Biosensor Based on Self‐Assembling Glucose Oxidase and Dendrimer‐Encapsulated Pt Nanoparticles on Carbon Nanotubes for Glucose Detection

A novel amperometric glucose biosensor based on layer‐by‐layer (LbL) electrostatic adsorption of glucose oxidase (GOx) and dendrimer‐encapsulated Pt nanoparticles (Pt‐DENs) on multiwalled carbon nanotubes (CNTs) was described. Anionic GOx was immobilized on the negatively charged CNTs surface by alternatively assembling a cationic Pt‐DENs layer and an anionic GOx layer. Transmission electron microscopy images and ζ‐potentials proved the formation of layer‐by‐layer nanostructures on carboxyl‐functionalized CNTs. LbL technique provided a favorable microenvironment to keep the bioactivity of GOx and prevent enzyme molecule leakage. The excellent electrocatalytic activity of CNTs and Pt‐DENs toward H₂O₂ and special three‐dimensional structure of the enzyme electrode resulted in good characteristics such as a low detection limit of 2.5 μM, a wide linear range of 5 μM–0.65 mM, a short response time (within 5 s), and high sensitivity (30.64 μA mM^?1 cm^?2) and stability (80% remains after 30 days).     

Dendritic Silver/Silicon Dioxide Nanocomposite Modified Electrodes for Electrochemical Sensing of Hydrogen Peroxide

A novel biosensor for hydrogen peroxide was prepared by immobilizing horseradish peroxidase (HPR) on newly synthesized dendritic silver/silicon dioxide nanocomposites, which were coated on a glassy carbon electrode. The modified electrode was characterized with XPS, SEM, and electrochemical methods. This biosensor showed a very fast amperometric response to hydrogen peroxide with a linear range from 0.7 to 120 μM, a limit of detection of 0.05 μM and a sensitivity of 1.02 mA mM^?1 cm^?2. The Michaelis‐Menten constant of the immobilized HRP was estimated to be 0.21 mM, indicating a high affinity of the HRP to H₂O₂ without loss of enzymatic activity. The preparation of the proposed biosensor was convenient, and it showed high sensitivity and good stability.     

Glucose Biosensors Based on Electrodes Modified with Ferrocene Derivatives Intercalated into Mg/Al Layered Double Hydroxides

Two amperometric biosensors based on glassy carbon electrodes (GC) modified with Mg/Al layered double hydroxides (LDHs) containing ferrocene‐carboxylate (Fc? CO₂H) or ferrocene‐sulfonate (Fc? SO₃H), as interlayer anions, and glucose oxidase (GOx) are presented. Amperometric detection of glucose involves the electrochemical oxidation of H₂O₂ mediated by the ferrocene derivative. Optimization of the biosensors construction and of the operative conditions was investigated and is discussed herein. The performances of the two biosensors were evaluated by chronoamperometry, working at low anodic potentials (+0.400 V for Fc? CO₂H and +0.500 V for Fc? SO₃H vs. SCE). The linearity extended up to 1.5 mM and 10.0 mM in batch and in flow conditions, respectively, for both biosensors, whereas the sensitivity was higher for the one based on Fc? CO₂H (4.8±0.3 versus 2.0±0.3 μA mM^?1cm^?2 in batch mode, and 63.9±0.4 versus 25.8±0.4 μA mM^?1cm^?2 in flow mode). The biosensors display rapid response time (less than 20 s), good reproducibility, as well as good operational stability. Glucose can be accurately determined in the presence of the most common interferences that coexist in blood serum if an oxidative membrane containing nanoparticles of MnO₂ is applied on the biosensors' surface.     

ITO electrode modified by a gold ion implantation technique for direct electrocatalytic sensing of hydrogen peroxide

We report on a non-enzymatic amperometric sensor for hydrogen peroxide (H₂O₂). It was fabricated by electrodeposition of multi-wall carbon nanotubes and polyaniline along with platinum nanoparticles on the surface of a glassy carbon electrode. The modification was probed by scanning electron microscopy and cyclic voltammetry. The resulting sensor exhibits a high sensitivity (748.4?μA·mM^?1·cm^?2), a wide linear range (7.0?μM–2.5?mM), a low detection limit (2.0?μM) (S/N?=?3), a short response time (>5?s), and long-term stability, and is not interfered by common species. It was successfully applied to determine H₂O₂ in disinfectants.

