1,720,995 research outputs found
Differentiation of micro spheres by narrow angle scattered light detection on low cost PMMA micro flow cytometer chip
No full textTrends in microfluidic systems for in situ chemical analysis of natural waters
Full text linkSpatially and temporally detailed measurement of ocean, river and lake chemistry is key to fully understanding the biogeochemical processes at work within them. To obtain these valuable data, miniaturised in situ chemical analysers have recently become an attractive alternative to traditional manual sampling, with microfluidic technology at the forefront of recent advances. In this short critical review we discuss the role, operation and application of in situ microfluidic analysers to measure biogeochemical parameters in natural waters. We describe recent technical developments, most notably how pumping technology has evolved to allow long-term deployments, and describe how they have been deployed in real-world situations to yield detailed, scientifically useful data. Finally, we discuss the technical challenges that still remain and the key obstacles that must be negotiated if these promising systems are to be widely adopted and used, for example, in large environmental sensor networks and on low-power underwater vehicles
A novel, low-cost, high performance dissolved methane sensor for aqueous environments
No full textA new method for in-situ detection and measurement of
dissolved methane in aqueous media/environments with a limit of detection
of 0.2 nM (3?, and t90~110s) and range (1-300 nM) is presented. The
detection method is based on refractive index (RI) modulation of a modified
PolyDiMethylSiloxane (PDMS) layer incorporating molecules of
cryptophane-A [1] which have a selective and reversible affinity for
methane [2]. The refractive index is accurately determined using surface
plasmon resonance (SPR) [3]. A prototype sensor has been repeatedly
tested, using a dissolved gas calibration system under a range of temperature
and salinity regimes. Laboratory-based results show that the technique is
specific, sensitive, and reversible. The method is suitable for miniaturization
and incorporation into in situ sensor technology
Development of sensor technology to facilitate in-situ measurement of damage in composite materials for spacecraft applications
No full textSpacecraft inhabit an environment, which presents many hazards to their structural integrity and continued operation, and are intrinsically expensive to repair. Naturally-occurring micrometeoroids and debris from previous missions can both produce significant impact damage, particularly in advanced materials such as carbon-fiber-reinforced plastic (CFRP). A sensor capable of recording impact events, and measuring the extent of the damage caused, would therefore be a useful tool in minimizing the risks and cost of spacecraft operation. This paper considers the use of multiplexed optical fiber Bragg grating based sensors for use in this application. It is envisaged that sensors should be used to optimize replacement schedules and prevent service failure. The interrogation systems have been developed as collaborative research between the Optoelectronics Research Centre and the Department of Engineering Materials at the University of Southampton, also involving a number of external collaborators (including ESA, and, in the UK, the following: DERA, Sensor Dynamics, NERC, and DTI). We utilize superluminescent erbium doped fibers as the light source and an acousto-optic-tuneable filter (AOTF) as the wavelength-selective element. Our latest developments in interrogation technology result in the creation of a high speed, high-resolution multiplexed sensor. This technology shows promise for assessing impact damage caused by low, high and hypervelocity impacts. The potential for counting and characterization of impinging particles from strain sensor readings (both transient and residual) is discussed
Hyperbaric biofilms on engineering surfaces formed in the deep sea
No full textBiofouling is a major problem for long-term deployment of sensors in the marine environment. This study showed that significant biofilm formation occurred on a variety of artificial materials (glass, copper, Delrin™ and poly-methyl methacrylate [PMMA]) deployed for 10 days at a depth of 4700 m in the Cayman Trough. Biofilm surface coverage was used as an indicator of biomass. The lowest biofilm coverage was on copper and PMMA. Molecular analyses indicated that bacteria dominated the biofilms found on copper, Delrin™ and PMMA with 75, 55 and 73% coverage, respectively. Archea (66%) were dominant on the glass surface simulating interior sensor conditions, whereas Eukarya comprised the highest percentage of microflora (75%) on the glass simulating the exterior of sensors. Analysis of Denaturing Gradient Gel Electrophoresis profiles indicated that copper and Delrin™ shared the same community diversity, which was not the case for glass and PMMA, or between PMMA and copper/Delrin™. Sequence alignment matches belonged exclusively to uncultivable microorganisms, most of which were not further classified. One extracted sequence found on glass was associated with Cowellia sp., while another extracted from the PMMA surface was associated with a bacterium in the Alterominidaceae, both γ-proteobacteria. The results demonstrate the necessity of understanding biofilm formation in the deep sea and the potential need for mitigation strategies for any kind of long-term deployment of remote sensors in the marine environment
Characterization of meta-Cresol Purple for spectrophotometric pH measurements in saline and hypersaline media at sub-zero temperatures
