Abstract
A highly porous optical-fiber cladding was developed for evanescent-wave fiber sensors, which contains sensor molecules, maintains guiding conditions in the optical fiber, and is suitable for sensing in aqueous environments. To make the cladding material (a poly(ethylene) glycol diacrylate (PEGDA) polymer) highly porous, a microsphere templating strategy was employed. The resulting pore network increases transport of the target analyte to the sensor molecules located in the cladding, which improves the sensor response time. This was demonstrated using fluorescein-based pH sensor molecules, which were covalently attached to the cladding material. Scanning electron microscopy was used to examine the structure of the templated polymer and the large network of interconnected pores. Fluorescence measurements showed a tenfold improvement in the response time for the templated polymer and a reliable pH response over a pH range of five to nine with an estimated accuracy of 0.08 pH units.
Highlights
Optical fiber sensing has been applied to a large range of measurement tasks, including voltage, strain, pressure, temperature, humidity, viscosity, and chemical species [1, 2]
Fluorescence measurements with the crossed-fiber scheme and this porous cladding material showed a tenfold improvement of the response time resulting from the pore network and a reproducible pH response
Any movement of the fibers could lead to unwanted changes in the measured sensor signal: the exponential dropoff of evanescent fields implies that small distance changes lead to exponentially amplified changes in the evanescent field strength
Summary
Optical fiber sensing has been applied to a large range of measurement tasks, including voltage, strain, pressure, temperature, humidity, viscosity, and chemical species [1, 2]. Resolved readout of individual sensors can be obtained by using a pulsed excitation light source and employing optical time-of-flight detection (OTOFD). In this technique, each sensor region has a unique optical pathlength from the source to the detector, and The Scientific World Journal. Microsphere templating with polystyrene microspheres was used to create highly porous crossed-fiber junctions with poly(ethylene) glycol diacrylate (PEGDA) hydrogel as a replacement cladding. Fluorescence measurements with the crossed-fiber scheme and this porous cladding material showed a tenfold improvement of the response time resulting from the pore network and a reproducible pH response
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