Hawkes P.W., Spence J.C.H. (Eds.) Science of Microscopy. V.1 and 2

Подождите немного. Документ загружается.

1060 M. Amrein

Force spectroscopy in AFM refers to the measurement of tip–sample

interaction forces at a point as the height of the cantilever base is varied.

This allows measurement of forces either pushing into the sample

(elasticity, rheology, etc.), or pulling away from the sample (adhesion,

including recognition of speciﬁ c molecular binding, unfolding, or

stretching of molecules bound between the tip and the sample surface).

Alternatively, manipulation of the surface, such as dissection or

alignment, is possible using the tip to apply forces and modify the

sample.

The ability to locally probe and manipulate a sample in addition to

imaging is a unique strength of AFM. The local experiments are as diverse

as the research questions and address both isolated macromolecular

structures and cells. This is demonstrated for a few examples.

4.2.1 Pulmonary Surfactant

A mixed lipid–protein ﬁ lm of pulmonary surfactant covers the hydrated

lung epithelia to the air. This highly cohesive and mechanically stable

ﬁ lm reduces the otherwise high surface tension of the air–aqueous

interface to almost zero as is required for the structural stability of the

alveolar lung and ease of breathing. The mechanical stability of the

ﬁ lm depends on a pattern of monolayer domains of disaturated phos-

pholipids intercepted by multilayer areas, containing the unsaturated

lipids also present in surfactant. This molecular architecture is con-

veyed to the ﬁ lm by the surfactant-speciﬁ c proteins SP-B and/or SP-C.

The proteins cross-link the multilayer areas to the monolayer.

This molecular arrangement has been discovered by AFM (von

Nahmen et al., 1997). First, a topographical image was obtained

(Figure 16–22). Then, the loading force was increased such as to physi-

cally remove the lipid stacks on top of the molecular monolayer.

After removal of the multilayers, the monolayer showed crevices on

the circumference of the earlier multilayer patch and holes, evenly

Figure 16–22. Functional pulmonary surfactant forms molecular ﬁ lms of molecular monolayer regions

and areas of monolayers with stacks of lipid bilayers cross-linked to it (left). Cross-linking is revealed

by physically removing the bilayers by an intentionally high load of the AFM probe (middle and

right).

Chapter 16 Atomic Force Microscopy in the Life Sciences 1061

distributed over the area earlier covered. This was indicative of a

cross-linking structure that had also been removed by the stylus. Mere

lipid layers, formed on top of a lipid monolayer in the absence of

surfactant proteins, left no traces behind after being removed by the

stylus.

Multilayers, cross-linked to the monolayer as opposed to multilayers,

merely adsorbed to the monolayer appear to be crucial for surfactant

function. At low surface tension, the interfacial ﬁ lm is subjected to high

lateral pressure. Cross-linked multilayered areas take up the lateral

load together with the monolayer. Otherwise, the load resides on the

monolayer alone. But lipid monolayer ﬁ lms containing unsaturated

lipids are not able to withstand a high ﬁ lm pressure without collapsing.

They therefore cannot reduce tension by a degree required for proper

function of the lung. This condition is likely responsible for lung failure

after acute lung injury where the surfactant is distinct by an elevated

level of cholesterol (Karagiorga et al., 2006). Excess cholesterol prevents

formation of cross-linked multilayer stacks and surface tension is high

(Gunasekara et al., 2005).

4.2.2 Collagen Matrices

Müller and his associates (Jang et al., 2003) used the atomic force micro-

scope to mechanically direct collagen into two-dimensional, 3-nm-

thick layers of deﬁ ned structure. During a critical, initial period of time

this structure was found to be highly malleable and the collagen mol-

ecules could be reoriented by the stylus of the AFM. After this time,

the collagen coating hardened and remained stable for several months

without loss of ﬁ ber orientation or mechanical strength. It was pro-

posed that collagen ﬁ ber formation in vivo may also have a critical

period during which cellular forces remodel a collagen network that

acts as a matrix for later tissue growth. In tissues, cells are indeed

thought to organize the collagen ﬁ brils by exerting tension on the

matrix, and the realignment forces required in the experiment (300 pN)

were within the range of forces that ﬁ broblasts can generate. Besides

explaining an important phenomenon on how tissue might organize

in vivo, this discovery might also ﬁ nd technical applications. Engi-

neered collagen matrices might ﬁ nd use as a platform for cell biological

and tissue engineering applications (Figure 16–23).

