Particle immobilisation techniques: Applications for microplastics and beyond

Emerging particulate pollutants, ranging from nanoparticles to microplastics, present multifaceted challenges in their detection and characterisation within the atmosphere. Particle immobilisation techniques, which we originally developed for the analysis of microplastics (MP), have demonstrated great versatility for experimental and methodological development, allowing per-particle manipulative investigations and sample persistence over extended periods under various treatments. These techniques may prove useful for wider applicability to other particulate pollutants.We have been immobilising particles below 100 µm to for the evaluation of purification methods and for conducting interlaboratory analytical comparisons (ILCs). In purification method evaluation, our immobilisation approaches withstand chemical treatments, enabling pre-post comparisons while preserving particle integrity and aiding in method validation. By immobilising MP on suitable substrates, we have established a framework for serial ILCs where the same sample is measured by all ILC participants, reducing inter-participant analytical variation by up to 77% compared to a conventional parallel ILC design using suspended samples.Beyond MP, these techniques have potential applications for atmospheric particulate pollutants such as soot or fly ash. The immobilisation concept, using filtration with inorganic adhesives, allows reproducibility in analytical assessments across different types of particulate matter. In addition, we discuss the opportunities and obstacles of particle immobilisations as routine procedures, which can help to build up persistent sample archives or to establish robust re-measureable QA/QC reference samples. Multi-method analyses such as correlative microscopy and microspectroscopy can benefit from the application of particle immobilisation techniques.