Insecticide-treated bed nets remain one of the most effective tools in malaria prevention, acting both as a physical barrier and as an insecticidal surface that kills or disables mosquitoes before they can transmit disease.
New research by a multidisciplinary research team from the University of Liverpool and the Liverpool School of Tropical Medicine (LSTM) uses surface science to assess how well malaria nets perform.
Published in Science Advances, the focus of the study was the phasing out of PFAS coatings, a group of synthetic fluorinated coating chemicals that have been valued for stability and performance. However, their environmental persistence and potential health risks have made their removal an important priority.
To understand the impact of removing PFAS, the team developed a novel multimodal evaluation platform combining chemical analysis, advanced surface imaging, and mosquito behavioural tracking.
Surface imaging and spectroscopic expertise provided by the University of Liverpool revealed striking differences in how the insecticide deltamethrin is presented on the surface of PFAS-free nets introduced since 2014.
Although these malaria nets met standard specifications for insecticide content, the study found that removing PFAS significantly altered how effectively the insecticide performs. Crucially, findings of the study demonstrate that efficacy is not determined solely by how much insecticide is present, but by how it is distributed on the net surface.
PFAS-based coatings were shown to produce smaller, more evenly distributed, non-crystalline deltamethrin particles. In contrast, PFAS-free coatings resulted in larger, more heterogeneous particles. These differences were linked to measurable changes in mosquito behaviour, including reduced irritancy and lower knockdown rates in resistant populations. Importantly, this effect varied across mosquito populations, with the most pronounced differences observed in resistant strains, while susceptible strains showed minimal change.
Professor Rasmita Raval, from the University of Liverpool’s Department of Chemistry and Director of the Surface Science Research Centre, whose team provided the surface imaging and spectroscopy expertise to the study, said: “This study shows that surface chemistry is not a minor formulation detail. Our work shows that two bed nets with the same amount of insecticide can behave very differently depending on how that insecticide is structured and presented at the surface.
“By linking surface presentation to mosquito response, we can better understand how to design formulations that are both environmentally responsible and biologically effective.
“This allows us to pinpoint why net performance declined after changes due to environmental pressures to stop using PFAS. Finally, a more detailed and nuanced understanding of effectiveness against susceptible and resistant mosquitoes emerges.
“This study benefits from the combination of University and LSTM’s research capabilities to create a powerful multimodal evaluation platform that can de-risk malaria control technologies at an early stage.”
Dr Hanafy Ismail, lead author and Lecturer in Vector Biology at the Liverpool School of Tropical Medicine, said: “Our findings show that insecticide quantity alone does not fully explain how a bed net performs. Surface presentation, bioavailability, and mosquito behaviour also matter. As malaria control tools evolve, we need integrated evaluation systems that can detect meaningful performance shifts early and help ensure that environmentally sustainable products remain effective for the communities that depend on them.”
A key message from the study is that environmental sustainability and malaria control must advance together and that multidisciplinary approaches are needed that consider chemical composition, surface properties and biological outcomes are needed.
Professor Raval is also Director of the Open Innovation Hub for Antimicrobial Surfaces, co-founder and co-Director of the National Biofilm Innovation Centre, and a member of the Liverpool City Region Innovation Board.
The paper `Multimodal platform for ITN efficacy: Surface chemistry, bioavailability, and mosquito behavior’ (doi: 10.1126/sciadv.aeb2023) is published in Science Advances.