4.2.3 Imaging and Unfolding a Bacterial Cell Wall Protein

Unfolding proteins and DNA and separating molecular binding

partners have become important and active offspring of AFM, referred

to as force spectroscopy. It provides insight into protein and DNA

folding and conformation about the nature of binding pockets. Müller

and his associates have used this technique in conjunction with

high-resolution imaging to gain insight into the interaction forces

between the individual protomers of a regular bacterial surface

layer, the hexagonally packed intermediate (HPI) layer of Deinococcus

radiodurans. After imaging the HPI layer, the AFM stylus was attached

to individual protomers by enforced stylus–sample contact to allow

force spectroscopy experiments. Imaging of the HPI layer after

recording force–extension curves allowed unfolding forces to be

1062 M. Amrein

correlated with the structures being unfolded. By using this approach,

individual protomers of the HPI layer were found to be removed

at pulling forces of ≈300 pN. Furthermore, it was possible to sequen-

tially unzip entire bacterial pores formed by six HPI protomers

(Figure 16–24).

4.2.4 Sphingolipid–Cholesterol Rafts

In the plasma membrane, nanoscopic, condensed sphingolipid–choles-

terol rafts “ﬂ oat” in a ﬂ uid matrix and likely act as prefabricated sub-

units of functional complexes. The functions these platforms perform

involve essential cellular processes such as the initiation and down-

regulation of signaling cascades that regulate cell growth, survival,

and death, or endo- and exocytosis. A rapidly growing list of diseases

has been identiﬁ ed as being related to rafts, including Alzheimer’s

Figure 16–23. After collagen microﬁ brils were assembled out of solution on

the supporting surface, their orientation has been changed in a controlled

manner using the stylus of an AFM in the central region of the image. For this,

the force was increased to 300 pN while the stylus was scanned over this

operator-deﬁ ned region. The collagen microﬁ brils in the region were now

aligned with the fast-scanning direction of the AFM stylus and were approxi-

mately perpendicular to the original orientation. The surface was then reim-

aged at low force to create the image. (From Jiang et al., 2004b, reproduced

with permission.)

Chapter 16 Atomic Force Microscopy in the Life Sciences 1063

and Parkinson’s diseases, muscular dystrophy, asthma and allergic

responses, hypertension, arteriosclerosis, and prion diseases. Bacteria

(e.g., Vibrio cholarae), viruses such as HIV-1, measles, and Ebola virus,

as well as parasites (e.g., malaria) depend on lipid rafts for their pur-

poses. Despite the outstanding importance of lipid rafts, most ques-

tions about how rafts are formed, composed, and behave in the plasma

membrane of living cells are not well understood. Although several

chemical groups that anchor proteins to rafts are known (e.g., the GPI,

dipalmitoyl group), it is not known why, and to what extent, certain

proteins become associated with one type and others to another kind

of raft. But even the most basic questions regarding the size of rafts

and whether they are transient structures are controversially discussed

(Figure 16–25).

Strong experimental evidence of the existence of rafts as entities of

deﬁ ned size and with an extended lifetime has come from measuring

the diffusion and stability over time of individual rafts in the plasma

membrane of BHK-21 cells by photonic force microscopy, a variety of

AFM (Hörber et al., 1992; Pralle et al., 2000). A bead in a laser trap was

scanned over a cell sample. Like with the tip of a cantilever-based

AFM, the height of the laser spot was readjusted by feedback when the

bead was forced out of the focal spot of the laser trap by the sample.

A topographical image of the sample was thus recorded. In a set of

experiments, beads were coated with antibodies against a raft-associ-

ated protein. After binding to the cell, the laser trap was kept still and

the diffusion of the bead attached to a raft was observed within the

narrow conﬁ nement of the laser focal spot. The diffusion reﬂ ected

the diffusion of the raft within the membrane and allowed the size of

Figure 16–24. The six protomers of an individual pore can be sequentially

pulled out of the HPI layer. Left: AFM topograph of the inner surface of the

HPI layer prior to (left) and after (right) the pulling experiment. Note that one

entire pore is missing. (Middle) The force-extension curve shows a sawtooth

pattern with six force peaks of about 300 pN each corresponding to the extrac-

tion of one protomer. The height of the force peaks corresponds to the binding

force for a protomer to its neighbors; the stretching distances between

protomer disruption events (7.3 ± 1.6 nm) corresponds to the length of the

molecular linker connecting a protomer to its neighbors. (From Engel et al.,

2000, reproduced with permission.)

