A sensitive DNA biosensor fabricated from gold nanoparticles, carbon nanotubes, and zinc oxide nanowires on a glassy carbon electrode

We outline here the fabrication of a sensitive electrochemical DNA biosensor for the detection of sequence-specific target DNA. Zinc oxide nanowires (ZnONWs) were first immobilized on the surface of a glassy carbon electrode. Multi-walled carbon nanotubes (MWCNTs) with carboxyl groups were then dropped onto the surface of the ZnONWs. Gold nanoparticles (AuNPs) were subsequently introduced to the surface of the MWNTs/ZnONWs by electrochemical deposition. A single-stranded DNA probe with a thiol group at the end (HS-ssDNA) was covalently immobilized on the surface of the AuNPs by forming an Au-S bond. Scanning electron microscopy (SEM) and cyclic voltammetry (CV) were used to investigate the film assembly process. Differential pulse voltammetry (DPV) was used to monitor DNA hybridization by measuring the electrochemical signals of [Ru(NH₃)₆]³⁺ bounding to double-stranded DNA (dsDNA). The incorporation of ZnONWs and MWCNTs in this sensor design significantly enhances the sensitivity and the selectivity. This DNA biosensor can detect the target DNA quantitatively in the range of 1.0 × 10⁻¹³ to 1.0 × 10⁻⁷ M, with a detection limit of 3.5 × 10⁻¹⁴ M (S/N = 3). In addition, the DNA biosensor exhibits excellent selectivity, even for single-mismatched DNA detection.     

Hybridization biosensor using sodium tanshinone IIA sulfonate as electrochemical indicator for detection of short DNA species of chronic myelogenous leukemia

Cyclic voltammetry (CV) was used to investigate electrochemical behavior of sodium tanshinone IIA sulfonate (STS) and the interaction between STS and salmon sperm DNA. STS had excellent electrochemical activity on the glassy carbon electrode (GCE) with a couple reversible redox peaks. In pH 4.0 phosphate buffer solution (PBS), the binding ratio between STS and salmon sperm DNA was calculated to be 1:1 and the binding constant was 1.67 × 10⁴ L/mol. A chronic myelogenous leukemia (CML, Type b3a2) DNA biosensor was developed by immobilizing covalently single-stranded CML DNA fragment to a modified GCE. The surface hybridization of the immobilized single-stranded CML DNA fragment with its complementary DNA fragment was evidenced by electrochemical methods using STS as a novel electrochemical indicator, with a detection limit of 6.7 × 10⁻⁹ M and a linear range from 2.0 × 10⁻⁸ M to 2.0 × 10⁻⁷ M. Selective determination of complementary ssDNA was achieved using differential pulse voltammetry (DPV).     

A DNA electrochemical sensor with poly-l-lysine/single-walled carbon nanotubes films and its application for the highly sensitive EIS detection of PAT gene fragment and PCR amplification of NOS gene

A sensitive and novel DNA electrochemical biosensor for the detection of the transgenic plants gene fragment by electrochemical impedance spectroscopy (EIS) was presented. The well-dispersed carboxylic group-functionalized single-walled carbon nanotubes (SWNTs) were dripped onto the carbon paste electrode (CPE) surface firstly, and poly-l-lysine films (pLys) were subsequently electropolymerized by cyclic voltammetry (CV) to prepare pLys/SWNTs/CPE. The morphology of pLys/SWNTs films was examined using a field emission scanning electron microscope (SEM). The pLys/SWNTs films modified electrode exhibited very good conductivity. DNA probes were easily immobilized on the poly-l-lysine films via electrostatic adsorption. The hybridization events were monitored with electrochemical impedance spectroscopy using [Fe(CN)₆]^3−/4− as indicator. The PAT gene fragment from phosphinothricin acetyltransferase gene was detected by this DNA electrochemical sensor. The dynamic detection range of this sensor to the PAT gene fragment was from 1.0 × 10⁻¹² to 1.0 × 10⁻⁷ mol/L. A detection limit of 3.1 × 10⁻¹³ mol/L could be estimated. The PCR amplification of NOS gene from the sample of a kind of transgenic modified bean was also detected satisfactorily by EIS.     

