A novel nonenzymatic hydrogen peroxide sensor based on multi-wall carbon nanotube/silver nanoparticle nanohybrids modified gold electrode

A novel strategy to fabricate hydrogen peroxide (H₂O₂) sensor was developed based on multi-wall carbon nanotube/silver nanoparticle nanohybrids (MWCNT/Ag nanohybrids) modified gold electrode. The process to synthesize MWCNT/Ag nanohybrids was facile and efficient. In the presence of carboxyl groups functionalized multi-wall carbon nanotubes (MWCNTs), silver nanoparticles (Ag NPs) were in situ generated from AgNO₃ aqueous solution and readily attached to the MWCNTs convex surfaces at room temperature, without any additional reducing reagent or irradiation treatment. The formation of MWCNT/Ag nanohybrids product was observed by transmission electron microscope (TEM), and the electrochemical properties of MWCNT/Ag nanohybrids modified gold electrode were characterized by electrochemical measurements. The results showed that this sensor had a favorable catalytic ability for the reduction of H₂O₂. The resulted sensor could detect H₂O₂ in a linear range of 0.05-17 mM with a detection limit of 5 × 10⁻⁷ M at a signal-to-noise ratio of 3. The sensitivity was calculated as 1.42 μA/mM at a potential of −0.2 V. Additionally, it exhibited good reproducibility, long-term stability and negligible interference of ascorbic acid (AA), uric acid (UA), and acetaminophen (AP).     

Highly sensitive electrochemical impedance spectroscopic detection of DNA hybridization based on Aunano-CNT/PANnano films

A polyaniline nanofibers (PAN_nano)/carbon paste electrode (CPE) was prepared via dopping PAN_nano in the carbon paste. The nanogold (Au_nano) and carbon nanotubes (CNT) composite nanoparticles were bound on the surface of the PAN_nano/CPE. The immobilization and hybridization of the DNA probe on the Au_nano-CNT/PAN_nano films were investigated with differential pulse voltammetry (DPV) and cyclic voltammetry (CV) using methylene blue (MB) as indicator, and electrochemical impedance spectroscopy (EIS) using [Fe(CN)₆]^3−/4− as redox probe. The voltammetric peak currents of MB increased dramatically owing to the immobilization of the probe DNA on the Au_nano-CNT/PAN_nano films, and then decreased obviously owing to the hybridization of the DNA probe with the complementary single-stranded DNA (cDNA). The electron transfer resistance (R_et) of the electrode surface increased after the immobilization of the probe DNA on the Au_nano-CNT/PAN_nano films and rose further after the hybridization of the probe DNA. The remarkable difference between the R_et value at the DNA-immobilized electrode and that at the hybridized electrode could be used for the label-free EIS detection of the target DNA. The loading of the DNA probe on Au_nano-CNT/PAN_nano films was greatly enhanced and the sensitivity for the target DNA detection was markedly improved. The sequence-specific DNA of phosphinothricin acetyltransferase (PAT) gene and the polymerase chain reaction (PCR) amplification of nopaline synthase (NOS) gene from transgenically modified beans were determined with this label-free EIS DNA detection method. The dynamic range for detecting the PAT gene sequence was from 1.0 × 10⁻¹² mol/L to 1.0 × 10⁻⁶ mol/L with a detection limit of 5.6 × 10⁻¹³ mol/L.     

A reusable capacitive immunosensor for detection of Salmonella spp. based on grafted ethylene diamine and self-assembled gold nanoparticle monolayers

