Several high resolution imaging techniques have been used over vastly diverse disciplines in science and engineering—from microscale with our light microscope to nanoscale with electron- or X-ray beam-mediated imaging techniques. These have been considered as routine laboratory techniques in order to visualize the micro- to nano-scale features of a certain material. How about seeing an actual bond?
AFM, or atomic force microscopy, have been recently been making news in the scientific community as it was used by two different groups to image actual bonds. This microscopic technique is based on a scanning probe, a cantilever with a tip. The tip is lowered closer to the surface of the sample until the forces between the tip to the surface are enough to cause a deflection in the cantilever, which is then correlated to a ‘signal’ that is processed to construct the image of the surface. It runs in either contact or non-contact mode, depending on the characteristics of the sample to be analyzed.
Just a month ago, researchers from China’s National Center for Nanoscience and Technology have published AFM images showing the first image of hydrogen bonds. The image was for 8-hydroxyquinoline, deposited on a copper surface. This is definitely groundbreaking, as this is showing that these bonds with weaker interactions than covalent bonds can also be visualized using this technique. This proves that AFM can be used as a tool to characterize submolecular features.
Earlier this year, another group at the University of California Berkeley have also used AFM in order to monitor a reaction. The group used oligo-(phenylene-1,2-ethynylene), immobilized the molecule on a silver substrate, and monitored the products upon heating. As a routine, organic chemists typically monitor a reaction just by thin layer chromatography (TLC), looking at how the spots develop in the plates over time. Imagine if this technique becomes a routine tool for synthetic chemists, just like NMR or MS— without a doubt, it would definitely revolutionize the way we confirm products by seeing actual bond forming and breaking.
The field seems to be more and more exciting, and maybe we just have to wait for another groundbreaking AFM news before the year ends. Given how direct and informative the images are that we can take from this technique, hopefully, researchers will be able to find a way to make it as a routine synthetic characterization tool someday. This will not only help synthetic chemists, but also materials scientists and other researchers that delve on nanotechnology.
Here’s the link to the papers, for reference:
Herdeline Ann Ardoña is a second year graduate student in the Department of Chemistry under Professor J.D. Tovar, co-advised by Professor Hai-Quan Mao.