Hydrodynamic and thermal cloaking effects have attracted interest among researchers using metamaterials. This paper explores an analytical solution using only isotropic materials to achieve cloaking under forced convective heat transfer. It is shown that, under a background of uniform flow and linearly varying temperature, a circular bilayer cloak with an inner layer made of impenetrable and insulated material and an outer layer made of a porous medium having a constant permeability and effective conductivity does not disturb the external flow and temperature fields. Moreover, the cloaked region is shielded from the external flow and temperature fields. Analytical temperature and velocity distributions within the porous outer layer are presented to demonstrate both the hydrodynamic and thermal cloaking effects of such a bilayer. Finally, numerical results, based on practically attainable material properties, are given to confirm the analytical model.

Heavy metal contaminants have serious consequences for the environment and human health. Consequently, effective methods for detecting their presence, particularly in water and food, are urgently required. Accordingly, the present study proposes a sensor capable of detecting mercury Hg(II) and lead Pb(II) ions simultaneously, using graphene oxide (GO) as a quenching agent and an aptamer solution as a reagent. In the proposed device, the aptamer sequences are labeled by FAM and HEX fluorescent dyes, respectively, and are mixed well with 500 ppm GO solution before injection into one inlet of the microchannel, and the heavy metal sample solution is injected into another inlet. The presence of Hg(II) and Pb(II) ions is then detected by measuring the change in the fluorescence intensity of the GO/aptamer suspension as the aptamer molecules undergo fluorescence resonance energy transfer (FRET). The selectivity of these two ions is also shown to be clear among other mixed heavy metal ions. The experimental results show that the aptamer sensors have a linear range of 10~250 nM (i.e., 2.0~50 ppb) for Hg(II) ions and 10~100 nM (i.e., 2.1~20.7 ppb) for Pb(II) ions. Furthermore, the limit of detection is around 0.70 ppb and 0.53 ppb for Hg(II) and Pb(II), respectively, which is lower than the maximum limits of 6 ppb and 10 ppb prescribed by the World Health Organization (WHO) for Hg(II) and Pb(II) in drinking water, respectively.

Harvesting blue energy from saline solutions has attracted much attention recently. Salinity-based power generation in nanopores is governed by both passive factors (e.g., the nanopore diameter, nanopore length, nanopore material, and pore density) and active factors (e.g., the concentration gradient, temperature, and pH environment). The present study performs COMSOL multiphysics numerical simulations based on the Poisson–Nernst–Planck equations, Navier–Stokes equations and heat transfer equation to examine the combined effects of the temperature gradient and pH level on the diffusion voltage and maximum power generation in single silica nanopores with lengths of 100 nm and 500 nm, respectively. In performing the simulations, the pH value is adjusted in the range of pH 5–11, the salinity concentration gradient is 100-fold and 1000-fold, respectively. Three different thermal conditions are considered, namely (1) isothermal-room temperature (298 K); (2) asymmetric thermal (temperature of low-concentration reservoir and high-concentration reservoir are 323 K and 298 K, respectively); and (3) isothermal-high temperature (323 K). The results show that the generated power varies significantly with both the pH level and the temperature conditions. In particular, the asymmetric thermal condition yields an effective improvement in the power generation performance since it reduces the surface charge density on the surface of the nanopore near the low-concentration end and therefore suppresses the ion concentration polarization (ICP) effect. The improvement in the energy harvesting performance is particularly apparent at pH levels in the range of 9–10 (about 100% higher than that of pH 7). Overall, the results confirm the feasibility of using active factors to enhance the power generation performance of salinity gradient-based nanopore systems.