Fast and accurate trace contaminant detection

Drugs, toxins and pesticides can be detected at nanogram/litre levels in just 40 minutes with a University of New South Wales (UNSW)-developed biosensor.

Biosensors are portable analytical devices that use biological molecules to selectively detect individual compounds 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 and the like.

The fast-reacting, ultrasensitive biochemiresistor developed by the UNSW-led team has potential uses in many biomedical or environmental analyses where extremely low levels of contaminants need to be accurately and quickly detected.

The developers tested it by detecting tiny traces of the veterinary antibiotic enrofloxacin in milk. The biochemiresistor was able to detect one nanogram of the antibiotic in a litre of neat milk in just 40 minutes.

The biochemiresistor uses gold-coated magnetic nanoparticles modified with antibodies that are selective for the 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.

The biosensor is particularly speedy because rather than the usual approach of waiting for the analyte to find the sensing surface, the magnetic nanoparticle biosensors go and get the analyte. Also, because 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 MH Lai. The team included other researchers from the Australian Centre for NanoMedicine and the former ARC Centre of Excellence for Functional Nanomaterials at UNSW. Their paper has been designated as a ‘Very Important Paper’ and published in the chemistry journal Angewandte Chemie.