| Single-walled carbon nanotubes (SWNTs) show potential for inclusion into a targeted drug delivery system. With appropriate functionalizations, they have been shown to effectively transport molecules across cell membranes without harming the cells. They also could be placed in cancer cells to target them for thermal ablations since SWNTs absorb near-infrared radiation, while live cells do not. Understanding the diffusion of SWNTs in human biological fluids would aid the design of such a system. Here the diffusional characteristics of SWNTs under physiologically relevant conditions are reported. The SWNTs were processed according to the method developed in our laboratory with initial concentration of 1 g-SWNT/L. The resultant SWNTs were well dispersed and shortened with the average length and diameter of 253 nm (±30.6 nm) and 1 nm, respectively. The in situ Brownian motions of individual SWNT was observed using fluorescence microscopy based on the SWNT staining methodology with 1-pyrenebutanoic succinimidyl ester (PSE). The PSE-staining technology enabled in situ, noninvasive imaging with nanometer resolution to monitor SWNTs in real time and to characterize their diffusional characteristics. Diffusion data were generated at 37°C under four different viscosities, which correspond to those of four human body fluids: plasma (1.2 cP), bile (2.6 cP), blood (4.2 cP), and cytoplasm (21.3 cP). In this study, the viscosities of the body fluids were simulated using glycerol. The estimated diffusion coefficients of the SWNTs in the four body fluids were 1.45 ± 0.652 × 104 nm2/s (plasma), 0.91 ± 0.205 × 104 nm2/s (bile), 0.59 ± 0.179 × 104 nm2/s (blood), and 0.26 ± 0.114 × 104 nm2/s (cytoplasm). The estimated diffusion coefficients of SWNT-DNA in the four body fluids were 1.45 ± 0.402 × 104 nm2/s (plasma), 0.62 ± 0.212 × 104 nm2/s (bile), 0.41 ± 0.142 × 104 nm2/s (blood), and 0.38 ± 0.257 x 104 nm2/s (cytoplasm). |
