Latest publications

Conversion coating on magnesium alloy sheet (AZ31) by vanillic acid treatment: Preparation, characterization and corrosion behavior

 
 
 

Highlights

 

New eco-friendly conversion coating prepared with a natural organic acid.

Corrosion performance similar to the observed for chromium and fluoride conversion coatings.

Detailed characterization of the coating using SEM, FTIR and XPS techniques.

Conversion coating with potential properties as a pre-treatment for polymer coatings.

 

Abstract

Herein we report the development and characterization of an eco-friendly protective layer of magnesium vanillate on the surface of a magnesium AZ31 alloy sheet, based on a treatment with 1.0 mmol L−1 vanillic acid aqueous solution. The coating composition was investigated by XPS and FTIR, and the corrosion behavior of the treated sheets was verified by potentiodynamic polarization and EIS. The results obtained show that the treatment improves corrosion protection and the adhesion of polymer coatings, being a promising treatment for corrosion protection of magnesium alloys.

Graphical abstract

Biosensors and Bioelectronics

Volume 102, 15 April 2018, Pages 70-79
Biosensors and Bioelectronics

Label-free electrochemical DNA biosensor for guanine and adenine by ds-DNA/poly(L-cysteine)/Fe3O4 nanoparticles-graphene oxide nanocomposite modified electrode

 
 
 

Highlights

 

A DNA biosensor based on ds-DNA/p(L-Cys)/Fe3O4 NPs-GO was designed.

The proposed DNA biosensor had a strongly electrocatalytic capability for A and G detection.

The contribution of ds-DNA, p(L-Cys) and GO at improving electrochemical detection was assessed.

The proposed biosensor exhibited high sensitivity and long-term stability.

The proposed biosensor could be profitable to evaluate DNA bases damage.

 

Abstract

In this study, we aim to design a simple and effective electrochemical DNA biosensorbased on a carbon paste electrode modified with ds-DNA/poly(L-cysteine)/Fe3O4nanoparticles-graphene oxide (ds-DNA/p(L-Cys)/Fe3O4 NPs-GO/CPE) for sensitive detection of adenine (A) and guanine (G). The electrocatalytic oxidation of A and G on the electrode was explored by differential pulse voltammetry (DPV) and cyclic voltammetry (CV). This sensor shows separated and well-defined peaks for A and G, by which one can determine these biological bases individually or simultaneously. The ds-DNA/p(L-Cys)/Fe3O4 NPs-GO/CPE exhibited an increase in peak currents and the electron transfer kinetics and decrease in the overpotential for the oxidation reaction of A and G. Under the optimal conditions a linear relationship is figured out between the peak current and the analytes' concentrations on a range of 0.01–30.0 μM and 0.01–25.0 μM for simultaneous determination of A and G, with detection limits of 3.48 and 1.59 nM, respectively. As well as, individually determination is resulted two linear concentration ranges of 0.01–30.0 μM for A and 0.01–25.0 μM for G with detection limits of 3.90 and 1.58 nM for A and G, respectively. The proposed biosensor exhibited some advantages in terms of simplicity, rapidity, high sensitivity, good reproducibility and long-term stability. Furthermore, the measurements of thermally denatured single-stranded DNA were carried out and the value of (G + C)/(A + T) of DNA was calculated as about 0.77 for various DNA samples. This study also ascertained that the proposed biosensor can be profitable to evaluate DNA basesdamage.

Journal of Electroanalytical Chemistry

Volume 813, 15 March 2018, Pages 67-74
Journal of Electroanalytical Chemistry

Sensor and biosensor application of a new redox mediator: Rosmarinic acid modified screen-printed carbon electrode for electrochemical determination of NADH and ethanol

 
 
 

Highlights

 

An NADH sensor based on rosmarinic acid modified screen-printed carbon electrode (SPCE/RA) is described.

Optimized working potential and pH for NADH determination were 0.25 V and 7.25, respectively.

SPCE/RA was further modified with alcohol dehydrogenase to develop an ethanol biosensor.

Biosensor showed sensitivity of 1.36 μA mM−1 linear range of 23.7–1000 μM, LOD of 7.1 μM and LOQ of 23.7 μM.

 

Abstract

The effects of rosmarinic acid (RA) immobilized onto a screen printed carbon electrode (SPCE) were investigated for the development of an NADH sensor and an ethanol biosensor. RA was electrodeposited on SPCE by cyclic voltammetry. Scan rate and number of cycles were optimized for electrodeposition. RA modified SPCE (SPCE/RA) was found to facilitate the electrocatalytic oxidation of NADH by the action of RA as a natural antioxidant mediator. pH and working potential were optimized for the determination of NADH with the developed SPCE/RA sensor. They were found as 7.25 and 0.25 V, respectively. Alcohol dehydrogenase (ADH) enzyme was immobilized onto this sensor to prepare a disposable amperometric ethanol biosensor. NAD+ was used as a cofactor for ADH. pH, working potential, amounts of ADH and NAD+ were optimized for the developed biosensor. The optimum values were found as 7.75, 0.20 V, 250 unit and 7 mM, respectively. Analytical characterization parameters for ethanol analysis were determined. The sensitivity, linear range, limits of detection and quantification were 1.36 μA mM−1, 23.71 μM–1000 μM, 7.1 μM and 23.7 μM, respectively. The repeatability, operational stability and storage life studies were performed. RA is found to enhance the operational stability of the biosensor. The developed biosensor has been tested on a few commercial alcoholic drinks for the analysis of their ethanol contents.