Gold nanoshell photomodification under a single-nanosecond laser pulse accompanied by color-shifting and bubble formation phenomena

Abstract

Laser-nanoparticle interaction is crucial for biomedical applications of lasers and nanotechnology to the treatment of cancer or pathogenic microorganisms. We report on the first observation of laser-induced coloring of gold nanoshell solution after a one nanosecond pulse and an unprecedentedly low bubble formation (as the main mechanism of cancer cell killing) threshold at a laser fluence of about 4 mJ cm(-2), which is safe for normal tissue. Specifically, silica/gold nanoshell (140/15 nm) suspensions were irradiated with a single 4 ns (1064 nm) or 8 ns (900 nm) laser pulse at fluences ranging from 0.1 mJ cm(-2) to 50 J cm(-2). Solution red coloring was observed by the naked eye confirmed by blue-shifting of the absorption spectrum maximum from the initial 900 nm for nanoshells to 530 nm for conventional colloidal gold nanospheres. TEM images revealed significant photomodification of nanoparticles including complete fragmentation of gold shells, changes in silica core structure, formation of small 20-30 nm isolated spherical gold nanoparticles, gold nanoshells with central holes, and large and small spherical gold particles attached to a silica core. The time-resolved monitoring of bubble formation phenomena with the photothermal (PT) thermolens technique demonstrated that after application of a single 8 ns pulse at fluences 5-10 mJ cm(-2) and higher the next pulse did not produce any PT response, indicating a dramatic decrease in absorption because of gold shell modification. We also observed a dependence of the bubble expansion time on the laser energy with unusually very fast PT signal rising (∼3.5 ns scale at 0.2 J cm(-2)). Application of the observed phenomena to medical applications is discussed, including a simple visual color test for laser-nanoparticle interaction.

Photothermal and accompanied phenomena of selective nanophotothermolysis with gold nanoparticles and laser pulses

“…By optimizing the laser pulse duration, particle size and shape, selective nanophotothermolysis can provide highly localized damage in a controlled manner potentially from a few nanometers (e.g., in DNA with a femtosecond laser) to tens of microns (the scale of single cancer cells) Figure 1 Phenomenological picture of the main effects during interaction of laser pulse with GNs in liquid environment with sequent increase of laser energy (from left to right) without harmful effects for the surrounding healthy tissue. This technology has potential at relatively low pulse laser energy for medical diagnosis at single cell, bacterium, or GN level, which can be used also as feedback for optimization and guidance of PT nanotherapy [3][4][5]18,21,[24][25][26][27][28][29][30][31][32][33][34]. It should be emphasized that temporally and spatially confined selective nanophotothermolysis with GNs as further development of photothermolysis dealt before mainly with micro-scale targets [37] are differ from PT therapy using irradiation of GNs with continuous wave (CW) lasers ( [27][28][29][30][31][32], see other references in reviews [33][34][35]) in term of main killing mechanism (bubble formation vs tissue coagulation), time exposure (second scale vs minute scale) and minimum damage sizes (few μm vs few mm).…”

“…Among recent achievement and tendency in development of selective nanophotothermolysis, one can to mention an observation unprecedented low bubble formation threshold around gold nanoshells at laser fluence 4 mJ/cm 2 , which is safe for normal tissue, use binary and multiple layer nanoparticles (e.g., integrated goldcarbon nanoparticles [5,24], silica-gold-coating nanoshells [25,26]) or significant enhancement (more than one order) of bubble formation around GNs by the use surrounding (or inside nanoparticles) media with appropriate thermodynamic properties, including low threshold evaporation (e.g. ethanol) [5,24].…”

Advanced contrast nanoagents for photoacoustic molecular imaging, cytometry, blood test and photothermal theranostics

“…in hollow NPs, SWNTs, or nanoshells) and surrounding water or preferentially to water (for solid NPs). For example, the ratio of characteristic times of heat conductivity for water and silica is about 6 (118). Thus, in gold nanoshells the shell and silica core reach thermal equilibrium first, and further NP cooling is due to heat transfer to surrounding water.…”

Laser-induced thermal dynamics and temperature localization phenomenon in tissues and cells doped with nanoshells

“…The appearance of plasmonic nanoparticles gave a new impetus to the development of laser medicine [3,4]. The possible applications include selective cancer cell imaging and killing by laser-induced hyperthermia [5][6][7][8], laser-assisted opening of drug containing microcapsules for the addressed drug delivery [9,10], laser-induced modification and defragmentation of the nanoparticles [10,11].The application of plasmon-resonant nanoparticles in oncology for enhanced selectivity and efficiency of laser-induced hyperthermia and photothermolysis of cancer cells labeled by nanoparticles is under investigation by many research groups [5][6][7][8][9][10].…”

“…There are many papers, see, for example [8,[11][12][13], analyzing the problems of heating of a medium doped by plasmonresonant nanoparticles under the action of pulse laser radiation. A detailed study of the dynamics of spatially multidimensional (2D instead of conventional 1D) distribution of temperature field, both within absorbing nanoparticle and in the immediate vicinity around it was made in [14,15].…”