Voltammetric study of interaction of Co(phen)3 with DNA at gold nanoparticle self-assembly electrode

Modifying electrode surfaces on the molecule scale allow developing new electrochemical biosensors. A new strategy for the immobilization of calf thymus DNA on the surface of gold nanoparticles which are co-immobilized at a gold electrode through 4,4^′-bis(methanethiol) biphenyl (MTP) molecule by assembly process is demonstrated. The DNA modified electrode was incubated in Co(phen)₃³⁺ solution of an aqueous buffer or an acetonitrile (AN) solution, then it was rinsed and placed in a Co(phen)₃³⁺ free buffer solution or AN solution, followed by cyclic voltammetric experiments. Clear redox peaks of Co(phen)₃³⁺ were observed both in an aqueous and AN solutions. The concentration of supporting electrolyte on electrochemical behavior was discussed. It was found that the surface coverage value of DNA molecules on modified gold nanoparticle and the redox current of adsorbed Co(phen)₃³⁺ were decrease with increasing the size of gold nanoparticles (6, 25, 42, 73, and 93 nm). In aqueous solution, the electron transfer rate constant of Co(phen)₃^3+/2+ redox couple became slow with increasing the diameter of gold nanoparticle, and the speed almost had nothing to do with the diameter in nonaqueous solution. The surface concentration of Co(phen)₃³⁺ adsorption on DNA modified electrode decreased and rate constant of adsorption kinetics increased with increasing the interactive temperature. In AN solution, the electrostatic interaction between DNA and Co(phen)₃^3+/2+ was greatly reduced, however, compare with in aqueous solution the interaction between DNA and reduced form of Co(phen)₃²⁺ was more strongly than oxidized form Co(phen)₃³⁺. The surface concentration of Co(phen)₃³⁺ adsorption on DNA modified electrode reach maximum value when the interactive temperature about 20 °C, and rate constant of adsorption kinetics nearly independent of the interactive temperature. The results show that the DNA can adsorb on the modified electrode firmly and the Co(phen)₃^3+/2+ adsorbed on DNA give good electrochemical response both in aqueous and nonaqueous solutions. It was confirmed that the DNA modified electrode can be applied in a nonaqueous system and the modified electrode can be used to investigate the interaction between DNA and electroactive species both in aqueous and nonaqueous systems.     

Low potential detection of glucose at carbon nanotube modified glassy carbon electrode with electropolymerized poly(toluidine blue O) film

A mediator glucose biosensor has been constructed by immobilizing glucose oxidase at electropolymerized poly(toluidine blue O) film on carbon nanotube modified glass carbon electrode. The toluidine blue O moieties served as redox mediators for enzymatic glucose oxidation and as polymeric network to maintain the biosensor activity. Great enhancement in current response was observed for the glucose biosensor. The detection potential could be decreased to −0.1 V (versus Ag|AgCl), where common interferences such as ascorbic acid, uric acid and acetamidophenol were not oxidized to cause interferences. The amperometric glucose biosensor offered a sensitivity of 14.5 mA M⁻¹ cm⁻² for the linear range of 1-7 mM.     

Tetracarboxylic acid cobalt phthalocyanine SAM on gold: Potential applications as amperometric sensor for H2O2 and fabrication of glucose biosensor

This report describes the applications of cobalt tetracarboxylic acid phthalocyanine (CoTCAPc) self-assembled monolayer (SAM) immobilized onto a preformed 2-mercaptoethanol (Au-ME) SAM on gold surface (Au-ME-CoTCAPc SAM) as a potential amperometric sensor for the detection of hydrogen peroxide (H₂O₂) at neutral pH conditions. The Au-ME-CoTCAPc SAM sensor showed a very fast amperometric response time of approximately 1 s, good linearity at the studied concentration range of up to 5 μM with a coefficient R² = 0.993 and a detection limit of 0.4 μM oxidatively. Also reductively, the sensor exhibited a very fast amperometric response time (∼1 s), linearity up to 5 μM with a coefficient R² = 0.986 and a detection limit of 0.2 μM. The cobalt tetracarboxylic acid phthalocyanine self-assembled monolayer was then evaluated as a mediator for glucose oxidase (GOx)-based biosensor. The GOx (enzyme) was immobilized covalently onto Au-ME-CoTCAPc SAM using coupling agents: N-ethyl-N(3-dimethylaminopropyl) carbodiimide (EDC) and N-hydroxy succinimide (NHS), and the results demonstrated a good catalytic behavior. Kinetic parameters associated with the enzymatic and mediator reactions were estimated using electrochemical versions of Lineweaver-Burk and Hanes equation, and the stability of the sensor was tested. The biosensor (Au-ME-CoTCAPc-GOx SAM) electrode showed good sensitivity (7.5 nA/mM) with a good detection limit of 8.4 μM at 3σ, smaller Michaelis-Menten constant (4.8 mM from Hanes plot) and very fast response time of approximately 5 s.     

