Nonlinear absorption in nanosystems of biological significance.
- PDF / 895,280 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 91 Downloads / 194 Views
Nonlinear absorption in nanosystems of biological significance. Marek Samoc, Katarzyna Matczyszyn, Marcin Nyk, Joanna Olesiak-Banska, Marta Gordel, Piotr Hanczyc, Radoslaw Kolkowski, Janusz Szeremeta, Dominika Wawrzynczyk, Magdalena Waszkielewicz, Jan Zareba Institute of Physical and Theoretical Chemistry, Wroclaw University of Technology, Wyb. Wyspianskiego 27, 50-370 Wroclaw, Poland ABSTRACT We have been studying a number of nanosystems that either have potential applications in bioimaging and/or light-activated therapies, or are bioderived. The standard Z-scan technique was routinely used for most of the measurements which were carried out in a wide wavelength range, typically from ~550 nm to 1.6 m. The range of nanoparticles studied has included colloidal semiconductor nanoparticles (e.g. CdS, CdSe), plasmonic nanoparticles, metal clusters, lanthanide-doped fluoride and oxide nanocrystals as well as core-shell systems. Among the bioderived systems studied especially interesting one is that of protein amyloid fibers. Many of these materials exhibit nonlinear absorption features due not only to the typical twophoton absorption processes, but also due to multiple-photon absorption taking place, especially at longer wavelengths (e.g. three- four- and five-photon processes). On the other hand, absorption saturation processes may prevail or compete with multi-photon absorption in certain wavelength ranges in some of these materials, especially those characterized by broadband absorption due to surface plasmon excitation. INTRODUCTION The term “nonlinear absorption” is usually meant to cover all effects that lead to the dependence of the absorbance of a material on light intensity. It therefore includes direct twophoton and multi-photon processes taking place without the involvement of any real intermediate states, which are the classical nonlinear optical (NLO) processes as well as sequential absorption mechanisms (as e.g. in reverse saturable absorption, RSA). In addition to that, nonlinear absorption includes also processes of saturation of absorption. Applications of various types of nonlinear absorption have been summarized in many review papers. Among the photonic, nanophotonic and biophotonic applications of systems with enhanced multiphoton absorption the most interesting ones are those related to biology and medicine. Efficient multiphoton absorbers are required for theranostic applications, providing the advantage of 3D resolution and, in the case of sufficient NLO performance1, possibility of imaging and addressing a single NLO species. Due to superlinear dependence of the two-photon absorption cross section on the size of -electron conjugated system, much work in the field of two-photon absorbers has been focused on synthesizing novel organic molecules with extended conjugation. The competitors of such nonlinear absorbers are those based on organometallic structures. There is evidence that large, dendrimeric molecules containing strategically placed metal centres may offer better nonlinear absorption perf
Data Loading...
