Method and apparatus for detecting an analyte

A sensor for detecting an analyte comprising:

• a) a FRET assay to be placed in contact with a sample containing said analyte, comprising a fluorescent energy donor moiety and an energy acceptor moiety, wherein the absorption band of the said energy acceptor at least partially overlaps both the emission band and absorption band of the fluorescent energy donor;
• b) a multi-wavelength radiation source for exciting the said FRET assay, the source comprising two or more distinct resolvable wavelengths such that at least two of the wavelengths are within the absorption band of the fluorescent energy donor and at least one of the wavelengths is within the absorption bands of both the fluorescent energy donor and the energy acceptor;
• c) one or more detectors for detecting radiation emitted from the said FRET assay upon excitation by radiation from the said multi-wavelength radiation source;
• and
• d) circuitry containing an algorithm to compare the detected radiation emitted from the said FRET assay when excited by at least one pair of the distinct excitation wavelengths and to calculate the concentration of analyte.