1,720,987 research outputs found
Characterisation of an irreversible bonding process for COC–COC and COC–PDMS–COC sandwich structures and application to microvalves
No full textA novel technique for bonding heterogeneous cyclic olefin co-polymer (COC) to a thin poly(dimethylsiloxane) (PDMS) membrane is described. This improved bonding technique successfully achieved precise, well-controlled, low temperature bonding of microfluidic channels. Microchannel and fluid control patterns were embossed on a COC substrate by hot embossing technique first. The method uses aminopropyltriethoxysilane (APTES) and 3-glycidoxypropyltrimethoxysilane (GPTMS) in combination to create an irreversible bond between the two materials. The change in surface properties and the influence of different surface chemical groups on surface adhesion properties has been characterised by contact angle, surface energy measurements, scanning electron microscopy (SEM), and atomic force microscopy (AFM), revealing a change in morphology and surface roughness. A lower wettability was also observed along with a reduced hydrophobic recovery of the surfaces. Bonding efficiency of the devices was evaluated by interface evaluation of cross-sectioning, peel off tests and leak tests. In addition, the performance of the bonds achieved after different surface treatments has been compared showing that this technique results in a higher burst pressures than methods applying only oxygen plasma or APTES. Using optimised bonding conditions a robust, effective microvalve made from a PDMS membrane was fabricated and successful valve closing or opening are shown. Because of advantages of facile fabrication, low cost and biocompatibility, this hybrid device can be pave the way in many applications such as fluidic manipulation in portable and disposable microfluidic devices
A Simple, Low-Cost Double Beam Spectrophotometer for Colorimetric Detection of Nitrite in Seawater
No full textThis paper reports on the optical detection system of a prototype nitrite sensor for seawater analysis. The sensor uses a colorimetric Griess reaction that produces an Azo dye with an absorption peak at 540 nm. A simple low-cost double beam spectrophotometer using a green light emitting diode (LED) light source, two integrated photo detectors and lock-in detection is described. A log-ratio amplifier is used to produce an output proportional to absorbance. The optical devices were mounted in a cast resin block to prevent shock and vibration. Experimental results show the detection system has a limit of detection of 0.1 µM
Development and first results of a new fast response microelectrode DO-sensor
No full textA new dissolved oxygen sensor for marine application was developed and first tests in the field were carried out. The sensor uses a micro-electrode as the sensing element that has an inherently fast response and an increased resistance to biofouling due to the properties of the electrode material, platinum, and the employed operation repime.Introduction of a cleaning cycle, where the potential applied to the electrode is altered, allows the elimination of material building up at the electrode surface as well as the reconditioning of the electrode surface, thus minimizing drift and the effect of bio-fouling.Micmdisc electrodes ranging between 10 and SO pm diameter have been tested. The sensor has been adapted to operate on a CTD system or on towed instrument platforms. Results of test cruises will be presented
An assessment of deep hot-water drilling as a means to undertake direct measurement and sampling of Antarctic subglacial lakes: experience and lessons learned from the Lake Ellsworth field season 2012/13
Full text linkIn the early hours of 25 December 2012, an attempt to explore Subglacial Lake Ellsworth, West Antarctica, using a specially designed hot-water drill, was halted. This UK project, involving several universities, the British Antarctic Survey and the National Oceanography Centre, had been in planning for 10 years. The project developed a full blueprint for subglacial lakes research, involving access to the subglacial environment through deep drilling, direct measurement and sampling of water and sediment by the construction of a probe and sediment corer, and environmental protocols to ensurecleanliness in line with international agreements on stewardship and protection of subglacial systems. Drilling was ceased after the main borehole failed to link with a subsurface cavity of water, built up over ~40 hours. Without this link, insufficient water was available to continue drilling downwards to the lake, ~3000m beneath the surface. On return to the UK, an external review of the programme was undertaken to formally assess the reasons for the fieldwork failure, and to make recommendations on the modifications necessary for success. From this review, the Lake Ellsworth programme formulated a pathway along which a second attempt to explore the lake can be developed. Here details of the Lake Ellsworth field experiment, the circumstances that led to its failure and the corrections required are presented. Hot-water drilling is still regarded as the only feasible scheme for assuring clean access to the subglacial environment. The lessons learned from the Lake Ellsworth experience are substantial, however, and demonstrate that considerable technological and methodological advances are necessary for successful future research on subglacial lakes beneath thick (>2 km) ice
Development and application of a microfluidic in-situ analyzer for dissolved Fe and Mn in natural waters
No full textThe redox sensitive trace metals iron and manganese are two important elements that help shape the biogeochemistry of aquatic systems and thus their measurement is important. Current laboratory methods are expensive, time consuming and cannot provide the spatial and temporal resolution needed to characterize these elements in natural waters. Here we describe the first autonomous analyzer capable of providing vertical profiles as well as routine in-situ determinations of dissolved Fe(II) and Mn in aquatic environments. The spectrophotometric sensor uses microfluidic methods (Lab-on-a-chip technology) and mixes reagents and samples using a novel in-cell diffusion process. Fe(II) and Mn can be measured with a frequency of up to 12 and 6 samples per hour respectively with limits of detection of 27 nM for Fe(II), 2.1% precision (n=20), and 28 nM for Mn, 2.4% precision (n=19). The device combines relatively low cost, low power usage, low reagent consumption, portability, and tolerance to pressures up to at least 170 bars, with high precision and accuracy. We present data from a successful demonstration of the sensor during a cruise to the Gotland and Landsort Deep Basins of the Baltic Sea
Development of a colorimetric microfluidic pH sensor for autonomous seawater measurements
