Magnetic elastomers have been widely pursued for sensing and actuation applications. Silicone-based magnetic elastomers have a number of advantages over other materials such as hydrogels, but aggregation of magnetic nanoparticles within silicones is difficult to prevent. Aggregation inherently limits the minimum size of fabricated structures and leads to non-uniform response from structure to structure. We have developed a novel material which is a complex of a silicone polymer (polydimethylsiloxane-co-aminopropylmethylsiloxane) adsorbed onto the surface of magnetite (γ-Fe203) nanoparticles 7–10 nm in diameter. The material is homogenous at very small length scales (< 100 nm) and can be crosslinked to form a flexible, magnetic material which is ideally suited for the fabrication of micro- to nanoscale magnetic actuators. The loading fraction of magnetic nanoparticles in the composite can be varied smoothly from 0 – 50% wt. without loss of homogeneity, providing a simple mechanism for tuning actuator response. We evaluate the material properties of the composite across a range of nanoparticle loading, and demonstrate a magnetic-field-induced increase in compressive modulus as high as 300%. Furthermore, we implement a strategy for predicting the optimal nanoparticle loading for magnetic actuation applications, and show that our predictions correlate well with experimental findings.

FhuA has a luminal cross-section of~3.1Â4.4 nm and is plugged by a globular N-terminal cork domain (C). Single-channel electrical recordings with extensive protein redesign of FhuA resulted in identifying four long extracellular loops (4L) that partially block the lumen upon the removal of the cork. The newly engineered protein, FhuA DC/D4L, was the result of a removal of almost 33% of the total number of amino acids of the wild-type FhuA (WT-FhuA) protein. The crown achievement in this work was combining direct genetic engineering with a refolding approach to produce this unusually-stable protein nanopore. Critical to its future nanotechnological applications, FhuA DC/ D4L was functional under structure-altering conditions, including low ion concentration and highly acidic aqueous phase. To tailor the FhuADC/D4L protein to the use in nanopore-based detection devices, we show that the FhuA-based nanopores function as stochastic biosensing elements. For example, we monitored the proteolytic activity of an enzyme at highly acidic pH and we were able to determine the kinetics of protein-DNA aptamer interactions at physiological salt concentration. These two assays have not been demonstrated with the existing nanopores.

No abstract