Pocket of resistance

The solution to HIV diagnosis in the third world could be provided by a portable protein detector powered by a nine volt battery.

The cost-effective Pocket uses a combination of silver-based chemistry, a diagnostic chip, and an optical sensor to do the same job as bulky, expensive and resource-hungry hospital machinery – at a fraction of the time and cost.

Researchers at Harvard University hope that their system, which has taken 18 months to develop, will provide a solution to diagnosis problems of infectious diseases – particularly in the third world where the infrastructure tosupport large-scale hospital machinery often does not exist.

A prototype of the device has been tested at Harvard with the HIV virus, but the researchers claim that the process is the same for any other infectious disease. A blood sample is applied to 2mm channels in the diagnostic chip, which is specially prepared with a ‘stripe’ of protein fragments from the HIV virus.

As the blood moves past this stripe, HIV antibodies in the blood sample – if there are any – bind tightly to the protein fragments on the stripe.

A second type of antibody – which recognises the antibodies, sticks to them and marks them with tiny gold spheres – is then added to the channels.

A solution of silver nitrate and an oxidising agent are then applied. Where the gold spheres are bound to the HIV molecules, the gold catalyses the oxidation of the silver ions to metallic silver, which deposits on to the walls of the channels.

A small red laser diode then shines light through the channels, and an integrated circuit with a photodetector registers how much the light is diminished by the silver layer. This allows the number of HIV antibodies to be quantified, just as precisely as laboratory methods but much quicker. An LCD shows the results.

‘Current laboratory diagnostic processes are mostly not suitable for use in developing nations; aside from the high cost and complex equipment, the necessary infrastructure, such as a power supply, is often lacking,’ said head researcher Professor George Whitesides.

Although the prototype is not yet ready for use outside of the laboratory, Prof Whitesides says that Pocket will run from a nine volt battery, and its components can be bought for a total of $45 (£23).

The researchers are now looking at the commercial viability of the device.

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