Probably not. Coffee and tea are very complex mixtures of hundreds of substances occurring naturally in the plant materials from which they are made and also formed from them by the brewing process in hot water. I don't know of anything specific enough to react or complex with only the caffeine out of all of those substances. My guess is that the analysis of caffeine in these beverages and others requires a complicated and expensive series of laboratory procedures, probably including extraction with organic solvents, chromatography, and mass spectrometry.