Microscopy and the Anthrax Attacks

In the fall of 2001, the Federal Bureau of Investigation (FBI) convened two blue-ribbon panels to determine how to best investigate a series of anthrax attacks. Letters containing bacillus anthracis, the spores that cause the disease anthrax, had been mailed to several news-media outlets and two U.S. senators. Five people died and 17 others were infected with a disease which, in its inhalational form, begins with cold or flu-like symptoms and eventually causes severe breathing problems.

A Matter of National Security

Still reeling from the terrorist attacks of 9/11, the FBI needed answers. Did the anthrax letters contain a weaponized form of bacillus anthracis, a naturally-occurring bacterium whose spores live in the soil and remain viable for decades? If so, did the anthrax letters provide proof of state-sponsored terrorism, or indicate that Al-Qaeda was capable of producing biological weapons? For answers to these questions, the FBI turned to Sandia National Laboratories of Albuquerque, New Mexico. A multi-program program facility, Sandia is renowned for its expertise in electron microscopy.

Silicon and Oxygen Signals

In February 2002, the first spore materials arrived at Sandia Labs. During the next six and a half years, a team of researchers examined over 200 samples. Material characterization analysts Joseph Michael, Paul Kotula, and Ray Goehner played especially important roles. After signing non-disclosure agreements (NDA) and receiving briefings from the FBI, the trio reviewed scanning electron microscopy (SEM) studies about the spores from another laboratory. These initial tests had revealed high silicon and oxygen signals – signs that the bacillus anthracis spores had been intentionally weaponized.

SEM and TEM

Seven years later and now released from their NDAs, the Sandia scientists described why they reversed these first findings. "The possible misinterpretation of the SEM results," Paul Kotula explained, "arose because SEM microanalysis is not a surface-sensitive tool". When anthrax is weaponized, B. anthracis is coated with lint-like silica nanoparticles that make the spores more respirable. Although "SEM cannot localize the elemental signal from whole spore bodies" with dimensions as small as 1 micron, Kotula explained, transmission electron microscopy (TEM) could.

Follow the Nanoparticles

With TEM, a beam of electrons is passed through a specimen that has been stained with phosphotungstic acid in order to block some electrons and form a "negative" image. The electrons then strike a platform that is covered with a substance that fluoresces, producing a glowing image which is then magnified by a light microscope. Using TEM, materials analysts from Sandia Labs determined that the silica in the anthrax spore samples had been incorporated as a natural-part of the spore formation process. "The spores we examined," Kotula noted, "lacked that fuzzy outer coating that would indicate that they'd been weaponized.

Later, DNA studies of the spores from the anthrax letters corroborated the Sandia studies.

Resources:

http://www.sandia.gov/news/resources/releases/2008/anthrax.html

http://en.wikipedia.org/wiki/2001_anthrax_attacks

http://en.wikipedia.org/wiki/Bacillus_anthracis

http://www.drjreid.com/phage_vocab.htm