1064 M. Amrein

the raft to be derived. For those rafts addressed by the selected antibod-

ies, these entities turned out to be about 50 nm in diameter. The experi-

ment also showed that these rafts were not transient structures within

the timeframe of the measurement (Figure 16–26).

Figure 16–25. The size and temporal stability of a lipid raft may be derived

by observing its diffusion within the plasma membrane. Observing the free

diffusion of a raft is problematic, because rafts collide frequently with the

elements of the cytoskeleton, anchored to the membrane. A more accurate

picture is derived from observation of the constraint diffusion of a raft offered

by photonic force microscopy. (From Pnalle et al., 2000, reproduced with

permission.)

Figure 16–26. Diffusion coefﬁ cients for raft proteins (PLAP, YFPGLGPI, HA)

and nonraft membrane proteins (hTfR∆t, LYFPGT46). The raft proteins diffuse

together with the lipid raft; the nonraft proteins diffuse freely in the ﬂ uid

phase of the plasma membrane. Depriving cells in culture of one of the

mandatory raft elements, cholesterol, abolishes rafts. As a consequence, the

former raft proteins diffuse individually in the membrane. (From Pnalle et

al., 2000, reproduced with permission.)

Chapter 16 Atomic Force Microscopy in the Life Sciences 1065

References

Allison, D. and Thundat, T. (1993). Imaging entire genetically functional DNA

molecules with the scanning tunneling microscope. J. Vac. Sci. Technol. A 11,

816.

Amrein, M., Stasiak, A., Gross, H. and Travaglini, G. (1988). Scanning tunneling

microscopy of recA-DNA complexes coated with a conducting ﬁ lm. Science

240, 514–516.

Amrein, M., Dürr, R., Stasiak, S., Gross, H. and Travaglini, G. (1989b). Scanning

tunneling microscopy of uncoated recA-DNA complexes. Science 243,

1708–1711.

Amrein, M., Dürr, R., Winkler, H., Travaglini, G., Wepf, R. and Gross, H.

(1989b). STM of freeze-dried and Pt-Ir-C-coated bacteriophage T4 poly-

heads. J. Ultrastruc. Mol. Struct. Res. 102, 170–177.

Amrein, M., Gross, H. and Guckenberger, R. (1993). STM of proteins and mem-

branes. In STM and AFM in biology (O. Marti and M. Amrein, Eds.), 127–175

(Academic Press, London).

Amrein, M., von Nahmen, A. and Sieber, M. (1997). A scanning force- and ﬂ uo-

rescence light microscopy study of the structure and function of a model

pulmonary surfactant. Eur. Biophys. J. 26(5), 349–357.

Arscott, P.G. and Bloomﬁ eld, V.A. (1993). STM of DNA and RNA (Academic

Press, San Diego).

Bader, H., Dorn, K., Hupfer, B. and Ringsdorf, H. (1985). Polymeric monolayers

and liposomes as models for biomembranes—how to bridge the gap between

polymer science and membrane biology. Adv. Polymer Sci. 64, 1–62.

Baró, A.M., Miranda, R., Alaman, J., Garcia, N., Binnig G., Rohrer, H., Gerber,

C. and Carracosa, J.L. (1985). Determination of surface topography of bio-

logical specimens at high resolution by scanning tunnelling microscopy.

Nature 315, 253–254.

Baumeister, W., Barth, M., Hegerl, R., Guckenberger, R., Hahn, M. and Saxton,

W.O. (1986). Three-dimensional structure of the regular surface layer (HPI

layer) of Deinococcus radioudurans. J. Mol. Biol. 187, 241–253.

Binnig, G. and Rohrer, H. (1982). Scanning tunneling microscopy. Helv. Phys.

Acta 55, 726–735.

Binnig, G. and Smith, D.P.E. (1986). Single-tube three-dimensional scanner for

scanning tunneling microscopy. Rev. Sci. Instrum. 57(8), 1688–1689.

Blackford, B.L. and Jericho, M.H. (1991). A metallic replica/anchoring tech-

nique for scanning tunneling microscope or atomic force microscope imaging

of large biological structures. J. Vac. Sci. Technol. B 9(2), 1253–1258.

