New “off-on-off” pH chemosensing bichromophore based on 2-hydroxyphenylhydrazone and 1,8-naphthalimide is synthesized. The probe, designed to operate by controlled photoinduced electron transfer (PET) and internal charge transfer (ICT) processes, shows a striking pH dependence of its absorption and emission properties. Due to the 1,8-naphthalimide unit the probe exhibits between pH 6 and 10 a centred at 548 nm (λ.ex = 400 nm) strong yellow-green fluorescence, however, beyond of this pH interval the emission of the probe is quenched. The “off-on-off” behaviour of the probe as a function of pH enables it to execute XNOR, IMPLICATION, XOR and INHIBIT logic gates. The INHIBIT logic gate as a borrow digit in conjunction with XOR logic gate as a difference digit executes a half-subtractor. Moreover, the parallel action of logic gates INHIBIT and XNOR executes a digital magnitude comparator.

Herein we pay attention to the design, synthesis and sensor activity of a novel biocompatible perylene-3,4,9,10-tetracarboxylic diimide (PDI) pH-probe in water. The synthesized compound shows selective fluorescence signalling properties as a function of pH (pKa value of 6.35 ± 0.02) which makes the probe suitable for pH determination in the physiological range. Thus prepared water soluble fluorescent system demonstrate low cytotoxicity to L929 cell lines from 330 μM to 1.3 μM and cell permeability in the lower concentration range. That findings show the high potential of the newly prepared PDI probe for monitoring of pH variations in bio-samples.

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This article studies the effects of Brownian motion and thermophoresis on unsteady mixed convection flow near the stagnation-point region of a heated vertical plate embedded in a porous medium saturated by a nanofluid. The plate is maintained at a variable wall temperature and nanoparticle volume fraction. The presence of a solid matrix, which exerts first and second resistance parameters, is considered in this study. A suitable coordinate transformation is introduced and the resulting governing equations are transformed and then solved numerically using the local nonsimilarity method and the Runge-Kutta shooting quadrature. The effects of various governing parameters on the flow and heat and mass transfer on the dimensionless velocity, temperature, and nanoparticle volume fraction profiles as well as the skin-friction coefficient, Nusselt number, and the Sherwood number are displayed graphically and discussed to illustrate interesting features of the solutions. The results indicate that as the values of the thermophoresis and Brownian motion parameters increase, the local skin-friction coefficient increases whereas the Nusselt number decreases. Moreover, the Sherwood number increases as the thermophoresis parameter increases, and decreases as the Brownian motion parameter increases. On the other hand, the unsteadiness parameter and the resistance parameters enhance the local skin-friction coefficient, local Nusselt number, and the local Sherwood number.

The unsteady mixed convection flow near the stagnation point region of a heated vertical plate in a porous medium saturated with a nanofluid is studied analytically and numerically using Buongiorno’s model. The model used for the nanofluid incorporates the effects of Brownian motion and thermophoresis. An appropriate similarity transforms are used and the resultant equations are solved using the fourth-fifth order Runge-Kutta method with shooting technique for different values of the parameters governing the problem. The effects of the governing parameters on fluid velocity, temperature, nanoparticle volume fraction, skin friction, Nusselt number and Sherwood number are discussed.