Renat R. Letfullin

Laser-induced explosion of gold nanoparticles: potential role for nanophotothermolysis of cancer

AIMS This article explores the laser-induced explosion of absorbing nanoparticles in selective nanophotothermolysis of cancer. METHODS This is realized through fast overheating of a strongly absorbing target during the time of a short laser pulse when the influence of heat diffusion is minimal. RESULTS On the basis of simple energy balance, it is found that the threshold laser fluence for thermal explosion of different gold nanoparticles is in the range of 25-40 mJ/cm(2). CONCLUSION Explosion of nanoparticles may be accompanied by optical plasma, generation of shock waves with supersonic expansion and particle fragmentation with fragments of high kinetic energy, all of which can contribute to the killing of cancer cells.

Modeling nanophotothermal therapy: kinetics of thermal ablation of healthy and cancerous cell organelles and gold nanoparticles.

UNLABELLED Nanoparticles are being researched as a noninvasive method for selectively killing cancer cells. With particular antibody coatings on nanoparticles, they attach to the abnormal cells of interest (cancer or otherwise). Once attached, nanoparticles can be heated with ultraviolet-visible/infrared or radiofrequency pulses, heating the surrounding area of the cell to its point of death. Researchers often use single-pulse or multi-pulse modes of laser heating when conducting nanoparticle ablation research. In this article, time-dependent simulations and detailed analyses are carried out for different nonstationary pulsed laser-nanoparticle interaction modes, and the advantages and disadvantages of single-pulse and multi-pulse (set of short pulses) laser heating of nanoparticles are shown. Simulations are performed for the metal nanoparticles in the biological surrounding medium as well as for healthy and cancerous cell organelles. FROM THE CLINICAL EDITOR External laser pulses can be used to generate heating of targeted metal nanoparticles for thermal ablation therapy of cancers, however the approach used in individual studies is idiosyncratic. In this manuscript, time-dependent simulations and analyses are used to determine the pros and cons of single versus multiple laser pulses for differential impact of healthy versus cancerous cell organelles.

Ultrashort Laser Pulse Heating of Nanoparticles: Comparison of Theoretical Approaches

The interaction between nanoparticles and ultrashort laser pulses holds great interest in laser nanomedicine, introducing such possibilities as selective cell targeting to create highly localized cell damage. Two models are studied to describe the laser pulse interaction with nanoparticles in the femtosecond, picosecond, and nanosecond regimes. The first is a two-temperature model using two coupled diffusion equations: one describing the heat conduction of electrons, and the other that of the lattice. The second model is a one-temperature model utilizing a heat diffusion equation for the phonon subsystem and applying a uniform heating approximation throughout the particle volume. A comparison of the two modeling strategies shows that the two-temperature model gives a good approximation for the femtosecond mode, but fails to accurately describe the laser heating for longer pulses. On the contrary, the simpler one-temperature model provides an adequate description of the laser heating of nanoparticles in the femtosecond, picosecond, and nanosecond modes.

Plasmonic Nanomaterials for Nanomedicine

Plasmonic nanoparticles are being researched as a noninvasive tool for ultrasensitive diagnostic, spectroscopic, and, recently, therapeutic technologies. With particular antibody coatings on nanoparticles, they attach to abnormal cells of interest (cancer or otherwise). Once attached, nanoparticles can be activated/heated with ultraviolet (UV)/visible/infrared (IR), radiofrequency (RF) or x-ray pulses, damaging the surrounding area of the abnormal cell to the point of death. Here, we describe an integrated approach to improved plasmonic therapy composed of nanomaterial optimization and the development of a theory for selective radiation nanophotothermolysis of abnormal biological cells with gold nanoparticles and self-assembled nanoclusters. The theory takes into account radiation-induced linear and nonlinear synergistic effects in biological cells containing nanostructures, with focus on optical, thermal, bubble formation, and nanoparticle explosion phenomena. On the basis of the developed models, we discuss new ideas and new dynamic modes for cancer treatment by radiation-activated nanoheaters, which involve nanocluster aggregation in living cells, microbubbles overlapping around laser-heated intracellular nanoparticles/clusters, and the laser thermal explosion mode of single nanoparticles (nanobombs) delivered to cells.

Absorption efficiency and heating kinetics of nanoparticles in the RF range for selective nanotherapy of cancer

UNLABELLED Radio-frequency (RF) waves have an excellent ability to penetrate into the human body, giving a great opportunity to activate/heat nanoparticles delivered inside the body as a contrast agent for diagnosis and treatment purposes. However the heating of nanoparticles in the RF range of the spectrum is controversial in the research community because of the low power load of RF waves and low absorption of nanoparticles in the RF range. This study uses a phenomenological approach to estimate the absorption efficiency of metal and dielectric nanoparticles in the RF range through a study of heating kinetics of those particles in radio wave field. We also discuss the specific features of heating kinetics of nanoparticles, such as a short time scale for heating and cooling of nanoparticles in a liquid biological environment, and the effect of the radiation field structure on the heating kinetics by single-pulse and multipulse RF radiation. FROM THE CLINICAL EDITOR In this study a phenomenological approach was applied to estimate the absorption efficiency of radiofrequency radiation (RF) by metal and dielectric nanoparticles. Such nanoparticles can be designed and used for therapeutic purposes, like for localized heating and to activate nanoparticles by RF. The authors also discuss the differences in heating kinetics using single-pulse and multi-pulse RF radiation.

