Introduction and Historic Overview -- Biochemical Components Used in Biosensor Assemblies: Enzymes -- Antibodies -- Protein / Peptide Receptors -- Nucleic Acids -- Whole Cells as Biosensing Elements -- Immobilization of Biochemical Elements of Biosensors -- Biosensor Signal Transducers: Electrochemical Transducers -- Optical Transducers -- Other Techniques -- How does it Work? - Case Studies -- Biosensors Prospects: Quo vadis? (Conclusion).