Eco-friendly spark-generated CoxOy nanoparticle-modified graphite screen-printed sensing surfaces for the determination of H2O2 in energy drinks

The modification of graphite screen-printed electrodes (SPEs) is reported using an eco-friendly and extremely fast method based on the direct cobalt pin electrode-to-SPE spark discharge at ambient conditions. This approach does not utilize any liquids or chemical templates, does not produce any waste, and allows the in-situ generation of CoxOy nanoparticles onto the electrode surface and the development of efficient electrocatalytic sensing surfaces for the determination of H2O2. Co-spark SPEs were characterized using scanning electron microscopy, energy-dispersive X-ray spectroscopy and x-ray photoelectron spectroscopy (XPS), revealing the formation of surface confined CoxOy nanoparticles and the diverse oxidation states of cobalt species. Co-spark SPEs were also characterized with cyclic voltammetry and electrochemical impedance spectroscopy. Redox transitions of the surface confined electrocatalysts are demonstrated by electrochemical polarization studies, showing the formation of different oxides (CoxOy), varying the XPS results. Amperometric measurements at 0.3 V vs. Ag/AgCl revealed a linear relationship between the current response and the concentration of H2O2 over the range 1 - 102 μM, achieving a limit of detection (3σ/m) of 0.6 μM. The interference effect of various electroactive species was effectively addressed by employing dual measurements in the absence and presence of the enzyme catalase. The analytical utility of the method was evaluated in antioxidant rich real-world samples, such as energy drinks, demonstrating sufficient recovery.

Spiers Memorial Lecture: Old but new organic electrosynthesis: history and recent remarkable developments

Organic electrosynthesis has a long history. However, this chemistry is still new. Recently, we have seen its second renaissance with organic electrosynthesis being considered a typical green chemistry process. Therefore, a number of novel electrosynthetic methodologies have recently been developed. However, there are still many problems to be solved from a green and sustainable viewpoint. After an explanation of the historical survey of organic electrosynthesis, this paper focuses on recent remarkable developments in new electrosynthetic methodologies, such as novel electrodes, recyclable nonvolatile electrolytic solvents and recyclable supporting electrolytes, as well as new types of electrolytic flow cells. Furthermore, novel types of organic electrosynthetic reactions will be mentioned.

Simultaneous Voltammetric Determination of Non-Steroidal Anti-Inflammatory Drugs (NSAIDs) Using a Modified Carbon Paste Electrode and Chemometrics

This work presents the simultaneous quantification of four non-steroidal anti-inflammatory drugs (NSAIDs), paracetamol, diclofenac, naproxen, and aspirin, in mixture solutions, by a laboratory-made working electrode based on carbon paste modified with multi-wall carbon nanotubes (MWCNT-CPE) and Differential Pulse Voltammetry (DPV). Preliminary electrochemical analysis was performed using cyclic voltammetry, and the sensor morphology was studied by scanning electronic microscopy and electrochemical impedance spectroscopy. The sample set ranging from 0.5 to 80 µmol L^-1 was prepared using a complete factorial design (3⁴) and considering some interferent species such as ascorbic acid, glucose, and sodium dodecyl sulfate to build the response model and an external randomly subset of samples within the experimental domain. A data compression strategy based on discrete wavelet transform was applied to handle voltammograms' complexity and high dimensionality. Afterward, Partial Least Square Regression (PLS) and Artificial Neural Networks (ANN) predicted the drug concentrations in the mixtures. PLS-adjusted models (n = 12) successfully predicted the concentration of paracetamol and diclofenac, achieving correlation values of R ≥ 0.9 (testing set). Meanwhile, the ANN model (four layers) obtained good prediction results, exhibiting R ≥ 0.968 for the four analyzed drugs (testing stage). Thus, an MWCNT-CPE electrode can be successfully used as a potential sensor for voltammetric determination and NSAID analysis.

