US scientists have developed a method for storing dry reagents on low-cost disposable cards. They claim the cards could be used for point-of-care diagnostics in the developing world, where high temperatures and a lack of refrigeration make it difficult to preserve reagent functions.

Samples containing malaria antigens pumped through the card cause red spots to form on the card

Paul Yager and colleagues from the University of Washington, Seattle, and Boston College, Chestnut Hill, demonstrated that their storage system works in an automated on-card microfluidic test for malaria. The card's main components are a porous membrane patterned with malaria antibodies and a fibrous pad containing gold-antibody conjugates in sugar. The sugar stabilises the dry conjugates and preserves their function as labelling agents. When Yager pumped samples containing malaria antigens through the card, the conjugates bound to the antigens, causing red spots to form on the card. They used a scanner to capture images of the cards and calculate the changes in spot intensity.

'The proposed on-card dry reagent storage method is a good solution for reagent storage issues,' says Christopher Ko, an expert in microfluidics and molecular diagnostics at the Samsung Advanced Institute of Technology, Suwon, South Korea. 'Of course, in order to be useful in the developing world, much more, in addition to dry reagent, is needed, such as eliminating the costly microfluidic pumps and scanners used in this study,' he adds.

Yager's team are working to develop a diagnostic system called the DxBox, which consists of a portable reader and disposable test cards. They aim to incorporate both immunoassays and nucleic acid assays on to the cards to allow them to test blood samples for multiple diseases at once.

'Our target markets will be under-resourced communities in areas such as rural India, Brazil and sub-Saharan Africa,' says Dean Stevens, a scientist in Yager's team. 'Our goal is to make the portable reader and each card fit within a reasonable diagnostic budget - a dollar per card would be an ideal, if challenging, goal.'

Freya Mearns

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