Membrane aids miniaturisation of diagnostic devices

A silicon membrane developed at the University of Rochester is set to help in the development of diagnostic devices the size of a credit card.

The ability to shrink laboratory-scale processes to automated chip-sized systems would improve biotechnology and medicine but one of the challenges of so-called lab-on-a-chip technology is the need for miniaturised pumps to move solutions through micro-channels.

Electroosmotic pumps (EOPs), devices in which fluids move through porous media in the presence of an electric field, are suited for this because they can be miniaturised.

EOPs however, require bulky, external power sources, which defeats the concept of portability but the silicon membrane developed at the University of Rochester could now make it possible to shrink the power source.

‘Up until now, electroosmotic pumps have had to operate at a very high voltage—about 10 kilovolts,’ said James McGrath, associate professor of biomedical engineering. ‘Our device works in the range of one-quarter of a volt, which means it can be integrated into devices and powered with small batteries.’

A porous membrane needs to be placed between two electrodes in order to create electroosmotic flow, which occurs when an electric field interacts with ions on a charged surface, causing fluids to move through channels.

The membranes previously used in EOPs have resulted in a significant voltage drop between the electrodes, forcing engineers to begin with bulky, high-voltage power sources.

The thin porous nanocrystalline silicon (pnc-Si) membranes used by McGrath and his team allow the electrodes to be placed much closer to each other, creating a much stronger electric field with a much smaller drop in voltage. As a result, a smaller power source is needed.

‘Up until now, not everything associated with miniature pumps was miniaturised,’ McGrath said in a statement. ‘Our device opens the door for a tremendous number of applications.’

Along with medical applications, it’s been suggested that EOPs could be used to cool electronic devices. As electronic devices get smaller, components are packed more tightly, making it easier for the devices to overheat. With miniature power supplies, it may be possible to use EOPs to help cool laptops and other portable electronic devices.

‘Due to scalable fabrication methods, the nanocrystalline silicon membranes are inexpensive to make and can be easily integrated on silicon or silica-based microfluid chips,’ added McGrath.

McGrath’s research paper is being published in Proceedings of the National Academy of Sciences.