Optical effect of diffractive multifocal focusing of radiation on a bicomponent diffraction system

It is shown for the first time, to our knowledge, that when a plane wave illuminates a certain type of bicomponent optical system, consisting of two plane screens with circular apertures on a given optical axis, a multifocal diffractive focusing effect can appear. Here the diffraction picture in the focal planes represents the circular nonlocal bands of the Fresnel zones with a bright narrow peak at the center, whose intensity can exceed by 6-10 times the value of the incident-wave intensity. The detected optical effect is observed across a wide range of wavelengths, lambda = 0.4-10(3) microm, and ratios of the aperture diameters d(1) >or= 2d(2) = 25-1000 lambda, and it is also insensitive to changes in the medium of the wave propagation. For the large diameters of input holes, d(1) = 2d(2) > 100 lambda, or for wavelengths in the radio-frequency region of the spectrum, the bicomponent diffraction system acts as a long-focus lens with a high-intensity Gaussian distribution of radiation, at times exceeding the initial intensity, persisting at large distances (z = 1-100 cm) from the diffraction system.

Custom-oriented wavefront sensor for human eye properties measurements

The problem of correct measurement of human eye aberrations is very important with the rising widespread of a surgical procedure for reducing refractive error in the eye, so called, LASIK (laser-assisted in situ keratomileusis). In this paper we show capabilities to measure aberrations by means of the aberrometer built in our lab together with Active Optics Ltd. We discuss the calibration of the aberrometer and show invalidity to use for the ophthalmic calibration purposes the analytical equation based on thin lens formula. We show that proper analytical equation suitable for calibration should have dependence on the square of the distance increment and we illustrate this both by experiment and by Zemax Ray tracing modeling. Also the error caused by inhomogeneous intensity distribution of the beam imaged onto the aberrometers Shack-Hartmann sensor is discussed.

Laser-induced synergistic effects around absorbing nanoclusters in live cells

Background and Objective: The application of nanotechnology for laser thermal-based killing of abnormal cells (e.g. cancer cells) targeted with absorbing nanoparticles (e.g. gold solid nanospheres, nanoshells, or rod) is becoming an extensive area of research. We develop an approach to enhance the efficiency of selective nanophotothermolysis of cancer cells through laser-induced synergistic effects around gold nanoparticles aggregated in nanoclusters on cell membrane. Study Design/Materials and Methods: A concept of selective target damages by laser-induced synergistic interaction of optical, thermal, and acoustic fields around clustered nanoparticles is presented with focus on overlapping bubbles from nanoparticles aggregated on cells membrane. The experimental verification of this concept in vitro was performed by the use a tunable laser pulses (420-570 nm, 8-12 ns, 0.1-300 μJ, laser flux of 0.1-10 J/cm2) for irradiation of MDA-MB-231 breast cancer cells targeted with primary antibodies to which selecttively 40-nm gold nanoparticles were attached by the means of secondary antibodies. The photothermal, electron and atomic force microscopes in combination with viability test (annexin -V-Propidium iodide) were employed to study the nanoparticles spatial organization, the dynamics of microbubble formations around the particles clusters, and cells damage. Results: An aggregation of nanoparticles on cell membrane was observed with simultaneous increase bubble formation phenomena, and red-shifted absorption due to plasmon-plasmon resonances into nanoclusters. It led to a significant enhancement, at least two orders of magnitude, of the efficiency of selectively killing cancer cells with nanosecond laser pulses. Conclusion: Described approach allows using relatively small nanoparticles which would be easier delivery to target site with further creation of nanoclusters with larger sizes which provide more profound thermal and related phenomena leading to more efficient laser killing of cancer cells. This nanocluster model might be promising also for treatment or modification different targets (e.g. bacteria, virus, vascular lesions, fat, etc.) as well as teh use different type energy deposition (focused ultrasound, microwave, magnetic field, etc.).

Theoretical and experimental investigations of the effect of diffractive multifocal focusing of radiation

The new optical effect of diffractive multifocal focusing of radiation, predicted earlier by theory, on a bicomponent diffraction system with small Fresnel numbers that consists of two plane screens with circular apertures on given optical axes, is confirmed experimentally. It is shown that the diffraction picture in the focal planes of such a system represents the circular nonlocal bands of the Fresnel zones with a bright narrow peak at the center, whose intensity in the experiment can exceed by six to ten times the value of the incident plane-wave intensity. Experimentally it is established that the diffractive multifocal focusing of radiation on real screens with axial circular apertures, whose diameters exceed the radiation wavelength, is insensitive to the rough external conditions: thickness of the screens, irregularities of the edges and nonideal form of the apertures, heterogeneity of the initial distribution of the incident-wave intensity, and changes in the medium of the wave propagation.

Bone tissue heating and ablation by short and ultrashort laser pulses

Biological hard tissues, such as those found in bone and teeth, are complex tissues that build a strong mineral structure over an organic matrix framework. The laser-matter interaction for bone hard tissues holds great interest to laser surgery and laser dentistry; the use of short/ultrashort pulses, in particular, shows interesting behaviors not seen in continuous wave lasers. High laser energy densities in ultrashort pulses can be focused on a small irradiated surface (spot diameter is 10-50 μm) leading to rapid temperature rise and thermal ablation of the bone tissue. Ultrashort pulses, specifically those in the picosecond and femtosecond ranges, impose several challenges in modeling bone tissue response. In the present paper we perform time-dependent thermal simulations of short and ultrashort pulse laser-bone interactions in singlepulse and multipulse (set of ultrashort pulses) modes of laser heating. A comparative analysis for both radiation modes is discussed for laser heating of different types of the solid bone on the nanosecond, picosecond and femtosecond time scales. It is shown that ultrashort laser pulses with high energy densities can ablate bone tissue without heating tissues bordering the ablation creator. This reaction is particularly desirable as heat accumulation and thermal damage are the main factors affecting tissue regrowth rates, and thus patient recovery times.