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Next to chromatography, spectroscopy or microscopy biosensors complete the available collection of tools to chemically analyse a complex sample. By definition, biosensors are compact analytical devices incorporating a biological or biologically derived sensing element intimately associated with a physicochemical transducer. The latter turns molecular recognition or biological response into a measurable, mostly electronic signal. Typical applications comprise pathogen detection, environmental monitoring, drug or toxicity screening as well as the analysis of clinical samples. This article gives a short overview about (1) general concepts of biosensor design, (2) biological components that are used for sensing, (3) the most important technical transducers and (4) some applications of molecular and cell‐based biosensors. Key Concepts A biosensor is a device that consists of (1) a biological element, which is used to specifically capture, convert or sense a target analyte and (2) a physicochemical transducer to convert the interaction with the analyte into a detectable signal. The group of biological sensing elements comprises biomolecules like antibodies, enzymes, nucleic acids or living bacteria, archaeans or eukaryotic cells. Even cell aggregates, tissues or organs may serve for biorecognition and sensing. Molecular biosensors detect target analytes either by capturing (antibodies, DNA, aptamers) or converting them (enzymes). Cell‐based biosensors indicate the presence of the analyte by expression of reporter genes or an integrated, often generic (w)holistic response of cell physiology. Electrochemical, optical, piezoelectric or calorimetric transducers are applied to quantify the interaction between analyte and sensing element.

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