Adsorption Of Glucose Oxidase Research Articles

Сенсорное покрытие на основе липидного ленгмюровского монослоя с молекулами фермента глюкозооксидазы

A sensor coating was created based on a Langmuir monolayer of 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE) with immobilized molecules of the enzyme glucose oxidase and its sensor properties were studied. The process of incorporation of glucose oxidase enzyme molecules into a Langmuir monolayer of phospholipid DPPE molecules was studied using the compression isotherm method. Adsorption of glucose oxidase molecules has an expanding effect on the Langmuir monolayer of DPPE and leads to an increase in the area per molecule from 32.5 Å2 to 49 Å2 and a decrease in the compression modulus of the monolayer from 133 mN/m to 83 mN/m. Also, the adsorption of glucose oxidase leads to an increase in the desorption coefficient of the monolayer into the kd subphase from 0.5·10-3 to 1.2·10-3. The morphology of films with immobilized enzyme molecules at different adsorption times was characterized by atomic force microscopy. Increasing the enzyme adsorption time leads to a decrease in the surface roughness of the formed film from 3.6 nm at 5 minutes to 2.4 nm at 60 minutes. The formed DPPE monolayers with immobilized enzyme molecules were transferred to graphite electrodes. Their sensory properties were studied using cyclic voltammetry and impedance measurements. The resulting coatings were sensitive to glucose in solutions with concentrations from 0 to 1 mg/ml. The presence of a linear concentration dependence of the maximum and minimum currents and resistances in the specified concentration range makes the created films promising for use as touch coatings.

PEDOT-Polyamine-Based Organic Electrochemical Transistors for Monitoring Protein Binding.

The fabrication of efficient organic electrochemical transistors (OECTs)-based biosensors requires the design of biocompatible interfaces for the immobilization of biorecognition elements, as well as the development of robust channel materials to enable the transduction of the biochemical event into a reliable electrical signal. In this work, PEDOT-polyamine blends are shown as versatile organic films that can act as both highly conducting channels of the transistors and non-denaturing platforms for the construction of the biomolecular architectures that operate as sensing surfaces. To achieve this goal, we synthesized and characterized films of PEDOT and polyallylamine hydrochloride (PAH) and employed them as conducting channels in the construction of OECTs. Next, we studied the response of the obtained devices to protein adsorption, using glucose oxidase (GOx) as a model system, through two different strategies: The direct electrostatic adsorption of GOx on the PEDOT-PAH film and the specific recognition of the protein by a lectin attached to the surface. Firstly, we used surface plasmon resonance to monitor the adsorption of the proteins and the stability of the assemblies on PEDOT-PAH films. Then, we monitored the same processes with the OECT showing the capability of the device to perform the detection of the protein binding process in real time. In addition, the sensing mechanisms enabling the monitoring of the adsorption process with the OECTs for the two strategies are discussed.

SELF-ASSEMBLED MULTILAYERS OF WATER GLUCOSE MODIFIED-CHITOSAN AND GLUCOSE OXIDASE FOR DETECTION OF GLUCOSE IN MILK SAMPLES

Background: A crucial aspect of electrochemical enzymatic biosensor development is the immobilization of the enzymes, as it directly influences the sensitivity of the bioelectrode. Among the different methods used to incorporate enzymes on the surface of the transducers, layer-by-layer (LbL) self-assembly based on electrostatic interaction with polyelectrolytes of opposite charge stands out due to its simplicity and reproducibility. Aims: The aim of the work was to develop an electrochemical glucose biosensor by LbL assembly of a new functionalized chitosan polycation and the enzyme glucose oxidase (GOx). Methods: Chitosan was chemically functionalized with glucose by the Maillard reaction. The resulting polycation, named G-Chit, is soluble in the medium compatible with the enzyme. The bioelectrode was obtained by alternating adsorption of G-Chit and GOx onto carbon paste electrodes. By selecting the number of bilayer of G-Chit/GOX, the enzyme concentration, and the pH, the electroanalytical performance of the biosensor was optimized. The electrochemical responses were characterized by cyclic voltammetry and chronoamperometry. Results: Under optimized experimental conditions, the biosensor exhibited a sensitivity of (0.81 ± 0.03) µA mM-1 in a glucose concentration range of (0.18 to 1.75) mM. Discussion: Results indicated that catalytic response increases both with the number of G-Chit/GOx bilayers and the enzyme concentration, obtaining the best responses for 3 bilayers and 2 mg mL-1, respectively, while the optimum working pH value was 7.0. Conclusions: The analytical response of the biosensor was tested in milk samples with negligible matrix effects, suggesting a potential application in other dairy products. Results show that G-Chit appears promising for the immobilization of enzymes.

