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Biomedical subjects

Erkang Wang

Publications and source records attributed to Erkang Wang.

At least 73 records · Page 4Linked to original sources
PubMed2003

Characterization and property of DNA incorporated bilayer lipid membranes.

Calf-thymus DNA-incorporated bilayer lipid membranes supported on a glassy carbon (GC) electrode was prepared by making layers of phosphatidylcholine dimyristoyl (DMPC) on GC electrode. DNA in the BLM was characterized by cyclic voltammetry, IR and AFM, and lipid layers formed on the GC electrode were demonstrated to be a bilayer lipid membrane by electrochemical impedance experiment. In IR and AFM experiments the findings indicated that DNA was incorporated into BLM. The ion channel of bilayer lipid membranes incorporated was studied. The result showed that the ion channel was opened in the presence of the stimulus quinacrine. In the absence of quinacrine the channel was switched. The process can repeat itself many times. The impedance spectroscopy measurements demonstrate that the stimulus quinacrine opens the channel for permeation of marker ion. The mechanism of forming an ion channel was investigated.

Animals↗
PubMed2003

Miniaturized tris(2,2'-bipyridyl)ruthenium(II) electrochemiluminescence detection cell for capillary electrophoresis and flow injection analysis.

The design and performance of a miniaturized chip-type tris(2,2'-bipyridyl)ruthenium(II) [Ru(bpy)3(2+)] electrochemiluminescence (ECL) detection cell suitable for both capillary electrophoresis (CE) and flow injection (FI) analysis are described. The cell was fabricated from two pieces of glass (20 x 15 x 1.7 mm), and the 0.5-mm-diameter platinum disk was used as working electrode held at +1.15 V (vs silver wire quasi-reference), the stainless steel guide tubing as counter electrode, and the silver wire as quasi-reference electrode. The performance traits of the cell in both CE and FI modes were evaluated using tripropylamine, proline, and oxalate and compared favorably to those reported for CE and FI detection cells. The advantages of versatility, sensitivity, and accuracy make the device attractive for the routine analysis of amine-containing species or oxalate by CE and FI with Ru(bpy)3(2+) ECL detection.

Journal Article↗
PubMed2003

Determination of biogenic amines by capillary electrophoresis with pulsed amperometric detection.

The biogenic amines, putrescine, cadaverine, spermidine and spermine were separated and quantified by capillary electrophoresis with pulsed amperometric detection. Detection potential of the pulsed amperometric detection was optimized as 0.6 V. Optimal separation of the biogenic amines was achieved using a separation buffer of 30 mM citrate at pH 3.5, while keeping the buffer in the detection cell as 20 mM NaOH. Using these conditions, the four biogenic amines were baseline separated. Extrapolated limits of detection for putrescine, cadaverine, spermidine and spermine were 400, 200, 100 and 400 nM for the standard mixture (polyamines dissolved in running buffer), respectively. These are lower than ultraviolet detection and comparable or even lower than laser-induced fluorescence detection results as reported in the literature. The number of theoretical plates was maintained at the 10(5) level, which is absolutely higher than any reported method. When applying capillary electrophoresis-pulsed amperometric detection to milk analysis, only spermidine was found in amounts varying between 0.1 and 0.5 mg/kg.

Animals↗
PubMed2003

Evaluation of a sol-gel derived carbon composite electrode as an amperometric detector for capillary electrophoresis.

In this paper, we report the construction and application of a sol-gel derived carbon composite electrode (CCE) as an amperometric detector for capillary electrophoresis. The electrochemical properties were characterized and compared with those of conventional carbon fiber and carbon paste electrode (CPE). Experimental results show that peak-to-peak noise of CCE was about 20% of CPE and electrode capacitance was comparatively low. When applied to the detection of dopamine and epinephrine, the optimal detection potential for CCE was 0.1 V lower than CPE under the same separation conditions; CCE with diameter of 75 and 100 microm could achieve a low detection limit of 3 x 10(-8) and 6 x 10(-8) M for the detection of epinephrine, which approaching that of the 33-microm diameter carbon fiber electrode. Also, the linearity for epinephrine at CCE was more than two orders of magnitude, which was slightly wider than that of carbon fiber electrode. Applications to real sample analysis were tested by the determination of betahistine dihydrochloride in tablets and human urine. Using CCE with diameter < or = 100 microm as an amperometric detector after capillary electrophoresis separation, a low detection limit and a wide linear range combined with excellent reproducibility were obtained. This CCE possesses of many advantages, namely, convenience, ease of fabrication, low cost and high stability.

Betahistine↗
PubMed2003

Investigation of the influence on conformational transition of DNA induced by cationic lipid vesicles.

Recent studies have focused on the structural features of DNA-lipid assemblies. In this paper we take nile blue A (NBA) as a probe molecule to study the influence of the conformational transition of DNA induced by didodecyldimethylammonium bromide (DDAB) cationic vesicles to the interaction between DNA and the probe molecules. We find that upon binding to DNA, a secondary conformational transition of DNA induced by the cationic liposome from the native B-form to the C-form resulted in the change of binding modes of NBA to DNA and different complexes are formed between DNA, DDAB and NBA.

Animals↗
PubMed2003

Discrete wavelets transform for signal denoising in capillary electrophoresis with electrochemiluminescence detection.

Discrete wavelets transform (DWT) was applied to noise on removal capillary electrophoresis-electrochemiluminescence (CE-ECL) electropherograms. Several typical wavelet transforms, including Haar, Daublets, Coiflets, and Symmlets, were evaluated. Four types of determining threshold methods, fixed form threshold, rigorous Stein's unbiased estimate of risk (rigorous SURE), heuristic SURE and minimax, combined with hard and soft thresholding methods were compared. The denoising study on synthetic signals showed that wave Symmlet 4 with a level decomposition of 5 and the thresholding method of heuristic SURE-hard provide the optimum denoising strategy. Using this strategy, the noise on CE-ECL electropherograms could be removed adequately. Compared with the Savitzky-Golay and Fourier transform denoising methods, DWT is an efficient method for noise removal with a better preservation of the shape of peaks.

Electricity↗
PubMed2003

Direct tris(2,2'-bipyridyl)ruthenium (II) electrochemiluminescence detection of polyamines separated by capillary electrophoresis.

Capillary electrophoresis (CE) with tris(2,2'-bipyridyl) ruthenium (II) (Ru(bpy)3(2+)) electrochemiluminescence (ECL) detection technique was developed for the analysis of four polyamines (putrescine (Put), cadaverine (Cad), spermidine (Spd), and spermine (Spm)) analysis. The four polyamines contain different amine groups, which have different ECL activity. There are several parameters which influence the resolution and ECL peak intensities, including the buffer pH and concentrations, separation voltage, sample injection, electrode materials, and Ru(bpy)3(2+) concentrations. Polyamines are separated by capillary zone electrophoresis in an uncoated fused-silica capillary (50 cmx25 micro m (ID) filled with acidic phosphate buffer (200 mmol/L phosphate, pH 2.0) - 1mol/L phosphoric acid (9:1 v/v) and a separation voltage of 5 kV (25 micro A), with end-column Ru(bpy)3(2+) ECL detection. A 5 mmol/L Ru(bpy)3(2+) solution plus 200 mmol/L phosphate buffer (pH 11.0) is added into the reagent reservoir. The calibration curve is linear over a concentration range of two or three orders of magnitude for the polyamines. The analysis time is less than 25 min. Detection limits for Put and Cad are 1.9x10(-7) mol/L and 7.6x10(-9) mol/L for Spd and Spm, respectively. Intraday and interday relative standard deviations of ECL peak intensities are less than 8%. The main advantages of this CE-ECL detection technique for polyamines analysis presented herein are the omission of chemical derivatization of the analytes and the high selectivity.

2,2'-Dipyridyl↗
PubMed2003

Growth of cationic lipid toward bilayer lipid membrane by solution spreading: scanning probe microscopy study.

