Hypericin Aggregation in Artificial Lipid Membranes

Abstract

The incorporation of hypericin (Hyp), a natural hydrophobic photosensitizer, to giant unilamellar vesicles (GUVs) was studied by fluorescence and Raman spectroscopies. The GUVs were prepared from DOPC by electro-formation on platinum electrodes. During the experiments, a single GUV was trapped in optical tweezers operated at 785 nm. The micro-shelter system developed previously for laser tweezers buffer exchange [1] was used to place the GUVs into aqueous solution of Hyp (2.10-6 M), where this compound forms non-fluorescence aggregates [2]. By contrast, Hyp can be well dissolved in lipid structures [3]. The incorporation of Hyp into the GUV was monitored by time-resolved fluorescence measurements at 488 nm excitation. The early increase of the fluorescence signal (belonging to Hyp monomers) was followed by a gradual signal weakening, which indicated in-membrane aggregation of Hyp. An unexpected formation of large (∼500 nm diameter) Hyp aggregates was observed on the GUV surface several minutes after mixing GUVs with Hyp. This observation was also confirmed by micro-Raman measurements.This work was supported by the APVV-0242-11 grant of the Slovak Ministry of Education, the FP7 EU CELIM 316310 project, the NanoBioSens project (ITMS 26220220107, 50%) funded by the European Regional Development Fund and by the EU Structural Fund ITMS 26240120040.[1] M. A. Omar, P. Miskovsky, G. Bano, Lab Chip 14, 1579-1584 (2014)[2] G. Bano, J. Stanicova, D. Jancura, J. Marek, M. Bano, J. Ulicný, A. Strejckova, P. Miskovský, J. Phys. Chem. B 115, 2417-2423 (2011)[3] A. Strejckova, J. Stanicova, D. Jancura, P. Miskovský, and G. Bano, J. Phys. Chem. B 117, 1280-1286 (2013)