Dielectrophersis Control of InAs based Nanowires for bio sensing

Semiconductor devices are increasingly being utilized in healthcare based sensor applications due their excellent ability to detect minute changes in their surroundings due via alterations in their electrical and optical properties. Recently there has been much interest in semiconductor nanowires, these wires are grown vertically upwards from a semiconductor surface, with nanowires having been demonstrated from a range of compound semiconductors including, Gallium Arsenide, Gallium Phosphide, Indium Arsenide and Indium Antimony. Growth of these wires is initiated either by initially depositing tiny metal droplets on the surface or by forming nanoscale holes in an oxide mask. The resultant nanowires can have lengths in excess of 1um and diameters below 100nm.

These nanowires are of particular interest for bio-sensing and healthcare applications for a number of reasons, firstly their small size makes them ideal to integrate molecules and other optical and electrical components. Secondly due to the cylindrical shape of the wires the majority of the charge resides on the surface making them especially sensitive to changes in their environment, for example arising from the presence of differing bio-markers.
However the vertical nature of the growth and resultant device geometry severely limits the exploitation of these nanowires as the nanowires are routinely planarised and encapsulated under a polymer layer. This results in a relatively large final device and also supresses much of the surface charge.

The proposed work here offers a step-change in the development of nanowire based sensors and devices by utilizing the process of dielectrophoresis. This is a process whereby the application of a non-uniform electric field results in a force upon a charged particle. By appropriately controlling the electric field it is possible to utilize this process to accurately move and position particles. To achieve this the nanowires will be removed from their native growth substrate and then dispersed in solvent before undergoing dielectrophoresis to position the wires at pre determined positions. This offers an attractive route to undertake nanowire bio-sensing and monitoring due to the ability to integrate the nanowires directly with microfluidics and other optical or electrical systems thus exploiting the accurate and reliable positioning offered by this technique.

A further advantage is that nanowire devices formed via this technique can be achieved in a horizontal rather than vertical configuration. This will make integration with other components much more straightforward and also enable the whole surface of the nanowire to interact with its environment, greatly enhancing the sensitivity of the wires to any changes in their environment. These potential benefits offer the possibility to greatly enhance the performance of nanowire based sensors and devices as well as enabling to be fabricated more efficiently and at a reduced cost.

Specifically this project aims to fabricate nanowire devices via dielectrophoresis, establishing relationships between the process parameters and the final devices electrical, optical and physical characteristics, opening a route for predictable device fabrication. Finally nanowire devices will be integrated with microfluidic systems to demonstrate an ionic flow sensor, allowing both the concentration and flow rate of liquids to be monitored in a compact lab on a chip device.

The semiconductor photonics industry is a critical area of the UK and EU economy which is estimated to reach over 600 billion Euros by 2020 and currently employs over 300,000 people directly, with a total impact of around 30 million jobs (figures for the EU). The EU has a number of world leading companies with global market share in some areas as high as 40%. Photonics is at the heart of solutions for a number of key societal challenges including healthcare, digital security, energy generation, energy efficiency, and climate change. Maintaining the competitiveness of the UK and EU semiconductor industry requires the continuous development of new materials, structures and devices with much of the fundamental research occurring in universities. Exemplary immediate impacts that we aim to generate include:

Training: There is an urgent need to train over 100,000 engineers and scientists each year to power the UK economy. This project provides ideal career development opportunities for the PDRAs and the students. The benefits will include enhancing their research methodologies, PhD completion for the students and communication of results at international conferences and appropriate high impact international journals. A number of students pursuing Bachelor and Master degrees will also benefit directly from this project by working on smaller scale research projects.

Economic: The worldwide semiconductor market was worth $335 billion in 2015 and is expected to grow to $390 billion by 2019. Semiconductor sensors currently account for $9 billion of the market and is expected to be one of the strongest growing sectors of the market over the coming years with growth predictions of around 4% per annum over this time frame. Similarly bio sensors is a rapid growing market with a large number of major companies investing in and developing new technologies especially for rapid diagnosis and point of care health based applications (for example Philips Healthcare, Roche, and Abbott). The applicant has undertaken some initial discussions with these companies to begin to raise interest and awareness of the potential of III-V nanowire based devices for bio sensors. To further develop and formalize these discussions it is intended to organize and hold a workshop towards the end of the project to fully disseminate the results and facilitate discussions to further commercialize and exploit the research.

Societal: The long term aims of this proposal have the potential to realize a new generation of biological and medical sensors that can be utilized in low cost, compact and highly efficient lab-on-a-chip systems for rapid and remote diagnosis. The research developed through this proposal will also have the potential to influence a range of other fields through the development of new semiconductor devices, for example telecommunications, defence and environmental monitoring. As such the results generated will be of direct benefit to developing a healthy, resilient and connected nation and therefore industry, government and the public will all have a strong interest in the work. The Semiconductor group at Liverpool has a number of formal and informal collaborations with major research institutions worldwide, the university also has extensive expertise in the health sciences and the associated development of biosensors, again with well-established partnerships with research groups worldwide and NHS institutions. The applicant intends to utilize these networks and contacts to enable interaction and dialogue with interested parties and to develop new collaborations. The University of Liverpool has also recently launched a new research to business incubator named Sensor City, which will provide a hub for small and medium sized companies to interact with university research in the area of sensor technologies.