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A method based on capillary electrophoresis with electrochemical detection has been developed for the separation and determination of epicatechin, emodin, syringic acid, vanillic acid, rhein, and protocatechuic acid in Spatholobus suberectus dunn and its medicinal preparations for the first time. The effects of a working electrode potential, pH and concentration of running buffer, separation voltage, and injection time on CE‐ED were investigated. Under the optimum conditions, the analytes could be separated in a 60 mmol L−1 borate buffer (pH 9.0) within 26 min. A 300 µm diameter carbon disk electrode has a good response at +0.95 V (vs. SCE) for all analytes. The response was linear over three orders of magnitude with detection limits (S/N=3) ranging from 5×10−8 g mL−1 to 2×10−7 g mL−1 for the analytes. The method has been successfully applied to the analysis of a real sample, with satisfactory results.

A sensitive, simple and rapid flow-injection chemiluminescence (FI–CL) method is described to determine tsumacide pesticide residue based on the CL reaction of the alkaline degradation product of tsumacide with acidic KMnO4 when rhodamine 6G was present. Under the optimum conditions, the relative CL intensity is linear with the concentration of tsumacide in the range of 2.0 × 10−3–0.20 mg/L. The detection limit is 6.6 × 10−4 mg/L (3σ) and the relative standard deviation for 2.0 × 10−2 mg/L tsumacide solution was 2.28% (intra-day) and 4.85% (inter-day). The proposed method has been applied to determine the residue of tsumacide in vegetable samples and the recovery test is very satisfactory. Copyright © 2007 John Wiley & Sons, Ltd.

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

In this paper, a microchip electrophoresis method based on on-line multiple-preconcentration techniques combining field-amplified sample stacking and reversed-field stacking was developed for highly efficient analysis of acrylamide in food products. The related mechanism as well as important parameters governing separation and preconcentration have been investigated in order to obtain maximum resolution and sensitivity. The best separation was achieved using a 100mM borate solution at pH 9.3 as running buffer, and a sensitivity enhancement factor of 432 was obtained using this concentration method under optimal conditions. The detection limit of acrylamide was 1ng/mL, which was comparable to those previously obtained using CE methods with on-line preconcentration techniques and was 41-700 times lower than those previously reported CE methods without concentration process. The proposed method also gave satisfactory and reliable results in the analysis of acrylamide in potato chips and French fries.

A new series of photoactive metallocyclodextrins with increased fluorescence intensity upon binding with ssDNAs/aptamers has been demonstrated to sensitively and selectively detect lysozyme. The detection mechanism relies on the formation of an aptamer–lysozyme complex, which leads to reduction of fluorescence intensity.

A method based on capillary electrophoresis with electrochemical detection (CE‐ED) has been developed for the first time for the separation and determination of isovanillic acid, vanillic acid, quercetin, rosmarinic acid, caffeic acid, and protocatechuic acid in Origanum vulgare L. and its medicinal preparations. The effects of working electrode potential, pH level, concentration of running buffer, separation voltage, and injection time on CE‐ED were investigated. Under the optimum conditions, the analytes could be separated in a 50 mmol L−1 borate buffer (pH 8.7) within 21 min. A 300‐µm diameter carbon disk electrode has a good response at +0.95 V (vs. SCE) for all analytes. The response was linear over three orders of magnitude with detection limits (S/N=3) ranging from 4×10−8 g mL−1 to 2×10−7 g mL−1 for the analytes. The method has been successfully applied to the analysis of real sample, with satisfactory results.

Gold electrodes were modified with submonolayers of mercaptoacetic acid (RSH) and further reacted with poly(amidoamine) (PAMAM) dendrimers (generation 4.0) to obtain thin films, on which DNA probe was later immobilized to afford a stable recognition layers. The characterization of the PAMAM/RSH-modified electrode was investigated by cyclic voltammetry (CV) and electrochemical impedance measurement. Differential pulse voltammogram (DPV) measurement was used to monitor DNA hybridization with daunomycin (DNR) as indicator. Experiments carried out with these novel materials not only showed an improved DNA attachment quantity on the dendrimers-modified electrodes compared to DNA sensors with oligonucleotides directly immobilized on Au electrodes, but also exhibited a high selectivity, sensitivity and stability for the measurement 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) 3 2+ -doped SNPs) as DNA tags, is described. In this protocol, Ru(bpy) 3 2+ -doped SNPs was used for DNA labeling with trimethoxysilylpropydiethylenetriamine(DETA) and glutaraldehyde as linking agents. The Ru(bpy) 3 2+ -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) 3 2+ 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 .

A method based on capillary electrophoresis with electrochemical detection has been developed for the separation and determination of epicatechin, kaempferol, chlorogenic acid, 4-hydroxybenzoic acid, quercetin and protocatechuic acid in hawthorn for the first time. The effects of working electrode potential, pH and concentration of running buffer, separation voltage and injection time on CE-ED were investigated. Under the optimum conditions, the analytes could be separated in a 60 mmol·L−1 borate buffer (pH 8.7) within 21 min. A 300 μm diameter carbon disk electrode has a good response at +0.95 V (vs. SCE) for all analytes. The response was linear over three orders of magnitude with detection limits (S/N=3) ranging from 3×10−8 to 2×10−7 g·mL−1 for the analytes. The method has been successfully applied to the analysis of real sample, with satisfactory results.

