Carbon nanotube clusters as universal bacterial adsorbents and magnetic separation agents.

The magnetic susceptibility and high bacterial affinity of carbon nanotube (CNT) clusters highlight their great potential as a magnetic bio-separation agent. This article reports the CNT clusters' capability as "universal" bacterial adsorbents and magnetic separation agents by designing and testing a multiwalled carbon nanotube (MWNT) cluster-based process for bacterial capturing and separation. The reaction system consisted of large clusters of MWNTs for bacterial capture and an external magnet for bio-separation. The designed system was tested and optimized using Escherichia coli as a model bacterium, and further generalized by testing the process with other representative strains of both gram-positive and gram-negative bacteria. For all strains tested, bacterial adsorption to MWNT clusters occurred spontaneously, and the estimated MWNT clusters' adsorption capacities were nearly the same regardless of the types of strains. The bacteria-bound MWNT clusters also responded almost instantaneously to the magnetic field by a rare-earth magnet (0.68 Tesla), and completely separated from the bulk aqueous phase and retained in the system. The results clearly demonstrate their excellent potential as highly effective "universal" bacterial adsorbents for the spontaneous adsorption of any types of bacteria to the clusters and as paramagnetic complexes for the rapid and highly effective magnetic separations.