Researchers Approach Lab on a Chip

Max Glaskin

Scientists striving to miniaturize equipment used in analysis systems have gained ground with the development of an optical emission detector on a glass chip. The device is 1000 times smaller than conventional devices and uses 10,000 times less power. The goal is to integrate the detector with on-chip gas chromatography.

The detector chip is being perfected by Andreas Manz and Jan C.T. Eijkel of the Zeneca/SmithKline Beecham Centre for Analytical Sciences at Imperial College, in collaboration with Herbert Stoeri at the Technical University of Vienna in Austria. Measuring just 14 x 30 mm, it uses a plasma to excite the molecules of the sample, and a photomultiplier tube from Hamamatsu Corp. of Bridgewater, N.J., measures the optical emission.

"The detection limit has now been improved to 3 x 10^-12 g/s in a volume of 50 nl," said Eijkel. "This sensitivity is the same or better than that achieved with a conventional flame ionization detector. We are now able to determine the concentration of most carbon-containing compounds using a very small sample."

The project, which began in 1997, has a way to go before completion, with commercialization of the work a distinct possibility. "Integration of the detector with a chip-based gas chromatograph is the next logical step, because it would eradicate the problems that can be caused by connecting two devices," Eijkel said. "It would be very nice if everything could be etched on one chip."

One difficulty is the short lifetime of the detector. Initially, sputtering caused the cathode to fail within 24 hours, but now the team, whose study was published in the July 15, 1999, issue of Analytical Chemistry, has a version that has run for 24 hours without problems.

The group is also trying to put more energy into the device. It uses just 10 mW, compared with 50 W in standard devices or even the 1 kW needed by inductively coupled plasmas for atomic emission spectrography.

"Unfortunately, at 10 mW we can only look at the molecular bands," said Eijkel. "We probably need more power to smash the molecules to bits so that we can see the atomic spectrum."