Zhihua Wang

Acetylsalicylic acid electrochemical sensor based on PATP–AuNPs modified molecularly imprinted polymer film

A novel electrochemical sensor based on molecularly imprinted polymer film has been developed for aspirin detection. The sensitive film was prepared by co-polymerization of p-aminothiophenol (p-ATP) and HAuCl(4) on the Au electrode surface. First, p-ATP was self-assembled on the Au electrode surface by the formation of Au-S bonds. Then, the acetylsalicylic acid (ASA) template was assembled onto the monolayer of p-ATP through the hydrogen-bonding interaction between amino group (p-ATP) and oxygen (ASA). Finally, a conductive hybrid membrane was fabricated at the surface of Au electrode by the co-polymerization in the mixing solution containing additional p-ATP, HAuCl(4) and ASA template. Meanwhile, the ASA was spontaneously imprinted into the poly-aminothiophenol gold nanoparticles (PATP-AuNPs) complex film. The amount of imprinted sites at the PATP-AuNPs film significantly increases due to the additional replenishment of ASA templates. With the significant increasing of imprinted sites and doped gold nanoparticles, the sensitivity of the molecular imprinted polymer (MIP) electrode gradually increased. The molecularly imprinted sensor was characterized by electrochemical impedance spectroscopy (EIS), differential pulse voltammetry (DPV), and cyclic voltammetry (CV). The linear relationships between current and logarithmic concentration were obtained in the range from 1 nmol L(-1) to 0.1 μmol L(-1) and 0.7 μmol L(-1) to 0.1 mmol L(-1). The detection limit of 0.3 nmol L(-1) was achieved. This molecularly imprinted sensor for the determination of ASA has high sensitivity, good selectivity and reproducibility, with the testing in some biological fluids also has good selectivity and recovery.

A novel molecularly imprinted impedimetric sensor for melamine determination

A novel molecularly imprinted (MIP) impedimetric sensor was promoted for selective detecting melamine (MEL). The Au electrode modified with MIP poly (2-mercaptobenzimidazole) (PMBI) was prepared by electrochemical polymerization of 2-mercaptobenzimidazole (2-MBI) with cyclic voltammetry (CV) in the presence of template molecule MEL. The surface morphology and structure of MIP PMBI are characterized by atomic force microscopy (AFM), infrared spectra (IR), electrochemical impedance spectroscopy (EIS), and CV. The main driving force of recognition is the π-donor-acceptor interaction between MEL and PMBI. The imprinted electrode could avoid the interference successfully. In addition, a linear response curve was obtained from 1.0×10(-8) M to 5.0×10(-5) M, with the detection limit of 3.0×10(-9) M. The sensor exhibits remarkable advantages, such as higher sensitivity, wider linear range and lower detection limit. The effective method has a potential application to monitor nonelectrochemically active substances in food analysis in the future.

2,4,6-tri(3,5-Dimethylpyrazoyl)-1,3,5-triazine modified carbon paste electrode for trace Cobalt(II) determination by differential pulse anodic stripping voltammetry.

A differential pulse anodic stripping voltammetry was developed for the sensitive and selective determination of Co(II) at 2,4,6-tri(3,5-dimethylpyrazoyl)-1,3,5-triazine modified carbon paste electrode in 0.1 mol l(-1) NH(4)Cl solution (pH 4.95). The oxidation peak of Co(II) was observed at 0.03 V(vs. Ag/AgCl) by scanning the potential in a positive direction. The analysis procedure consisted of an open circuit accumulation step in stirred sample solution. This was followed by medium exchange to a clean solution and subsequently an anodic potential scan was effect to obtain the voltammetric peak. The current was proportional to the concentration of the Co(II) ion in a range of 1x10(-8)-1x10(-6) mol l(-1) for 3 min accumulation and in the range of 1x10(-9)-1x10(-8) mol l(-1) for 5 min accumulation; most of metal ions do not interfere with the determination. The developed method was applied to Co(II) determination in potable water.

A Novel Amperometric Sensor for Salicylic Acid Based on Molecularly Imprinted Polymer-Modified Electrodes

A novel electrochemical MIP-sensor for salicylic acid (SA) has been synthesized firstly by electropolymerizing o-phenylenediamine on glassy carbon electrode in presence of template molecule (salicylic acid). The response of the sensor to SA is investigated by square wave voltammetry (SWV). The linearity is obtained over a concentration range of 6 × 10−5 ∼ 1 × 10−4 mol/L (R2 = 0.9961). And the detection limit of SA is about 2 × 10−5 mol/L. The sensor exhibits good selectivity for salicylic acid by virtue of the interaction between molecularly imprinted binding sites and the template.

A molecularly imprinted electrochemical enzymeless sensor based on functionalized gold nanoparticle decorated carbon nanotubes for methyl-parathion detection

Functionalized gold nanoparticles (FuAuNP) have potential applications because of their specific functional groups. p-Aminothiophenol (p-ATP) possesses double functional groups that can be used to form an S–Au bond and oligoaniline. Based on molecular imprinting technology and electrochemical technology, a novel enzymeless methyl-parathion (MP) sensor has been constructed with nanocomposites. The template molecule (MP) is embedded in the imprinting sites by p-ATP molecular self-assembly and FuAuNP electro-polymerization. The imprinting effective sites and the conductive performance are improved by gold nanoparticles decorated carbon nanotube nanocomposites (AuNP–MCNT). The linear relationships between peak current and MP concentration are obtained in the range from 0.1 to 1.1 ng mL−1 and 1.1 to 11 ng mL−1, respectively. The detection limit can be achieved as low as 0.08 ng mL−1 (3σ) with relative standard deviation of 3.8% (n = 5). This sensor was also applied for the detection of MP in apples and vegetables, with average recoveries between 95.2% and 105.7% (RSD < 5%). The results mentioned above show that the novel electrochemical sensor is an ideal device for the real-time determination of MP in real samples.

