Unfortunately, DLS does not provide insight into particle formation, as the particles appear to form reversible aggregates during synthesis. However, the final product nanoparticles can be subjected to DLS analysis. While for the Ref particles, the sizes determined by DLS and SEM are similar (see diameters in Table and Table ), DLS delivers much larger diameters d than the SEM image analysis for P1 -P6. The smaller the particles are, the more strongly they seem to aggregate in solution. The particles can be redispersed by ultra-sonication, indicating that the aggregation is reversible (see Figure ). Reversible interactions between particles might indicate that our polyimidazole particles will also attract large amounts of biomacromolecules in biological media. This is a well-known phenomenon in biomedical applications of particles, where a so-called protein corona is formed around the particles. This protein corona often leads to opsonization (a process triggering the immune system to engulf and kill pathogens) and uptake by macrophages, reducing the circulation time of the nanoparticles and therefore their chance to reach the tumor. To analyze this, we perform protein adsorption experiments (see Supporting