Nanogaps and biomolecules

Abstract

Nanogaps and BioMolecules. Molecular electronic transport characterization is an active part of the research field in nanotechnology. The main underlying idea is to use single molecules as active elements in nano-devices [1]. As a consequence, the proper fabrication of a molecule-electrode contact is a crucial issue [2],[3] and several applications can be thus envisioned. For example, in biosensing it is fundamental the electrochemical detection of different crucial biomarkers upon the investigation and variation of the electric conduction of the metal-molecule-metal junction. Possible applications involve the biomedical diagnostics and the monitoring of biological systems. In particular, the detection of single protein might become the starting point for monitoring drugs, developing clean energy systems, fabricating bio-opto-electronic transistors, and other innovative devices and systems. The Fabrication of Nanogaps. NanoGap Electrodes (defined as a pair of electrodes separated by a nanometer-sized gap, NGEs) are fundamental tools for characterizing the electric properties of material at the nanometer scale, even at the molecular scale. They are also important building blocks for the fabrication of nanometer-sized devices and circuits. Molecular-based devices possess unique advantages for electronic applications with respect to conventional components [4], such as lower cost, lower power dissipation and higher efficiency. Specific molecules can be not only recognized, but also self-assembled on such NGEs, thus leading to elaborated geometries for the study of distinct optical and electronic properties. A variety of specific electronic functions performed by single molecules, including rectifiers [5],[6], switches [7],[8] and transistors [9]-[12], have been designed and studied. Devices based on NGEs [13]-[16], with functional molecules inserted in the desired positions, have great potential as building blocks for super-integrated circuits, and thus can be more likely used in practical applications. Moreover, since the NGEs are fabricated before the molecular component insertion, the junction can be characterized with and without molecules in place, thus facilitating the distinction of the intrinsic molecule properties. As most of the NGEs present a planar configuration, it would be easier to take the underlying substrate as a gate contact to tune the electrical properties of the molecular components. Furthermore, these structures do not require feedback to maintain the mutual arrangement (comparing with conducting tips' Atomic Force Microscope) and are less stochastic with respect to electrochemical cells. Typical dimensions of target molecules are well below 5 nm, and the fabrication of gaps around this dimension is very challenging, since it goes beyond the capability of traditional microfabrication technologies. In addition, if the gap is too small, molecules can be deposited in a tense and distorted state, resulting in unexpected performances. Several effective and creative methods of fabricating NGEs with ...