The present invention provides a method of detecting changes in the refractive index at the surface of a localized surface plasmon resonance (LSPR) detection system. The method includes generating an insoluble product from an enzymatic substrate using an immobilized enzyme, wherein the insoluble product accumulates at a LSPR supporting surface. The method also includes detecting changes in the reflected or transmitted light of the surface arising from the presence of the insoluble product using LSPR.