A highly sensitive ascorbic acid sensor using a Ni–Pt electrode

An amperometric sensor that measured ascorbic acid by the oxidation of the ascorbic acid on a Ni–Pt electrode was fabricated. The Ni component of the Ni–Pt alloy played a crucial role as a modifier that developed an erinaceous surface, which enlarged the sensing area and increased the sensitivity of the electrode. The Pt₈₂Ni₁₈ electrode exhibited the best sensitivity of 333 μA cm⁻² mM⁻¹ for ascorbic acid sensing. This electrode was further tested for reproducibility of the sensitivity, endurance, and interference; it exhibited excellent performance compared with electrodes reported in the literature.     

Amperometric bienzyme glucose biosensor based on carbon nanotube modified electrode with electropolymerized poly(toluidine blue O) film

The amperometric bienzyme glucose biosensor utilizing horseradish peroxidase (HRP) and glucose oxidase (GOx) immobilized in poly(toluidine blue O) (PTBO) film was constructed on multi-walled carbon nanotube (MWNT) modified glassy carbon electrode. The HRP layer could be used to analyze hydrogen peroxide with toluidine blue O (TBO) mediators, while the bienzyme system (HRP + GOx) could be utilized for glucose determination. Glucose underwent biocatalytic oxidation by GOx in the presence of oxygen to yield H₂O₂ which was further reduced by HRP at the MWNT-modified electrode with TBO mediators. In the absence of oxygen, glucose oxidation proceeded with electron transfer between GOx and the electrode mediated by TBO moieties without H₂O₂ production. The bienzyme electrode offered high sensitivity for amperometric determination of glucose at low potential, displaying Michaelis-Menten kinetics. The bienzyme glucose biosensor displayed linear response from 0.1 to 1.2 mM with a sensitivity of 113 mA M⁻¹ cm⁻² at an applied potential of −0.10 V in air-saturated electrolytes.     

A new electrochemical biosensor for hydrogen peroxide using HRP/AgNPs/cysteamine/p-ABSA/GCE self-assembly modified electrode

An electrochemical hydrogen peroxide biosensor was designed by immobilizing horseradish peroxidase (HRP) on Ag nanoparticles/cysteamine/p-aminobenzene sulfonic acid/glassy carbon (GC) electrode. Ag nanoparticles can act as tiny conduction centers on electrodes that adsorb redox enzymes, facilitating the transfer of electrons with no requiring any loss of biological activity. The forerunner film was first electropolymerized on the glassy carbon electrode with p-aminobenzene sulfonic acid (p-ABSA) by cyclic voltammetry. The cysteamine (CA) was bound on the surface of the film by electrostatic force, then Ag nanoparticles were immobilized on the cysteamine monolayer, and lastly HRP was adsorbed onto the surfaces of the Ag nanoparticles. A dramatic decrease in the overvoltage of H₂O₂ was observed with improved sensitivity, which makes the modified electrodes of great promise for oxidase-based amperometric biosensors. The biosensor responded to H₂O₂ in the linear range from 1.2×10⁶ mol/L to 9.8×10³ mol/L with a detection limit of 1.1×10⁸ mol/L. Moreover, the obtained biosensor exhibited good accuracy and high sensitivity.     

