Deciphering the Transition From Tunneling to Band-Like Transport in Protein-Templated Biohybrid Junctions

Protein-templated metal nanoclusters (MNCs) offer a unique strategy for integrating the structural precision of biological scaffolds with the quantum electronic characteristics of atomically precise metallic cores. Despite this promise, the fundamental principles governing charge transport in such biohybrid systems remain limited. Here, we report a systematic investigation of electron transport in Au/BSA-MNCs/Au Nanowire junctions incorporating a series of bovine serum albumin (BSA)-templated metal nanoclusters of copper, silver, and gold (CuNC, AgNC, and AuNC). Incorporation of MNCs yields up to a 17-fold increase in current relative to native BSA junctions. The conductivity follows the trend AuNC > AgNC > CuNC, a disparity that fragment-level Density Functional Theory (DFT) analysis attributes to the greater structural robustness and enhanced orbital delocalization of AuNC and AgNC, which together facilitate stronger electronic coupling with proximal protein residues. Temperature-dependent charge transport measurements (I-V-T) further reveal a systematic evolution from tunneling-dominated to increasingly band-like transport across the BSA-MNC series, governed by the extent of electronic delocalization imparted by the metal core. Collectively, these findings provide molecular-level insight into charge transport in protein-templated MNCs and establish structure-property design principles for the next-generation bioelectronic materials.