Optical sensor with layered plasmon structure for enhanced detection of chemical groups by SERS

A method of detecting chemical groups in an analyte with an amplification factor of at least 1010, comprising

• (a) binding the analyte to the surface of plasmon resonance particles in a an optical device composed of (a) a substrate;
• (b) a plasmon resonance mirror formed on a sensor surface of the substrate;
• (c) disposed over said mirror, a plasmon resonance particle layer composed of a periodic array of such plasmon resonance particles having (i) a coating effective to binding analyte molecules, (ii) substantially uniform particle sizes and shapes in a selected size range between 50-200 nm (ii) a regular periodic particle-to-particle spacing that is less than the wavelength of the laser excitation beam, and (d) an optically transparent dielectric layer having a selected thickness in the thickness range between 2-40 nm separating said mirror from said particle layer;
• (b) irradiating analyte molecules bound to said particles with a visible-light laser excitation beam, and
• (c) recording the Raman spectrum produced by said irradiating.