Electrochemical impedance spectroscopy for study of amyloid beta-peptide interactions with (-) nicotine ditartrate and (-) cotinine

Immobilization of amyloid beta (Abeta) (1-40) peptide on Au-colloid modified gold electrodes has been studied. Colloidal Au was self-assembled onto gold electrodes through the thiol groups of 1,6-hexanedithiol monolayer. Next, buffered aqueous solution of Abeta (1-40) peptide existing in the beta-sheet structure in the acidic media was dropped on the electrode surface. Each step of electrode modification has been confirmed with cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The changes of the resistance of the layer with deposited Abeta (1-40) peptide, occurred under stimulation by different concentration of (-) nicotine ditartrate and (-) cotinine were measured with EIS and were used for the calculation of association constants. The gentle measuring conditions applied in electrochemical impedance spectroscopy, together with suitable environment for biomolecules immobilization created by Au-colloid, might be recommended as the analytical tool for assessing the effectiveness of potential drugs used in Alzheimer's disease (AD) therapy.     

A novel detection strategy for odorant molecules based on controlled bioengineering of rat olfactory receptor I7

In this study, we report a dose-dependent detection of odorant molecules in solution by rat olfactory receptor I7 (OR I7) in its membrane fraction. The OR I7 is immobilized on a gold electrode by multilayer bioengineering based on a mixed self-assembled monolayer and biotin/avidin system, which allows for a well-controlled immobilization of the bioreceptor within its lipid environment. The odorant detection is electronically performed in a quantitative manner by electrochemical impedance spectroscopy (EIS) measurements on samples and controls.     

Electrochemical optical waveguide lightmode spectroscopy (EC-OWLS): a pilot study using evanescent-field optical sensing under voltage control to monitor polycationic polymer adsorption onto indium tin oxide (ITO)-coated waveguide chips

A new technique has been developed that combines evanescent-field optical sensing with electrochemical control of surface adsorption processes. This new technique, termed "electrochemical optical waveguide lightmode spectroscopy" (EC-OWLS), proved efficient in monitoring molecular surface adsorption and layer thickness changes of an adsorbed polymer layer examined in situ as a function of potential applied to a waveguide in a pilot study. For optical sensing, a layer of indium tin oxide (ITO) served as both a high-refractive-index waveguide and a conductive electrode. In addition, an electrochemical flow-through fluid cell was provided, which incorporated working, reference, and counter electrodes, and was compatible with the constraints of optical sensing. Poly(L-lysine)-grafted-poly(ethylene glycol) (PLL-g-PEG) served as a model, polycation adsorbate. Adsorption of PLL-g-PEG from aqueous buffer solution increased from 125 to 475 ng/cm(2 )along a sigmoidal path as a function of increasing potential between 0 and 1.5 V versus the Ag reference electrode. Upon buffer rinse, adsorption was partially reversible when a potential of >/=0.93 V was maintained on the ITO waveguide. However, reducing the applied potential back to 0 V before rinsing resulted in irreversible polymer adsorption. PLL-g-PEG modified with biotin demonstrated similar adsorption characteristics, but subsequent streptavidin binding was independent of biotin concentration. Applying positive potentials resulted in increased adsorbed mass, presumably due to polymer chain extension and reorganization in the molecular adlayer.     

Voltage Biasing, Cyclic Voltammetry, & Electrical Impedance Spectroscopy for Neural Interfaces

Electrical impedance spectroscopy (EIS) and cyclic voltammetry (CV) measure properties of the electrode-tissue interface without additional invasive procedures, and can be used to monitor electrode performance over the long term. EIS measures electrical impedance at multiple frequencies, and increases in impedance indicate increased glial scar formation around the device, while cyclic voltammetry measures the charge carrying capacity of the electrode, and indicates how charge is transferred at different voltage levels. As implanted electrodes age, EIS and CV data change, and electrode sites that previously recorded spiking neurons often exhibit significantly lower efficacy for neural recording. The application of a brief voltage pulse to implanted electrode arrays, known as rejuvenation, can bring back spiking activity on otherwise silent electrode sites for a period of time. Rejuvenation alters EIS and CV, and can be monitored by these complementary methods. Typically, EIS is measured daily as an indication of the tissue response at the electrode site. If spikes are absent in a channel that previously had spikes, then CV is used to determine the charge carrying capacity of the electrode site, and rejuvenation can be applied to improve the interface efficacy. CV and EIS are then repeated to check the changes at the electrode-tissue interface, and neural recordings are collected. The overall goal of rejuvenation is to extend the functional lifetime of implanted arrays.     

