Ion Density Deviations in Polyelectrolyte Microcapsules: Influence on Biosensors

Polyelectrolyte microcapsules loaded with fluorescent dyes have been proposed as biosensors to monitor local pH and ionic strength for diagnostic purposes. In the case of charged microcapsules, however, the local electric field can cause deviations of ion densities inside the cavities, potentially resulting in misdiagnosis of some diseases. Using nonlinear Poisson-Boltzmann theory, we systematically investigate these deviations induced by charged microcapsules. Our results show that the microcapsule charge density, as well as the capsule and salt concentrations, contribute to deviations of local ion concentrations and pH. Our findings are relevant for applications of polyelectrolyte microcapsules with encapsulated ion-sensitive dyes as biosensors.Comment: 9 pages, 7 figure

Magnetic ordering and structural phase transitions in strained ultrathin SrRuO3_{3}/SrTiO3_{3} superlattice

Ruthenium-based perovskite systems are attractive because their Structural, electronic and magnetic properties can be systematically engineered. SrRuO$_3$/SrTiO$_3$ superlattice, with its period consisting of one unit cell each, is very sensitive to strain change. Our first-principles simulations reveal that in the high tensile strain region, it transits from a ferromagnetic (FM) metal to an antiferromagnetic (AFM) insulator with clear tilted octahedra, while in the low strain region, it is a ferromagnetic metal without octahedra tilting. Detailed analyses of three spin-down Ru-t$_{2g}$ orbitals just below the Fermi level reveal that the splitting of these orbitals underlies these dramatic phase transitions, with the rotational force constant of RuO$_6$ octahedron high up to 16 meV/Deg$^2$, 4 times larger than that of TiO$_6$. Differently from nearly all the previous studies, these transitions can be probed optically through the diagonal and off-diagonal dielectric tensor elements. For one percent change in strain, our experimental spin moment change is -0.14$\pm$0.06 $\mu_B$, quantitatively consistent with our theoretical value of -0.1 $\mu_B$.Comment: 3 figures, 1 supplementary material, accepted by Phys. Rev. Let

Highly Ordered Mesoporous Hydroxide Thin Films through Self-Assembly of Size-Tailored Nano-Building Blocks: A Theoretical- Experimental Approach

Mesoporous crystalline (hydr)oxides of low-valence metal ions (M(II) and M(III)) are highly demanded in the context of various applications. In this study, we demonstrate key factors to the successful formation of ordered mesoporous films through the Assembly of Nano-Building Block (ANBB) approach using a colloidal solution of crystalline M(OH)2 (M = Mn, Fe, Co, Ni, and Cu). The colloidal system of α-Ni(OH)2 is presented in-depth as a typical example. Crystal growth and aggregation kinetics of the NBB were tuned by synthetic parameters. Nanometer-sized NBBs of tailored size between oligomer scale to over 20 nm were obtained. The films prepared from α-Ni(OH)2 NBBs with a diameter of ≤ 7.5 nm showed ordered mesostructures through evaporation-induced self-assembly in the presence of supramolecular templates. Coarse-grained simulation suggests that there is a threshold diameter of NBB toward the formation of wellordered mesostructures. It was found that, as well as limiting the diameter of NBB, inhibition of an aggregation of NBBs by using coordinative additives or diluting the NBB colloidal solution were essential to control the assembly of NBBs and templates into the ordered mesostructures. The results obtained here open up the synthesis of ordered mesoporous materials with a crystalline wall of variety of chemical compositions containing low-valence metal elements.The present work was partially supported by JSPS KAKENHI, JSPS bilateral program, ABTLuS (LNLS proposal SAXS1 18927), ANPCyT (PICT 2014-3687 and 2015-3526), UBACyT (20020130100610BA), The Sumitomo Foundation, Izumi Science and Technology Foundation and Deutsche Forschungsgemeinschaft-CONICET under grant Mu1674/15-1

Slowing down of accelerated structural relaxation in ultrathin polymer films

We demonstrate with molecular simulation that the acceleration of structural relaxation, also known as physical aging, commonly experimentally observed in thin polymer films slows down at extremely small thicknesses. This phenomenon can be attributed to an inversed free volume diffusion process caused by the sliding motion of chain molecules. Our findings provide direct evidence of the relationship between the sliding motion of short chain fragments and the structural relaxation of ultrathin polymer films, and also verify the existence of a new confinement effect at the nanoscale.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Phase separation in mixed polymer brushes on nanoparticle surfaces enables the generation of anisotropic nanoarchitectures

Anisotropic nanoparticle arrangements formed via phase separation in mixed polymer brushes and site-specific functionalization are studied by experiment and simulation.</p