May 29, 2012 By
Bob Beale Schematic: Magnets are used to assemble
nanoparticles, coated with antibodies to enrofloxacin, between two electrodes:
when antibodies leave the nanoparticles the electrical resistance falls. (Phys.org) -- A whole new class of biosensor
that can detect exceptionally small traces of contaminants in liquids in just
40 minutes has been developed by a UNSW-led team of researchers. Known as a biochemiresistor, it meets a
long-standing challenge to create a sensor that is not only super-sensitive to
the presence of chemical compounds but responds quickly. It has countless
potential uses for detecting drugs, toxins and pesticides for biomedical or
environmental analysis. In a paper published in the prestigious
chemistry journal Angewandte Chemie the researchers describe how they
successfully tested the new sensor by detecting tiny traces in milk of the
veterinary antibiotic enrofloxacin. The journal has singled out the study for
attention as a “Very Important Paper”. Only 5% of papers published by the
journal are so designated. “Enrofloxacin is an antibiotic used in the agricultural
industry that can be transferred to the food chain,” notes co-author Scientia
Professor Justin Gooding, of the UNSW School of Chemistry and the Australian
Centre for Nanomedicine. “Our biochemiresistor was able to detect enrofloxacin
in neat milk in 40 minutes, at level as low as one nanogram in a litre of milk.
To put that number in perspective, a nanogram is a billionth of a gram and is
the mass of a single cell. “While that is impressive enough, the sensor is a
general concept that can be widely applied across many different fields.” A biosensor is a portable analytical device
that uses biological molecules to detect selectively just one compound within a
mix of many others. Small biosensors are already in daily use testing the
safety of drinking water, for checking diabetic blood-sugar levels and for
pregnancy tests The biochemiresistor uses gold-coated magnetic
nanoparticles modified with antibodies that are selective for the chemical
constituent – or analyte - of interest. The nanoparticles are dispersed into
the sample for analysis and if the analyte is present some of the antibodies
detach from the nanoparticles. Using a magnet, the nanoparticles are then
assembled into a film between two electrodes and the electrical resistance is
measured. The more analyte is present, the more antibodies leave the
nanoparticles and the lower the resistance in the nanoparticle film. “This new type of biosensor is rapid in response because the magnetic
nanoparticle biosensors go and get the analyte rather than the usual approach
of waiting for the analyte to find the sensing surface,” says Gooding. “The biochemiresistor is also more sensitive than the usual biosensor
because, as the nanoparticles are dispersed throughout the sample, the entire
sample is analysed, not just a small portion of the solution.” The
study’s lead author is Leo M.H. Lai.
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