Gold nanoparticles to observe the interaction of molecules in liquid

Thanks to a new device that is the size of a human hair, it is now possible to detect molecules in a liquid solution and observe their interactions. This is of major interest for the scientific community, as there is currently no reliable way of examining both the behavior and the chemical structure of molecules in a liquid in real time.

This process could potentially make a whole new class of measurements possible by bringing together infrared detection techniques and gold nanoparticles, which would be a critical step in understanding basic biological functions as well as key aspects of disease progression and treatment. This could also prove useful for studying the behaviour of proteins, medicines and cells in the blood or pollutants in water.

The device is based on infrared absorption spectroscopy. Infrared light can already be used to detect elements: The beam excites the molecules, which start to vibrate in different ways depending on their size, composition and other properties. It's like a guitar string vibrating differently depending on its length. The unique vibration of each type of molecule acts as a signature for that molecule.

This technique works very well in dry environments but not at all well in aqueous environments. A large number of molecules need to be present for them to be detected. It's also more difficult to detect molecules in water, as when the beam goes through the solution, the water molecules vibrate as well and interfere with the target molecule's. To get rid of this problem, the researchers have developed a system capable of isolating the target molecules and eliminating interferences.

The device is made up of miniature fluidic chambers with nano scale gold particles on one side of its cover. Now to catch a particular molecule gold nanoparticle is attached with specific antibodies. Once the target element is introduced in to the small chamber, nanoparticles get attached to the target element. This technique makes it possible to isolate the target molecules from the rest of the liquid. But this is not the only role the nanoparticles play. They are also capable of concentrating light in nanometer-size volumes around their surface as a result of plasmonic resonance.

In the chamber, the beam doesn't need to pass through the whole solution. Instead, it is sent straight to the nanoparticle, which concentrates the light. Caught in the trap, the target molecules are the only ones that are so intensely exposed to the photons. The reaction between the molecules and the infrared photons is extremely strong, which means they can be detected and observed very precisely. This technique enables to observe molecules in-situ as they react with elements in their natural environment. This could prove extremely useful for both medicine and biology.