Single-walled carbon nanotubes as a photo-thermo-acoustic cancer theranostic agent: theory and proof of the concept experiment.

Theranostics is the emerging field of medicine that uniquely combines diagnostic techniques and active agents to diagnose and treat medical conditions simultaneously or sequentially. Finding a theranostic agent capable to cure the affected cells and being safe for the healthy ones is the key for successful treatment. Here, we demonstrate that agglomerated single-walled carbon nanotubes (SWCNTs) are promising theranostic agent that enables photo-activated 'cold' destruction of the cancer cells keeping their environment alive. The absorption of picosecond pulses by SWCNT agglomerates results in the mechanical (due to photoacoustic effect) rather than photothermal cancer cell destruction, which was visualized by micro-Raman and ultrafast near-infrared CARS. The developed theoretical model allows us to distinguish photothermal, photoacoustic, and photothermoacoustic regimes of the cancer cell destruction, and also to optimize SWCNT-based theranostics recipe.

Circular photocurrent in the carbon nanowall film.

We report the helicity-dependent photocurrent in the carbon nanowall film synthesized on the silicon substrates by the chemical vapor deposition technique. The film is composed of multilayer graphene flakes grown along the substrate normal. We measured the transverse photocurrent generated in the film under irradiation with nanosecond laser pulses by depositing two conductive electrodes along the plane of incidence. The measurements were performed by using elliptically polarized fundamental, second-, third-, and fourth-harmonics beams of the Nd:YAG laser. We revealed that the shorter the excitation wavelength, the higher the magnitude of the helicity-dependent transverse photocurrent generated in the film. In particular, at wavelengths of 266 and 355 nm, the photocurrent strongly depends on the degree of the circular polarization of the laser beam while, at the wavelength of 1064 nm, the transverse photocurrent is almost helicity independent.

Interplay of the photon drag and the surface photogalvanic effects in the metal-semiconductor nanocomposite.

Photon drag effect (PDE) and surface photogalvanic effect (SPGE) can be observed in centrosymmetric media and manifest themselves in photocurrents, the magnitude and polarity of which depend on wavevector and polarization of the excitation laser beam. PDE photocurrent originates from the transfer of the photon momentum to a free charge carrier, while SPGE photocurrent is due to diffuse scattering of the photoexcited carriers in the subsurface layer. However, despite the different underlying physical mechanisms, these photocurrents have almost indistinguishable dependencies on the polarization and the angle of incidence of the excitation laser beam. In this paper, we observe for the first time a competition between PDE and SPGE in the film containing metal (Ag-Pd) and semiconductor (PdO) nanocrystallites. We show that, depending on the angle of incidence, polarization azimuth and wavelength of the excitation laser beam, the interplay of the PDE and SPGE leads to the generation of either monopolar or bipolar nanosecond current pulses. The experiments performed allow us to visualize the contributions both these effects and obtain light-to-current conversion efficiency in a wide spectral range. Our experimental findings can be employed to control the magnitude and polarity of the light-induced current by polarization of the excitation laser beam.

Myocardial Protection against Ischemic and Reperfusion Injuries (Experimental Study).

The effects of hypoxic, hyperoxic, and hypoxic-hyperoxic preconditioning were examined in the prospective study on narcotized and artificially ventilated rabbits. Under artificial circulation, acute myocardial ischemia was modeled by ligation of anterior descending coronary artery, which was followed by reperfusion. The degree of ventricular arrhythmias was assessed, and the ischemic area was evaluated in percent of the area at risk. Microscopic characterization of the myocardium was employed to assess the cardioprotective effect of hypoxic and/or hyperoxic preconditioning. According to Kruskal-Wallis test, the greatest resistance of the myocardium to ischemic and reperfusion injury was observed after hypoxic-hyperoxic preconditioning (H=42.459; p=0.009). The rabbits subjected to this type of preconditioning demonstrated the least damaged myocardium in comparison with nonconditioned controls.

Revealing the nanoparticles aspect ratio in the glass-metal nanocomposites irradiated with femtosecond laser.

