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Shown are images produced from an analysis of lipids in a rat
brain tissue sample. The first (labeled a) is an optical image,
and the others are ion images created from desorption electrospray
ionization analysis of select lipids. Two-dimensional images from
the DESI technology, developed in the lab of Graham Cooks, further
the technology's potential applications for the detection of
diseases. (Image courtesy of Angewandte Chemie)
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This tool has a wide range of applications and
could be used in the future to address many medical issues, said
Graham Cooks, Purdue's Henry B. Hass Distinguished Professor of
Analytical Chemistry in whose lab DESI was developed.
"This technology could be used to aid surgeons in
precisely and completely removing cancerous tissue," he said. "With
these images, we can see the exact location of tumor masses and can
detect cancerous sites that are indistinguishable to the naked eye."
Current surgical methods rely on the trained eye of
a pathologist who views stained tissue slices under a microscope to
assess what tissue must be removed.
This study was the first to take the graphical data
presented by DESI mass spectrometry and turn it into a two-dimensional
image of the tissue, said Demian Ifa, a member of Cooks' research team.
"The ability to produce an image is a great advance,"
he said. "It is much more practical to have an image that can quickly
and easily be interpreted. It brings the technology much closer to
being ready for the clinical setting."
A paper detailing the study has been selected as a
"very important paper" by the journal Angewandte Chemie and is
currently posted online. Cooks, Ifa, Justin Wiseman, and Qingyu Song,
all from Purdue's Department of Chemistry, authored the paper, which
will be featured on the cover of the print publication. Less than 5
percent of the journal's manuscripts earn the very important paper
designation, according to the journal.
Several technical papers have been published about
DESI experiments since the method was announced two years ago as an
alternative to traditional mass spectrometry techniques.
Conventional mass spectrometry requires chemical
separations, manipulations of samples and containment in a vacuum
chamber for assessment. DESI researchers modified a mass spectrometer,
which is commonly used in biological sciences, to speed and simplify
the time-consuming and labor-intensive analytical process, Ifa said.
Mass spectrometry works by first turning molecules
into ions, or electrically charged versions of themselves, so they
have mass and can be detected and analyzed. The DESI procedure does
this by positively charging water molecules by spraying a stream of
water in the presence of an electric field. These charged molecules
contain an extra proton and are called ions. When the charged water
droplets hit the surface of the sample being tested, they transfer
their extra proton to molecules in the sample, turning them into ions.
The ionized molecules are then vacuumed into the mass spectrometer,
where the masses of the ions are measured and the material analyzed.
"Through analysis of the abundance of certain ions
and mass ratios, the contents of the sample can be identified," Cooks
said. "This information can be used to precisely determine the
location of cancerous tissue and borders of tumors."
In this study, researchers mapped the distribution
of fatty substances called lipids in a rat brain. The team was able to
create a high-resolution image with a spatial resolution of less than
500 micrometers, meaning the image distinguishes small details
separated by less than 1/100th of an inch. The researchers evaluated
the sample by spraying small sections of it with the charged water
droplets, obtaining data for each section and then combining the data
sets to create an analysis of the sample as a whole, Ifa said.
Software was used to map the information and create a two-dimensional
image showing the distribution and intensity of selected ions.
The team is now working on the technique to improve
the image resolution and has placed an instrument in the Indiana
University School of Medicine, Cooks said.
Cooks' research team has also designed and built a
portable mass spectrometer using the DESI technology. It is roughly
the size of a shoebox and weighs about 40 pounds, compared to around
600 pounds for a conventional mass spectrometer. The portable
instrument runs on batteries and can be carried anywhere, allowing the
technology to more easily be used for field applications like
explosives detection.
Cooks' most recent DESI research was conducted in
Purdue's Bindley Biosciences Center at Discovery Park and is
associated with Purdue's Center for Sensing Science and Technology.
Funding for this research came from the Office of
Naval Research and the Indianapolis company Prosolia Inc., which is
commercializing DESI. |
