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Online hashing methods aim to learn compact binary codes of the new data stream, and update the hash function to renew the codes of the existing data. However, the addition of new data streams has a vital impact on the retrieval performance of the entire retrieval system, especially the similarity measurement between new data streams and existing data, which has always been one of the focuses of online retrieval research. In this paper, we present a novel scalable supervised online hashing method, to solve the above problems within a unified framework. Specifically, the similarity matrix is established by the label matrix of the existing data and the new data stream. The projection of the existing data label matrix is then used as an intermediate term to approximate the binary codes of the existing data, which not only realizes the semantic information of the hash codes learning but also effectively alleviates the problem of data imbalance. In addition, an alternate optimization algorithm is proposed to efficiently make the solution of the model. Extensive experiments on three widely used datasets validate its superior performance over several state-of-the-art methods in terms of both accuracy and scalability for online retrieval task.

Considering the heat capacity inside vertical spiral ground heat exchanger (VSGHEX) in the simulation is one of the most noteworthy challenge to design the ground source heat pump (GSHP) system with VSGHEXs. In this paper, a new simulation model for VSGHEXs is developed by combining the ICS model with the CaRM. The developed simulation model can consider the heat capacity inside VSGHEX and provide dynamic calculation with high speed and appropriate precision. In order to apply the CaRM, the equivalent length was introduced. Then, the equivalent length was approximated by comparing the results of the CaRM and the numerical calculation. In addition, the calculation model of the VSGHEX was integrated into the design and simulation tool for the GSHP system. The accuracy of the tool was verified by comparing with the measurements. The error between supply temperatures of the measurements and calculation is approximately 2 °C at the maximum. Finally, assuming GSHP systems with VSGHEXs, whose spiral diameter was 500 mm and depth was 4 m, were installed in residential houses in Japan, the required numbers of VSGHEXs were estimated. The results showed a strong correlation between the total heating or cooling load and the required number. Therefore, the required number can be estimated by using the simplified approximate equation.

Qualitative and quantitative detection of DNA was achieved by a "sandwich" DNA sensor through SG/TC (substrate generation and tip collection) mode of scanning electrochemical microscopy (SECM). The "sandwich" DNA structure was formed by the hybridization of thiol-tethered oligodeoxynucleotide probes (capture probe), assembled on the gold substrate surface, with target DNA and biotinylated indicator probe. HRP (horseradish peroxidase)-wrapped SiO2 nanoparticles were linked to the sandwich structure through biotin-streptavidin interaction. Hydroquinone (H2Q) was oxidized to benzoquinone (BQ) at the modified substrate surface where sequence-specific hybridization had occurred through the HRP-catalyzed reaction in the presence of H2O2. The detection was based on the reduction of BQ generated on the modified substrate by SECM tip. For SECM imaging experiment, we structured the microsensor platform through localized desorption of 1-dodecanethiol monolayer. Approach curves were employed for quantitative detection of DNA concentration. The detection limit of complementary DNA was as low as 0.8pM. This technique is promising for the application on electrochemical DNA chip.

The human neuroblastoma SH-SY5Y cell line has been used as a model to study mechanisms of neurotransmitter release. In order to study the mechanism of SH-SY5Y single cell exocytosis stimulated by different stimulants, including high K+ , 3-(1-nitroso-2-pyrrolidinyl) pyridine and nicotine, a type of indium tin oxide (ITO) micro-pore electrode was used to obtain the corresponding amperometric response time. When the cell is stimulated by 0.1 M K+ , almost immediate exocytosis could be detected, due to the rapid depolarization of cell membrane. However, the stimulations with 1 mM nicotine and 3-(1-nitroso-2-pyrrolidinyl) pyridine result in a short delay between stimulation and exocytosis, which can be correlated with the time needed for binding of the stimulant to the nicotinic acetylcholine (ACh) receptor and the induction of post-binding phenomena. Thus, the response time of SH-SY5Y single cell exocytosis is significantly affected by the exocytosis mechanisms.

In this work, a simple and sensitive electrochemical method was developed to determine Sudan I by cyclic voltammetry and differential pulse voltammetry using a glassy carbon electrode modified with a chitosan/carbon nanotube composite. In cyclic voltammetry, Sudan I exhibited a well-defined oxidation peak located at 0.72 V at the multi-walled carbon nanotube (MWCNT)/chitosan-modified GCE. The determination conditions, including pH, scan rate, and chitosan: MWCNT mass ratio at the modified electrode, were optimized. Under the optimum experimental conditions, Sudan I could be linearly detected by differential pulse voltammetry with a detection limit of 3.0 × 10-8 mol?L-1.

