Derek Bruzewicz and his colleagues have found a new application for the desktop plotter. They have used it to create an impressively simple microfluidics device that can be produced without a clean room or photolithographic equipment.

According to Bruzewicz and colleagues, second-hand desktop plotters can be had for as little as $50. Other simple components of their device are paper and the commonly used organic polymer poly(dimethylsiloxane), or PDMS, which is cheap, can be diluted in hexane solvent and is flexible when cured. The team's study is described in Analytical Chemistry (D. A. Bruzewicz et al. Anal. Chem. 10.1021/ac702605a; 2008).

The system works like this. By replica moulding, the pens of the plotter are replaced with PDMS versions that can deliver various types of 'ink'. The purpose of the ink, when cured, is to create channels in a filter-paper substrate, and after experimenting with the possibilities Bruzewicz et al. found that a syrupy mixture of 3:1 PDMS:hexane did just fine. Having chosen the appropriate paper, the trick then is to use the plotter to draw channel shapes, with the PDMS syrup penetrating the full depth of the paper to create water-tight chambers in various patterns.

One form the device takes is what the authors call a “dip star”. Filter paper is patterned with eight PDMS channels radiating out from the centre; in principle, each of these channels can be loaded with a different chemical indicator. The flexibility of the channels means that the paper can be folded, with the centre becoming one corner that can be dipped into the fluid to be assayed. The channels are at least 1 millimetre wide. In keeping with the guiding principle of the system, the readout equipment is similarly widely available: the human eye.

The authors have tested different types of the device with well-tried colorimetric assays for identifying excess protein and glucose in urine, and found they performed well, with no cross-contamination between channels.

Another pattern, shown here, is a variant on the dip star. It shows that channels can be printed over a large area of paper, and can be designed for loading by multipipette rather than dipping.