The monitoring of illicit drugs is now of major importance. Key areas of analysis include the detection of illicit use by drivers, workplace testing, forensic investigations and general monitoring to detect or reduce abuse. Thus, the development of a highly sensitive and reliable array-based assay for saliva, an assay-friendly matrix for detection of illicit drugs, would be of major benefit. This thesis describes the production and affinity maturation of antibodies for the detection of illicit drugs and their application in ELISA, Biacore surface plasmon resonance -based biosensor assays and, finally, in a multidrug-based assay.