Investigation on the surface morphologies of reduced graphene oxide coating on the interfacial characteristics and electro-catalytic capacity of enzymatic glucose sensors

In this study, reduced graphene oxide (rGO) were subject to ultrasonic treatment to acquire varied morphologies, and the enzymatic glucose sensors were constructed by coating the rGO onto indium tin oxide electrodes and physically linking glucose oxidase to the rGO coatings. The effects of the surface morphologies of the rGO coatings on the interfacial characteristics and the electro-catalytic capacity of the enzymatic glucose sensors were systematically investigated. It turns out that, the rGO coating with a rough surface is more hydrophilic, and exhibits uniform glucose oxidase adsorption and higher electron migration rate at the solid/liquid interface between the analytical liquid and the working electrode. As a result, the corresponding glucose sensor shows excellent electro-catalytic capacity towards glucose with a broader linear range of 0–10.0 mM, a higher sensitivity of 38.9 μA·mM−1·cm−2, and a lower detection limit of 0.1 μM (signal-to-noise ratio of 3). Additionally, the as-prepared glucose sensor exhibits excellent accuracy for detecting actual blood samples as well as superior resistance to interference from other substances (such as L-phenylalanine, urea, ascorbic acid, uric acid, NaCl, and KCl). These results establish the theoretical and experimental foundation for the application of rGO coating in the field of biosensors.

Precipitation-based microscale enzyme reactors coupled with porous and adhesive elastomer for effective bacterial decontamination and membrane antifouling on-demand

Bacterial contamination of water environments can cause various troubles in various areas. As one of potential solutions, we develop enzyme-immobilized elastomer, and demonstrate the uses of enzyme reactions on-demand for effective microbial decontamination and antifouling. Asymmetrically-structured elastomer is prepared by combining two polydimethylsiloxane (PDMS) layers with different degrees of crosslinking: highly-crosslinked and lightly-crosslinked PDMS layers. At the surface of highly-crosslinked PDMS layer, porous structure with average diameter of 842 nm is formed by dissolving pre-packed and entrapped latex beads. Lightly-crosslinked PDMS on the other side, due to its adhesive nature, enables iterative attachments on various materials under either dry or wet condition. Glucose oxidase (GOx) is immobilized by using the pores at the surface of highly-crosslinked PDMS matrix via a ship-in-a-bottle protocol of precipitation-based microscale enzyme reactor (p-MER), which consists of GOx adsorption, precipitation and chemical crosslinking (EAPC). As a result, crosslinked enzyme aggregates (CLEAs) of GOx not only are well entrapped within many pores of highly-crosslinked PDMS layer (ship-in-bottle) but also cover the external surface of matrix, both of which are well connected together. Highly-interconnected network of CLEAs themselves effectively prevents enzyme leaching, which shows the 25% residual activity of GOx under shaking at 200 rpm for 156 days after 48% initial drop of loosely-bound p-MER after 4 days. In presence of glucose, the underwater attachment of biocatalytic elastomer demonstrates the generation of hydrogen peroxide via p-MER-catalyzed glucose oxidation, exhibiting effective biocidal activities against both gram-positive S. aureus and gram-negative E. coli. Adhesion-induced GOx-catalyzed reaction also alleviates the biofouling of membrane, suggesting its extendibility to various engineering systems being suffered by biofouling. This study of biocatalytic elastomer has demonstrated its new opportunities for the facile and on-demand enzyme-catalyzed reactions in various environmental applications, such as bactericidal treatment, water treatment/purification, and pollutant degradation.

Assemblies of two multimeric enzymes using mesoporous silica microspheres toward cascade reaction fields

A highly efficient, rapid cascade reaction system with coupled enzyme reactions is developed using mesoporous silica microspheres having a large pore diameter of 24.5 nm as an immobilization scaffold for two multimeric enzymes. The simultaneous adsorption of glucose oxidase and catalase on the pores of the mesoporous silica microspheres cause aggregation of the two enzymes, resulting in extremely low adsorbed amounts of the enzymes. The present study overcomes this limitation by immobilizing the two enzymes sequentially on the mesoporous silica pores, which significantly increases the decomposition ratio of hydrogen peroxide (an intermediate product). The localization and assembly of the two enzymes encapsulated in the mesopores were confirmed by labeling with fluorescent dyes for direct visualization and by detection of the fluorescence resonance energy transfer between the two enzymes, respectively, under a confocal laser scanning microscope field. The activity in the cascade reaction by the dual enzyme–mesoporous silica composite was significantly improved via the dense arrangement of the two enzymes on the surface of the mesoporous silica microspheres.

