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Dataset supporting the University of Southampton Doctoral Thesis "Rapid point-of-care testing solutions to meet clinical needs"
No full textDataset supporting the University of Southampton Doctoral Thesis "Rapid point-of-care testing solutions to meet clinical needs".
Dataset consists of Graphpad Prism files and jpg files
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Domain engineering techniques and devices in lithium niobate
No full textThis thesis presents the results from investigations directed at novel approaches to domain engineering single-crystal congruent lithium niobate at the micron/sub-micron scale for practical device applications. Experimental etch-rate measurements from a parametric study of etch-rates and etch-quality of single-crystal lithium niobate z-faces, as a function of specific ratios for mixtures of HF/HNO3, to ascertain whether the widely-employed 1:2 mixture was in fact optimum for achieving the largest differential etch-rates between lithium niobate z-faces, revealed that pure HF produced an etch-rate that is a factor of two higher than that for the more frequently used 1:2 mixture. The observed etch-quality as compared to the 1:2 ratio was also improved for either pure HF or HF/HNO3 in a 1:4 ratio. A discussion of the etch-chemistry involved, and an explanation of the observed difference in etch-rates between the +z and -z faces has been proposed. The experimental results are also suggestive of a second differential etch-rate between virgin and newly poled z-faces. The observed variation in the differential etch-rate as a function of time-delay following poling, was suggestive of small atomic displacements following poling, and was quantified by the evidenced shifts in six major Raman spectral peaks. The noticeable modifications in the etch-behaviour of undoped congruent z-cut lithium niobate by pre-illumination with sub-picosecond UV-laser radiation of 248 nm wavelength at energy fluences below the ablation threshold, demonstrates the potential applicability of this technique for µm-scale surface structuring of lithium niobate. An innovative technique for surface domain-inversion, based on the conventional e-field poling, but involving an intentional over-poling step, was employed to fabricate 1D and 2D periodic structures with good domain uniformity. Domain periods as short as ~1µm have been achieved, and the technique shows full compatibility with standard waveguide fabrication techniques in lithium niobate. Quasi-phase matched harmonic generation at the fundamental wavelength of 1.064 µm, by means of the first-order (G10) reciprocal lattice vector, from a surface hexagonally poled planar annealed proton exchanged waveguide, with domain period of 6.7 µm, was demonstrated. First-order quasi-phase matched blue light generation with reasonable efficiencies at 413.17 nm, with domain periods of 2.47 µm from a surface poled Ti-indiffused channel waveguide was also demonstrated. Finally a novel route, sequentially employing techniques such as photolithographic patterning, e-field poling, direct-bonding and domain-sensitive differential wet etching for the fabrication of free-standing piezoelectric micro-cantilevers in single-crystal lithium niobate, with MEMS/MOEMS end-applications, was demonstrated
UV laser induced surface microstructures in congruent lithium niobate single crystals
No full textUltra violet illumination of the -z face of lithium niobate single crystals, under specific conditions, results in an organized arrangement of submicron etch-resistant features that reflect the illuminating intensity distribution. Consequently, spatially resolved illumination can produce periodic structures with submicron periodicity. Furthermore, a size self-adjustment of the submicron etch resistant features was observed which is related to characteristic lengths (e.g. grating period) of the overall structure. The effect occurs for a narrow range of illuminating intensities and is attributed to a photo-induced electrostatic charge distribution which modifies the electrochemical interaction of the acid with the surface. The size and periodicity of the structures which can be achieved with this method are suitable for the fabrication of 2D photonic crystal structures in this electro-optically tunable material
Efficient blue light generation from surface periodically poled Ti-indiffused channel waveguides
No full textWe report first-order quasi-phase matched blue light generation at 413.17 nm, in a surface-poled Ti-indiffused channel waveguide in lithium niobate. For 70mW of incident c.w. pump, 3.46 mW (uncorrected for reflection losses) was generated at the second harmonic
Bacterial pathogen detection using laser-structured paper-based diagnostic sensors
No full textAntimicrobial resistance has been recently identified by the World Health Organisation as a global threat and the need for novel diagnostic tools has been stressed. Current routine empirical antibiotic therapy protocol involves laboratory-based bacterial culture testing which can take up to 2-3 days. However, if the specific microbe species causing an infection can be quickly identified earlier on, it will allow doctors to prescribe a specific targeted antimicrobial instead of using a broad spectrum antimicrobial. In this work, we will present our preliminary results on the use of a laser-based fabrication technique of paper-based diagnostic tests via photo-polymerisation. The technique allows the creation of hydrophobic barriers through the whole thickness of the paper, and therefore the creation of fluidic channels and test zones in many different shapes, sizes and patterns. The laser-based direct-write procedure is non-contact, non-lithographic and mask-less and uses a low-power 405nm diode laser. The laser-structured paper can then be infused with chromogenic agars that allow the growth and detection of different bacteria. These devices are analogues of the commonly available agar plates and will allow the timely detection of multiple pathogens at the point-of-care. These paper-based diagnostic sensors fabricated via our laser-based technology are cheap, easy-to-use and allow rapid testing of either pathogens or their antimicrobial resistance to antibiotics
Towards AMR testing using paper-based diagnostic sensors