A simple, reliable and reproducible method, based on capillary zone electrophoresis with amperometric detection (CZE-AD), has been developed for simultaneous determination of four active ingredients in Vc Yinqiao tablets including paracetamol, vitamin C, caffeic acid and chlorogenic acid. A carbon-disk electrode was used as working electrode and 0.95 V (versus SCE) was selected as detection potential. The optimal conditions of CZE experiment were 30 mmol·L−1 borate solution (pH 9.5) as running buffer, 14 kV as separation voltage and 8 s (14 kV) as electro-kinetic sampling time. Under the selected optimum conditions, paracetamol, vitamin C, caffeic acid and chlorogenic acid could be perfectly separated within 22 min, and their detection limits (S/N=3) ranged from 5×10−7 to1×10−6 mol·L−1. This proposed method demonstrated good reproducibility with relative standard deviations of less than 3% for both migration time and peak current (n=7). The utility of this method was demonstrated by monitoring a kind of compound medicine named Vc Yinqiao tablets and the assay results were satisfactory.

In this paper, a simple, rapid and sensitive flow-injection chemiluminescence method has been developed for the determination of metoprolol tartrate, which acts as a kind of sensitizer in the chemiluminescence emission from the redox of SO 3 2− with Ce(IV) in acidic medium. Under the optimized conditions, the proposed method allows the measurement of metoprolol tartrate over the range of 1.5 × 10 −8 to 7.3 × 10 −6 mol/L with a detection limit of 4.7 × 10 −9 mol/L (3 σ ), and the relative standard deviation for 7.3 × 10 −7 mol/L metoprolol tartrate ( n = 11) is 2.20%. The utility of this method was demonstrated by determining metoprolol tartrate in tablets and human urine sample.

A label-free electrochemical impedance based protein biosensor was introduced by using aptamer as recognition tool. Our sensing protocol utilizes the affinity interaction between the thrombin and the self-assembled DNA aptamer on gold electrode. This specific interaction increases the electrode interfacial electronic transfer resistance. The resistance signal is then “amplified” by using guanidine hydrochloride to denature the captured thrombin for increasing the hydrated radius of the thrombin, consequently blocking the electron transfer from solution to electrode. The sensor sensitivity is improved using this strategy and as low as 1.0 � 10 � 14 mol L � 1 thrombin (enzymatic activity 10 U/mg) can be detected out.

In this paper, we present an electrochemical impedance-based DNA biosensor by using a composite material of polypyrrole (PPy) and multiwalled carbon nanotubes (MWNTs) to modify glassy carbon electrode (GCE). The polymer film was electropolymerized onto GCE by cyclic voltammetry (CV) in the presence of carboxylic groups ended MWNTs (MWNTs-COOH). Such electrode modification method is new for DNA hybridization sensor. Amino group ended single-stranded DNA (NH2-ssDNA) probe was linked onto the PPy/MWNTs-COOH/GCE by using EDAC, a widely used water-soluble carbodiimide for crosslinking amine and carboxylic acid group. The hybridization reaction of this ssDNA/PPy/MWNTs-COOH/GCE resulted in a decreased impedance, which was attributed to the lower electronic transfer resistance of double-stranded DNA than single-stranded DNA. As the result of the PPy/MWNTs modification, the electrode obtained a good electronic transfer property and a large specific surface area. Consequently, the sensitivity and selectivity of this sensor for biosensing DNA hybridization were improved. Complementary DNA sequence as low as 5.0×10−12 mol L−1 can be detected without using hybridization marker or intercalator. Additionally, it was found that the electropolymerization scan rate was an important factor for DNA biosensor fabrication. It has been optimized at 20 mV s−1.

A method based on capillary electrophoresis with electrochemical detection has been developed for the separation and determination of epicatechin, isovanillic acid, vanillic acid and myricetin in Dioscorea bulbifera L. and its medicinal preparations. The effects of working electrode potential, pH and concentration of running buffer, separation voltage and injection time were investigated. Under optimum conditions, the analytes could be separated in a 40 mmol L−1 borate buffer (pH 8.7) within 15 min. A 300 μm diameter carbon disk electrode has a good response at + 0.95 V (vs. SCE) for all analytes. The response was linear over three orders of magnitude with detection limits (S/N = 3) ranging from 3.0 × 10−8 g mL−1 to 1.0 × 10−7 g mL−1. The method has been successfully applied to the analysis of real samples.

