I have prepared a chitosan coating solution by dissolving 0.5 g chitosan in 50 ml of 1% acetic acid, which was stirred for 24 hrs in a magnetic stirrer.

5ml of chitosan solution was added dropwise to 30 ml of SLN formulation under magnetic stirring at 320 rpm for 24 hrs.

DLS checked particle size before and after chitosan coating. Before coating, particle size was below 350 nm. After chitosan coating, it showed above 2000 nm. But SEM images showed particle size in 100-200 nm.

DLS showing bigger size can be due to aggregation?

How can I interpret the differences in size between SEM & DLS?

Please suggest suitable methods for chitosan coating.