Research On Visualization Of The Sedimentation Process Of Polydopamine Nanoparticles

Centrifugal is a common technique used to analyze and separate substances,it has become increasingly important in chemistry,biology and medicine.Analytical ultracentrifugation(AUC)can predict theoretically the sedimentation of nanoparticles in a preparative ultracentrifugation(PUC)tube,as the sedimentation coefficient of the particles can be determined by an AUC cell.Some researchers have combined the two techniques for ordering of nanoparticles,but a detailed study about the sedimentation behavior of nanoparticles in PUC tubes has not yet been performed.Convective flow of solution was often ignored by researchers when applying the theory based on AUC to PUC,yet the fact that the hypothesis of convective-free sedimentation is only valid on the sector-shaped AUC cells.Therefore,it's necessary to explore the sedimentation of nanoparticles in PUC tubes.Polydopamine(PDA)is a eumelanin-like material that can efficiently convert near infrared(NIR)light into heat.In this paper,based on the ability of PDA nanoparticles,a new method which could provide a visualization of the sedimentation process in PUC tubes was developed.The main work includes:(1)Monodispersed,stable PDA nanoparticles were prepared via solution oxidation method.Then the sedimentation process of PDA nanoparticles in AUC cells was studied.It was found that a clear sedimentation boundary appeared when PDA settled in an AUC cell.The ls-g*(s)model of the Sedfit software was applied to fit experimental data to calculate sedimentation coefficient distributions of PDA nanoparticles.Further analysis concluded that only slight agglomeration was present in the PDA nanoparticles suspensions.(2)The sedimentation process of PDA nanoparticles in PUC tubes was studied.We firstly used sedimentation coefficient to calculate centrifugal time for a complete sedimentation in a PUC tube.The results from experiment and image analysis indicated that the sedimentation coefficient determined from AUC could be used to predict the necessary sedimentation time of nanoparticle in a PUC tube.In addition,based on the photo-thermal conversion ability of PDA nanoparticles,we established a method which could provide a visualization of the concentration distribution evolution of PDA nanoparticles in PUC tubes.The study also indicated that the geometry of the tube affected the sedimentation behavior of the particles.Tubes with larger rotation radius and smaller inner diameter would be beneficial to reproduce a sedimentation process in a PUC tube similar to that in an AUC cell.