In this paper, we present an impedance-based DNA biosensor using thionine intercalation to amplify DNA hybridization signal. Beacon single-stranded DNA (ssDNA) probe and mercaptoacetic acid were self-assembled onto a Au electrode by forming AuS bonds. These beacon ssDNAs were hybridized with the complementary sequences around the loop structure. Then thionine was intercalated into the double-stranded DNA (dsDNA) immobilized on the Au electrode surface. Due to the neutralization of the negative charges of dsDNA by the intercalated thionine, the electronic transfer resistance (Ret) of the DNA modified Au electrode was significantly diminished. Herein, the decreased value of Ret resulted from the thionine intercalating into dsDNA was employed as the hybridization signal. SDS was used to reduce the unspecific adsorption between ssDNA and thionine. Several experimental conditions, including the surface coverage of ssDNA probe on Au electrode, the hybridization temperature and time were all optimized. Moreover, the hybridization reactions of the unstructured linear ssDNA probe and the structured beacon ssDNA probe with their complementary sequences were compared in this work. The sensitivity of the presented DNA biosensor highlighted that the intercalation of thionine into dsDNA was an efficient approach to amplify the hybridization signal using impedance detection technique. Additionally, in this DNA biosensing protocol, beacon ssDNA has a good ability to distinguish target DNA sequences. This results in a higher specificity than using traditional unstructured DNA probe.

In this paper, capillary zone electrophoresis with amperometric detection (CZE–AD) was firstly applied to the simultaneous separation and determination of nitroaniline positional isomers. The three analytes could be perfectly analyzed by using the buffer of extreme pH. The effects of several important factors were investigated to find optimum conditions. A carbon-disk electrode was used as working electrode. The optimal conditions were 40 mmol/L tartaric acid–sodium tartrate (pH 1.2) as running buffer, 17 kV as separation voltage and 1.10 V (versus saturated calomel reference electrode, SCE) as detection potential. Under the optimum conditions, o-, m- and p-nitroaniline were separated successfully and good linearity, reproducibility and recovery results were obtained. The detection limit for m-nitroaniline was as low as at 9.06 × 10−9 mol/L. This proposed method demonstrated long-term stability and reproducibility with relative standard deviations of less than 1.8% for migration time and 1.1% for peak areas. The utility of this method was demonstrated by monitoring dyestuff wastewater and the assay results were satisfactory.

The development of nanostructured polymers has opened up novel fundamental and applied frontiers, which has attracted tremendous interest in recent years. We have recently developed techniques for the micro-lithographic formation of conducting polymer patterns on the micrometer scale and for coating conducting polymers on individual aligned carbon nanotubes. The micro- and nano-fabrication facilitates the use of conducting polymers for various applications ranging from multicolor polymer light-emitting displays to biosensors. More recently, we have demonstrated the controlled syntheses of conducting polymer microcontainers through electrochemical generation of surfactant (i.e. β-napthalenesulfonic acid, β-NSA)-stabilized H 2 gas bubbles on the working electrode, followed by electrochemical polymerization of pyrrole around the wall of the “soap bubble” template. By pre-patterning the working electrode surface with non-conducting polymers through micro-contact printing (μCP) or plasma patterning, we have also produced conducting polymer microcontainers in a patterned fashion. Furthermore, potential applications of the patterned and non-patterned conducting polymer microcontainers have been demonstrated, for example, by immobilizing glucouse oxidase (GOX) onto the conducting polymer microcontainers for glucose sensing. This paper provides a brief summary of our work on micro- and nano- fabrication of conducting polymer for various potential applications.

The discovery of carbon nanotubes (CNTs) about a decade ago has brought fascinating evolutions in electronics, material industry, as well as bio-techniques for DNA analysis, gene therapy, drug delivery etc. It has also dramatically promoted the development of DNA biosensing techniques, especially electrochemical DNA biosensor. The application of CNTs in electrochemical DNA biosensors includes two main aspects: on one hand, using CNTs as a novel substrate not only enables immobilization of DNA molecules but also serves as a powerful amplifier to amplify signal transduction event of DNA hybridization. On the other hand, CNTs can also be employed as a powerful carrier to pre-concentrate enzymes or electroactive molecules for electrochemical sensing of DNA hybridization as a novel indicator. In this review, we place emphasis on recent studies of CNTs-based electrochemical DNA biosensors based on these two aspects, with advantages and disadvantages of each aspect introduced herein.

In this work, the application of a conducting polymer, poly(thionine), modified electrode as matrix to DNA immobilization as well as transducer to label-free DNA hybridization detection was introduced. The electropolymerization of thionine onto electrode surface was carried out by a simple two-step method, which involved a preanodization of glassy carbon electrode at a constant positive potential in thionine solution following cyclic voltammetry scans in the solution. Electrochemical detection was performed by differential pulse voltammetry in the electroactivity potential domain of poly(thionine). The resulting poly(thionine) modified electrode showed a good stability and electroactivity in aqueous media during a near neutral pH range. Additionally, the pendant amino groups on the poly(thionine) chains enabled poly(thionine) modified electrode to immobilize phosphate group terminated DNA probe via covalent linkage. Hybridization process induced a clear decrease in poly(thionine) redox current, which was corresponding to the decrease in poly(thionine) electroactivity after double stranded DNA was formed on the polymer film. The detection limit of this electrochemical DNA hybridization sensor was 1.0×10−10 mol/L. Compared with complementary sequence, the hybridization signal values of 1-base mismatched and 3-base mismatched samples were 63.9% and 9.2%, respectively.

