mediators covalently coupled directly to glucose oxidase (GOX). To accomplish this, we applied polymer-based protein engineering to grow poly(N-(3-dimethyl(ferrocenyl)methylammonium bromide)propyl acrylamide (pFcAc) via atom-transfer radical polymerization from initiator molecules attached to the GOX surface. The use of these GOX-pFcAc conjugates allowed the fabrication of simple, paper-based glucose biosensors through crosslinking with the carrier protein human serum albumin (HSA) within a viscous chitosan solution and drop casting onto carbon paper strips. Chit-GOX-pFcAc-HSA-carbon paper biosensors yielded a glucose sensitivity of 0.33±0.01μAmM−1cm−2 and exhibited selectivity when challenged with other sugars. The ease of sensor fabrication further afforded a tailorable response through variation of GOX-pFcAc concentration upon crosslinking and drop casting. The reported approach shows the glucose sensing capabilities of a system that merges the characteristics of bioelectronics fabricated using redox-containing polymer networks with those based on the surface modification of enzymes with electron relays.

Recent Advances in Enzyme Based Glucose Biosensors for Biomedical Applications

Recent Advances in Enzyme Based Glucose Biosensors for Biomedical Applications

Robust Brain Hyperglycemia during General Anesthesia: Relationships with Metabolic Brain Inhibition and Vasodilation.

Glucose is the main energetic substrate for the metabolic activity of brain cells and its proper delivery into the extracellular space is essential for maintaining normal neural functions. Under physiological conditions, glucose continuously enters the extracellular space from arterial blood via gradient-dependent facilitated diffusion governed by the GLUT-1 transporters. Due to this gradient-dependent mechanism, glucose levels rise in the brain after consumption of glucose-containing foods and drinks. Glucose entry is also accelerated due to local neuronal activation and neuro-vascular coupling, resulting in transient hyperglycemia to prevent any metabolic deficit. Here, we explored another mechanism that is activated during general anesthesia and results in significant brain hyperglycemia. By using enzyme-based glucose biosensors we demonstrate that glucose levels in the nucleus accumbens (NAc) strongly increase after iv injection of Equthesin, a mixture of chloral hydrate and sodium pentobarbital, which is often used for general anesthesia in rats. By combining electrochemical recordings with brain, muscle, and skin temperature monitoring, we show that the gradual increase in brain glucose occurring during the development of general anesthesia tightly correlate with decreases in brain-muscle temperature differentials, suggesting that this rise in glucose is related to metabolic inhibition. While the decreased consumption of glucose by brain cells could contribute to the development of hyperglycemia, an exceptionally strong positive correlation (r = 0.99) between glucose rise and increases in skin-muscle temperature differentials was also found, suggesting the strong vasodilation of cerebral vessels as the primary mechanism for accelerated entry of glucose into brain tissue. Our present data could explain drastic differences in basal glucose levels found in awake and anesthetized animal preparations. They also suggest that glucose entry into brain tissue could be strongly modulated by pharmacological drugs via drug-induced changes in metabolic activity and the tone of cerebral vessels.

Parsing glucose entry into the brain: novel findings obtained with enzyme-based glucose biosensors.

Extracellular levels of glucose in brain tissue reflect dynamic balance between its gradient-dependent entry from arterial blood and its use for cellular metabolism. In this work, we present several sets of previously published and unpublished data obtained by using enzyme-based glucose biosensors coupled with constant-potential high-speed amperometry in freely moving rats. First, we consider basic methodological issues related to the reliability of electrochemical measurements of extracellular glucose levels in rats under physiologically relevant conditions. Second, we present data on glucose responses induced in the nucleus accumbens (NAc) by salient environmental stimuli and discuss the relationships between local neuronal activation and rapid glucose entry into brain tissue. Third, by presenting data on changes in NAc glucose induced by intravenous and intragastric glucose delivery, we discuss other mechanisms of glucose entry into the extracellular domain following changes in glucose blood concentrations. Lastly, by showing the pattern of NAc glucose fluctuations during glucose-drinking behavior, we discuss the relationships between “active” and “passive” glucose entry to the brain, its connection to behavior-related metabolic activation, and the possible functional significance of these changes in behavioral regulation. These data provide solid experimental support for the “neuronal” hypothesis of neurovascular coupling, which postulates the critical role of neuronal activity in rapid regulation of vascular tone, local blood flow, and entry of glucose and oxygen to brain tissue to maintain active cellular metabolism.

Highly-ordered perpendicularly immobilized FWCNTs on the thionine monolayer-modified electrode for hydrogen peroxide and glucose sensors

