Meet the Scientists
“We take a group called an N-halamine, which is a cyclic compound, and we modify a
polymer so as to bond these structures onto the polymer. And then in all cases, once the
polymer is coated onto a surface one can just expose that surface to a dilute solution of
household bleach. That, of course, is aqueous chlorine. The chlorine binds to a nitrogen
on the group that’s been put on the polymer. So what you then have is a source of antimicrobial chlorine. As we all know, chlorine is used to disinfect most of the water supply
in America. This is the same idea except that the chlorine is bound to the surface until
it’s needed. When a microbe lands on the surface, it extracts the oxidative chlorine from
this polymer and it’s killed by an oxidation process.”
Dr. Worley says that this N-halamine-containing polymer can be easily coated onto the
surface of the same plastic food wrap that grocers and consumers now use. He adds that this
same polymer could be used to coat nearly any surface that you’d want to keep free of bacteria, including paint that might be used in food processing plants or hospitals, and a variety
of fabrics.
Arun Bhunia, Ph. D.
Advance Warning Systems
No matter how successful chemists and other scientists are at developing methods for keeping our food free of pathogens, one fact remains. Bacteria are nearly impossible to eliminate completely from certain foods. Some, including ground beef and turkey, pose special
problems.
Even small numbers of bacteria can quickly multiply to dangerous levels on the large
surface area in ground meat. Chemists are responding to that challenge with new ways for
rapidly and accurately detecting contaminated food before it reaches our dinner plates.
“In light of all the recent outbreaks we’ve had with different food products, primarily
meat and ground beef, and fruits and vegetables, one of the ways we could have impact
in terms of controlling these pathogens is to develop some rapid method of testing. Some
of the traditional methods take a long time to get positive or negative results. Sometimes
it can take a week or 10 days. By this time products will have been sold or will have
been consumed, so that’s not going to provide us with a strategy to reduce food-borne
outbreaks. So for that reason, we need rapid methods that can give us results in a day or
in some cases a few hours.”
Raj Mutharasan, Ph.D.
That was chemist Arun Bhunia of Purdue University, who is developing technology for
detecting food pathogens. One of these systems uses living cells as biosensors.
“And in that sensor we are actually allowing a million cells to be embedded in a three-dimensional configuration in the shape of a well, and when you have any pathogens or
toxins, they cause damage to those cells, and you can detect the pathological action on
those cells.”
Jacob Petrich, Ph.D.
Diving Board Detectors
Taking a different approach, Drexel University chemical engineer Raj Mutharasan is using
tiny cantilevers — miniature devices about the thickness of a dime that resemble a diving
board — to detect a wide variety of foodborne pathogens in as little as 10 minutes.
Over the past year, Dr. Mutharasan and his colleagues have published several papers,
including two in the ACS’s Analytical Chemistry, demonstrating that their new sensor can
detect trace amounts of E. coli contamination on spinach, spring lettuce mix, ground beef,
apple juice, milk, and drinking water.
The key to this device is a property called the piezoelectric effect. Piezoelectricity refers to
the ability of some materials to generate an electrical signal as they bend. Dr. Mutharasan’s
team creates their cantilevers by first depositing a thin layer of a lead-based ceramic material
onto a flexible slab of glass wired to circuitry that can measure the electrical signal from the
cantilevers. They then coat these cantilevers with antibodies that recognize specific bacteria
or bacterial toxins — the chemicals that pathogens release that actually make us sick.