Electrochemical impedimetric immunosensor for insulin like growth factor-1 using specific monoclonal antibody-nanogold modified electrode

An electrochemical impedimetric immunosensor was developed for ultrasensitive determination of insulin-like growth factor-1 (IGF-1) based on immobilization of a specific monoclonal antibody on gold nanoparticles (GNPs) modified gold electrode. Self-assembly of colloidal gold nanoparticles on the gold electrode was conducted through the thiol groups of 1,6-hexanedithiol (HDT) monolayer as a cross linker. The redox reactions of [Fe(CN)(6)](4-)/[Fe(CN)(6)](3-) on the electrode surface was probed for studying the immobilization and determination processes, using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The interaction of antigen with grafted antibody recognition layer was carried out by soaking the modified electrode into antigen solution at 37°C for 3 h. The immunosensor showed linearity over 1.0-180.0 pg mL(-1) and the limit of detection was 0.15 pg mL(-1). The association constant between IGF-1 and immobilized antibody was calculated to be 9.17×10(11) M(-1). The proposed method is a useful tool for screening picogram amounts of IGF-1 in clinical laboratory as a diagnostic test.     

Label-free impedimetric immunosensor for ultrasensitive detection of cancer marker Murine double minute 2 in brain tissue

The detection of cancer biomarkers is as important tool for the diagnosis and prognosis of cancer such as brain cancer. Murine double minute 2 (MDM2) has been widely studied as prognostic marker for brain tumor. Here we describe development of a new sensitive label free impedimetric immunosensor for the detection of MDM2 based on cysteamine self assembled monolayers on a clean polycrystalline Au electrode surface. The amine-modified electrodes were further functionalized with antibody using homobifunctional 1,4-phenylene diisothiocyanate (PDITC) linker. The assembly processes of the immunosensor had been monitored with cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques using Fe(CN)(6)(3-/4-) solution as redox probe. The impedance changes upon binding of MDM2 protein to the sensor surface was utilized for the detection of MDM2. The increase in relative electron-transfer resistance (ΔR/R(0)%) values was linearly proportional to the concentration of tumor marker MDM2 in the wide dynamic range of 1pg/ml-1μg/ml. The limit of detection was 0.29pg/ml in phosphate buffer saline (PBS) and 1.3pg/ml in mouse brain tissue homogenate, respectively. The immunosensor showed a good performance in comparison with ELISA for the analysis of the MDM2 in the cancerous mouse brain tissue homogenates. Moreover, the immunosensor had a good selectivity against epidermal growth factor receptor (EGFR) protein, long-storage stability and reproducibility. It might be become a promising assay for clinical diagnosis and early detection of tumors.     

Modification of carbon nanotubes with redox hydrogel: improvement of amperometric sensing sensitivity for redox enzymes

This study demonstrated that redox hydrogel-modified carbon nanotube (CNT) electrodes can be developed as an amperometric sensor that are sensitive, specific and fast and do not require auxiliary enzymes. A redox polymer, poly(vinylimidazole) complexed with Os(4,4'-dimethylbpy)(2)Cl (PVI-dmeOs) was electrodeposited on Ta-supported multi-walled CNTs. The resulted PVI-dmeOs thin film did not change the surface morphology of the CNTs, but turned the CNT surface from hydrophobic to hydrophilic, as studied by scanning electron microscopy (SEM) and static water contact angle measurements. Cyclic voltammetry measurements in a Fe(CN)(6)(3-) solution and electrochemical impedance measurements in an equimolar Fe(CN)(6)(3-/4-) solution demonstrated that the PVI-dmeOs hydrogel thin film was electronic conductive with a resistance of about 15Omega. The PVI-dmeOs/CNT electrodes sensed rapidly, sensitively and specifically to model redox enzymes (glucose oxidase (GOD) and lactate oxidase (LOD)) in amperometric experiments in electrolyte solutions containing the substrates of the measured redox enzymes. Both the CNT substrate and the thin PVI-dmeOs film enhanced the sensing sensitivities. Exploration of the mechanisms suggests that the PVI-dmeOs film may enhance the sensing sensitivities by wiring the enzyme molecules through the redox centers tethered on the mobile redox polymer backbones to the CNT electrodes.     