Blodgett, K.A. and Langmuir, I. (1937). Phys. Rev. 51, 2492.

Brisson, A., Olofsson, A. and Ringler, P. (1994). Two-dimensional crystalliza-

tion of proteins on planar lipid ﬁ lms and structure determination by electron

crystallography. Biol. Cell 80, 221–228.

Budó, A. (1976). Theoretische Mechanik (VEB Deutscher Verlag der Wissen-

schaften, Berlin).

Butt, H.-J. (1991). Measuring electrostatic, van der Waals, and hydration forces

in electrolyte solutions with an atomic force microscope. Biophys. J. 60,

1438–1444.

Butt, H.-J. (1992). Measuring local surface charge densities in electrolyte solu-

tions with a scanning force microscope. Biophys. J. 63, 578–582.

Butt, H.-J., Jaschke, M. et al. (1995). Measuring surface forces in aqueous solu-

tion with the atomic force microscope. Bioelect. Bioenerg. 38, 191–201.

Chang, L., Kious, T., Yorgancioglu, M., Keller, D. and Pfeiffer, J. (1993). Cyto-

skeleton of living, unstained cells imaged by scanning force microscopy.

Biophys. J. 64, 1282–1286.

1066 M. Amrein

Ducker, W.A., Senden, T.J. and Pashley, R.M. (1991). Direct measurements of

colloidal forces using an atomic force microscope. Nature 353, 239–241.

Engel, A. and Müller, D.J. (2000). Observing single biomolecules at work with

the atomic force microscope. Nature Struct. Biol. 7(9), 715–718.

Engel, A., Hoenger, A., Hefti, A., Henn, C., Ford, R.C., Kistler, F. and Zulauf,

M. (1992). Assembly of 2-D membrane protein crystals: dynamics, crystal

order, and ﬁ delity of structure analysis by electron microscopy. J. Struct.

Biol. 109, 219–234.

Fisher, K.A., Yanagimoto, K. and Stoeckenius, W. (1977). Purple membrane

bound to polylysine glass: effects of pH and light. J. Cell Biol. 75, 200a.

Fisher, K.A., Yanagimoto, K. and Stoeckenius, W. (1978). Oriented adsorption

of purple membrane to cationic surfaces. J. Cell Biol. 77, 611–621.

Fritz, M., Radmacher, M. and Gaub, H.E. (1994). Granula motion and mem-

brane spreading during activation of human platelets imaged by atomic

force microscopy. Biophys. J. 66(5), 1328–1334.

Guckenberger, R., Wiegräbe, W., Hillebrand, A., Hartmann, T., Wang, Z. and

Baumeister, W. (1989). Scanning tunneling microscopy of a hydrated bacte-

rial surface protein. Ultramicroscopy 31, 327–332.

Guckenberger, R., Heim, M., Cevc, G., Knass, H.F., Weigräbbe, W. and

Hillebrand, A. (1994). Scanning tunneling microscopy of insulators and

biological specimens based on lateral conductivity of ultrathin water ﬁ lms.

Science 266, 1538–1540.

Gunasekara, L., Schürch, S., Schoel, W.M., Nag, K., Leonenko, Z., Haufs, M.

and Amrein, M. (2005). Pulmonary surfactant function is abolished by an

elevated proportion of cholesterol. Biochim. Biophys. Acta 1737, S27–35.

Haltia, T. and Freire, E. (1995). Forces and factors that contribute to the struc-

tural stability of membrane proteins. Bba-Bioenergetics 1228(1), 1–27.

Han, W., Lindsay, S.M. and Jing, T.W. (1996). A magnetically driven oscillating

probe microscope for operation in liquids. Appl. Phys. Lett. 69(26), 4111–4113.

Hansma, P. (1996). New AFM technology for better biological imaging. Am.

Phys. Soc. 41, 515.

Hansma, P.K., Cleveland, J.P., Radmacher, M., Walters, D.A., Hillner, P.E.,

Bezanilla, M., Fritz, M., Vie, D., Hansma, H.G. and Prater, C.B. (1994).

Tapping mode atomic force microscopy in liquids. Appl. Phys. Lett. 64(13),

1738–1740.

Harris, C.M. (1987). Shock and Vibration Handbook (McGraw-Hill, New York).

