Imaging Cellular and Viral Materials with Small Cantilevers Developed for High Speed Atomic Force Microscopy
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Imaging Cellular and Viral Materials with Small Cantilevers Developed for High Speed Atomic Force Microscopy Georg E Fantner1, Tzvetan Ivanov2, Katerina Ivanova2, David Gray1, Ivo W Rangelow2, Paul K Hansma3, and Angela M Belcher1 1 Department for Materials Science and Engineering, Massachusetts Institute of Technology, cambridge, MA, 02139 2 Institute for Mikro- and Nanoelektronics, TU-Ilmenau, Ilmenau, Germany 3 Department of Physics, University of California Santa Barbara, Santa Barbara, CA, 93117 ABSTRACT High speed atomic force microscopy (AFM) holds the promise of investigating dynamic systems in real time with single molecule resolution. With the big push towards understanding more complex systems such as cell mechanics or cell-cell and cell-virus interactions, a tool is required that can extract information about these processes in real time in a physiological environment. Atomic force microscopy has been successfully used for investigations of many biological systems and materials in real life conditions, but taking AFM images takes too long to follow many biologically relevant processes. Therefore, attempts have been made to develop high speed AFM by reengineering all the components of an AFM system and much progress has been made. To be useful for investigations of biological systems however, it is often essential to keep imaging forces low in order to get good image quality and not to damage the sample. In this paper we will discuss new small AFM cantilevers we’ve developed to combine high resonance frequencies for faster imaging with low spring constants for gentle imaging. INTRODUCTION Already soon after its invention, researchers saw the need to increase the speed at which AFMs record images. Barret and Quate reported already in 1991 an AFM scanning several hundred lines per second[1] and Hörber et al. used a high speed AFM for investigations on cell surfaces in 1992[2]. Since then, several research groups have worked to improve upon AFM equipment to increase the scan speed. Developments in all components of an AFM have been performed such as the use of self sensing and self actuating cantilevers [3-6], specialized control techniques [7-14], improved scanner design [15-20], data acquisition [21, 22] and alternative sensing and actuation techniques[23, 24]. Using these techniques, scan speeds of 10s of images per second have been reported for special samples and situations. With all these improvements, the question is what component of the system is currently the bottleneck and what kind of performance increase would be required. Previously we reported on a scanner design that allows scanning of up to 6000 lines per second with 15µm X,Y scan range and 4 µm Z range which allows triangular scanning and scan rotation[15, 25]. Our data acquisition system based on Labview and a commercial DAQ card allows image capture of up to 30 images per second[21]. Given these allowable scan speeds, the limiting factor is the response time of the cantilever and its interaction with the sample. If the cantil
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