The growth of cationic lipid dioctadecyldimethylammonium bromide (DODAB) toward bilayer lipid membrane (BLM) by solution spreading on cleaved mica surface was studied by atomic force microscopy (AFM). Bilayer of DODAB was formed by exposing mica to a solution of DODAB in chloroform and subsequently immersing into potassium chloride solution for film developing. AFM studies showed that at the initial stage of the growth, the adsorbed molecules exhibited the small fractal-like aggregates. These aggregates grew up and expanded laterally into larger patches with time and experienced from monolayer to bilayer, finally a close-packed bilayer film (5.4+/-0.2 nm) was approached. AFM results of the film growth process indicated a growth mechanism of nucleation, growth and coalescence of dense submonolayer, it revealed the direct information about the film morphology and confirmed that solution spreading was an effective technique to prepare a cationic bilayer in a short time.

Aluminum Silicates↗
PubMed2003

Lipid membrane immobilized horseradish peroxidase biosensor for amperometric determination of hydrogen peroxide.

Stable films of didodecyldimethylammonium bromide (DDAB, a synthetic lipid) and horseradish peroxidase (HRP) were made by casting the mixture of the aqueous vesicle of DDAB and HRP onto the glassy carbon (GC) electrode. The direct electron transfer between electrode and HRP immobilized in lipid film has been demonstrated. The lipid films were used to supply a biological environment resembling biomembrane on the surface of the electrode. A pair of redox peaks attributed to the direct redox reaction of HRP were observed in the phosphate buffer solution (pH 5.5). The cathodic peak current increased dramatically while anodic peak decreased by addition of small amount H(2)O(2). The pH effect on amperometric response to H(2)O(2) was studied. The biosensor also exhibited fast response (5 s), good stability and reproducibility.

Biosensing Techniques↗
PubMed2003

Hydrogen peroxide biosensor based on microperoxidase-11 entrapped in lipid membrane.

A highly catalytic activity microperoxidase-11 (MP-11) biosensor for H(2)O(2) was developed to immobilizing the heme peptide in didodecyldimethylammonium bromide (DDAB) lipid membrane. The enzyme electrode thus obtained responded to H(2)O(2) without electron mediator or promoter, at a potential of +0.10 V versus Agmid R:AgCl. A linear calibration curve is obtained over the range from 2.0 x 10(-5) to 2.4 x 10(-3) M. The biosensor responds to hydrogen peroxide in 15 s and has a detection limit of 8 x 10(-7) M (S/N=3) Providing a natural environment with lipid membrane for protein immobilization and maintenance of protein functions is a suitable option for the design of biosensors.

Biosensing Techniques↗
PubMed2003

Liposome-mediated conformation transition of DNA detected by molecular probe: methyl green.

Recent studies have focused on the structural features of DNA-lipid assemblies. In this paper, we take methyl green (MG) as a probe molecule to detect the conformational change of DNA molecule induced by dimethyldioctadecylammonium bromide (DDAB) liposomes before the condensation process of DNA begins. DDAB-induced DNA topology changes were investigated by cyclic voltammetry (CV), circular dichroism (CD) and UV-VIS spectrometry. We find that upon binding to DNA, positively charged liposomes induce a conformational transition of DNA molecules from the native B-form to the C motif. Conformational transition in DNA results in the binding modes of MG to DNA, changing and being isolated from DNA to the solution. More stable complexes are formed between DNA and DDAB. That is also proved by the melting study of DNA.

Animals↗
PubMed2002

Direct electron transfer between hemoglobin and a glassy carbon electrode facilitated by lipid-protected gold nanoparticles.

We synthesized a kind of gold nanoparticle protected by a synthetic lipid (didodecyldimethylammonium bromide, DDAB). With the help of these gold nanoparticles, hemoglobin can exhibit a direct electron transfer (DET) reaction. The formal potential locates at -169 mV vs. Ag/AgCl. Spectral data indicated the hemoglobin on the electrode was not denatured. The lipid-protected gold nanoparticles were very stable (for at least 8 months). Their average diameter is 6.42 nm. It is the first time to use monolayer-protected nanoparticles to realize the direct electrochemistry of protein.

Carbon↗
PubMed2002

Concentration-dependent behavior of nisin interaction with supported bilayer lipid membrane.