Preparation and Electrochemical Characterization of an Enzyme Electrode Based on Catalase Immobilized onto a Multiwall Carbon Nanotube‐Thionine Film

The present study was aimed at investigating the use of a mixture multiwall carbon nanotube (MWCNT) and thionine (Th) dye in designing of a thionine‐based electrochemical biosensor containing catalase (Ct) enzyme (MWCNT‐Nafion‐Th/Ct) onto a glassy carbon electrode (GCE). The effects of pH, MWCNT concentration and thionine concentration on electrochemical response were explored for optimum analytical performance. The modified electrode exhibited a pair of well‐defined, quasi‐reversible peaks at formal potential (E^o′) = ‐0.218 ± 0.017 V vs. Ag/AgCl corresponding to the Th_ox/Th_red redox couples in the presence of MWCNT, Nafion, and Ct. The electrochemical parameters, including charge‐transfer coefficient (0.36), and apparent heterogeneous electron transfer rate constant (4.28 ± 0.26 s^?1) were determined. Using differential pulse voltammetry, the prepared enzyme electrode exhibited a linear response to hydrogen peroxide (H₂O₂) in the range of 10.0‐100.0 μM with a detection limit 8.7 μM and a sensitivity of 6051.0 μA mM^?1 cm^?2.     

Electrocatalysis via Direct Electrochemistry of Myoglobin Immobilized on Colloidal Gold Nanoparticles

The direct electron transfer between immobilized myoglobin (Mb) and colloidal gold modified carbon paste electrode was studied. The Mb immobilized on the colloidal gold nanoparticles displayed a pair of redox peaks in 0.1 M pH 7.0 PBS with a formal potential of –(0.108 ± 0.002) V (vs. NHE). The response showed a surface‐controlled electrode process with an electron transfer rate constant of (26.7 ± 3.7) s ^?1 at scan rates from 10 to 100 mV s^?1 and a diffusion‐controlled process involving the diffusion of proton at scan rates more than 100 mV s^?1. The immobilized Mb maintained its activity and could electrocatalyze the reduction of both hydrogen peroxide and nitrite. Thus, the novel renewable reagentless sensors for hydrogen peroxide and nitrite were developed, respectively. The activity of Mb with respect to the pseudo peroxidase with a K_M^app value of 0.65 mM could respond linearly to hydrogen peroxide concentration from 4.6 to 28 μM. The sensor exhibited a fast amperometric response to NO₂^? reduction and reached 93% of steady‐state current within 5 s. The linear range for NO₂^? determination was from 8.0 to 112 μM with a detection limit of 0.7 μM at 3σ.     

Electroanalysis of Dopamine at RuO2 Modified Vertically Aligned Carbon Nanotube Electrode

Electrochemical behavior of dopamine at the RuO₂‐modified vertically aligned carbon nanotubes electrode was investigated by cyclic voltammetry, differential pulse voltammetry and chronoamperometry. The RuO₂‐modified carbon nanotube electrode showed higher electrocatalytic activity towards the oxidation of dopamine than the MWNTs electrode in 0.10 M phosphate buffer solution. At an applied potential of +0.4 V, the RuO₂/MWNTs electrode exhibited a wide detection range up to 3.6×10^?3 M with detection limit of 6.0×10^?8 M (signal/noise=3) for dopamine determination. Meanwhile, the optimized sensor for dopamine displayed a sensitivity of 83.8 μA mM^?1 and response time of 5 s with addition of 0.20 mM dopamine. In addition, DPV experiment revealed that interfering species such as ascorbic acid and uric acid could be effectively avoided. The RuO₂/MWNTs electrode presents stable, highly sensitive, favorable selectivity and fast amperometric response of dopamine.     

