**1. Introduction**

A biosensor is a device that converts a biological response to a chemical molecule into signals with optical, thermal, or electrical properties, according to the definition provided by the International Union of Pure and Applied Chemistry (IUPAC). The biological response is achieved by specific biochemical reactions accompanied by isolated enzymes, tissues, immune systems, organelles, or cells. From this perspective, it is possible to characterize a biosensor with three main components: (i) a biological recognition system (bioreceptor) that selectively detects the chemical compound and possesses an appropriate binding site, (ii) a transducer that converts biochemical/ physicochemical interactions resulting from specific binding into measurable signals, and (iii) a signal processing system that detects changes in electrical current, mass, temperature, or optics based on their intensity and translates them into information that is interpretable. While biosensors are classified based on the type of bioreceptor, such as DNA, enzyme, glucose, and cholesterol biosensors, a significant classification is also made based on the type of transducer utilized. This type of classification includes electrochemical, acoustic, piezoelectric, thermometric, magnetic biosensors, as well as optical biosensors. In **Figure 1**, the schematic of the fundamental principles of biosensors is given. Biosensors find extensive applications in monitoring the quality of soil–water–food triangle, environmental monitoring, detection of toxins in

**Figure 1.** *The schematic of the fundamental principles of biosensor.*

defense, pharmaceutical industry, prosthetic devices, biotechnology, and biomedical engineering. They play a crucial role in diagnosing and treating diseases, as evident from the growing number of articles in the literature. This section of the book focuses on significant advancements in health and biomedicine achieved through the use of biosensors in recent years. It covers the current potential applications, limitations, and future prospects of biosensors in these fields.
