A biosensor is a device that signals the presence of a target. Aptamers are the « bio » part of biosensors for the detection of any kind of target: small molecules, proteins, cells. Aptamers can be associated with different modalities of signal transduction: fluorescence, colorimetry, electrochemistry, etc. The Novaswitch technology is of particular interest for engineering biosensors for small molecules. Indeed, we developed sensors for detecting fungicides and antibiotics.