Electrochemical impedance immunosensor based on gold nanoparticles and aryl diazonium salt functionalized gold electrodes for the detection of antibody

Electrodes modified with passivating organic layers have been shown to, here and previously, to exhibit good Faradaic electrochemistry upon attachment of gold nanoparticles (AuNP). Due to their low background capacitances these constructs have good potential in electrochemical sensing. Herein is reported the application of these electrode constructs for impedance based immunosensing. The immunosensor was constructed by modifying a gold electrode with 4-thiophenol (4-TP) passivating layers by diazonium salt chemistry. Subsequently, the attachment of AuNP and then a biotin derivative as a model epitope to detect anti-biotin IgG were carried out. The interfacial properties of the modified electrodes were evaluated in the presence of Fe(CN)(6)(4-/3-) redox couple as a probe by cyclic voltammetry and electrochemical impedance spectroscopy. The impedance change, due to the specific immuno-interaction at the immunosensor surface was utilized to detect anti-biotin IgG. The increase in charge-transfer resistance (R(ct)) was linearly proportional to the concentration of anti-biotin IgG in the range of 5-500 ng mL(-1), with a detection limit of 5 ng mL(-1).     

Investigation of interfacial capacitance of Pt,Ti and TiN coated electrodes by electrochemical impedance spectroscopy

Electrochemical processes at the electrode-electrolyte (body fluid) interface are of ultimate importance for stimulating/sensing electrode function. A high electrode surface area is desirable for safe stimulation through double-layer charging and discharging. Pt and Pt-Ir alloys have been the most common electrode materials. The use of TiN coating as the surface layer on the electrode has found increasing interest because of its metal-like conductivity, excellent mechanical and chemical properties, and the fact that it can be deposited with a high surface area. In this work, electrochemical impedance spectroscopy (EIS), which is a sensitive and non-destructive technique and widely used for characterization of electrical properties of electrode-electrolyte interfaces, was applied to investigate pure Pt and Ti, and TiN coated electrodes exposed to a phosphate-buffered-saline (PBS) solution. Platinized Pt and Ti were also studied for comparison. The capacitance value of the electrodes in PBS was obtained through quantitative analysis of the EIS spectra. The results reveal that the capacitance of the TiN coated electrodes with a rough surface is several hundreds times higher than that of a smooth Pt surface. Platinization of Ti can also increase the capacitance to the same extent as platina. EIS has been shown to be a powerful technique for characterization of stimulating/sensing electrodes.     

A novel sensor based on electrochemical polymerization of diglycolic acid for determination of acetaminophen

Diglycolic acid (DA) polymer was coated on glassy carbon (GC) electrode by cyclic voltammetry (CV) technique for the first time. The electrochemical performances of the modified electrode were investigated by CV and electrochemical impedance (EIS). The obtained electrode showed an excellent electrocatalytic activity for the oxidation of acetaminophen (ACOP). A couple of well-defined reversible electrochemical redox peaks were observed on the ploy(DA)/GC electrode in ACOP solution. Compared with bare GC electrode, the oxidation peak potential of ACOP on ploy(DA)/GC electrode moved from 0.289 V to 0.220 V. Meanwhile, the oxidation peak current was much higher on the modified electrode than that on the bare GC electrode, indicating DA polymer modified electrode possessed excellent performance for the oxidation of ACOP. This kind of capability of the modified electrode can be enlisted for the highly sensitive and selective determination of ACOP. Under the optimized conditions, a wide linear range from 2 × 10(-8) to 5.0 × 10(-4)M with a correlation coefficient 0.9995 was obtained. The detection limit was 6.7 × 10(-9)M (at the ratio of signal to noise, S/N=3:1). The modified electrode also exhibited very good stability and reproducibility for the detection of ACOP. The established method was applied to the determination of ACOP in samples. An average recovery of 100.1% was achieved. These results indicated that this method was reliable for determining ACOP.     

