Nitrobenzoxadiazole-Appended Cell Membrane Modifiers for Efficient Optoporation with Noncoherent Light.

FL NBD-BAMPEG2k , bearing a nitrobenzoxadiazole (NBD) unit and an oleyl terminus conjugated via a poly(ethylene glycol) (PEG) spacer ( Mn = 2,000), was designed to fluorescently label cell membranes by docking its hydrophobic oleyl terminus. During laser scanning microscopy in a minimal essential medium (MEM), human hepatocellular carcinoma Hep3B cells labeled with FL NBD-BAMPEG2k appeared to undergo optoporation at their plasma membrane. We confirmed this unprecedented possibility by a series of cellular uptake experiments using negatively charged and therefore membrane-impermeable quantum dots (QDs; Dh = 4.7 nm). Detailed studies indicated that the photoexcited NBD unit can generate singlet oxygen (1 O2 ), which oxidizes the constituent phospholipids to transiently deteriorate the cell membrane. Reference membrane modifiers FL NBD-Oleyl and FL NBD-BAMPEG8k having shorter or longer hydrophilic spacers between the NBD and oleyl units showed a little or substantially no optoporation. For understanding these results, one must consider the following contradictory factors: (1) The photosensitized 1 O2 generation efficiently occurs only when the NBD unit is in aqueous media, and (2) the lifetime of 1 O2 in aqueous media is very short (3.0-3.5 μs). As supported experimentally and computationally, the hydrophilic spacer length of FL NBD-BAMPEG2k is optimal for compromising these factors. Further to note, the optoporation using FL NBD-BAMPEG2k is not accompanied by cytotoxicity.