Introduction
During these hard months we are all reading a lot about the dramatic consequences of the COVID-19 outbreak. Many people passed away due to late diagnoses, especially in the early stage of the outbreak: identification is indeed one the main problems when you deal with an unknown virus.
In this article we will just have a chat about some optical techniques very relevant to identify different viruses and pollutants.
At the end of 2019 a team of researchers from the Penn State University developed a device based on the use of carbon nanotubes.
This device is called VIRRIONS: it is defined like a matrix of nanotubes, sized to be suitable to several viruses: Zika and Ebola were some of the viruses used as a target.
The nanotubes are enriched with gold particles to improve the conductivity.
Subsequentely, the viruses are identified thanks to the produced signal (vibration) through Raman spectroscopy.
How does this technique work?
Raman spectroscopy takes advantage of the interactions between light and materials to get details about different materials: indeed it is based on the vibrations (intramolecular and also inter molecular) of a material .
When photons hit the molecules of a media ( gas, liquid, solid) several photons are diffused mantaining the same energy of the incident photons. This phenomenon is known as elastic scattering. Though after the diffusion, a very small quantity of photons has a different frequency. These "rebel" photons were discovered by Chandrasekhara Venkata Raman who won the Nobel Prize for Physics in 1930.
Raman spectroscopy is very helpful especially to detect some chemical bonds like carbon-carbon or suplhur-sulphur.
Where are microplastics?
One of the most recent applications of this techniqe is microplastics detection.
First of all: what are microplastics?
There are several very specific definitions but we will define them as plastics particles smaller than 5 mm. They come from shards of plastic objects which have been released into the environment and decomposed (packages, synthetic textile fibers just to name a few).
Microplastics are already widely present in the sea and they are damaging the whole ecosystem.
Talking about food and beverages, microplastics might be present in fish, molluscs and crustaceans. These particles accumulate in the intestine of the animals, so from this point of view eating fish might be less risky than eating shellfish as the majority of people discards the intestine of fishes.
(I have a friend who is a chef in a restaurant, his top dish is monkfish liver, I really hope he will never read this article. In case he is reading, I hope that we will still remain friends).
Unfortunately also salt and drinking water might contain microplastics.
Moreover, several commercial products are contaminated as well: soap, exfoliant creams and body scrubs, which contain polyethylene.
This material increases the oiliness of body creams and it helps to bond together all the ingredients. Like when you make a cake and you put eggs, just less tasty.
Now that we discussed about the diffusion of microplastics, let’s see how we can detect them with spectroscopy.
Microplastics detection
According to a very interesting study from Leibniz University Hannover, Raman spectroscopy can be very helpful to observe microplastics in streaming tap water.
To carry out this reserach, several sampling solutions containing water contaminants and different microplastics were prepared and analysed. Among the studied materials we find: polyamide, polyethylene and polystyrene.
The other substances added to “simulate” real water conditions were humic compounds and surfactants (present in many detergents).
This study proved that it is possible to identify single particles from 5 different types of microplastics in streaming tap water through the interpretation of their Raman spectrum.
What is interesting to see is that this works even in contaminated waters.
Indeed the Raman signal of one single particle in pure water was very close to the signal in presence of surfactants. Thanks to this work it was possible to detect particles with size close to 0,1 mm.
At the moment there are several interesting studies about microplastics detection, but one of the main challenges remains the detection of microplastic in real time. This could be a great turning point as it would make water filtrations more efficient. Regards this issue, there is a cool project ongoing called AquaVision, developed during the CERN Entrepreneuship Student Programme 2019. This promising new venture aims to develop the first real time microplastics detector by taking advantage of an optical technology originally used at the Large Hadron Collider at CERN. It is very nice to see that the use of optical methods for air and water quality monitoring is now gaining a foothold. Even if Raman Spectroscopy is very powerful, choosing the right materials is always crucial due to the high reactivity of substances like microplastics and to the persistence of viruses. In particular, doing research about viruses always involves some risk, but it is worth it as it is the only way to save people’s life. Regards the COVID-19 , we have the proof of how devastating superficiality and lack of accurate information can be. We are definitely witnessing something which is unprecedented. Luckily technology still allows us to create networks and to help each other: just think of the people working at Isinnova, who together with Renato Favero (Hospital Gardone Valtrompia) managed to convert snorkeling masks into ventilators for oxygen therapy. What a fantastic idea, just amazing!
When you face some extremely complicated situations, you really need to find creative solutions. More generally speaking, what is nice about technology and science is that many techniques are very adaptive and powerful: maybe when the spectrophotometer was invented in 1935 people would have never imagined that the same technique could have been applied also for viruses identification and environmental sciences, but so it is!
author:
Giulia Ioselli
Credits:
Microplastics Detection in Streaming Tap Water with Raman Spectroscopy
Ann-Kathrin Kniggendorf, Christoph Wetzel and Bernhard Roth
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