Spm And Sicm Lecture

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Spm And Sicm Lecture

  1. 1. Scanning Probe Microscopy in general  No use of optics.  A probe senses a physical quantity which changes when the probe approaches the sample surface.  Sample or probe is moved by some kind of microactuator. Methods to obtain information:  Constant current mode: the probe is moved at a specified distance above the surface thus following the topology of the specimen. The height dependend signal (current) is kept constant this way. Slow scans, surfaces may be irregular.  Constant height mode: the height of the probe above the suface is fixed. The changes in the signal can be recorded. Fast scans, surfaces should be more even.
  2. 2. Scanning Tunneling Microscopy - STM  The scanning probe consists of a  Signal: Tunneling current metallic tip biased with a voltage  Probe: Metallic tip against a conducting sample surface.  Resolution: Down to subÅ  The voltage induces a tunneling  Requisites: Conducting Surface, current between tip and surface. usually UHV  Can be used for microstructuring: by reversing the bias polarity single atoms can be picked up from the surface.
  3. 3. Atomic Force Microscopy - AFM  The AFM operates by measuring  Signal: Deflection of cantilever attractive or repulsive forces  Probe: Diamond tip on cantilever between the tip and the sample.  Resolution: Down to 10pm  In ist repulsive contact mode a  Requisites: Regular surface, UHV for detection apparatus measures the high resolutions vertical deflection of the cantilever while it is draged over sthe surface.  In so called non-contact mode, the AFM derives topographic images from measurements of attractive forces. The lever is exited with a vibration at ist resonance frequency. When the tip is now attraced by near atoms (van der Waals forces) the vibration frequenca changes.
  4. 4. Other techniques  Friction force microskopy (FFM)  Magnetic force microskopy (MFM)  Electrostatic force microskopy (EFM)  Scanning thermal microskopy (SThM)  Optical absorption microskopy  Scanning acoustic microskopy (SAM)  Molecular dip-stick microskopy  Shear force microskopy (ShFM)  Scanning near-field optical microskopy (SNOM)
  5. 5. Patch clamp technique  Patch-clamping is an electro- physiological method used to monitor the ion current of single ion-channels in the membranes of living cells.  Currents are in the pA range – thus they are hard to distinguish from background noise.  Forming of a „Gigaseal“  Various configurations  „loose patch“ configuration is used in the SICM method  Publication: Neher and Sakmann. Die Erforschung von Zellsignalen mit der Patch-Clamp-Technik. Spektrum der Wissenschaft, pages 48–56, May 1992.
  6. 6. Scanning ion conductance microscopy - SICM Working conditions:  Isolating samples  Probe: Micropipette  Environment: conductive liquid  Opening diameter of the pipette determines the resolution (500nm-  Atmospheric pressure 20nm)  Ideally suited for living cells.  Measurement of ion currents.  contact free Developed 1989 by Hansma Group, University of Santa Barbara.
  7. 7. SICM - Principle  Ion current is flowing between bath electrode and electrode in the pipette.  Approach of the pipette towards the isolating sirface.  current drop  detection of the surface.  Backstepping.
  8. 8. SICM – Model  Resistance: R =L/Aκ  Frustrum: RF =Lk/rpriπκ  Hollow cylinder: RH =ln( ro/ri)/2πhκ  Total resistance: RT = RK +RH =U/I  Resolved for the current: I =Uκπ/((Lk/rpri)+ln( ro/ri)/2h)  Saturation current (h  ∞): Isat = lim(Uκπ/((Lk/rpri)+ln( ro/ri)/2h))  =Uκπ/(Lk/rpri)  Normalized quantity: I/ Isat  It is possible to estimate the opening diameter from the measured resistance.
  9. 9. SICM – Approaching curves
  10. 10. SICM - Setup
  11. 11. SICM – Setup description 1. (a) Optical microscope 1. Piezo controller (b) Object table 2. Patch-clamp amplifier (c) Condenser 3. Oscilloscope 2. Micro-manipulator 4. Function generator 3. Piezo-actuator 5. Vibration damping 4. Headstage 6. Connection to PC – data acquisition 5. Pipette holder  Farady cage (not shown) 6. Micropipette  Pipette puller (not shown)
  12. 12. SICM – Signal diagram  Pipette movement: Lateral: via Piezo controller (commands over RS232). Vertical: per Modulationvoltage.  Output signal of the EPC7 unit: Proportional to the ion current, signal gets sampled. The vertical piezo position is controlled by a voltage delivered by the analog output of the NI-DAQ card. This method is much faster than the step-by-step method used in the approach function. The controlling voltage is dropped in a slope, thus the pipette is moved towards the surface. While the pipette moves the output of the patch-clamp amplifier (the actual ion-current) is sampled at 1 KHz and analyzed in realtime. An average of 20 samples is taken and compared with the last measurement by the data acquisition hardware. If the difference exceeds a defined ratio, the voltage slope is stopped and the position of the tip is determined by the function readheight.
