[tt] 'Sketch your own' lab-on-a-chip could save lives

[Eugen Leitl]

http://technology.newscientist.com/article/dn14790-sketch-your-own-labonachip-could-save-lives.html?DCMP=ILC-hmts&nsref=news4_head_dn14790


'Sketch your own' lab-on-a-chip could save lives

    * 12:24 23 September 2008

    * NewScientist.com news service

    * Colin Barras

A microfluidic device in paper: the "Africa" pattern is placed over
photoresist-soaked paper. Where exposed to sunlight, the resist becomes
impermeable, leaving a network of channels (Image: Lab on a Chip)

Simply putting pen to paper on a sunny day offers a way to make lab devices
to help test for disease.

Devices for testing water quality and identifying pathogens can now be made
using the right paper, ink and sunlight. The method could help developing
countries access the latest lab techniques.

Microfluidic chips are blocks of glass or plastic containing labyrinths of
tiny channels no more than a few hundred micrometres in width.

These channels can manipulate fluids with great precision, thanks to
capillary forces that draw liquid through the chip and a lack of turbulence
at small scales. Such chips offer a way to shrink down and streamline lab
procedures involving several steps, such as testing for disease bacteria DNA.
Several solutions can be loaded into one chip, and the results read out not
long after.

However, making these delicate devices is complicated and expensive, so they
do not reach remote areas of the developing world where they offer greatest
benefit.

Usually, a copper mould of each design is needed to cast the chips out of
plastic. Now, though, researchers at Harvard have developed a simple way to
make the devices out of paper instead.  Masked marvel

George Whitesides and colleagues realised that the pores naturally present in
paper can carry liquids in a similar way to standard chips.

All they needed was a way to make impermeable "walls" to confine the fluids
into narrow channels. They achieved this using a polymer liquid that sets
hard when exposed to UV light, called photoresist. It is used in industry to
etch designs onto silicon chips.

To make the paper chips, the researchers soak a piece of normal office paper
in photoresist. They then cover one side with a transparency and draw the
desired pattern of channels on top with a pen.

When the paper is exposed to sunlight, the photoresist sets hard, apart from
the area of the paper that is masked beneath the inked-on pattern. The
transparency is then peeled off, and the paper quickly washed to remove any
still-liquid photoresist.

The final product, once dried, is a sheet of impermeable paper with a tiny
network of permeable channels embedded within it – in other words, a
microfluidic device.

Drawing onto the transparency by hand is, of course, not very precise. But
Whitesides says designs could simply be printed onto the transparency using
an inkjet printer.  Thinking ink

"Paper-based microfluidic devices probably won't be sensitive enough to
detect every disease, but they are sensitive enough for many useful
applications," says Andres Martinez, one of Whitesides' colleagues.

Aaron Wheeler, a microfluidics expert at the University of Toronto in
Ontario, Canada, is impressed with the idea. The Whitesides group has helped
popularise microfluidics over the last decade, he says.

Wheeler is also interested in making microfluidic devices more accessible.
And he, too, is using ink, but his team is attempting to find a cheap and
simple way to create the traditional copper moulds.

In his latest work (Lab on a Chip, DOI: 10.1039/b804050h), a pattern is inked
directly onto the sheet of copper before a chemical is used to etch away a
thin layer from exposed areas. Copper beneath the ink remains intact, forming
an embossed pattern that is used to cast microfluidic devices from plastic.

Journal reference: Whitesides paper: Lab on a Chip (DOI: 10.1039/b811135a)