Improved immobilization of DNA to graphite surfaces, using amino acid modified clays.

Assessment of the interaction of small molecules with DNA, hybridization assays for DNA sequence analysis and diagnostics and the investigation of DNA damage involves the immobilization of an array of oligonucleotides onto a solid substrate. Herein, a new nano sized DNA-based biosensor containing valine (Val) amino acid organo-modified Cloisite Na+ as a new bionanohybrid film for the immobilization of DNA was developed. The Cloisite-Val organoclay was synthesized by a cation-exchange method, which involves the displacement of the sodium cations of Cloisite Na+ with the ammonium ions of the Val-amino acid. The synthesized materials were characterized with different methods such as FT-IR spectroscopy, TEM, SEM, XRD and electrochemical impedance spectroscopy (EIS). The nanostructured film was deposited at the surface of a working graphite electrode and utilized for the surface modification with double-stranded DNA. It was found that the electrode modification with DNA and Cloisite-Val leads to an enhanced sensitivity in the DNA voltammetric detection compared with other modified electrodes that were used for this work. The efficiency of DNA immobilization was followed by means of EIS and voltammetry. Immobilization is much more rapid when using the Cloisite-Val modified graphite support than when employing conventional supports. The stability of the immobilized DNA over several days has been found to be much higher when using the new support than in preparations using conventional ones.

A new strategy for the selective determination of glutathione in the presence of nicotinamide adenine dinucleotide (NADH) using a novel modified carbon nanotube paste electrode.

A novel electrochemical sensor for the simultaneous determination of glutathione (GSH) and nicotinamide adenine dinucleotide (NADH) is described. The sensor is based on a carbon paste electrode (CPE) modified with benzamide derivative and multiwall carbon nanotubes. This mixture makes a modified electrode that is sensitive for the electrochemical detection of these compounds. Under optimum conditions and at pH 7.0, oxidation of GSH occurs at a potential of about 330 mV less positive than that at an unmodified CPE. The voltammetric peak currents are linearly dependent on GSH and NADH concentrations in the ranges 0.09-300 µmol L(-1) GSH and 5.0-600 µmol L(-1) NADH. The detection limits found for GSH and NADH were 0.05 µmol L(-1) and 1.0 µmol L(-1), respectively. The electrochemical sensor was also used for the determination of GSH in urine, pharmaceutical and hemolysed erythrocyte samples.

Highly sensitive voltammetric sensor based on catechol-derivative-multiwall carbon nanotubes for the catalytic determination of captopril in patient human urine samples.

A new catechol-derivative compound, N-(3,4-dihydroxyphenethyl)-3,5-dinitrobenzamide, was synthesized and used to construct a modified-carbon nanotubes paste electrode. The electro-oxidation of captopril at the surface of the modified electrode was studied using cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy. Under the optimized conditions, the differential pulse voltammetric peak current of captopril increased linearly with captopril concentration in the ranges of 6.4×10(-8) to 3.2×10(-48) mol L(-1). The detection limit was 3.4×10(-8) mol L(-1) captopril. The diffusion coefficient and kinetic parameters (such as electron transfer coefficient and the heterogeneous rate constant) for captopril oxidation were also determined. The RSD% for 0.5 and 10.0 µmol L(-1) captopril were 2.1% and 1.6%, respectively. The proposed sensor was successfully applied for the determination of captopril in human patient urine and tablet samples.

Solid-phase molecularly imprinted pre-concentration and spectrophotometric determination of isoxicam in pharmaceuticals and human serum.

A selective molecularly imprinted polymer (MIP) has been synthesized for isoxicam pre-concentration, followed by its spectrophotometric determination based on hydrogen bonding interactions between examined drug and alizarin yellow GG. This method is able to evaluate isoxicam in range of 1.0 x 10(-3) to 20.0 microg mL(-1), with a limit of determination of 1.0 ng mL(-1). The retention capacity and pre-concentration factor of prepared sorbent are 18.5 mg g(-1) and 200, respectively; and the prepared MIPs can be reused at least for five times. The MIP capability for isoxicam selection and extraction from the solution is higher than non-imprinted polymer (NIP). Under optimum conditions, this procedure can be successfully applied to assay trace amounts of isoxicam in pharmaceutical and biological samples.