A low-cost medical diagnostic device for conditions including Chlamydia and gonorrhoea promises to break the cycle of infection by returning results in 30 minutes.
The automated device, developed by Dr Julien Reboud, a Research Fellow at Glasgow University’s Division of Biomedical Engineering, can make a diagnosis with a small sample – such a finger prick of blood – and can be used by anyone without any specialist training.
On July 17, 2013, Reboud was joint winner of The Royal Academy of Engineering ERA Foundation Entrepreneurs Award for young business-minded researchers in electro-technology.
The device – dubbed Saw Dx – requires a low-cost, disposable microchip containing a sample to be placed into its reader, which would propagate ultrasonic waves across the chip.
The ultrasound agitates the sample it in a very specific way, depending what function is needed, such as temperature cycling of the sample or opening cells to release their DNA.
In doing so it removes the processing required in larger, laboratory-based diagnostic machines that can have a footprint of up to 1m2. Such machines process a large number of samples simultaneously but take a number of hours to return results. Similarly, finding the DNA of a pathogen also requires a number of steps to identify, amplify, and detect the anomaly.
Reboud said a degree of expertise is required to use the machines and a number of companies have tried to simplify and miniaturise the process with microfluidic systems.
He said, ‘The difficulty with lab-on-chip (LOC) – trying to make all of these functions into a microchip – is difficult because most of the actuation requires different mechanisms.
‘For example, if I wanted to move samples between two different stages in the device I would need a pump and I’d need channels.
‘Then at one stage I would do the extraction of DNA, which includes mixing reagents together – so this means two channels, two reservoirs, two pumps et cetera.
‘Then I’d need a different mechanism to do the amplification, which is based on temperature cycling, so it means we need a heater, which is usually a resistive heater so you need electronics. Finally, an optical set-up is required for detection.
‘So, in one test you’ve got three different actuation mechanisms that are put together. Usually it means this LOC is not LOC, its more like a chip surrounded by lots of instrumentation and its actually quite a large chip as well.’
By contrast Saw Dx is a shoebox-sized, single-step device powered by a rechargeable mobile phone battery that contains an actuation mechanism to create ultrasound. This, said Reboud, is done by applying a voltage through a piezoelectric material.
He said, ‘These soundwaves…are the same frequencies as the ones used in medical imaging for pregnancy, for example, but they actually travel at the surface so they are a bit like earthquakes…mechanical deformations [are made] at the surfaces.
‘What we do is put the disposable piece – the low cost microchip – in contact with that surface which carries the wave so the waves actually refract – a bit like an optical set-up or prism – into this microchip and then continue propagating in the microchip at the surface where the sample is going to be and so the sample gets actuated.
‘The clever bit is in using what we call acoustic holograms,’ continued Reboud. ‘These are microstructures – [photonic lattices] printed or etched on the surface of the disposable chip that actually do the shaping of the waves. When the wave attracts with this – to these structures – it can change shape and we can control this shape by controlling the design of the structures as well as the frequency of the wave. So by simply switching the frequency we can switch between different functions without requiring different actuators. It means the footprint of the chip becomes a lot smaller.’
Reboud said a Saw DX prototype is capable of a whole assay (analytical procedure) but only for one pathogen. This has impressed clinicians who are pushing for Saw DX to detect three and five pathogens and part of the £20,000 ERA award will be put toward this, plus the development of a multiplex assay.
Looking to the future, Reboud is in the process of creating a spin out and anticipates a two year ‘regulatory pathway’ to get Saw Dx onto the market. He added that initial production runs will be done in Scotland at relatively high volume manufacture, giving the chip – including reagents – a price point of approximately £5.
‘The reader itself is very cheap, all the components are off the shelf and costs maybe £200 to £300,’ said Reboud.
According to Glasgow University, the commercial potential for Saw DX is huge in the developed world – the molecular diagnostic test market was worth nearly $5bn in 2010. SAW Dx could potentially meet the growing demand for home tests for STIs – the Centers for Disease Control and Infection estimate that there are 19.7 million new STIs every year in the US alone.