Bioassays work on paper

New analytical techniques with ever smaller volumes, multiple functionalities, and the ability to run masses of assays in parallel, tend to rely on ever more expensive materials and equipment. Researchers at Harvard, US have now bucked this trend by developing a bioassay tool that can be printed on paper. 

Chemistry professor George Whitesides, famous for his numerous nanotech inventions including soft lithography, developed the printing technique. His group at Harvard used commercially available photoresist in place of ink. Photoresist is an insulating substance that polymerises under UV light and is routinely used in chip fabrication. 

In this application, however, the researchers used the photoresist for its water-repelling property rather than for its electronic qualities. They printed a small trefoil-shaped pattern including three interlinked reaction chambers and a capillary stem onto commercial chromatography paper. Finding that the entire paper had become somewhat hydrophobic after the printing, they had to introduce an additional oxidative cleansing step to neutralise any unpolymerised photoresist. 

The Harvard group demonstrated possible applications of the technique by using the miniature trefoil pattern, just over one centimetre wide, to analyse urine samples for glucose and protein, using established colour reactions.

This paper patterning offers an intentionally simple approach. ’We are interested in trying to develop the lowest cost, simplest assays that we can,’ Whitesides told Chemistry World. Even the photoresist technology may ultimately be replaced, he said, by the highly optimised techniques currently used for printing newspapers and magazines. The hope is that such paper-based diagnostic assays could provide a more affordable alternative to existing clinical methods, especially for health monitoring in developing countries and in all places far from hospitals equipped with expensive technology. 

Dominique Vanhecke of the Max-Planck Institute for Molecular Genetics in Berlin, Germany, sees great potential for the new development. ’The method is appealing as it offers the prospect for the production of cost-effective and low-tech biological or clinical assays,’ she told Chemistry World. ’Some further work has to be done to evaluate the reproducibility of the assays performed on such patterned paper, the shelf life of the modified paper and the reagents applied to it and the development of objective read-out systems compatible with its low-tech application,’ warned Vanhecke. ’However, the application of the technique appears infinite as patterned paper could not only be used for the development of various multi-reagent based assays but also for the collection, transport and storage of DNA and RNA containing biological samples such as fresh unconcentrated clinical samples.’ 

Michael Gross