ABSTRACT
This chapter provides an introduction to the charge transport (CT) characteristics of molecular devices built using complex biological backbones. This field has emerged as a subset of the molecular electronics discipline, which has brought a large variety of new tools to study CT in molecular electronic devices down to the single-molecule level. We try to show the importance of this biomolecular electronics field from both the fundamental and technological perspectives.The appearance of the first examples of single-molecule three-terminal devices within molecular electronics evolved into electrochemically gated single-molecule devices, allowing the first fundamental studies of CT in individual biomolecules bridged between two macroscopic electrodes. This chapter describes the latest examples of such novel biomolecular wires that are contributing to the definition of the emerging discipline of biomolecular electronics. Along with these detailed descriptions,
a survey of the latest advances on interfacing proteins and nucleic acids to electrodes is presented. 8.1 Introduction
Building up efficient electronic nanodevices by profiting from nature optimized biomolecular machinery is a clear challenge for today’s scientific and engineering communities [1]. Thousands of years of natural evolution have resulted in highly sophisticated and specialized molecular architectures that are able to transport charge and/or energy with astonishing efficiency [2-4]. The dream of exploiting such properties has motivated researchers for decades in fields such us bioelectronics, and with the advent of nanoscience, the field has experienced a new boom [5-7]. The ultimate goal of this field is the integration of a biological motif into an electronic platform that allows the transduction of the target signal and its easy implementation into a device. Taking advantage of biomolecular properties to design functional electronic devices poses two clear challenges: First, we need to fill the knowledge gap of the fundamental mechanisms behind biological energy/ charge transfer, and second, we need to efficiently engineer the biomolecule/electrode interface to achieve a stable hybrid bio-electronic platform.Generally speaking, the ongoing research within the field of bioelectronics is still at a very phenomenological level. A number of fundamental questions need to be answered in order to push this field to the next level. These include: What are the main charge/energy pathways located in a complex biomolecule? How can they be effectively hybridized with an electrode surface? Where should “the electrical plugs” be allocated in such biological molecular structures? And what anchoring chemistry should then be developed? To this aim, a huge amount of information has yet to be experimentally addressed such as the exact role that different molecular motifs have on biological charge/energy transport processes, e.g., a-helix, b-sheet, random coil, etc., the role of intramolecular interactions like for instance molecular orbital coupling, H-bonding, etc., and the role of the molecular dynamics, e.g., fluctuations between different conformers, interactions with partner molecules, etc. Answering these and other fundamental questions will place us in position to address a systematic strategy
to fully integrate active biomolecular components onto metal/semiconductor platforms.The complexity of this particular topic calls for the use of novel interdisciplinary approaches in order to shed new light onto the fundamental mechanisms behind biological charge transport and fill the gap between the well-known crystallographic structure of a biomolecular complex and the final functional bioelectronic device.
