Method and Device for Detecting Analytes

A method of determining the concentration of a predefined analyte in a fluid or fluid sample, the method comprising:

• a) providing a SERS substrate comprising predefined receptor molecules capable of binding predefined competitor molecules;
• b) contacting the SERS substrate with the fluid or fluid sample comprising said analyte in a concentration to be determined and comprising a predetermined amount of said competitor molecules;
• c) radiating the SERS substrate with a monochromatic light source thereby generating a SERS signal having a level indicative of the amount of competitor molecules bound to the receptor molecules of the SERS substrate;
• d) determining the level of the SERS signal while radiating the SERS substrate with the monochromatic light source;
• e) determining a concentration of the analyte in the fluid or fluid sample based on the level of the measured SERS signal.