Since Waston and Crick established the double helical structure of DNA in 1953, nucleic acid research has become one of the most important fields in life science. Therefore, DNA biosensors based on DNA hybridization plays a more and more important role in DNA analysis. This review briefly introduces our group's research work in the electrochemical DNA biosensor field including DNA immobilization schemes and hybridization marking techniques. The representative immobilization techniques are adsorption on the surface, covalent attachment on a functional surface, embedding in a polymeric matrix, and the self‐assembled monolayer method. The formation of double‐stranded DNA upon hybridization is commonly detected in connection with the use of an appropriate electro‐active hybridization intercalator, or labeling DNA by a simple electro‐active molecule or a powerful nanoparticle.

A simple, reliable and reproducible method, based on capillary zone electrophoresis with amperometric detection (CZE-AD), was developed for simultaneous determination of 3-amino-3-azabicyclo[3,3,0]octane (aminoheterocycle) and 3-azabicyclo[3,3,0]octane (azabicycle) in gliclazide bulk drug. The optimal conditions of CZE-AD were 50 mM borate solution (pH 9.0) as running buffer, 14 kV as separation voltage and 0.95 V (versus SCE) as detection potential. Under the selected optimum conditions, the two analytes could be perfectly separated within 9 min. The linearity range of aminoheterocycle was from 1.0 × 10 −6 to 1.0 × 10 −3 M and that of azabicycle was from 2.0 × 10 −6 to 1.0 × 10 −3 M. Their detection limits were 5.0 × 10 −7 and 1.0 × 10 −6 M, respectively, (S/N = 3). This proposed method demonstrated long-term stability and reproducibility with relative standard deviations of less than 2% for both migration time and peak current. It has been successively used for the determination of these two analytes in gliclazide bulk drug, and the assay results were satisfactory.

We have demonstrated that specific DNA sequences could be covalently immobilized onto acid-oxidized and plasma-activated carbon nanotubes. While various functional supramolecular structures could be prepared by self-assembling of the acid-oxidized carbon nanotubes attached with DNA chains of complementary sequences, the DNA-immobilized aligned carbon nanobues have been demonstrated to be significant for sensing complementary DNA and/or target DNA chains of specific sequences with a high sensitivity and selectivity.

Platinum nanoparticles were used in combination with multi-walled carbon nanotubes (MWCNTs) for fabricating sensitivity-enhanced electrochemical DNA biosensor. Multi-walled carbon nanotubes and platinum nanoparticles were dispersed in Nafion, which were used to fabricate the modification of the glassy carbon electrode (GCE) surface. Oligonucleotides with amino groups at the 5′ end were covalently linked onto carboxylic groups of MWCNTs on the electrode. The hybridization events were monitored by differential pulse voltammetry (DPV) measurement of the intercalated daunomycin. Due to the ability of carbon nanotubes to promote electron-transfer reactions, the high catalytic activities of platinum nanoparticles for chemical reactions, the sensitivity of presented electrochemical DNA biosensors was remarkably improved. The detection limit of the method for target DNA was 1.0 × 10−11 mol l−1.

A rapid and sensitive flow-injection chemiluminescence method is described for the determination of meloxicam based on its reaction with N -bromosuccinimide (NBS) in alkaline medium. Under the optimum conditions, the proposed method allows the measurement of meloxicam over the range of 2.2 × 10 −7 to 2.8 × 10 −5 mol/l with a detection limit of 7.7 × 10 −8 mol/l. The relative standard deviation for 11 parallel measurements of 2.8 × 10 −6 mol/l meloxicam is 2.14%. The method has been applied satisfactorily to the determination of meloxicam in pharmaceutical preparations. The results agree well with those obtained by spectrophotometry. The mechanism of the chemiluminescence reaction is briefly explained with spectroscopic evidence.

It was found that the weak chemiluminescence produced from the reaction of dobutamine hydrochloride with luminol in alkaline solution could be strongly enhanced by potassium ferricyanide and potassium ferrocyanide. Based on this found, a new flow injection chemiluminescence method is proposed for the determination of dobutamine hydrochloride. Under the optimum conditions, the proposed method has a linear range of 1.0 × 10 −10 to 1.0 × 10 −7 g ml −1 , with a detection limit of 2.6 × 10 −11 g ml −1 for dobutamine hydrochloride (3 σ ). A complete analysis could be performed in 40 s including washing and sampling, giving a throughout of about 90 h −1 . The relative standard deviation (R.S.D.) for 11 parallel measurements of 1.0 × 10 −8 g ml −1 dobutamine is 1.23%. The proposed method has been applied for the determination of dobutamine hydrochloride in its pharmaceutical formulations. The results obtained compared well with those by an official method. The possible mechanism of this chemiluminescence reaction was also proposed.