A sensitive electrochemical aptasensor for thrombin detection is presented based on the host-guest recognition technique. In this sensing protocol, a 15 based thrombin aptamer (ab. TBA) was dually labeled with a thiol at its 3′ end and a 4-((4-(dimethylamino)phenyl)azo) benzoic acid (dabcyl) at its 5′ end, respectively, which was previously immobilized on one Au electrode surface by Au S bond and used as the thrombin probe during the protein sensing procedure. One special electrochemical marker was prepared by modifying CdS nanoparticle with β-cyclodextrins (ab. CdS-CDs), which employed as electrochemical signal provider and would conjunct with the thrombin probe modified electrode through the host–guest recognition of CDs to dabcyl. In the absence of thrombin, the probe adopted linear structure to conjunct with CdS-CDs. In present of thrombin, the TBA bond with thrombin and transformed into its special G-quarter structure, which forced CdS-CDs into the solution. Therefore, the target-TBA binding event can be sensitively transduced via detecting the electrochemical oxidation current signal of Cd of CdS nanoparticles in the solution. Using this method, as low as 4.6 pM thrombin had been detected.

A new electrochemical aptamer molecular beacon (MB) was designed by the carminic acid (CA) covalently linking at the each end of a special single-stranded stem-loop shaped oligonucleotide and named as CAs-MB. CA is an electrochemically active molecule and two CA molecules at the ends of molecular beacon stem were closed enough to associate each other to be as CA dimer. The dimer was electrochemically inactive. It separated into two CA monomers and produced the electrochemical signal while CAs-MB combined with target. In this protocol, the detection strategy of CAs-MB for thrombin is based on electrochemical active–inactive switching between monomer and dimer forms of CA. In order to enhance the electrochemical signal, magnetic nanobeads (MNB) was applied by connecting CAs-MB with MNB through a duplex of DNA. With the magnetic enrichment, the detection limit for thrombin reached to 42.4 pM. The experiment results showed that this type of electrochemical active–inactive switching aptamer molecular beacon allowed the direct detection of target proteins in the solution with no requirement of removing uncombined CAs-MB. Besides, CAs-MB/MNB can be easily regenerated by using 2 M NaCl solution to cleave the thrombin from the aptasensor.

This communication reports on a new electrochemical method to detect the hybridization specificity by using host–guest recognition technique. A hairpin DNA with dabcyl-labeled at its 3′ and NH2 group at 5′ terminal was combined with CdS nanoparticle to construct a double-labeled probe (DLP), which could selectively hybridize with its target DNA in homogeneous solution. A β-CD modified Poly(N-acetylaniline) glassy carbon electrode was used for capturing the dabcyl label in DLP. When without binding with target DNA, the DLP kept its stem-loop structure which shielded the dabcyl molecule due to the loop of the hairpin DNA and CdS nanoparticle blocking dabcyl enter into the cavity of these β-CD molecules on the electrode. However, in present of complementary sequence, the target-binding DLP was incorporated into double stranded DNA, causing the DLP’s loop-stem structure opened and then the dabcyl was easily captured by the β-CD modified electrode. During electrochemical measurement, the signal from the dissolved Cd2+ was used for target DNA quantitative analysis. Keywords: DNA, Electrochemical, Homogeneous, Cyclodextrins, Double-labeled probe

A solid-state electrochemiluminescence (ECL) biosensing switch system based on special ferrocene-labeled molecular beacon aptamer (Fc-MBA) has been developed successfully for thrombin detections. Such special switch system includes two main parts, an ECL substrate and an ECL intensity switch. The ECL substrate was made by modifying the complex of Au nanoparticle and Ruthenium (II) tris-(bipyridine) (Ru(bpy)(3)(2+)-AuNPs) onto Au electrode. A molecular beacon aptamer labeled by ferrocene acted as the ECL intensity switch. The loop bases of the ECL intensity switch are designed with special anti-thrombin aptamer sequence which could be combined with its target protein via the reaction between aptamer and thrombin. During the reactions, the molecular beacon aptamer opened its stem-loop, and the labeled Fc was consequently kept away from the ECL substrate. Such structural change resulted in an obvious ECL intensity increment due to the decreased quenching effect of Fc to the ECL substrate. The analytic results are sensitive and specific.

