Plasmons: A physics concept related to my chemistry investigation

Katherine Rivera 

Physicists say that physics is in everything and everywhere. In our lives we see and do things that are related or can be explained by physics all the time. Working in my new investigation I realized that I found in my project a concept completely related to physics. I decided to research more about it because I was curious about how a physical concept was related to my investigation in chemistry.  It was necessary to research more on this topic because it is fundamental factor to establish my investigation conclusions. 

The existence of surface plasmons was predicted by Rufus Ritchie in 1957. In the following two decades, surface plasmons were extensively studied by many scientists. Superficial plasmons are contained by all metallic surfaces. An explanation of plasmos can be that there are waves of “superficial light”, more complicated than normal light waves because they involve the free electrons on the metal surface.  One of the most promising development areas of Superficial Plasmon is as molecular sensors. The objective is to detect the presence of molecules and their properties. To do so, Raman spectroscopy is used to do an analysis. We can say that each Raman Spectra is like the molecule’s fingerprint. When the light, with same wavelength of the plasmon, hits on the metal particle it produces a resonant effect associated to an increase on the intensity of the electromagnetic field of the metallic particle. In normal conditions, detecting molecules by Raman requires the presence of a trillion of molecules.  Thirty years before, it was discovered, that when the molecules are absorbed on the metal surface (silver or gold), the Raman signal increases by a magnitude of 10 to 15. The reason of this increment is the excitation produced by incident light of the superficial plasmons. This excitation makes the electric field of the molecule much larger.  I use the surface enhancement Raman Scattering (SERS) technique. It is a surface-sensitive technique that enhances Raman scattering by molecules adsorbed on rough metal surfaces. The increase in intensity of the Raman signal for adsorbates on particular surfaces occurs because of an enhancement in the electric field provided by the surface. When the incident light in the experiment strikes the surface, localized surface plasmons are excited.  Basically Plasmons give an induced electric field produced by an external electric field, in this case the laser of the Raman. The purpose is to create a sensor that detects pathogens on environmental matrixes. Incrementing the signal with SERS will be very helpful. Plasmons are very helpful for me in my investigation because I depend on them to obtain a good Raman Spectra.  

It is very interesting that in everything you do you can find concepts related to physics.  All students should be autodidact and research everything about nature that they find interesting. By doing this we will have a broader knowledge of our environment, a bigger picture. It is important to not only stay with what we learn in class. We should never be satisfied of what we know.