Electrochemical detection of DNA hybridization using a water-soluble branched polyethyleneimine-cobalt(III)-phenanthroline indicator and PNA probe on Au electrodes

An electrochemical method for the detection of DNA hybridization using a novel electroactive, cationic, and water-soluble branched polyethyleneimine (BPEI)-cobalt(III)-phenanthroline(phen) polymeric indicator and single-stranded neutral peptide nucleic acid (PNA) probe on the Au electrode was developed. The indicator possesses some free amine groups, as well as cationic cobalt complexes in the polymer chain. It does not bind to neutral PNA capture probe alone. However, the indicator strongly interacts with the negatively charged backbone of the complementary oligonucleotide bound to the PNA probe through electrostatic interactions. The coordination spherical moieties also interact with the probe by embedding into the double-helix structure of PNA-DNA. These two interactions enable transduction of hybridization, producing a clear electrical signal in differential pulse voltammetry (DPV). The correlation against non-complementary DNA, three-base and one-base mismatch DNA was sharp, and the signal of indicator for the target DNA demonstrated a linear relationship within the concentration range of 5.0 × 10⁻⁹ to 2.5 × 10⁻⁷ M (R = 0.9940) with a detection limit of 5.6 × 10⁻¹⁰ M. These studies showed that the novel polymeric indicator and single-stranded PNA probe could be used to fabricate an electrochemical biosensor for DNA detection. This technique can provide an alternative route for expanding the range of detection methods available for DNA hybridization.     

A novel electrochemical DNA biosensor based on graphene and polyaniline nanowires

A novel DNA biosensor based on oxidized graphene and polyaniline nanowires (PANIws) modified glassy carbon electrode was developed. The resulting graphene/PANIw layers exhibited good DPV current response for the complementary DNA sequences. The good electron transfer activity might be attributed to the effect of graphene and PANIw. Graphene and PANIw nanolayers film with highly conductive and biocompatible nanostructure were characterized by scanning electron microscopy (SEM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The immobilization of the probe DNA on the surface of electrode was largely improved due to the unique synergetic effect of graphene and PANIw. Under optimum conditions, the biosensor exhibited a fast amperometric response, high sensitivity and good storage stability for monitoring DNA. The current response of the sensor increases linearly with the concentration of target from 2.12 × 10⁻⁶ to 2.12 × 10⁻¹² mol l⁻¹ with a relative coefficient of 0.9938. The detection limit (3σ) is 3.25 × 10⁻¹³ mol l⁻¹. The results indicate that this modified electrode has potential application in sensitive and selective DNA detection.     

Electrochemical detection of avian influenza virus H5N1 gene sequence using a DNA aptamer immobilized onto a hybrid nanomaterial-modified electrode

A sensitive electrochemical method for the detection of avian influenza virus (AIV) H5N1 gene sequence using a DNA aptamer immobilized onto a hybrid nanomaterial-modified electrode was developed. To enhance the selectivity and sensitivity, the modified electrode was assembled with multi-wall carbon nanotubes (MWNT), polypyrrole nanowires (PPNWs) and gold nanoparticles (GNPs). This electrode offered a porous structure with a large effective surface area, highly electrocatalytic activities and electronic conductivity. Therefore, the amount of DNA aptamer immobilized onto the electrode was increased while the accessibility of the detection target was maintained. The biosensor is based on the hybridization and preferred orientation of a DNA aptamer immobilized onto a modified electrode surface with its target (H5N1 specific sequence) present in solution. It is selective for the H5N1 specific sequence, and the signal of the indicator was approximately linear to log(concentration) of the H5N1 specific sequence from 5.0 × 10⁻¹² to 1.0 × 10⁻⁹ M (R = 0.9863) with a detection limit of 4.3 × 10⁻¹³ M. These studies showed that the new hybrid nanomaterial (MWNT/PPNWs/GNPs) and the DNA aptamer could be used to fabricate an electrochemical biosensor for gene sequence detection. Furthermore, this design strategy is expected to have extensive applications in other biosensors.     

