07 Nov 2003
Optical sensors help defend against the threat from biological terrorism.
As scientists search for the best way to detect biological warfare agents it seems that the answer may lie with laser-induced breakdown spectroscopy (LIBS).
The technique, which involves firing laser pulses at a target and analyzing the light spectra that is emitted from the resulting microplasma, is traditionally used for analyzing the composition of metal.
Now, research groups from France (Applied Optics 42 6184) and the US (Applied Optics 42 6205) have demonstrated that LIBS can identify the presence of different strains of bacteria and distinguish them from harmless substances such as pollen.
The benefit of the approach is that it is potentially very fast, sensitive and can operate in the field without the need for any sample preparation -- all the requirements of an ideal biohazard detector.
A US collaboration from Edgewood Chemical Biological Center and the US Army Research Laboratories used LIBS to analyze biosamples of mold, protein, pollen and bacterial spores deposited on silver substrates.
The samples were exposed to single 30 mJ laser pulses from a Q-switched Nd:YAG and the emitted light was collected by a high-resolution (0.1 nm) broadband (200-980 nm) spectrometer.
Principal-component analysis [PCA] software then matched the different optical spectra to the different substances.
“The PCA revealed three distinct clusters, which comprised the pollens and ovalbumin [protein] in one cluster, the molds in the second cluster and the bacteria in the third,” say the researchers in their paper. “Additional discrimination within the three bacilli types studied appears feasible with a more rigorous approach.”
In a similar piece of research, a French team from the Centre d’Etudes du Bouchet and the Ecole Nationale Superieure de Chimie de Paris have used time-resolved LIBS (TRELIBS) to analyze bacterial material and pollen that had been freeze-dried and compressed into pellets.
100 mJ pulses from a Nd:YAG laser were focused onto the pellets containing eight different biological agents which included three simulated strains of Anthrax and two pollen species. As in the US case, a series of optical spectra were collected by a high-resolution spectrometer.
By analyzing the relative strength of phosphorous and carbon emission lines at 253 and 247 nm the French team say that they could distinguish between all the pellets.
“At least for a set of eight compounds, TRELIBS has shown a good ability to detect and sort species,” say the French team in its paper. “These are preliminary studies however and overall sensitivity has to be determined as does an extension to direct measurements of contaminated surfaces or in ambient air.”