Surface chemistry and electronics of semiconductor-nanosystem junctions II: enzyme immobilisation, charge transport aspects and scanning probe micropscopy imaging

Photoelectrochemically prepared and vapor-phase-induced surface nanotopographies are used for immobilization of enzymes at specific surface sites. The specific nanostructure of step-bunched silicon where the step edges are negatively charged and that of MoTe2, characterized by negatively charged triangular growth defects, are successfully employed for enzyme immobilization. It is shown that, at pH values below the isoelectric point of the enzyme reverse transcriptase (RT), electrostatic interaction via the Debye length of 3–4 nm and the shorter ranged van der Waals attraction superimpose for enzyme adsorption at negatively charged surface sites. Scanning tunneling microscopy (STM) images of reverse transcriptases deposited onto the layered semiconductor MoTe2 are interpreted in analogy to semiconductor–insulator–metal (MIS) device physics by analyzing the electronic properties of the junction between Pt tip (metal), biomolecule (insulator), and n-MoTe2 (semiconductor). The uninhibited current flow in constant-current STM experiments is tentatively interpreted by salvation-assisted detrapping of electrons along the circumference of the proteins where biological water is present. Imaging of the RTs on step-bunched silicon surfaces with tapping mode atomic force microscopy shows spatially selective deposition at negatively charged step edges.