Tag Archives: chromatography

How do you scratch an electronic nose?

I don’t know, but I thought that was a pretty catchy lead in for introducing some new technology that could help “sniff out” dangerous chemicals in the environment and possibly even detect explosives from their trace chemical signatures.

Imagine, if you will, a machine the size of a small automobile and costing significantly more, shrunk down to the size of a postage stamp, costing a few hundred dollars.  Oh, and did I mention that they do the same thing?  Well, they do.

That’s what Dr. Masoud Agah and his team have been working to accomplish.  Using an NSF Career grant, Agah is trying to develop materials, structures and processes that will result in a gas chromatograph that could fit easily inside your cell phone.

Chromatography is a technique used to separate out individual chemical components from a mixture.  The mixture, which can be a liquid but in this case is a gas, is basically forced through a tube (called a column) that has been filled with a special material called a stationary phase.  The stationary phase is chemically treated to react with the sample as it flows by, slowing its progress down slightly through this temporary interaction.  Each component of the mixture will react with the stationary phase slightly differently, which means that the different components will take different amounts of time to flow through the column.  If you make the column long enough, all the different components of the gas mixture will come out at different times.  This allows you to either analyze the mixture for its constituents, or even collect each of them into a different container, in effect producing purified gasses from mixtures.

In Agah’s lab, he has found a way to pack all that scientific goodness into a very small space, using manufacturing techniques originally developed for the computer-chip industry.  Agah etches tiny trenches in silicon wafers that replace the chromatographic column described above, and then coats them with a special molecular material that functions as the stationary phase.  Because the trenches are microscopic, he can etch very long channels by simply arranging them in tiny spiral structures.  That way, he can get many inches of column length onto a structure the size of a postage stamp.  And, they are very inexpensive to fabricate.

So what, you say.  Well, let me tell you.

Let’s say you are a passenger in a commercial airplane on your way from somewhere to, oh, say,  Detroit.  And it’s Christmas Day.  And let’s say that another passenger has hidden on his person in very intimate places, some materials that when mixed together could explode.  Wouldn’t you be happy to know that such a person has been screened out of the passenger line before you boarded the plane by a security person with a handheld wand that can sniff out one part in a trillion of the potentially explosive materials?

If Dr. Agah is successful, and of course if some company steps up to take his technology to the market, then this scenario could be a reality someday in the not-too-distant future.

Leave a comment

Filed under Materials, Sensing

Tiny structures have big impact on environmental sensing

Micro-electro-mechanical systems (MEMS) are microscopic structures fabricated by etching away tiny amounts of silicon using similar processes as are used to make computer chips.  These small electronic and mechanical structures are already being used in a number of commercial applications such as, for example, the sensors used to deploy airbags in an automobile crash.

But the use of MEMS in sensing applications goes much farther than that.  At Virginia Tech, two different research groups are applying these techniques to create tiny, ultrasensitive devices to detect chemical and biological materials for medical, environmental and security applications.

Dr. Masoud Agah, under an NSF Career grant, has been working on developing many MEMS devices in his MicrON research group.  The current research at VT MEMS Lab centers on the development of CMOS-compatible three-dimensional silicon micromachining techniques, smart microchip coolers, micro gas analyzers for environmental and healthcare applications, and biochips for cancer diagnosis and cancer treatment monitoring. In addition, the lab is pursuing research to merge MEMS (top-down approach) and nanotechnology (bottom-up approach) in order to enhance the performance of the microsystems.

In the Center for Photonics Technology (CPT), Dr. Anbo Wang‘s group is using the same fabrication techniques to create tiny sensors on the tip of an optical fiber only a couple of microns in diameter.  In one of CPT’s latest inventions, the MEMS structure is used to detect trace amounts of chemical and biological materials, as well as serving as a tunable optical filter.  The new device is activated using only light traveling inside the fiber, and so requires no external electrical or mechanical energy, making it perfect for applications in hazardous or remote  environments.

Both of these MEMS technologies create the opportunity to improve detection of trace materials, and will be important in medical and environmental sensing applications, including those relating to security.

1 Comment

Filed under Materials, Sensing