Adsorption equilibrium and kinetics of microorganisms on single-wall carbon nanotubes

Adsorption equilibrium and kinetics of pure and mixed cultures of Escherichia coli and Staphylococcus aureus on single-walled carbon nanotubes (CNT) aggregates were studied in an effort to develop CNT-based biosensors for quick detection of these bacteria in water. Batch experiments were carried out to measure the adsorption kinetics and equilibrium of pure and mixed culture of E. coli and S. aureus on the CNT aggregates at ambient temperature and various culture concentrations. The CNT aggregates can adsorb significant amounts of E. coli and S. aureus bacteria with different size and shape characteristics. The smaller size S. aureus has a five to ten times faster diffusion rate than E. coli and about 100 times higher adsorption affinity with the carbon nanotube aggregates. Freundlich adsorption model correlates well both the pure component and mixture adsorption equilibrium data. It is quite possible the CNT aggregates have separate adsorption sites for both E. coli and S. aureus. The combined high adsorption affinity and fast adsorption kinetics for S. aureus suggest that even unmodified single-wall carbon nanotubes can selectively differentiate S. aureus and E. coli in water. Transmission electron microscopic analysis qualitatively confirmed the adsorption results and provides direct visualization of the adsorbed bacteria on carbon nanotube aggregates. Both bacteria form biofilms on carbon nanotube aggregates and have a strong tendency to connect with each other rather than with the carbon surface.