Nisin is a positively charged antibacterial peptide that binds to the negatively charged membranes of gram-positive bacteria. The initial interaction of the peptide with the model membrane of negatively charged DPPG (dipalmitoylphosphatidylglycerol) was studied by cyclic voltammetry and a.c. impedance spectroscopy. Nisin could induce pores in the supported bilayer lipid membrane, thus, it led to the marker ions Fe(CN)(6)(3-/4-) crossing the lipid membrane and giving the redox reaction on the glassy carbon electrode (GCE). Experimental results suggested that the pore formation on supported bilayer lipid membrane was dependent on the concentration of nisin and it included three main concentration stages: low, middling, high concentration.

Algorithms↗
PubMed2002

Colloid chemical approach to nanoelectrode ensembles with highly controllable active area fraction.

A novel "bottom-up" approach to highly controllable nanoelectrode ensembles (NEEs) has been developed using colloidal nanoparticle self-assembly techniques. This solution-based strategy allows flexible control over nanoelectrode size, shape, and interspacing of the as-prepared NEEs. Atomic force microscopy (AFM) was proved to be a powerful tool to monitor the NEE topography, which yields parameters that can be used to calculate the fractional nanoelectrode area of the NEEs. AFM, ac impedance, and cyclic voltammetry studies demonstrate that most of nanoelectrodes on the NEEs (at least by 9-min self-assembly) are not diffusionally isolated under conventional ac frequency range and scan rates. As a result, the NEEs behave as "nanoelectrode-patch" assemblies. Besides, the as-prepared NEEs by different self-assembling times show an adjustable sensitivity to heterogeneous electron-transfer kinetics, which may be helpful to sensor applications. Like these NEEs constructed by other techniques, the present NEEs prepared by chemical self-assembly also exhibit the enhancement of electroanalytical detection limit consistent with NEE theory prediction.

Colloids↗
PubMed2002

Capillary electrophoresis with amperometric detection of curcumin in Chinese herbal medicine pretreated by solid-phase extraction.

In the present study, curcumin from Chinese herbal medicine turmeric was determined by capillary electrophoresis with amperometric detection (CE-AD) pretreated by a self-designed, simple, inexpensive solid-phase extraction (SPE) cartridge based on the material of tributyl phosphate resin. An average concentration factor of 9 with the recovery of > 80% was achieved when applied to the analysis of curcumin in extracts of tumeric. Under the optimized CE-AD conditions: a running buffer composed of 15 mM phosphate buffer at a pH 9.7, separation voltage at 16 kV, injection for 6 s at 9 kV and detection at 1.20 V, CE-AD with SPE exhibited low detection limit as 3 x 10(-8) mol/l (S/N = 3), high efficiency of 1.0 x 10(5) N, linear range of 7 x 10(-4) -3 x 10(-6) mol/l (r = 0.9986) for curcumin extracted from light petroleum. The method developed resulted in enhancement of the detection sensitivity and reduction of interference from sample matrix in complicated samples and exhibited the potential application for routine analysis, especially in food, because a relatively complete process of sample treatment and analysis was described.

Curcumin↗
PubMed2002

Conformational transition of DNA induced by cationic lipid vesicle in acidic solution: spectroscopy investigation.

The conformational transition of DNA induced by the interaction between DNA and a cationic lipid vesicle, didodecyldimethylammonium bromide (DDAB), had been investigated by circular dichroism (CD) and UV spectroscopy methods. We used singular value decomposition least squares method (SVDLS) to analyze the experimental CD spectra. Although pH value influenced the conformation of DNA in solution, the results showed that upon binding to double helical DNA, positively charged liposomes induced a conformational transition of DNA molecules from the native B-form to more compact conformations. At the same time, no obvious conformational changes occurred at single-strand DNA (ssDNA). While the cationic lipid vesicles and double-strand DNA (dsDNA) were mixed at a high molar ratio of DDAB vesicles to dsDNA, the conformation of dsDNA transformed from the B-form to the C-form resulting in an increase in duplex stability (DeltaT(m)=8+/-0.4 degrees C). An increasing in T(m) was also observed while the cationic lipid vesicles interacted with ssDNA.

Cations↗