Scientists in Switzerland have developed a one-step microfluidic chip that can detect disease markers in a single drop of blood serum. The chip could be used for cheap, quick and versatile point-of-care diagnostics, they claim.

The chip, made by Emmanuel Delamarche and Luc Gervais from IBM Research, Rüschlikon, contains capillary valves and pumps plus two types of antibodies - detection antibodies (dAbs), which fluoresce under light excitation, and capture antibodies (cAbs). When the pair introduced a serum sample on to the chip, capillary forces drew it into the microfluidic channel, where the dAbs bound to complementary analytes in the serum. The analyte-dAbs complexes then flowed through the chip into the cAbs-patterned reaction chamber, where they were captured and the fluorescence measured using an external fluorescence reader. This one-step fluorescence immunoassay could simplify disease diagnosis, claims Gervais.

The device only requires sample addition to trigger a cascade of events powered by capillary forces

The duo demonstrated that the chip can detect C-reactive protein, an inflammation and cardiac marker, at a concentration of 10 nanograms per millilitre in less than three minutes. It can even detect concentrations lower than 1 nanogram per millilitre within 14 minutes.

Most point-of-care devices currently available require large sample sizes and off-chip processing or can only detect a small number of markers. 'The main novelty is that this is an autonomous device that only requires the addition of sample to perform analysis,' states Gervais, adding that it needs only five microlitres of sample. The system can draw the sample in without introducing air bubbles, a known problem in microfluidics. Gervais also draws attention to the system's versatility: 'You could have 16 different capture antibodies and analyse up to 16 different analytes.'

'It is a very powerful system because it's very sensitive and extremely easy to use,' says David Holmes, a microfluidics expert at the University of Southampton, UK. 'You can have sample preparation, sample labelling, sample analysis all done in the one chip, rather than moving from test tube to test tube.'

Gervais says they now plan to try the device with difference disease markers and improve its range of detectable concentrations.

Yuandi Li

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