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Abstract: Living microalgal cells differ from other cells that are used as objects for optical micromanipulation, in that they have strong light absorption in the visible range, and by the fact that their reaction centers are susceptible to photodamage. We trapped cells of the microalga Trachydiscus minutus using optical tweezers with laser wavelengths in the range from 735nm to 1064nm. The exposure to high photon flux density caused photodamage that was strongly wavelength dependent. The photochemical activity before and after exposure was assessed using a pulse amplitude modulation (PAM) technique. The photochemical activity was significantly and irreversibly suppressed by a 30s exposure to incident radiation at 735, 785, and 835nm at a power of 25mW. Irradiance at 885, 935 and 1064nm had negligible effect at the same power. At a wavelength 1064nm, a trapping power up to 218mW caused no observable photodamage. [Copyright &y& Elsevier]

Recently a non-contact organization of sub-micron colloidal particles in the vicinity of liquid–solid interface attracted great attention in connection with the development of imaging techniques using total internal reflection. We focus here on the theoretical description of the optical forces acting on a sub-micron particle placed in an interference field created by two counter-propagating evanescent waves. We study the behavior of nanoparticles by means of Rayleigh approximation, and also the behaviour of sub-micron particles by Lorentz–Mie scattering theory. Numerical results show how these forces depend on the particle size and angle of incidence of both beams. The alternating dependence on the bead size was proven experimentally, and the sub-micron beads behavior was experimentally studied in the motional evanescent standing wave. Self-organization of the beads into linear chains was also observed. [ABSTRACT FROM AUTHOR]

Abstract: We report on the application of laser-induced breakdown spectroscopy (LIBS) to the determination of elements distinctive in terms of their biological significance (such as potassium, magnesium, calcium, and sodium) and to the monitoring of accumulation of potentially toxic heavy metal ions in living microorganisms (algae), in order to trace e.g. the influence of environmental exposure and other cultivation and biological factors having an impact on them. Algae cells were suspended in liquid media or presented in a form of adherent cell mass on a surface (biofilm) and, consequently, characterized using their spectra. In our feasibility study we used three different experimental arrangements employing double-pulse LIBS technique in order to improve on analytical selectivity and sensitivity for potential industrial biotechnology applications, e.g. for monitoring of mass production of commercial biofuels, utilization in the food industry and control of the removal of heavy metal ions from industrial waste waters. [Copyright &y& Elsevier]