What does this do? Atomic force microscropy

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.

H-BOND

http://goo.gl/g66C1A

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.

REACTION

http://www.sciencemag.org/content/340/6139/1434

 

 

 

 

 

 

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:

http://www.sciencemag.org/content/early/2013/09/25/science.1242603.abstract

http://www.sciencemag.org/content/340/6139/1434

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.

What Does This Do? HPLC

Recently, I have been using a machine called a HPLC quite a lot in my research. This has lead to quite a lot of questions like, “What is an HPLC? What does it actually do?” mostly asked by my grandma.

So, HPLC stands for High-Performance Liquid Chromatography, which is a mouthful. One will also hear it referred to by an older term, High Pressure Liquid Chromatography. You can see why most scientists are lazy and just refer to it as HPLC.

Erin Gallagher at the HPLC.

Erin Gallagher at the HPLC.

What a HPLC actually does is force a liquid mixture, which you want separated, through a tube of packed beads (called a column) at high pressure. In this liquid mixture there is some component that you want to separate from the rest of the mixture, whether it is a protein you need purified after synthesis or a drug from a urine sample. This is how doctors monitor that you are getting the right dosage of a drug and one of the ways that cocaine and other illicit drugs are tested for1.

As the sample passes through the column certain components in the sample will be attracted to the packed beads. Those components will take longer to get through the column because they keep getting stuck to the beads as they go through the column. This means that some components in the mixture will fly through the column, while others will take much longer to get through the column because those components keep sticking to the beads and then unsticking. This process is how the HPLC separates the mixture into the different parts. The sample can be separated using size, polarity, or several other chemical properties.

A detector is attached at the end of the column to identify what is coming off the column when. The detector can use many different types of detection, from ultra violet/visible light to mass spectroscopy, to figure out what component of the mixture is coming off of the column at what time.

Overall, the HPLC helps scientist separate and identify, and sometimes even quantify, parts of a liquid mixture.

1) Heit et al. Urine drug testing in pain medicine. Journal of Pain and Symptom Management March 2004. Pages 260–267

http://www.sciencedirect.com/science/article/pii/S088539240300530X

For a more thorough walk through and some awesome diagrams of HPLC see:

Harris, Daniel C.. Exploring Chemical Analysis. 4th ed. New York: W. H. Freeman and Company, 2009. Print.

 

Erin Gallagher is a second year PhD student in Peter Searson’s Materials Science and Engineering lab.