No full textAccurate pH measurements in polar waters and sea ice brines require pH indicator dyes characterized at near-zero and below-zero temperatures and high salinities. We present experimentally determined physical and chemical characteristics of purified meta-Cresol Purple (mCP) pH indicator dye suitable for pH measurements in seawater and conservative seawater-derived brines at salinities (S) between 35 and 100 and temperatures (T) between their freezing point and 298.15 K (25 °C). Within this temperature and salinity range, using purified mCP and a novel thermostated spectrophotometric device, the pH on the total scale (pHT) can be calculated from direct measurements of the absorbance ratio R of the dye in natural samples aspHT=−log(kT2e2)+log(R−e11−Re3e2)Based on the mCP characterization in these extended conditions, the temperature and salinity dependence of the molar absorptivity ratios and − log(kT2e2)of purified mCP is described by the following functions: e1 = −0.004363 + 3.598 × 10−5T, e3/e2 = −0.016224 + 2.42851 × 10−4T + 5.05663 × 10−5(S − 35), and − log(kT2e2) = −319.8369 + 0.688159 S −0.00018374 S2 + (10508.724 − 32.9599 S + 0.059082S2) T−1 + (55.54253 − 0.101639 S) ln T −0.08112151T. This work takes the characterisation of mCP beyond the currently available ranges of 278.15 K ≤ T ≤ 308.15 K and 20 ≤ S ≤ 40 in natural seawater, thereby allowing high quality pHT measurements in polar systems
A novel portable filtration system for sampling and concentration of microorganisms: Demonstration on marine microalgae with subsequent quantification using IC-NASBA
Full text linkThis paper presents a novel portable sample filtration/concentration system, designed for use on samples of microorganisms with very low cell concentrations and large volumes, such as water-borne parasites, pathogens associated with faecal matter, or toxic phytoplankton. The example application used for demonstration was the in-field collection and concentration of microalgae from seawater samples. This type of organism is responsible for Harmful Algal Blooms (HABs), an example of which is commonly referred to as “red tides”, which are typically the result of rapid proliferation and high biomass accumulation of harmful microalgal species in the water column or at the sea surface. For instance, Karenia brevis red tides are the cause of aquatic organism mortality and persistent blooms may cause widespread die-offs of populations of other organisms including vertebrates. In order to respond to, and adequately manage HABs, monitoring of toxic microalgae is required and large-volume sample concentrators would be a useful tool for in situ monitoring of HABs. The filtering system presented in this work enables consistent sample collection and concentration from 1 L to 1 mL in five minutes, allowing for subsequent benchtop sample extraction and analysis using molecular methods such as NASBA and IC-NASBA. The microalga Tetraselmis suecica was successfully detected at concentrations ranging from 2 × 105 cells/L to 20 cells/L. Karenia brevis was also detected and quantified at concentrations between 10 cells/L and 106 cells/L. Further analysis showed that the filter system, which concentrates cells from very large volumes with consequently more reliable sampling, produced samples that were more consistent than the independent non-filtered samples (benchtop controls), with a logarithmic dependency on increasing cell numbers. This filtering system provides simple, rapid, and consistent sample collection and concentration for further analysis, and could be applied to a wide range of different samples and target organisms in situations lacking laboratories
Autonomous reagent-based microfluidic pH sensor platform
Full text linkA portable sensor has been developed for in situ measurements of pH within aqueous environments.The sensor design incorporates microfluidic technology, allowing for the use of low volume of samples and reagents, and an integrated low cost detection system that uses a light emitting diode as light source and a photodiode as the detector. Different combination of dyes has been studied in order to allow for a broader pH detection range, than can be obtained using a single dye. The optimum pH range for this particular dye combination was found to be between pH 4 and pH 9.The reagents developed for pH measurement were first tested using bench-top instrumentation and once optimised, the selected formulation was then implemented in the microfluidic system.The prototype system has been characterised in terms of pH response, linear range, reproducibility and stability. Results obtained using the prototype system are in good agreement with those obtained using reference instrumentation, i.e. a glass electrode/pH meter and analysis via spectrophotometer based assays.The reagent (mixture #3) is shown to be stable for over 8 months, which is important for long term deployments. A high reproducibility is reported with a global RSD of ?1.8% across measurements of 90 samples, i.e. with respect to concentrations reported by a calibrated pH meter.A series of real water samples from multiple sources were also analysed using the portable sensor system, of which the global error found was 3.84% showing its feasibility for real-world applications
The anti-bacterial effect of an electrochemical anti-fouling method intended for the protection of miniaturised oceanographic sensors
No full textAn electrochemical anti-fouling method, based upon the generation of chlorine from seawater, was applied to a proprietary design of Lab on a Chip conductivity, temperature and dissolved oxygen sensor. The method was evaluated using PCR after a six-week field trial in which it significantly reduced the burden of bacterial biofouling
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