Demonstration of sub-femtomole sensitivity for small molecules with microsphere ring resonator sensors

Ian M. White; Hesam Oveys; Xudong Fan

doi:10.1117/12.644866

27 February 2006 Demonstration of sub-femtomole sensitivity for small molecules with microsphere ring resonator sensors

Ian M. White, Hesam Oveys, Xudong Fan

Proceedings Volume 6092, Ultrasensitive and Single-Molecule Detection Technologies; 60920U (2006) https://doi.org/10.1117/12.644866
Event: SPIE BiOS, 2006, San Jose, California, United States

Abstract

Optical microsphere resonators can function as highly sensitive bio/chemical sensors due to the large Q-factor, which leads to high light-matter interaction. The whispering gallery modes (WGM) arise at the surface of the microsphere, creating a highly enhanced optical field that interacts with matter on or near the microsphere surface. As a result, the spectral position of the WGM is extremely sensitive to refractive index changes near the surface, such as when bio/chemical molecules bind to the sphere. We show the potential feasibility of a microsphere ring resonator as a sensor for small molecules by demonstrating detection of sub-femtomole changes in SiO₂ molecules at the surface of the microsphere. In this experiment, the silica molecules act as an excellent model for small molecule analytes because of their 60 Dalton molecular weight, and because we know nearly the exact quantity of molecules at the surface, which enables a sensitivity characterization. We measure the spectral shifts in the WGMs when low concentrations of hydrofluoric acid (HF) are added to a solution that is being probed by the microsphere. As the HF molecules break apart the SiO₂ molecules at the sphere surface, the WGMs shift due to the sub-nano-scale decrease in the size of the microsphere. These calculations show that the sensitivity of this microsphere resonator is on the order of 500 attomoles. Our results will lead to the utilization of optical microspheres for detection of trace quantities of small molecules for such applications as drug discovery, environmental monitoring, and enzyme detection using peptide cleavage.

Citation Download Citation

Ian M. White, Hesam Oveys, and Xudong Fan "Demonstration of sub-femtomole sensitivity for small molecules with microsphere ring resonator sensors", Proc. SPIE 6092, Ultrasensitive and Single-Molecule Detection Technologies, 60920U (27 February 2006); https://doi.org/10.1117/12.644866

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KEYWORDS

Molecules

Sensors

Optical spheres

Silica

Resonators

Refractive index

Target detection

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