• Nekoreguojami


2023. 07. 27 -

PhD student has developed a sensor that promises a breakthrough in the food industry

PhD student Vytautas Žutautas
Vytautas Žutautas never thought he would ever do chemistry in his life. Growing up in Žemaitija, near Plateliai, he chose then VGTU, where he graduated with a Bachelor's degree in bioengineering and a Master's degree in nanobiotechnology. Later, encouraged by his lecturer, he became a PhD student in chemistry at the Center for Physical Sciences and Technology (FTMC), working in the Department of Nanoengineering. As he puts it - by accident.
"I didn't want to study chemistry after 12th grade. I understand its principles, but all those formulas... It's hard to remember them. But when I entered the PhD programme, it was only half a year later that I noticed that I had already become a chemist myself," Vytautas laughs.
His field of work is electrochemistry, which is somewhat different from "normal" chemistry. As he says, the former is easier for him to understand - and offers new opportunities for science: "For example, the polymerisation of folic acid does not occur naturally. But with electrochemistry, we can do it."
FTMC PhD student eventually realised that the formulas weren't as scary as they seemed: "The important thing is not to remember everything, but to learn where to look for information. Most of the formulas I use in my work I wouldn't be able to say from memory now - but it's easy to find them."
The young scientist and his colleagues published a paper in the international journal Chemosensors in June. He has developed a next-generation pH sensor that is expected to come in handy in the food industry - and to further improve the quality of various products.
(pH scale with samples. 7 indicates neutral pH (blood), increasing alkalinity as you go up and acidity as you go down. Illustration: Anatomy & Physiology, Connexions Web / Wikimedia Commons )
Just 10 minutes instead of an hour
But first, let's go back to 2022. At the ESEAC International Electrochemistry Conference in Vilnius, V. Žutautas won 2nd place in the Best Scientific Poster category. It briefly presents the main facts about the research and its results.
The Lithuanian presentation was on a pH sensor developed using a glassy carbon electrode, chitosan and a folic acid polymer; pH indicates how much of a liquid contains hydrogen ions (H+ ), in other words, how acidic or alkaline the liquid is. pH 7 is a neutral measure; the lower the number, the more acidic the solution will be, and conversely, a higher pH means a more alkaline solution.
The sensor developed by Žutautas thus consists of a glassy carbon electrode (molten carbon, with a very smooth surface like glass) on which a tape of chitosan (a chemical derived from crustacean shells) is coated. Folic acid (yes, the same that pregnant women drink) is then "stuck" on top. This is done by polymerisation, when several monomer molecules are combined to form a polymer.
"Folic acid responds to pH, so when the charge is changed, there is a change in the electric current - and from that we can determine what the pH is," says the scientist.
His sensor detected pH readings between 6 and 9, and is more "alkaline", making it suitable for use in the food industry, especially for cleaning equipment and dishes.
"This is very important because, for example, a change in pH can determine the quality, flavour and hardness of meat. They are also used to check washing machines or dishes after they have been rinsed - as these washings use very alkaline liquids.
The sensor can be attached to the surface of a factory conveyor and, when liquid falls on it, an electric current causes the device to recognise the change in pH," he says.
(Photo: Pexels.com)
The sensitivity of the pH sensor described in this poster ranged from 34-38 millivolts per pH. In studies by scientists around the world, this figure can be as high as 50 millivolts - but Vytautas says his device has the advantage of speed: it detects a change in pH in about 10 minutes, while elsewhere you have to wait for half an hour or an hour.
The ESEAC conference committee appreciated the Lithuanian's achievements - and the event was very useful for him: 'There was a lot of talk about the methodologies that I used. And when I was standing by my poster, a scientist came up to me and told me some useful things about chitosan that I hadn't known before. This was useful for further research."
Flexible graphene instead of glass
Vytautas is due to defend his thesis in the autumn. The topic of the thesis (which is the basis for the above-mentioned article published in an international journal) is very similar, but with different main sensor electrodes (electrical conductors). After trying several options, Žutautas finally settled on a laser-induced graphene electrode.
This uses polyimide - a tape that does not conduct electricity. Using a laser, the polyimide is burned until a thin layer of graphene forms on its surface. The resulting electrode is flexible, flat and therefore more adaptable (and easier to place) than the usual larger and rigid glass electrode.
The sensitivity of a sensor based on this is around 30 millivolts per pH.
(A prototype pH sensor developed by V. Žutautas and his colleagues. Photo from personal archive)
When Vytautas talks about his discovery, the word "accidentally" comes up again. What happened?
"Interestingly, laser-induced graphene is highly hydrophilic, so it gets wet quickly. When it is produced, grooves are formed. During the tests, water would get into them and spread all over the electrode. Therefore, if you wet one spot, the liquid will spread all over it. And that's a problem, so we looked for a way to make graphene hydrophobic, waterproof.
As I coated the electrode with chitosan during the tests to improve adhesion to folic acid and stability, I accidentally discovered that chitosan is hydrophobic - at least the dry chitosan film. I started to coat the surface of the electrode with it to insulate it from the electric current.
We also used nail polish to stop the electric current. But at the same time it penetrates the carbon and blocks the whole signal. Then we first coated the surface with chitosan and then with nail polish - and then we were fine. The electric current was only flowing through the bottom, so we solved the problem of how to insulate the sensor in whatever shape we wanted."
(Testing a pH sensor developed by V. Žutautas and his colleagues. Photo from personal archive)
In the food industry, similar pH sensors already play an important role and are widely and extensively used. But the FTMC team has something new and better to offer.
We mentioned the speed of pH detection, but according to Vytautas, that's not all: "In industry, most pH sensors are glass, but ours is flat and flexible. It is a few millimetres thick and can be fitted into any container or device with very small gaps. Ordinary sensors would not fit into them. The 'sensitive' part of our sensor, which measures pH, could be on the outside, while the rest, with all the electronics, is 'hidden' inside the container or device."
The PhD student also highlights another distinct advantage. Conventional sensors need to be calibrated before each pH measurement, i.e. the measuring instrument needs to be adjusted to give the correct reading within the tolerance. This is normally done by checking that the sensor reading corresponds to a reference standard (in this case, the pH scale).
Meanwhile, FTMC sensor only needs to be calibrated once, and this stability can remain virtually unchanged for months. "It is faster, more convenient and does not require additional solutions," explains the PhD student.
(PhD student Vytautas Žutautas. Photo: FTMC)
Promising new plans
With the development of the new pH sensor, FTMC's task (as is often the case) is how to get industry interested in the device. But Vytautas Žutautas' discoveries will not end there: if all goes well, a new exciting project on laser-induced graphene sensors is planned for autumn. "And I'll probably be part of the team for this project", he smiles.
What will he do with the team?
"We want to develop a sensor-patch applied to wounds. It would contain graphene to improve wound healing, and also to detect the stage of the wound based on pH and other readings.
In this case we plan to cooperate with several foreign scientific institutes. They would produce the patch itself, develop the graphene, and we would do all the electrochemistry," says Vytautas.
Written by Simonas Bendžius
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