A versatile method for preparing nanoporous polypyrrole (PPy) film using electrogenerated nanobubbles as templates on highly oriented pyrolytic graphite (HOPG) is presented using in situ electrochemical atomic force microscopy (EC-AFM). Keywords: Polypyrrole, Nanobubbles, Highly oriented pyrolytic graphite, Electrochemical atomic force microscopy

We report a new kind of electrochemical molecular beacon, termed “electrochemically active–inactive switching molecular beacon”, for direct detection of DNA in homogenous solution. The electrochemical molecular beacon consists of a stable stem-loop oligonucleotide carrying two carminic acid moieties (acting as electrochemical reporter) attached at its termini. In a close form, the electrochemical signal is quenched because two carminic acid moieties are close enough to associate into dimer. In the presence of the complementary DNA target, the electrochemical molecular beacon undergoes a conformational transformation from closed (hairpin) to open (linear) structure, which is associated with an increase in electrochemical signal. We found that the electrochemical molecular beacon is as effective as conventional molecular beacon in signaling the presence of complementary target and discriminating targets that differ by a single nucleotide. The proposed electrochemical molecular beacon has a great potential for investigating the interactions of DNA-protein and developing electrochemical real-time polymerase chain reaction. Keywords: DNA, Electrochemical molecular beacon, Molecular recognition, Nucleotides, Probe

Aligned carbon nanotubes (ACNTs) electrode has been developed for the direct protein electrochemistry and enzyme-biosensor study involving two types of nanoparticles. Pt nanoparticles (Ptnano) were electro-modified on the ACNTs’ each tube, greatly increasing the electrode surface area for locating protein and also its electronic transfer ability. Glucose oxidase (GOD) with chitosan (CS) and CdS nanoparticles electrochemically coated on each tube of ACNTs–Ptnano by the electrodeposition reaction of CS when pH value passing its pKa. The CdS nanoparticles between ACNTs electrode and GOD have stimulated the GOD’s direct electron transfer during its redox reaction of FAD/FADH2. The CS–GOD–CdS/ACNTs–Ptnano electrode also offer sensitive response to the substrate of glucose with detection limit of 46.8 μM (S/N = 3) and apparent Michaelis–Menten constant of 11.86 mM. Keywords: Aligned carbon nanotubes, Glucose oxidase, Chitosan, Direct electron transfer, Biosensor

A simple preparation scheme is described for the quantitative analysis of a magnesium niobate sample using slurry introduction axially viewed inductively coupled plasma optical emission spectrometry. Relationships between the stability of slurries and the conditions, such as particle size, pH, dispersant and amount of dispersant, were investigated experimentally. The MgNb(2)O(6) slurry sample was prepared by adding the dispersant sodium polyacrylate and agitation in an ultrasonic bath to ensure good dispersion. Under optimization of pH and amount of dispersant, an analysis of minor and trace impurities (Ba, Ca, Cr, Cu, Fe, Mn, Ni, Pb) in magnesium niobate was accomplished. Applying a paired t test, we showed that the results were in agreement at a 95% confidence level with the reference values obtained by a fusion method for a magnesium niobate sample, which verified that the calibration curves could be established by aqueous standards. Analytical results demonstrate that the factors that affected the accuracy of determination for MgNb(2)O(6) are mainly the particle size of the sample and the stability of slurry.

A thionine modified aligned carbon nanotubes (ACNTs) electrode was fabricated and was used to electrochemically determine nitrite. The thionine modified ACNTs electrode exhibited enhanced electrocatalytic behavior to the oxidation of nitrite. The electrochemical mechanism of the thionine/ACNTs electrode towards the oxidation of nitrite was discussed. The thionine modified ACNTs electrode exhibited fast response towards nitrite with a detection limit of 1.12 × 10−6 mol L−1 and a linear range of 3 × 10−6 – 5 × 10−4 mol L−1. The proposed method was successfully applied in the detection of nitrite in real samples. Keywords: Thionine, Aligned carbon nanotubes, Nitrite, Modified electrode, Electrocatalytic oxidation

A reliable and reproducible method, capillary zone electrophoresis with amperometric detection (CZE-AD), has been developed for separation and quantification of levodopa methyl ester (LDME) and its biotransformation products levodopa (L-DOPA) and dopamine (DA) in rat serum. A carbon-disk electrode was used as working electrode. The optimum conditions for CZE detection were 50 mmol L(-1) phosphate solution at pH 7.0 as running buffer, 17 kV as separation voltage, 1.0 V (vs Ag/AgCl, 3.0 mol L(-1)) as detection potential, and sample injection for 8 s at 17 kV. The linear ranges were from 2.4 x 10(-2) to 2.2 microg mL(-1) for LDME, 2.9 x 10(-1) to 49.5 microg mL(-1) for L-DOPA, and 1.4 x 10(-2) to 1.5 microg mL(-1) for DA with correlation coefficients of 0.9997, 0.9994, and 0.9999, respectively. The detection limits for LDME, L-DOPA, and DA were 14.6, 98.0, and 9.7 ng mL(-1), respectively. Recoveries were 80.3% for LDME, 93.5% for L-DOPA, and 86.5% for DA. This method was applied to serum samples after intravenous injection of LDME and L-DOPA to rats.