Electrochemical characterization of cetyltrimethyl ammonium bromide modified carbon paste electrode and the application in the immobilization of DNA

A cetyltrimethyl ammonium bromide modified carbon paste electrode (CTAB/CPE) was developed in this work based on the surface modification method. The improved electrochemical response of K₄Fe(CN)₆ at this electrode indicated that CTAB could change the surface property of carbon paste electrodes (CPEs), which was demonstrated by the electrochemical impedance spectroscopy (EIS). In 0.1 mM [Fe(CN)₆]^3−/4−, a low exchange current (i₀) of 2.72×10⁻⁷ A at bare CPE was observed while that at CTAB/CPE was 6.79×10⁻⁵ A. The effect of CTAB concentration on the electrode quality revealed that CTAB formed a compact monolayer on the electrode surface with high density of positive charges directed outside the electrode. This electrode showed strong accumulation ability toward Fe(CN)₆⁴⁻ and can also accumulate Co(phen)₃²⁺ by the adsorption of the organic ligands in the hydrophobic area of the monolayer. The electrode was applied to the immobilization of DNA, which was characterized by the isotherm adsorption of Co(phen)₃²⁺.     

Porphyrin-functionalized gold nanoparticles for selective electrochemical detection of peroxyacetic acid

Two layers of cationic iron(III) meso-tetrakis (N-methylpyridinum-4-yl)porphyrin (FeTMPyP) and anionic gold nanoparticles (GNPs) were alternately assembled on a poly(diallyldimethylammonium chloride)-wrapped carbon nanotube (PDDA-CNT)-modified electrode via electrostatic interactions. The porphyrin-functionalized gold nanoparticles were characterized by scanning electron microscopy and UV–vis absorption spectrometry. The (FeTMPyP–GNP)₂/PDDA-CNT modified electrode showed two stable and well-defined peaks at −0.112 V and −0.154 V, which were attributed to the GNP-accelerated redox process of Fe(III)TMPyP/Fe(II)TMPyP. The modified electrode possessed excellent electrocatalytic behavior for the reduction of peroxyacetic acid (PAA). The resulting biosensor exhibited a fast amperometric response to PAA (∼3 s), with a wide linear range from 2.5 × 10⁻⁶ M to 1.05 × 10⁻³ M and a detection limit of 0.5 μM at a signal-to-noise ratio of 3. More importantly, H₂O₂ did not interfere with the detection. Thus, this biosensor enabled highly sensitive detection of PAA without removing H₂O₂ and showed a promising potential in practical applications.     

Wiring horseradish peroxidase on gold nanoparticles-based nanostructured polymeric network for the construction of mediatorless hydrogen peroxide biosensor

Gold electrodes were functionalized with an electropolymerized matrix of Au nanoparticles modified with 2-mercaptoethanesulfonic acid, 3-mercaptophenyl boronic acid and p-aminothiophenol. The resulting nanostructured electroconductive matrix was used as support for the oriented immobilization of horseradish peroxidase to construct a reagentless amperometric biosensor for H₂O₂. The electrode, poised at 0.0 mV, exhibited a rapid response within 8 s and a linear calibration range from 5 μM to 1.1 mM H₂O₂. The sensitivity of the biosensor was determined as 498 μA/M cm², and its detection limit was 1.5 μM H₂O₂ at a signal-to-noise ratio of 3. The electrode retained 95% and 72% of its initial activity after 21 and 40 days of storage at 4 °C.     

Glucose biosensor based on multiwalled carbon nanotubes grown directly on Si

An amperometric biosensor based on covalent immobilization of glucose oxidase (GOx) on multiwalled carbon nanotubes (MWCNTs) with potassium ferricyanide as the redox mediator was developed. The MWCNTs were grown directly on a layered structure of Co/Ti/Cr on a SiO₂/Si substrate by microwave-heated chemical vapor deposition. The mediator helps to shuttle the electrons between the immobilized GOx and the MWCNT electrode, therefore operating at a potential of 0.25 V vs. the saturated calomel electrode. This potential precludes the interfering compounds from oxidization. The sensitivity of biosensors to glucose was found to depend on the acid pretreatment and GOx reaction times. The steady-state response of the optimized biosensor exhibits a sensitivity of 20.6 μA mM⁻¹ cm⁻², a linear range of up to 8 mM, and a response time of <5 s.     

