Porous Silicon Lights Way For New Analytical Devices
Researchers at Purdue University (West Lafayette, IN; 765-494-5302) and the Scripps Research Institute (La Jolla, CA) have discovered a technique called desorption ionization on silicon (DIOS). Based on pulsed laser desorption/ionization from a porous silicon surface, the technique streamlines analytical analyses and provides new tools for molecular pharmaceutical analyses and lab-on-a-chip development.
About DIOS (Back to Top)
Desorption mass spectrometry has undergone significant improvements since the original experiments were performed over 90 years ago, the most dramatic change occurring in the early 1980s with the introduction of an organic matrix. Most recently, Purdue University chemist Jillian Buriak, an assistant professor of chemistry, teamed with Jing Wei and Gary Siuzdak of the Scripps Research Institute to develop DIOS as a new desorption/ionization strategy for biomolecular mass spectrometry.
DIOS uses porous silicon to trap analytes deposited on a sample surface. Laser radiation then vaporizes and ionizes these molecules. DIOS has been demonstrated for biomolecules at the femtomole and attomole level with little or no fragmentation, in contrast to what is typically observed with other direct desorption/ionization approaches. The ability to perform these measurements without a matrix makes DIOS more amenable to small-molecule analysis. Because porous silicon can be easily chemically and structurally modified, it can optimize the ionization characteristics of the sample surface for biomolecular applications.
"This is the first application that combines the unique properties of porous silicon with the capability of mass spectrometry for biochemical analyses," Buriak says. "Our technique can dramatically simplify many of these processes and will allow scientists to simultaneously test large numbers of compounds in a fraction of the time required by current methods."
In 1998, Buriak developed a way to stabilize the surface of porous silicon so that it can withstand the rigors of industrial use. Earlier this year, she developed ways to use white light to perform specific chemical reactions on porous silicon by exposing the surface to certain compounds.
While investigating the light-absorbing characteristics of porous silicon, Buriak teamed with Siuzdak, who uses mass spectrometry to study biomolecular complexes. Buriak and Siuzdak found that porous silicon not only stood up to the high buffer conditions required by living molecules, but also could be used in place of traditional matrix substances for a wide range of biomolecules--including sugars, peptides, drug molecules, and other small molecules. In addition, the porous silicon matrix did not generate the background ions, or "noise," associated with other matrix substances used with mass spectrometry techniques.
"We've shown that you can replace a number of matrices with just porous silicon for a wide range of compounds," Buriak says. "This may allow researchers to automate some processes that now require human intervention."
Applications (Back to Top)
DIOS allows researchers to use matrix-assisted laser spectrometry for small-molecule analyses, such as those conducted by pharmaceutical companies to develop drugs. Before this technique, matrix-assisted laser spectrometry had limited use for analyzing low-molecular-weight molecules, because the matrix caused significant interference, making it difficult to distinguish the matrix from the sample, Buriak says.
Because most current computer technology is based on silicon, DIOS can be incorporated easily into manufacturing processes already in place, Buriak says. Porous silicon might also be combined with new upcoming technologies, such as micro-fluidic devices, to create lab-on-a-chip technology.
The research was reported in the May 20, 1999, issue of Nature.
For more information, call Jillian Buriak at Purdue at 765-494-5302, or e-mail her at buriak@purdue.edu.