Fabrication of a novel capacitive immunosensor based on grafted ethylene diamine and self-assembled gold nanoparticle monolayer on glassy carbon electrode for the detection of Salmonella spp. is described for the first time. In the present study, the Salmonella spp. monoclonal antibodies (denoted as McAbs) was immobilized on gold nanoparticles. Interaction of McAbs and Salmonella spp. was detected directly using the electrochemical impedance spectroscopy (EIS) technique. The experimental results showed that the concentration of antigen was measured through the relative change in capacitance in the corresponding specific binding of Salmonella spp. and McAbs. Under the optimized conditions, the relative changes in capacitance were proportional to the logarithmic values of Salmonella spp. concentrations in the range of 1.0 × 10² to 1.0 × 10⁵ CFU mL⁻¹ (r = 0.991) with the detection limit of 1.0 × 10² CFU mL⁻¹. The stability of proposed immunosensor could be estimated by determining the relative change in capacitance, which remained almost the same in two months and decreased gradually to 85.3% of initial value after four months’ storage. The used immunosensor could be regenerated repeatedly by immersing in glycine-HCl buffer solution (pH 2.8). Finally, the proposed immunosensor was successfully used for the detection of Salmonella spp. in lab-processed commercial pork samples.     

Construction of a novel molecularly imprinted sensor for the determination of O,O-dimethyl-(2,4-dichlorophenoxyacetoxyl)(3′-nitrophenyl)methinephosphonate

A novel voltammetric sensor for O,O-dimethyl-(2,4-dichlorophenoxyacetoxyl)(3′-nitrophenyl)methinephosphonate (Phi-NO₂) based on molecularly imprinted polymer (MIP) film electrode is constructed by using sol-gel technology. The sensor responds linearly to Phi-NO₂ over the concentration range of 2.0 × 10⁻⁵ to 1.0 × 10⁻⁸ mol L⁻¹ and the detection limit is 1.0 × 10⁻⁹ mol L⁻¹ (S/N = 3). This sensor provides an efficient way for eliminating interferences from coexisting substances in the solution. The high sensitivity, selectivity and stability of the sensor demonstrates its practical application for a simple and rapid determination of Phi-NO₂ in cabbage samples.     

Electrochemical deoxyribonucleic acid biosensor based on carboxyl functionalized graphene oxide and poly-l-lysine modified electrode for the detection of tlh gene sequence related to vibrio parahaemolyticus

A carboxyl functionalized graphene oxide (GO-COOH) and electropolymerized ploy-l-lysine (PLLy) modified glassy carbon electrode (GCE) was fabricated and used for the construction of an electrochemical deoxyribonucleic acid (DNA) biosensor. The NH₂ modified probe ssDNA sequences were immobilized on the surface of GO-COOH/PLLy/GCE by covalent linking with the formation of amide bonds, which was stable and furthur hybridized with the target ssDNA sequence. Differential pulse voltammetry (DPV) was used to monitor the hybridization events with methylene blue as electrochemical indicator, which gave a sensitive reduction peak at −0.287 V (vs. SCE). Under the optimal conditions the reduction peak current was proportional to the concentration of tlh gene sequence in the range from 1.0 × 10⁻¹² to 1.0 × 10⁻⁶ mol L⁻¹ with a detection limit as 1.69 × 10⁻¹³ mol L⁻¹ (3σ). The polymerase chain reaction products of tlh gene from oyster samples were detected with satisfactory results, indicating the potential application of this electrochemical DNA sensor.     

Sensors based on galvanic cell generated electrochemiluminescence and its application

In this paper, a novel electrochemiluminescence (ECL) imaging sensor array was developed for determination of hydrogen peroxide (H₂O₂), which was based on Cu/Zn alloy galvanic cell generated ECL. In alkaline solution, Cu/Zn galvanic cell was formed because of corrosion effect, the galvanic cell could supply stable potential for ECL generation of luminol, and the weak ECL emission could be enhanced by H₂O₂. The galvanic cell sensor array was designed by putting Cu/Zn alloy in 96-well microtiter plates separately. The relative ECL intensity was proportional with the concentration of hydrogen peroxide in the range of 1.0 × 10⁻⁶ to 1.0 × 10⁻⁴ mol l⁻¹ and the detection limit was 3.0 × 10⁻⁷ mol l⁻¹ (3σ), the relative standard deviation (R.S.D.) for 11 parallel measurements of 1.0 × 10⁻⁵ mol l⁻¹ H₂O₂ was 4.0%.     

