Optical microresonators as single-particle absorption spectrometers


Optical measurements of nanoscale objects offer major insights into fundamental biological, material and photonic properties. In absorption spectroscopy, sensitivity limits applications at the nanoscale. Here, we present a new single-particle double-modulation photothermal absorption spectroscopy method that employs on-chip optical whispering-gallery-mode (WGM) microresonators as ultrasensitive thermometers. Optical excitation of a nanoscale object on the microresonator produces increased local temperatures that are proportional to the absorption cross-section of the object. We resolve photothermal shifts in the resonance frequency of the microresonator that are smaller than 100 Hz, orders of magnitude smaller than previous WGM sensing schemes. The application of our new technique to single gold nanorods reveals a dense array of sharp Fano resonances arising from the coupling between the localized surface plasmon of the gold nanorod and the WGMs of the resonator, allowing for the exploration of plasmonic–photonic hybridization. In terms of the wider applicability, our approach adds label-free spectroscopic identification to microresonator-based detection schemes.

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Figure 1: Microresonator-based absorption spectroscopy.
Figure 2: Representative spectroscopic measurements on single AuNRs.
Figure 3: Progression of Fano lineshapes within the absorption spectrum of an AuNR coupled to a set of WGMs.
Figure 4: Schematic demonstrating the coupled oscillator model of coherent WGM–LSP interaction.
Figure 5: Correlation of fine-resolution AuNR absorption spectra.
Figure 6: Fine and coarse spectra and comparison with theory.


  1. 1

    Baaske, M. D., Foreman, M. R. & Vollmer, F. Single-molecule nucleic acid interactions monitored on a label-free microcavity biosensor platform. Nat. Nanotech. 9, 933–939 (2014).

    ADS  Article  Google Scholar 

  2. 2

    Dantham, V. et al. Label-free detection of single protein using a nanoplasmonic-photonic hybrid microcavity. Nano Lett. 13, 3347–3351 (2013).

    ADS  Article  Google Scholar 

  3. 3

    Yu, W., Jiang, W. C., Lin, Q. & Lu, T. Cavity optomechanical spring sensing of single molecules. Nat. Commun. 7, 12311 (2016).

    ADS  Article  Google Scholar 

  4. 4

    Zijlstra, P., Paulo, P. M. & Orrit, M. Optical detection of single non-absorbing molecules using the surface plasmon resonance of a gold nanorod. Nat. Nanotech. 7, 379–382 (2012).

    ADS  Article  Google Scholar 

  5. 5

    Ozdemir, S. et al. Highly sensitive detection of nanoparticles with a self-referenced and self-heterodyned whispering-gallery Raman microlaser. Proc. Natl Acad. Sci. USA 111, 3836–3844 (2014).

    Article  Google Scholar 

  6. 6

    Lu, T. et al. High sensitivity nanoparticle detection using optical microcavities. Proc. Natl Acad. Sci. USA 108, 5976–5979 (2011).

    ADS  Article  Google Scholar 

  7. 7

    Li, B.-B. et al. Single nanoparticle detection using split-mode microcavity Raman lasers. Proc. Natl Acad. Sci. USA 111, 14657–14662 (2014).

    ADS  Article  Google Scholar 

  8. 8

    Swaim, J., Knittel, J. & Bowen, W. Detection of nanoparticles with a frequency locked whispering gallery mode microresonator. Appl. Phys. Lett. 102, 183106 (2013).

    ADS  Article  Google Scholar 

  9. 9

    Mader, M., Reichel, J., Hänsch, T. W. & Hunger, D. A scanning cavity microscope. Nat. Commun. 6, 7249 (2015).

    ADS  Article  Google Scholar 

  10. 10

    Muskens, O. L. et al. Quantitative absorption spectroscopy of a single gold nanorod. J. Phys. Chem. C 112, 8917–8921 (2008).

    Article  Google Scholar 

  11. 11

    Li, Z., Mao, W., Devadas, M. S. & Hartland, G. V. Absorption spectroscopy of single optically trapped gold nanorods. Nano Lett. 15, 7731–7735 (2015).

