Quantitative detection of doping substances by a localised surface plasmon sensor.

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 nanostructures, 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.