Electrochemical biosensor based on the interaction between copper(II) complex with 4,5-diazafluorene-9-one and bromine ligands and deoxyribonucleic acid

The copper complex of 4,5-diazafluorene-9-one (dafone) and bromine ligands ([Cu(dafone)₂]Br₂) was prepared and its interaction with double-stranded salmon sperm DNA (dsDNA) in pH 8.0 Britton-Robinson (B-R) buffer solution was studied by electrochemical experiments at the glassy carbon electrode (GCE). It was revealed that Cu(dafone)₂Br₂ could bind with salmon sperm DNA strands mainly by intercalation mode. The binding number of [Cu(dafone)₂]Br₂ for each salmon sperm dsDNA chain and equilibrium constant of the binding reaction were calculated to be 3 and 2.8 × 10¹² L³ mol⁻³, respectively. The Cu(dafone)₂Br₂ was further utilized as a new electrochemical DNA indicator for the detection of human hepatitis B virus (HBV) DNA fragment by differential pulse voltammetry (DPV). The difference of its electrochemical responses occurred between hybridized dsDNA duplex and probe DNA was explored to assess the selectivity of the developed electrochemical DNA biosensor. The constructed electrochemical DNA biosensor achieved a detection limit of 3.18 × 10⁻⁹ mol L⁻¹ for complementary target DNA and also realized a robust stability and good reusability.     

DNA Langmuir-Blodgett modified glassy carbon electrode as voltammetric sensor for determinate of methotrexate

A highly sensitive electrochemical biosensor for the detection of trace amounts of methotrexate has been designed. Double stranded (ds)DNA molecules are immobilized onto a pretreated glassy carbon electrode (GCE(ox)) surface with Langmuir-Blodgett (LB) technique. The adsorptive voltammetric behaviors of methotrexate on DNA-modified electrode were explored by means of cyclic voltammetry (CV) and square wave voltammetry (SWV). The oxidation mechanism was proposed and discussed in this work. In addition, the optimum experimental conditions for the detection of methotrexate were explored, and the currents measured by SWV presented a good linear property as a function of the concentrations of methotrexate in the range of 2.0 × 10⁻⁸ to 4.0 × 10⁻⁶ mol L⁻¹, with an LOD of 5.0 × 10⁻⁹ mol L⁻¹. The method proposed was applied for the determination of methotrexate in pharmaceutical dosage and diluted human urine with wonderful satisfactory successfully.     

Functionalized carbon nanotube-bienzyme biocomposite for amperometric sensing

An approach to design a biocomposite bienzyme biosensor with the aim of evaluating its suitability as an amperometric sensor using functionalized multiwalled carbon nanotubes (MWCNTs) is presented. The biosensor is based on a bienzyme-channelling configuration, employing the enzymes glucose oxidase (GOx) and horseradish peroxidase (HRP), which were immobilized with toluidine blue (TB) functionalized MWCNTs. The proposed method demonstrates an easy electron transfer between the immobilized enzymes and the electrode via functionalized MWCNTs in a Nafion matrix. Co-immobilization of GOx and HRP was employed to establish the feasibility of fabricating highly effective bienzyme-based biosensors for low-level glucose determination. Bienzyme immobilized TB functionalized MWCNTs were attached to a glassy carbon electrode, and the electrochemical behavior of the sensor was studied using electrochemical impedance spectroscopy, cyclic voltammetry and chronoamperometry. The excellent electrocatalytic activity of the biocomposite film resulted in the detection of glucose under reduced over potential with a wider range of determination from 1.5 × 10⁻⁸ M to 1.8 × 10⁻³ M and with a detection limit of 3 × 10⁻⁹ M. The sensor showed a short response time (within 2 s), good stability and anti-interferant ability. The proposed biosensor exhibits good analytical performance in terms of repeatability, reproducibility and shelf-life stability.     

