Published: March 13th, 2013
Fluorescent-core microcavity sensors employ a high-index quantum-dot coating in the channel of silica microcapillaries. Changes in the refractive index of fluids pumped into the capillary channel cause shifts in the microcavity fluorescence spectrum that can be used to analyze the channel medium.
This paper discusses fluorescent core microcavity-based sensors that can operate in a microfluidic analysis setup. These structures are based on the formation of a fluorescent quantum-dot (QD) coating on the channel surface of a conventional microcapillary. Silicon QDs are especially attractive for this application, owing in part to their negligible toxicity compared to the II-VI and II-VI compound QDs, which are legislatively controlled substances in many countries. While the ensemble emission spectrum is broad and featureless, an Si-QD film on the channel wall of a capillary features a set of sharp, narrow peaks in the fluorescence spectrum, corresponding to the electromagnetic resonances for light trapped within the film. The peak wavelength of these resonances is sensitive to the external medium, thus permitting the device to function as a refractometric sensor in which the QDs never come into physical contact with the analyte. The experimental methods associated with the fabrication of the fluorescent-core microcapillaries are discussed in detail, as well as the analysis methods. Finally, a comparison is made between these structures and the more widely investigated liquid-core optical ring resonators, in terms of microfluidic sensing capabilities.
Chemical sensing systems that require only small sample volumes and that can be incorporated into hand-held or field-operable devices could lead to the development of a wide range of new technologies. Such technologies could include field diagnostics for diseases and pathogens,1 environmental contaminants,2 and food safety.3 Several technologies are being actively explored for microfluidic chemical sensors, with devices based on the physics of surface plasmon resonances (SPR) among the most advanced.4 These sensors are now capable of detecting many specific biomolecules and have achieved commercial success, although mainly....
1. Preparation of Materials
Small deviations in the capillary fabrication procedure can lead to significant changes in the sample success rate. In Figure 5(a-d), we show representative examples of failed capillaries as well as a successful one. Generally, the visual indication of a successful sample is a red fluorescence combined with a high intensity at the capillary walls and a featureless interior. The fluorescence spectrum also clearly indicates the difference between success and failure (Figure 5e). A .......
Fluorescent-core microcavities can be used as refractometric sensors. While there are isolated examples of "rolled up" microtubes that could act as microfluidic sensors,22 compared to microtubes, capillaries will be easier to integrate into microfluidic setups and have considerable practical advantages, since they are easily handled and simple to interface with an analysis setup. Using conventional Fourier analysis methods, wavelength shifts that are at least an order of magnitude smaller than the pitc.......
|Table of Materials
|flexible microbore tubing
|polyethylene, tygon, etc
|Mascot, Norland NOA
|HSQ dissolved in MIBK
Table 1. List of materials used.
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