title: Photonic force microscope based on optical tweezers and two-photon excitation for biological applications.
abstract: A new scanning probe microscope, the photonic force microscope (PFM), based on optical tweezers and two-photon absorption processes for biological applications is described. Optical tweezers are used to trap a fluorescent latex bead with a diameter of 200 nm in an aqueous solution in all three dimensions. The fluorescent dye is chosen to fulfill the two-photon absorption criterion for the 1064-nm line of a Nd:YVO4 laser. The intensity of the fluorescence emission is utilized as a very sensitive position sensor along the optical axis. Two-dimensional images are formed by laterally scanning the trapped latex bead across biological samples while recording the two-photon-induced fluorescences intensity. A scanning probe image of the outer surface of a small neurite from a cultured rat hippocampal neuron is shown, which is hardly visible under differential interference contrast microscopy. The lateral resolution is given by the bead diameter; the axial resolution is 40 nm. Under the experimental conditions the maximal imaging force applied by the probe is below 5 pN.
authors.affiliation: Cell Biophysics Programme, European Molecular Biology Laboratory, Heidelberg, Germany.
authors.forename: E L
authors.initials: EL
authors.lastname: Florin
authors.forename: A
authors.initials: A
authors.lastname: Pralle
authors.forename: J K
authors.initials: JK
authors.lastname: Hörber
authors.forename: E H
authors.initials: EH
authors.lastname: Stelzer
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D005453:Fluorescence; D005456:Fluorescent Dyes; D006624:Hippocampus / Q000196:embryology; D007091:Image Processing, Computer-Assisted; D007834:Lasers; D007840:Latex; D008853:Microscopy / Q000295:instrumentation / Q000379:methods*; D008863:Microspheres; D009474:Neurons / Q000648:ultrastructure*; D010316:Particle Size; D017785:Photons; D051381:Rats
chemical_list: D005456:Fluorescent Dyes; D007840:Latex