Pacific Northwest National Laboratory scientists
devise new imaging technique for biological sample
When trying to understand how cells respond to toxins,
scientists want to do as little sample preparation as
possible: preparing cells by immersing them in chemicals or
drying them out can erase vital information. At PNNL,
scientists proved that a new ionization technique they
developed in 2009 can provide a fingerprint and locate
proteins, amino acids, and other chemicals in cells that
make up tissues or microbial communities using mass
spectrometry. "The beauty of the technique is that it
doesn't require any sample preparation," said Dr. Julia
Laskin, who led the LDRD research project at PNNL. "Here,
you just take your sample, slice it, and put it in front of
the instrument for analysis."
Why it Matters
Known as Nanospray Desorption Electrospray Iionization
(nano-DESI), the technique efficiently allows scientists to
determine which molecules reside in a precise spot on a
sample. With this information, researchers can learn more
about how diverse biological samples, such as tissues and
microbes, respond to environmental factors. For example,
biochemists can see how the marine microbe Shewanella
oneidensis alters metals to remediate hazardous
materials in the soil, or how S. oneidensis can
change very soluble hexavalent uranium to less soluble
form, limiting its movement in groundwater. Another
opportunity lies with medical researchers learning how
nicotine and other toxins affect brain cells.
"Great discoveries often require great tools," said Dr.
Louis Terminello, who leads PNNL's Chemical Imaging
Initiative. "The discoveries needed to solve today's
problems aren't something that you're going to get by
eyeballing a sample."
From the start, the team was convinced that the liquid
bridge used in nano-DESI could be scaled down to analyze
small areas on biological samples. With adjustments, the
team scaled down the probe to analyze an area of 10
µm in diameter, about the size of a single red blood
cell or mid-sized bacteria. "With this probe, we are
getting down to individual cells,"
The team first analyzed rat brain tissues, which provide an
outstanding test case for the technique, because they are
very dense and yield high signals. The nano-DESI was able
to draw up and analyze the molecules from different regions
on the sample. Then, the team moved onto kidney tissues,
and again analyzed micrometer-sized areas.
With each sample, the nanoDESI generated reams of mass
spectra. Because existing software packages could not
process the data, the work fell to team member Brandi
Heath, who read the charts and determined the fatty acids,
amino acids, lipids, and other molecules that resided at
different locations on the tissue. "Compared to other
online liquid extraction techniques, nano-DESI has about an
order of magnitude better spatial resolution," Laskin
added. "It is comparable, spatially, to what laser-based
techniques can give."
The team is working on two efforts related to their work
with nanoDESI, including understanding and visualizing the
mass spectrometry data on the fly, and analyzing different
microbial communities of DOE interest.
Laskin J, BS Heath, PJ Roach, L Cazares, and OJ Semmes.
2012. "Tissue Imaging Using Nanospray Desorption
Electrospray Ionization Mass Spectrometry." Analytical
Chemistry 84(1):141-148. DOI: 10.1021/ac2021322
PNNL project team members include Julia Laskin, Brandi
Heath, and Patrick Roach, PNNL; and Lisa Cazares and O.
John Semmes at the Eastern Virginia Medical School provided
the tissue samples.