Ru(bpy)3-doped silica nanoparticle DNA probe for the electrogenerated chemiluminescence detection of DNA hybridization

A sensitive electrogenerated chemiluminescence (ECL) detection of DNA hybridization, based on tris(2,2′-bipyridyl)ruthenium(II)-doped silica nanoparticles (Ru(bpy)₃²⁺-doped SNPs) as DNA tags, is described. In this protocol, Ru(bpy)₃²⁺-doped SNPs was used for DNA labeling with trimethoxysilylpropydiethylenetriamine(DETA) and glutaraldehyde as linking agents. The Ru(bpy)₃²⁺-doped SNPs labeled DNA probe was hybridized with target DNA immobilized on the surface of polypyrrole (PPy) modified Pt electrode. The hybridization events were evaluated by ECL measurements and only the complementary sequence could form a double-stranded DNA (dsDNA) with DNA probe and give strong ECL signals. A three-base mismatch sequence and a non-complementary sequence had almost negligible responses. Due to the large number of Ru(bpy)₃²⁺ molecules inside SNPs, the assay allows detection at levels as low as 1.0 × 10⁻¹³ mol l⁻¹ of the target DNA. The intensity of ECL was linearly related to the concentration of the complementary sequence in the range of 2.0 × 10⁻¹³ to 2.0 × 10⁻⁹ mol l⁻¹.     

Voltammetric determination of paraquat at DNA-gold nanoparticle composite electrodes

A novel electroanalytical method for the detection of paraquat using DNA modified gold nanoparticles immobilized at a gold electrode is demonstrated. The electrode surface was first modified using the self-assembly of gold nanoparticles (NPs) followed by the simple adsorption of DNA onto the NPs, which was straightforward, fast and cost effective. The DNA-nanoparticle composite sensor was then characterized in terms of electrochemical responses both in the absence and in the presence of paraquat using cyclic voltammetry, differential pulse voltammetry and square wave voltammetry. The DNA-NPs composite electrode proved to work adequately as a biosensor for the quantitative analysis of paraquat concentrations, taking advantage of utilizing both the modified gold nanoparticles and the interaction between DNA with paraquat molecules. In addition, the NPs modified electrode demonstrated good sensitivity and stability towards the first reversible reduction step of the double charged paraquat ion. Good linearity between paraquat concentration and peak current was observed for the concentration range of 5.0 × 10⁻⁶ to 1.0 × 10⁻³ M when using differential pulse voltammetry. The use of modified electrodes improves the performance of the biosensor in the presence of interfering species in particular when square wave voltammetry is used.     

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.     

Polyaniline Langmuir-Blodgett film modified glassy carbon electrode as a voltammetric sensor for determination of Ag ions

A highly sensitive electrochemical sensor made of a glassy carbon electrode (GCE) coated with a Langmuir-Blodgett film (LB) containing polyaniline (PAn) doped with p-toluenesulfonic acid (PTSA) (LB/PAn-PTSA/GCE) has been used for the detection of trace concentrations of Ag⁺. UV-vis absorption spectra indicated that the PAn was doped by PTSA. The surface morphology of the PAn LB film was characterized by atomic force microscopy (AFM). The electrochemical properties of this LB/PAn-PTSA/GCE were studied using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry. The LB/PAn-PTSA/GCE was used as a voltammetric sensor for determination of trace Ag⁺ at pH 5.0 using linear scanning stripping voltammetry. Under the optimal experimental conditions, the stripping current was proportional to the Ag⁺ concentration over the range from 6.0 × 10⁻¹⁰ mol L⁻¹ to 1.0 × 10⁻⁶ mol L⁻¹, with a detection limit of 4.0 × 10⁻¹⁰ mol L⁻¹. The high sensitivity, selectivity, and stability of this LB/PAn-PTSA/GCE also demonstrated its practical utility for simple, rapid and economical determination of Ag⁺ in water samples.     

Sensitive DNA impedance biosensor for detection of cancer, chronic lymphocytic leukemia, based on gold nanoparticles/gold modified electrode

A simple and sensitive DNA impedance sensor was prepared for the detection of chronic lymphocytic leukemia. The DNA electrochemical biosensor is worked based on the electrochemical impedance spectroscopic (EIS) detection of the sequence-specific DNA related to chronic lymphocytic leukemia. The ssDNA probe was immobilized on the surface of the gold nanoparticles. Compared to the bare gold electrode, the gold nanoparticles-modified electrode could improve the density of the probe DNA attachment and hence the sensitivity of the DNA sensor greatly. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy were performed in a solution containing 1.0 mmol L⁻¹ K₃[Fe(CN)₆]/K₄[Fe(CN)₆] and 50 mmol L⁻¹ phosphate buffer saline pH 6.87 plus 50 mmol L⁻¹ KCl. In the CV studied, the potential was cycled from 0.0 to +0.65 V with a scan rate of 50 mV s⁻¹. Using EIS, the difference of the electron transfer resistance (ΔR_et) was linear with the logarithm of the complementary oligonucleotides sequence concentrations in the range of 7.0 × 10⁻¹²–2.0 × 10⁻⁷ mol L⁻¹, with a detection limit of 1.0 × 10⁻¹² mol L⁻¹. In addition, the DNA sensor showed a good reproducibility and stability during repeated regeneration and hybridization cycles.     

