Protein biosensing with fluorescent microcapillaries

Abstract

Capillaries with a high-index fluorescent coating represent a new type of whispering-gallery-mode (WGM) microcavity sensor. By coating silicon quantum dots (Si-QDs) onto the channel wall of a microcapillary, a cylindrical microcavity forms in which the optical confinement arises from the index contrast at the interface between the QD layer and the glass capillary wall. However, the ability to functionalize the QD layer for biosensing applications is an open question, since the layer consists of a mixture of Si-QDs embedded in a glassy SiOx matrix. Here, we employ a polyelectrolyte (PE) multilayer approach to functionalize the microcapillary inner surface and demonstrate the potential of this refractive index sensing platform for label-free biosensing applications, using biotin-neutravidin as a specific interaction model.

Dynamic Self-Referencing Approach to Whispering Gallery Mode Biosensing and Its Application to Measurement within Undiluted Serum

“…From the responses of the two spheres it is clear that binding is occurring on the biotinylated sphere, with equilibrium being reached after approximately 200 seconds, while the reference sphere spectrum remains relatively stable throughout the measurement with deviations towards the end of the measurement. This result is consistent with our previous demonstrations of fiber tip 1 and fluorescent microcapillary 36 sensing. We also note that the presence of the reference sphere does not have any effect on the biotinylated sphere's performance.…”

Whispering Gallery Mode Devices for Sensing and Biosensing

“…The highest sensitivity is reported over 400 nm/RIU for thin disks [173] and up to 250 nm/RIU for the second-order radial mode of thick capillaries with a high-index fluorescent coating [8], although values of around 10 nm/RIU are more common. The concentration detection limit for neutravidin was in the nM range [118]; considerably higher than the best results for evanescent measurements (again, illustrating the trade-offs in sensitivity vs. durability and experimental simplicity between the two techniques).…”

“…This is likely to be due to the lower Q factor often related to the free space detection approach which eventually constrains the detection limit to the nanomolar range [108,118,151]. Improvement of the performance is therefore necessary for fluorescent microresonators beyond the technical advantages enabled by the free space excitation and collection of the WGM signal.…”

“…A physisorption-based surface functionalization process, using bovine serum albumin (BSA) directly deposited onto the sensor surface and subsequently cross-linked with antibodies [107], has been used with fluorescent polystyrene microspheres, while a PE-based surface functionalization process has also been used with both fluorescent polystyrene microspheres [108] and glass capillaries [118,119], demonstrating the applicability of such approach for biosensing applications involving whispering gallery modes. Biomolecule immobilization, non-specific binding, and specific orientation The deposition of either silanes or PE multilayers is merely the first step of a complex process.…”

Optical Microbubble Resonators with High Refractive Index Inner Coating for Bio-Sensing Applications: An Analytical Approach

“…On the other hand, Lane and coworkers theoretically and experimentally proved high sensing performance, both as refractometer and biosensor, for silica microcapillaries coated with a thin layer of silicon quantum dots [22,23,24]. As an alternative, Rowland and coauthors considered the case of a sub-wavelength, high refractive index polymeric layer, doped with a dye, as a fluorescent coating for the inner side of thick-walled silica capillaries [25].…”