Scotch on Whisky
10 August 2019 - Biosensing
Can you taste the difference between an 12-year old Glenfiddich and an 15-year old Glenfiddich? According to a group of Scottish researchers you can not and they have therefore devised a laboratory method that can. (Macias et al. DOI) (TheGuardian report).
The newly developed biosensor is based on surface plasmon resonance and a microarray. If you want to some freshening up on SPR and the Wikipedia page to tltr, this youtube video by David Coulter really brings home the message: at a certain angle of incident laser light a nanolayer of gold stops transmitting light or reflecting it (like a black hole) and instead all energy is transferred to a layer of resonating and oscillating electrons on top of the gold surface. As this layer is extremely sensitive to the particular local chemical environment it can be used as a biosensor.
The microarray is described as an optical tongue. A slice of borosilicate glass was covered in squares of 100 by 100 nm by 50 nm of two metals gold an aluminium (fabricated by electron-beam lithography on PMMA). The metal surfaces where then chemically modified with decanethiol associating with gold and hexamethyldisilazane associating with aluminium. In two other regions of the tongue the chemical modification was different or absent getting a total variable count of 6.
The microarray was then exposed to the whiskies and the results were run through principal component analysis (again a very useful youtube video here explaining PCA) and is it possible to tell a 12 year old from a 15 year old? The answer is yes. Of course this was not the purpose of the research (just kidding here), a practical implementation is counterfeit detection In a related statistical tool called linear discriminant analysis it was also possible for the biosensor to identify an unknown whisky sample.