No full textOveruse of broad spectrum antimicrobial agent means that resistance to them can evolve rapidly in microbe populations, and hence when a broad spectrum treatment is really crucial, it is less effective at saving the patient. Furthermore, once the bacteria become resistant, it can then exacerbate the prevalence of antibiotic resistance. Current routine empirical antibiotic therapy protocol involves laboratory based bacterial culture testing which can take up to 2-3 days. As a result, the only option available to the clinician is the treatment of the patient using an empirical antibiotic prescription. Such treatments can either prove to be ineffective, or potentially worsen the patient’s condition. However, if the specific microbe species causing an infection can be quickly identified earlier on, it will allow doctors to prescribe a specific targeted antimicrobial instead of using a broad spectrum antimicrobial. Therefore, early diagnosis and prompt correct antibiotic treatment is important for clinical recovery and prevention of this serious antibiotic resistance. In this work, we will present our preliminary results on the use of a laser-based fabrication technique in the development of paper-based diagnostic tests which are analogues of the commonly available pregnancy 'dipstick' testing kits, and which will allow the timely detection of multiple pathogens at the point-of-care, either in the clinic or in the community. These paper-based diagnostic sensors fabricated via our laser-based technology are cheap, easy-to-use and allow rapid testing of either pathogens or their antimicrobial resistance to antibiotics.<br/
Electro-optic solid state beam deflection: resolution considerations and 2-D implementation
No full textA simpler, alternative to 'prism type' electro-optic (EO) solid state deflectors has been recently demonstrated. This device is essentially a single interface version of a conventional deflector, but significant deflection is achieved by setting the input beam at grazing incidence to the interface (where, additionally, it can act as an EO switch). The increased deflection seen near TIR is, however, made at the expense of increased divergence of the output beam. Overall deflection can be a misleading quantity to determine the performance of a deflector as this could always be increased with suitable lenses. A more reliable figure of merit is the number of separate resolvable spots that can be imaged from the deflector output. Here we analyze the achievable resolution for a single interface deflector. It can be seen that with a suitably sized device, significant resolution can be attained from a single interface deflector as shown in Fig.1. The resolution is shown here as a function of temperature since if the deflector were to be working at visible wavelengths if would necessarily be heated to avoid photo-refractive effects. Additionally heating has a secondary role in increasing resolution due to the intrinsic n term in the EO equation. Although there are still issues to overcome in terms of the output beam quality of a single interface deflector, it does possess one major advantage over the previous, multiple interface deflectors. Due to its simplicity it can be fashioned to function in 2 dimensions (Fig.2). This would be the first ever report to our knowledge of a 2D EO solid state beam deflector
Laser direct-write for fabrication of three-dimensional paper-based devices
No full textWe report the use of a laser-based direct-write (LDW) technique that allows the design and fabrication of three-dimensional (3D) structures within a paper substrate that enables implementation of multi-step analytical assays via a 3D protocol. The technique is based on laser-induced photo-polymerisation, and through adjustment of the laser writing parameters such as the laser power and scan speed we can control the depths of hydrophobic barriers that are formed within a substrate which, when carefully designed and integrated, produce 3D flow paths. So far, we have successfully used this depth-variable patterning protocol for stacking and sealing of multi-layer substrates, for assembly of backing layers for two-dimensional (2D) lateral flow devices and finally for fabrication of 3D devices. Since the 3D flow paths can also be formed via a single laser-writing process by controlling the patterning parameters, this is a distinct improvement over other methods that require multiple complicated and repetitive assembly procedures. This technique is therefore suitable for cheap, rapid and large-scale fabrication of 3D paper-based microfluidic devices
Programmable delay in paper-based devices using laser direct writing
No full textDemand for low-cost alternatives to conventional medical diagnostic tools has been the driving force that has spurred significant developments in the diagnostics field. Paper-based fluidics, proposed by the Whitesides’ group in 2007 has been regarded as one such alternative, and consequently, this field has been progressing rapidly and a range of paper-based fluidic devices that implement different assays have since been demonstrated. Research into the development of methodologies that control, and in particular delay the flow of fluids in these devices is an urgently needed requirement that would enable greater functionalities in such paper-based devices.In this work, to control fluid-flow, we report the use of a new approach that is based on the laser-based photo-polymerisation technique that we have reported earlier for the creation of fluidic patterns (channels/wells) in paper. The delay or slowing down, of the fluid-flow in a fluidic channel is achieved via the introduction of barriers aligned across the direction of the fluid-flow – in a fashion similar to how speed-bumps enable traffic-calming control on a road. The schematic in Figure 1a shows how the delay can be introduced via the creation/insertion of barriers which are solid and impermeable and by controlling the ‘depth’ of the solid/impregnable barriers (Figure 1) to allow for controlled leakage of the fluids under the barriers. The control over the depth of the barriers is obtained by simply adjusting the laser-writing parameters such as the output power and writing/scanning speed. We observe that solid/impregnable barriers of various depths decrease the fluid flow by a rate that is proportional to their depth. Having patterned these barriers at pre-defined locations in the fluidic channel, using a pulsed laser operating at 266nm (20Hz, 10ns) we have achieved flow-delays with a time span ranging from few minutes to over an hour. We have also performed a study to understand the influence of the number of barriers and their position on the flow-delay, and this is shown in Figure 2.Since the channels and flow-delay barriers can be written via a common laser-writing procedure, this technique has a distinct advantage over certain other methods that require specialist operating environments, or custom-designed equipment to enable both these aspects. We believe this rapid and versatile technique is therefore suited for fabrication of ‘sample-in-read-out’ type automated paper-based microfluidic devices that can implement single/multistep analytical assays
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