The Chemistry of the test process.

The development of the colorimetric dipstick bioassay is based on the printing of enzyme-doped silica "inks" containing small gold nanoparticles that are co-entrapped with the enzyme and printed on a paper substrate.

The bioactive dipstick is immersed in a solution containing the test analyte (a substrate for the enzyme) and a Au(III) salt. It produces a product that leads to reduction of the Au(III) onto the entrapped nanoparticles, producing particle growth and a corresponding increase in colour intensity. Shades of colour can be correlated to the amount of substrate or enzyme inhibitor present.

This is the first demonstration that gold nanoparticles can be grown when entrapped in silica and the first report of sol-gel-based inks being used to produce a dipstick-based bioassay.

Preliminary results show that the assay is sufficiently sensitive to allow detection of our test compound either by eye or with a digital camera and image analysis software in approximately five minutes--avoiding the need for expensive and sophisticated instrumentation.

John Brennan, MCIC

Daniel Drolet is an Ottawa writer whose work has appeared in more than two dozen newspapers and magazines across Canada in the last year.