VOLTAMMETRIC DETECTION OF TRACES OF COPPER USING A CARBON PASTE ELECTRODE MODIFIED WITH TETRAPHENYLPORPHYRIN

ABSTRACT The voltammetric detection of copper(II) was carried out at a carbon paste electrode (CPE) modified with tetraphenylporphyrin (TPP). The analysis procedure consisted of an open circuit preconcentration step in stirred sample solution. This was followed by medium exchange to a pure electrolyte solution (Britton-Robinson buffer pH = 6) where the accumulated copper(II) was reduced at −0.8 V vs. Hg/Hg2SO4 and subsequently an anodic potential scan was effect to obtain the voltammetric peak. The parameters and conditions such as pH of the analyte solution and supporting electrolyte, preconcentration time, CPE composition, its activation and regeneration, and others, were studied in detail. The detection limit of the proposed procedure was found to be 2.0 × 10−9 mol l−1 of Cu(II) in the analyte solution for a preconcentration time of 12 min. Applying suitable preconcentration times, a linear calibration graph from 9.0 × 10−8 to 5.0 × 10−5 mol l−1 of Cu(II) was established. Multiple determinations (n = 8), following a preconcentration–measurement–regeneration cycle, gave a relative standard deviation of 4.5% at Cu(II) concentration of 1.0 × 10−7 mol l−1. The proposed method was applied to the determination of Cu(II) in a real sample of residue solution after extraction and a mineral sample of Jinchuan Corporation.

Electrochemical detection of β-1,3-glucanase gene from transgenic capsicums using asymmetric PCR generated by a detecting probe and an anchoring probe

A design for recognition of beta-1,3-glucanase gene (Glu) specific sequence based on probe extension was described. The detecting probe DNA and the anchoring prober were hybridized with the same target DNA firstly, then the probes were extended by DNA polymerase reaction. After that the double strand DNA was denatured, and the extended detecting probe was immobilized on a glassy carbon electrode via nanoparticle gold (AuNP). In electrochemical detection (cyclic voltammetry, CV and differential pulse voltammetry, DPV), an increased peak current (i(p)) of the indicator (methylene blue, MB) was obtained compared with the probe without extension. Three differently long DNAs of Glu specific sequence were employed as the target: oligonucleotide acid, molecular cloning vector DNA and total genome DNA of transgenic capsicum. The estimated DPV detection limits for three targets of oligonucleotide, the molecular cloning vector DNA and genome DNA were 2.6x10(-13), 6.0x10(-13) and 8.0x10(-13)moll(-1) respectively.

An Electrochemical Assay of β-1,3-Glucanase Gene from Transgenic Capsicum Using Asymmetric PCR

5′-Thiol-derivatized specific DNA probes were added to the single primer polymerase chain reaction (asymmetric PCR) solution. In the PCR process, the DNA probes extended in the presence of target; the extended probes were then immobilized on a glassy carbon electrode (GCE) via gold nanoparticles. Finally, methylene blue and the extended probes were combined and the electrochemical signals were measured. This signal was higher than that of the GCE modified only by the original probe. When there was no target in PCR solution, the probe did not extend and the signal did not increase. The specific sequences of the β-1,3-glucanase gene were detected successfully from three targets with different length: oligonucleotide, molecule clone vector DNA, and total genome DNA of transgenic capsicum. The detection limits of 2.6 × 10−13, 7.8 × 10−13, and 9.1 × 10−13 moll−1 for oligonucleotide, molecule clone vector DNA, and total transgenic capsicum genome DNA were estimated.

Development and application of the tartrazine voltammetric sensors based on molecularly imprinted polymers

ABSTRACT A modified glassy carbon electrode was prepared as an electrochemical voltammetric sensor based on molecularly imprinted polymer film for tartrazine (TT) detection. The sensitive film was prepared by copolymerization of tartrazine and acrylamide on the carbon nanotube-modified glassy carbon electrode. The performance of the imprinted sensor was investigated by cyclic voltammetry, differential pulse voltammetry, and electrochemical impedance spectroscopy in detail. Under the optimum conditions, two dynamic linear ranges of 8 × 10−8 to 1 × 10−6 mol L−1 and 1 × 10−6 to 1 × 10−5 mol L−1 were obtained, with a detection limit of 2.74 × 10−8 mol L−1(S/N = 3). This sensor was used successfully for tartrazine determination in beverages.

Binding mode of Co(en) 3+3 with calf thymus DNA

The binding mode of Co(en) (en = ethylenediamine) to calf thymus DNA is investigated using electrochemical and spectroscopic methods. Binding constant value (K = 1.284 × 103 L/mol) is found to be the same by the two methods. Both isomers show the same CV behavior associated with binding to B-form DNA. CD spectra results show no enantoselectivety for both isomers binding to DNA. All of this evidence suggests that the Co(en) complex binds to DNA by an electrostatic mode.