Optical sensor with enhanced sensitivity

A surface plasmon resonance (SPR) sensor to determine the presence and quantity of biological or chemical entities in an analyte, said sensor comprising:

• a metal periodic structure deposited as a thin layer of a noble metal, comprising a one dimensional array of nanoslits or a two dimensional array of nanoholes on a transparent dielectric substrate;
• a nm-thick layer of transparent dielectric protection layer on top of the metal periodic structure;
• and
• a functionalization layer, which acts as a binding layer to biological or chemical entities in an analyte that is in contact with the functionaliztion layer;
• wherein:
• the spaces perforated in the metal are at least partially filled by a material with a refractive index as close as possible to that of the substrate;
• the thickness of the metal layer is no more than 100 nm;
• the refractive index, transparency and the thickness of the dielectric protection nanolayer are chosen so that it does not affect the sensor sensitivity;
• the thickness of the dielectric protection layer is no more than 20 nm;
• and
• the presence of the material in the spaces perforated in the metal distances the analyte material from the metal-substrate interface, thereby improving the signal to noise ratio for the spectral/angular peak corresponding to the plasmon excited at the metal-substrate interface allowing this spectral peak to be used as a reference relative to which the spectral peaks corresponding to the plasmon excited at the metal-analyte interface is measured.