Rapid, label-free analysis of both semi-conducting and metallic carbon nanotubes from cultured cell samples

The success of almost all medical applications of carbon nanotubes (CNTs) will ultimately depend on how many CNTs are bound-to and/or taken-up by cells. Statistically meaningful measures of the amounts of cell-associated CNTs are therefore required to evaluate the effectiveness of these applications, as well as to accurately assess the biocompatibility/cytotoxicity of the unique CNT constructs involved in each application. Unfortunately, current methods to detect cell-associated CNTs are either unable to detect both semi-conducting and metallic single-walled CNTs (SWNTs), are not suited to analyze a large population of cells in a timely fashion, and/or require the attachment of a reporter label. Recently, we described a rapid, sensitive, inexpensive, and label-free sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis (PAGE) method that can quantitate the amount of SWNTs in biological samples (Wang et al., Anal. Chem. 2009, 81, 2944). The method is also distinctive in that it can measure the rate at which SWNTs enter living cells. For example, an uptake rate of 30 femtograms SWNTs/day/cell was determined when normal rat kidney (NRK) cells were exposed to growth medium containing 98 micrograms/mL of protein-coated CoMoCAT SWNTs. Using NRK cells, HiPco SWNTs containing metallic SWNT structures, and microprobe Raman spectroscopy with 632.8-nm laser excitation, we demonstrate a further advantage of the SDS-PAGE method in that it retains both semi-conducting and metallic SWNTs in biological samples. Furthermore, using SDS-PAGE/Raman spectroscopy, we demonstrate that the electronic structure of non-targeting, protein-coated SWNTs is not a key factor of the NRK cell uptake mechanism.