    ADS  Article  Google Scholar 

  12. 12

    Cognet, L., Berciaud, S., Lasne, D. & Lounis, B. Photothermal methods for single nonluminescent nano-objects. Anal. Chem. 80, 2288–2294 (2008).

    Article  Google Scholar 

  13. 13

    Yorulmaz, M. et al. Single-particle absorption spectroscopy by photothermal contrast. Nano Lett. 15, 3041–3047 (2015).

    ADS  Article  Google Scholar 

  14. 14

    Bailey, R. C. Applications of optical microcavity resonators in analytical chemistry. Annu. Rev. Anal. Chem. 9, 1–25 (2016).

    Article  Google Scholar 

  15. 15

    Gaiduk, A., Yorulmaz, M., Ruijgrok, P. & Orrit, M. Room-temperature detection of a single molecule's absorption by photothermal contrast. Science 330, 353–356 (2010).

    ADS  Article  Google Scholar 

  16. 16

    Celebrano, M., Kukura, P., Renn, A. & Sandoghdar, V. Single-molecule imaging by optical absorption. Nat. Photon. 5, 95–98 (2011).

    ADS  Article  Google Scholar 

  17. 17

    Chong, S., Min, W. & Xie, X. Ground-state depletion microscopy: detection sensitivity of single-molecule optical absorption at room temperature. J. Phys. Chem. Lett. 1, 3316–3322 (2010).

    Article  Google Scholar 

  18. 18

    Piliarik, M. & Sandoghdar, V. Direct optical sensing of single unlabelled proteins and super-resolution imaging of their binding sites. Nat. Commun. 5, 4495 (2014).

    ADS  Article  Google Scholar 

  19. 19

    Moerner, W. E. & Kador, L. Optical detection and spectroscopy of single molecules in a solid. Phys. Rev. Lett. 62, 2535–2538 (1989).

    ADS  Article  Google Scholar 

  20. 20

    Kador, L., Latychevskaia, T., Renn, A. & Wild, U. P. Absorption spectroscopy on single molecules in solids. J. Chem. Phys. 111, 8755–8758 (1999).

    ADS  Article  Google Scholar 

  21. 21

    Gerhardt, I. et al. Strong extinction of a laser beam by a single molecule. Phys. Rev. Lett. 98, 033601 (2007).

    ADS  Article  Google Scholar 

  22. 22

    Rezus, Y. et al. Single-photon spectroscopy of a single molecule. Phys. Rev. Lett. 108, 093601 (2012).

    ADS  Article  Google Scholar 

  23. 23

    Armani, D., Kippenberg, T., Spillane, S. & Vahala, K. Ultra-high-Q toroid microcavity on a chip. Nature 421, 925–928 (2003).

    ADS  Article  Google Scholar 

  24. 24

    Aoki, T. et al. Observation of strong coupling between one atom and a monolithic microresonator. Nature 443, 671–674 (2006).

    ADS  Article  Google Scholar 

  25. 25

    Xiao, Y.-F. et al. Strongly enhanced light-matter interaction in a hybrid photonic-plasmonic resonator. Phys. Rev. A 85, 031805 (2012).

    ADS  Article  Google Scholar 

  26. 26

    Link, S. & El-Sayed, M. A. Spectral properties and relaxation dynamics of surface plasmon electronic oscillations in gold and silver nanodots and nanorods. J. Phys. Chem. B 103, 8410–8426 (1999).

    Article  Google Scholar 

  27. 27

    Arnold, S., Shopova, S. & Holler, S. Whispering gallery mode bio-sensor for label-free detection of single molecules: thermo-optic vs. reactive mechanism. Opt. Express 18, 281–287 (2010).

    ADS  Article  Google Scholar 

  28. 28

    Heylman, K. & Goldsmith, R. Photothermal mapping and free-space laser tuning of toroidal optical microcavities. Appl. Phys. Lett. 103, 211116 (2013).