Use of biologically designed gold nanowire for biosensor application

A highly sensitive tyrosinase (TYR)-based amperometric biosensor is prepared using biologically designed gold nanowires (AuNWs) for pesticide detection. The AuNWs were synthesized by dodecapeptide Midas-11 and were modified with the formation of self-assembled monolayer (SAM), followed by covalent binding with TYR. The prepared TYR-AuNWs-SPCE (screen printed carbon electrode) was compared with bare, AuNWs-, modified-AuNWs-SPCE by the measurement of cyclic voltammetry. The quantitative relationship between the inhibition percentage and the pesticide concentration at the TYR-AuNWs-SPCE was obtained by measuring the current response in various concentrations of pesticides. The reasonable detection range of parathion was determined to be 0.1 ppt through 10 ppb (R ² =0.990) with 0.087 ppt of detection limits. The higher sensitivity and wider detection range of the TYR-based biosensor was achieved by the use of biologically synthesized AuNWs.     

Novel amperometric glucose biosensor based on an ether-linked cobalt(II) phthalocyanine-cobalt(II) tetraphenylporphyrin pentamer as a redox mediator

The development of cobalt(II) phthalocyanine-cobalt(II) tetra(5-phenoxy-10,15,20-triphenylporphyrin), (CoPc-(CoTPP)₄) pentamer as a novel redox mediator for amperometric enzyme electrode sensitive to glucose is described. A glassy carbon electrode (GCE) was first modified with the pentamer, then followed by the immobilization onto the GCE-CoPc-(CoTPP)₄ with glucose oxidase (GOx) through cross-linking with glutaraldehyde in the presence of bovine serum albumin (BSA) and Nafion^® cation-exchange polymer. The proposed biosensor displayed good amperometric respose charateristics to glucose in pH 7.0 PBS solution; such as low overpotentials (+400 mV versus Ag|AgCl), very fast amperometric response time (∼5 s), linear concentration range extended up to 11 mM, with 10 μM detection limit. The biosensor exhibited electrochemical Michaelis-Menten kinetics and showed an average apparent Michaelis-Menten constant (K^′M) of 14.91 ± 0.46 mM over a storage period of 2 weeks.     

Amperometric hydrogen peroxide biosensor based on a modified gold electrode with silver nanowires

A novel amperometric biosensor for the detection of hydrogen peroxide (H₂O₂) was prepared by immobilizing horseradish peroxidase (HRP) on highly dense silver nanowire (Ag-NW) film. The modified electrode was characterized using UV–Vis spectroscopy, scanning electron microscopy, X-ray diffraction, and transmission electron microscopy. The electrochemical performances of the electrode were studied by cyclic voltammetry and chronoamperometry. The HRPs immobilized on the surface of Ag-NWs exhibited an excellent electrocatalytic response toward reduction of H₂O₂. The resulting Ag-NW modified sensor showed a sensitivity of ~2.55 μA μM⁻¹ (correlation coefficient r = 0.9969) with a linear range of 4.8 nM–0.31 μM. Its detection limit was 1.2 nM with a signal-to-noise ratio of 3. The Michaelis–Menten constant K_M^app and the maximum current density I _max of the modified electrode were 0.0071 mM and 8.475 μA, respectively. The preparation process of the proposed biosensor was convenient, and the resulting biosensor showed high sensitivity, low detection limit and good stability.     

A novel multienzyme electrode for the determination of citrate

A novel amperometric biosensor for the determination of citric acid in food samples and fermentation broths has been developed. The sensor is composed of citrate lyase (CL, EC 4.1.3.6), oxaloacetate decarboxylase (OAC, EC 4.1.1.3) and pyruvate oxidase (POP, EC 1.2.3.3), co-immobilized in gelatin, and an amperometric transducer. A Clark-type O₂-electrode and a modified Clark-type H₂O₂-electrode were alternatively used as a transducer. The biosensor covers a linear detection range from 1 μmol dm^?3 to 1 mmol dm^?3 citrate, with a response time of 2·5 min for the steady state response. The lower detection limit for citrate is 0·5 μmol dm^?3. The response of the sensor remained constant for 8 days and decreased to 25% after 18 days at 20–23°C. The results obtained from citrate determinations in food samples and fermentation broths agree well with those determined by enzymatic sample anlaysis. The relative standard deviation for citrate determinations with the new biosensor was 2·2% (n = 7).     

