Introduction

The integration of conventional CMOS device with biological systems has the potential to revolutionise the way that sensing devices are perceived. As semiconductor devices shrink towards the scale of biological macro-molecules, it becomes realistic to suppose that a direct connection can be made between the proteins which govern the majority of biological functions and CMOS semiconductors (Fig 1a). The ability to monitor the behaviour of biological systems in vivo, in real time or to be able to monitor single molecule interactions, will be of massive benefit to the medical and pharmaceutical industries in the search for future drugs and therapies.

Since the structure function relationships of biologically important proteins are currently poorly understood we have developed a simulation method, based on Self-Consistent Brownian Dynamics, which is capable of simulating the trajectories of individual ions in complex simulation domains over biological relevant timescales. We aim to be able to simulate the interaction of ions in solution with semiconductor devices and we have used continuum drift diffusion simulation to demonstrate that it is possible to sense the position of individual ions using a double gate MOSFET.

Bio-Nano-CMOS Devices

(a)	(b)
Fig. 1 (a) The Kcsa bacterial potassium channel from Streptomyces Lividans acting as the second gate in a 4nm double gate Bio-Nano-MOSFET. Note that the relative scales are approximately correct. (b) Due to it's robust structure and the ease with which targeted mutations can be performed,α-Haemolysin is currently under investigation as a customisable sensor component.

Under the auspices of the Bio-Nano-Technology IRC we are currently investigating the possibility of using ion channel proteins in conjunction with nano-scale MOSFETs to directly sense the motion of charged carriers across membranes. Using the commercial Drift Diffusion simulator Synopsys taurus, we have investigated the effect of coupling a nano-scale MOSFET with a biological domain (Fig 2a), in order to discover whether we can: (a) Use the MOSFET to sense the position of charged groups and ions within the structure of the protein, and (b) Modify the MOSFET current based on conditions within the biological regions (Fig 2b).

(a)	(b)
Fig. 2 (b) The potential profile through a model Bio-Nano transistor. The double gate MOSFET has had it's top gate replaced with a channel mimetic structure in the Synopsys Taurus simulation package. These Drift diffusion simulations can then be used to investigate the properties and optimisation of these device configurations. (b) The sensitivity of the MOSFET drain current to the position of a single charge in the biological domain of the simulation.