    ADS  Article  Google Scholar 

  29. 29

    Black, E. An introduction to pound-drever-hall laser frequency stabilization. Am. J. Phys 69, 79–87 (2001).

    ADS  Article  Google Scholar 

  30. 30

    Carmon, T. et al. Feedback control of ultra-high-Q microcavities: application to micro-Raman lasers and microparametric oscillators. Opt. Express 13, 3558–3566 (2005).

    ADS  Article  Google Scholar 

  31. 31

    Barnes, J., Gagliardi, G. & Loock, H.-P. Absolute absorption cross-section measurement of a submonolayer film on a silica microresonator. Optica 1, 75–83 (2014).

    ADS  Article  Google Scholar 

  32. 32

    Weng, W., Anstie, J. D. & Luiten, A. N. Refractometry with ultralow detection limit using anisotropic whispering-gallery-mode resonators. Phys. Rev. Appl. 3, 044015 (2015).

    ADS  Article  Google Scholar 

  33. 33

    Heylman, K., Knapper, K. & Goldsmith, R. Photothermal microscopy of nonluminescent single particles enabled by optical microresonators. J. Phys. Chem. Lett. 5, 1917–1923 (2014).

    Article  Google Scholar 

  34. 34

    Knapper, K. A., Heylman, K. D., Horak, E. H. & Goldsmith, R. H. Chip-scale fabrication of high-Q all-glass toroidal microresonators for single-particle label-free imaging. Adv. Mater. 28, 2945–2950 (2016).

    Article  Google Scholar 

  35. 35

    Keng, D., Tan, X. & Arnold, S. Whispering gallery micro-global positioning system for nanoparticle sizing in real time. Appl. Phys. Lett. 105, 071105 (2014).

    ADS  Article  Google Scholar 

  36. 36

    Schliesser, A., Anetsberger, G., Rivière, R., Arcizet, O. & Kippenberg, T. J. High-sensitivity monitoring of micromechanical vibration using optical whispering gallery mode resonators. New J. Phys. 10, 095015 (2008).

    ADS  Article  Google Scholar 

  37. 37

    Fano, U. Effects of configuration interaction on intensities and phase shifts. Phys. Rev. 124, 1866–1878 (1961).

    ADS  Article  Google Scholar 

  38. 38

    Anderson, P. W. Localized magnetic states in metals. Phys. Rev. 124, 41–53 (1961).

    ADS  MathSciNet  Article  Google Scholar 

  39. 39

    Miroshnichenko, A. E., Flach, S. & Kivshar, Y. S. Fano resonances in nanoscale structures. Rev. Mod. Phys. 82, 2257–2298 (2010).

    ADS  Article  Google Scholar 

  40. 40

    Li, B.-B. et al. Experimental observation of Fano resonance in a single whispering-gallery microresonator. Appl. Phys. Lett. 98, 021116 (2011).

    ADS  Article  Google Scholar 

  41. 41

    Barclay, P. E., Santori, C., Fu, K.-M., Beausoleil, R. G. & Painter, O. Coherent interference effects in a nano-assembled diamond NV center cavity-QED system. Opt. Express 17, 8081–8197 (2009).

    ADS  Article  Google Scholar 

  42. 42

    Kroner, M. et al. The nonlinear Fano effect. Nature 451, 311–314 (2008).

    ADS  Article  Google Scholar 

  43. 43

    Stern, L., Grajower, M. & Levy, U. Fano resonances and all-optical switching in a resonantly coupled plasmonic–atomic system. Nat. Commun. 5, 4865 (2014).

    ADS  Article  Google Scholar 

  44. 44

    Giannini, V., Francescato, Y., Amrania, H., Phillips, C. C. & Maier, S. A. Fano resonances in nanoscale plasmonic systems: a parameter-free modeling approach. Nano Lett. 11, 2835–2840 (2011).

    ADS  Article  Google Scholar 

  45. 45

    Foreman, M. R. & Vollmer, F. Level repulsion in hybrid photonic-plasmonic microresonators for enhanced biodetection. Phys. Rev. A 88, 023831 (2013).

