SPR imaging study of DNA wrapped single wall carbon nanotube (ssDNA-SWCNT) adsorption on a model biological (collagen) substrate

Abstract

The adsorption kinetics of single stranded-DNA dispersed single wall carbon nanotubes (ssDNA-SWCNTs) onto an immobilized collagen layer in a microfluidic channel was probed using surface plasmon resonance imaging (SPRi). The adsorption was measured for a range of both nanotube and solution parameters including the nanotube concentration, nanotube length, solution pH, and the type of medium (buffer and river water). The kinetic adsorption data suggests that the adsorption of the nanotubes to the collagen layer is irreversible in HEPES buffer, pH ≈ 7.4, at room temperature, with the nanotube adsorption displaying two different kinetic adsorption regimes for different concentration ranges. A stretched exponential function fit indicates that a transition of adsorption kinetics from single exponential (>40 μg/mL) to non-exponential kinetics (<40 μg/mL) occurs as the nanotube concentration decreases, suggesting that a diffusion-limited process was predominant at lower concentrations (<40 μg/mL). Adsorption measurements as a function of nanotube length also displayed differences in the apparent adsorption processes. Adsorption of shorter nanotubes (≈ 40 nm) was found to follow single exponential kinetics, while longer nanotubes (≈ 300 nm) adsorbed much more slowly, consistent with adsorption partially influenced by diffusion-limited processes. Finally, to evaluate the potential differences in adsorption for unintentionally released nanotubes in a riparian environment, nanotubes were stably dispersed in a sample of river water and exposed to the collagen layer. Compared to the adsorption under HEPES buffer the nanotubes in the river water were found to exhibit a reduced rate of adsorption. It is likely that passivation of the collagen layer by dissolved organic species could thus affect the fate of released nanotubes in a natural environment.