Carbon nanotubes have been proposed as support materials for numerous applications, including the development of DNA sensors. One of the challenges is the immobilization of DNA or other biological molecules on the sidewall of carbon nanotubes. This paper introduces a new fabrication of DNA-carbon nanotubes particles using the layer-by-layer (LBL) technique on single-walled carbon nanotubes (SWCNTs). Poly(diallyldimethylammonium) (PDDA), a positively charged polyelectrolyte, and DNA as a negatively charged counterpart macromolecule are alternatively deposited on the water-soluble oxidized SWCNTs. Pure DNA/PDDA/SWCNTs particles can be prepared and separated by simple unltracentrifugation. The characterization of DNA/PDDA/SWCNTs particles was carried out by scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-visible spectroscopy, Raman spectroscopy, and thermogravimetric analysis (TGA). An electrode modified by the DNA/PDDA/SWCNTs particles shows a dramatic change of the electrochemical signal in solutions of tris(2,2'-bipyridyl)ruthenium(II) ((Ru(bpy)(3)2+) as a reporting redox probe. A preliminary application of the DNA-modified carbon nanotubes in the development of DNA sensors used in the investigation of DNA damage by nitric oxide is presented.

In this paper, the electrochemical behavior of luminol in weakly acidic solution was studied. It is found that Co 2+ remarkably enhances the electrochemiluminescence (ECL) of luminol in citric acid–sodium citrate buffer solution (pH = 4.0) when a pulse potential (−1.8 to +1.0 V, versus Ag/AgCl) is applied to the Pt electrode. The selectivity for Co 2+ is very good because most of the other water-soluble metal ions do not interfere. A sensitive and selective ECL method for determination of Co 2+ is proposed. After optimization of the reaction conditions and electrochemical parameters influencing the relative ECL intensity, the linear range responding to Co 2+ is 5.0 × 10 −12 to 1.0 × 10 −7 mol/L, and the detection limit is 2.0 × 10 −12 mol/L. The relative standard deviation for 5.0 × 10 −10 mol/L cobalt(II) is 3.7% ( n = 11).

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 novel sensitive electrochemical biosensor based on magnetite nanoparticle for monitoring DNA hybridization by using MWNT–COOH/ppy-modified glassy carbon electrode is described. In this new detection system, mercapatoacetic acid (RSH)-coated magnetite nanoparticles, capped with 5′-(NH 2 ) oligonucleotide, is used as DNA probe to complex 29-base polynucleotide target (a piece of human porphobilinogen deaminase PBGD promoter from 170 to 142). Target sequence hybridized with the probe results in the decrease of the reduction peak current of daunomycin connected with probe. The response of non-complementary sequence was almost the same as the blank, and the response of three-base mismatched sequence within 29-base polynucleotide was obviously distinguished from complementary sequence, which can easily identify point mutation of DNA. The equation of calibration plot is i p (μA) = 0.8255 − 0.0847 c target oligonucleotide × 10 13 in the range of 6.9 × 10 −14 to 8.6 × 10 −13 mol/L, and correlation coefficient is 0.9974. The detective limit is 2.3 × 10 −14 mol/L of target oligonucleotide. This device can be optimized for the detection of complex sequence.

A novel method, capillary electrophoresis with amperometric detection, has been established for rapid and effective measurement of levodopa (L-dopa), and benserazide (BS) and its impurity (R,S)-2-amino-3-hydroxypropanohydrazide (Ro-04-1419) in co-beneldopa pharmaceutical formulations. Suitable separation and amperometric detection conditions were investigated and optimized. The optimum conditions of CZE detection were 40 mm phosphate solution at pH 5.3 as running buffer, 17 kV separation voltage, carbon-disk working electrode, 0.95 V (relative to Ag/AgCl) as detection potential, and sample injection for 8 s at 17 kV. The linear ranges were from 1.25 to 50 μg mL−1 for L-dopa, 1.2 × 10−1 to 25.5 μg mL−1 for BS, and 1.0 × 10−2 to 4.4 × 10−1 μg mL−1 for Ro-04-1419, with correlation coefficients of 0.9994, 0.9951, and 0.9933, respectively. The detection limits for L-dopa, BS, and Ro-04-1419 were 0.38, 0.02, and 0.004 μg mL−1, respectively. Average recoveries were 100.2% for L-dopa, 102.4% for BS, and 90.8% for Ro-04-1419. This method was successfully applied to co-beneldopa granules and tablets.

A simple and practical method for electrochemical DNA hybridization assay has been developed to take advantage of magnetic nanoparticles for ssDNA immobilization and zinc sulfide nanoparticle as oligonucleotide label. Magnetic nanoparticles were prepared by coprecipitation of Fe2+ and Fe3+ with NH4OH, and then amino silane was coated onto the surface of magnetite nanoparticles. The magnetic nanoparticles have the advantages of easy preparation, easy surface modification and low cost. The target ssDNA with the phosphate group at the 5′ end was then covalently immobilized to the amino group of magnetite nanoparticles by forming a phosphoramidate bond in the presence of 1-ethyl-3-(3-dimeth-ylaminopropyl)carbodiimide (EDAC). The zinc sulfide (ZnS) nanoparticle-labeled oligonucleotides probe was used to identify the target ssDNA immobilized on the magnetic nanoparticles based on a specific hybridization reaction. The hybridization events were assessed by the dissolution of the zinc sulfide nanoparticles anchored on the hybrids and the indirect determination of the dissolved zinc ions by anodic stripping voltammetry (ASV) at a mercury film glassy carbon electrode (GCE). The proposed method couples the high sensitivity of anodic stripping analysis for zinc ions with effective magnetic separation for eliminating nonspecific adsorption effects and offers great promise for DNA hybridization analysis.

