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A new label-free electrochemical DNA biosensor is presented based on carbon paste electrode (CPE) modified with gold (Au) and platinum (Pt) nanoparticles to prepare the bimetallic nanocomposite electrode. The proposed sensor was made by immobilization of 15-mer single stranded oligonucleotide probe related to p53 gene for detection of DNA plasmid samples. The hybridization detection relied on the alternation in the guanine oxidation signal following hybridization of the probe with complementary genomic DNA. The technique of differential pulse voltammetry (DPV) was used for monitoring guanine oxidation. To optimize the performance of the modified CPE, different electrodes were prepared in various percentages of Au and Pt nanoparticles. The modified electrode containing 15% Au/Pt bimetallic nanoparticles (15% Au/Pt-MCPE) was selected as the best working electrode. The selectivity of the sensor was investigated using plasmid samples containing non-complementary oligonucleotides. The detection limit of the biosensor was studied and calculated to be 53.10 pg μL −1 .

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The electrically conducting magnetic nanofluid of Fe3O4-water was made to flow in a heat exchanger. Afterwards, the ferrohydrodynamics (FHD) and magnetohydrodynamics (MHD) effects of the nanofluid on the enhancement of the overall heat transfer coefficient of the heat exchanger were studies at different nanofluid concentrations, inlet temperatures, and different constant magnetic field intensities. The study dealt with both laminar and turbulent nanofluid flows. The electrical conductivity of the magnetic nanofluid was determined by a Jenway 4510 conductivity meter. By using the experimental data, a Sprint CFD code identified the hydrodynamic and thermal behavior of the nanofluid flow in the presence of constant magnetic fields of intensities of 0, 0.05, 0.1 and 1 Tesla. The results showed that an increase in the concentration of Fe3O4-water nanofluid enhanced its electrical conductivity so considerably that the nanofluid, at the volume fraction of 1%, was observed to be 12.5 times more electrically conductive than distilled water. Also, it was shown that increase in magnetic field intensity had an enhancing effect on the overall heat transfer coefficient, and the effect was stronger at higher magnetic nanofluid concentrations. Furthermore, due to generation of chainlike structures by the FHD effect of the Fe3O4 magnetic nanoparticles, the nanoparticles increased the effective thermal conductivity of the nanofluid and, consequently, the overall heat transfer coefficient in both the laminar and turbulent regimes. Finally, unlike the turbulent flow, the laminar regime allowed for the MHD effect having only a negligible effect on the enhancement of the overall heat transfer coefficient. This was due to velocities in the laminar regime being small.