Biosensors are considered to be devices of interest for environmental monitoring. The peculiar characteristics of biosensors allow them to complement current field screening and monitoring methods, especially when continuous, real-time, in situ monitoring is required. However, biosensors still face problems of stability, detection sensitivity, and reliability of the biomolecular recognition element. In recent years, new binding molecules have been introduced in many areas of science. In this chapter, the different natural or synthetic molecules employed in the development of biosensors for environmental monitoring are reviewed, with special emphasis on innovative (bio)receptors claimed to overcome stability concerns of traditional sensing elements. The key role of nucleic acids in the identification of new smart bioreceptors is described.