Rapid Prototyping of a High Sensitivity Graphene Based Glucose Sensor Strip

A rapid prototyping of an inexpensive, disposable graphene and copper nanocomposite sensor strip using polymeric flexible substrate for highly sensitive and selective nonenzymatic glucose detection has been developed and tested for direct oxidization of glucose. The CuNPs were electrochemically deposited on to the graphene sheets to improve electron transfer rates and to enhance electrocatalytic activity toward glucose. The graphene based electrode with CuNPs demonstrated a high degree of sensitivity (1101.3±56 μA/mM.cm²), excellent selectivity (without an interference with Ascorbic Acid, Uric Acid, Dopamine, and Acetaminophen), good stability with a linear response to glucose ranging from 0.1 mM to 0.6 mM concentration, and detection limits of 0.025 mM to 0.9 mM. Characterization of the electrodes was performed by scanning electron microscopy (FESEM and SEM). The electrochemical properties of the modified graphene electrodes were inspected by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and amperometry.     

New antibody immobilization method via functional liposome layer for specific protein assays

A specific protein assay system based on functional liposome-modified gold electrodes has been demonstrated. To fabricate such assay system, a liposome layer was initially grown on top of a gold layer. The liposome layer contained two kinds of functional molecules: biotin molecules for the binding sites of streptavidin and N-(10,12-pentacosadiynoic)-acetylferrocene molecules for the facile redox probe in electrochemical detections. Then, streptavidin was attached on the functional liposme-modified layer using the interaction of streptavidin-sbiotin complex. On the streptavidin-attached surface, antibody molecules, anti-human serum albumin antibodies could be immobilized without any secondary antibodies. AFM imaging of the streptavidin-attached liposome surface revealed a uniform distribution of closely packed streptavidin molecules. In situ quartz-crystal microbalance and electrochemical measurements demonstrated that the wanted antibody-antigen reactions should occur with high specificity and selectivity. Our specific antibody assay system, based on a functional liposome modified electrode, can be developed further to yield sophisticated structures for numerous protein chips and immunoassay sensors.     

Study of human serum albumin-TiO(2) nanocrystalline electrodes interaction by impedance electrochemical spectroscopy.

The adsorption of human serum albumin (HSA) onto nanocrystalline TiO(2) electrodes was studied by electrochemical impedance spectroscopy (EIS) in function of pH and electrode potential. The characterization and physico-chemical properties of the TiO(2) electrode were investigated by scanning electron microscopy (SEM), UV-photoelectron spectroscopy (UPS), cyclic voltammetry and capacitance measurements. The impedance response of the particulate TiO(2) electrode/protein interface was fitted using an equivalent circuit model to describe the adsorption process. The adsorbed protein layer, which is formed as soon as the protein is injected into the solution and becomes in contact with the electrode, was investigated as a function of electrode potential and solution pH. The measurements were performed under pseudo-steady-state and steady-state conditions, which gave information about the different states of the system. With the pseudo-steady state measurements, it was possible to determine two rate constants of the protein adsorption process, which correspond to two different states of the protein. The shortest one was associated with the first contact between the protein and the substrate and the second relaxation time, with the protein suffering an structural rearrangement due to the interaction with the TiO(2) electrode. It was detected that at sufficiently long times (approx. 1 h, where the system was under steady state conditions), a quasi-reversible protein adsorption mechanism was established. The measurements performed as a function of frequency under steady-state conditions, an equivalent circuit with a Warburg element gave the better fitting to data taken at -0.585 V closer to the oxide flat band potential and it was associated with protein diffusion. Experimental results obtained at only one frequency as a function of potential could be fitted to a model that takes into account non-specific and probable specific protein adsorption, which renders to be potential- and pH-dependent. Low capacity values were obtained in the whole potential range, which were measured in the presence and in the absence of the protein layer. The capacity dependence on potential and pH were associated with the generation of surface states on TiO(2). A surface state concentration of 4.1x10(18) cm(-2) was obtained by relating the parallel capacitance with oxide surface states arising from the protein-oxide interaction.     

