It鈥檚 small, square, made of silicon, and it鈥檚 an amplifier 鈥� for DNA.
These chips, which measure less than 10 millimetres across, contain a reaction
chamber, heater, and sample and reagent inputs 鈥� all the elements needed
to perform the polymerase chain reaction (PCR), a standard method of making
thousands or millions of copies of fragments of genetic material.
The technique is widely used: to make enough material for a 鈥楧NA fingerprint鈥�
in forensic work, for example, or in the study of ancient genetic material.
Standard PCR instruments are the size of a mic-rowave oven, cost about
$10 000 and run on mains electricity. But Allen North-rup, an engineer at
Lawrence Livermore National Laboratory in California, has put the essential
components onto a chip which consumes about 1 watt. 鈥楾he next step will
be to incorporate the reactor chip into a handheld, battery-powered portable
diagnostic kit,鈥� he says.
Advertisement
Roche Molecular Systems of Alameda in California is now developing ways
to read the DNA as it is synthesised on the chip. One potential use is testing
for viruses such as HIV. Tests have already been carried out with fragments
of HIV.
If the project succeeds, every hospital ward and molecular biology laboratory
could within a few years be equipped with a PCR device costing less than
$1000. As well as being smaller and cheaper than existing models, this
PCR-on-a-chip should be faster and more accurate than large versions,
which in the course of the amplification process heat and then cool test
tubes placed in blocks of aluminium. The metal鈥檚 mass makes precise temperature
control difficult.
But simply passing current through the silicon heats the well in the
chip where the DNA fragments are held, says Northrup. 鈥業t will amplify
samples in a few minutes, versus half an hour or more for today鈥檚 tabletop
devices. And we can control the heating of such small samples very accurately,
so it will copy the DNA with greater fidelity than today鈥檚 desktop instruments.鈥�
