Biosensors that can reliably detect target analytes in minimally prepared complex samples in real time represent one of the greatest challenges for remote environmental monitoring, point-of-use diagnostics, personalized medicine, and national security. Among the various biosensor transducer technologies (electrochemical, optical, acoustical, mechanical, calorimetric), electrochemical transducers have recently become popular because of their adaptability to automation and portability, high sensitivity, small dimensions, low cost, and compatibility with microfabrication techniques. Diamond is one of the most precious materials in the world with unmatched physical and chemical properties, such as the hardness, extreme chemical stability, high thermal conductivity, very high acoustic speed, very low friction coefficient, etc. Films with large grain size (i.e., high surface roughness), low diamond purity, or large stress are undesirable for device integration and performance. In the 1990s, a new class of diamond material, nanocrystalline diamond emerged. Chemical vapor deposition is the principal technology for manufacturing diamond films.