Formation of spin-polarized current in antiferromagnetic polymer spintronic field-effect transistors.

We have theoretically investigated the feasibility of constructing a spintronic field-effect transistor with the active channel made of a polymer chain with the antiferromagnetic coupling oriented in the source-to-drain direction. We found two different device function regimes controlling the on-chain spin-charge carrier density by tuning the gate voltage. At higher charge carrier densities, the source-drain current linearly increases with decreasing charge carrier densities. In this regime, no polymer spin-polarized current is observed. Upon reaching a critical gate voltage, the current decreases with decreasing charge densities. It is accompanied by the formation of spin-polarized current, generated by an on-chain process, which can be related to spin-charge spatial distribution symmetry breaking caused either by an application of the source-to-drain voltage (higher spin polarization near the drain), or the breakdown of the Peierls dimerization near chain ends. Numerical simulation of the transistor characteristics suggests that the design of a polymer spintronic field-effect transistor is in principle feasible.

Gate voltage impact on charge mobility in end-on stacked conjugated oligomers.

We present a model of the charge transport in thin film organic field-effect transistors with the active channel made of linear conjugated chains stacked on the substrate with end-on-orientation. The transport was simulated in a box consisting of 25 polymer chains, in which the delocalized quantum orbital eigenstates of the on-chain hole distribution were calculated. The inter-chain charge transfer was solved semi-classically. The full self-consistent distribution of charge density and electric field was determined for various applied gate and source-drain voltages. We found that the dependence of charge mobility on gate voltage is not monotonic: it first increases with increasing gate voltage for a limited interval of the latter, otherwise it decreases with the gate voltage. Next, we found formation of the second resonant peak for higher gate voltages. The mobility dependence on the gate voltage confirmed that the current flowing through the active semiconductor layer should be described not only as the hole transfer between adjacent repeat units of the neighbouring chains, but also as the transfer of coherences among on-chain repeat units. The presented model can also give a new insight into the charge transport in organic field-effect transistors with a novel vertical architecture.

Computational study on the interactions and orientation of monoclonal human immunoglobulin G on a polystyrene surface.

Having a theoretical understanding of the orientation of immunoglobulin on an immobilized solid surface is important in biomedical pathogen-detecting systems and cellular analysis. Despite the stable adsorption of immunoglobulin on a polystyrene (PS) surface that has been applied in many kinds of immunoassays, there are many uncertainties in antibody-based clinical and biological experimental methods. To understand the binding mechanism and physicochemical interactions between immunoglobulin and the PS surface at the atomic level, we investigated the binding behavior and interactions of the monoclonal immunoglobulin G (IgG) on the PS surface using the computational method. In our docking simulation with the different arrangement of translational and rotational orientation of IgG onto the PS surface, three typical orientation patterns of the immunoglobulin G on the PS surface were found. We precisely analyzed these orientation patterns and clarified how the immunoglobulin G interacts with the PS surface at atomic scale in the beginning of the adsorption process. Major driving forces for the adsorption of IgG onto the PS surface come from serine (Ser), aspartic acid (Asp), and glutamic acid (Glu) residues.