Hayward, S.B., Grano, D.A., Glaeser, R.M. and Fisher, K.A. (1978). Molecular

orientation of bacteriorhodopsin within the purple membrane of Halobacte-

rium halobium. Proc. Natl. Acad. Sci. USA 75(9), 4320–4324.

Hegner, M., Wagner, P. and Semenza, G. (1993). Immobilizing DNA on gold

via thiol modiﬁ cation for atomic force microscopy imaging in buffer solu-

tions. FEBS Lett 336(3), 452–456.

Hegner, M., Dreier, M., Wagner, P., Semenza, G. and Güntherodt, H.J. (1996).

Modiﬁ ed DNA immobilized on bioreactive self-assembled monolayer on

gold for dynamic force microscopy imaging in aqueous buffer solution. J.

Vac. Sci. Technol. 14, 1418–1421.

Henderson, E., Haydon, P.G. and Sakaguchi, D.S. (1992). Actin ﬁ lament dynam-

ics in living glial cells imaged by atomic force microscopy. Science 257,

1944–1945.

Heuberger, M., Dietler, G. and Schlapbach, L. (1996). Elastic deformations of

tip and sample during atomic force microscope measurements. J. Vac. Sci.

Technol. B 14(2), 1250–1254.

Hoh, J.H. and Schoenenberger, C.-A. (1994). Surface morphology and mechani-

cal properties of MDCK monolayers by atomic force microscopy. J. Cell Sci.

107(5), 1105–1114.

Chapter 16 Atomic Force Microscopy in the Life Sciences 1067

Hoh, J.H., Sosinski, G.E., Revel, J.-P. and Hansma, P.K. (1993). Structure of the

extracellular surface of the junction by atomic force microscopy. Biophys. J.

65, 149–163.

Hörber, J.K.H., Häberle, W., Ohnesorge, F., Binnig, G., Liebich, H.G., Czerny,

C.P., Bahnel, H. and Mayr, A. (1992). Investigation of living cells in the

nanometer regime with the scanning force microscope. Scan. Microsc. 6(4),

919–930.

Israelachvili, J. (1991). Intermolecular & Surface Forces (Academic Press,

London).

Jacobson, B.S. and Branton, D. (1977). Plasma membrane: rapid isolation and

exposure of the cytoplasmic surface by use of positively charged beads.

Science 195, 302–304.

Jap, B.K., Zulauf, M., Scheybani, T., Hefti, A., Baumeister, W., Aebi, U. and

Engel, A. (1992). 2D crystallization: from art to science. Ultramicroscopy 46,

45–84.

Jiang, F., Hörber, H., Howard, J. and Muller, D.J. (2004a). Assembly of collagen

into microribbons: effects of pH and electrolytes. J. Struct. Biol. 148(3),

268–278.

Jiang, F.Z., Khairy, K., Poole, K., Howard, J. and Muller, D.J. (2004b). Creating

nanoscopic collagen matrices using atomic force microscopy. Microsc. Res.

Techni. 64, 435–440.

Karagiorga, G., Nakos, G., Galiatson, E. and Lekka, M.E. (2006). Biochemical

parameters of bronchoalveolar lavage ﬂ uid in fat embolism. Intensive Care

med. 32, 116–123.

Karrasch, S., Dolder, M., Schabert, F., Ramsden, J. and Engel, A. (1993). Cova-

lent binding of biological samples to solid supports for scanning probe

microscopy in buffer solution. Biophys. J. 65, 2437–2446.

Kasas, S. and Ikai, A. (1995). A method for anchoring round shaped cells for

atomic force microscope imaging. Biophys. J. 68(5), 1678–1680.

Kellenberger, E. and Kistler, J. (1979). The physics of specimen preparation. In

Advances in Structure Research by Diffraction Methods (W.H.R. Mason, Ed.),

III, 49–79 (Friedrich Vieweg, Wiesbaden).

Kellenberger, E., Häner, M. and Wurtz, M. (1982). The wrapping phenomenon

in airdried and negatively stained preparations. Ultramicroscopy 9,

139–150.

Knapp, H., Wiegräbe, W., Heim, M., Eschrich, R. and Guckenberger, R. (1995).

Atomic force microscope measurements and manipulation of Langmuir-

Blodgett ﬁ lms with modiﬁ ed tips. Biophys. J. 69, 708–715.

Knebel, D., Amrein, M. and Reichelt, R. (1997). A fast and versatile scan-unit

for scanning probe microscopy. Scanning 19(4), 264–268.

