Aptamers can be raised against small molecules. This includes contaminants, pesticides, drug residues, allergens, endocrine disrupting components,… Aptamers can be selected and used in non physiological conditions. They can discriminate between closely related molecules differing by only a few chemical groups. These characteristics provide aptamers with major advantages over antibodies. In addition aptamers are highly versatile molecules that can be associated to many different signal transduction modalities (fluorescence, colorimetry, electrochemistry, surface plasmon resonance) for engineering biosensors.