[1][2] These methods can be used to measure the mechanical properties of single polymer molecules or proteins, or individual chemical bonds.
[8] As a single-molecule technique, as opposed to typical ensemble spectroscopies, it allows a researcher to determine properties of the particular molecule under study.
In all of these techniques, a biomolecule, such as protein or DNA, or some other biopolymer has one end bound to a surface or micrometre-sized bead and the other to a force sensor.
Molecules adsorbed on a surface are picked up by a microscopic tip (nanometres wide) that is located on the end of an elastic cantilever.
In a more sophisticated version of this experiment (Chemical Force Microscopy) the tips are covalently functionalized with the molecules of interest.
This kind of set-up can measure forces as low as 10 pN (10−11 N), the fundamental resolution limit is given by the cantilever's thermal noise.
In biophysics, single-molecule force spectroscopy can be used to study the energy landscape underlying the interaction between two bio-molecules, like proteins.
Here, one binding partner can be attached to a cantilever tip via a flexible linker molecule (PEG chain), while the other one is immobilized on a substrate surface.
So far, a number of theoretical models exist describing the relationship between loading rate and rupture force, based upon different assumptions and predicting distinct curve shapes.
Biomolecules, such as DNA, RNA or proteins, can be individually tethered between the microspheres and a surface and then probed by the acoustic forces exerted by the piezo sensor.
[15] Viral proteins also can be studied by AFS, for instance this technique was used to explore DNA compaction along with other single-molecule approaches.
A strongly focused laser beam has the ability to catch and hold particles (of dielectric material) in a size range from nanometers to micrometers.
Optical tweezers allow the measurement of piconewton forces and nanometer displacements which is an ideal range for many biological experiments.
AFS devices allow the statistical analysis of the mechanical properties of biological systems by applying picoNewton forces to hundreds of individual particles in parallel, with sub-millisecond response time.
Moreover, force spectroscopy can be used to investigate the enzymatic activity of proteins involved in DNA replication, transcription, organization and repair.
The tip is pushed on the surface, allowing for contact between the two molecules, and then retracted until the newly formed bond breaks up.
[22] Recently this technique has been used in cell biology to measure the aggregative stochastic forces created by motor proteins that influence the motion of particles within the cytoplasm.