Avidin and Glucose Oxidase‐non‐covalently Functionalized Multi‐walled Carbon Nanotubes: A New Analytical Tool for Building a Bienzymatic Glucose Biosensor

We report an innovative supramolecular architecture for bienzymatic glucose biosensing based on the non‐covalently functionalization of multi‐walled carbon nanotubes (MWCNTs) with two proteins, glucose oxidase (GOx) (to recognize glucose) and avidin (to allow the specific anchoring of biotinylated horseradish peroxidase (b‐HRP)). The optimum functionalization was obtained by sonicating for 10 min 0.50 mg mL^?1 MWCNTs in a solution of 2.00 mg mL^?1 GOx+1.00 mg mL^?1avidin prepared in 50 : 50 v/v ethanol/water. The sensitivity to glucose for glassy carbon electrodes (GCE) modified with MWCNTs‐GOx‐avidin dispersion and b‐HRP (GCE/MWCNTs‐GOx‐avidin/b‐HRP), obtained from amperometric experiments performed at ?0.100 V in the presence of 5.0×10^?4 M hydroquinone, was (4.8±0.3) μA mM^?1 (r²=0.9986) and the detection limit was 1.2 μM. The reproducibility for 5 electrodes using the same MWCNTs/GOx‐avidin dispersion was 4.0 %, while the reproducibility for 3 different dispersions and 9 electrodes was 6.0 %. The GCE/MWCNT‐GOx‐avidin/b‐HRP was successfully used for the quantification of glucose in a pharmaceutical product and milk.     

Ultramicrobiosensor for the Selective Detection of Glutamate

Carbon fiber microelectrodes, able to detect catecholamine release from single cells, have significantly contributed to our present understanding of the mechanism of secretory neurotransmission. In spite of their obvious advantages, there are only a few amperometric sensors (characterized by appropriate size, sensitivity, and selectivity) able to measure the release of other (not easily oxidizable) neurotransmitters at cellular level. The present work describes the fabrication and characterization of an ultramicrobiosensor for the selective detection of glutamate. The developed sensor has a size of 2.5–15 μm in diameter, a sensitivity of 0.62 mA mM^?1 cm^?2, and a detection limit of 5 μM. The excellent selectivity of the sensor (achieved using electrodeposition of Ru, Rh, and poly(m‐phenylenediamine)) makes it a promising candidate for monitoring glutamate release at single cell level.     

Synthesis of Ferrocene Based Naphthoquinones and its Application as Novel Non‐enzymatic Hydrogen Peroxide

At present, a highly sensitive hydrogen peroxide (H₂O₂) sensor is fabricated by ferrocene based naphthaquinone derivatives as 2,3‐Diferrocenyl‐1,4‐naphthoquinone and 2‐bromo‐3‐ferrocenyl‐1,4‐naphthoquinone. These ferrocene based naphthaquinone derivatives are characterized by H‐NMR and C‐NMR. The electrochemical properties of these ferrocene based naphthaquinone are investigated by cyclic voltammetry (CV), differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS) on modified glassy carbon electrode (GCE). The modified electrode with ferrocene based naphthaquinone derivatives exhibits an improved voltammetric response to the H₂O₂ redox reaction. 2‐bromo‐3‐ferrocenyl‐1,4‐naphthoquinone show excellent non‐enzymatic sensing ability towards H₂O₂ response with a detection limitation of 2.7 μmol/L a wide detection range from 10 μM to 400 μM in H₂O₂ detection. The sensor also exhibits short response time (1 s) and good sensitivity of 71.4 μA mM^?1 cm^?2 and stability. Furthermore, the DPV method exhibited very high sensitivity (18999 μA mM^?1 cm^?2) and low detection limit (0.66 μM) compared to the CA method. Ferrocene based naphthaquinone derivative based sensors have a lower cost and high stability. Thus, this novel non‐enzyme sensor has potential application in H₂O₂ detection.     

