French researchers have shown that Raman spectroscopy is ideal for studying microdroplets with potential as high-throughput reactors.

Galder Cristobal from the Rhodia-CNRS laboratory in Pessac and colleagues found that the well-established technique can be used to examine reactions performed in microdroplets. Such droplets, with volumes less than one billionth of a litre, can be suspended in an inert carrier fluid and channelled through microfluidic devices. Possible applications of this technology include high-throughput reaction systems and methods for safely analysing very exothermic reactions, said Cristobal.

In order to analyse the products of reactions in microdroplets, fluorescence detection is often used. Although this is a very sensitive technique, Cristobal said it cannot always distinguish between different molecules. The team overcame this weakness by using confocal Raman spectroscopy. This technique involves laser irradiation of a molecule, and provides information on the types of chemical bonds present. Reactants and products often contain different types of bonds, and so Raman spectroscopy provides a way of monitoring the progress of a reaction.

One drawback of Raman spectroscopy is that a lot of molecules are required to give a good spectrum, but Cristobal's team got around this by modifying the microfluidic devices to allow longer acquisition times. Studies on a simple model system established the feasibility of using Raman spectroscopy, which Cristobal said is 'ideally suited to probe fluid mixing in such droplets'.

Cristobal said that their work 'paves the way for future studies involving systematic investigations of complex chemical reactions by Raman spectroscopy'. Todd Thorsen, a microfluidics expert from the Massachusetts Institute of Technology, US, agreed, saying that this method 'holds great potential for high-throughput screening of both organic and inorganic target compounds'.

David Barden