Analysis of individual nanoscale block copolymer vesicles by atomic force microscopy combined with time-resolved fluorescence microscopy

We report on the analysis of individual dye loaded block copolymer (BCP) vesicles via a combination of confocal laser scanning microscopy (CSLM)/fluorescence lifetime imaging microscopy (FLIM) on the one hand and atomic force microscopy (AFM) on the other hand. AFM measurements on ATTO 647N-loaded poly(styrene-block-poly(acrylic acid)) (PS115-b-PAA15) vesicles were carried out with high spatial resolution and afforded morphology and dimensions of BCP vesicles on solid substrates. By contrast the CSLM and FLIM data are diffraction limited, but from the time resolved fluorescence data information on the local vicinity of the reporter dye can be extracted. In the combined experiment individual dye-loaded vesicles and vesicle aggregates were discerned, analyzed metrologically by AFM and in more detail by CSLM and FLIM. On the basis of FLIM data the partitioning of the reporter dye was analyzed. The dye resides preferentially in the hydrophilic corona inside the vesicles. The dye concentration in the polymersome was about 90 times higher than in the solution used for encapsulation. These results underline that the combination of AFM with sensitive optical techniques, especially FLIM, is a promising approach for obtaining a deeper understanding of molecular interactions and nanoenvironments in supramolecular macromolecular structures and beyond.