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04/14/2004
Sopranos Singing Softly
Last week I took my first walk outdoors after returning home
from Marco Island. As I walked by the home of a former mayor
of our town, what should I see in his yard but two wild turkeys!
This was the first time I’d seen turkeys wandering about in our
town. The next day my wife saw a turkey in our own back yard.
This unexpected wildlife in our vicinity makes life more
interesting but I miss the sounds of the surf and the seabirds
during my walks on the beach on Marco.
Let’s talk about some other sounds. I understand that a new
trend is for expectant parents to acquire ultrasound portraits of
their unborn children to display and/or preserve for posterity.
Ultrasound has its more serious uses, of course, notably in other
forms of medical diagnosis. It was ultrasound that detected the
possibility of a tumor in my kidney that was confirmed by MRI.
It was ultrasound that was used to help initiate the purported
nuclear fusion in the “sonofusion” experiments we discussed a
few weeks ago.
We aren’t biologically equipped to hear ultrasound but there are
other interesting sounds that can be heard. One of them, if real,
must be about the softest sound imaginable. I must caution you
that, so far as I know, the research on this soft sound has not yet
been published in a scientific journal and there is some
skepticism about its reality. I learned of it in an article titled
“Signal Discovery” by Mark Wheeler in the March issue of
Smithsonian magazine. The article deals with the work of James
Gimzewski, a chemist at UCLA. A word about Gimzewski’s
credentials – he came to UCLA by way of IBM’s Zurich research
lab where he was a world leader in nanotechnology. He and his
coworkers in Zurich accomplished feats such as making the
world’s smallest abacus with beads less than a nanometer in size
or a spinning molecular propeller less than a couple nanometers
in size. In other words, he knows how to handle really tiny stuff!
Jim was lured from IBM by UCLA and his work there has been
influenced significantly by the events of 9/11/2001. He was at a
conference in Italy where he met an Italian medical researcher,
Carlo Ventura. Ventura was interested in childhood heart
abnormalities and was working with stem cell precursors to heart
cells. Gimzewski was taken with the fact that living heart cells
keep beating when placed in a dish with appropriate nutrients. If
something vibrates, it must produce a sound. After all, sound is
produced by something vibrating, your radio speaker, for
example, that pushes and pulls on the molecules in the air. The
pushing and pulling generates the sound waves that we hear if
the vibrations are in our frequency range.
Gimzewski wondered if he couldn’t “hear” the heart cells beating
and Ventura said that he would send him some of his heart cells
to study. Unfortunately, 9/11 intervened and by the time a
package of stem cells from Sardinia hit U. S. Customs, biological
warfare came to mind and the shipment was held up until it was
clear the cells posed no threat. By the time they reached
Gimzewski, they were beating no longer! Gimzewski wasn’t to
be denied, however, and asked his biochemistry colleagues at
UCLA if they couldn’t give him some yeast cells to listen to. LA
Weekly.com, an alternative newspaper’s Web site has an
interview of Gimzewski with Margaret Wertheim, who describes
him as easily mistaken for a refugee from a British rock band. I
imagine his biochemistry colleagues thought his idea of listening
to yeast cells “singing” rather odd, to say the least.
In the past, we’ve talked about various kinds of so-called
scanning probe microscopes that permit the imaging of
individual atoms. The first of these, known as the scanning
tunneling microscope, was invented at the IBM Zurich lab where
Gimzewski did his nano work. At UCLA, he and his graduate
student, Andrew Pelling, set to work using the atomic force
microscope (AFM), another type of scanning probe microscope.
The AFM has a tiny point that is normally dragged ever so
lightly across a surface and a computer converts the bumps and
valleys into a picture. Gimzewski and Pelling took an AFM and,
instead of dragging the point, held it lightly on the surface of a
yeast cell. Sure enough, they found that the cell membrane did
“beat”, raising and lowering the point.
Surprisingly, the cells were vibrating quite rapidly, around 1,000
times a second. The AFM measurements indicated that the cell
wall moved up and down by 3 nanometers, in the neighborhood
of 10 atom diameters. The distance the cell wall moves in and
out determines how loud the sound is, while the frequency
determines the pitch. Actually, if our ears were supersensitive,
we should be able to hear the yeast cells singing. On the musical
scale, the note C that lies two octaves above middle C
corresponds to a frequency of 1,056 cycles per second. When I
plunked that key on our piano, my aging ears had no trouble
hearing it. At about a thousand cycles per second, those
vibrating yeast cells are “singing soprano”, as the LA Weekly
article put it.
Of course, with only a movement of a few nanometers, the
volume is too low for us to hear. It’s just as well. If cells do
sound off, we would be inundated by sound if we could hear
them all! Gimzewski and Pelling next decided to sprinkle the
cells with alcohol. The cells started vibrating at a higher
frequency, a higher pitch. Were they screaming before they
died? When the cells were dead, they emitted a low (very low!)
rumbling sound that Gimzewski attributes to random atomic
motion, not to rhythmic beating.
The researchers have looked at other types of cells and found that
they emit sound at different frequencies. For example, bone cells
sing at a lower frequency than the yeast cells. Mutant yeast cells
were found to sound different from normal yeast cells. This has
spurred the hope that listening to cells might prove to be a good
diagnostic tool for various diseases. As I mentioned, Gimzewski
hadn’t published his results as of the time the article was written
and there are skeptics who think the vibrations could have other
origins, perhaps even in the tip of the AFM itself. Gimzewski
and his colleagues agree that more work is needed to determine
whether what he calls “sonocytology” will be of practical value.
I listened to an interview of Gimzewski by Quentin Cooper of
the BBC on the BBC Web site. The interview took place last
year and included another interviewee, Matthew Cooper, the
chief scientific officer of a company called Abukio. I don’t think
the two Coopers are related. Matthew and his colleagues are
“listening” to viruses using a completely different technique. An
article by Helen Pearson, dated August 31, 2001, on the Nature
Web site indicates that they coat a quartz crystal about the size of
a dime with an antibody to which human herpes virus was
attached.
Quartz crystals in an electrical field vibrate. As the voltage on
the crystal is increased the crystal vibrates faster and faster and
finally the bonds between the antibodies and the viruses are
broken. When a bond breaks, a burst of sound is emitted that is
likened to a rifle shot. The characteristics of the sound are
apparently dependent on the nature of the virus and the strength
of the bond being broken. In these cases the frequency of the
sound is beyond our hearing capability. Once again, the hope
here is that the distinctive sounds emitted by different viruses or
other biological entities may prove to be useful in the medical
field.
For example, listening to cells or viruses might eliminate the
need for some expensive and time-consuming tests. As I look
forward to a CT scan next week, with the associated swallowing
and injection of dyes, I certainly would prefer to have some cells
“sing” for the diagnosticians. I wish Gimzewski and Cooper
well in their quests.
Allen F. Bortrum
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