To the best of my information, attached paper (cited below) is the very first publication describing use of Scanning Tunneling Microscopy (a member of SPM microscopes) in the elucidation of liposome-DNA structures.

I appreciate if someone comment on this or show us an older publication on the topic.

Note: Unfortunately author names appear in strange characters on the journal page (attached). The citation below is the correct one. Perhaps strange for young scientists to know that back then in 1997's there was no "email attachment" neither PDF!

Zareie, M. H., Mozafari, M. R., Hasirci, V., & Piskin, E. (1997). Scanning tunnelling microscopy investigation of liposome-DNA-Ca2+ complexes. Journal of Liposome Research, 7(4), 491-502.