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ANALYTICAL CURRENTS
Red alert—biosensor identifies bacteria in the air In the event of a biological warfare attack, there will likely be no warning. But what if there were a sensor that could identify bacterial agents in the air before humans are exposed? Frances S. Ligler and co-workers at the Naval Research Laboratory, Georgetown University, Geocenters, Kaman Sciences, and Nova have designed a sensor that can do just that. The system integrates an air sampler and an automated fluidics system with an antibody-based fiber-optic biosensor, a radio transceiver, and a remotely piloted unmanned air vehicle (UAV). It is capable of collecting aerosolized bacteria, identifying them, and transmitting the data to the operator. No manual operations are necessary—everything is done remotely from the ground. For field-testing purposes, the system was set up to detect the harmless bacteria Bacillus subtilis var. niger (Bsn). Fluorescently labeled anti-Bsn antibodies were immobilized onto a fiber-optic probe by conventional cross-linking methods; however, the sensitivity was insufficient to identify the low levels expected during aerosol releases. To improve sensitivity the researchers turned to an avidin-biotin cross-linking method, which minimizes the denaturation caused by direct immobilization of the antibody on the glass fiber and reduces steric hindrances by limiting the number of sites the antibody uses to attach itself to the surface of the probe By binding the anti-Bsn antibody through an avidin-biotin bridge the sensitivity was improved nearly 1000-fold giving a detection limit of 3000 colony-forming units/mL One of the most challenging aspects of the system is the sampling requirement. Standard air samplers for collecting aerosol particles into aqueous reservoirs are typically too heavy, inefficient, and require too much power for remote applications. To overcome these limitations, the researchers built a small plastic cyclone, engineered to take advantage of the air flow produced from a moving airplane. At
Immunoassay on a fiber-optic probe.
air speeds common for the UAV platform, sampling volumes were estimated to be > 100 L air/min. The biosensor system has potential for warning military troops prior to exposure
MALDI takes a bite out of crime The quest for a competitive edge is driving some athletes and animal trainers to use performance-enhancing drugs. But cheaters beware. Andrew T. Kicman and colleagues at King's College and the Horseracing Forensic Laboratory (both in the United Kingdom) have found a way to identify growth hormones using MALDI-TOFMS. Growth hormones (GHs), like anabolic steroids, help athletes by increasing lean body mass and reducing fat. Both kinds of drugs are illegal in many countries, including the United States, Australia, and the United Kingdom, unless prescribed for specific medical conditions. Aid both have been banned by the International Olympic Committee. Still, the popularity of "doping" with GHs is rising a Chinese swimmer was caught with them before January's world championships because there aren't any reliable tests for them. But, as Kicman and colleagues show, MALDI's ability to map peptides
to biological agents. In addition, it may also find use in environmental monitoring applications where it is not feasible for die operator to be present. (Environ. Sci. Technol. 1998,32, 2461-66)
is perfect for that task. The researchers were able to identify human, equine, porcine, and bovine GH by performing tryptic digests followed by MALDITOFMS analysis. Using only a few routinely observed fragments, the researchers could discriminate among the four GHs—even between equine and porcine GH, which differ by only three amino acids. Because the method requires a large amount of material, it is designed for law-enforcement officers who want to identify what they've seized. But the researchers think the technique can be adapted to screening because they have already detected human chorionic gonadotropin, another banned hormone, in urine samples. In addition, the method seems to be sensitive enough to detect GH doping in horses and greyhounds. Testing is impractical right now because recombinant and endogenous equine GH differ by just one methionine residue as do recombinant and endogenous porcine GH which identical to the canine hormones (Rapid Commun Mass Spectrom 1998 12 975-81)
Analytical Chemistry News & Features, October 1, 1998 6 3 5 A
