Monitoring heavy metals with a virus
A student’s interest in environmental sensors leads researchers toward a new sensor for heavy metals
Viruses are not always bad news. Although they cause disease in millions of people each year, some may turn out to have an unexpected use in sensors detecting heavy metals in the environment, food and medicines.
“Heavy metal contamination in water is a huge problem,” says Amy Szuchmacher Blum of the research team at McGill University in Montreal, Canada. Through a chance discovery, one of her students found that the natural fluorescence of a virus she was working on reduces when it binds to ions of heavy metals. Using this, the team could then quantify heavy metal levels by simply measuring the light emitted from part of the virus.
Blum and her colleagues published their discovery in the journal Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy. “We are pretty excited by our results,” Blum adds, pointing to the clear potential to form the basis of an inexpensive sensing technology.
Most viruses are composed of a coating of protein molecules that protects a small core of genetic material—either DNA or RNA. Blum and her colleagues were investigating how the coat proteins of Tobacco Mosaic Virus (TMV) interact with heavy metal ions, without thinking of sensor possibilities. As part of this work, they were comparing the protein in its natural state and in a denatured state in which the normal folded structure of the protein is disrupted by heat or chemical treatments.
“My student, Serene Bayram, noticed a large difference in heavy metal binding between the intact and denatured protein,” Blum explains. Although the research group does not usually work on sensors, Bayram happened to be very interested in sensing applications. Prompted by this interest, the researchers began investigating the sensing possibilities "as a side project” and soon realized they had stumbled on the basis of a possible sensor. Some aspects of the ability to distinguish between different ions depend on differences Bayram found in their interaction with the native and denatured protein states.
Preliminary “proof of concept” results reveal that the altered fluorescence when a selected mutant form of the native or denatured coat protein binds to heavy metal ions is sufficiently sensitive to detect and distinguish between ions of cadmium, lead, zinc and nickel.
Current heavy metal sensing systems either require complex instrumentation or have low sensitivity and limited selectivity, so the opportunities for improved methods are clear. The TMV protein can be mass produced easily and cheaply. Blum believes that using viral proteins in biotechnology applications has great potential, as they are very robust molecules that can tolerate a lot of processing while retaining their structure and function. They also possess suitable chemical groups to allow easy attachment to the surfaces of biosensing chips.
The McGill team are now considering using genetic modification of the virus to enhance and vary the interaction of the coat protein with different ions. This may lead to ways to build more versatility and sensitivity on top of the existing capabilities.
“Making commercial sensors is far from our area of expertise,” says Blum, “but we hope that our results might be picked up by people who can build on them.”
Blum, A. Z. et al.: “Sensing of heavy metal ions by intrinsic TMV coat protein fluorescence,” Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2018)