Plasmonic Nanoparticle-Generated Photothermal Bubbles and Their Biomedical Applications

Abstract

This article is focused on the optical generation and detection of photothermal vapor bubbles around plasmonic nanoparticles. We report physical properties of such plasmonic nanobubbles and their biomedical applications as cellular probes. Our experimental studies of gold nanoparticle-generated photothermal bubbles demonstrated the selectivity of photothermal bubble generation, amplification of optical scattering and thermal insulation effect, all realized at the nanoscale. The generation and imaging of photothermal bubbles in living cells (leukemia and carcinoma culture and primary cancerous cells), and tissues (atherosclerotic plaque and solid tumor in animal) demonstrated a noninvasive highly sensitive imaging of target cells by small photothermal bubbles and a selective mechanical, nonthermal damage to the individual target cells by bigger photothermal bubbles due to a rapid disruption of cellular membranes. The analysis of the plasmonic nanobubbles suggests them as theranostic probes, which can be tuned and optically guided at cell level from diagnosis to delivery and therapy during one fast process. Keywordscell; imaging; laser; plasmonic nanoparticle; photothermal; theranostics; vapor bubble Biomedical applications of plasmonic nanoparticles (NPs) have demonstrated their biocompatibility [1,2], excellent optical scattering [3][4][5][6][7] and photothermal (PT) [8][9][10][11][12] properties and high photo-and thermal stability in comparison to any molecular optical absorbers. The combination of PT-sensing techniques [13] with plasmonic properties of the NPs has shown very promising results with a detection limit of several nanometers [14]. However, the sensitivity of PT sensing requires an increase in the laser-induced temperature, which may cause thermal damage to cells and tissues. Laser-induced PT phenomena include the initial thermalization of NPs that, in turn, rapidly causes several environmental thermal processes: the heating of the surrounding media [15][16][17] (due to thermal diffusion), its vaporization (if the temperature exceeds the vaporization threshold) and the generation of acoustic and shock waves [18]. Pulses that are too long (or continuous optical activation) cause a large spatial spread of the thermal field (many orders of magnitude larger than NP size) due to the thermal diffusion. This limits the selectivity and safety of NP-based PT diagnostics and therapy. Ultra-short laser pulses concentrate the thermal field within the NP but generate pressure (and shock) waves that also spread over a large volume and may cause uncontrollable damage [19]. The sensitivity, safety and specificity of NP methods are limited at cell and molecular levels by the strong scattering background of a highly heterogeneous bioenvironment and also by the incidental (nonspecific) accumulation of NPs in normal cells and tissues. Therefore, despite the apparent advantages of nanomaterials, their biomedical application does not yet bring a significant gain on the established methods. NIH Public AccessAutho...

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