  13. 13. SICM – Manufacturing pipette tips  In principle the required small opening diameters are obtained by heating up a glass tube until it begins to melt. Then a longitudinal force is applied, pulling the tube apart until it is tearing. To get reproducible tips so called pullers are used.  In the puller the clamped glass tube is heated up by a platinum filament or by a laser beam. The force is applied by electromagnets or by gravity. Often the tubes are pulled with varying forces or in several pulling cycles.
  14. 14. SICM – Pipette tip SEM
  15. 15. SICM - Using the SICM  Fill and mount the tip  Enter liquid and measure saturation current  Find a sample object  Bring the tip into position  Approach the surface  Start scan
  16. 16. SICM – Picture of red blood cells
  17. 17. SICM – 3D picture
  18. 18. SICM - A single cell
  19. 19. SICM - Outlook Proposed improvements:  Reprogramming the software  A faster computer  Acquisition of a pipette puller  Use of the computer as function generator  Construction of a perfusion chamber Experiments:  Calibration  Frequency – and step-responses  Manufacturing and behavior of micropipettes  Localization of ion channels
  20. 20. Bibliography 1  [Aea88] Alexander and Schneir et al. An atomic resolution afm implemented using an optical lever. Journal of Applied Physics, 65:164–167, 1988.  [AP03] Alexeev and Popkov. Magnetic Force Microscopy. NTMDT, State Institute for Physical Problems, Moscow, 2003. http://www.ntmdt.ru/applicationnotes/MFM/.  [Bea82] Binnig and Rohrer et al. Surface studies by scanning tunneling microscopy. Physical Review Letters, 49:57–61, 1982.  [BQG86] Binnig, Quate, and Gerber. Atomic force microscopy. Phys. Rev. Lett., 56:930–933, 1986.  [BR87] Binnig and Rohrer. Scanning tunneling microscopy – from birth to adolescence. Rev. Mod. Phys., 59:615–625, 1987.  [CGL92] A. Cavali´e, R. Grantyn, and H. D. Lux. Practical Electrophysiological Method, chapter Fabrication of patch clamp pipettes, pages 235–241. Wiley-Liss, New York, 1992.  [Dea89] Drake and Prater et al. Imaging crystals, polymers, and processes in water with the atomic force microscope. Science, 243:1586–1589, March 1989.  [Hea89] Hansma and Drake et al. The scanning ion-conductance microscope. Science, 24:641–643, February 1989.
  21. 21. Bibliography 2  [Kam95] Jörg Kamp. Aufbau und Erprobung eines kombinierten Rasterionenleitungs- und Scherkraftmikroskops. Diploma thesis, Physikalisches Institut der Westfälischen Wilhelms-Universität, March 1995. in german language.  [KBM97] Korchev, Bashford, and Milovanovic. Scanning ion conductance microscopy of living cells. Biophysical Journal, 73:653–658, August 1997.  [Kea00] Korchev and Negulyaev et al. Functional localization of single active ion channels on the surface of a living cell. Nature Cell Biology, pages 616–619, September 2000.  [KMB97] Korchev, Milovanovic, and Bashford. Specialized ion-conductance microscope for imaging of living cells. Journal of Microscopy, 188(1):17– 23, October 1997.  [MDH87] Marti, Drake, and Hansma. Atomic force microscopy of liquid-covered surfaces: Atomic resolution images. Appl. phys. Lett., 51:484–486, 1987.  [Mea88] Marti and Elings et al. Scanning probe microscopy of biological samples and other surfaces. Journal of Microscopy, 152:803–809, 1988.  [ND96] Numberger and Draguhn. Patch-Clamp Technik. Spektrum Akademischer Verlag, 1996.  [NS92] Neher and Sakmann. Die Erforschung von Zellsignalen mit der Patch- Clamp-Technik. Spektrum der Wissenschaft, pages 48–56, May 1992. in german language.
  22. 22. Bibliography 3  [OR95] O´Reilly and Richardson. A practical vibration isolation workstation for electrophysiology. journal of Neuroscientific Methods, 60:175–180, 1995.  [PH91] Prater and Hansma. Improved scanning ion-conductance microscope using microfabricated probes. Review of Scientific Instruments., 62(11):2634–2637, November 1991.  [PLH96] Proksch, Lal, and Hansma. Imaging the internal and external pore structure of membranes in fluid: Tappingmode scanning ion conductance microscopy. Biophysical Journal, 71:2155–2157, October 1996.  [Sch90] E. Schwab. Aufbau und Erprobung eines kombinierten Rasterionenleitungsmikroskops (RILM). Diploma thesis, Wiesbaden, 1990. in german language.  [Sch00] Stefan Schraml. Setup of a SICM. WE-Heraeus Ferienkurs Nanophysik, Sept. 2000. poster presentation.  [WW86] Williams and Wickramasinghe. Scanning thermal profiler. Appl. Phys. Lett., 49:1587–1589, 1986. Contact: DI Stefan Schraml sschraml@gmx.net ©2005

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