Force spectroscopy is a technique used to study interactions at the molecular level. Here are the main techniques used in force spectroscopy:

1. Atomic Force Microscopy (AFM): AFM involves a sharp probe that scans the surface of the sample. It measures the force between the probe and the sample, allowing for high-resolution imaging and force measurements. Detailed interaction forces can be quantified by measuring the deflection of the cantilever, which is correlated with the distance between the cantilever and the sample.

   

2. Optical Tweezers: This method uses a highly focused laser beam to apply forces to, and manipulate, small particles and biological molecules. It allows the measurement of forces in the piconewton range and can be used to study molecular motors, nucleic acids, and protein interactions.

   

3. Magnetic Tweezers: In this technique, magnetic fields are used to manipulate magnetic nanoparticles, which can be attached to molecules of interest. This is particularly useful for studying the mechanics of DNA and protein-DNA interactions under force.

4. Bio-Membrane Force Probe (BFP): BFP uses a calibrated red blood cell as a force probe to study the interaction forces between molecules with high sensitivity. It allows the measurement of a wide range of forces while observing the kinetics of molecular interactions.

5. Surface Force Apparatus (SFA): SFA measures the interaction forces between surfaces (e.g., thin films) as they are brought into contact and separated. It is used primarily in the study of lubricants, adhesion, and surface interactions at the molecular level.

6. Single Molecule Force Spectroscopy (SMFS): This involves pulling on individual molecules with an AFM or optical tweezers to study their mechanical properties and dissociation forces.

Each technique has its own advantages and limitations for specific applications. They are chosen based on the required force sensitivity, resolution, and the biological or material system under study.

For more detailed information, refer to specific sources such as Nature Reviews Methods Primers or Science Direct.