Killing and Aggregation of Bacteria in Solution by Charged Colloids

Harmful planktonic bacteria pose significant threats to human health and industrial productivity. While various methods have been developed to eliminate bacteria in solution, effective and straightforward strategies for both killing bacteria and subsequently removing them remain challenging. In this study, we propose a versatile strategy that combines killing and aggregation of planktonic bacteria using colloidal particles with charges opposite those of the bacteria. The electrostatic attraction between the colloids and bacteria enhances close contact, enabling the colloids to effectively disrupt bacterial membranes and compromise their structural integrity. Additionally, this interaction induces the generation of reactive oxygen species, which further damages bacterial DNA. Notably, the colloidal particles also function as bacteria linkers, promoting the aggregation of bacteria through electrostatic attraction and thereby facilitating their separation from the solution. However, an excessively high concentration of the colloidal particles was found to eliminate bacterial aggregates and restore a dispersed state, as the bacteria become completely coated by the particles, thus disrupting the particles' linker function. This work highlights the significant potential of charged colloidal particles in antibacterial applications and provides a simple and effective approach for killing and removing planktonic bacteria.