Quantitative detection of doping substances by a localised surface plasmon sensor

5 pages, 2 figures.Within this communication, consistent evidence of a quantitative biosensing principle for steroidal residue analysis is presented. Our approach uses a simple method for the quantitative determination of an anabolic agent called stanozolol (Sz). Sz (Mw 328) is widely used in sports, horse racing and as a growth promoter in animals for human consumption. Through the use of localised surface plasmons (LSPs), sustained by three-dimensional noble metal nano-structures, we have developed a highly specific, label-less immunosensor for the detection of this small organic molecule to low levels (nM range). A main practical advantage over conventional flat extended film surface plasmon resonance (SPR) systems is the simplicity of the optical configuration, since there is no need for cumbersome total internal reflection illumination, thus making integration easier. In addition, the active area of the LSP-based sensor is smaller, decreasing the minimum detectable number of molecules involved in the binding event. Assay times are short and the set-up is comprised of relatively cheap instrumentation. Detection levels found here are comparable with SPR, even at this early stage of development and with further modifications, we envisage sensing down to pM (10−12) levels.The authors thank Mr. J.-Pablo Salvador for kindly providing all the immunoreagents. This work was supported by the Spanish Ministry of Science and Technology (TIC2003- 01038 and AGL2002-04635-C04-03) and by the European Commission (IST-2003-508774 and NMP2-CT-2003- 505485) and the Regional Development Fund. MPK thanks the Ministerio de Educacion, Cultura y Deporte for his fellowship under the National Program of Mobility for Professors and Researchers.Peer reviewe