Assembly of electroactive layer-by-layer films of hemoglobin and polycationic poly(diallyldimethylammonium)

Layer-by-layer (PDDA/Hb)(n) films were assembled by alternate adsorption of positively charged poly(diallyldimethylammonium) (PDDA) and negatively charged hemoglobin (Hb) at pH 9.2 from their aqueous solutions on pyrolytic graphite electrodes and other substrates. The assembly process was monitored and confirmed by quartz crystal microbalance (QCM), UV-vis spectroscopy, and cyclic voltammetry (CV). CVs of (PDDA/Hb)(n) films showed a pair of well-defined, nearly reversible peaks at about -0.34 V vs SCE at pH 7.0, characteristic of Hb heme Fe(III)/Fe(II) redox couple. Positions of Soret absorption band and infrared amide II band of Hb in (PDDA/Hb)(8) films suggest that Hb in the films keeps its secondary structure similar to its native state. The electrochemical parameters of (PDDA/Hb)(8) films were estimated by square wave voltammetry, and the thickness of the PDDA/Hb bilayer was estimated by QCM and scanning electron microscopy. Trichloroacetic acid and nitrite (NO(2)(-)) were catalytically reduced at (PDDA/Hb)(8) film electrodes. The electrochemical catalytic reactions of O(2) and H(2)O(2) on (PDDA/Hb)(8) films were also studied.     

A biocompatible titanium nitride nanorods derived nanostructured electrode for biosensing and bioelectrochemical energy conversion

In this study, a facile method is proposed to fabricate biocompatible TiN nanorod arrays through solvent-thermal synthesis and subsequent nitridation in ammonia atmosphere. The TiN nanorod arrays are potential excellent nanostructured electrodes owing to their good electronic conductivity and large surface area. These nanostructured electrodes not only deliver superior electrocatalytic activity (the limit of detection, LOD is 0.5 μM) and highly selective sensing towards H(2)O(2), but also exhibit excellent biocompatibility with horseradish peroxidase (HRP) in a highly sensitive enzymatic biosensor for H(2)O(2) (the LOD can reach to 0.05 μM). Furthermore, a novel biocatalytic cathode based Li air fuel cell (bio-Li-air fuel cell) is explored based on the combination of TiN nanorod arrays and laccase (LAC) for electrochemical energy conversion. These results demonstrate that TiN nanorod arrays can be served as excellent nanostructured electrodes for multifunctional bioelectrochemical applications.     

Polypyrrole nanotube array sensor for enhanced adsorption of glucose oxidase in glucose biosensors

A novel amperometric biosensor based on polypyrrole (PPy) nanotube array deposited on a Pt plated nano-porous alumina substrate and its performances are described. Glucose oxidase (GOx) enzyme was selected as the model enzyme in this study. Commercially available nano-porous alumina discs were used to fabricate electrodes in order to study the feasibility of enzyme entrapment by physical adsorption. A PPy/PF6- film comprising of nanotube array was synthesized using a solution containing 0.05 M Pyrrole and 0.1 M NaPF6 at a current density of 0.3 mA/cm2 for 90 s. The immobilization was done by physical adsorption of 5 microL of GOx (from a stock solution of 2 mg/mL of 210 U/mg) on each electrode. A sensitivity of 7.4 mA cm(-2) M(-1) was observed with PPy nanotube array where the maximum tube diameter was 100 nm. A linear range of 500 microM-13 mM and a response time of about 3 s were observed with a nanotube array where the maximum tube diameter was 200 nm. The synthesized nanotube arrays were characterized by galvanostatic electrochemical technique. Calculated value of apparent Michaelis-Menten constant (Km) was 7.01 mM. The use of nano-porous template electrodes leads to an efficient enzyme loading and provides an increased surface area for sensing the reaction. These factors contribute to increase the characteristic performances of the novel biosensor.     

New amperometric and potentiometric immunosensors based on gold nanoparticles/tris(2,2'-bipyridyl)cobalt(III) multilayer films for hepatitis B surface antigen determinations

Two generic, fast, sensitive and novel electrochemical immunosensors have been developed. Initially, a layer of plasma-polymerized Nafion film (PPF) was deposited on the platinum electrode surface, then positively charged tris(2,2'-bipyridyl)cobalt(III) (Co(bpy)(3)(3+)) and negatively charged gold nanoparticles were assembled on the PPF-modified Pt electrode by layer-by-layer technique. Finally, hepatitis B surface antibody (HBsAb) was electrostatically adsorbed on the gold nanoparticles surface. Electrochemical behavior of the {Au/Co(bpy)(3)(3+)}(n) multilayer film-modified electrodes was studied. Cyclic voltammetry, electrochemical impedance spectroscopy (EIS) were adopted to monitor the regular growth of the multilayer films. The performance and factors influencing the performance of the resulting immunosensors were studied in detail. The multilayer film-modified immunosensor was used for hepatitis B surface antigen (HBsAg) determination via the amperometric and potentiometric immunosensor systems, and both systems provided the same linear ranges from 0.05 to 4.5 microg/mL with different detection limits for the amperometric system 0.005 microg/mL and for the potentiometric system 0.015 microg/mL. The immunosensors were used to analyse HBsAg in human serum samples. Analytical results of clinical samples show that the developed immunoassay is comparable with the enzyme-linked immunosorbent assays (ELISAs) method, implying a promising alternative approach for detecting HBsAg in the clinical diagnosis. In addition, the multilayer films also showed better stability for 1 month at least.     

