Binding of bacteria to magnetic nanoparticles in suspension: Experiments and kinetic models

With the rise of antimicrobial-resistant and multi-drug-resistant bacteria, the use of magnetic nanoparticles (MNPs) has become a promising tool for separation processes in conjunction with in vitro diagnostics for the rapid identification of bacterial species in various medical and biological fluids. However, there are few studies on the time required for MNPs to successfully capture and remove bacteria from suspensions. This study presents two mathematical models that describe the kinetics of bacterial capture using polydopamine-coated MNPs (pDA-MNPs) in phosphate-buffered saline. The model parameters are derived from data from the capture of Staphylococcus aureus, Staphylococcus epidermidis, and Streptococcus mutans, which exhibit high adherence to pDA-MNPs. Results show that during the first 3 min, bacterial capture and removal by magnetic particles show second-order kinetics overall, and first order each with respect to bacterial concentration and to magnetic particle concentration. At longer times, the data are better fit by a model of fast and slow parallel capture mechanisms. pDA-MNPs capture S. epidermidis faster than S. aureus, and capture S. mutans more slowly than the other bacterial species. Rate constants derived at very high bacterial concentrations (~10⁸ CFU/mL) were also found to fit experimental data collected at very low concentrations (~750 CFU/mL), showing applicability of the model spanning several orders of magnitude in bacterial concentration. Analysis of the kinetic parameters provides insights into optimizing the time and MNP concentrations necessary to achieve a desired bacterial capture efficiency in medical or environmental diagnostic applications.