Effect of alumina contents on phase stability and mechanical properties of magnesium fluorapatite/alumina composites.

The aim of the present work was twofold: to prepare biphasic magnesium fluorapatite (MFA) composites with different amounts of alumina using a two-step sintering process, and to evaluate the effects of various amounts of alumina on the mechanical properties, phase stability, and densification of the composite samples. Initially, MFA powders were prepared with different amounts of alumina by mechanical activation and the MFA composite samples were subsequently prepared using the two-step sintering (TSS) method. In order to determine the appropriate temperature of the first step sintering, conventional sintering of MFA/50% alumina was carried out at temperatures in the range of 1000-1300°C. X-ray diffraction and scanning electron microscopy (SEM) techniques were used to characterize the prepared MFA/alumina composites. The results showed fracture toughness and hardness in the MFA/50% alumina composite samples to increase as a result of alumina addition to their maximum values of 5.82±1.05MPam(1/2) and 22.09±3.5GPa, respectively.

Direct detection and discrimination of double-stranded oligonucleotide corresponding to hepatitis C virus genotype 3a using an electrochemical DNA biosensor based on peptide nucleic acid and double-stranded DNA hybridization.

Development of an electrochemical DNA biosensor for the direct detection and discrimination of double-stranded oligonucleotide (dsDNA) corresponding to hepatitis C virus genotype 3a, without its denaturation, using a gold electrode is described. The electrochemical DNA sensor relies on the modification of the gold electrode with 6-mercapto-1-hexanol and a self-assembled monolayer of 14-mer peptide nucleic acid probe, related to the hepatitis C virus genotype 3a core/E1 region. The increase of differential pulse voltammetric responses of methylene blue, upon hybridization of the self-assembled probe with the target ds-DNA to form a triplex is the principle behind the detection and discrimination. Some hybridization experiments with non-complementary oligonucleotides were carried out to assess whether the developed DNA sensor responds selectively to the ds-DNA target. Diagnostic performance of the biosensor is described and the detection limit was found to be 1.8 x 10(-12) M in phosphate buffer solution, pH 7.0. The relative standard deviation of measurements of 100 pM of target ds-DNA performed with three independent probe-modified electrodes was 3.1%, indicating a remarkable reproducibility of the detection method.

Electrochemical detection of short sequences of hepatitis C 3a virus using a peptide nucleic acid-assembled gold electrode.

Development of an electrochemical DNA biosensor, using a gold electrode modified with a self-assembled monolayer composed of a peptide nucleic acid (PNA) probe and 6-mercapto-1-hexanol, is described. The sensor relies on covalent attachment of the 14-mer PNA probe related to the hepatitis C virus genotype 3a (pHCV3a) core/E1 region on the electrode. Covalently self-assembled PNA could selectively hybridize with a complementary sequence in solution to form double-stranded PNA-DNA on the surface. The increase of peak current of methylene blue (MB), upon hybridization of the self-assembled probe with the target DNA in the solution, was observed and used to detect the target DNA sequence. Some hybridization experiments with noncomplementary oligonucleotides were carried out to assess whether the suggested DNA sensor responds selectively to the target. Diagnostic performance of the biosensor is described and the detection limit was found to be 5.7 x 10(-11)M with a relative standard deviation of 1.4% in phosphate buffer solution, pH 7.0. This sensor exhibits high reproducibility and could be used for detection of the target DNA for seven times after the regeneration process.

Immobilization and voltammetric detection of human interleukine-2 gene on the pencil graphite electrode.

The immobilization and differential pulse anodic voltammetry (DPAV) of a 20-mer oligonucleotide related to the human interleukine-2 (hIL-2) using renewable pencil graphite electrode (PGE) is described. The influences of electrochemical pretreatment of PGE on the ability of the electrode in hIL-2 adsorption, and conditions of hiIL-2 immobilization on PGE including immobilization potential and time, sodium chloride concentration as well as stirring of the solution were studied and optimum conditions were suggested. Accordingly, the electrochemical pretreatment of the polished PGE by electrostatic procedure at 1.80V for 5min in 0.50M acetate buffer solution of pH 4.8 is proposed as the optimum pre-treatment procedure. Similarly, the obtained optimum conditions for immobilization of hIL-2 on the activated PGE was an immobilization duration of 5min at applied potential of 0.50V. Trace levels of hIL-2 was readily detected following only 5min immobilization period with detection limit of 6nM.

Developing an electrochemical deoxyribonucleic acid (DNA) biosensor on the basis of human interleukine-2 gene using an electroactive label.

Development of an electrochemical DNA biosensor based on a human interleukine-2 (IL-2) gene probe, using a pencil graphite electrode (PGE) as transducer and methylene blue (MB) as electroactive label is described. The sensor relies on the immobilization of a 20-mer single stranded oligonucleotide probe (hIL-2) related to the IL-2 gene on the electrode. The hybridization between the probe and its complementary sequence (chIL-2) as the target was studied by square wave voltammetry (SWV) of MB accumulated on the PGE. In this approach the extent of hybridization is evaluated on the basis of the difference between SWV signals of MB accumulated on the probe-PGE and MB accumulated on the probe-target-PGE. Some hybridization experiments with non-complementary oligonucleotides were carried out to assess whether the suggested DNA sensor responds selectively to the target. Some experimental variables affecting the performance of the biosensor including: polishing of PGE, its electrochemical activation conditions (i.e., activation potential and activation time) and probe immobilization conditions on the electrodes (i.e., immobilization potential and time) were investigated and the optimum values of 1.80 V and 300 s for PGE activation, and -0.5 V and 400s for the probe immobilization on the electrode were suggested.