An improved DNA biosensor built by layer-by-layer covalent attachment of multi-walled carbon nanotubes and gold nanoparticles

In this work, we synthesized a type of compound, MWCNTs-CONH-(CH₂)₂-SH, via carboxylation, and investigated a thickness-tunable multilayer films DNA biosensor built by layer-by-layer (LBL) covalent attachment of gold nanoparticles (GNPs) and multi-walled carbon nanotubes (MWCNTs) on an Au electrode. Fourier transform infrared (FT-IR) spectra were used to identify the products formed in the step of carboxylation; scanning electron microscopy (SEM) and cyclic voltammetry (CV) were used to study the film assembly process. The hybridization events were monitored through measurement the signal of intercalated doxorubicin by differential pulse voltammetry (DPV), and the oxidation peak currents show a good linear relationship with the logarithm of the concentration of target DNA from 5.0 × 10⁻¹⁰ to 1.0 × 10⁻¹¹ M with a detection limit of 6.2 pM. The improved DNA biosensor has a good stability and reproducibility.     

Electrochemical sensing based on graphene oxide/Prussian blue hybrid film modified electrode

A novel graphene oxide (GO)/Prussian blue (PB) hybrid film was constructed by electropolymerizing Prussian blue onto the GO modified glassy carbon electrode, and its electrochemical behaviors were studied. Raman spectra were used to investigate the successful formation of the GO/PB hybrid film. Electrochemical experiments showed that the graphene oxide greatly enhanced electrochemical reactivity of the PB. Moreover, a much higher Prussian blue (PB) loading (6.388 × 10⁻⁸ mol cm⁻²) is obtained as compared to the bare glass carbon surface (3.204 × 10⁻⁹ mol cm⁻²). The GO/PB hybrid film modified electrode was used for the sensitive detection of hydrogen peroxide. The sensor exhibited a wide linearity range from 5.0 × 10⁻⁶ to 1.2 × 10⁻³ M with a detection limit of 1.22 × 10⁻⁷ M (S/N = 3), high sensitivity of 408.7 μA mM⁻¹ cm⁻² and good reproducibility. Furthermore, with glucose oxidase (GOD) as a model, the GO/PB/GOD/chitosan composite-modified electrode was also constructed.The resulting biosensor exhibited good amperometric response to glucose with linear range from 0.1 to 13.5 mM at 0.1 V, good reproducibility and detection limit of 3.43 × 10⁻⁷ M (S/N = 3). In addition, the biosensor presented high selectivity and long-term stability. Therefore, the PB/GO hybrid films-based modified electrode may hold great promise for electrochemical sensing and biosensing applications.     

Electrochemical and spectroscopic properties of dendritic cobalto-salicylaldiimine DNA biosensor

A metallodendrimer-based electrochemical DNA biosensor was constructed by a layer-by-layer assembly of cobalt(II) salicylaldiimine metallodendrimer (SDD-Co(II)) and a 21 bases oligonucleotide NH₂-5′-GAGGAGTTGGGGGAGCACATT-3′ (pDNA) on a gold electrode. The complementary oligonucleotide was 5′-AATGTGCTCCCCCAACTCCTC-3′ (tDNA). UV-visible spectra of SDD-Co(II) in 1:1 (v/v) acetone-ethanol solution showed absorption bands at 325 nm and 365-420 nm related to π-π* intra-dendrimer transitions and d-π* metal-dendrimer charge transfer transitions, respectively. Square-wave voltammetry (SWV) characterisation of the Au|SDD-Co(II)|pDNA biosensor system in phosphate buffer saline solution of pH 7.4, indicated a reversible one-electron electrochemical process with a formal potential, E°′, value of +210 mV. Electrochemical impedance spectroscopy (EIS) data confirmed that the hybridisation of the biosensor's pDNA with the tDNA to form double-stranded DNA (dsDNA) resulted in an increase of the impedimetric charge transfer resistance, R_ct, value from 6.52 to 12.85 kΩ. The limit of detection (LOD), calculated as 3σ of the background noise, and sensitivity of the sensor were 1.29 kΩ/nmol L⁻¹ and 0.34 pmol L⁻¹, respectively.     

