Abstract
A fluorescence-based enzyme activity assay has been demonstrated within a small-core microstructured optical fiber (MOF) for the first time. To achieve this, a reflection-based automated alignment system has been developed, which uses feedback and piezoelectric actuators to maintain optical alignment. The auto-alignment system provides optical stability for the time required to perform an activity assay. The chosen assay is based on the enzyme proprotein convertase 5/6 (PC6) and has important applications in women’s health.
Highlights
Optical fibers are a promising technology for biological sensing, with benefits such as multiplexing and a small size that allows them to be used as minimally invasive probes [1]
A subset of microstructured optical fiber (MOF) are suspended-core fibers (SCFs) that are of particular interest as they are relatively simple to fabricate and fill [9,10,11,12,13,14], while still enabling small volume, high efficiency fluorescence sensing to be performed [15,16]
High sensitivities are achieved by reducing the core diameter to values well below the dimensions of standard single-mode fiber, and this effect has been demonstrated for both fluorescence sensing [16] and surfaced enhanced Raman scattering (SERS) sensing [17,18]
Summary
Optical fibers are a promising technology for biological sensing, with benefits such as multiplexing and a small size that allows them to be used as minimally invasive probes [1]. One clear drawback in using such small-core fibers is the difficulty in maintaining a stable optical alignment, meaning that over time the efficiency with which light is coupled into the core changes significantly This is a particular issue for sensing applications involving intensity-based measurements, such as absorption [9,11] or fluorescence spectroscopy [14,22]. We demonstrate a practical alternative to splicing for improving coupling stability into small-core MOFs based on optical feedback from the reflection of light from the end face of the fiber core This auto-alignment system uses piezoelectric actuators to maintain the optimum coupling position into a small-core fiber and allows intensity-based measurements to be made over long time scales, while still providing one free fiber end for sample collection. It is anticipated that the sensor described in this paper could provide a new diagnostic tool to assess women’s endometrial receptivity: an important aspect of fertility
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