Investigation of plasma-functionalized multiwalled carbon nanotube film and its application of DNA sensor for Legionella pneumophila detection

A novel multiwall carbon nanotube (MWCNT) electrode functionalized with oxygen plasma treatment was prepared and characterized, and its DNA sensing ability for Legionella pneumophila (L. pneumophila) detection was examined using electrochemical measurement. A well-patterned MWCNT working electrode (WE) on a Pt track was fabricated using photolithography, transfer methods and an etching technique. The MWCNT WE was functionalized by oxygen plasma treatment prior to applying for DNA sensor. The surface morphology of the plasma-functionalized MWCNT (pf-MWCNT) WEs were observed by scanning electron microscope (SEM) and the change of chemical composition was characterized by X-ray photoelectron spectroscopy (XPS), and electrochemical measurements were performed using CV with ferricyanide/ferrocyanide redox couple. Effective areas of working electrodes were calculated to be 0.00453 cm² for pristine MWCNT electrode and 0.00747-0.00874 cm² for pf-MWCNT electrodes with different plasma treatment times. Differential pulse voltammetry (DPV) was carried out in methylene blue solution for DNA sensing. The pf-MWCNT based DNA sensor was successfully operated in a target concentration range of 10 pM to 100 nM and had a lower detection limit than a pristine MWCNT based DNA sensor.     

Characterization of gold-thiol-8-hydroxyquinoline self-assembled monolayers for selective recognition of aluminum ion using voltammetry and electrochemical impedance spectroscopy

Gold electrode surface is modified via covalent attachment of a synthesized thiol functionalized with 8-hydroxyquinoline, p-((8-hydroxyquinoline)azo) benzenethiol (SHQ), for the first time. The behavior of the nanostructured electrode surface (Au–SHQ) is characterized by electrochemical techniques including cyclic and differential pulse voltammetry (CV and DPV), and electrochemical impedance spectroscopy (EIS). The modified surface is stable in a wide range of potentials and pHs. A surface pK_a of 6.0 ± 0.1 is obtained for Au–SHQ electrode using surface acid/base titration curves constructed by CV and EIS measurements as a function of pH. These results helped to determine the charge state of the surface as a function of pH. The gold modified electrode surface showed good affinity for sensing the Al(III) ion at pH 5.5. The sensing process is based on (i) accumulation and complex formation between Al(III) from the solution phase and 8HQ function on the Au electrode surface (recognition step) and (ii) monitoring the impedance of the Au–SHQ–Al(III) complex against redox reaction rate of parabenzoquinone (PBQ) (signal transduction step). The PBQ is found to be a more suitable probe for this purpose, after testing several others. Thus, the sensor was tested for quantitative determination of Al(III) from the solution phase. At the optimized conditions, a linear response, from 1.0 × 10⁻¹¹ to 1.2 × 10⁻⁵ M Al(III) in semi-logarithmic scale, with a detection limit of 8.32 × 10⁻¹² M and mean relative standard deviation of 3.2% for n = 3 at 1.0 × 10⁻⁷ M Al(III) is obtained. Possible interferences from coexisting cations and anions are also studied. The results show that many ions do not interfere significantly with the sensor response for Al(III). Validity of the method and applicability of the sensor are successfully tested by determination of Al(III) in human blood serum samples.     

An electrochemical DNA-sensor developed with the use of methylene blue as a redox indicator for the detection of DNA damage induced by endocrine-disrupting compounds

