350 ISSN 1990-7931, Russian Journal of Physical Chemistry B, 2008, Vol. 2, No. 3, pp. 350–353. © Pleiades Publishing, Ltd., 2008. Original Russian Text © N.N. Denisov, L.A. Shcheglova, S.K. Sekatskii, G. Dietler, V.A. Nadtochenko, 2008, published in Khimicheskaya Fizika, 2008, Vol. 27, No. 5, pp. 27–30. INTRODUCTION In recent times, methods for studying single mole- cules with the use of atomic force microscopy (AFC) have been intensely developed. This field of AFC is known as single-molecule force spectroscopy. In this connection, the development of methods of chemical binding of a test molecule to a solid substrate is of con- siderable importance. For example, in atomic-force- microscope measurements, the probe surface may be covered by antibodies, whereas the substrate surface, by antigens (Fig. 1). Studying the degree of expansion on the force applied to an antibody–antigen complex, one can obtain unique information on the conforma- tion changes in such a molecule and reveal distinc- tions between monoclonal and polyclonal antibodies [1–4]. The aim of the present work was to (1) develop a method for binding a bovine serum albumin (BSA) molecule to a calcite (CaCO 3 ) surface and (2) study the force curve for a BSA–BSA polyclonal antibody by using single-molecule force spectroscopy. Therefore, this system is especially suitable for working out a method for grafting a protein molecule onto a CaCO 3 STRUCTURE OF CHEMICAL COMPOUNDS. SPECTROSCOPY Single-Molecule Force Spectroscopy of a Protein Globule Covalently Bound to a Calcite Surface N. N. Denisov a , L. A. Shcheglova c , S. K. Sekatskii c , G. Dietler c , and V. A. Nadtochenko a, b a Semenov Institute of Chemical Physics, Russian Academy of Sciences, ul. Kosygina 4, Moscow, 119991 Russia b Moscow Institute (University) of Physics and Technology, Dolgoprudnyi, Moscow oblast, 141700 Russia c Laboratoire de Physique de large Matière Vivante, IPMC, BSP, Ecole Polytechnique Fédérale de Lausanne, Lausanne, CH-1015 Switzerland Received December 18, 2006 Abstract—Two methods of covalent grafting of a protein onto a calcite surface were developed. Single-mole- cule force spectroscopy was used to examine the characteristics of individual albumin–albumin polyclonal body complexes. The practical applicability of the proposed method of covalent grafting of a protein to a calcite sur- face was demonstrated. DOI: 10.1134/S1990793108030032 Photodiode Antibody Antigen – Diode laser Probe Sample Rupture force Z-piezo Nanoscope IIIa Fig. 1. Schematic of the experimental setup for single-molecule force spectroscopy measurements.