Technologies for fighting airborne germs

JRC explains | 16 April 2024 | Joint Research Centre

During the COVID-19 pandemic, most of us made a rather intimate acquaintance with some of these technologies. And many of us are still confused about exactly how they work and what are the mechanisms behind them.

This JRC explainer helps you better understand the technologies that are established, but also those that are emerging: a peek into the future, for being better prepared for the next reappearance of an airborne disease.

In a separate article about a JRC-HERA study, we tell you what an expert group employing the JRC foresight process tipped to be the most impactful technology, and delve into the trade-offs involved in deploying these technologies.

Detection technologies

Particle counters

The condensation particle counter type relies on aerosol – particles floating through the air – getting pressed through a laser beam. Based on the obstacles they create for the beam, their sizes are measured one by one.

Advantage: the results are seen immediately and can be obtained with a cheap hand-held device. They can tell us how clean a room is in terms of ultrafine particles

Drawback: it cannot tell what the particles exactly are, if they are of biological or non-biological nature. For that, other detection technologies are needed

Soundbite: a good first step. The increase of particles of a certain size can give us a general hint whether the concentration of a pathogen, an organism carrying disease, is on the up

Filters

Particles travelling in the air get stuck on the barriers made up by filters.

Advantage: They can work with huge amounts of air, up to 1000 litres per minute. They are cheap and also efficient in preventing the spreading of germs

Drawback: they collect the particles, but cannot tell what they are. They can also denature particles, which means that the molecular structure of pathogens gets changed, making detection more difficult

Soundbite: turn to them for preventing germs from spreading and for collecting them, but concrete detection must be left to other technologies

Cyclonic and impactor aerosol samplers

In the cyclonic type, particles in a stream of air are channelled by a centrifuge to crash onto a collection wall. Impactor ones are based on the same principle, but use different geometry

Advantage: can collect a large sample quickly. It costs little and is straightforward to use

Drawback: like filters, they often denature particles, meaning that detection is left to technologies that can recognise pathogen debris. They do not work very well with small particles

Soundbite: quick collection of particles, but no detection

Condensation aerosol samplers

In a condensation tube, a droplet of water forms around the particles, making them fall onto a surface, ready to be collected

Advantage: as opposed to other sampling methods, it is more gentle and keeps the molecular structure of particles intact

Drawback: slow, bulky, and requires specialist skills to operate. It only collects particles, does not identify them

Soundbite: if you have time on your hands and not destroying small pathogens is important, condensation aerosol samplers could be your choice

Cell cultures

This tried-and-tested method involves leaving aerosols in an environment with favourable conditions for a longer period of time and checking the result

Advantage: can detect certain pathogens, although its efficiency has its limits, with sample contamination and oversampling threatening to mess up the results

Drawback: it takes days to obtain a result and only works with samples that were not denatured. It also requires a lab environment

Soundbite: this is the method that you probably saw and experienced back in school. It might not be the future of detecting airborne pathogens though

Nucleic acid amplification (NAA)-based techniques

The now famous polymerase chain reaction (PCR) test relies on this technology. Primers, short stretches of nucleic acid, are used to bind the DNA of the particle to be identified. The number of DNA copies is then doubled several times in repeated thermal cycles. The quantity and size of DNA pieces are then checked thanks to an electric current

Advantage: the gold standard for pathogen analysis. Thanks to amplification, it can identify even small quantities of a pathogen with ultra-high efficiency

Drawback: the genomic sequence of pathogens has to be known beforehand, so it is not suitable for identifying entirely new germs. Obtaining a result can take hours, if not days. It is costly and requires specialised operators

Soundbite: as the benchmark in detection, NAA-based techniques are here to stay, but require some development to be suitable for quick on-site diagnosis

Direct identification through physico-chemical properties

For example, spectroscopy (which looks at how split light and matter interplay) and spectrometry (which gives quantitative measurements of such interplay) can help spot pathogens thanks to the differences in the biochemical make-up of these, benefitting from the observation that all molecules emit and absorb light at their own unique wavelengths

Advantage: if it works, it could be real-time, automated, and reliable, acting as an early warning tool

Drawback: often the differences in biochemical properties are very subtle, requiring advancements in artificial intelligence and algorithms to perceive patterns in them

Soundbite: a call from the future. If artificial intelligence learns enough, in the future this set of technologies can be a game-changer in the early detection of epidemics

Sequencing technologies

Next-Generation sequencing and protein sequencing can reveal the genetic and proteomic composition of samples, meaning that they can show us the order of the four building blocks in the pathogen molecules and tell us more about the proteins in them

