Sub-wavelength fluorescent polymer coatings to convert standard glass capillaries into robust microfluidic refractometric sensors

Abstract

A capillary microresonator platform for label-free refractometric sensing is demonstrated by coating the interior of thick-walled silica capillaries with a sub-wavelength layer of high refractive index, dye-doped polymer. No intermediate processing, such as etching or tapering, of the capillary is required. Side illumination and detection of the polymer layer reveals a fluorescence spectrum that is periodically modulated by the presence of whispering gallery modes within the layer. The fabricated capillary resonators exhibited sensitivities to changes in internal refractive index of up to 29.44 nm/RIU, demonstrated by flowing through aqueous dilutions of glucose. Thick walled capillaries are used in order to readily allow interfacing with existing biological and chemical sensing and separation platforms such as capillary electrophoresis or gas chromatography where such capillaries are routinely used. The interior polymer coating method described here could enable the use of a wide range of materials for the design of optofluidic label-free sensors integrated with industry standard (bio)chemical analytical separation platforms. © 2013 Copyright SPIE.