In this paper, we innovatively immobilized few-walled carbon nanotubes (FWCNTs) perpendicularly on Au surface through conductive thionine instead of aminoalkanethiols so as to improve electrochemical properties. Because FWCNTs own smaller aggregates, stronger chemical corrosion resistant, and higher conductivity than single-walled carbon nanotubes (SWCNTs), and thionine is a good electron transfer mediator can provide amino and sulfhydryl groups playing the same function as insulating aminoalkanethiols. The strategy for obtaining perpendicularly aligned FWCNTs (p-FWCNTs) is electrostatically assembled thionine and 11-amino-n-undecanethiol (AUT) on Au surface via Au-S bond to provide amino groups for covalently combining terminus-carboxylated FWCNTs, we confirmed and compared the results by AFM, Raman spectroscopy and electrochemical methods. In order to prove the constructed basement has excellent electrochemical properties can provide a good platform for sensors fabrication, we developed a novel non-enzymatic hydrogen peroxide (H2O2) sensor by electrodepositing Pt nanoparticles (PtNPs) on p-FWCNTs/Thionine/Au electrode surface, and verified the result by TEM, EDX and electrochemical techniques. Furthermore, polyallylamine (PAA) and poly(vinyl sulfate) (PVS) permselective layer, poly(diallyldimethylammonium) (PDDA) and glucose oxidase (GOx) multilayer films were layer-by-layer self-assembled on p-FWCNTs/Thionine/Au surface to fabricate a glucose biosensor. Either the non-enzymatic H2O2 sensor or the enzyme-based glucose biosensor showed good sensitivity, selectivity, reproducibility and stability, both them had been applied for biological sample analysis with satisfactory results. The results show that the p-FWCNTs/Thionine/Au electrode can work as an ideal platform for the development of highly sensitive sensors, coupled with p-FWCNTs are rich in functional groups could be used for fabricating diverse sensors.

Direct Electron Transfer at a Glucose Oxidase–Chitosan-Modified Vulcan Carbon Paste Electrode for Electrochemical Biosensing of Glucose

This article describes the investigation of direct electron transfer (DET) between glucose oxidase (GOD) and the electrode materials in an enzyme-catalyzed reaction for the development of improved bioelectrocatalytic system. The GOD pedestal electrochemical reaction takes place by means of DET in a tailored Vulcan carbon paste electrode surfaces with GOD and chitosan (CS), allowing efficient electron transfer between the electrode and enzyme. The key understanding of the stability, biocatalytic activity, selectivity, and redox properties of these enzyme-based glucose biosensors is studied without using any reagents, and the properties are characterized using electrochemical techniques like cyclic voltammogram, amperometry, and electrochemical impedance spectroscopy. Furthermore, the interaction between the enzyme and the electrode surface is studied using ultraviolet-visible (UV-Vis) and Fourier transform infrared (FTIR) spectroscopy. The present glucose biosensor exhibited better linearity, limit of detection (LOD = 0.37 ± 0.02 mol/L) and a Michaelis-Menten constant of 0.40 ± 0.01 mol/L. The proposed enzyme electrode exhibited excellent sensitivity, selectivity, reproducibility, and stability. This provides a simple "reagent-less" approach and efficient platform for the direct electrochemistry of GOD and developing novel bioelectrocatalytic systems.

ZnO Nanotube Arrays as Biosensors for Glucose

Highly oriented single-crystal ZnO nanotube (ZNT) arrays were prepared by a two-step electrochemical/chemical process on indium-doped tin oxide (ITO) coated glass in an aqueous solution. The prepared ZNT arrays were further used as a working electrode to fabricate an enzyme-based glucose biosensor through immobilizing glucose oxidase in conjunction with a Nafion coating. The present ZNT arrays-based biosensor exhibits high sensitivity of 30.85 μA cm−2 mM−1 at an applied potential of +0.8 V vs. SCE, wide linear calibration ranges from 10 μM to 4.2 mM, and a low limit of detection (LOD) at 10 μM (measured) for sensing of glucose. The apparent Michaelis−Menten constant KMapp was calculated to be 2.59 mM, indicating a higher bioactivity for the biosensor.

Miniaturized glucose biosensor modified with a nitric oxide-releasing xerogel microarray

An enzyme-based glucose biosensor modified to release nitric oxide (NO) via a xerogel microarray is reported. The biosensor design is as follows: (1) glucose oxidase (GOx) is immobilized in a methyltrimethoxysilane (MTMOS) xerogel layer; (2) a blended polyurethane/hydrophilic polyurethane coating prevents enzyme leaching and imparts selectivity for glucose; and (3) micropatterned xerogel lines (5 microm wide) separated by distances of 5 or 20 microm provide NO-release capability. This configuration allows for increased glucose sensitivity relative to sensors modified with NO-releasing xerogel films since significant portions of the sensor surface remain unmodified. Glucose diffusion to the GOx layer is thus less inhibited. The micropatterned NO-releasing biosensors generate sufficient NO levels to reduce both Pseudomonas aeruginosa and platelet adhesion without significantly compromising the enzymatic activity of GOx. The glucose response, linearity and stability of the NO-releasing micropatterned sensors are reported.

Enzyme-based glucose biosensor using a dye couple system

We have developed a new type of enzyme-based glucose biosensor based on a dye couple system. A concentration dependence of glucose on a test strip containing physically adsorbed glucose oxidase, peroxidase and dye couple have been optically measured. The application of this method permits the exploitation of the biosensor during a period of more than 300 days.

Biotechnology-based recognition elements

The author discusses technology, applications, and opportunities for biosensors. The following topics are considered: the shape of the myoglobin molecule; a schematic structure of an antibody showing the different regions of the molecule; the form of the membrane-bound acetylcholine receptor protein; forces responsible for interactive behavior between receptors and ligands; a photolithographic technique for the production of a peptide library on a chip; the principle of affine chromatography; the structure of a glucose electrode developed by Leland Clark; interferences with an enzyme-based glucose biosensor; components of biosensors; a glucose sensor based on fiber optics. >