A high-performance capillary electrophoretic (CE) method with electrochemical detection (ED) has been developed for determination of the pharmacologically active flavonoids in Ginkgo biloba L. and phytopharmaceuticals containing its extract. Epicatechin, catechin, rutin, apigenin, luteolin, and quercetin are important flavonoids in this plant. Operated in a wall-jet configuration, a 300 micro m diameter carbon-disk electrode was used as working electrode with good response to the six analytes at +1000 mV (relative to the SCE). Under the optimum conditions, the analytes were separated within 22 min in a borax buffer (pH 9.0). Excellent linearity was obtained over two orders of magnitude and detection limits (S/N=3) ranged from 1.4 x 10(-7) to 5.0 x 10(-7) g mL(-1) for all six analytes. The method was successfully used for assay of Ginkgo biloba L. and its phytopharmaceuticals after a relatively simple extraction procedure; the results obtained were satisfactory.

The electrochemical reduction mechanism of ethidium bromide was first studied by spectroelectrochemistry. This reduction was proved to be a two-step process by cyclic voltammetry, differential pulse voltammetry and spectroelectrochemistry, in which each step was proved to be a one-electron transfer process by a spectropotentiostatic fluorescence technique. Hydroethidine was confirmed to be the final product by comparing the spectrum of the product of the electrochemical reduction to that of the product of the chemical reduction of ethidium bromide, and a carbon-centered radical was concluded to be a reasonable intermediate product during the electrochemical reduction of ethidium bromide.

The fluorescence spectral characteristics and interaction of bis(ethylene)tin(bis(salicylidene)ethylenediamine) [Et2Sn(salen)] with DNA are described. The polarity of the solvent has a strong effect on the fluorescence characteristics of Et2Sn(salen). Et2Sn(salen) bound to DNA showed a marked decrease in the fluorescence intensity with a bathochromic shift of the excitation and emission peaks. A hypochromism in the UV absorption spectra was also observed. KI quenching and competitive binding to DNA between Et2Sn(salen) and ethidium bromide (EB) were studied in connection with other experimental observations to show that the interactive model between Et2Sn(salen) and DNA is an intercalative one. The pH and salt effect on the fluorescence properties was also investigated. The intrinsic binding constant was estimated to be 1.071 x 10(5) mol L(-1) in base pairs and the binding site number is 1.98, respectively. A linear relationship between F/F0 and the concentration of calf thymus DNA covers 5.1 x 10(-6) - 2.41 x 10(-4) mol L(-1), which can be utilized for determining traces of calf thymus DNA with a detection limit of 1.1 x 10(-7) mol L(-1) in base pairs.

A kind of delayed predator-prey system with harvesting is considered in this paper. The influence of harvesting and delay is investigated. Our results show that Hopf bifurcations occur as the delayτpasses through critical values. By using of normal form theory and center manifold theorem, the direction of Hopf bifurcation and the stability of the bifurcating periodic solutions are obtained. Finally, numerical simulations are given to support our theoretical predictions.

An enzyme-based solid-state electrochemiluminescence (ECL) sensing platform for sensitive detection of a single point mutation is developed successfully using p53 tumor suppressor gene as a model analyte. A composite of multiwalled carbon nanotubes and Ruthenium (II) tris-(bipyridine) (MWNTs–Ru(bpy)32+) was prepared and coated on an electrode surface, which was covered by polypyrrole (PPy) to immobilize ssDNA. Then, the ssDNA recognized the gold nanoparticle (AuNP)-labeled p53 tumor suppressor gene, and produced AuNP-dsDNA electrode with AuNP layer. The surface adsorbed the glucose-dehydrogenase (GDH) molecules for producing ECL signal. This system combined enzyme reaction with ECL detection, and it can recognize sequence-specific wild type p53 sequence (wtp53) and muted type p53 sequence (mtp53) with discrimination of up to 56.3%. The analytic results were sensitive and specific. It holds promise for the diagnosis and management of cancer.

