http://experimentationlab.berkeley.edu/sites/default/files/AFMImages/butt_AFM.pdf

Force measurements with the atomic force microscope: Technique, interpretation and applications

Solvation force profiles for three room-temperature ionic liquids (ILs), ethylammonium nitrate (EAN), propylammonium nitrate (PAN), and 1-ethyl-3-methylimidazolium acetate (C2mimAc) confined between Si3N4 tips and mica, silica, and graphite have been measured using an atomic force microscope. The measurements reveal oscillatory behavior in all cases, with the size of the oscillations corresponding to the physical dimension of the ion pair. The surface charge and roughness and the orientation of cations at the interface are critical determinants of solvation layer formation in ILs. The greatest number of solvation layers is observed for EAN on highly charged, atomically smooth mica. Fewer and more compressible layers are observed for PAN due to its increased molecular flexibility. The lower surface charge and increased roughness of silica produces fewer solvation layers for both EAN and PAN compared to mica. For the EAN− and PAN−graphite systems, any attractive interaction with the substrate is due to the ...

Structure in Confined Room-Temperature Ionic Liquids

/pdf/proteins-platelets-and-blood-coagulation-at-biomaterial-46rpezep52.pdf

Proteins, platelets, and blood coagulation at biomaterial interfaces.

Chemical force microscopy (CFM) in water was used to map the surface hydrophobicity of UV/ozone-treated poly(dimethylsiloxane) (PDMS; Sylgard 184) as a function of the storage/recovery time In addition to CFM pull-off force mapping, we applied indentation mapping to probe the changes in the normalized modulus These experiments were complemented by results on surface properties assessed on the micrometer scale by X-ray photoelectron spectroscopy and water contact-angle measurements Exposure times of <_30 min resulted in laterally homogeneously oxidized surfaces, which are characterized by an increased modulus and a high segmental mobility of PDMS As detected on a sub-50-nm level, the subsequent "hydrophobic recovery" was characterized by a gradual increase in the pull-off forces and a decrease in the normalized modulus, approaching the values of unexposed PDMS after 8-50 days Lateral imaging on briefly exposed PDMS showed the appearance of liquid PDMS in the form of droplets with an increasing recovery time Longer exposure times (60 min) led to the formation of a hydrophilic silica-like surface layer Under these conditions, a gradual surface reconstruction within the silica-like layer occurred with time after exposure, where a hydrophilic SiOx-enriched phase formed <100-nm-sized domains, surrounded by a more hydrophobic matrix with lower normalized modulus These results provide new insights into the lateral homogeneity of oxidized PDMS with a resolution in the sub-50-nm range

Nanoscale hydrophobic recovery: A chemical force microscopy study of UV/ozone-treated cross-linked poly(dimethylsiloxane).

Single molecule mechanochemistry of macromolecules

It has been found that a common shipping and packaging material for commercial AFM cantilever tips, poly(dimethylsiloxane) (PDMS), causes a thin layer of silicone oil contamination on AFM cantilever tips. Due to the similarity of elemental compositions between silicone oils and AFM cantilevers (both contain silicon and oxygen), it is difficult to detect such contaminants with the widely used surface characterization technique, X-ray photoelectron spectroscopy (XPS), since XPS provides mainly elemental and short-range chemical information. However, by using static time-of-flight secondary-ion mass spectrometry (TOF-SIMS), a technique that is extremely surface-sensitive, silicone oils on AFM cantilevers can easily be identified by their molecular fragments. A simple dip cleaning procedure using a mixture of concentrated sulfuric acid and hydrogen peroxide (piranha solution) was found to be an easy and effective way to remove organic contamination, including silicone oils, from AFM cantilever tips. It has al...

Organic and Inorganic Contamination on Commercial AFM Cantilevers

We report for the first time an atomic force microscopy (AFM) investigation of the dependence of unbinding force on temperature at controlled loading rate. AFM force measurements of biotin−avidin interactions were acquired at various temperatures ranging from 13 to 37 °C using force loading rates that are slow enough to ignore dissipative friction and to assume thermal equilibrium. With our established Poisson statistical analysis method, the unbinding force at a fixed loading rate between an individual biotin−avidin pair was extracted and was found to decrease by ∼5-fold with increasing temperature over this range. On the basis of a thermodynamic model similar to that of Bell, but developed here with additional insights, the bond stiffness, effective unbinding length, and the critical unbinding energy per biotin−avidin complex were estimated. This work takes quantitative AFM studies to the next level by allowing energies to be determined from force measurements.

/pdf/temperature-dependence-of-the-biotin-avidin-bond-rupture-2bfz89ra4n.pdf

Temperature Dependence of the Biotin−Avidin Bond-Rupture Force Studied by Atomic Force Microscopy

It is known that bond strength is a dynamic property that is dependent upon the force loading rate applied during the rupturing of a bond. For biotin−avidin and biotin−streptavidin systems, dynamic force spectra, which are plots of bond strength vs loge(loading rate), have been acquired in a recent biomembrane force probe (BFP) study1 at force loading rates in the range 0.05−60 000 pN/s. In the present study, the dynamic force spectrum of the biotin−streptavidin bond strength in solution was extended from loading rates of ∼104 to ∼107 pN/s with the atomic force microscope (AFM). A Poisson statistical analysis method was applied to extract the magnitude of individual bond-rupture forces and nonspecific interactions from the AFM force−distance curve measurements. The bond strengths were found to scale linearly with the logarithm of the loading rate. The nonspecific interactions also exhibited a linear dependence on the logarithm of loading rate, although not increasing as rapidly as the specific interaction...

Loading-rate dependence of individual ligand-receptor bond-rupture forces studied by atomic force microscopy

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Organic and Inorganic Contamination on Commercial AFM Cantilevers

Temperature Dependence of the Biotin−Avidin Bond-Rupture Force Studied by Atomic Force Microscopy

Loading-rate dependence of individual ligand-receptor bond-rupture forces studied by atomic force microscopy