Towards microstructured optical fibre sensors: surface analysis of silanised lead silicate glass

While protocols to surface functionalise silica glass platforms are well-established, the surface coating of other glass types have received limited attention. Here we fully characterise the surface attachment of a fluoroionophore on extruded lead silicate glass slides and demonstrate these slides as a model for investigating the surface chemistry in a microstructured optical fibre (MOF). This model system allows the utilization of multiple, complementary surface-sensitive techniques that cannot be used within the internal surface of the fibre structure. In characterising the fluoroionophore attachment, we observe that the fluorescence intensity from fluorescence imaging, the atomic nitrogen percentage measured by X-ray photoelectron spectroscopy (XPS), the carbonyl bond component (287.5 eV) in the XPS high resolution carbon spectrum, and Principal Component Analysis (PCA) of the time-of-flight secondary ion mass spectrometry (ToF-SIMS) data can be used to provide relative quantification of the concentration of an attached fluoroionophore. We also show the first use of ToF-SIMS imaging and depth profiling of the Pb content within a glass substrate to provide information on the coverage provided by the coating and the relative thickness of an organic coating. Combined, these techniques provide a comprehensive picture of the coated glass surface that facilitates fibre sensor development.Herbert T. C. Foo, Heike Ebendorff-Heidepriem, Christopher J. Sumby, Tanya M. Monr

Surface analysis and treatment of extruded fluoride phosphate glass preforms for optical fiber fabrication

First published: 20 April 2016Fabrication of fluoride phosphate glass optical fibers using the extrusion method for preform fabrication has been studied using the commercial Schott N-FK51A glass. The extrusion step was found to create a surface layer of differing composition from the bulk glass material, leading to defects drawn down onto the optical fiber surface during fiber fabrication, resulting in high loss and fragile fibers. Similar phenomena have also been observed in other fluoride-based glasses. Removal of this surface layer from preforms prior to fiber drawing was shown to improve optical fiber loss from >5 dB/m to 0.5–1.0 dB/m. The removal of this surface layer is therefore necessary to produce low-loss fluoride phosphate optical fibers.Christopher A. G. Kalnins, Nigel A. Spooner, Tanya M. Monro, and Heike Ebendorff-Heideprie

Driving down the Detection Limit in Microstructured Fiber-Based Chemical Dip Sensors

We present improvements to fluorescence sensing in soft-glass microstructured optical fibers that result in significantly improved sensitivity relative to previously published results. Concentrations of CdSe quantum dots down to 10 pM levels have been demonstrated. We show that the primary limitation to the sensitivity of these systems is the intrinsic fluorescence of the glass itself

Microstructured optical fiber-based biosensors: reversible and nanoliter-scale measurement of zinc ions

Published: May 6, 2016Sensing platforms that allow rapid and efficient detection of metal ions would have applications in disease diagnosis and study, as well as environmental sensing. Here, we report the first microstructured optical fiber-based biosensor for the reversible and nanoliter-scale measurement of metal ions. Specifically, a photoswitchable spiropyran Zn(2+) sensor is incorporated within the microenvironment of a liposome attached to microstructured optical fibers (exposed-core and suspended-core microstructured optical fibers). Both fiber-based platforms retains high selectivity of ion binding associated with a small molecule sensor, while also allowing nanoliter volume sampling and on/off switching. We have demonstrated that multiple measurements can be made on a single sample without the need to change the sensor. The ability of the new sensing platform to sense Zn(2+) in pleural lavage and nasopharynx of mice was compared to that of established ion sensing methodologies such as inductively coupled plasma mass spectrometry (ICP-MS) and a commercially available fluorophore (Fluozin-3), where the optical-fiber-based sensor provides a significant advantage in that it allows the use of nanoliter (nL) sampling when compared to ICP-MS (mL) and FluoZin-3 (μL). This work paves the way to a generic approach for developing surface-based ion sensors using a range of sensor molecules, which can be attached to a surface without the need for its chemical modification and presents an opportunity for the development of new and highly specific ion sensors for real time sensing applications.Sabrina Heng, Christopher A. McDevitt, Roman Kostecki, Jacqueline R. Morey, Bart A. Eijkelkamp, Heike Ebendorff-Heidepriem, Tanya M. Monro, and Andrew D. Abel

Nanodiamond in tellurite glass Part I: origin of loss in nanodiamond-doped glass

Tellurite glass fibers with embedded nanodiamond are attractive materials for quantum photonic applications. Reducing the loss of these fibers in the 600-800 nm wavelength range of nanodiamond fluorescence is essential to exploit the unique properties of nanodiamond in the new hybrid material. In the first part of this study, we report the effect of interaction of the tellurite glass melt with the embedded nanodiamond on the loss of the glasses. The glass fabrication conditions such as melting temperature and concentration of NDs added to the melt were found to have critical influence on the interaction. Based on this understanding, we identified promising fabrication conditions for decreasing the loss to levels required for practical applications.Comment: 13 pages, 6 figure

Enhanced radiation dosimetry of fluoride phosphate glass optical fibres by terbium (III) doping

Published 1 Nov 2016Fluoride phosphate (FP) glass fibres have been developed for radiation dosimetry based on the mechanism of optically stimulated luminescence (OSL). Doping with Tb³⁺ ions improved the materials sensitivity; for samples melted in oxidising conditions, OSL intensity was increased from 8.8 × 10⁵ cnts/g/Gy for undoped glass to 812.3 × 10⁵ cnts/g/Gy for Tb³⁺-doped glass. The radiation sensor performance of Tb³⁺-doped glass fibres under both beta and X-ray irradiation demonstrated the capability of the fibres for radiation dosimetry applications.Christopher A. G. Kalnins, Heike Ebendorff-Heidepriem, Nigel A. Spooner and Tanya M. Monr

An optical fibre sensor for remotely detecting water traces in organic solvents

First published online 26 Aug 2016Tetraphenylpyrazine-triphenylamine (TPP-TPA) was used to detect water traces in organic solvents by monitoring the shift of the fluorescence peak wavelength. This wavelength based method avoids the intrinsic problems of fluorescence intensity change based methods. The use of optical fibres for the detection provides a remote and field-deployable sensing ability.Mengke Han, Ming Chen, Heike Ebendorff-Heidepriem, Cheng Fang, Anjun Qin, Hu Zhang, Ben Zhong Tang, Youhong Tang and Yinlan Rua

High precision extrusion of glass tubes

Precision glass tubes for analytical instrumentation often require tight tolerances in their inner and outer diameter, which makes them cumbersome to fabricate. The extrusion method is a potential method for the fabrication of precision glass tubes, however, the effects of die swell and taper which occur during the extrusion process can distort the final product. This work aims to determine the tolerances that can be achieved for glass tubes fabricated using the extrusion method by comparing the extent of the die swell and tapering on tubes extruded under a variety of extrusion parameters. Lead-silicate glass tubes of 6.5 mm outer diameter and 0.50 mm inner diameter were fabricated with a taper of less than 1 % for the outer diameter and less than 5 % for the inner diameter over 200 mm lengths. This target geometry was achieved using a volume flow rate of 4.7 mm3/s, a glass viscosity of 107.2 Pa.s and a die geometry that accommodated a 12 % offset due to die swell. This result indicates the extrusion method is a viable method for producing glass tubes with tight tolerances for applications in analytical instrumentation.Christopher A. G. Kalnins, Kyle J. Bachus, Andrew Gooley and Heike Ebendorff-Heideprie