Fluorescence-based sensing with optical nanowires: a generalized model and experimental validation

Abstract

OSA grants to the Author(s) (or their employers, in the case of works made for hire) the following rights:(b)The right to post and update his or her Work on any internet site (other than the Author(s') personal web home page) provided that the following conditions are met: (i) access to the server does not depend on payment for access, subscription or membership fees; and (ii) any such posting made or updated after acceptance of the Work for publication includes and prominently displays the correct bibliographic data and an OSA copyright notice (e.g. "© 2009 The Optical Society"). Abstract:A model for the fluorescence sensing properties of small-core high-refractive-index fibers (optical nanowires) is developed and compared quantitatively with experiment. For the first time, higher-order modes and loss factors relevant to optical nanowires are included, which allows the model to be compared effectively with experiment via the use of fluorophore filled suspended optical nanowires. Numerical results show that high-index materials are beneficial for fluorescence-based sensing. However, both numerical and experimental results show that the fluorescence signal is relatively insensitive to core size, except for low concentration sensing where nanoscale fiber cores are advantageous due to the increased evanescent field power.

Interferometric-type optical biosensor based on exposed core microstructured optical fiber

“…Due to the high numerical aperture of ECF (glass-air or glass-water interfaces) and the difficulty in fabricating the ECF core small enough to support a single mode regime guidance (which requires sub-micrometer core diameters), the ECFs that have been developed to date are multimode fibers. To estimate the number of modes that are supported by the ECF we have performed a simple calculation using a step-index optical fiber model, which we have used previously as an approximation for suspended-core microstructured optical fiber [22]. Using the refractive index values for silica glass as the core, air as the cladding, and a core diameter of 7.5 µm, a step-index fiber can propagate 68 modes.…”

Quantification of the fluorescence sensing performance of microstructured optical fibers compared to multi-mode fiber tips

“…While comparison has previously been made between D-shaped and tapered fibers [16], to date a comparison between SCFs and tip fibers has not been covered. Previous work has examined the fluorescence capture into the guided modes of these SCFs [24], and then verified these theoretical results against experimental data [25]. In this study we seek to extend this to give a direct comparison of expected fluorescence intensities in comparable conditions.…”

“…A full vectorial model to simulate the captured fluorescence was used, based on a model previously presented in [25,30]. This model is based on a step-index glass-ethanol geometry, which is a close approximation to the suspended-core fiber geometry.…”

Suspended core optical fibers for biological applications using UV wavelengths

“…It is known that small core diameter fibers have a greater overlap between the guided mode field and fluid within the holes and thus can achieve improved fluorescence sensing performance 10 . However, there are practical advantages to using a larger core fiber such as better coupling stability and the larger hole diameters in such fibers, which increases filling speeds and also improves surface functionalisation coating processes as holes are less easily blocked.…”

“…Fig. 4(b) shows the effect of including the coupling of a linearly polarized Gaussian input beam with a waist of 0.65 x fiber diameter (as suggested by Buck for multi-mode fiber 9 ) and confinement loss for a W-shape structure with an inner cladding diameter equal to 10 times the core diameter 10 . The results show a power fraction (relative to the laser power) of 11% at 375 nm for a 0.5 µm core diameter fiber or 0.1% for a 4.0 µm core diameter fiber.…”