PERSON OF THE MONTH
Dr Firat Güder
Imagine a cheap, NFC-enabled paper sensor that can reveal if food is still safe to eat, saving mountains of waste. That’s exactly what Dr Güder and his team have been working on at Imperial College London.
BROCCOLI PAST THE best-before date? Bin it. One in three Britons chucks food once the use-by date passes, wasting millions of tons of food annually – but two-thirds of it is actually safe to eat, as that date has no bearing on the real condition of the food languishing in your fridge.
There could be a solution beyond the sniff test. In a paper published in ACS Sensors, researchers at Imperial College London have created cheap and simple sensors made from biodegradable, non-toxic cellulose paper that detect spoilage gases, the very same you’re sniffing your old milk for. Scan the NFC-enabled sensor with your phone to find out if your lunch is safe to eat.
Costing pennies each, such sensors could replace use-by dates, giving us more time to eat our groceries without risking illness and resulting in less food waste. Dr Firat Güder, lead author of the research, explains how these smart sensors work.
Where did this idea come from? People building paper-based devices use paper mostly as a carrier of things, but they don’t really exploit the intrinsic chemical properties of paper. I was interested in making near-zero cost devices… I was going through an old book involving paper making and saw this interesting fact that at moderate relative humidity, paper actually carries a substantial amount of water. This means that, without ever adding water to a piece of paper, you can do chemistry with it. It looks and feels dry, but it’s always wet.
I’ve always been interested in applications for sensing in food, and this was a very natural marriage between what I’ve been interested in and what I started looking into – it turns out, [paper] was really suitable for this.
How do these sensors work?
It’s a piece of paper with electric contacts on it, and we measure the conductivity of the paper, which is essentially measuring the layer of water that’s in the paper. As the gases [produced from rotting food] come into contact and dissolve in this layer of water, they dissociate into ions, increasing the electrical conductivity of the paper. So, if we have more gases, the paper becomes more conductive and so on. Really, all we do is just take a piece of paper, print some electrical contacts on it, and measure its conductivity – that’s it.
How does that then connect with your phone?
In the work we just published, we took a piece of paper and integrated onto it an NFC tag… we put our sensor parallel with the microchip that’s on these tags. When the electrical conductivity of the paper increases to a certain level, the majority of the power goes through the sensor and not the chip. So when there are gases, the chip no longer works. So the tag is not readable anymore. It’s an on/off sensor: the food has gone bad or it’s still okay. In the future, we will continue to work on a new generation of tags that actually give a number, like there’s a specific amount of gases that means the food will most likely be fully spoiled in the next few days.
How do you know if it’s accurate?
We have an existing method for checking food quality using microbiology… and the results are highly correlated. That’s also how we can establish in the first instance a cut-off value. We look at the signal that we read from the sensor, then run the cultures and say when they reach a certain level we know that food is no longer okay to eat. And then we use that as a threshold – we can say you should not consume this because this level [of gases] is correlated with a dangerous level of microbes in the food.
How long until this is in supermarkets?
We’ve launched a startup company called BlakBear, which is leading the commercialisation effort. We’ve partnered with a packaging manufacturer and have applied for some grants. Depending on how the financing works, we’re hoping that in the next three to five years we’ll see this in grocery stores.
Who else does this benefit?
We’re hoping to use it for biomedical applications in the developing world. We’ve been looking into developing a kidney function test by measuring breath ammonia, which we think will be useful in rural and remote clinics. For food, retailers have a huge interest in this technology, as it allows them to reduce costs and do dynamic pricing, rather than just apply discount stickers on the use-by date. But when people think about food waste they don’t really think about it as a multidimensional problem. With wasted food, there are also plastics in packaging – it’s environmentally costly. We need to start thinking about these things.