Prussian blue: from advanced electrocatalyst to nanozymes defeating natural enzyme

The pathway from the advanced electrocatalyst to nanozymes defeating natural enzyme is reviewed. Prussian blue, being the most advantageous electrocatalyst for hydrogen peroxide reduction, is obviously the best candidate for mimicking peroxidase activity. Indeed, catalytically synthesized Prussian blue nanoparticles are characterized by the catalytic rate constants, which are significantly (up to 4 orders of magnitude) higher than for enzyme peroxidase. Displaying in addition the enzymatic specificity in terms of an absence of oxidase-like activity, catalytically synthesized Prussian blue nanoparticles can be referred to as nanozymes. The latter provide the most versatile method for surface covering with the electrocatalyst, allowing to modify non-traditional materials like boron-doped diamond. For stabilization, Prussian blue core can be covered with nickel hexacyanoferrate shell; the resulting core-shell nanozymes still defeat natural enzyme in terms of activity. Discovering the catalytic pathway of nanozymes "artificial peroxidase" action, we have found the novel advantage of nanozymes over the corresponding biological catalysts: their dramatically (100 times) improved bimolecular rate constants.

Non-Enzymatic Glucose Biosensor Based on Highly Pure TiO2 Nanoparticles

This study proposes a non-enzymatic glucose sensor fabricated by synthesizing high-purity TiO₂ nanoparticles in thermal plasma and depositing it directly on a substrate and then depositing chitosan–polypyrrole (CS-PPy) conductive polymer films by electrochemical method. The structural properties of the deposited TiO₂ nanoparticles were analyzed by X-ray diffraction (XRD) and dynamic light scattering (DLS) system. The chemical composition and structural properties of the TiO₂ nanoparticle layer and the conductive polymer films were confirmed by X-ray photoelectron spectroscopy (XPS) spectra and scanning electron microscope (SEM). The glucose detection characteristics of the fabricated biosensor were determined by cyclic voltammetry (CV). CS-PPy/TiO₂ biosensor showed high sensitivity of 302.0 µA mM⁻¹ cm⁻² (R² = 0.9957) and low detection limit of 6.7 μM. The easily manufactured CS-PPy/TiO₂ biosensor showed excellent selectivity and reactivity.

Polyphenol oxidase-based electrochemical biosensors: A review

The detection of phenolic compounds is relevant not only for their possible benefits to human health but also for their role as chemical pollutants, including as endocrine disruptors. The required monitoring of such compounds on-site or in field analysis can be performed with electrochemical biosensors made with polyphenol oxidases (PPO). In this review, we describe biosensors containing the oxidases tyrosinase and laccase, in addition to crude extracts and tissues from plants as enzyme sources. From the survey in the literature, we found that significant advances to obtain sensitive, robust biosensors arise from the synergy reached with a diversity of nanomaterials employed in the matrix. These nanomaterials are mostly metallic nanoparticles and carbon nanostructures, which offer a suitable environment to preserve the activity of the enzymes and enhance electron transport. Besides presenting a summary of contributions to electrochemical biosensors containing PPOs in the last five years, we discuss the trends and challenges to take these biosensors to the market, especially for biomedical applications.

Enzyme-Based Biosensors: Tackling Electron Transfer Issues

This review summarizes the fundamentals of the phenomenon of electron transfer (ET) reactions occurring in redox enzymes that were widely employed for the development of electroanalytical devices, like biosensors, and enzymatic fuel cells (EFCs). A brief introduction on the ET observed in proteins/enzymes and its paradigms (e.g., classification of ET mechanisms, maximal distance at which is observed direct electron transfer, etc.) are given. Moreover, the theoretical aspects related to direct electron transfer (DET) are resumed as a guideline for newcomers to the field. Snapshots on the ET theory formulated by Rudolph A. Marcus and on the mathematical model used to calculate the ET rate constant formulated by Laviron are provided. Particular attention is devoted to the case of glucose oxidase (GOx) that has been erroneously classified as an enzyme able to transfer electrons directly. Thereafter, all tools available to investigate ET issues are reported addressing the discussions toward the development of new methodology to tackle ET issues. In conclusion, the trends toward upcoming practical applications are suggested as well as some directions in fundamental studies of bioelectrochemistry.