Electropolymerized Diphenylamine on Functionalized Multiwalled Carbon Nanotube Composite Film and Its Application to Develop a Multifunctional Biosensor

Diphenylamine (DPA) monomers have been electropolymerized on the amino‐functionalized multiwalled carbon nanotube (AFCNT) composite film modified glassy carbon electrode (GCE) by cyclic voltammetry (CV). The surface morphology of PDPA‐AFCNT was studied using field‐emission scanning electron microscopy (FE‐SEM). The interfacial electron transfer phenomenon at the modified electrode was studied using electrochemical impedance spectroscopy (EIS). The PDPA‐AFCNT/GCE represented a multifunctional sensor and showed good electrocatalytic behavior towards the oxidation of catechol and the reduction of hydrogen peroxide. Rotating‐disk electrode technique was applied to detect catechol with a sensitivity of 1360 µA mM^?1 cm^?2 and a detection limit of 0.01 mM. Amperometric determination of hydrogen peroxide at the PDPA‐AFCNT film modified electrode results in a linear range from 10 to 800 µM, a sensitivity of 487.1 µA mM^?1 cm^?2 and detection limit of 1 µM. These results show that the nano‐composite film modified electrode can be utilized to develop a multifunctional sensor.     

Simple Electrodeposition of Dendritic Pd Without Supporting Electrolyte and Its Electrocatalytic Activity Toward Oxygen Reduction and H2O2 Sensing

Metallic palladium (Pd) electrocatalysts for oxygen reduction and hydrogen peroxide (H₂O₂) oxidation/reduction are prepared via electroplating on a gold metal substrate from dilute (5 to 50 mM) aqueous K₂PdCl₄ solution. The best Pd catalyst layer possessing dendritic nanostructures is formed on the Au substrate surface from 50 mM Pd precursor solution (denoted as Pd‐50) without any additional salt, acid or Pd templating chemical species. The Pd‐50 consisted of nanostructured dendrites of polycrystalline Pd metal and micropores within the dendrites which provide high catalyst surface area and further facilitate reactant mass transport to the catalyst surface. The electrocatalytic activity of Pd‐50 proved to be better than that of a commercial Pt (Pt/C) in terms of lower overpotential for the onset and half‐wave potentials and a greater number of electrons (n) transferred. Furthermore, amperometric i–t curves of Pd‐50 for H₂O₂ electrochemical reaction show high sensitivities (822.2 and ?851.9 µA mM^?1 cm^?2) and low detection limits (1.1 and 7.91 µM) based on H₂O₂ oxidation H₂O₂ reduction, respectively, along with a fast response (<1 s).     

Disposable Amperometric Biosensor Based on Poly‐L‐lysine and Fe3O4 NPs‐chitosan Composite for the Detection of Tyramine in Cheese

An amperometric tyramine biosensor based on poly‐L‐lysine (PLL) and Fe₃O₄ nanoparticles (Fe₃O₄NP) modified screen printed carbon electrode (SPCE) was developed. PLL was formed on the SPCE by the electropolymerization of L‐lysine. Subsequently, Fe₃O₄NP suspension prepared in chitosan (CH) solution was casted onto the PLL/SPCE. Tyrosinase (Ty) enzyme was immobilized onto the modified Fe₃O₄?CH/PLL/SPCE and the electrode was coated with Nafion to fabricate the Ty/Fe₃O₄?CH/PLL/SPCE. Different techniques including scanning electron microscopy, chronoamperometry (i–t curve), cyclic voltammetry and electrochemical impedance spectroscopy were utilized to study the fabrication processes, electrochemical characteristics and performance parameters of the biosensor. The analytical performance of the tyramine biosensor was evaluated with respect to linear range, sensitivity, limit of detection, repeatability and reproducibility. The response of the biosensor to tyramine was linear between 4.9×10^?7–6.3×10^?5 M with a detection limit of 7.5×10^?8 M and sensitivity of 71.36 μA mM^?1 (595 μA mM^?1 cm^?2). The application of the developed biosensor for the determination of tyramine was successfully tested in cheese sample and mean analytical recovery of added tyramine in cheese extract was calculated as 101.2±2.1 %. The presented tyramine biosensor is a promising approach for tyramine analysis in real samples due to its high sensitivity, rapid response and easy fabrication.     

