A surface plasmon resonance-based biochip to reveal traces of ephedrine

Ephedrine is a crucial chemical precursor for clandestinely produced amphetamine and its related drugs. Also, ephedrine is intentionally added to illegal preparations of methamphetamine or amphetamine because it is cheaper than the other two drugs. Consequently there is a pressing need to prevent the entry of ephedrine into commerce. Therefore the challenge calls for non-invasive techniques that provide data on the presence of ephedrine even in trace amounts. In this paper we describe the synthesis of a new ephedrine derivative with a carbon linker featuring an amino reactive group, and its conjugation to the glutamine binding protein (GlnBP) from E. coli as a carrier protein for the production of polyclonal antibodies against ephedrine. Proof-of-principle results of an efficient SPR-based indirect competitive immunoassay for the detection and quantification of ephedrine are presented. The detection limit of the assay was about 33 ng ml(-1).