The taste of success: Future applications of BRET-based biosensors
In modern animals, these senses are known as taste and smell. We humans, for example, have five main taste modalities; sour and salty, mediated by ion channels, and sweet, bitter and savoury (umami), mediated by G-protein coupled receptors (GPCRs). Bitter is the most complex of these; humans express over 40 different bitter receptor genes to detect a wide range of potential alkaloid toxins. Our sense of smell is even more complex, as we express many hundreds of different olfactory GPCRs. Taste and smell receptors are found in many places besides the tongue and olfactory system, but that is a story for another day.
The extraordinary sensitivity and selectivity of the olfactory systems of animals, especially dogs, mice and rats, prompted the invention of the “electronic nose” or E-nose concept. Generally credited to Persaud and Dodd (1982), the idea was to replicate the array of sensors found in the human nose, with an array of differentially selective solid-state sensors to do the same job. Although arrays of many types of solid-state sensors have been tested, none of them have ever approached the performance of a real nose. It is possible they never will. In order to compete with a sniffer dog, in less than a second you need to be able to discriminate tens or even hundreds of thousands of different odour combinations and pick up individual scents at parts per trillion, and possibly parts per quadrillion level.
But long before human engineers struggled with this problem, evolution solved it for us. Our sense of smell helps us find food, recognise competitors, mates, predators and prey, and avoid pathogens and toxins. Taste is even more critical. It’s the last line of defence when we put something into our mouths. Is this nutritious? Is it going to poison us or make us sick? Get that wrong and you won’t be contributing to the gene pool for long. Because the stakes are so high, taste sensors are exquisitely tailored to do their job. So ion channels and GPCRs, usually the research domain of neuroscientists and pharmacologists, as well as other types of chemosensory proteins have huge potential to underpin a new generation of truly biomimetic electronic noses and tongues.
The rapid development of biosensors has brought substantial advances in detection and quantification of biological interactions. The technology fuses a biological sensor (to interact with the analyte being tested or detected) with a component that can detect or transmit a signal. These biosensors offer exceptional versatility in its application, spanning all scientific disciplines including agriculture, biomedicine, food and environmental research.
Dr Stephen Trowell, who recently left Australia’s Commonwealth Scientific and Industrial Research Organisation, CSIRO, actively pursued this biomimetic sensing approach for the last decade or so of his 30 year research career. His mission now is to commercialise "on the spot" chemical biosensing for a wide range of practical applications. The new venture at PPB Technology draws on over a decade of biosensor development by the dedicated CSIRO biosensors research group.
“We first got into this work to search for a way to replicate the acute sense of smell that dogs and other animals possess. If we could improve on the solid state electronic noses of the time it would help in a whole variety of areas. Helping winemakers was an early goal but we quickly started working on sniffing out explosives,” Stephen said.
To develop the olfactory biosensor, Stephen and his team stitched together olfactory GPCRs with a “Bright Light” bioluminescent resonance energy transfer (BRET) readout. “We believed that such a system would have the sensitivity and stability required for commercial applications,” Stephen explained, “We were lucky enough to be doing this in the early days of CSIRO's National Flagships Program. I was given the resources I needed to recruit a first rate team and get on with the job. To cut a long story short, we succeeded (Dacres, H., et al. (2011). "Greatly enhanced detection of a volatile ligand at femtomolar levels using bioluminescence resonance energy transfer (BRET). "Biosensors & Bioelectronics 29(1): 119-124.). And the first olfactory biosensor we made is still one of the most sensitive available.”
It was clear that these novel ‘olfactory biosensors’ could also have wider commercial applications across a variety of industries. Steven’s colleague, Dr Helen Dacres (team leader at the Biosciences team at the CSIRO), subsequently developed two other families of BRET-based biosensors: A BRET-based maltose biosensor and several selective and very sensitive BRET-based biosensors for detecting protease activity. These simplified and highly sensitive models demonstrated the true potential of BRET-based biosensors not only for traditional research purposes, but also for various industry applications. “The potential benefits of applying the maltose and protease BRET-based biosensors were so obvious that the food industry found us, so to speak,” said Stephen. “Food processors immediately identified the value of the BRET-based biosensors for measuring proteases and sugars in food production”.
“Throughout this research we absolutely relied upon BMG LABTECH’s microplate readers. I think we bought one of the very first instruments, a POLARstar, that was sold in Australia. Since then, the lab has owned a POLARstar Optima (I remember personally testing that instrument against the competitors; Ed. the POLARstar Optima was discontinued in 2015) and we recently added two CLARIOstars. These instruments have been the workhorses for our biosensor development and characterisation, and a range of other research in our laboratory. The instrument’s capability to select a wavelength emitted and select a large band pass serves this work extremely well,” Stephen said.
With these novel BRET-based biosensors already capturing the attention of various industries, the future for Stephen’s new venture at PPB Technology looks bright. Stephen aims for PPB Technology to be a global leader in point of care diagnostic tests for food, veterinary, agricultural, manufacturing, environmental and human health applications. “I have always been motivated to use the fruits of research to make a difference in the world outside academia. I am really looking forward to exploiting the opportunities of BRET-based biosensors. PPB Technology enters the market with food diagnostic tests for on the spot analysis of foods, beverages and other biological samples. In an era of uncertainty about food safety, quality and provenance, PPB Technology will give producers, processors and consumers the tools they need to make fast decisions with confidence,” Stephen said.
For further information about Steven Trowell and PPB Technology, visit https://www.linkedin.com/in/stephen-trowell-20529119.