Multiply osmium-labeled reporter probes for electrochemical DNA hybridization assays: detection of trinucleotide repeats

In electrochemical DNA hybridization assays target or probe DNAs end-labeled with electroactive compounds have been frequently used. We show that multiple osmium labels yielding faradaic (at carbon or mercury electrodes) and catalytic signals (at mercury electrodes) can be easily covalently bound to DNA molecules. We use (GAA)(7) (T)(n) oligodeoxynucleotides (ODNs) with n ranging between 5 and 50. (T)(n) tails are selectively modified with osmium tetroxide,2,2'-bipyridine leaving the (GAA)(7) repeat intact for the DNA hybridization. These ODNs are applied as reporter probes (RP's) in DNA hybridization double-surface (DS) assay using magnetic beads for the DNA hybridization and pyrolytic graphite (PGE) or hanging mercury drop (HMDE) electrodes for the electrochemical detection. We show that in difference to the usual single-surface methods (where the RP has to be bound to target DNA near to the surface to communicate with the electrode) in the DS assay the RP can be bound to DNA regardless of its position and can used for the determination of the length of DNA repetitive sequences. Several fmols or about a hundred of amol of a RP with osmium-labeled (T)(50) tail can be detected at PGE and HMDE, respectively, at 1-2 min accumulation time.     

Electrochemical DNA sensing using osmium complexes as hybridization indicators

A surface-based method for the study of the interactions of DNA with redox-active osmium complexes is described. The study was carried out using gold electrodes modified with DNA by adsorption and [Os(bpy)3]3+/2+ (bpy=2,2'-bipyridyl) or [Os(phen)3]3+/2+ (phen=1,10-phenantroline) as electrochemical indicators. The method, which is simple and reagent saving, allows the accumulation of osmium complexes on the DNA layer. The amount of osmium complex bound by the layer of double-stranded (dsDNA) or single-stranded DNA (ssDNA) adsorbed at gold electrodes was estimated from the cyclic voltammetric (CV) peak charge of osmium complex reduction. The dissociation constants (K) for the oxidized and reduced forms of a bound species are also estimated. [Os(phen)3]3+/2+ was applied to a probe for electrochemical DNA sensing. A thiol-linked single-stranded DNA probe was immobilized through the S-Au bonding to 70 pmol/cm2 on a gold electrode. Following hybridization with the complementary DNA, the osmium complex was electrochemically accumulated on the double-stranded DNA layer and the differential pulse voltammogram for this electrode gave an electrochemical signal due to the redox reaction of [Os(phen)3]3+/2+ that was bound to the double-stranded DNA on the electrode.     

Electrical recognition of label-free oligonucleotides upon streptavidin-modified electrode surfaces

For the purpose of developing a direct label-free electrochemical detection system, we have systematically investigated the electrochemical signatures of each step in the preparation procedure, from a bare gold electrode to the hybridization of label-free complementary DNA, for the streptavidin-modified electrode. For the purpose of this investigation, we obtained the following pertinent data; cyclic voltammogram measurements, electrochemical impedance spectra and square wave voltammogram measurements, in Fe(CN)₆ ³⁻/Fe(CN)₆ ⁴⁻ solution (which was utilized as the electron transfer redox mediator). The oligonucleotide molecules on the streptavidin-modified electrodes exhibited intrinsic redox activity in the ferrocyanide-mediated electrochemical measurements. Furthermore, the investigation of electrochemical electron transfer, according to the sequence of oligonucleotide molecules, was also undertaken. This work demonstrates that direct label-free oligonucleotide electrical recognition, based on biofunctional streptavidin-modified gold electrodes, could lead to the development of a new biosensor protocol for the expansion of rapid, cost-effective detection systems.