Electrical characteristics of amyloid beta peptides in vertical junctions

Assembled amyloid beta (Aβ) peptides have been considered pathological assemblies involved in human brain diseases, and the electron transfer or electron transport characteristics of Aβ are important for the formation of structured assemblies. Here, we report the electrical characteristics of surface-assembled Aβ peptides similar to those observed in Alzheimer’s patients. These characteristics correlate to their electron transfer characteristics. Electrical current–voltage plots of Aβ vertical junction devices show the Aβ sequence dependence of the current densities at both Aβ monomers (mono-Aβs) and Aβ oligomers (oli-Aβs), while Aβ sequence dependence is not clearly observed in the electrical characteristics of Aβ planar field effect transistors (FETs). In particular, surface oligomerization of Aβ peptides drastically decreases the activity of electron transfer, which presents a change in the electron transport pathway in the Aβ vertical junctions. Electron transport at oli-Aβ junctions is symmetric (tunneling/tunneling) due to the weak and voltage-independent coupling of the less redox-reactive oli-Aβ to the contacts, while that at mono-Aβ junctions is asymmetric (hopping/tunneling) due to redox levels of mono-Aβ voltage-dependently coupled with contact electrodes. Consequently, through vertical junctions, the sequence- and conformation-dependent electrical characteristics of Aβs can reveal their electron transfer activities. Improvements to biomolecule/vertical device interfaces have given researchers a new tool to characterize the neurotoxins associated with brain disease. Assembly of amyloid beta peptides into fibrils has been identified as contributing to the onset of Alzheimer’s disease. Sohyeon Seo and Hyoyoung Lee from Sungkyunkwan University in Suwon, South Korea, and colleagues report that conductivity measurements can help predict the chemical activity of amyloid beta peptide structures. The team’s device integrates the peptides into a vertical junction layout by immobilizing them onto monolayer-coated gold electrodes. Correlating the device’s conductivity with microscopically determined chemical structures revealed that current flow depended on the peptide’s amino acid sequences. Drastic drops in conductivity were observed when the electrode-bound monomer peptides assembled into fibrils, indicating the presence of a different mechanism of current flow. Experimental descriptions of Aβ oligomers (oli-Aβs) assembled on surfaces as compared with Aβ monomers (mono-Aβs) are crucial to understanding changes in chemical reactivity. Here, we fabricated Aβ molecular junctions between linker molecular layered electrodes using different Aβ segments and report that electron transport pathways changed from asymmetric hopping across monomeric Aβ junctions to symmetric tunneling across oligomeric Aβ junctions.