NAD(P)-dependent glucose dehydrogenase: Applications for biosensors, bioelectrodes, and biofuel cells

This review discusses the physical and chemical properties of nicotinamide redox cofactor dependent glucose dehydrogenase (NAD(P) dependent GDH) and its extensive application in biosensors and bio-fuel cells. GDHs from different organisms show diverse biochemical properties (e.g., activity and stability) and preferences towards cofactors, such as nicotinamide adenine dinucleotide (NAD⁺) and nicotinamide adenine dinucleotide phosphate (NADP⁺). The (NAD(P)⁺) play important roles in biological electron transfer, however, there are some difficulties related to their application in devices that originate from their chemical properties and labile binding to the GDH enzyme. This review discusses the electrode modifications aimed at immobilising NAD⁺ or NADP⁺ cofactors and GDH at electrodes. Binding of the enzyme was achieved by appropriate protein engineering techniques, including polymerisation, hydrophobisation or hydrophilisation processes. Various enzyme-modified electrodes applied in biosensors, enzymatic fuel cells, and biobatteries are compared. Importantly, GDH can operate alone or as part of an enzymatic cascade, which often improves the functional parameters of the biofuel cell or simply allows use of cheaper fuels. Overall, this review explores how NAD(P)-dependent GDH has recently demonstrated high potential for use in various systems to generate electricity from biological sources for applications in implantable biomedical devices, wireless sensors, and portable electronic devices.

Diamine oxidase-modified screen-printed electrode for the redox-mediated determination of histamine

Histamine is an important biogenic amine because of its role in immune responses and the regulation of physiological functions. It is also used as a food freshness indicator, so its maximum concentration in fish is legally regulated. Although several robust and sensitive methods for histamine detection are already available, it continues to be a challenge to develop simple and portable devices that allow rapid histamine screening at any point of the fish production chain. Thus, in this work, a simple, miniaturized and low-cost sensor for histamine analysis was developed. The construction of the sensor only takes 30 min and consists of the immobilization of the enzyme diamine oxidase on the surface of a screen-printed carbon electrode by cross-linking. The quantification of histamine was achieved by chronoamperometry (+ 0.2V, 120 s) using hexacyanoferrate (III) as a redox mediator. This selective sensor provided a low limit of detection (0.97 mg L−1) and accurate and precise results and was successfully applied to the analysis of spiked tuna and mackerel extracts, obtaining recovery values of 99–100%. Moreover, the sensor shows good stability, maintaining 87.7% of its initial signal after 35 days.

Electrochemical sensor based on incorporation of gold nanoparticles, ionic liquid crystal, and β-cyclodextrin into carbon paste composite for ultra-sensitive determination of norepinephrine in real samples

A novel, reliable electrochemical sensor is fabricated for direct and sensitive determination of norepinephrine (NE) based on gold nanoparticles, ionic liquid crystal, and β-cyclodextrin modified carbon paste electrode, namely AuILCCDCPE. The ionic liquid crystal (ILC) played a key role in improving the current response of electro-oxidation of NE compared with other ionic liquids modified electrodes. The ILC increased the ionic conductivity of the paste and formed noncovalent interactions with both host (CD) and guest (NE) compounds. The solid state structure of the ILC helped in the formation of ordered films in the paste. Furthermore, CD and Au nanoparticles raised the stability and the electrocatalytic ability of the proposed sensor. Under optimized conditions, the fabricated electrochemical sensor showed a good electrochemical response towards NE in human urine in the linear dynamic ranges of 0.05–10 μmol/L and 20–300 μmol/L with a correlation coefficient of 0.999 and detection limit of 3.12 × 10−9 mol/L in the low concentration range. The practical analytical performance of the sensor was attained for determination of NE in real samples with satisfied recovery results. This sensor has great ability to be extended for electrochemical applications in assays of other drugs.

Extracellular electron transfer features of Gram-positive bacteria

Electroactive microorganisms possess the unique ability to transfer electrons to or from solid phase electron conductors, e.g., electrodes or minerals, through various physiological mechanisms. The processes are commonly known as extracellular electron transfer and broadly harnessed in microbial electrochemical systems, such as microbial biosensors, microbial electrosynthesis, or microbial fuel cells. Apart from a few model microorganisms, the nature of the microbe-electrode conductive interaction is poorly understood for most of the electroactive species. The interaction determines the efficiency and a potential scaling up of bioelectrochemical systems. Gram-positive bacteria generally have a thick electron non-conductive cell wall and are believed to exhibit weak extracellular electron shuttling activity. This review highlights reported research accomplishments on electroactive Gram-positive bacteria. The use of electron-conducting polymers as mediators is considered as one promising strategy to enhance the electron transfer efficiency up to application scale. In view of the recent progress in understanding the molecular aspects of the extracellular electron transfer mechanisms of Enterococcus faecalis, the electron transfer properties of this bacterium are especially focused on. Fundamental knowledge on the nature of microbial extracellular electron transfer and its possibilities can provide insight in interspecies electron transfer and biogeochemical cycling of elements in nature. Additionally, a comprehensive understanding of cell-electrode interactions may help in overcoming insufficient electron transfer and restricted operational performance of various bioelectrochemical systems and facilitate their practical applications.

