Ferrocene heteroconjugation of DNA duplex aids Fowler–Nordheim tunnelling

DNA has emerged as a promising self-assembling material in molecular electronics. Beyond the research on DNA tiles and DNA origami, increasing attention is now being directed towards three-dimensional architectures that may endow electromechanic nanodevices. In this report, we present a method to impart electrical conductivity to DNA: a ferrocene-derivatised psoralen that binds with opposing thymines at T-A/A-T sites, resulting in a covalent cross-link in double-stranded DNA. We found that a thiol-modified, 10-mer DNA formed a 1:1 conjugate, which further self-assembled on Au substrates, allowing for the simultaneous imaging of surface topography and current distribution using conductive atomic force microscopy. The electrical junction thus formed resembles a metal/insulator/metal diode; the current-voltage characteristics were well described using the Fowler–Nordheim tunnelling theory, incorporating an electronic state of psoralen derived from ab initio calculations as the barrier potential. Untreated DNAs and psoralen conjugates lacking the ferrocene moiety exhibited no conductivity. Therefore, a process analogous to dopant incorporation into inorganic semiconductor materials has become feasible for inherently insulating DNA. As no pre-derivatisation of the host DNA is required, any DNA supramolecular structure can be post-processed after synthesis, offering broad versatility. Our findings provide a significant step towards integrating DNA supramolecular chemistry with molecular electronics.