Knebel, D., Sieber, M., Reichelt, R., Galla, H.J. and Amrein, M. (2002). Scanning

force microscopy at the air-water interface of an air bubble coated with

pulmonary surfactant. Biophys. J. 82(1 Pt 1), 474–480.

Lantz, M.A., O’Shea, S.J. and Welland, M.E. (1994). Force microscopy imaging

in liquids using ac techniques. Appl. Phys. Lett. 65(4), 409–411.

Lindsay, S.M. and Tao, N.J. (1993). Potentiostatic deposition of molecules for

SXM. In STM and AFM in Biology (O. Marti and M. Amrein, Eds.), 229–258

(Academic Press, London).

Matsko, N. and Mueller, M. (2004). AFM of biological material embedded in

epoxy resin. J. Struct. Biol. 146(3), 334–343.

Mazia, D., Schatten, G. and Sale, W. (1975). Adhesion of cells to surfaces coated

with polylysin: applications to electron microscopy. J. Cell. Biol. 66,

198–200.

Miles, M.J. and McMaster, T.J. (1993). Protein Assemblies and Single Molecules

Imaged by STM (Academic Press, San Diego).

1068 M. Amrein

Miles, M.J., McMaster, T., Carr, H.J., Tatham, A.S., Shewry, P.R., Field, J.M.,

Belton, B.S., Jeenes, D., Hanley, B. and Whittam, M. (1990). Scanning tun-

neling microscopy of biomacromolecules. J. Vac. Sci. Technol. A 8(1),

698–702.

Müller, D.J. and Büldt, G. (1995). Force-induced conformational change of

bacteriorhodopsin. J. Mol. Biol. 249, 239–243.

Müller, D.J., Baumeister, W. and Engel, A. (1996). Conformational change of

the hexagonally packed intermediate layer imaged by atomic force micros-

copy. J. Bacteriol. 78, 3025–3030.

Müller, D.J., Amrein, M. and Engel, A. (1997a). Adsorption of biological mole-

cules to a solid support for scanning probe microscopy. J. Struct. Biol. 119(2),

172–188.

Müller, D.J., Engel, A. and Amrein, M. (1997b). Preparation techniques for the

observation of native biological systems with the atomic force mocroscope.

Biosensors Bioelectron. 12(8), 867–877.

Nahmen von, A., Schenk, M., Sieber, M. and Amrein, M. (1997). The structure

of a model pulmonary surfactant as revealed by scanning force microscopy.

Biophys. J. 72, 463–469.

Poole, K., Khairy, K., Friedrichs, J., Franz, C., Cisneros, D.A. Howard, J. and

Mueller, D. (2005). Molecular-scale topographic cues induce the orientation

and directional movement of ﬁ broblasts on two-dimensional collagen sur-

faces. J. Mol. Biol. 349, 380–386.

Pralle, A., Keller, P., Florin, E.-L., Simons, K. and Horber, J.K.H. (2000) Sphin-

golipod-cholesterol rafts diffuse as small entities in the plasma membrane

of mammalian cells. J. Cell Biol. 148, 997–1008.

Putman, C.A.J., Van der Werf, K.O., Degrooth, B.G., Vanhulst, N.F. and Greve,

J. (1994). Tapping mode atomic force microscopy in liquid. Appl. Phys. Lett.

64(18), 2454–2456.

Sarid, D., Ed. (1991). Scanning Force Microscopy with Application to Electric, Mag-

netic and Atomic Forces (Oxford University Press, New York).

Schabert, F.A. and Engel, A. (1994). Reproducible acquisition of Escherichia coli

porin surface topographs by atomic force microscopy. Biophys. J. 67,

2394–2403.

Schäffer, T.E., Cleveland, J.P., Ohnesorge, F., Walters, D.A. and Hansma, P.K.

(1996). Studies of vibrating atomic force microscope cantilevers in liquid. J.

Appl. Phys. 80(7), 3622–3627.

Schenk, M., Amrein, M., Dietz, P. and Reichelt, R. (1994). Simultaneous STM/

AFM Imaging of Biological Macromolecular Assemblies: Experimental Set-up and

First Results. 13th International Congress on Electron Microscopy (Les Edi-

tions de Physique Les Ulis, Paris).

Schenk, M., Amrein, M. and Reichelt, R. (1996). An electret microphone as a

force sensor for combined scanning probe microscopies. Ultramicroscopy 65,

109–118.