Flow injection tyrosinase biosensor for direct determination of acetaminophen in human urine

An amperometric biosensor compatible with a flow injection analysis (FIA) for highly selective determination of acetaminophen (APAP) in a sample of human urine was developed. This biosensor is also suitable for use in the routine pharmaceutical practice. To prove this statement, two different commercially available pharmaceutical formulations were analyzed. This nano-(bio)electroanalytical device was made from a commercially available screen-printed carbon electrode covered by a thin layer of non-functionalized graphene (NFG) as amperometric transducer. A biorecognition layer was prepared from mushroom (Agaricus bisporus) tyrosinase (EC 1.14.18.1) cross-linked using glutaraldehyde, where resulting aggregates were covered by Nafion^®, a known ion exchange membrane. Owing to the use of tyrosinase and presence of NFG, the developed analytical instrument is able to measure even at potentials of 0 V. Linear ranges differ according to choice of detection potential, namely up to 130 μmol L^-1 at 0 V, up to 90 μmol L^-1 at -0.1 V, and up to 70 μmol L^-1 at -0.15 V. The first mentioned linear range is described by the equation I_p [μA] = 0.236 - 0.1984c [μmol L^-1] and correlation coefficient r = 0.9987; this equation was used to quantify the content of APAP in each sample. The limit of detection of APAP was estimated to be 1.1 μmol L^-1. A recovery of 96.8% (c = 25 μmol L^-1, n = 5 measurements) was calculated. The obtained results show that FIA is a very selective method for APAP determination, being comparable to the chosen reference method of reversed-phase high-performance liquid chromatography.

Morphological/nanostructural control toward intrinsically stretchable organic electronics

The development of intrinsically stretchable electronics poses great challenges in synthesizing elastomeric conductors, semiconductors and dielectric materials.

Fabrication of a promising immobilization platform based on electrochemical synthesis of a conjugated polymer

Since conjugated polymers are an important class of materials with remarkable properties in biosensor applications, in this study, a novel glucose biosensor based on a conjugated polymer was fabricated via the electropolymerization of the monomer 10,13-bis(4-hexylthiophen-2-yl)dipyridol[3,2-a:2',3'-c]phenazine onto a graphite electrode surface. Glucose oxidase (GOx) was used as the model biological recognition element. As a result of the enzymatic reaction between GOx and glucose, the glucose amount was determined by monitoring the change in the oxygen level associated with substrate concentration via the amperometric detection technique. The proposed system possessed superior properties with K_M^app value of 0.262 mM, 2.88 × 10^-3 mM limit of detection and 105.12 μA mM^-1 cm^-2 sensitivity. These results show that conjugated polymer film provides an effective and stable immobilization matrix for the enzyme. Finally, the biosensor was applied successfully to several commercially available beverage samples for glucose determination proving an inexpensive and highly sensitive system applicable for real time analyses.

Comparative Investigation of Peripheral and Nonperipheral Zinc Phthalocyanine-Based Polycarbazoles in Terms of Optical, Electrical, and Sensing Properties

In this study, nonperipherally alkyl-linked carbazole conjugated novel zinc(II) phthalocyanine was synthesized by cyclotetramerization reaction of 6-(9 H-carbazol-9-yl)hexane-1-thiol and 3,6-bis(tosyloxy) phthalonitrile in a one-step reaction. Optical, electrical, and sensing properties of this super structured polycarbazole obtained by electropolymerization are compared with peripherally alkyl-linked polycarbazole-based zinc(II) phthalocyanine. It has been found that the attachment of alkyl-linked carbazoles to the phthalocyanine molecule in either peripheral or nonperipheral positions has a great effect on the optical and electrical properties and sensing ability of the resulting polycarbazole derivatives. P(n-ZnPc) has the highest electrochromic contrast (70.5%) among the derivatives of zinc(II) phthalocyanines in the literature. In addition to these, the sensor platform has been successfully established, and analytical optimizations have been carried out. When the sensors prepared with zinc(II) phthalocyanine are examined, it was specified that the n-ZnPc- co-TP/GOx was ranked first in the literature with high sensor response and stability. As a result, by changing of the peripheral and nonperipheral position of phthalocyanines, their physical properties can be tuned to meet the requirements of desired technological application.

