Optimization of ssDNA-SWCNT Ultracentrifugation via Efficacy Measurements

Photoluminescent single-walled carbon nanotubes (SWCNT) hold substantial potential for a variety of applications in biology and medicine. Improved preparation of such materials requires optimization of various parameters, including those pertaining to ultracentrifugation techniques for removing non-photoluminescent carbonaceous materials. In this work, we investigated single-stranded DNA (ssDNA)-SWCNT preparations, which are widely used and exhibit strong photoluminescence (PL). We found, however, that total PL is not well-described by SWCNT concentration, and that it is much more sufficiently described by a comparison of SWCNT E₂₂ transition peaks with surrounding baseline absorbance from non-fluorescent carbonaceous material. We used this metric, defined as efficacy, in optimizing techniques for centrifugation and subsequent fractionation. We found that increased centrifugal forces removed substantial non-photoluminescent material, but also more SWCNT mass, yielding less-concentrated but more-pure fluorescent SWCNT samples. Thus, a tradeoff exists between decreased sensor material and increased sensor quality, one which might be considered for each novel SWCNT-based nanosensor construct. We anticipate these studies serving as a basis for improved applied nanosensor development.