Abstract
The photoacoustic effect 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 affect the integrity of nearby cellular membranes, opening transient pores (photoporation). In this study, we have evaluated the effect 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 effect causes transient openings in membranes, allowing diffusion fluxes driven by gradient concentrations. With CHO cells, we have shown that this effect 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 flow 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 48 h. 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 50 mJ/cm2).
Highlights
The photoacoustic effect is generated when a variable light interacts with a strongly light-absorbing material
Long-term cell survival can only be expected if they are able, after the laser treatment, to adhere again to a surface, spread and divide trying to cover the surface. We propose that these long-term studies on cell viability are necessary to support the idea that the photoacoustic effect is a valid intracellular delivery technique for living cells
Size distribution of the carbon nanoparticles (cNP) suspension was determined by dynamic light scattering (DLS)
Summary
The photoacoustic effect is generated when a variable light interacts with a strongly light-absorbing material. Vaporization of the surrounding water and generation of acoustic emissions can impact nearby cells thermally -by contact with the hot bubblesand mechanically -by fluid mechanical forces- to physically disrupting cell membranes with transient holes, as proposed in the seminal works in this field of Dr Prausnitz group[13,14,15,16,17,18,19] They have called this phenomenon “transient nanoparticle energy transduction” (TNET). To corroborate the occurrence of these transient membrane holes, we have investigated the effect of the photoacoustic treatment on liposomes, as model cell membranes, to gain insight into the mechanism by which membranes are disrupted by this kind of physical distress To this aim vesicles were loaded with fluorescent water-soluble molecules, and vesicle leakage was studied by measuring fluorescence lifetimes of the corresponding dye in vesicle suspensions prepared and treated in different ways. Intracellular delivery to and release from Chinese hamster ovarian (CHO) cells were monitored by confocal and multiphoton excitation microscopy
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