In this paper, we report a new strategy for electrochemical DNA detection in homogeneous solution based on the host-guest molecule recognition technique. In this sensing protocol, a novel dually labeled DNA probe (DLP) in a stem-loop structure was employed, which was designed with dabcyl labeled at one end as a guest molecule, and with Au nanoparticle labeled at the other end as electrochemical tag to indicate the hybridization occurrence. One α-CD/MCNTs/GCE was used for capturing the DNA hybridization and electrochemical signal transduction. Before the hybridization, the DLP remained in the stem-loop structure, which forced the dabcyl molecular to be closed to the Au nanoparticle. Due to the steric effect of the Au nanoparticle, the dabcyl was prevented from conjugating with the α-CD on the electrode and resulting in that the DLP could not be captured by the electrode. After hybridized with the target DNA, the target-binding DLP caused the DLP's loop-stem structure opened and then the dabcyl molecule was easily entering the cavity of the α-CD modified electrode and resulting in that the DLP could be captured by the α-CD modified electrode and the capture efficiency was proportion with the concentration of the target DNA. Therefore, the target hybridization event can be sensitively transduced via detecting the electrochemical reduction current signal of AuCl(4)(-) of Au nanoparticles labeled at the DLP. Using this strategy, as low as 2.6×10(-10) M DNA target had been detected with excellent differentiation ability for even single mismatch.

A simple, fast, and reliable method based on capillary electrophoresis with electrochemical detection (CE-ED) was developed for the separation and determination of rutin, ferulic acid, vanillic acid, chlorogenic acid, quercetin and caffeic acid in Radix Astragali and its medicinal preparations. The effects of several important factors, such as detection potential, pH, running buffer concentration, separation voltage and injection time, were investigated to acquire the optimum conditions. Under the optimum conditions, the analytes could be separated within 17 min in a 75 cm length capillary at a separation voltage of 18 kV in a 10 mmol/L borate buffer (pH 8.2). A 300 microm diameter carbon disk electrode generated a good response at +0.95 V (vs. saturated calomel electrode (SCE)) for all analytes. The relationship between peak currents and analyte concentrations was linear over about three orders of magnitude with detection limits (S/N = 3) ranging from 78 microg/L to 110 microg/L for all analytes. The average recoveries were 96.0%-103.0% with the relative standard deviations of 1.9%-3.6% (n=3). This method has been successfully used for the determination of these analytes in real samples, and the assay results were satisfactory.

A new method has been developed for the simultaneous determination of diflubenzuron and triflumuron residues in greasy wool by reversed-phase high performance liquid chromatography (HPLC). The pesticides were extracted by hexane-ether from greasy wool and cleaned up with gel permeation chromatography (GPC) and solid phase extraction (SPE). The pesticides were analyzed by HPLC-diode array detector (DAD) and quantified by external standard method. The linear ranges of diflubenzuron and triflumuron were 0.41 -41 mg/L and 0.38 - 38 mg/L, and the correlation coefficients were 0.999 6 and 0.999 9, respectively. The limits of detection were 0.22 mg/kg for diflubenzuron and 0.18 mg/kg for triflumuron; the limits of quantification were 0.73 mg/kg for diflubenzuron and 0.60 mg/kg for triflumuron. The average recoveries of pesticides spiked levels from 0.76 to 10.25 mg/kg in greasy wool samples were in the range of 86.3% - 96.7%, and the relative standard deviations were 4.2% - 8.7%. The method developed shows little interferences, good recovery and repeatability. It is suitable for the simultaneous determination of diflubenzuron and triflumuron in greasy wool samples.

The simultaneous determination of three isomers of phenylenediamines (o, m, and p-phenylenediamine) and two isomers of dihydroxybenzenes (catechol and resorcinol) in hair dyes was performed by capillary zone electrophoresis coupled with amperometric detection (CZE-AD). The effects of working electrode potential, pH and concentration of running buffer, separation voltage, and injection time on CZE-AD were investigated. Under the optimum conditions the five analytes could be perfectly separated in 0.30 mol L(-1) borate-0.40 mol L(-1) phosphate buffer (pH 5.8) within 15 min. A 300 μm diameter platinum electrode had good responses at +0.85 V (versus SCE) for the five analytes. Their linear ranges were from 1.0 × 10(-6) to 1.0 × 10(-4) mol L(-1) and the detection limits were as low as 10(-7) mol L(-1) (S/N = 3). This working electrode was successfully used to analyze eight kinds of hair dye sample with recoveries in the range 91.0-108.0% and RSDs less than 5.0%. These results demonstrated that capillary zone electrophoresis coupled with electrochemical detection using a platinum working electrode as detector was convenient, highly sensitive, highly repeatable and could be used in the rapid determination of practical samples.