    ADS  Article  Google Scholar 

  46. 46

    Foreman, M. R. & Vollmer, F. Theory of resonance shifts of whispering gallery modes by arbitrary plasmonic nanoparticles. New J. Phys. 15, 083006 (2013).

    ADS  Article  Google Scholar 

  47. 47

    Gallinet, B. & Martin, O. J. Analytical description of Fano resonances in plasmonic nanostructures. Am. Inst. Phys. Conf. Proc. 1398, 73–75 (2011).

    ADS  Google Scholar 

  48. 48

    Langbein, D. Non-retarded dispersion energy between macroscopic spheres. J. Phys. Chem. Solids 32, 1657–1667 (1971).

    ADS  Article  Google Scholar 

  49. 49

    Wiersig, J. Structure of whispering-gallery modes in optical microdisks perturbed by nanoparticles. Phys. Rev. A 84, 063828 (2011).

    ADS  Article  Google Scholar 

  50. 50

    Zhang, S., Bao, K., Halas, N. J., Xu, H. & Nordlander, P. Substrate-induced Fano resonances of a plasmonic nanocube: a route to increased-sensitivity localized surface plasmon resonance sensors revealed. Nano Lett. 11, 1657–1663 (2011).

    ADS  Article  Google Scholar 

  51. 51

    Zhang, Y., Wen, F., Zhen, Y.-R., Nordlander, P. & Halas, N. J. Coherent Fano resonances in a plasmonic nanocluster enhance optical four-wave mixing. Proc. Natl Acad. Sci. USA 110, 9215–9219 (2013).

    ADS  Article  Google Scholar 

  52. 52

    Zhang, Y. et al. Coherent anti-stokes Raman scattering with single-molecule sensitivity using a plasmonic Fano resonance. Nat. Commun. 5 ( 2014).

  53. 53

    Jager, J. et al. High-Q silica microcavities on a chip: from microtoroid to microsphere. Appl. Phys. Lett. 99, 181123 (2011).

    ADS  Article  Google Scholar 

  54. 54

    Link, S., Burda, C., Nikoobakht, B. & El-Sayed, M. Laser-induced shape changes of colloidal gold nanorods using femtosecond and nanosecond laser pulses. J. Phys. Chem. B 104, 6152–6163 (2000).

    Article  Google Scholar 

  55. 55

    Leviton, D. & Frey, B. Temperature-dependent absolute refractive index measurements of synthetic fused silica. Proc. SPIE 6273, 62732K (2006).

    ADS  Article  Google Scholar 

  56. 56

    Rokhsari, H., Spillane, S. M. & Vahala, K. J. Loss characterization in microcavities using the thermal bistability effect. Appl. Phys. Lett. 85, 3029–3031 (2004).

    ADS  Article  Google Scholar 

  57. 57

    Fernandes, L. A. Birefringence and Bragg Grating Control in Femtosecond Laser Written Optical Circuits PhD thesis, Universidade do Porto (2012).

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We thank M. Stolt and S. Jin for technical assistance with electron microscopy, A. Sheth for useful references regarding the statistical analysis and N. Eason (nipaeason.com) for graphic design contributions to this work. This work was partially supported by the NSF under award numbers DBI-1556241 and UW-MRSEC DMR-1121288 (R.H.G.), CHE-1253775 (D.J.M.), DGE-1256082 (N.T.), and DGE-1256259 (K.A.K.).

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K.D.H. and E.H.H. built the spectrometer and carried out the measurements and analysis with help from R.H.G. N.T., S.C.Q. and C.C. formulated the theoretical model and performed simulations with help from D.J.M. K.A.K. fabricated the resonators. K.D.H., N.T., R.H.G. and D.J.M. wrote the paper with contributions from all co-authors.

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Correspondence to David J. Masiello or Randall H. Goldsmith.

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The authors declare no competing financial interests.

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Heylman, K., Thakkar, N., Horak, E. et al. Optical microresonators as single-particle absorption spectrometers. Nature Photon 10, 788–795 (2016). https://doi.org/10.1038/nphoton.2016.217

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