Biosensors are devices that detect the presence of microbials such as bacteria, viruses or a range biomolecules, including proteins, enzymes, DNA and RNA. For example, they are routinely applied for monitoring the glucose concentration in blood, quality analysis of fresh and waste water and for food control. Nanomaterials are ideal candidates for building sensor devces: where in just a few molecules can alter the properties so drastically that these changes may be easily detected by optical, electrical or chemical means. Recent advantages have radically increased the sensitivity of nanomaterial-based biosensors, making it possible to detect one particular molecule against a background of billions of others. Focusing on the materials suitable for biosensor applications, such as nanoparticles, quantum dots, meso- and nanoporous materials and nanotbues, this text enables the reader to prepare the respective nanomaterials for use in actual devices by appropriate functionalization, surface processing or directed self-assembly. The emphasis throughout is on electrochemical, optical and mechancial detection methods, leading to solutions for today's most challenging tasks. The result is a reference for researchers and developers, disseminating first-hand information on which nanomaterial is best suited to a particular application - and why.