Ruth Leben

Deutsches Rheuma-Forschungszentrum Berlin, ein Leibniz-Institut, Berlin, Germany

Cutting Edge Session Part I: Wednesday, September 29^th, 2021: 4:00pm – 5:00pm

Towards ultra-deep three-photon tissue oxygenation imaging in murine lymphoid organs

To study dynamic cellular processes of the immune system, it is essential to image deep into scattering tissues of lymphoid organs such as lymph node, spleen or bone marrow – the regions of interest. Two- photon microscopy has therefore become a widely used and popular tool in the biomedical sciences because it reaches these areas. Nevertheless, it offers relatively low resolution and imaging depth when it comes to imaging ultra-deep through optically dense tissue such as cortical bone. Here three- photon microscopy provides an imaging technique, which excitation light penetrates deeper into due to lesser scattering, at higher excitation wavelengths and the contrast increases due to the higher order of nonlinear excitation.

Especially in the bone marrow, the survival of cells ensuring immunological memory over long periods of time as well as the survival of hematopoietic stem cells depends on tissue oxygenation. Several phosphorescent nanoparticles have been developed that sense partial pressure of oxygen pO2 and are applicable in living organs.

Here we present a study on the three-photon excitability and detectability of pO2-sensitive nanoparticles dissolved in micropore water. To enable three-photon excitation a new optical parametric amplifier (OPA) at 2MHz repetition rates, emitting 1300 nm to 1700 nm wavelength was used.

Thee-photon excited conjugated polymer based phosphorescent nanoparticles may offer valuable insights in cell and tissue oxygenation ultra-deep in living tissue, in vivo.