Eur. Phys. J. Special Topics 223, 1971–1988 (2014)
https://doi.org/10.1140/epjst/e2014-02240-9

Regular Article

Enhanced nanoparticle detection with liquid droplet resonators

¹ Max-Planck-Institute for the Science of Light, Laboratory of Nanophotonics and Biosensing, Günther-Scharowsky-Straße 1, 91058 Erlangen, Germany
² Consiglio Nazionale delle Ricerche, Istituto Nazionale di Ottica (INO), via Campi Flegrei 34 – Comprensorio A. Olivetti, 80078 Pozzuoli, Naples, Italy
³ Department of Chemistry, Queen's University, Kingston, K7L 3N6, Ontario, Canada

^a e-mail: matthew.foreman@mpl.mpg.de

Received: 10 June 2014
Revised: 4 August 2014
Published online: 6 October 2014

Abstract

Whispering gallery mode particle sensing experiments are commonly performed with solid resonators, whereby the sensing volume is limited to the weak evanescent tail of the mode near the resonator surface. In this work we discuss in detail the sensitivity enhancements achievable in liquid droplet resonators wherein the stronger internal fields and convenient means of particle delivery can be exploited. Asymptotic formulae are derived for the relative resonance shift, line broadening and mode splitting of TE and TM modes in liquid droplet resonators. As a corollary the relative fraction of internal and external mode energy follows, which is shown to govern achievable sensitivity enhancements of solute concentration measurements in droplet sensors. Experimental measurements of nanoparticle concentration based on whispering gallery mode resonance broadening are also presented.