No full textHigh quality carbonate chemistry measurements are required in order to fully understand the dynamics of the oceanic carbonate system. Seawater pH data with good spatial and temporal coverage are particularly critical to apprehend ocean acidification phenomena and their consequences. There is a growing need for autonomous in situ instruments that measure pH on remote platforms. Our aim is to develop an accurate and precise autonomous in situ pH sensor for long term deployment on remote platforms. The widely used spectrophotometric pH technique is capable of the required high-quality measurements. We report a key step towards the miniaturization of a colorimetric pH sensor with the successful implementation of a simple microfluidic design with low reagent consumption. The system is particularly adapted to shipboard deployment: high quality data was obtained over a period of more than a month during a shipboard deployment in northwest European shelf waters, and less than 30 mL of indicator was consumed. The system featured a short term precision of 0.001 pH (n = 20) and an accuracy within the range of a certified Tris buffer (0.004 pH). The quality of the pH system measurements have been checked using various approaches: measurements of certified Tris buffer, measurement of certified seawater for DIC and TA, comparison of measured pH against calculated pH from pCO2, DIC and TA during the cruise in northwest European shelf waters. All showed that our measurements were of high quality. The measurements were made close to in situ temperature (+0.2 ̊C) in a sampling chamber which had a continuous flow of the ship’s underway seawater supply. The optical set up was robust and relatively small due to the use of an USB mini-spectrometer, a custom made polymeric flow cell and an LED light source. The use of a three wavelength LED with detection that integrated power across the whole of each LED output spectrum indicated that low wavelength resolution detectors can be used instead of the current USB mini spectrophotometer. Artefacts due to the polychromatic light source and inhomogeneity in the absorption cell are shown to have a negligible impact on the data quality. The next step in the miniaturization of the sensor will be the incorporation of a photodiode as detector to replace the spectrophotometer
Clean subglacial access: prospects for future deep hot-water drilling
Full text linkAccessing and sampling subglacial environments deep beneath the Antarctic Ice Sheet presents several challenges to existing drilling technologies. With over half of the ice sheet believed to be resting on a wet bed, drilling down to this environment must conform to international agreements on environmental stewardship and protection, making clean hot-water drilling the most viable option. Such a drill, and its water recovery system, must be capable of accessing significantly greater ice depths than previous hot-water drills, and remain fully operational after connecting with the basal hydrological system. The Subglacial Lake Ellsworth (SLE) project developed a comprehensive plan for deep (greater than 3000?m) subglacial lake research, involving the design and development of a clean deep-ice hot-water drill. However, during fieldwork in December 2012 drilling was halted after a succession of equipment issues culminated in a failure to link with a subsurface cavity and abandonment of the access holes. The lessons learned from this experience are presented here. Combining knowledge gained from these lessons with experience from other hot-water drilling programmes, and recent field testing, we describe the most viable technical options and operational procedures for future clean entry into SLE and other deep subglacial access targets.<br/
Chemical sensors for in situ data collection in the cryosphere
Full text linkGlaciers and ice sheets are recognised as important components of global biogeochemical cycles. Chemical sensors have great potential for in situ monitoring in the cryosphere and are available for many analytes of interest, but they are frequently unsuitable for deployment since meltwaters are cold, turbid, experience freeze-thaw cycles and display low ionic strength and concentrations of target analytes. Here, we review in situ chemical sensors currently available for measurement of biogeochemically important analytes and assess their suitability for deployment. These include standard parameters such as dissolved oxygen and pH, along with macronutrients (nitrate/nitrite and phosphate), micronutrients (iron and manganese) and biogenic gases (methane). Where no commercial alternatives are available, we discuss sensors currently in development, and their applicability to these extreme environments. The information presented has great relevance for future science in polar environments, and for the ultimate goal of obtaining in situ data from extreme, inaccessible subglacial environments
Field assessment of a new membrane-free microelectrode dissolved oxygen sensor for water column profiling
No full textThis article reports on the field trials of a membrane-free amperometric microelectrode dissolved oxygen sensor, which were performed during oceanographic cruise D279 of RRS Discovery. The sensor was used to obtain full depth oxygen profiles while mounted on a wire-operated CTD (conductivity, temperature, depth) instrument. A stable performance was achieved by carefully designed electrochemical cleaning conditions of the sensing platinum microdisk cathode. The flow issues inherent to moving probes were resolved by a novel stop-flow cell fitted with a pumping system for sample exchange and flow control. The details of the sensor operation, calibration, and construction, including the flow control system, are described. The sensor response is validated by calibration and by an analytical approach that yields oxygen data directly from the current readings. The accuracy of the microelectrode response is critically assessed using Winkler titrations on bottle samples taken during the relevant sensor deployments. The results lead to the conclusion that due to high accuracy, fast response time, and lack of membrane-related problems the device is particularly suitable for moving probes and high spatial resolution water column oxygen profiling
A Novel Integration of an Ultraviolet Nitrate Sensor On Board a Towed Vehicle for Mapping Open-Ocean Submesoscale Nitrate Variability
No full textInitial results from a deployment of the SUV-6 ultraviolet spectrophotometer, integrated with the SeaSoar towed vehicle, are presented. The innovative, combined system measures nitrate concentration at high spatial resolution (4 m vertically, 5 km horizontally), high sensitivity (0.2 ?M), and concomitantly with temperature, salinity, and dissolved oxygen. The authors demonstrate that this approach constitutes a powerful new tool for quantifying the role of mesoscale and submesoscale vertical nutrient fluxes to the euphotic zone, using measurements from a high-resolution survey of an eddy dipole in the Iceland Basin during the summer of 2007
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