Abstract:In medical applications of laser and nanotechnology to diagnosis and treat cancer or microorganisms, understanding of lased-induced photothermal (PT) and accompanied phenomena around nanoparticles are crucial for optimization and bringing this promising technology to bedside. We analyzed the main PT-based effects in and around gold nanoparticles under action of short (nano-, pico-, and femtosecond) laser pulses with focus on photoacoustic effects due to the thermal expansion of nanoparticles and liquid around them, thermal protein denaturation, explosive liquid vaporization, melting and evaporation of nanoparticle, optical breakdown initiated by nanoparticles and accompanied to shock waves and explosion (fragmentation) of gold nanoparticles. Characteristic parameters for these processes such as the temperature and pressures levels, and laser intensity thresholds among others are summarized to provide basis for comparison of different mechanisms of selective nanophotothermolysis and diagnostics of different targets (e.g., cancer cells, bacteria, viruses).

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Investigations of laser interaction with metal (gold) nanoparticles is of a great interest for laser applications in nanotechnology, engineering, and medicine. The first problem of laser interaction is to determine the optical properties of metal nanoparticles, that determines following photophysical and photochemical processes. The calculation of efficiency factors of absorption, scattering and extinction for spherical gold nanoparticles with radiuses in the range 5-100 nm and for some laser wavelengths is performed. The estimation of absorbed laser radiation energy by gold nanoparticles, their maximal temperatures and comparison with experimental data is made. The importance of the use of correct values of optical parameters of nanoparticles is demonstrated. Absorption efficiency factor K abs versus the radius r0 of the spherical Au nanoparticle embedded in water

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This review presents a platform for the description of the thermal processes of laser–nanoparticle interactions and their applications.

Recently, several groups of investigators (Anderson, Halas, Zharov, El-Sayed and their co-workers (Pitsillides et al 2003 Biophys. J. 84 4023-31, Zharov et al 2003 Appl. Phys. Lett. 83 4897-9, Zharov et al 2004 Proc. SPIE 5319 291-9, Loo et al 2005 Nano Lett. 5 709-11, Gobin et al 2007 Nano Lett. 7 1929-34, Fu et al 2008 Nanotechnology 19 045103, Huang et al 2006 J. Am. Chem. Soc. 128 2115-20, Jain et al 2006 J. Phys. Chem. B 110 7238-48, Jain et al 2007 Nano Today 2 18-29)) demonstrated, through pioneering results, the great potential of laser thermal therapy of cells and tissues conjugated with gold nanoparticles. It was also proposed to use combined diagnostics and therapy on the basis of nanoparticle selection for achievement of efficient contrast for laser imaging applications, as well as for photothermal therapy. However, the current understanding of the relationship between optical properties (absorption, backscattering) of nanoparticles, the efficiency of nanoparticle heating and the possibility to use them for combined imaging and therapy is limited. Here, we report the results of computer modeling of optical absorption and backscattering properties and laser heating of gold and silica-gold spherical nanoparticles for laser combined imaging and photothermal treatment of cells and tissues conjugated with nanoparticles. The efficiencies of nanoparticle heating and backscattering by nanoparticles, depending upon their radii, structure and optical properties of the metal, were investigated. This paper focuses on the analysis and determination of appropriate ranges of nanoparticle sizes for the purposes of laser combined imaging and photothermal treatment. The possibility to use spherical gold and silica-gold nanoparticles in determined ranges of radii for these purposes for laser wavelengths 532 and 800 nm is investigated.

Processes of laser interaction with metal (gold) nanoparticles are of great interest for laser applications in nanotechnology, engineering, and medicine. Optical properties of nanoparticles determine photophysical and photochemical processes during laser treatment. Computer calculation of efficiency factors of absorption, scattering and extinction of radiation by ellipsoidal gold nanoparticles (two-dimensional ellipsoids of revolution) with small semiaxes in the range 5-100 nm, for some values of aspect ratio and angle of orientation of ellipsoid with respect to direction of laser radiation propagation and for some laser wavelengths is performed. The estimation of absorbed and scattered laser radiation energy by gold ellipsoidal nanoparticles, their maximal temperatures and comparison with experimental data is made. Efficiency factor of absorption for the prolate Au ellipsoid embedded into water versus the ellipsoid small semiaxis r b

Applications of nanoparticles (NPs) as photothermal (PT) and photoacoustic (PA) labels and agents for diagnosis and therapy of cancer and other diseases in laser medicine are fast growing areas of research. Many potential benefits include possibility for imaging with higher resolution and treatment of deeper tissues containing NPs, killing of individual abnormal cells, etc. Nevertheless, despite successful results, there is a lack of focused analysis of requirements to NPs for optimization of PT/PA applications, especially with pulsed lasers. Here, we present a platform for analysis of NP properties (e.g., optical, thermal, acoustic, structural, and geometric), allowing to select their parameters in the presence of different ambient tissues. The several types of NPs are described, which provide significant increased conversion of laser pulse energy in PT/PA phenomena. These NPs make it possible to use them with maximal efficiency for detection and killing single malignant cells labeled with minimal amount of NPs and in laser nanomedicine.