Multilayer membranes via layer-by-layer deposition of PDDA and DNA with Au nanoparticles as tags for DNA biosensing

A novel Au nanoparticles (Au-NPs)-based protocol for DNA hybridization detection based on assembly of alternating DNA and poly(dimethyldiallylammonium chloride) (PDDA) multilayer films by layer-by-layer (LBL) electrostatic adsorption has been studied. Electrochemical impedance spectroscopy (EIS) and UV-vis absorbance measurements were used to study the film assembly. All the results indicate that the uniform multilayer can be obtained on the polypyrrole (PPy) coated electrode surface and the hybridization reaction can be amplified by the layer-by-layer progress. The hybridization was detected by the reductive signal of Au-NPs and nonspecific adsorption was greatly eliminated by an unrelated DNA sequence to the target DNA. Under optimum conditions, a significant sensitivity enhancement had been obtained, and the detection limit was down to 3.20 × 10⁻¹⁴ M when 6 layers assembled. The DNA biosensor has good stability and reproducibility.     

An electrochemical DNA biosensor developed on novel multinuclear nickel(II) salicylaldimine metallodendrimer platform

An electrochemical DNA biosensor (EDB) was prepared using an oligonucleotide of 21 bases with sequence NH₂-5′-GAGGAGTTGGGGGAGCACATT-3′ (probe DNA) immobilized on a novel multinuclear nickel(II) salicylaldimine metallodendrimer on glassy carbon electrode (GCE). The metallodendrimer was synthesized from amino functionalized polypropylene imine dendrimer, DAB-(NH₂)₈. The EDB was prepared by depositing probe DNA on a dendrimer-modified GCE surface and left to immobilize for 1 h. Voltammetric and electrochemical impedance spectroscopic (EIS) studies were carried out to characterize the novel metallodendrimer, the EDB and its hybridization response in PBS using [Fe(CN)₆]^3−/4− as a redox probe at pH 7.2. The metallodendrimer was electroactive in PBS with two reversible redox couples at E°′ = +200 mV and E°′ = +434 mV; catalytic by reducing the E_pa of [Fe(CN)₆]^3−/4− by 22 mV; conducting and has diffusion coefficient of 8.597 × 10⁻⁸ cm² s⁻¹. From the EIS circuit fitting results, the EDB responded to 5 nM target DNA by exhibiting a decrease in charge transfer resistance (R_ct) in PBS and increase in R_ct in [Fe(CN)₆]^3−/4− redox probe; while in voltammetry, increase in peak anodic current was observed in PBS after hybridization, thus giving the EDB a dual probe advantage.     

Electrochemical study on cobalt film modified glassy carbon electrode and its application

A novel electroactive material for ascorbic acid (AA) determination was successfully prepared by plating/potential cycling method. The cobalt film was first deposited on the surface of glassy carbon electrode (GCE) in CoSO₄ solution by potential cycling, and then a cobalt film on the surface of GCE was activated by potential cycling in 0.1 mol L⁻¹ NaOH. The electrochemical performance of the resulted film (Co/GCE) and factors affecting its electrochemical activity were investigated by cyclic voltammetry and amperometry. This film electrode exhibited good electrocatalytic activity to the oxidation of AA. This biosensor had a fast response of AA less than 3 s and excellent linear relationships were obtained in the concentration range of 3 × 10⁻⁷ to 1 × 10⁻⁴ mol L⁻¹ with a detection limit of 2 × 10⁻⁷ mol L⁻¹ (S/N = 3) under the optimum conditions. Moreover, the selectivity, stability and reproducibility of this biosensor were evaluated with satisfactory results.