Graphene oxide/gold nanoparticle/graphite fiber microelectrodes for directing electron transfer of glucose oxidase and glucose detection

A promising electrochemical sensor is investigated using graphene oxide (GO)/gold nanoparticle (AuNP)-modified graphite electrodes to enhance charge transport in electrochemical biosensors and increase the sensitivity for glucose detection. An efficient charge transfer pathway is formed by interconnected GO nanosheets and AuNP along the graphite fiber (GF) electrode (GFE). The positive GO can adsorb glucose oxidase (GOD) by electrostatic attraction. The detected response current of the sensor is linearly related to the glucose concentration within a detection limit of 1.2 μM. Furthermore, this glucose sensor has high stability, good reproducibility and excellent selectivity for various oxidizable molecules such as dopamine (DA), uric acid (UA), ascorbic acid (AA) and other molecules causing chaff interference (fructose, lactose and galactose). It is worth noting that this work shows a new method using covalent bonds and self-assembly on the surface of GF for fabricating excellent electrochemical glucose biosensors.

Biomimetic magnetite/polydopamine/β-cyclodextrins nanocomposite for long-term glucose measurements

A highly selective, sensitive, and long-term stable glucose biosensor was developed, based on β-cyclodextrins (β-CDs) grafted onto magnetite/polydopamine (Fe3O4/PDA) with adsorbed glucose oxidase (GOx) from Aspergillus niger. The properties of the nanoplatform were determined by transmission electron microscopy (TEM), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FT-IR), Bradford assay, electrokinetic analysis (zeta potential), non-invasive light scattering (NIBS) and measurement of the polydispersity index (PdI). The biosensor’s operating conditions were optimized, and the optimal conditions were used in tests on model and real glucose solution. Results for the biosensor showed a broad linear range (1–26 mM glucose), with sensitivity as high as 115.74 μA mM−1 cm−2 and a limit of detection (LOD) of 1.55 μM. The results show the biosensor to be an interesting potential tool for use in many areas where glucose measurement is essential. Moreover, the proposed system demonstrated long-term stability, up to 9 months. Furthermore, excellent selectivity against ascorbic acid, uric acid, L-cysteine and sugars such as saccharose, maltose and fructose was confirmed.

In-situ Neutron Reflectometry Study on Adsorption of Glucose Oxidase at Mesoporous Aluminum Oxide Film.

In the present study, the adsorption of glucose oxidase (GOD) to a mesoporous aluminum oxide (MAO) film was examined with in-situ neutron reflectometry (NR) measurements. The MAO film was deposited on a cover glass slip and a Si disc, and its pore structure was characterized by X-ray reflectometry (XRR) and NR. The Si disc with MAO film was applied for an in-situ NR experiment, and its NR profiles before/after adsorption of GOD were continuously measured with a flow cell. The results indicated that the negatively-charged GOD molecules hardly penetrate into the narrow pore channel (pore diameter = ca. 10 nm) with opposite surface charge.

Kinetics of photo-stimulated adsorption of enzyme molecules onto n- and p-type silicon

We report on a change in the surface density of glucose oxidase (GOx) molecules on surface of Si/SiO2/polyethyleneimine structures depending on type of Si conductivity, adsorption time and white-light illumination of a substrate during GOx adsorption. It is clearly shown by AFM images that the dependence of GOx adsorption on adsorption time and illumination is different for n-Si and p-Si substrates. The results can be explained by the electrostatic interaction between GOx molecules and the surface charge of Si, which depends on illumination.

The influence of illumination and ionic strength of a solution on the formation of biosensor structure based on a silicon substrate and glucose oxidase molecules

We report on a change in parameters of a sensitive layer of field effect biosensor based on a silicon transducer and glucose oxidase (GOx) enzyme molecules. Change in the parameters of the enzyme layer occurs due to the white-light illumination of a Si substrate during the GOx adsorption. It was found that the addition of certain value of NaCl salt concentration, which depends on the presence of a polyethylenimine buffer layer on the semiconductor surface, led to a more prominent effect of photo-assisted adsorption of GOx molecules.

