The technique involves using molecularly imprinted polymers (MIPs), also known as polymeric antibody-mimics because of their ability to bond to a target molecule.
They are made from monomers which resemble amino acid structures and interact with bacteria in similar ways to antibodies, said Dr Marloes Peeters of the Advanced Materials group at Newcastle University School of Engineering, and principal investigator for the EPSRC-funded project. The polymers can be tailored to give them an affinity to bond to a particular target, such as a strain of bacteria that has developed resistance to antibiotics.
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In previous work Dr Peeters’ group had demonstrated that the binding of the target to an MIP altered the conduction of heat through the polymer, leading to a temperature differential that is dependent on the concentration of the target bacteria. This can be measured in the lab by inserting the sensor into a flow cell, connected to a thermal sensor (a thermocouple device). This has been patented as the Heat Transfer Method.
The current project, running till June 2020, seeks to improve the sensitivity of the method by replacing MIP microstructures with nanolayers. The original structures were built on a polyurethane substrate which was several microns thick and impaired the heat flow, said Dr Peeters.
Experiments with electrochemical deposition methods were disappointing but the team has now developed an effective approach using photolithography. This allows more control over the structure and thickness of the layers, is quicker, and is easier to fine tune to suit different monomers, said Dr Peeters.
The group has recorded successful results with antibiotics, and instead of trying to use the technique to try to directly identify bacteria with antimicrobial resistant properties, it is now planning to monitor the susceptibility of bacteria to antibiotics.
The flow cell allows bacterial concentration and the concentration of antibiotics to be measured over a period of time. This can be done in situ and provides instant feedback, as opposed to the usual method of sending bacterial samples to be cultured, where results can take several days.
Work is also under way to “array format” the MIP structure to make it possible to measure multiple compounds at the same time, which has also required a redesign of the flow cell.
The MIP sensor would be imprinted in such a way as to target a mixture of bacteria simultaneously. Microbiologists have identified the fact that there is a limited set of bacteria which are most commonly found in infections or in contaminated food or water.
“Ideally you would have a sensor which is not directed towards just one target, but could pick up different things, so say you’ve identified the four most hazardous strains of bacteria which cause 90 per cent of all infections, that’s ideally what we would like to do because that’s what industry wants,” said Dr Peeters.
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