Properties of Dendrimer‐Encapsulated Pt Nanoparticles Doped Polypyrrole Composite Films and Their Electrocatalytic Activity for Glucose Oxidation

A type of novel electroanalytical sensing nanobiocomposite material was prepared by electropolymerization of pyrrole containing poly(amidoamine) dendrimers‐encapsulated platinum nanoparticles (Pt‐PAMAM), and glucose oxidase (GOx). The Pt nanoparticles encapsulated in PAMAM are nearly monodisperse with an average diameter of 3 nm, and they provide electrical conductivity. Polypyrrole acts as a polymer backbone to give stable and homogeneous cast thin films, and it also defines the electrical conductivity. Both Polypyrrole and PAMAM can provide a favorable microenvironment to keep the bioactivity of enzymes such as glucose oxidase. The homogeneity of GOx/Pt‐PAMAM‐PPy nanobiocomposite films was characterized by atomic force microscopy (AFM). Amperometric biosensors fabricated with these materials were characterized electrochemically using cyclic voltammetry (CV), electrochemical impedance spectra (EIS) and amperometric measurements in the presence of hydrogen peroxide or glucose. All those show the resultant biosensor sensitivity was strongly enhanced within the nanobiocomposite film. The optimized glucose biosensor displayed a sensitivity of 164 μA mM^?1 cm^?1, a linear range of 0.2 to 600 μM, a detection limit of 10 nM, and a response time of <3 s.     

Minimally‐invasive Microneedle‐based Biosensor Array for Simultaneous Lactate and Glucose Monitoring in Artificial Interstitial Fluid

Here we report the first mediated pain free microneedle‐based biosensor array for the continuous and simultaneous monitoring of lactate and glucose in artificial interstitial fluid (ISF). The gold surface of the microneedles has been modified by electrodeposition of Au‐multiwalled carbon nanotubes (MWCNTs) and successively by electropolymerization of the redox mediator, methylene blue (MB). Functionalization of the Au‐MWCNTs/polyMB platform with the lactate oxidase (LOX) enzyme (working electrode 1) and with the FAD‐Glucose dehydrogenase (FADGDH) enzyme (working electrode 2) enabled the continuous monitoring of lactate and glucose in the artificial ISF. The lactate biosensor exhibited a high sensitivity (797.4±38.1 μA cm^?2 mM^?1), a good linear range (10–100 μM) with a detection limit of 3 μM. The performance of the glucose biosensor were also good with a sensitivity of 405.2±24.1 μA cm^?2 mM^?1, a linear range between 0.05 and 5 mM and a detection limit of 7 μM. The biosensor array was tested to detect the amount of lactate generated after 100 minutes of cycling exercise (12 mM) and of glucose after a normal meal for a healthy patient (10 mM). The results reveal that the new microneedles‐based biosensor array seems to be a promising tool for the development of real‐time wearable devices with a variety of sport medicine and clinical care applications.     

Electrochemical Determination of Uric Acid Using a Multiwalled Carbon Nanotube Platinum–Nickel Alloy Glassy Carbon Electrode

Platinum–nickel nanoparticles were synthesized by a reduction procedure. The Pt–Ni/C composite was characterized by X-ray diffraction, infrared spectroscopy, transmission electron microscopy, and electrochemical analysis. The measurements show that the Pt–Ni/multiwalled carbon nanotubes provided higher electrocatalytic activity for the oxidation of uric acid than Pt–Ni/carbon black. The sensor prepared from the characterized material provided a long linear dynamic range from 0.1 to 240.4?µM with a detection limit of 0.03?µM and a sensitivity of 41.21?µA?mM^?1?cm^?2. The reported modified electrode also provided excellent selectivity, good stability, and satisfactory reproducibility for the determination of uric acid.     

Electrochemical nanostructured biosensors: carbon nanotubes versus conductive and semi-conductive nanoparticles

