Label-free single molecule spectroscopy and detection

A label-free detection and characterization system, comprising:

• an optical source;
• an optical path having a first end and a second end, said optical path arranged to be optically coupled to said optical source at said first end;
• an optical resonator disposed proximate said optical path along a side of said optical path between said first and second ends, said optical resonator having an optical whispering-gallery mode and being optically coupled to said optical path through an evanescent field to excite said optical whispering-gallery mode;
• an optical receiver arranged to be optically coupled to said second end of said optical path,
• wherein said optical source is frequency locked to a resonance frequency of said optical resonator and provides light sufficiently intense to provide four-wave mixing while being coupled with said optical resonator to generate a comb spectrum received by said optical receiver, and
• wherein said comb spectrum provides characteristic changes of the optical resonator at the resonance frequency in the presence of a substance in contact with said optical resonator to provide detection and characterization of said substance.