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THE first chip to be made of diamond has been built by Swedish researchers,
who say it is a crucial step towards the goal of creating a 鈥渓ab-on-a-chip鈥�.
These portable devices will be able to analyse tiny samples quickly and easily
in remote places. They are likely to be used to monitor disease or pollution, or
to analyse DNA.

The diamond chip, which is about the size of a book of matches, analyses
proteins by ionising the molecules and subjecting them to an electric field.
This separates positive and negatively charged ions and pulls the lighter
molecules more quickly than the heavier ones.

The team created their diamond chip by depositing carbon vapour onto a
silicon mould in a vacuum. By building up the structure in layers and removing
the silicon chemically, the were able to create complex three-dimensional
devices.

Any material used to build a lab on a chip has to be extremely versatile. It
needs to have good surface properties to allow the fluid to move easily, and it
mustn鈥檛 contaminate the tiny sample. It must have excellent thermal properties
to dissipate heat, and good optical properties so that materials can be
identified by their fluorescence. On top of all that, it must have the right
kind of electrical properties to be able to manipulate fluids with electric
fields.

鈥淯nlike other materials, diamond has all these properties,鈥� says Klas Hjort,
a materials scientist in the 脜ngstr枚m Laboratory at Uppsala University,
Sweden, who leads the team that built the diamond microchips. 鈥淲ith diamond
chips we can use stronger electric fields because the heat dissipates so well,鈥�
says Stellan Hjert茅n, a biochemist who is part of the team. 鈥淭hat means
we can carry out the separation more quickly using smaller samples.鈥�

Researchers who have used glass to build their labs-on-a-chip have found that
attaching electrodes disrupts fluid flow at these small scales. But with
diamond, electrodes can be created by doping with boron to create conducting
areas.

Using diamond for the entire structure keeps the properties of various parts
of the device consistent. 鈥淭he surface properties of microfluidic devices are
very important,鈥� says Hjort.

Unlike silicon, diamond structures will not allow currents to leak. 鈥淚t is
very difficult to get good, thick insulating layers on silicon and you are
always afraid of ionic contamination,鈥� says Hjort. 鈥淲e have had several groups
specifically ask us to build devices without using silicon.鈥�

Andrew De Mello, a chemist specialising in microfluidics at Imperial College,
London, says the work done by Hjort鈥檚 team is impressive. 鈥淲hen you get down to
carrying out reactions your structural material needs to be very robust and
diamond is obviously very inert,鈥� he says.

鈥淭he biggest challenge ahead is to improve the quality of our diamond,鈥� says
Hjort. 鈥淏ut we think we know how.鈥