There are several definitions in use, but a common one is that any particle with at least one dimension less than a micron is a nanoparticle. An alternative definition is ‘particles with all three dimensions less than 100 nm’. Nanoparticles may be of any shape (flat, rod’shaped or spherical).

Note that a micron is one millionth of a metre, and a nanometre is one thousandth of a micro (i.e. there are one thousand million nanometers in a meter). For comparison, a human hair is about sixty microns thick.

For comparison, viruses vary in size from a few tens of nanometers to hundreds of nanometres. Bacteria also vary in size, but are much larger than viruses with typical sizes greater than one micron (or one thousand nanometres).

Nanoparticles often behave chemically differently to their bulk equivalent, and as this behaviour depends on size, shape and surface chemistry, the properties of such nanoparticles can be tuned. Naturally occurring peptides are a special case of nanoparticle with properties developed by natural evolution.

The use of antimicrobial nanostructures and/or particles provides an alternative to currently used antimicrobial chemicals such as quaternary ammonium compounds, about which there are some environmental concerns.

We will explore several independent approaches to antimicrobial surfaces, some of which might be combined in practice. On the one hand, we will physically alter the surface structure using pulsed lasers to make a nano-corrugated surface that is ‘uncomfortable’ for microbes (e.g. because it is not wettable, the ‘lotus effect’). We can also instead use nanoparticles to make such a structured surface, and may hold them in place using a binding matrix that itself has antimicrobial properties (like human skin). Finally, we can synthesize inorganic nanoparticles and peptides which have antimicrobial properties. Silver and copper are well known to have such properties, and by making ‘core-shell’ nanoparticles which combine two or more materials we will optimize the resulting properties.

This is of concern to the project, and will form part of our criteria for the selection of materials. For our materials to have an adverse effect upon the environment, the nanoparticles must both first be lost from the surface, and have and retain an undesirable environmental effect. We will seek to avoid such materials, and will carry out tests to ensure the safety of our antimicrobial surfaces.

A peptide is a chain of amino acids. Amino acids are the building blocks of proteins, so peptides can be thought of as a part of a protein. Some peptides (either naturally occurring or synthetic) have antimicrobial properties and are then known as antimicrobial peptides (AMPs). See also ‘bioinspired peptides’.

We can observe the properties (and mechanisms) of natural peptides, and then synthesize artificial peptides that combine desirable features by copying the relevant parts of the natural peptide (often supported by computer modelling). The resulting novel peptides are known as ‘bioinspired’. An example for this project would be the use of several Human Elastin-Like Polypeptides (HELPs) designed at the University of Trieste.

We are not completely certain what the impact of the novel materials would be, because there is uncertainty about how many people are actually infected via the surface transfer of pathogens. Part of the project’s work will be to improve our knowledge of this area, and (subject to prior safety testing and ethical approval) to measure the (hopefully beneficial!) effect of our new materials in a nursing home.

We aim for a lifetime of at least one month before a new coating is required (or cleaning to restore the original nanostructure). This timescale is inspired by the standards for hospitals and by the performance of current products.

These are historical terms used by chemists to distinguish between molecules that have a structure largely consisting of carbon atoms (termed ‘organic’), and those that don’t (termed ‘inorganic’). Note that ‘organic’ molecules and particles do not necessarily arise from a lifeform, and ‘organic’ in this context has nothing to do with organic farming.

‘Activity’ here refers to a measurable effect upon the lifetime or growth of microbes. For bacteria, we measure this by counting how many bacterial colonies develop within a given time, compared to our reference surfaces. Our references are material surfaces with well known properties – we will compare the antimicrobial activity of our new surfaces to the results from stainless steel, copper, and a commercially available antimicrobial coating.

The COVID-19 pandemic reminded us all of how important basic hygiene is to avoid cross-infection, and how easily such aerosol-transmitted infections can spread – both directly through the air, but also via a surface where the droplets come to rest. That infections can be spread via surfaces has been known since 19th century studies on puerperal fever (then a significant cause of maternal mortality). The emergence of antibiotic resistant bacteria makes it more important then ever to avoid infection in the first place.