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An interdisciplinary research team from the Schools of Engineering and Chemistry at the University of Edinburgh (in association with Nanoflex Ltd), has overcome some of the constraints associated with conventional nano-scale electrode arrays, to develop the first precision-engineered nanoelectrode array system with the promise of high-volume and low-cost.*
Such miniaturised electrode arrays have the potential to provide a faster and more sensitive response to, for example, biomolecules than current biosensors. This would make them invaluable components in the increasingly sensitive devices being developed for biomedical sensing and electrochemical applications.
Typically, the signal from a single nanoelectrode is too small to be readily sensed. However combining the outputs from a large number of identical nanoelectrodes means that their collective output is large enough to be easily measured. Traditionally the production of arrays of well-defined, reproducible nanoscale structures is extremely expensive due to its use of state-of-the-art lithographic tools. However, depositing uniform films of conductive and insulating materials, of well-controlled nanoscale thickness, has been relatively straightforward for a long time.
Therefore the University of Edinburgh research team worked on the premise that electrodes with an exposed nanoscale surface in the vertical plane, rather than the horizontal, could be readily achieved using more widely available micro-lithographic systems. This was the core premise of the research programme that has led to the development of the Microsquare Nanoband Edge Electrode (MNEE) array technology.
Their paper in IET Nanobiotechnology describes the development of the MNEE array, which is made up of a conductive film of nano-scale thickness, sandwiched between two micro-scale insulating layers. The nanoscale edge is exposed by etching vertically through the upper insulating layer and thin conducting layer, and through to a specified depth into the lower insulating layer. This results in an exposed band of the nanoscale conducting layer around the complete perimeter of the square cavity at a known depth.
The arrays are made up of a rectangular pattern of these square cavities which, using this method, can be manufactured quickly, repeatably, cost-effectively and in high volume.
In addition to detailing the method of manufacture of a MNEE array the paper demonstrates it to be a sensitive bioelectroanalytical detector. Each MNEE array combines the best properties of microelectrodes – such as steady-state response – with those of nanoelectrodes – including high-diffusional rate and high signal-to-noise ratio, while avoiding the low current limitation of single nanoelectrodes.
In future, by substituting low temperature fabrication techniques for some of the existing high-temperature processes, it will be possible to integrate MNEE arrays with complementary metal oxide semiconductor (CMOS) silicon chips. This will pave the way for smart, low-cost, high-performance nanoelectrode array systems in, for example, the same way that CMOS-compatible imaging chips paved the way for ubiquitous camera phones.
Acknowledgements
The work is part of a larger R&D programme on the development of smart sensors at the University of Edinburgh. It involves staff and students from the Schools of Engineering and Chemistry thus providing the required broad set of skills and experience. The resulting MNEE technology is currently being commercialised by Nanoflex Ltd.
*This piece was based on the article, Nanoscale electrode arrays produced with microscale lithographic techniques for use in biomedical sensing applications, published in IET Nanobiotechnology, Vol.7 issue 4, with permission of the Institution of Engineering and Technology. It will be free to view until the end of September.
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