Gel Electrophoresis Method to Measure the Concentration of Single-Walled Carbon Nanotubes Extracted from Biological Tissue

A rapid and sensitive method to detect single-walled carbon nanotubes (SWNTs) in biological samples is presented. The method uses polyacrylamide gel electrophoresis (PAGE) followed by quantification of SWNT bands. SWNTs dispersed in bovine serum albumin (BSA) were used to develop the method. When BSA−SWNT dispersions were subjected to sodium dodecyl sulfate (SDS)−PAGE, BSA passed through the stacking gel, entered the resolving gel, and migrated toward the anode as expected. The SWNTs, however, accumulated in a sharp band at the interface between the loading well and the stacking gel. The intensities from digitized images of these bands were proportional to the amount of SWNTs loaded onto the gel with a detection limit of 5 ng of SWNTs. To test the method, normal rat kidney (NRK) cells in culture were allowed to take up SWNTs upon exposure to medium containing various concentrations of BSA−SWNTs for different times and temperatures. The SDS−PAGE analyses of cell lysate samples suggest that BSA−SWNTs enter NRK cells by fluid-phase endocytosis at a rate of 30 fg/day/cell upon exposure to medium containing 98 μg/mL SWNTs.