Single-molecule experiment
A single-molecule experiment is an experiment that investigates the properties of individual molecules. Single-molecule studies may be contrasted with measurements on an ensemble or bulk collection of molecules, where the individual behavior of molecules cannot be distinguished, and only average characteristics can be measured. Since many measurement techniques in biology, chemistry, and physics are not sensitive enough to observe single molecules, single-molecule fluorescence techniques caused a lot of excitement, since these supplied many new details on the measured processes that were not accessible in the past. Indeed, since the 1990s, many techniques for probing individual molecules have been developed.
Single polymer molecules (0.4 nm thick chains) recorded under aqueous media at different pH using an AFM. Drastic change of polymer chain conformation is observed at a small change of pH.
Atomic force microscopy (AFM) or scanning force microscopy (SFM) is a very-high-resolution type of scanning probe microscopy (SPM), with demonstrated resolution on the order of fractions of a nanometer, more than 1000 times better than the optical diffraction limit.
An atomic force microscope on the left with controlling computer on the right
Fig. 3: Typical configuration of an AFM. (1): Cantilever, (2): Support for cantilever, (3): Piezoelectric element (to oscillate cantilever at its eigen frequency), (4): Tip (Fixed to open end of a cantilever, acts as the probe), (5): Detector of deflection and motion of the cantilever, (6): Sample to be measured by AFM, (7): xyz drive, (moves sample (6) and stage (8) in x, y, and z directions with respect to a tip apex (4)), and (8): Stage.
Fig. 5: Topographic image forming by AFM. (1): Tip apex, (2): Sample surface, (3): Z-orbit of Tip apex, (4): Cantilever.
Electron micrograph of a used AFM cantilever. Image width ~100 micrometers