A new selective and sensitive biosensing strategy for electrochemical impedance spectroscopy (EIS) measurement of DNA hybridization is described. The detection approach relied on the doping of nucleic acid probes within electropolymerized polypyrrole (PPy) film onto a carboxylic group-functionalized multi-walled carbon nanotubes (MWNTs-COOH) modified electrode and monitoring the impedance changes provoked by the metallation of helix DNA after hybridization. Oligonucleotide probes served as the solo counter anions during the growth of conducting PPy film on the carbon nanotube modified electrode. As a consequence of hybridization and the formation of metallized double-stranded DNA (M-DNA), significant changes in electrochemical impedance values (both in real component Zre and imaginary component Zim) coming from the change of electronic transport resistance of the modified electrode were observed, especially a visible decrease in the Zre. Based on the unique response ΔZre after hybridization and metallation at 5469 Hz, only the complementary DNA sequence had an obvious signal of the impedance decrease when compared with 1-base, 3-base mismatched and non-complementary sequences; hybridization amounts of 1-base, 3-base mismatched sequences were obtained only 35.7 and −5.8% responses. The protocol also offered high sensitivity with the detection limitation was 5×10−11 M using 3 S.D., n=11. Results showed that Zn2+-DNA had the best ability to transport electrons in M-DNA double-stranded chains when compared with Co2+-DNA and Ni2+-DNA on the same condition.

A simple, reliable and reproducible method, based on capillary zone electrophoresis with amperometric detection (CZE-AD), has been developed for simultaneous determination of five active ingredients in complicated traditional Chinese medicines including chlorogenic acid, caffeic acid, aloe-emodin, emodin and rhein. A carbon-disk electrode was used as working electrode. The optimal conditions of CZE detection were 30 mM borate solution (pH 9.5) as running buffer, 18 kV as separation voltage and 1.00 V (versus Ag/AgCl) as detection potential. There was excellent linearity between current response and analyte concentration over two orders of magnitude, while the limits of detection were 1.1 x 10(-7), 3.0 x 10(-7), 1.5 x 10(-7), 2.9 x 10(-7), 1.4 x 10(-6) mol/l for aloe-emodin, emodin, rhein, chlorogenic acid and caffeic acid, respectively (S/N = 3). The utility of this method was demonstrated by monitoring a kind of complicated Chinese medicine named Huangdan Yinchen Keli. Two samples manufactured by different companies were monitored with satisfactory results.

A novel electrochemical DNA biosensor based on methylene blue (MB) and zirconia (ZrO2) thin films modified gold electrode for DNA hybridization detection is presented. Zirconia thin films were electrodynamically deposited onto the bare gold electrode in an aqueous electrolyte of ZrOCl2 and KCl by cycling the potential between −1.1 and +0.7 V (versus Ag/AgCl) at a scan rate of 20 mV s−1. Oligonucleotide probes with phosphate group at the 5′ end were attached onto the zirconia thin films because zirconia is affinity for phosphoric group. The surface density of the immobilized DNA molecules at the zirconia interface was investigated by fluorescence spectroscopy method. Hybridization was induced by exposure of the ssDNA-containing Au electrode to complementary ssDNA in solution. The decreases in the peak currents of MB, an electroactive label, were observed upon hybridization of probe with the target. The cathodic peak current (ip) of MB after hybridization with the target DNA was linearly related to the logarithmic value of the target DNA concentration ranging from 2.25×10−10 to 2.25×10−8 mol l−1. A detection limit of 1.0×10−10 mol l−1 of oligonucleotides can be estimated.

We report a method for the detection of DNA hybridization in connection to lead sulfide (PbS) nanoparticle tags and electrochemical stripping measurement of the lead. A kind of lead sulfide nanoparticle with free carboxyl groups on its surface was synthesized in aqueous solution. The nanoparticle was used as a marker to label a sequence-known oligonucleotide, which was then employed as a DNA probe for identifying a target ssDNA immobilized on a PPy modified electrode based on a specific hybridization reaction. The hybridization events were monitored by the oxidation dissolution of the lead sulfide anchored on the hybrids and the indirect determination of the lead ions by anodic stripping voltammetry (ASV). The detection limit is 0.3 pmol L−1 of target oligonucleotides. The PbS nanoparticle combining its easy conjugation to the DNA molecule with the highly sensitive stripping voltammetry detection of lead shows its promising application in the electrochemical DNA hybridization analysis assay.

We have demonstrated the controlled synthesis of conducting-polymer microcontainers through the electrochemical generation of surfactant (i.e., β-naphthalenesulfonic acid, β-NSA)-stabilized H2 gas bubbles on the working electrode, followed by electrochemical polymerization of pyrrole around the wall of the “soap-bubble” template. It was noticed that the density, shape, and wall thickness of the polypyrrole microcontainers thus prepared could be regulated by controlling the electrochemical potential applied for the generation of H2 gas and the experimental conditions (e.g., the surfactant concentration, number of the cyclic voltammetric scanning) for the electropolymerization of pyrrole. By pre-patterning the working electrode surface with non-conducting polymers using microcontact printing (μCP) or plasma patterning, we have also produced conducting-polymer microcontainers in a patterned fashion. Furthermore, potential applications of the patterned and non-patterned conducting-polymer microcontainers have been demonstrated; for example, through the encapsulation of appropriate fluorescence-labeled molecules (e.g., fluorescein cadaverin) into the conducting-polymer microcontainers by sealing their opened mouths with sequential electropolymerization of pyrrole. The resulting closed microcontainers could then be used for controlled releases.

