CHAPTER 4 B IOLOGICAL AND B IOMIMETIC S YSTEMS IN C HEMICAL S ENSORS R. Jelinek S. Kolusheva 1. INTRODUCTION Sensors are generally defined as multifunctional assemblies composed of matrix-bound chemically or biologically active substances that can facilitate specific recognition of the species of interest (analytes), and are further directly coupled to a physicochemical transducer that supplies an output signal. Biosensors are specifically defined as assemblies and devices designed to detect and report on biological events and processes. Figure 4.1 depicts schematically a biosensor construct, in which a biological interaction trig- gers a signal detected by an external recording and analysis device. The functionality and performance of sensor devices are determined in large part by the materials comprising the sensors, their molecular structures and organization, and the chemical and physical properties of the molecular constituents. The aim of this chapter is to demonstrate the power of biology in providing platforms and concepts for the design and construction of sensors. The chapter is thematically divided into sections that discuss several classes of biologically inspired sensors, although overlap among the different topics naturally exists. The first sections focus on sensors composed of polymers (primarily conjugated polymers) and biological molecules. We summarize both the more traditional applications based on conductive polymers as well as new developments in which the sensor transduction mechanisms rely on conjugated polymers that exhibit interesting chromatic properties. The use of membranes as vehicles and porous matrixes for chemical and biological sensors 201