Manganese oxide nanocomposites with improved surface area prepared by one-pot surfactant route for electro catalytic and biosensor applications

Braunite phase manganese oxide is naturally available in manganese–silicate rocks with minor amount of silicate content. New synthetic route is attempted to prepare the manganese oxide nanoparticle and silica incorporated manganese oxide nanocomposite in the present study. XRD patterns reveal the braunite phase formation for as synthesized manganese oxide nanocomposite and silica incorporated MnO₂ nanocomposite materials. Improved BET surface area values are achieved by one step surfactant assisted method (i.e., 82 and 151 m²/g) compared to conventional route prepared manganese oxide nanomaterial. Flaky pastry type morphology was observed for as synthesized Si–MnO₂ nanocomposites. Cyclic voltammetry studies predict the electrocatalytic activity of manganese oxide nanoparticle and Si–MnO₂ nanocomposite in presence of electroactive redox couple. Si–MnO₂ nanocomposite modified glassy carbon (GC) electrode shows the effective electroactive response in presence of Fe²⁺/Fe³⁺ redox couple at 0.69 V with current density of 0.343 × 10⁻⁵ A/cm² compared to manganese oxide nanoparticle modified GC electrode. The biosensor responses for ascorbic acid have been tested in the present study and manganese oxide nanoparticle modified GC electrode shows effective response at low concentration of (1 × 10⁻⁵ M) ascorbic acid in phosphate buffer solution. Manganese oxide nanoparticle modified electrode shows the better response with current density value of 0.115 × 10⁻⁵ A/cm² compared to Si–MnO₂ nanocomposite.     

Functionalized single-walled carbon nanotubes/polypyrrole composites for amperometric glucose biosensors

This article reports an amperometric glucose biosensor based on a new type of nanocomposite of polypyrrole (PPY) with p-phenyl sulfonate-functionalized single-walled carbon nanotubes (SWCNTs-PhSO₃⁻). An environmentally friendly functionalization procedure of the SWCNTs in the presence of substituted aniline and an oxidative species was adopted. The nanocomposite-modified electrode exhibited excellent electrocatalytic activities towards the reduction or oxidation of H₂O₂. This feature allowed us to use it as bioplatform on which glucose oxidase (GOx) was immobilized by entrapment in an electropolymerized PPY/SWCNTs-PhSO₃⁻ film for the construction of the glucose biosensor. The amperometric detection of glucose was assayed by applying a constant electrode potential value necessary to oxidize or reduce the enzymatically produced H₂O₂ with minimal interference from the possible coexisting electroactive compounds. With the introduction of a thin film of Prussian blue (PB) at the substrate electrode surface, the PPY/GOx/SWCNTs-PhSO₃⁻/PB system shows synergy between the PB and functionalized SWCNTs which amplifies greatly the electrode sensitivity when operated at low potentials. The biosensor showed good analytical performances in terms of low detection (0.01 mM), high sensitivity (approximately 6 μA mM⁻¹ cm⁻²), and wide linear range (0.02 to 6 mM). In addition, the effects of applied potential, the electroactive interference, and the stability of the biosensor were discussed. The facile procedure of immobilizing GOx used in the present work can promote the development of other oxidase-based biosensors which could have a practical application in clinical, food, and environmental analysis.     

Highly sensitive and selective dopamine detection by an amperometric biosensor based on tyrosinase/MWNT/GCE

Dopamine (3,4-dihydroxylphenyl ethylamine) is the most significant neurotransmitter in the human nervous system. Abnormal dopamine levels cause fatal neurological disorders, and thus measuring dopamine level in actual samples is important. Although electrochemical methods have been developed for detecting dopamine with high accuracy, certain substances (e.g., ascorbic acid) in actual samples often interfere with electrochemical dopamine detection. We developed tyrosinase-based dopamine biosensor with high sensitivity and selectivity. An electrochemically pretreated tyrosinase/multi-walled carbon nanotube-modified glassy carbon electrode (tyrosinase/MWNT/GCE) was prepared as an amperometric biosensor for selective dopamine detection. For optimizing the biosensor performance, pH, temperature, and scan rate were investigated. The electrochemically pretreated tyrosinase/MWNT/GCE exhibited not only the highest sensitivity (1,323 mAM^?1 cm^?2) compared to previously reported tyrosinase-based dopamine sensors, but also good long-term stability, retaining 90% of initial activity after 30 days. Additionally, ascorbic acid, a major interfering substances, was not oxidized at the potential used to detect dopamine oxidation, and the interfering effect of 4mM ascorbic acid was negligible when monitoring 1mM dopamine. Consequently, the electrochemically pretreated tyrosinase/MWNT/GCE is applicable for highly selective and sensitive dopamine detection in actual samples including interfering substances, thereby extending the practical use to monitor and diagnose neurological disorders.     