A Photoelectrochemical Biosensor Fabricated using Hierarchically Structured Gold Nanoparticle and MoS2 on Tannic Acid Templated Mesoporous TiO2

AbstractIn a tannic acid assisted synthesis of mesoporous TiO2, tannic acid was used as a cost effective and non‐toxic template for pore formation. Meanwhile, a gold nanoparticles (Au NPs) deposited TiO2 nanocomposite was coated on an indium tin oxide electrode for the fabrication of a photoelectrochemical (PEC) biosensing system. Upon the formation of anatase structure, the electrode was coated with MoS2 for effective visible light absorption. The mesoporous structure led to an enhanced surface area by improving Au NPs and glucose oxidase adsorption. Incorporation of Au NPs led to an enhanced photonic efficiency due to the generation of Schottky barriers. The obtained nanocomposite was used for the light‐driven, real‐time, and selective PEC glucose sensing. Under visible light irradiation, the enzyme immobilized electrodes yielded significant photocurrent improvement owing to the releasing electron donor H2O2. The obtained PEC biosensor demonstrated acceptable reproducibility and stability with a sensitivity of 4.42 μA mM−1 cm−2 and a low detection limit of 1.2 μM glucose. Also, the linear measurement range was found to be 0.004–1.75 mM glucose. The results indicated that the proposed production method of mesoporous TiO2 will pave the way for a green chemistry based porous material production, along with the extension of the implementation of semiconductors in PEC biosensing systems.

Two-Dimensional Metal-Organic Framework/Enzyme Hybrid Nanocatalyst as a Benign and Self-Activated Cascade Reagent for in Vivo Wound Healing.

Metal-organic frameworks (MOFs)-based peroxidase mimics have been seldom applied in the biomedical field, especially in vivo. One of the main reasons is their optimum reactions occur in strong acidic environments with a pH of 3-4, severely limiting their applications in living systems where neutral pH is usually required. Other types of peroxidase mimics also suffer such a fatal defect. Additionally, the direct introduction of the relatively high concentrated and toxic reaction reagent H2O2 would induce undesired damage to normal tissues. Herein, a MOF-based hybrid nanocatalyst as a benign and self-activated cascade reagent has been constructed. Owing to better catalytic performance compared with three-dimensional bulk MOF, an ultrathin two-dimensional (2D) MOF (2D Cu-TCPP(Fe)) nanosheet is chosen as a model of peroxidase mimic to physically adsorb glucose oxidase (GOx) for fabricating such a hybrid nanocatalyst. Nontoxic glucose can be continuously converted into abundant gluconic acid and H2O2 by GOx, avoiding the direct use of relatively high concentrated and toxic H2O2 and minimizing the harmful side effects. The generated gluconic acid can decrease the pH value from 7 to 3-4, dramatically activating the peroxidase-like activity of 2D Cu-TCPP(Fe) nanosheets. Meanwhile, the produced H2O2 is used for subsequent catalysis of activated 2D Cu-TCPP(Fe) nanosheets, leading to efficient generation of an extremely toxic hydroxyl radial and antibacterial capacity. In vitro and in vivo results illustrate the designed benign and self-activated cascade reagent possesses a robust antibacterial effect with negligible biotoxicity.

The Influence of an Amorphous Silicon Layer on the Adsorption Properties of a Semiconductor Structure under Photostimulation Conditions

The photostimulated adsorption of glucose oxidase (GOx) on the surface of single-crystalline Si wafers with an amorphous silicon (a-Si) layer was examined. Estimation of the difference between the surface coverage by GOx molecules deposited under illumination and in the dark showed that this value increased for the structures with a-Si layer by a factor of 2.5 in the case of n-Si and by a factor of 1.5 in the case of p-Si. It is revealed that the n-Si/a-Si structures can be used for preliminary photostimulation of the GOx adsorption process.

Влияние слоя аморфного кремния на адсорбционные свойства полупроводниковой структуры в условиях фотостимуляции

AbstractThe photostimulated adsorption of glucose oxidase (GOx) on the surface of single-crystalline Si wafers with an amorphous silicon (a-Si) layer was examined. Estimation of the difference between the surface coverage by GOx molecules deposited under illumination and in the dark showed that this value increased for the structures with a-Si layer by a factor of 2.5 in the case of n -Si and by a factor of 1.5 in the case of p -Si. It is revealed that the n -Si/a-Si structures can be used for preliminary photostimulation of the GOx adsorption process.

