Biotin was grafted onto boron doped nanocrystaline diamond electrode through a four-step-chemical process. First step of grafting was electro-chemical reduction of p-4,nitro diazonium salts. The grafting was characterized using X-ray Photoelectron Spectroscopy (XPS), Atomic Force Microscopy (AFM) and fluorescence analysis. XPS analysis and curve fitting procedure lead to the identification of different bond states of carbon present in the grafted film and highlights difference of coverage rate between samples. AFM highlights the non-mononuclear aspect of the diazonium electrografting. Fluorescence measurements with avidin recognition prove the efficient of the grafting.