Membrane Protein Incorporation into Nano-Bioelectronics: An insight into Rhodopsin Controlled SiNW-FET Devices

Biological systems use different energy sources to interact with their environments by creating ion gradients, membrane electric potentials, or a proton motive force to accomplish strikingly complex tasks on the nanometer length scale, such as energy harvesting, and whole organism replication. Most of this activity involves a vast arsenal of active and passive ion channels, membrane receptors and ion pumps that mediate complex and precise transport across biological membranes. Despite the remarkable rate of progress exhibited by modern microelectronic devices, they still cannot compete with the efficiency and precision of biological systems on the component level. At the same time, the sophistication of these molecular machines provides an excellent opportunity to use them in hybrid bioelectronic devices where such a combination could deliver enhanced electronic functionality and enable seamless bi-directional interfaces between man-made and biological assemblies.;Artificial membrane systems allow researchers to study the structure and function of membrane proteins in a matrix that approximates their natural environment and to integrate these proteins in ex-vivo devices such as electronic biosensors, thin-film protein arrays, or bio-fuel cells. Since most membrane proteins have vectorial functions, both functional studies and applications require effective control over protein orientation within a lipid bilayer. In our work, we have explored the role of the bilayer surface charge in determining transmembrane protein orientation and functionality during formation of proteoliposomes. We reconstituted a model vectorial ion pump, proteorhodopsin, in liposomes of opposite charges and varying charge densities and determined the resultant protein orientation. Antibody-binding assay and proteolysis of proteoliposomes showed physical evidence of preferential orientation, and functional assays verified vectorial nature of ion transport in this system. Our results indicate that the manipulation of lipid composition can indeed control orientation of an asymmetrically charged membrane protein, proteorhodopsin, in liposomes.;One-dimensional inorganic nanostructures, which have critical dimensions comparable to the sizes of biological molecules, form an excellent materials platform for building such integrated structures. Researchers already use silicon nanowire-based field effect transistors functionalized with molecular recognition sites in a diverse array of biosensors. In our group, we have been developing a platform for integration of membrane protein functionality and electronic devices using a 1-D phospholipid bilayer device architecture. In these devices, the membrane proteins reside within the lipid bilayer that covers a nanowire channel of a field-effect transistor. This lipid bilayer performs several functions: it shields the nanowire from the solution species; it serves as a native-like environment for membrane proteins and preserves their functionality, integrity, and even vectorality. In this work, we show that a 1-D bilayer device incorporating a rhodopsin proton pump allows us to couple light-driven proton transport to a bioelectronic circuit. We also report that we were able to adapt another distinctive feature of biological signal processing---their widespread use of modifiers, co-factors, and mediator molecules---to regulate and fine-tune the operational characteristics of the bioelectronic device. In our example, we use co-assembly of protein channels and ionophores in the 1-D bilayer to modify the device output levels and response time.