A S‐Layer Protein of Bacillus anthracis as a Building Block for Functional Protein Arrays by In Vitro Self‐Assembly

S‐layer proteins create a cell‐surface layer architecture in both bacteria and archaea. Because S‐layer proteins self‐assemble into a native‐like S‐layer crystalline structure in vitro, they are attractive building blocks in nanotechnology. Here, the potential use of the S‐layer protein EA1 from Bacillus anthracis in constructing a functional nanostructure is investigated, and apply this nanostructure in a proof‐of‐principle study for serological diagnosis of anthrax. EA1 is genetically fused with methyl parathion hydrolase (MPH), to degrade methyl parathion and provide a label for signal amplification. EA1 not only serves as a nanocarrier, but also as a specific antigen to capture anthrax‐specific antibodies. As results, purified EA1–MPH forms a single layer of crystalline nanostructure through self‐assembly. Our chimeric nanocatalyst greatly improves enzymatic stability of MPH. When applied to the detection of anthrax‐specific antibodies in serum samples, the detection of our EA1–MPH nanostructure is nearly 300 times more sensitive than that of the unassembled complex. Together, it is shown that it is possible to build a functional and highly sensitive nanosensor based on S‐layer protein. In conclusion, our present study should serve as a model for the development of other multifunctional nanomaterials using S‐layer proteins.     

Direct Fabrication of Freestanding and Patterned Nanoporous Junctions in a 3D Micro‐Nanofluidic Device for Ion‐Selective Transport

In the field of micro‐nanofluidics, a freestanding configuration of a nanoporous junction is highly demanded to increase the design flexibility of the microscale device and the interfacial area between the nanoporous junction and microchannels, thereby improving the functionality and performance. This work first reports direct fabrication and incorporation of a freestanding nanoporous junction in a microfluidic device by performing an electrolyte‐assisted electrospinning process to fabricate a freestanding nanofiber membrane and subsequently impregnating the nanofiber membrane with a nanoporous precursor material followed by a solidification process. This process also enables to readily control the geometry of the nanoporous junction depending on its application. By these advantages, vertically stacked 3D micro‐nanofluidic devices with complex configurations are easily achieved. To demonstrate the broad applicability of this process in various research fields, a reverse electrodialysis‐based energy harvester and an ion concentration polarization‐based preconcentrator are produced. The freestanding Nafion‐polyvinylidene fluoride nanofiber membrane (F‐NPNM) energy harvester generates a high power (59.87 nW) owing to the enlarged interfacial area. Besides, 3D multiplexed and multi‐stacked F‐NPNM preconcentrators accumulate multiple preconcentrated plugs that can increase the operating sample volume and the degree of freedom of handling. Hence, the proposed process is expected to contribute to numerous research fields related to micro‐nanofluidics in the future.