title: Label-free, single-molecule detection with optical microcavities.
abstract: Current single-molecule detection techniques require labeling the target molecule. We report a highly specific and sensitive optical sensor based on an ultrahigh quality (Q) factor (Q > 10(8)) whispering-gallery microcavity. The silica surface is functionalized to bind the target molecule; binding is detected by a resonant wavelength shift. Single-molecule detection is confirmed by observation of single-molecule binding events that shift the resonant frequency, as well as by the statistics for these shifts over many binding events. These shifts result from a thermo-optic mechanism. Additionally, label-free, single-molecule detection of interleukin-2 was demonstrated in serum. These experiments demonstrate a dynamic range of 10(12) in concentration, establishing the microcavity as a sensitive and versatile detector.
authors.affiliation: Department of Applied Physics, MC 128-95, California Institute of Technology, Pasadena, CA 91125, USA.
authors.forename: Andrea M
authors.initials: AM
authors.lastname: Armani
authors.forename: Rajan P
authors.initials: RP
authors.lastname: Kulkarni
authors.forename: Scott E
authors.initials: SE
authors.lastname: Fraser
authors.forename: Richard C
authors.initials: RC
authors.lastname: Flagan
authors.forename: Kerry J
authors.initials: KJ
authors.lastname: Vahala
mesh_terms: D000818:Animals; D000906:Antibodies; D002417:Cattle; D002623:Chemistry Techniques, Analytical / Q000379:methods*; D007376:Interleukin-2 / Q000032:analysis* / Q000097:blood / Q000276:immunology; D007834:Lasers; D055095:Optics and Photonics; D013696:Temperature
chemical_list: D000906:Antibodies; D007376:Interleukin-2