Information on mechanical properties is important in many applications. AM-FM Viscoelastic Mapping Mode lets you quickly and gently image viscoelastic properties including storage modulus and loss tangent with nanoscale spatial resolution. Its very wide operating range, from less than 1 MPa to hundreds of GPa, makes it a highly versatile technique. AM-FM Mode is available on all MFP-3D™ and Cypher™ family AFMs and is one of many options in Asylum’s NanomechPro™ Toolkit for nanomechanical measurements.

Capabilities and Benefits

Asylum’s exclusive AM-FM Viscoelastic Mapping Mode1 is a flexible, convenient tool for nanomechanical characterization. With a range of applicability that spans a remarkable six orders of magnitude in storage modulus (from less than 1 MPa to hundreds of GPa), it is a general-purpose technique for anything from biomaterials and polymers to metals and ceramics. AM-FM Mode provides elastic information including storage modulus, Young’s modulus, and contact stiffness and viscoelastic information including viscoelastic loss tangent and loss modulus. AM-FM Mode gets results by operating at two cantilever resonances simultaneously. As the name indicates, the first resonance is used for tapping mode imaging, also known as amplitude modulation (AM), while a higher resonance mode is operated in frequency modulation (FM). At resonance, the cantilever frequency and phase respond sensitively to changes in sample properties. Small frequency and phase shifts can be measured with very high precision and accuracy, reducing uncertainty and increasing sensitivity. You can use raw output signals to quickly visualize relative contrast and identify sample components; or you can use the observed amplitude, phase, and frequency data to make quantitative estimates of mechanical properties based on built-in or your own models.

Because AM-FM Mode works like tapping mode in the repulsive regime, it is familiar and straightforward to use. It also has the other advantages of tapping mode including fast scanning, high spatial resolution, and gentle forces. On high speed, low-noise systems such as Asylum’s Cypher S and ES AFMs, modulus mapping in AM-FM Mode can routinely operate at line scan rates as fast as 20 Hz (equivalent tip velocity 300 μm/s) and forces as low as 50 pN.2 Low forces mean less sample deformation, typically only a few nanometers, which both minimizes damage and maximizes spatial resolution. Because the FM amplitude is just a tiny fraction of the AM amplitude and is at a different frequency, topographic imaging operates the same as in standard tapping mode. This makes AM-FM Mode very stable and reliable to operate.

Atomic force microscopy (AFM) is able to reveal many properties about a material. Most commonly, it is used to obtain topographical information, but it can also probe mechanical stiffness, electrical conductance, resistivity, and magnetism. Researchers have used it to study interactions between enzymes and their substrates1, structural changes in injured or diseased tissue2, macromolecular interactions between lipids3 and analysis of nucleic acid organization and structure4, to name a few applications. AFM performs analyses on a micro and nanoscale, allowing it to quantify phenomena as miniscule as van der Waals forces, electrostatic interactions, and molecular bonds5. AFM is also able to produce high-resolution, detailed images of sample surfaces, displaying micro and nanoscale properties of materials as flat as cleaved mica or as non-uniform as a cell. An interesting aspect to AFM is its ability to measure multiple micro- and nanoscale properties in a single test on samples that are unfixed, unstained, and alive. Of particular use in many fields is the imultaneous measurement of topographical features and mechanical properties.

Traditional light microscopy is able to reveal a wealth of information about a sample, especially a biological one. Light microscopy can tell investigators the shape of a cell, localization of subcellular structures within the cell, and even organization of cellular infrastructure, among many other parameters. But a limitation with these optical data is that we are unable to measure, in a directly quantifiable way, the mechanical properties of that cell; these properties give investigators important information about the cell’s cytoskeletal organization and phenotype. The cell’s stiffness, quantified by measuring the elastic modulus of the cell, is different at various points across its surface; cells tend to be softer over the cytoplasm and stiffer over cytoskeletal structures. Generally speaking, AFM is able to assess both mechanical and topographical properties of any material, including cells, simultaneously in a single assay.