An electrochemical biosensor capable of indirect detection of DNA damage induced by any one of the three endocrine-disrupting compounds (EDCs) – bisphenol A (BPA), 4-nonylphenol (NP) and 4-t-octylphenol (OP), has been researched and developed. The methylene blue (MB) dye was used as the redox indicator. The glassy carbon electrode (GCE) was modified by the assembled dsDNA/graphene oxide-chitosan/gold nano-particles to produce a dsDNA/GO-CS/AuNPs/GCE sensor. It was characterized with the use of electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and scanning electron microscopy (SEM) techniques. The loading/release of the MB dye by the dsDNA/GO-CS/AuNPs film was investigated, and the results showed that the process was reversible. Based on this, the sensor was used to measure the difference between the loading capabilities of intact and damaged dsDNA in the films. The sensor was then successfully applied to detect DNA damage electrochemically. The differential pulse voltammetry (DPV) peak current ratio for MB, observed before and after DNA damage, increased linearly in the presence the BPA, NP or OP compounds; the treatment range was 10–60 min, and the respective damage rates were 0.0069, 0.0044 and 0.0031 min⁻¹, respectively. These results were confirmed by the binding constants: 2.09 × 10⁶ M⁻¹ (BPA-DNA), 1.28 × 10⁶ M⁻¹ (NP-DNA) and 9.33 × 10⁵ M⁻¹ (OP-DNA), all of which were obtained with the use of differential pulse stripping voltammetry (DPSV).     

Synergistic effects of nano-ZnO/multi-walled carbon nanotubes/chitosan nanocomposite membrane for the sensitive detection of sequence-specific of PAT gene and PCR amplification of NOS gene

The remarkable synergistic effects of the zinc oxide (ZnO) nanoparticles and multi-walled carbon nanotubes (MWNTs) were developed for the ssDNA probe immobilization and fabrication of the electrochemical DNA biosensor. The ZnO/MWNTs/chitosan nanocomposite membrane-modified glassy carbon electrode (ZnO/MWNTs/CHIT/GCE) was fabricated and the ssDNA probes were immobilized on the modified electrode surface. The preparation method is quite simple and inexpensive. The hybridization events were monitored by differential pulse voltammetry (DPV) using methylene blue (MB) as an indicator. As compared with previous MWNTs-based DNA biosensors, this composite matrix combined the attractive biocompatibility of ZnO nanoparticles with the excellent electron-transfer ability of MWNTs and fine membrane-forming ability of CHIT increased the DNA attachment quantity and complementary DNA detection sensitivity. The approach described here can effectively discriminate complementary DNA sequence, noncomplementary sequence, single-base mismatched sequence and double-base mismatched sequence related to phosphinothricin acetyltransferase (PAT) gene in transgenic corn. Under optimal conditions, the dynamic detection range of the sensor to PAT gene complementary target sequence was from 1.0 × 10⁻¹¹ to 1.0 × 10⁻⁶ mol/L with the detection limit of 2.8 × 10⁻¹² mol/L. The polymerase chain reaction (PCR) amplification of nopaline synthase (NOS) gene from the real sample of one kind of transgenic soybeans was also satisfactorily detected with this electrochemical DNA biosensor, suggesting that the ZnO/MWNTs/CHIT nanocomposite hold great promises for sensitive electrochemical biosensor applications.     

Flow injection chemiluminescence sensor based on core–shell magnetic molecularly imprinted nanoparticles for determination of sulfadiazine

A novel flow injection chemiluminescence (FI-CL) sensor for determination of sulfadiazine (SDZ) using core–shell magnetic molecularly imprinted polymers (MMIPs) as recognition element is developed. Briefly, a hydrophilic MMIPs layer was produced at the surface of Fe₃O₄@SiO₂ magnetic nanoparticles (MNPs) via combination of molecular imprinting and reversible stimuli responsive hydrogel. And it provided the MMIPs with excellent adsorption capacity and rapid adsorption rate due to the imprinted sites mostly situated on the surface of MMIPs. Then the prepared SDZ-MMIPs were packed into flow cell to establish a novel FI-CL sensor. The sensor provided a wide linear range for SDZ of 4.0 × 10⁻⁷ to 1.0 × 10⁻⁴ mol L⁻¹ with a detection limit of 1.54 × 10⁻⁷ mol L⁻¹. And the relative standard deviation (RSD) for the determination of 1.0 × 10⁻⁶ mol L⁻¹ SDZ was 2.56% (n = 11). The proposed method was applied to determine SDZ in urine samples and satisfactory results were obtained.     

