ИСТИНА

Nanodiamonds are considered as a perspective tool in the development of drug delivery platform. Possessing a developed surface containing a large number of functional groups, nanodiamonds are able to adsorb various substances, including polymers. In present work we studied the adsorption of chitosan on nanodiamonds. We used tritium as a tracer of chitosan surface concentration. Tritium label was introduced into the chitosan molecules by means of tritium thermal activation method according to the procedure described in reference. Tritium labeled chitosan was dissolved in 0.02 N HCl, mixed with nanodiamond suspension and incubated during 48 hours at room temperature followed by centrifugation and radioactivity measuring for both supernatant and precipitate. It was found that adsorption isotherm of chitosan is of Langmuir type. The values of maximum adsorption and Langmuir constant are controlled by zeta potential of nanodiamonds. In the cases of negative zeta potential of initial nanodiamonds maximum adsorption was as much as 3 times higher than for positively charged materials indicating the dominant role of electrostatic interactions. Since significant amount of chitosan was irreversibly adsorbed on the surface of positively charged particles we can expect the essential contribution of Van der Waals interaction between chitosan and nanodiamond surface. Stability of chitosan-nanodiamond composites was analyzed in water, PBS, 0.01 N HCl and serum albumin in PBS (40 g/L) at 37°C during 48 hours. Albumin in PBS was found to be the best desorbing agent for chitosan. Charge compensation by counterion in presence of buffer or HCl results in higher desorption confirmed the dominating ionic mechanism of chitosan binding to nanodiamond surface. Modification of nanodiamonds with chitosan affected its stability in the aqueous suspensions that was controlled by zeta potential measuring as a function of chitosan surface concentration. Peculiarities of chitosan adsorption on nanodiamonds will be discussed in the presentation.