Photoacoustic efect applied on model membranes and living cells: direct observation with multiphoton excitation microscopy and long-term viability analysis

Abstract

The photoacoustic efect is generated when a variable light interacts with a strongly light-absorbing material. In water, it may produce hot bubbles and shock waves that could afect the integrity of nearby cellular membranes, opening transient pores (photoporation). In this study, we have evaluated the efect of pulsed laser-irradiated carbon nanoparticles (cNP) on model membranes and on Chinese hamster ovary (CHO) cells. Fluorescence lifetime measurements of calcein-loaded liposomes support the notion that the photoacoustic efect causes transient openings in membranes, allowing difusion fuxes driven by gradient concentrations. With CHO cells, we have shown that this efect can induce either intracellular delivery of calcein, or release of cellular compounds. The latter process has been recorded live with multiphoton excitation microscopy during pulsed infrared laser irradiation. Calcein loading and cell viability were assayed by fow cytometry, measuring necrotic cells as well as those in early apoptosis. To further assess long-term cell recovery after the rather harsh treatment, cells were reseeded and their behaviour recorded for 48h. These extended studies on cell viability show that pulsed laser cNP photoporation may be considered an adequate intracellular delivery technique only if employed with soft irradiation conditions (below 50mJ/cm2).