Development of integrated chemiluminescence flow sensor for the determination of adrenaline and isoprenaline

A novel integrated chemiluminescence (CL) flow sensor for the determination of adrenaline and isoprenaline is developed based on the enhancing effect of analytes on CL emission of luminol oxidized by periodate in alkaline solution. The analytical reagents luminol and periodate are immobilized on anion exchange resins, respectively, and packed in a glass tube to construct a reagentless sensor. The proposed sensor allows the determination of adrenaline and isoprenaline over the range from 2.0×10⁻⁸ to 1.0×10⁻⁵ g ml⁻¹ and 2.0×10⁻⁷ to 5.0×10⁻⁵ g ml⁻¹, respectively. The detection limits are 7.0×10⁻⁹ g ml⁻¹ for adrenaline and 5.0×10⁻⁸ g ml⁻¹ for isoprenaline with a relative standard deviation of 1.7% for the 1.0×10⁻⁷ g ml⁻¹ adrenaline (n=11) and 2.1% for 1.0×10⁻⁶ g ml⁻¹ isoprenaline (n=11). The sample throughput was 60 samples h⁻¹. The sensor has been successfully applied to the determination of adrenaline and isoprenaline in pharmaceutical preparations.     

Aptamer-quantum dots conjugates-based ultrasensitive competitive electrochemical cytosensor for the detection of tumor cell

A novel competitive electrochemical cytosensor was reported by using aptamer (Apt)-quantum dots (Qdots) conjugates as a platform for tumor cell recognition and detection. The complementary DNA (cDNA), aptamer and Qdots could be assembled to the gold electrode surface. When the target cells existed, they could compete with cDNA to bind with Apt-Qdots conjugates based on the specific recognition of aptamer to MUC1 protein overexpressed on the cell surface, which resulted in the denaturation of double-stranded DNA structure and the release of the Apt-Qdots conjugates from the electrode. Electrochemical stripping measurement was then employed to determine the Cd²⁺ concentration in Qdots left at the electrode. The peak current was inversely proportional to the logarithmic value of cell concentration ranging from 1.0 × 10² to 1.0 × 10⁶ cells mL⁻¹ with a detection limit of 100 cells mL⁻¹. Meanwhile, the recognition of aptamer to the target cells could be clearly observed through the strong fluorescence from Qdots. This is an example of the combination of aptamer and nanoparticles for the application of cell analysis, which is essential to cancer diagnosis and therapy.     

Selective detection of dopamine in the presence of uric acid using a gold nanoparticles-poly(luminol) hybrid film and multi-walled carbon nanotubes with incorporated β-cyclodextrin modified glassy carbon electrode

Gold nanoparticles-poly(luminol) (Plu-AuNPs) hybrid film and multi-walled carbon nanotubes with incorporated β-cyclodextrin modified glassy carbon electrode (β-CD-MWCNTs/Plu-AuNPs/GCE) was successfully prepared for simultaneous determination of dopamine (DA) and uric acid (UA). The surface of the modified electrode has been characterized by X-ray photo-electron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDS), field-emission scanning electron microscope (SEM) and transmission electron microscope (TEM). Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and differential pulse voltammetry (DPV) have been used to investigate the β-CD-MWCNTs/Plu-AuNPs composite film. Gold nanoparticles anchored into poly(luminol) film exhibited catalytic activity for DA. MWCNTs with incorporated β-CD can greatly promote the direct electron transfer. In 0.10 M phosphate buffer solution (PBS, pH 7.0), the DPV response of the β-CD-MWCNTs/Plu-AuNPs/GCE sensor to DA is about 8-fold as compared with the Plu-AuNPs/GCE sensor, and the detection limit for DA is about one order of magnitude lower than the Plu-AuNPs/GCE sensor. The steady-state current response increases linearly with DA concentration from 1.0 × 10⁻⁶ to 5.6 × 10⁻⁵ M with a low detection limit (S/N = 3) of 1.9 × 10⁻⁷ M. Moreover, the interferences of ascorbic acid (AA) and uric acid (UA) are effectively diminished. The applicability of the prepared electrode has been demonstrated by measuring DA contents in dopamine hydrochloride injection.     