We studied a femtosecond laser shaping of silver nanoparticles embedded in soda-lime glass. Comparing experimental absorption spectra with the modeling based on Maxwell Garnett approximation modified for spheroidal inclusions, we obtained the mean aspect ratio of the re-shaped silver nanoparticles as a function of the laser fluence. We demonstrated that under our experimental conditions the spherical shape of silver nanoparticles changed to a prolate spheroid with the aspect ratio as high as 3.5 at the laser fluence of 0.6 J/cm2. The developed approach can be employed to control the anisotropy of the glass-metal composites.

Flexible transparent graphene/polymer multilayers for efficient electromagnetic field absorption.

Thanks to its high electrical conductivity, a graphene plane presents a good shielding efficiency against GHz electromagnetic radiations. Several graphene planes separated by thin polymer spacers add their conductivities arithmetically, because each of them conserves the intrinsic properties of isolated graphene. Maximum absorption of radiations for frequency around 30 GHz is achieved with six separated graphene planes, which is the optimum number. This remarkable result is demonstrated experimentally from electromagnetic measurements performed in the Ka band on a series of multilayers obtained by piling 1, 2, 3... graphene/PMMA units on a silica substrate. Theoretical calculations convincingly explain the observed absorption and transmission data in the GHz domain. It is concluded that graphene/PMMA multilayers can be used as an efficient optically transparent and flexible shielding media.

Multilayered graphene in K(a)-band: nanoscale coating for aerospace applications.

We report on the experimental study of electromagnetic (EM) properties of multilayered graphene in K(a)-band synthesized by catalytic chemical vapor deposition (CVD) process in between nanometrically thin Cu catalyst film and dielectric (SiO2) substrate. The quality of the produced multilayered graphene samples was monitored by Raman spectroscopy. The thickness of graphene films was controlled by atomic force microscopy (AFM) and was found to be a few nanometers (up to 5 nm). We discovered, that the fabricated graphene, being only some thousandth of skin depth, provided remarkably high EM shielding efficiency caused by absorption losses at the level of 35-43% of incident power. Being highly conductive at room temperature, multilayer graphene emerges as a promising material for manufacturing ultrathin microwave coatings to be used in aerospace applications.

On the modeling of spectral map of glass-metal nanocomposite optical nonlinearity.

The spectral map of the nonlinear absorption coefficient of glass-copper nanocomposite in the pump-probe scheme constructed with the use of a simple anharmonic oscillator model reproduced well the spectral map obtained in the experiment. It is shown that spectral features in nonlinear response of glass-metal nanocomposites (GMN) can be engineered by varying the size of nanoparticles. The pronounced dependence of the magnitude of the third-order nonlinearity on the particles size explains the diversity of experimental data related to nonlinear optical response of GMNs in different experiments. Performed modeling proves that silver GMN demonstrate much sharper spectral dependence than copper ones due to strong frequency dependence of local field enhancement factor for silver nanoparticles.

Electric field imprinting of sub-micron patterns in glass-metal nanocomposites.

We demonstrate that the dissolution of 10 nm metal nanoparticles localized in the subsurface layer of silicate glass by static electric field can be employed to alter the optical density and surface profile of the glass-metal composite with spatial resolution of 200 nm. The developed technique, which can be referred to as electric field imprinting (EFI), offers an attractive alternative to conventional micro- and nano-pattering techniques.

Femtosecond absorption dynamics in glass-metal nanocomposites.

We report strong optical nonlinearity of glasses embedded with copper and silver nanoparticles. In pump-probe experiments with copper-doped glasses, the observed absorption bleaching with picosecond relaxation time is as high as 22%. Transmission femtosecond measurementsreveal the reverse saturable absorption with nonlinear absorption coefficient of 10(-10)cm/W in both copper- and silver-doped nanocomposites.

Efficient two-photon light amplification by a coherent biexciton wave.

A reversible coupling between photon pair states and a long-lived, highly coherent biexciton wave in CuCl allows efficient phase-sensitive two-photon amplification or attenuation of ultrashort light pulses. We demonstrate a gain of 350 cm(-1) for a pump intensity of 1 MW/cm(2), nearly 2 orders of magnitude higher than that achievable with conventional parametric crystal amplifiers. We develop a theoretical model that describes this new type of parametric converter where the light pump is replaced by a coherent biexciton wave and show that it is well suited for the generation of entangled photons and the squeezing of an optical beam with ultrafast time gating.