P1 − Combined AFM-SECM with Insulated Conductive Cantilevers
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P1 − Combined AFM-SECM with Insulated Conductive Cantilevers
Poster . P1 − Combined AFM-SECM with Insulated Conductive Cantilevers Keywords: AFM, conductive cantilevers, OmpF, porin, SECM Patrick D. Bosshart1, Patrick L.T.M. Frederix1, Mohamed Chami1, Terunobu Akiyama2, Maurizio R. Gullo2, Nicolaas F. de Rooij2, Urs Staufer2, Andreas Engel1 1: NCCR Nanoscale Science, M.E. Müller Institute, Biozentrum, University of Basel Klingelbergstrasse 70, CH-4056 Basel; Switzerland 2: NCCR Nanoscale Science, Institute for Microtechnology, University of Neuchâtel Rue Jacquet-Droz 1, CH-2007 Neuchâtel; Switzerland Email: [email protected] Homepage: http://www.mih.unibas.ch; http://www-samlab.unine.ch With the atomic force microscope (AFM) biomolecules and membranes can be imaged at nanometer lateral resolution once all conditions are optimized[1]. With cantilevers that incorporate a small electrode near or at the tip apex scanning electrochemical microscopy (SECM) can be carried out at the same time and functional data can be recorded in parallel. This has been used to study enzyme activity [2, 3]. Functional experiments can also be carried out on thin layers, like porous membranes [4], which are adsorbed on or above a conductive support. Of particular interest for structural biology is the study of structural and conductive properties of membrane proteins embedded in lipid bilayers. Here, we present electrochemical experiments where a conductive cantilever [5-7] approaches platinum supports covered with two types of membrane patches that are packed with different proteins: outer membrane porin F (OmpF) from E. coli, and the bacterial proton pump bacteriorhodopsin (bR) from H. salinarum. OmpF is an unspecific pore, which allows particles with a molecule mass MR<550Da to diffuse through [8] and shows voltage gating [9]. Consequently, the open pores of OmpF should be sufficiently large to pass redox molecules (like Ru(NH3)63+/2+, MR=203Da). On the other hand, the membrane patches containing bR only transport protons and are impermeable for the redox molecules. This expected difference in conductivity could be confirmed by combined AFM-SECM. In addition, by applying a potential across membranes that incorporate OmpF a change in conductivity is observed that can be ascribed to voltage-gating. References 1. Müller, et al. 1999; Biophys. J. 76: 1101 2. Kueng, et al. 2003; Angew. Chem. Int. Ed. Engl. 42: 3238 3. Kranz, et al. 2004; Ultramicrosc. 100: 127 4. Kueng, et al. 2005; Angew. Chem. Int. Ed. Engl. 44: 3419 5. Akiyama, et al. 2004; Jap. J. Appl. Phys. 43: 3865 6. Frederix, et al. 2005; Nanotechn. 16: 997 7. Gullo, et al. 2006; Anal. Chem. 78: 5436 8. Nakae 1976; Biochem. Biophys. Res. Comm. 71: 877 9. Schindler and Rosenbusch 1978; PNAS 75: 3751 . th 6 Int. Workshop − Scanning Probe Microscopy in Life Sciences − 9 October 2007 in Berlin www.spm-workshop.jpk.com 1/2 Poster . . th 6 Int. Workshop − Scanning Probe Microscopy in Life Sciences − 9 October 2007 in Berlin www.spm-workshop.jpk.com 2/2
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