title: Simultaneous topography and recognition imaging using force microscopy.
abstract: We present a method for simultaneously recording topography images and localizing specific binding sites with nm positional accuracy by combining dynamic force microscopy with single molecule recognition force spectroscopy. For this we used lysozyme adsorbed to mica, the functionality of which was characterized by enzyme immunoassays. The topography and recognition images were acquired using tips that were magnetically oscillated during scanning and contained antibodies directed against lysozyme. For cantilevers with low Q-factor (approximately 1 in liquid) driven at frequencies below resonance, the surface contact only affected the downward deflections (minima) of the oscillations, whereas binding of the antibody on the tip to lysozyme on the surface only affected the upwards deflections (maxima) of the oscillations. The recognition signals were therefore well separated from the topographic signals, both in space (Delta z approximately 5 nm) and time (approximately 0.1 ms). Topography and recognition images were simultaneously recorded using a specially designed electronic circuit with which the maxima (U(up)) and the minima (U(down)) of each sinusoidal cantilever deflection period were depicted. U(down) was used for driving the feedback loop to record the height (topography) image, and U(up) provided the data for the recognition image.
authors.affiliation: Institute for Biophysics, Atomic Physics and Surface Science, Johannes Kepler University of Linz, A-4040 Linz, Austria.
authors.forename: Cordula M
authors.initials: CM
authors.lastname: Stroh
authors.forename: Andreas
authors.initials: A
authors.lastname: Ebner
authors.forename: Manfred
authors.initials: M
authors.lastname: Geretschläger
authors.forename: Günter
authors.initials: G
authors.lastname: Freudenthaler
authors.forename: Ferry
authors.initials: F
authors.lastname: Kienberger
authors.forename: A S M
authors.initials: AS
authors.lastname: Kamruzzahan
authors.forename: Sandra J
authors.initials: SJ
authors.lastname: Smith-Gill
authors.forename: Hermann J
authors.initials: HJ
authors.lastname: Gruber
authors.forename: Peter
authors.initials: P
authors.lastname: Hinterdorfer
mesh_terms: D000538:Aluminum Silicates / Q000737:chemistry; D000818:Animals; D000906:Antibodies / Q000737:chemistry; D000937:Antigen-Antibody Reactions; D002138:Calibration; D007091:Image Processing, Computer-Assisted; D007124:Immunoenzyme Techniques; D018625:Microscopy, Atomic Force / Q000295:instrumentation* / Q000379:methods*; D009113:Muramidase / Q000737:chemistry* / Q000648:ultrastructure; D009991:Oscillometry; D012984:Software; D013499:Surface Properties; D013997:Time Factors
chemical_list: D000538:Aluminum Silicates; D000906:Antibodies; D009113:Muramidase; C011934:mica