New Biosensor Detects Extremely Low
Bacteria Concentrations Quickly, Easily And Reliably
of Article: http://www.sciencedaily.com/releases/2009/07/090720134517.htm
ScienceDaily (July 21, 2009) — Bacterial diseases are usually
detected by first enriching samples, then separating, identifying, and
counting the bacteria. This type of procedure usually takes at least two
days after arrival of the sample in the laboratory. Tests that work faster,
in the field, and without complex sample preparation, whilst being precise
and error-free, are thus high on the wish list. A Spanish research team
headed by Jordi Riu and F. Xavier Rius at the University Rovira i Virgili
in Tarragona has now developed a new technique to make this wish come true.
With a novel biosensor,
they have been able to detect extremely low concentrations of the
typhi. As reported in the journal Angewandte Chemie, their new method is
based on electrochemical measurements by means of carbon nanotubes equipped
with aptamers as bacteria-specific binding sites. If bacteria bind to the
aptamers, the researchers detect a change in electrical voltage.
Aptamers are synthetic,
short DNA or RNA strands that can be designed and made to bind a specific
target molecule. An aptamer that specifically binds to salmonella has
recently been developed. The Spanish researchers chose to use this aptamer
for their biosensor. By means of additional functional groups, they
securely anchored the aptamers to carbon nanotubes, which were deposited
onto an electrode in an ultrathin layer.
In the absence of salmonella,
the aptamers fit closely against the walls of the carbon nanotubes. If the
biosensor is put into a salmonella-containing sample, the microbes stick to
the aptamers like flies to flypaper. This influences the interaction
between the aptamers and the nanotubes, which makes a change in the
electrode voltage noticeable within seconds.
Using this biosensor, the
researchers were able to detect a bacterial concentration equivalent to one
salmonella bacterium in 5 mL of medium. Quantitative measurements were
possible down to a concentration of about 1000 salmonella per milliliter.
This biosensor is specific: it does not react to bacteria other than Salmonella typhi.
"Our new technique makes the detection of micro-organisms as fast and
simple as the measurement of pH value," say Riu and Rius.
This graphic shows an aptamer attached to an
electrode coated with single-walled carbon nanotubes interacts selectively
with bacteria. The resulting electrochemical response is highly accurate
and reproducible and starts at ultra-low bacteria concentrations, providing
a simple, selective method for pathogen detection. (Credit: Copyright
1. Zelada-Guillén et al. Immediate Detection of
Living Bacteria at Ultralow Concentrations Using a Carbon Nanotube Based
Potentiometric Aptasensor. Angewandte
Chemie, 2009; NA DOI: 10.1002/ange.200902090
Adapted from materials provided by Wiley-Blackwell, via EurekAlert!, a service