Skip to main content
U.S. flag

An official website of the United States government

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

Separation of bacteria, protozoa and carbon nanotubes by density gradient centrifugation



Monika Mortimer, Elijah Petersen, Bruce A. Buchholz, Patricia Holden


Sustainable production and use of carbon nanotube (CNT)-enabled materials requires efficient assessment of CNT environmental hazards, including their potential for bioaccumulation and biomagnification in environmental receptors. Microbes as abundant organisms responsible for nutrient cycling in soil and water are important ecological receptors for studying the effects of CNTs. Quantification of CNT association with microbial cells requires efficient separation of CNT-associated cells from individually dispersed CNTs and CNT agglomerates. Here, we demonstrate optimized procedures for separation of bacteria (Pseudomonas aeruginosa) from unbound multiwall carbon nanotubes (MWCNT) and MWCNT agglomerates using sucrose density gradient. We demonstrate separation of protozoa (Tetrahymena thermophila) from MWCNTs, bacterial agglomerates, and protozoan fecal pellets by centrifugation in iodixanol solution. The location of free MWCNTs in the density gradients after centrifugation was determined by quantification of 14C-labeled MWCNTs; the localization and purity of microbes was determined by optical microscopy. The separation and concentration of live microbes was achieved without affecting their viability; protozoan intracellular content of MWCNTs and bacteria was also unaffected. The optimized methods contribute to improved efficiency and accuracy in quantification of MWCNT association with bacteria and accumulation in protozoan cells, thus supporting improved assessment of CNT bioaccumulation.
International journal of nanomedicine


Mortimer, M. , Petersen, E. , Buchholz, B. and Holden, P. (2016), Separation of bacteria, protozoa and carbon nanotubes by density gradient centrifugation, International journal of nanomedicine, [online], (Accessed April 22, 2024)
Created October 11, 2016, Updated October 12, 2021