Surface plasmon resonance signal enhancement for immunoassay of small molecules.

Sensitive detection of small molecules using surface plasmon resonance (SPR) presents significant challenges as the antigen cannot serve as a signal generator because of its low mass; efficient binding of the target requires the binding event to be spaced from the sensor surface through a specialist linker conjugation. Competitive immunoassay of steroid hormones can be performed by conjugation through a rationally designed linker system at positions distant from existing antigenic functional groups. The binding signal from the primary antibody can then be further enhanced by sequential addition of secondary antibody or conjugated gold nanoparticles which can produce 13-fold signal enhancements through both their mass and co-operative plasmon coupling.