Preparation of cobalt-tetraphenylporphyrin/reduced graphene oxide nanocomposite and its application on hydrogen peroxide biosensor

A novel cobalt-tetraphenylporphyrin/reduced graphene oxide (CoTPP/RGO) nanocomposite was prepared by a π–π stacking interaction and characterized by ultraviolet–visible absorption spectroscopy (UV–vis), Fourier transform infrared spectroscopy (FTIR) and electrochemical impedance spectroscopy (EIS). The CoTPP/RGO nanocomposite exhibited high electrocatalytic activity both for oxidation and reduction of H₂O₂. The current response was linear to H₂O₂ concentration with the concentration range from 1.0 × 10⁻⁷ to 2.4 × 10⁻³ mol L⁻¹ (R = 0.998) at the reductive potential of −0.20 V and from 1.0 × 10⁻⁷ to 4.6 × 10⁻⁴ mol L⁻¹ (R = 0.996) at the oxidative potential of +0.50 V. The H₂O₂ biosensor showed good anti-interfering ability towards oxidative interferences at the oxidative potential of +0.50 V and good anti-interfering ability towards reductive interferences at the reductive potential of −0.20 V.     

Biosensor for multiplex detection of two DNA target sequences using enzyme-functionalized Au nanoparticles as signal amplification

Multiplex electrochemical detection of two DNA target sequences in one sample using enzyme-functionalized Au nanoparticles (AuNPs) as catalytic labels for was proposed. This DNA sensor was fabricated using a “sandwich” detection strategy, involving two kinds of capture probes DNA immobilized on glassy carbon electrode (GCE), and hybridization with target DNA sequences, which further hybridized with the reporter DNA loaded on the AuNPs. The AuNP contained two kinds of DNA sequences, one was complementary to the target DNA, while the other was noncomplementary to the target. The noncomplementary sequences were linked with horseradish peroxidase (HRP) and alkaline phosphatase (ALP), respectively. Enhanced detection sensitivity was obtained where the AuNPs carriers increased the amount of enzyme molecules per hybridization. Electrochemical signals were generated from the enzymatic products produced from the substrates catalyzed by HRP and ALP. Under optimal conditions, a 33-mer sequence could be quantified over the ranges from 1.5 × 10⁻¹³ to 5.0 × 10⁻¹² M with a detection limit of 1.0 × 10⁻¹³ M using HRP-AuNP as labels, and a 33-mer sequence could be quantified over the ranges from 4.5 × 10⁻¹¹ M to 1.0 × 10⁻⁹ M with a detection limit of 1.2 × 10⁻¹¹ M using ALP-AuNP as labels.     

A highly sensitive non-enzymatic glucose sensor based on a simple two-step electrodeposition of cupric oxide (CuO) nanoparticles onto multi-walled carbon nanotube arrays

A novel, stable and highly sensitive non-enzymatic glucose (Glc) sensor was developed using vertically well-aligned multi-walled carbon nanotubes array (MWCNTs) incorporated with cupric oxide (CuO) nanoparticles. The MWCNTs array was prepared by catalytic chemical vapor deposition on a tantalum (Ta) substrate, while a simple and rapid two-step electrodeposition technique was used to prepare the CuO-MWCNTs nanocomposite. First, Cu nanoparticles were deposited onto MWCNTs at constant potential and then they were oxidized into CuO by potential cycling. The electrocatalytic activity of CuO-MWCNTs array was investigated for Glc under alkaline conditions using cyclic voltammetry and chronoamperometry. The sensor exhibited a linear response up to 3 mM of Glc and sensitivity of 2190 μA mM⁻¹ cm⁻², which is two to three orders of magnitude higher than that of most non-enzymatic Glc sensors reported in the literature. The sensor response time is less than 2 s and detection limit is 800 nM (at signal/noise = 3). When tested with human blood serum samples, the sensor exhibited high electrocatalytic activity, stability, fast response and good selectivity against common interfering species, suggesting its potential to be developed as a non-enzymatic Glc sensor.     

