Biological-microscopy-capable Nanoelectronic Devices

Advanced biosensors featuring nanoscale electronic devices have been the subject of intense research interest for many years. For the most part, such devices have been developed on traditional Si/SiO2 substrates for use as purely electronic sensors without any capacity for simultaneous optical microscopy. In parallel, biological microscopy has made major leaps forward both in resolution and the simplicity and reduced cost of the infrastrucure, for example, 3D printed high-resolution microscopes using cellphone cameras are a thriving development frontier. Biological microscopy methods use ultrathin glass, a highly unconventional substrate for nanoscale electronic devices. This 'substrate mismatch' has led to nanoscale electronic biosensors and advanced biological microscopy evolving in isolation despite an interest in similar biological targets and questions. We are currently working on nanoscale electronic devices designed such that biological microscopy can be performed at the device simultaneously with the electrical measurements.


Novel Materials for Electronics

Conduction in electronics is all about electrons but in biological systems it's all about ions because free electrons don't remain free long enough in those systems. An important challenge in bioelectronics is thus the transduction of electronic signals into ionic signals and vice versa. Nanomaterials, e.g., semiconductor nanowires or carbon nanotubes, can have an interesting role here. Their high surface-to-volume ratio means electronic conduction is readily influenced by their external ionic environment. This can be mediated by ion-conductive polymer materials to enable devices with solid-solid ion-to-electron transduction interfaces. We began in this direction by making the first nanowire transistors with multiple independently controllable ion-gel gate structures, first with poly(ethylene oxide), and more recently using the ionomer Nafion. We are presently exploring other ion-active materials both for coupling with traditional semiconductors and independent use.


Beyond Semiconductor Nanowire Devices

Semiconductor nanowires have been a focus of major efforts internationally for many years. All the way through this nanowires were nanowires, high-aspect ratio rod-like structures with nanoscale diameter and microscale length, with their growth on a crystalline substrate templated either by a metal nanoparticle or a hole in an amorphous oxide mask. We have recently been working on an interesting variant of the oxide mask approach where a rectangular slot in the mask is used to grow a 2D nanofin. These structures are essentially a nanowire that is 'stretched' in one direction in the sense that the growth mechanics, crystal structure and faceting is the same as a nanowire but the resulting object is 2D rather than 1D. These nanofins can be transferred to sit flat on a separate substrate, and then used as 'nanoscale Hall bars' for the creation of device structures that aren't possible with nanowires due to their limited dimensionality.