Meet the Scientists
... this is where we really ought to apply most
of our effort to address this problem of being able
to detect biological threat agents ...
“When I started this work, I first looked at the listing of Category A pathogens that’s
published by the NIH, and if you look at the category A pathogens, about 75 percent of
them are viral in nature. So my thought was that this is where we really ought to apply
most of our effort to address this problem of being able to detect biological threat agents
— bacteria, viruses, and toxins — that have been put in a weaponized form.”
Troy A. Alexander, Ph. D.
Optical Fingerprints
The product of Dr. Alexander’s research is a device that generates what is essentially an optical fingerprint. Within minutes, it can identify specific bioterrorism threats. In a paper that
he published in ACS’s Analytical Chemistry, Dr. Alexander describes experiments in which
he used viruses from the smallpox family as a proof of concept for this device.
“When you start to look at work that’s been done with pox viruses, you quickly realize
that they are unique in the sense that they are invariant irrespective of what the animal
host is or even what part of the world they come from. In that respect, they are a good
model system to start with, and more closely to our application, smallpox is still a really
big threat that can be used in a military application or a bioterrorism threat.”
John Mark Carter, Ph.D.
The device that Dr. Alexander created is based on a technology known as SERS, short for
surface enhanced Raman spectroscopy. SERS works like this: When infrared light shines
onto a precisely machined gold surface, known as a SERS substrate, it excites the electrons
in the metal atoms and causes them to ripple in unison across the gold surface, much like
waves on pond.
When a virus particle or bacterium lands on the SERS substrate, it gets energized by those
ripples and gives off light at multiple wavelengths. That pattern of light, or spectral signature, depends on the exact type of virus or bacterium stuck to the SERS substrate. For example, smallpox virus produces one spectral signature, while the closely related cowpox virus
produces a different signature.
Even better, using software that can run on a personal computer, Dr. Alexander found that
his device can analyze the light emitted from the SERS substrate and identify specific pox
viruses within a matter of minutes even when there are multiple types of viruses present on
the substrate. That’s an important finding because in the real world, the air is full of harmless
viruses and bacteria that might interfere with the detection of bioterrorism agents.
And in fact, Dr. Alexander has already shown that this device can detect and identify
members of the Bacillus family of bacteria that includes anthrax, and could find use with
other threat agents, too.
“Yes, this could be extended to include not only the pox viruses but also Bacillus spores and
also it’s very easily applicable to chemical threat agents such as mustard gas and VX, and
one of the big challenges, of big military interest right now, is detection of explosive materials. It could really be used to develop a broadly applicable sensor platform that could
be used to sense all of those different categories of agents of interest.… For more civilian
applications, this could be used in football stadiums, airports, shopping malls, areas where
you have high volume, high numbers of people, and it could be really easily automated.”
“Chemical Radar”
In 1935, Sir Robert Watson-Watt, a British physicist, developed the first practical radar system. By 1939, at the outbreak of World War II, the United Kingdom had installed a string