Development of a gold nanoparticles based chemiluminescence imaging assay and its application

In this paper, a novel gold nanoparticles based protein immobilization method was designed. Biocomposites of gold nanoparticles and proteins were successfully coated on poly(methyl methacrylate) (PMMA) plates and polystyrene microtiter plates. The proteins could be immobilized on solid materials with high density and better bioactivity. Based on above design, chemiluminescence (CL) imaging assay for determination of H₂O₂ and recombinant human interleukin-6 (rHu IL-6) was developed. The linear range and the loading capability were greatly improved when compared with imaging assay performed with direct proteins immobilization. Under the selected experimental conditions, a linear relationship was obtained between the CL intensity and the concentration of H₂O₂ in the range of 1.0 × 10⁻⁶ to 1.0 × 10⁻⁴ mol L⁻¹, and rHu IL-6 in the range of 2.0-312.0 pg mL⁻¹. The detection limits were 2 × 10⁻⁷ mol L⁻¹ (3σ) for H₂O₂ and 0.5 pg mL⁻¹ for rHu IL-6 with relative standard deviation of 3.8% for 3.0 × 10⁻⁵ mol L⁻¹ H₂O₂, and 4.4% for 39.0 pg mL⁻¹ rHu IL-6. This method has been applied to the determination of rHu IL-6 in human serum with satisfactory results.     

Electrochemical determination of L-phenylalanine at polyaniline modified carbon electrode based on β-cyclodextrin incorporated carbon nanotube composite material and imprinted sol-gel film

A sensitive and selective electrochemical sensor based on a polyaniline modified carbon electrode for the determination of l-phenylalanine has been proposed by utilizing β-cyclodextrin (β-CD) incorporated multi-walled carbon nanotube (MWNT) and imprinted sol-gel film. The electrochemical behavior of the sensor towards l-phenylalanine was investigated by cyclic voltammetry (CV), differential pulse voltammetry (DPV), and amperometric i-t curve. The surface morphologies of layer-by-layer assembly electrodes were displayed by scanning electron microscope (SEM). The response mechanism of the imprinted sensor for l-phenylalanine was based on the inclusion interaction of β-CD and molecular recognition capacity of the imprinted film for l-phenylalanine. A linear calibration plot was obtained covering the concentration range from 5.0 × 10⁻⁷ to 1.0 × 10⁻⁴ mol L⁻¹ with a detection limit of 1.0 × 10⁻⁹ mol L⁻¹. With excellent sensitivity, selectivity, stability, reproducibility and recovery, the electrochemical imprinted sensor was used to detect l-phenylalanine in blood plasma samples successfully.     

Electrical detection of deoxyribonucleic acid hybridization based on carbon-nanotubes/nano zirconium dioxide/chitosan-modified electrodes

A novel and sensitive electrochemical DNA biosensor based on nanoparticles ZrO₂ and multi-walled carbon nanotubes (MWNTs) for DNA immobilization and enhanced hybridization detection is described. The MWNTs/nano ZrO₂/chitosan-modified glassy carbon electrode (GCE) was fabricated and oligonucleotides were immobilized to the GCE. The hybridization reaction on the electrode was monitored by differential pulse voltammetry (DPV) analysis using electroactive daunomycin as an indicator. Compared with previous DNA sensors with oligonucleotides directly incorporated on carbon electrodes, this carbon nanotube-based assay with its large surface area and good charge-transport characteristics increased DNA attachment quantity and complementary DNA detection sensitivity. The response signal increases linearly with the increase of the logarithm of the target DNA concentration in the range of 1.49 × 10⁻¹⁰ to 9.32 × 10⁻⁸ mol L⁻¹ with the detection limit of 7.5 × 10⁻¹¹ mol L⁻¹ (S/N = 3). The linear regression equation is I = 32.62 + 3.037 log C_DNA (mol L⁻¹) with a correlation coefficient value of 0.9842. This is the first application of carbon nanotubes combined with nano ZrO₂ to the fabrication of an electrochemical DNA biosensor with a favorable performance for the rapid detection of specific hybridization.