“May the Force Be with You!” Force–Volume Mapping with Atomic Force Microscopy

Abstract

Information of the chemical, mechanical, and electrical properties of materials can be obtained using force volume mapping (FVM), a measurement mode of scanning probe microscopy (SPM). Protocols have been developed with FVM for a broad range of materials, including polymers, organic films, inorganic materials, and biological samples. Multiple force measurements are acquired with the FVM mode within a defined 3D volume of the sample to map interactions (i.e., chemical, electrical, or physical) between the probe and the sample. Forces of adhesion, elasticity, stiffness, deformation, chemical binding interactions, viscoelasticity, and electrical properties have all been mapped at the nanoscale with FVM. Subsequently, force maps can be correlated with features of topographic images for identifying certain chemical groups presented at a sample interface. The SPM tip can be coated to investigate-specific reactions; for example, biological interactions can be probed when the tip is coated with biomolecules such as for recognition of ligand−receptor pairs or antigen−antibody interactions. This review highlights the versatility and diverse measurement protocols that have emerged for studies applying FVM for the analysis of material properties at the nanoscale.

Tripeptide Self-Assembled Monolayers as Biocompatible Surfaces for Cytochrome c Electrochemistry

“…With higher concentrations of diluent, the diluent changes the microenvironment under the protein and the chemistry of the SAM. 49 The cyt c rate constants measured closely follow the predicted tunneling distances dictated by the diluent as reported by Yue et al 22 The shorter chain diluent alkanethiol only supports a portion of the longer peptide chain, allowing the peptide to fold over to the plane of the closest approach to the electrode surface and decrease the effective tunneling distance. Pendant hemin molecules display similar effects on k 0 with the added diluent containing 2, 6, and 11 carbons, showing the rates decreasing from 300 to 90 s −l , respectively.…”

Nanomechanical Mapping of Hard Tissues by Atomic Force Microscopy: An Application to Cortical Bone

“…Force mapping via AFM is an elegant and comprehensive method to characterize quantitatively the spatial distribution of mechanical properties of biological tissues at micro/nano scale. Given a sample topography, typically elasticity maps (stiffness or Young’s modulus) can be constructed collecting the stiffness values obtained by AFM nanoindentation [ 1 ]. This technique is ideal to investigate biological samples from neurons [ 2 ], cells [ 3 , 4 , 5 , 6 ], microorganisms [ 7 , 8 ], and soft bone tissues down to single collagen fibrils [ 9 , 10 , 11 , 12 ], where its extreme force sensitivity enables the detection of moduli ranging from a few of Pa to several MPa.…”

Automated analysis of soft material microindentation

“…Typical mechanical property mapping with an AFM is limited by the scan range of commercial instruments to regions smaller than 80 × 80 μm. 22 Furthermore, the vertical movement range may be < 10 μm, leading to data acquisition issues for uneven biological samples. 82 With the larger experimental setup and probe applied here, samples with lateral dimensions of multiple centimetres, and height fluctuations of hundreds of micrometres can be conveniently mapped.…”

“…These measurements may provide high resolutions nanoscale mapping of mechanical properties over localised areas (typically 100 Â 100 mm or smaller). [21][22][23] However, indentation measurements conducted with small probes and sub-micrometre indentation depths may be significantly influenced by highly localised or surface features. 24 Furthermore, the small probes employed are more susceptible to significant changes in contact area due to adhesive fouling when measuring soft samples.…”