## Thursday, 16 June 2016

### Detecting 70 molecules in a billion by converting a blu-ray disc into a chemical sensor

At the Photon Factory (the lab I used to work at) Dr Michel Neuwoudt our expert Raman spectroscopist had been hard at work detecting contaminants in milk using a technique called Raman spectroscopy which she has recently published (doi:10.3168/jds.2015-10342). Prof. David Williams, Dr Cather Simpson and Michel started this project after the melamine scandal in New Zealand where melamine was put into baby milk formula to make it appear as if the protein content of the milk was higher than it was. This fooled people because the test for protein naively digests everything in the product and measures the nitrogen content of the mixture. Melamine has a huge number of nitrogen molecules so it appeared as if the milk had more protein than it did. I had been playing around with using Blu-ray discs colour sensors. We thought about whether the nanostructures on the Blu-ray disc could be able to enhance the weak singles you measure using Raman spectroscopy and so along with other in the lab Reece, Nina, Andy (Xindi) and Jenny Malström we started the project.
Molecule of melamine showing large number of nitrogens Link

The paper we recently published first as a conference article and then as a journal article in Analytical and Bioanalytical Chemistry converts a Blu-ray disc into a sensor that can detect accurately and reproducibly down to 70 parts per billion of melamine.

 Front cover of journal showing the gold nanoparticles on top of the Blu-ray disc. You can also see the pattern of the nanostructure of the Blu-ray grating the gold was deposited on.

The technique we used is called Raman spectroscopy which measures the vibration of molecules using a laser (see this video for more details). This effect is very weak and so cannot be used for low concentrations of molecules. To enhance the signal and amplify it we use a surface which has small antennas that are tuned to the light we are using. The electrons on the surface of these metal nanoparticles start to oscillate with the electric field of light and so you get regions on the metal where the electric field is much higher.

 Plasmon resonance as the electrons move in the electric field of light which is an electromagnetic wave Link

## Saturday, 16 April 2016

### Periodic Table of Popularity

What are the most popular elements of the periodic table? Elements come into and out of fashion, so I thought it would be interesting to look at the 2016 rankings of elements. To do this, I searched for each element in a Google Scholar search where the element had to be in the title of the paper. I took this to mean that the article was largely about the element and this removes issues around whether all of the text of an article is searchable by Google. The title is usually the first thing Google indexes.

Here is the data presented in various different graphs.

## Elemental podium

Here is a sort of podium where the height relates to the number of search results for each element in a title. You can see that carbon is at the top of the elemental podium.

However, the 3D bar graph distorts the data beyond recognition. Let's try some other representations.

## Rankings

Ranking the elements with a bar plot shows what the most popular elements are and makes it much easier to compare. Carbon is the outright winner with 789,000 search results. Carbon is very reactive and has lots of interesting chemistry. It is the basis of all organic life on earth, so it is unsurprising that it is the most popular for researchers.

The next few elements are atoms nearby carbon that bond with it, for example Hydrogen, Oxygen, Nitrogen. Transition metals come in very popular with Iron, Copper, Zinc, Gold, Silver and Lead. Silicon is what the semiconductor industry is based on so lots of research on Silicon.

There are two ways to view these rankings. Either feel sorry about the lesser studied elements and do some research on them or publish something about carbon and you will probably get the most people interested. I am currently taking the first approach.

## Hot spots

A heat map gives a better view of where hot spots in the periodic table are concentrated.
Below is a periodic table if you have forgotten the different regions of the table. avAround carbon there is a lot of heat. The top of the alkali metals are also quite hot. The transition metals first row are quite hot particularly Iron which is the most stable element. There is also a hot spot around group 11 with Copper (Cu), Gold (Au) and Silver (Ag). Some of the amazing properties that make these elements so interesting are their relativistic effects.

## Abundance

Something else to consider is whether the ranking has anything to do with the amount of these materials on earth as the trends for popularity are for the more abundant elements at the top of the periodic table but also it is important to see if we are spending too much time on elements which we really don't have enough of.
To scale these values I divided the popularity by the amount of the substance in the earth's crust. Large numbers indicate a lot of attention for substances we don't have a lot of.

Something to think about for finite resources is how to move the attention to elements which are more abundant. So, for example, the element scoring highest in the scaled popularity is Ruthenium. We have tiny amounts of this in the earths crust yet we have a lot of research on this element. This is mainly because Ruthenium is used in dye sensitised solar cells, data storage elements for electronics and as a catalyst. Therefore, ways to replace Ruthenium in dye sensitised solar cells is of interest.

I will update this each year and see if there is any changes in the ranking.