Electrochemical preparation and electrocatalytic properties of PEDOT/ferricyanide film-modified electrodes

The poly(3,4-ethylenedioxy thiophene) (PEDOT)/ferricyanide (FCN) film was synthesized by a potentiostatic and also using potentiodynamic methods namely cyclic voltammetric and chronoamperometric techniques. The EQCM technique was used to study the mechanism of the incorporation of ferricyanide ions on the PEDOT film. The UV-vis absorption results too confirmed the presence of ferricyanide with the PEDOT film. The electrocatalytic oxidation of ascorbic acid was carried out on a glassy carbon electrode modified with the PEDOT/FCN film through cyclic voltammetry, chronoamperometry and rotating disk electrode (RDE) voltammetry as diagnostic techniques. It was found that the catalytic current depended on the concentration of ascorbic acid. The number of electron transfer involved in the rate-determining step was found to be 1 and transfer coefficient (α) equal to 0.476. The diffusion coefficient of ascorbic acid was also estimated through the chrono amperometric and rotating disk electrode methods. The D values of ascorbic acid obtained by through the cyclic and chronoamperometric methods were found to be 4.4103 × 10⁻⁶ and 4.9595 × 10⁻⁶ cm² s⁻¹, respectively. This modified electrode was also used for the simultaneous determination of ascorbic acid and dopamine.     

A new amperometric glucose biosensor based on platinum nanoparticles/polymerized ionic liquid-carbon nanotubes nanocomposites

A new amperometric glucose biosensor has been developed based on platinum (Pt) nanoparticles/polymerized ionic liquid-carbon nanotubes (CNTs) nanocomposites (PtNPs/PIL-CNTs). The CNTs was functionalized with polymerized ionic liquid (PIL) through directly polymerization of the ionic liquid, 1-vinyl-3-ethylimidazolium tetrafluoroborate ([VEIM]BF₄), on carbon nanotubes and then used as the support for the highly dispersed Pt nanoparticles. The electrochemical performance of the PtNPs/PIL-CNTs modified glassy carbon (PtNPs/PIL-CNTs/GC) electrode has been investigated by typical electrochemical methods. The PtNPs/PIL-CNTs/GC electrode shows high electrocatalytic activity towards the oxidation of hydrogen peroxide. Taking glucose oxidase (GOD) as the model, the resulting amperometric glucose biosensor shows good analytical characteristics, such as a high sensitivity (28.28 μA mM⁻¹ cm⁻²), wide linear range (up to 12 mM) and low detection limit (10 μM).     

Seed-mediated growth of platinum nanoparticles on carbon nanotubes for the fabrication of electrochemical biosensors

Platinum nanoparticles (PtNPs) were prepared by seed-mediated growth method with Au nanoparticles (AuNPs) playing the role of seeds. Carbon nanotubes (CNTs) and AuNPs were first dropped onto the surface of glassy carbon (GC) electrode, and then the electrode was immersed into growth solution which contains H₂PtCl₆ and ascorbic acid. PtNPs were successfully grown onto the CNT surface due to the chemical reduction of Pt(IV). The electrode modified with AuNP_seed/PtNP/CNT film displayed excellent electrochemical response to H₂O₂ at 0.45 V versus saturated calomel electrode (SCE) with sensitivity much larger than that of PtNP/CNT and AuNP_seed/PtNP modified electrodes. Glucose oxidase was selected as a model enzyme and electrodeposited onto the AuNP_seed/PtNP/CNT modified electrode in the presence of a detergent. The resulting biosensor enabled selective determination of glucose with high sensitivity of 4.49 μA mM⁻¹, quick response time about 2 s, low-detection limit of 0.5 μM and wide linear range from 1 μM to 4 mM with a correlation coefficient 0.9998. Thus, the modified electrode proved to be a nice electrochemical biosensing platform for the fabrication of oxidase-based biosensors.