A novel, sensitive DNA hybridization detection protocol, based on DNA-quantum dots nanoconjugates coupled with electrochemical impedance spectroscopy (EIS) detection, is described. The amino-linked ss-DNA probe was covalently immobilized onto a self-assembled mercaptoacetic acid monolayer modified gold electrode; after hybridization with the target ssDNA-CdS nanoconjugates, EIS was used to detect the change of interfacial electron-transfer resistance (Ret) of the redox marker, [Fe(CN)6]4−/3−, from solution to transducer surface. The results showed that when target ssDNA-CdS nanoconjugates hybridized with probe oligonucleotide, a double helix film formed on the electrode, a remarkably increased Ret value was observed. Only complementary DNA sequence had an obvious signal compared with three-base mismatched or non-completely matched sequences under the optimized experimental conditions. Due to having more negative charges, space resistance and the semiconductor property, CdS nanoparticle labels on target DNA could improve the sensitivity to two orders of magnitude when compared with non-CdS tagged DNA sequences.

A new biosensing strategy for direct electrochemical detection of DNA hybridization by AC impedance measurement is described. The indicator or label free approach was developed on the basis of the carbon nanotubes coupled with a conductive polymer polypyrrole (PPy). Multi-walled carbon nanotubes functionalized with carboxylic group (MWNTs-COOH) were modified on the glassy carbon electrode (GCE) and the oligonucleotide probes were doped within the electro-polymerized PPy films by serving as the sole counter anion during the growth of the conducting films. Before and after hybridization reaction with the complementary DNA sequences, a decrease of impedance values was observed as a result of the reduction of the electrode resistance. Hybridization amounts of the one-base, two-base and three-base mismatched sequences were obtained only in a 51%, 18% and 8.2% response when compared to that for the complementary matched sequence. Such unique response is attributed to the concomitant conductivity changes of the PPy-polymerized carbon nanotubes, and offers great promise for reagentless DNA hybridization analysis.

A simple and reproducible method, based on micellar electrokinetic capillary chromatography (MECC) with amperometric detection (AD), for the separation and determination of the biogenic amines and their precursor amino acids was studied in this paper. The optimal conditions of separation and detection of typtamine, tyramine, tryptophan and tyrosine were 0.020 mol l −1 borate–NaOH (pH 10.35) containing 0.03 mol l −1 sodium dodecylsulphate (SDS) as running buffer, 20 kV as separation voltage, and +800 mV (vs. SCE) as detection potential. Under the optimum conditions, the four analytes were separated completely within 15 minutes, and good linearity, reproducibility and recovery results were obtained. Based on three times standard deviation of a low level sample, the detection limits for the four analytes were as low as at 10 −7 mol l −1 level. This method was also successfully used in the analysis of actual rice spirit, and satisfactory assay results were obtained.

It has been long recognized that surface properties are of paramount importance for a broad range of materials and a large variety of devices. The recent development of nanoscience and nanotechnology has opened up novel fundamental and applied frontiers in surface functionalization and characterization. At the nanometre scale, the high surface-to-volume ratio characteristic of most nanomaterials has been demonstrated to have a tremendous influence of many fundamental material properties and device performance. In this paper, we present some of the important issues on the surface functionalization and characterization of polymers and carbon nanotubes for certain biomedical and optoelectronic applications and summarize our recent research activities along this line.

Besides the running buffer, pH of buffer, separation voltage and sampling time, the diluting agent was studied in this paper as one of the important factors influencing the sensitivity in capillary electrophoresis (CE) with amperometric detection (AD) when electrokinectic sampling was used. Clonidine hydrochloride, hydrochlorothiazide and rutin, which are positively charged, neutral and negatively charged, respectively, in aqueous solutions, could be perfectly separated by CE with 25 mmol x L(-1) Na(2)B(4)O(7) - 50 mmol x L(-1) NaH(2)PO(4) as running buffer and detected by measuring their current responses with AD. Before CE running, some kinds of diluents including water, methanol, formamide, running buffer, hydrochloric acid and sodium hydroxide were, respectively, applied to dilute the stock solutions of above three analytes and their effects on the sensitivity of CE-AD were investigated. The results showed that for electrokinetic injection, the current responses of these three analytes were greatly affected in different ways when different diluting agents were used. This method was applied to simultaneously determine the active ingredients in one Chinese compound hypotensor named Zhen Ju Jiang Ya Pian, in which the contents of clonidine hydrochloride, hydrochlorothiazide and rutin is very different as 0.03 mg : 5 mg : 20 mg per tablet, and satisfactory results were obtained by adjusting their sensitivity by selecting the suitable diluting agent.