A simple and rapid capillary electrophoresis (CE) with electrcochemical detection (ED) method has been established for the simultaneous determination of seven active ingredients in the stems and roots of Gaultheria leucocarpa var. yunnanensis and its medicinal preparation, including (+)-catechin, rutin, gentisic acid, vallinic acid, salicylic acid, quercetin, and protocatechuic acid. The effects of working potential, pH, and concentration of running buffer, separation voltage, and injection time on CE‐ED are systematically investigated. Under the optimum conditions, the seven analytes could be completely separated within 23 min in a borax running buffer (pH 8.7). A good linear relationship is obtained over three orders of magnitude with detection limits (signal-to-noise ratio = 3) ranging from 5 ◊ 10 ‐8 g/mL to 3 ◊ 10‐7 g/mL for the analytes. The proposed method is successfully used in the analysis of real samples after a relatively simple extraction procedure, and the assay results are satisfactory.

An ultrasensitive and highly specific electrochemical aptasensor for detection of thrombin based on gold nanoparticles and thiocyanuric acid is presented. For this proposed aptasensor, aptamerI was immobilized on the magnetic nanoparticles, aptamerII was labeled with gold nanoparticles. The magnetic nanoparticle was used for separation and collection, and gold nanoparticle offered excellent electrochemical signal transduction. Through the specific recognition for thrombin, a sandwich format of magnetic nanoparticle/thrombin/gold nanoparticle was fabricated, and the signal amplification was further implemented by forming network-like thiocyanuric acid/gold nanoparticles. A significant sensitivity enhancement had been obtained, and the detection limit was down to 7.82 aM. The presence of other proteins such as BSA and lysozyme did not affect the detection of thrombin, which indicates a high specificity of thrombin detection could be achieved. This electrochemical aptasensor is expected to have wide applications in protein monitoring and disease diagnosis.

Synthesis of the novel Cu@Au alloy nanoparticle and its application in an electrochemical DNA hybridization detection assay is described in this article. We report a low-temperature method for generating core-shell particles consisting of a core of Cu and a thin layer of Au shell that can be readily functionalized with oligonucleotides. Core-shell Cu@Au particles were successfully labeled to a 5′-alkanethiol capped oligonucleotides probe that is related to the colitoxin gene. The DNA genetic sensing assay relies on the electrostatic adsorption of target oligonucleotides onto conducting polypyrrole (PPy) surface at the glassy carbon electrode (GCE), and its hybridization to the alloy particle–oligonucleotides DNA probe. Hybridization events between probe and target were monitored by the release of the copper metal atoms anchored on the hybrids by oxidative metal dissolution and the indirectly determination of the solubilized Cu 2+ ions by sensitive anodic stripping voltammetry (ASV). The detection limit is 5.0 pmol l −1 of target oligonucleotides. The Cu@Au core-shell nanoparticles combining the surface modification properties of Au with the good electrochemical activity of Cu core shows their perspective application in the electrochemical DNA hybridization analysis assay.

A novel and sensitive electrochemical DNA biosensor based on multi-walled carbon nanotubes functionalized with a carboxylic acid group (MWNTs-COOH) for covalent DNA immobilization and enhanced hybridization detection is described. The MWNTs-COOH-modified glassy carbon electrode (GCE) was fabricated and oligonucleotides with the 5'-amino group were covalently bonded to the carboxyl group of carbon nanotubes. The hybridization reaction on the electrode was monitored by differential pulse voltammetry (DPV) analysis using an electroactive intercalator 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 dramatically increased DNA attachment quantity and complementary DNA detection sensitivity. This is the first application of carbon nanotubes to the fabrication of an electrochemical DNA biosensor with a favorable performance for the rapid detection of specific hybridization.

Aligned carbon nanotubes (ACNTs) were modified with polypyrrole (PPy) via electropolymerization. Because of the large specific surface area and excellent electrical conductivity of ACNTs, continuous electropolymerization was able to be carried out, forming a thick PPy coating on the ACNTs. The resulting nanocomposite possessed a core-shell structure with ACNTs as the core, PPy as the shell, and nanoparticles of PPy on the top, and displayed high performance supercapacitance properties.