Direct Electron Transfer of Dehydrogenases for Development of 3rd Generation Biosensors and Enzymatic Fuel Cells

Dehydrogenase based bioelectrocatalysis has been increasingly exploited in recent years in order to develop new bioelectrochemical devices, such as biosensors and biofuel cells, with improved performances. In some cases, dehydrogeases are able to directly exchange electrons with an appropriately designed electrode surface, without the need for an added redox mediator, allowing bioelectrocatalysis based on a direct electron transfer process. In this review we briefly describe the electron transfer mechanism of dehydrogenase enzymes and some of the characteristics required for bioelectrocatalysis reactions via a direct electron transfer mechanism. Special attention is given to cellobiose dehydrogenase and fructose dehydrogenase, which showed efficient direct electron transfer reactions. An overview of the most recent biosensors and biofuel cells based on the two dehydrogenases will be presented. The various strategies to prepare modified electrodes in order to improve the electron transfer properties of the device will be carefully investigated and all analytical parameters will be presented, discussed and compared.

Square wave voltammetry at carbon paste electrode modified with surfactant for alpha tocopheryl acetate determination in cosmetics

The aim of this study was describe electrochemical properties of a carbon paste electrode (CPE) bulk modified with 30% (w/w) surfactant sodium dodecyl sulphate (CPE/SDS) and demonstrates its application in the determination of α‑tocopheryl acetate (α‑TAc), known as vitamin E acetate, in selected cosmetic products, especially body creams. In addition to anionic SDS, cationic hexadecylpyridinium chloride monohydrate (CPC) was also tested as possible modifier. It was found that selection of surfactant type and its content significantly affect an electrical conductivity and mechanical stability of these heterogeneous electroanalytical sensors in pure organic solvents. Under this study, it was found that CPC is a totally inappropriate mediator due to very high backgroundcurrent. Together with other lipophilic vitamins characterized by antioxidant activity (dominantly retionoids), this completely synthetic substance is widely used as significant cosmetic additive due its preservative properties. Monitoring of its content in cosmetic products is usually performed by high‑performance liquid chromatography (HPLC) with UV detection. This standard analytical protocol is always burdened with the complex and time‑consuming preparation of the sample before analysis. For that reason, robust and simple electroanalytical method based on anodic oxidation of the α‑TAc at CPE/SDS by square wave voltammetry (SWV) performed in pure organic electrolyte (99.8% acetonitrile containing 0.1 mol·L‑1 LiClO4) was developed. Moreover, simple dissolution of sample in supporting electrolyte using ultrasonic bath and subsequent filtering through a stacked filter included all the necessary procedures for sample preparation. The linear range from 0.1 to 1.2 mmol·L‑1and limit of detection 37 µmol·L‑1 were found at pulse amplitude 10 mV and frequency 10 Hz as optimum. In analysis of selected cosmetics, the developed electroanalytical method was not validated using comparison with standard HPLC. At least, the recovery was verified by analysis of model sample and value 95.8% was calculated.

Analytical Parameters of an Amperometric Glucose Biosensor for Fast Analysis in Food Samples

Amperometric biosensors based on the use of glucose oxidase (GOx) are able to combine the robustness of electrochemical techniques with the specificity of biological recognition processes. However, very little information can be found in literature about the fundamental analytical parameters of these sensors. In this work, the analytical behavior of an amperometric biosensor based on the immobilization of GOx using a hydrogel (Chitosan) onto highly ordered titanium dioxide nanotube arrays (TiO₂NTAs) has been evaluated. The GOx–Chitosan/TiO₂NTAs biosensor showed a sensitivity of 5.46 μA·mM⁻¹ with a linear range from 0.3 to 1.5 mM; its fundamental analytical parameters were studied using a commercial soft drink. The obtained results proved sufficient repeatability (RSD = 1.9%), reproducibility (RSD = 2.5%), accuracy (95–105% recovery), and robustness (RSD = 3.3%). Furthermore, no significant interferences from fructose, ascorbic acid and citric acid were obtained. In addition, the storage stability was further examined, after 30 days, the GOx–Chitosan/TiO₂NTAs biosensor retained 85% of its initial current response. Finally, the glucose content of different food samples was measured using the biosensor and compared with the respective HPLC value. In the worst scenario, a deviation smaller than 10% was obtained among the 20 samples evaluated.