A novel, sensitive electrochemical DNA hybridization detection assay, using cadmium sulfide (CdS) nanoclusters as the oligonucleotide labeling tag, is described. The assay relies on the hybridization of the target DNA with the CdS nanocluster oligonucleotide DNA probe, followed by the dissolution of the CdS nanoclusters anchored on the hybrids and the indirect determination of the dissolved cadmium ions by sensitive anodic stripping voltammetry (ASV) at a mercury-coated glassy carbon electrode (GCE). The results showed that only a complementary sequence could form a double-stranded dsDNA-CdS with the DNA probe and give an obvious electrochemical response. A three-base mismatch sequence and non-complementary sequence had negligible response. The combination of the large number of cadmium ions released from each dsDNA hybrid with the remarkable sensitivity of the electrochemical stripping analysis for cadmium at mercury-film GCE allows detection at levels as low as 0.2 pmol L(-1) of the complementary sequence of DNA.

In this paper, capillary zone electrophoresis with amperometric detection (CZE-AD) was firstly applied to the simultaneous determination of rutin (RT) and hydrochlorothiazide (HCT) in compound Chinese herb medicines and human urine samples. The two analytes could be perfectly analyzed within 12 min and showed significant current responses at carbon electrode under the optimum conditions. It was found that the linear range of HCT was from 2.0 x 10(-6) to 1.0 x 10(-4) mol l(-1) and that of RT was from 1.0 x 10(-6) to 1.0 x 10(-4) mol l(-1). Their sensitivity was determined by linear regression and calculated as 7.02 x 10(4) and 2.17 x 10(5) nA l mol(-1), respectively, and their detection limits were 5.0 x 10(-7) and 2.0 x 10(-7) mol l(-1), respectively (S/N=3). Above results demonstrated that this method was of high sensitivity, good repeatability, high selectivity and could be used in metabolic kinetics studies of medicines. Satisfactory results were obtained when this method was used to simultaneously analyze the amounts of RT and HCT in one general compound Chinese herb medicine-Zhen Ju jiang Ya Pian and human urine samples.

An electrochemical detection method for analyzing sequence-specific DNA using gold nanoparticle DNA probes and subsequent signal amplification step by silver enhancement is described. The assay relies on the electrostatic adsorption of target oligonucleotides onto the sensing surface of the glassy carbon electrode (GCE) and its hybridization to the gold nanoparticle-labeled oligonucleotides DNA probe. After silver deposition onto gold nanoparticles, binding events between probe and target were monitored by the differential pulse voltammetry (DPV) signal of the large number of silver atoms anchored on the hybrids at the electrode surface. The signal intensity difference permits to distinguish between the match of two perfectly matched DNA strands and the near-perfect match where just one base pair was wrong. Coupled with this ‘nanoparticle-promoted’ reduction of silver signal amplification method, the sensitivity of this electrochemical DNA biosensor has been increased by approximately two orders of magnitude and a detection limit of 50 pM of complementary oligonucleotides was obtained.

The electrogenerated chemiluminescence (ECL) behavior of N-(4-aminobutyl)-N-ethylisoluminol (ABEI) was studied and it was found that ABEI could produce emission light when oxidized at a +1.0 V (vs. Ag/AgCl) potential in alkaline solution. The addition of H2O2 markedly improved the ECL sensitivity. The pH value of the solution as well as the H2O2 concentration and working potential all have influences on the ECL response. Under optimal conditions, ABEI can be detected in the range 1.3 x 10(-6)-6.5 x 10(-12) mol L(-1). A detection limit of 2.2 x 10(-12) mol L(-1) for ABEI was obtained at a signal-to-noise ratio of 3. ABEI was then used as a marker to label a known sequence oligonucleotide, which was used as a DNA probe for identifying a target ssDNA immobilized on a PPy modified electrode based on a specific hybridization reaction. The hybridization events were evaluated by the ECL measurements. The results showed that only a complementary sequence could form a double-stranded DNA with the DNA probe and give a strong ECL response. A three-base mismatch sequence and non-complementary sequence have no response. The intensity of the ECL was linearly related to the concentration of the complementary sequence in the range 9.6 x 10(-11)-9.6 x 10(-8) mol L(-1), the detection limit was 3.0 x 10(-11) mol L(-1).

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.

Chiral nematic mesoporous silica (CNMS) has attracted widespread attention due to some unique features, such as its nematic structure, chirality, large pore size, high temperature resistance, low cost, and ease of preparation. We first reported the use of CNMS as a stationary phase for capillary gas chromatography (GC). The CNMS-coated capillary column not only gives good selectivity for the separation of linear alkanes, aromatic hydrocarbons, polycyclic aromatic hydrocarbons (PAHs), and isomers but also offers excellent enantioselectivity for chiral compounds. Compared with enantioseparations on commercial β-DEX 120 and Chirasil-l-Val columns, a CNMS-coated capillary column offers excellent enantioselectivity, chiral recognition complementarity, and the separation of analytes within short elution times. It can also be potentially applied in high-temperature GC at more than 350 °C. This work indicates that CNMS could soon become very attractive for separations.