James Baker 's University of Michigan spinoff NanoBio created a white, creamy liquid substance called NanoProtect.

FORBES: Nanotech On The Front Lines

They are working with the Farmwatch scheme in the Test Valley to introduce a liquid substance which can be added to fuel to "chemically tag" it.

BBC: Heating oil 'tagged' to tackle rural theft in Hampshire

However, by making something out of ions that are bulky and asymmetrical (they have names such as 1-butyl-3-methylimidazolium and hexafluorophosphate, which are as complicated as the ions they represent), the attractive electrical forces can be kept so far apart that the resulting substance is a liquid at room temperature.

ECONOMIST: Ionic solvent