Cells can be subjected to different chemical treatments in a continuous sequence using a chip designed by US scientists.

James Sturm and colleagues at Princeton University have tested a method that can handle complex sequential cell analyses.

An asymmetric arrangement of posts directs particles across multiple reagent streams

On-chip experiments produce faster results than conventional approaches and use smaller sample and reagent volumes. But their application to biological systems is limited because sequential treatments are often required, causing reagent mixing that is difficult to reverse.

Sturm's chip has an asymmetric arrangement of posts that causes cells to move across the surface at an angle. Parallel streams of reagents, known as microfluidic channels, flow over the chip so that the cells pass through each chemical zone without any cross-contamination.

Sturm's team demonstrated the technique could be used for labelling and washing a blood cell, which proved to be much simpler than other methods currently used. They also broke down a bacterial cell on the chip and removed the intact chromosome.

'For whole bacterial chromosome isolation, the method is without peer,' comments co-worker Keith Morton. He says he hopes the technique will advance whole chromosome research. The next challenge is to design a system capable of more complex reactions.

Harold Craighead of Cornell University, Ithaca, US, an expert in biomolecule microfluidics, says, 'This approach presents exciting new possibilities for continuous analysis of cells, bacteria, and biomolecules.'

Harriet Brewerton