Efficient synthesis of EDOT modified ABBB-type unsymmetrical zinc phthalocyanine: optoelectrochromic and glucose sensing properties of its copolymerized film

A new EDOT-based monomer bearing zinc phthalocyanine was synthesized and the electrochromic and biosensing properties of electropolymers derived from it were investigated.

Enhancing biosensor properties of conducting polymers via copolymerization: Synthesis of EDOT-substituted bis(2-pyridylimino)isoindolato-palladium complex and electrochemical sensing of glucose by its copolymerized film

1,3-Bis(2-pyridylimino)isoindoline derivative bearing 3,4-ethylenedioxythiophene (EDOT-BPI) and its palladium complex (EDOT-PdBPI) were synthesized and characterized by FT-IR, ¹H NMR, ¹³C NMR, UV-Vis spectroscopies and via mass spectrometric analysis. Polymerization of EDOT-PdBPI and copolymerization with 4-amino-N-(2,5-di(thiophene-2-yl)-1H-pyrrol-1-yl)benzamide (HKCN) were carried out by an electrochemical method. In addition, P(EDOT-PdBPI-co-HKCN) modified graphite rod electrode was improved for amperometric glucose sensor based on glucose oxidase (GOx). In this novel biosensor matrix, amino groups in HKCN were used for the enzyme immobilization. On the other hand, EDOT-PdBPI used to mediate the bioelectrocatalytic reaction. Amperometric detection was carried out following oxygen consumption at -0.7V vs. the Ag reference electrode in phosphate buffer (50mM, pH 6.0). The novel biosensor showed a linear amperometric response for glucose within a concentration range of 0.25mM to 2.5mM (LOD: 0.176mM). Amperometric signals at 1mM of glucose were 17.9μA under anaerobic conditions. Amperometric response of the P(EDOT-PdBPI-co-HKCN)/GOx electrode decreased only by 13% within eight weeks. The P(EDOT-PdBPI-co-HKCN)/GOx electrode showed good selectivity in the presence of ethanol and phenol. This result shows that, modification of the proposed biosensor by copolymerization of amine functionalized monomer, which is indispensable to the enzyme immobilization, with palladium complex bearing monomer, which is mediate the bioelectrocatalytic reaction, have provided to give perfect response to different glucose concentrations.

Assembly of polyoxometalates and Ni-bpy cationic units into the molecular core–shell structures as bifunctional electrocatalysts

Four core–shell organic–inorganic hybrid materials composed of polyoxometalates and Ni-bpy units were designed and synthesized, which exhibited bifunctional electrocatalytic activity for the reduction of NO₂⁻ and water oxidation.

Electrochemical oxidation of dihydronicotinamide adenine dinucleotide (NADH): comparison of highly oriented pyrolytic graphite (HOPG) and polycrystalline boron-doped diamond (pBDD) electrodes

NADH electro-oxidation is faster, but more prone to fouling, at HOPG compared to pBDD.

Polyoxometalate-based supramolecular architecture constructed from a purely inorganic 1D chain and a metal–organic layer with efficient catalytic activity

A new polyrotaxane structure constructed from a pure inorganic polyoxometalate-based 1D chain, exhibited efficient catalytic activity for desulfurization and electrocatalytic redox activity.

Development of amperometric glucose biosensor based on Prussian Blue functionlized TiO2 nanotube arrays

Amperometric biosensors consisting of oxidase and peroxidase have attracted great attention because of their wide application. The current work demonstrates a novel approach to construct an enzymatic biosensor based on TiO₂ nanotube arrays (TiNTs) as a supporting electrode on which Prussian Blue (PB)-an “artificial enzyme peroxidase” and enzyme glucose oxidase (GOx) have been immobilized. For this, PB nanocrystals are deposited onto the nanotube wall photocatalytically using the intrinsic photocatalytical property of TiO₂, and the GOx/AuNPs nanobiocomposites are subsequently immobilized into the nanotubes via the electrodeposition of polymer. The resulting electrode exhibits a fast response, wide linear range, and good stability for glucose sensing. The sensitivity of the sensor is as high as 248 mA M⁻¹ cm⁻², and the detection limit is about 3.2 μM. These findings demonstrate a promising strategy to integrate enzymes and TiNTs, which could provide an analytical access to a large group of enzymes for bioelectrochemical applications including biosensors and biofuel cells.