NanoPhotonics Centre, Department of Physics
Q&A Session 13:15 - 13:45 on Monday 21st September
Come and watch our video about how we use light and tiny pieces of gold to see objects one hundred thousand times smaller than a human hair!
Who are we?
Materials behave differently when they're cut up small. Take sand for example, which is made of tiny pieces of stone. Sand becomes sticky when wet which is why it's possible to build sandcastles, but water can’t stick larger pieces of rock together. Even more extreme changes happen to materials when they are a thousand times smaller than human hair at the ‘nanoscale’.
In the NanoPhotonics Centre, we look at different ways to manipulate light and matter at the nanoscale using a relatively simple technique called ‘self-assembly’ to create complex and tiny structures. We can use this for lots of different applications like ultra-low-energy electronic switches and colourful displays, but today we are going to talk about sensing molecules at very low concentration.
What do we do?
Sensing molecules
In the video you will hear that we need special techniques to see very small things - it just isn't possible to use a regular microscope to see molecules. What we do instead is called spectroscopy.
Visible light is made up of all the colours that we can see. Those colours each correspond to different energy. Blue/violet light has the highest energy, then comes green, yellow and red.
When you shine a laser at molecules, it makes them shake and vibrate. This costs energy which comes from the laser. If you look very carefully at the light after it has interacted with molecules using something called a spectrometer, then you will find new colours appear which tell you which vibration happened.
What about plasmonics?
We need to use spectroscopy to "see" molecules that are too small for a microscope. In the video, you will hear that it can be hard to detect very small amounts of molecules.
The signal (this means how strong the peaks are) depends on the light’s brightness (this means the strength of the laser you use) and the concentration (this means the number of molecules).
So when there aren't enough molecules, we need a really strong laser? Yes, but while that can help, it isn't the easiest solution and can burn the molecules. If we want to detect molecules in your body then we need the laser to be in a healthcare setting with you. It can get both dangerous and expensive to have really strong lasers. What we do instead is use a science trick called ‘plasmonics’ to confine the laser light exactly where we need it.
When you shine a laser on a tiny gold sphere (a nanoparticle), it causes the metal electrons to oscillate all together. This wave of electrons interacts with the light waves and effectively concentrates light at the surface of the nanoparticle.
So all we have to do is put the molecules onto the surface of the nanoparticle and we get much stronger signals!
In conclusion, we use spectroscopy as way to see things too small for a microscope. When there aren’t many molecules around, we use gold nanoparticles to create plasmons. Those plasmons enhance our signals and allow us to see at very low concentrations.
Have a look at our group website or get in touch for more information!
Further Information:
https://www.np.phy.cam.ac.uk/about-us/about
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