Change in the surface density of immobilized enzyme molecules induced by photoelectron processes in a silicon substrate

We report on a change in the number of adsorbed glucose oxidase molecules depending on both salt concentration and illumination of a silicon substrate during glucose oxidase adsorption on its surface. Glucose oxidase molecules were adsorbed from its aqueous solution onto a silicon substrate either with a polyethyleneimine layer or without it. Based on obtained atomic force microscopy (AFM) data, it was found that addition of salt led to a more prominent effect of photo-assisted adsorption. In addition, illumination led to a monotonic change in adsorbed enzyme coverage (either decrease or increase depending on silicon substrate conductivity type), while variation of salt concentration resulted in the nonmonotonic change. The obtained results can be used for fabrication of biosensors with easily controllable parameters such as sensitivity, lower limit of analytic detection, etc.

Graphene Quantum Dots Electrochemistry and Development of Ultrasensitive Enzymatic Glucose Sensor

AbstractGraphene quantum dots (GQDs) - zero-dimensional materials - are sheets of a few nanometers in lateral dimension and exhibit quantum confinement and edge site effects where sp2-bonded carbon nanocore surrounded with edged plane functional moieties is promising as advanced electroactive sensing platforms. In this work, GQDs are synthesized by solvothermal and hydrothermal techniques, with optimal size of 5 nm. Their potential in fundamental (direct electron transfer) and applied (enzymatic glucose biosensor) electrochemistry are demonstrated. Glucose oxidase (GOx) immobilized on glassy carbon (GC) electrodes modified with GQDs are investigated by means of cyclic voltammetry, differential pulse voltammetry, and amperometry. Well-defined quasi-reversible redox peaks observed under various electrochemical parameters helped to determine diffusion coefficient (D) and first-order electron transfer rate (kET). The cyclic voltammetry curves showed homogeneous ion transport for GQD with D ranging between 8.45 × 10−9 m2 s−1 and 3 × 10−8 m2 s−1 following 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 10 μM and 3 mM with limit of detection 1.35 μM and sensitivity 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 high performance and stability of GQDs is attributed to sufficiently large surface-to-volume ratio, excellent biocompatibility, abundant hydrophilic edge site density, and partially hydrophobic planar sites 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.

The Hydrogen-Bonded Ferrocenylmethanol: Mediation of Electron Transfer for Physically Adsorbed Glucose Oxidase

The mechanism of electron transfer of ferrocenylmethanol through the self-assembled monolayer (SAM) of mercaptosuccinic acid (MSA) on gold was investigated. A key finding is that the hydrogen-bonded FcMeOH plays the role of a mediator in the electron transfer involving the physically adsorbed glucose oxidase at the MSA SAM surface. The space-conformation of the hydrogen-bonding between FcMeOH and MSA was obtained by computational methods. The FcMeOH interacts with MSA via the strong hydrogen bond with the short distance around 1.9 Å at two different binding sites, approving the statements of hydrogen-bonding. The intermolecular hydrogen-bonding between redox mediator (FcMeOH) and the artificial self-assembled monolayer (MSA) is evident, and the mechanistic study of heterogeneous electron transfer kinetics is meaningful for the biosensor applications.

Hamiltonian replica exchange simulations of glucose oxidase adsorption on charged surfaces.

The Hamiltonian replica exchange Monte Carlo (H-REMC) algorithm was applied to study protein adsorption and its performance was compared with that of the temperature replica exchange Monte Carlo (T-REMC). Comparisons indicate that the simulation results are consistent but the computational efficiency is improved for H-REMC. H-REMC could accurately and efficiently identify the preferred orientations of glucose oxidase (GOx) on charged surfaces; different preferential GOx orientations on different surfaces and solution conditions could be spotted with a much fewer number of simulation runs. On positively charged surfaces, when electrostatic interactions dominate, the negatively charged GOx can be easily adsorbed with the "standing" orientation for which the substrate-binding domain is accessible to substrates. As the surface charge densities decrease and ionic strengths increase, there is an increasing contribution from the van der Waals (vdW) interactions, and thus more possible orientations appear. When the vdW interactions dominate, the unfavorable "front-lying" becomes the preferred orientation for which the substrate-binding domain is blocked by the surface. On negatively charged surfaces, though GOx has a net charge of -30 e under physiological conditions, the charged groups are unevenly distributed over the protein surface; the positive potential regions in the "back" of GOx enable the protein to be adsorbed on negatively charged surfaces with the "back-lying" orientation. The H-REMC provides an alternative method to accurately and efficiently probe the lowest-energy orientation of proteins adsorbed on surfaces for biotechnological applications.

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.