Background After the PCR workshop, we continue our adventure in do-it-yourself biology by giving you yet another tool to explore your health, environment and food. This time we'll build a spectrometer, an instrument which is able to detect the exact light wavelengths absorbed or emitted by a substance. In the same way a fingerprint identifies each individual human, from the light spectrum it is possible to identify and quantify different substances. Many DIY spectrometers have been developed by citizen science…