Seelert, H., Poetsch, A., Dencher, N.A., Engel, A., Stahlberg, H. and Muller, D.J.

(2000). Structural biology: proton-powered turbine of a plant motor. Nature

405, 418–419.

Sellers, H., Ulman, A., Schnidman, Y. and Eilers, J.E. (1993). Structure and

binding of alkanethiolates on gold and silver surfaces—implications for

self-assembled monolayers. J. Am. Chem. Soc. 115(21), 9389–9401.

Stemmer, A., Hefti, A., Aebi, U. and Engel, A. (1989). Scanning tunneling and

transmission electron microscopy on identical areas of biological specimens.

Ultramicroscopy 30, 263–280.

Tortonese, M., Barret, R.C. and Quate, C.F. (1993). Atomic resolution with an

atomic force microscope using piezoresistive detection. Appl. Phys. Lett. 62,

834–836.

Chapter 16 Atomic Force Microscopy in the Life Sciences 1069

Travaglini, G., Rohrer, H., Amrein, M. and Gross, H. (1987). Scanning tunneling

microscopy on biological matter. Surf. Sci. 181, 380–390.

Voelker, M.A., Hameroff, S.R., He, J.D., Dereniak, E.L., MeCuskey, R.S.,

Schneiker, C.W., Chvapil, T.A., Bell, T.S. and Weiss, L.B. (1988). STM imaging

of molecular collagen and phospholipid membranes. J. Microsc. 152,

557–573.

Wagner, D., Moy, V.T., Hofman, U.G., Benoit, M., Ludwig, M. and Gaub, H.E.

(1994). AFM—The Art of Touching Molecules (Invited). 13th International Con-

gress on Electron Microscopy (Les Editions de Physique Les Ulis, Paris).

Wagner, P., Hegner, M., Guntherodt, H.J. and Semenza, G. (1995a). Formation

and in-situ modiﬁ cation of monolayers chemisorbed on ultraﬂ at template-

stripped gold surfaces. Langmuir 11(10), 3867–3875.

Wagner, P., Hegner, M., Kernen, P., Zauga, F. and Semenza, G. (1995b). Cova-

lent immobilization of native biomolecules onto Au (111) via N-hydroxysuc-

cinimide ester functionalized self-assembled monolayers for scanning probe

microscopy. Biophys. J. 70, 2052–2066.

Wang, Z., Hartmann, T., Baumeister, W. and Guckenberger, R. (1990). Thick-

ness determination of biological samples with a z-calibrated scanning tun-

neling microscope. Proc. Natl. Acad. Sci. USA 87, 9343–9347.

Weisenhorn, A.L., Maivald, P., Butt, H.-J. and Hansma, P.K. (1992). Measuring

adhesion, attraction, and repulsion between surfaces in liquids with an

atomic-force microscope. Phys. Rev. B 45(19), 11226–11232.

Weisenhorn, A.L., Khorsandi, M., Kasas, S., Gotzos, V. and Butt, H.-J. (1993).

Deformation and height anomaly of soft surfaces studied with an AFM.

Nanotechnology 4, 106–113.

Welland, M.E., Miles, M.J., Lambert, N., Morris, V.J., Loombs, J.H. and Pethia,

J.B. (1989). Structure of the globular protein vicilin revealed by scanning

tunnelling microscopy. Int. J. Biol. Macromol. 11(1), 29–32.

Wildhaber, I., Gross, H., Engel, A. and Baumeister, W. (1985). The effects of

air-drying and freeze-drying of the structure of a regular protein layer.

Ultramicroscopy 16, 411–422.

Wolf, H., Ringsdorf, H., Delamarche, E., Takami, T., Kang, H., Michel, B.,

Gerber, C., Jaschke, M. Butt, H.J. and Bamberg, E. (1995). End-group-

dominated molecular order in self-assembled monolayers. J. Phys. Chem.

99(18), 7102–7107.

Yang, J., Mou, J. and Shao, Z. (1996). The effect of deformation on the lateral

resolution of force microscopy. J. Microsc. 182(2), 106–113.

Zasadzinski, J.A.N., Schneir, J., Gurley, J., Elings, V. and Hansma, P.K. (1988).

Scanning tunneling microscopy of freeze-fracture replicas of biomembranes.

Science 239, 1013–1015.