The aim of this work was to demonstrate that various types of nanostructures provide different gains in terms of sensitivity or detection limit albeit providing the same gain in terms of increased area. Commercial screen printed electrodes (SPEs) were functionalized with 100 µg of bismuth oxide nanoparticles (Bi₂O₃ NPs), 13.5 µg of gold nanoparticles (Au NPs), and 4.8 µg of multi-wall carbon nanotubes (MWCNTs) to sense hydrogen peroxide (H₂O₂). The amount of nanomaterials to deposit was calculated using specific surface area (SSA) in order to equalize the additional electroactive surface area. Cyclic voltammetry (CV) experiments revealed oxidation peaks of Bi₂O₃ NPs, Au NPs, and MWCNTs based electrodes at (790 ± 1) mV, (386 ± 1) mV, and (589 ± 1) mV, respectively, and sensitivities evaluated by chronoamperometry (CA) were (74 ± 12) µA mM^?1 cm^?2, (129 ± 15) ±A mM^?1 cm^?2, and (54 ± 2) ±A mM^?1 cm^?2, respectively. Electrodes functionalized with Au NPs showed better sensing performance and lower redox potential (oxidative peak position) compared with the other two types of nanostructured SPEs. Interestingly, the average size of the tested Au NPs was 4 nm, under the limit of 10 nm where the quantum effects are dominant. The limit of detection (LOD) was (11.1 ± 2.8) ±M, (8.0 ± 2.4) ±M, and (3.4 ± 0.1) ±M for Bi₂O₃ NPs, Au NPs, and for MWCNTs based electrodes, respectively.     

A Complete Electroenzymatic Choline Microprobe Based on Nanostructured Platinum Microelectrodes and an IrOx On‐probe Reference Electrode

A microelectrode array microprobe with a choline sensing site and an on‐probe reference electrode was constructed by depositing permselective polymer films and choline oxidase (ChOx) on one microelectrode, and iridium oxide (IrOx) on another, both of which were coated previously with a nanostructured Pt deposit. Scanning electron microscopy (SEM) of the nanostructured Pt layer revealed a unique pillar‐like, “nanograss” structure. Polyphenylenediamine (PPD) and Nafion were coated sequentially on the working (i. e. sensing) electrode surface to serve as the permselective polymer films. The microsensor exhibited high sensitivity to choline (123±13 μA mM^?1 cm^?2), low detection limit (3.2±0.8 μM), and fast response time (3–5 s). The choline sensor also was tested at physiological concentrations of electroactive interfering species common to brain extracellular fluid (i. e. ascorbic acid, dopamine, DOPA, and DOPAC) and showed excellent selectivity. Selectivity likely was aided by the relatively low potential of 0.35 V vs. IrOx that was made possible by the enhanced H₂O₂ electrooxidation activity of the underlying nanostructured Pt‐coated working electrode. Thus, Pt “nanograss” appears to be an excellent electrode surface modification for creation of high performance electroenzymatic biosensors.     

Electrodeposition of Three‐Dimensional Porous Platinum Film on Removable Polyaniline Template for High‐Performance Electroanalysis

Three‐dimensional porous platinum (Pt_por) films are prepared based on Pt electrodeposition on polyaniline (PANI) modified electrodes followed by selective dissolution of PANI with HNO₃. Electrochemical quartz crystal microbalance data suggest that the PANI‐H₂PtCl₆ interaction involves redox and coordination reactions, depending on the working potential. The Pt_por shows better electrocatalytic performance than the Pt/PANI and conventionally electrodeposited Pt. The Pt_por modified glassy carbon electrode (GCE) can electrocatalyze the oxidation of H₂O₂ with a sensitivity of 414 µA cm^?2 mM^?1 and a detection limit of 9 nM, and the chitosan‐glucose oxidase/Pt_por/GCE can sense glucose with a sensitivity of 93.4 µA cm^?2 mM^?1.     

Urchin‐like Ag Nanowires as Non‐enzymatic Hydrogen Peroxide Sensor

Urchin‐like Ag nanowires were prepared by reacting AgNO₃(aq) with Cu metal in the presence of cetyltrimethylammonium chloride and HNO₃(aq) on a screen printed carbon electrode at room temperature. The diameters of the nanowires were about 100 nm, while the lengths were up to 10 μm. Cyclic voltammetric experiments using the Ag nanowires as the working electrode showed electrocatalytic H₂O₂ reduction. The electrode exhibited a high sensitivity of 4705 μA mM^‐1 mg^‐1 cm^‐2 from 50 μM to 10.35 mM and a measurable detection limit of 10 μM in amperometric detection. This is the first report on Ag NWs for non‐enzymatic H₂O₂ sensing.