LAUSR

In this study, we quantitatively detected adsorption and desorption of DNA molecules that competed with sodium cholate (SC) molecules on single-walled carbon nanotubes (SWNTs) by fluorescence spectroscopy. In previous studies, competitive adsorption and/or replacement were studied based on techniques such as near-infrared (NIR) absorbance and photoluminescence (PL) spectroscopy of SWNTs. In those studies, adsorption of organic molecules was detected as spectral changes in SWNTs, but not in organic molecules. In this study, we employed fluorescent-labeled DNA (Fc-DNA) to detect competitive adsorption through quenching of fluorescent dyes that were attached to DNA molecules. Through this approach, the adsorption behaviors of DNA molecules could be directly determined. Hence, we found that Fc-DNA molecules adsorbed on SWNT surfaces that were pre-wrapped with SC when the SC concentration was reduced. However, when SC concentrations recovered after three days of incubation, detachment of Fc-DNA molecules was observed. In addition, our method could be applied to evaluate the adsorption of fluorescent dyes on SWNT surfaces instead of DNA molecules. Hence, our method is effective in studying competitive adsorption of organic molecules on SWNT surfaces. The obtained information is complementary to that obtained from NIR spectroscopy of SWNTs.