Advantage: they provide a wealth of information on pathogens

Drawback: requires a lab to perform, it is expensive and can take weeks

Soundbite: provides the most detailed image, but has severe limitations

Decontamination technologies

Filtration / Ventilation

This well-established technology works by capturing particles in an airflow by filters made of materials such as activated carbon fibre or polypropylene fibre

Advantage: it is highly efficient in collecting larger particles, can be used simply and easily, and is already part of many building designs. It was found by experts to be the most impactful in fighting airborne pathogens

Drawback: filters require regular replacement. Otherwise, germs can gather on them and can become sources of contamination

Soundbite: simple and conventional, ventilation and filtration go a long way in getting rid of pathogens. You can do a lot by just opening a window

UV radiation

Ultraviolet (UV) radiation is a time-tested method for sterilising surfaces. It works by damaging the genetic material of pathogens

Advantage: it is indeed very efficient against viruses and bacteria

Drawback: at certain wavelengths within the UV range, it can damage human skin and eyes, or it can create ozone, which is harmful to humans. It has limited use against spores

Soundbite: very good at cleaning objects, but be careful of exposing humans to it and remember, it does not work from behind the corner, the UV radiation must directly shine on the pathogen

Electrostatic capture

Particles are exposed to a strong electric field, making them settle on a collection layer

Advantage: it can be integrated into HVAC (Heating, Ventilation, and Air Conditioning) filtering and employed without interrupting building use

Drawback: it can take a while to reduce contamination with this technology. It also uses quite some electricity

Soundbite: not without advantages, but not very green

Thermal inactivation

By affecting cell structure and proteins, high heat is great at killing pathogens

Advantage: this technology is one of the most performant ones. Over 99% of bio-aerosols can be inactivated in 0.2 seconds by applying 350 ◦C

Drawback: generating this much heat uses up a lot of energy

Soundbite: bulletproof, but very wasteful of energy

Plasma-based inactivation (including ozone)

Plasma is matter so extremely hot that electrons are snatched from atoms, creating ions (charged atoms or molecules), UV photons, and neutral molecules (e.g. reactive oxygen species). These reactive chemical species come in contact with pathogens in the air, damaging their cells, DNA, and proteins. Ozone, a pale gas with strong oxidising traits, can similarly disrupt pathogens’ ability to survive

Advantage: it has high efficacy and it is compatible with HVAC filtration

Drawback: creating plasma discharges is expensive and for fighting pathogens, it must be done in a just-in-time manner. Ozone irritates the airways and the lungs

Soundbite: can be suitable in certain settings, such as the food industry

Chemical aerosolization

Aerosolization with chemical products, for example sodium hypochlorite (a chemical compound used in bleach), is an established method for disinfecting rooms as it can eliminate microorganisms

Advantage: thanks to its oxidising and hydrolysing (the breaking of chemical bonds) properties, aerosolization with sodium hypochlorite is very efficient in cleaning indoor environments. If used in a fogging system, it can even clean difficult-to-reach areas. It is also quite cheap.

Drawback: by-products are harmful to humans, so they must not be present without protective equipment when disinfection takes place. Getting rid of these by-products can take a lot of time and expenditure. It can corrode materials

Soundbite: chemicals are very effective against airborne pathogens, but if not dosed and handled correctly, they can kill not only germs

Microwaves radiation

Electromagnetic radiation with long wavelengths causes vibrations in pathogens, breaking their cell membranes

Advantage: easy-to-use, can be even integrated into mobile phones, and used in a plug-and-play manner. It requires little energy and has an efficacy of 90%

Drawback: although already commercialised, some more research and development is needed to fully exploit this technology

Soundbite: you could have an app for disinfecting personal space

Lysozyme-based bactericides

Lysozymes are enzymes that protect against microbes. They are present in the tissues and secretions of animals and plants, bolstering the immune system

Advantage: it is efficient and requires little energy

Drawback: the readiness of this technology is still in its infancy. Certain lysozymes can only fight certain bacteria

Soundbite: more research is needed to synthesise lysozymes that can be used against a broader range of pathogens and fully exploit this defence inspired by nature

Photocatalytic Oxidation

This technology combines the effects of light (photons) with catalytic oxidation (oxidation made faster by substances called catalysts). Light (for example UV radiation) interacts with a semiconductor (material especially suitable to control the flow of electric current) (usually titanium dioxide) in the presence of a photocatalyst (material that makes chemical reactions easier to occur). As a result, on the surface of the photoactive material, reactive oxygen species are created, that can – as in the case of plasma-based inactivation – disrupt the workings of pathogens

Advantage: this technology can be effective against substances that are normally difficult to decompose, it can be also deployed against airborne pathogens

Drawback: more research is needed as the fundamental mechanics of using photocatalysts for air disinfection are yet poorly understood

Soundbite: promising, but more research is needed to optimise it