Trends in microfluidic systems for in situ chemical analysis of natural waters

Spatially 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

Procedures to Improve Sensor Data Quality

The oceans play an important role in aspects of global sustainability, including climate change, food security and human health. Because of its vast dimensions, internal complexity, and limited accessibility, efficient monitoring and predicting of the ocean forms a collaborative effort of regional and global scale. A key requirement for ocean observing is the need to follow well-defined approaches. Summarized under “Ocean Best Practices” (OBP) are all aspects of ocean observing that require proper and agreed-on documentation, from manuals and standard operating procedures for sensors, strategies for structuring observing systems and associated products, to ethical and governance aspects when executing ocean observing. In Task 6.2 we have developed new tools, and organized workshops with outcomes of Best Practice manuals and scientific publications. The focus has been on improving accuracy of trace element measurements in seawater and also of marine omics analysis, and enhancing reliability, interoperability and quality of sensor measurements for dissolved oxygen, nutrients and carbonate chemistry measurements

Autonomous reagent-based microfluidic pH sensor platform

A 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

Realistic measurement uncertainties for marine macronutrient measurements conducted using gas segmented flow and Lab-on-Chip techniques

Highlights • Accounting for systematic bias is required for a realistic analytical uncertainty • Gas segmented flow techniques achieved a combined uncertainties of 1-4 % • Lab-on-Chip nitrate + nitrite analysers achieved a combined uncertainties < 5% Abstract Accurate and precise measurements of marine macronutrient concentrations are fundamental to our understanding of biogeochemical cycles in the ocean. Quantifying the measurement uncertainty associated with macronutrient measurements remains a challenge. Large systematic biases (up to 10 %) have been identified between datasets, restricting the ability of marine biogeochemists to distinguish between the effects of environmental processes and analytical uncertainty. In this study we combine the routine analyses of certified reference materials (CRMs) with the application of a simple statistical technique to quantify the combined (random + systematic) measurement uncertainty associated with marine macronutrient measurements using gas segmented flow techniques. We demonstrate that it is realistic to achieve combined uncertainties of ~1-4 % for nitrate + nitrite (ΣNOx), phosphate (PO43-) and silicic acid (Si(OH)4) measurements. This approach requires only the routine analyses of CRMs (i.e. it does not require inter-comparison exercises). As CRMs for marine macronutrients are now commercially available, it is advocated that this simple approach can improve the comparability of marine macronutrient datasets and therefore should be adopted as ‘best practice’. Novel autonomous Lab-on-Chip (LoC) technology is currently maturing to a point where it will soon become part of the marine chemist’s standard analytical toolkit used to determine marine macronutrient concentrations. Therefore, it is critical that a complete understanding of the measurement uncertainty of data produced by LoC analysers is achieved. In this study we analysed CRMs using 7 different LoC ΣNOx analysers to estimate a combined measurement uncertainty of < 5%. This demonstrates that with high quality manufacturing and laboratory practices, LoC analysers routinely produce high quality measurements of marine macronutrient concentrations

Exploring ocean biogeochemistry using a lab-on-chip phosphate analyser on an underwater glider

The ability to make measurements of phosphate (PO43–) concentrations at temporal and spatial scales beyond those offered by shipboard observations offers new opportunities for investigations of the marine phosphorus cycle. We here report the first in situ PO43– dataset from an underwater glider (Kongsberg Seaglider) equipped with a PO43– Lab-on-Chip (LoC) analyser. Over 44 days, a 120 km transect was conducted in the northern North Sea during late summer (August and September). Surface depletion of PO43– (<0.2 μM) was observed above a seasonal thermocline, with elevated, but variable concentrations within the bottom layer (0.30–0.65 μM). Part of the variability in the bottom layer is attributed to the regional circulation and across shelf exchange, with the highest PO43– concentrations being associated with elevated salinities in northernmost regions, consistent with nutrient rich North Atlantic water intruding onto the shelf. Our study represents a significant step forward in autonomous underwater vehicle sensor capabilities and presents new capability to extend research into the marine phosphorous cycle and, when combined with other recent LoC developments, nutrient stoichiometry

Lab-on-chip for in situ analysis of nutrients in the deep sea

Microfluidic reagent-based nutrient sensors offer a promising technology to address the global undersampling of ocean chemistry but have so far not been shown to operate in the deep sea (>200 m). We report a new family of miniaturized lab-on-chip (LOC) colorimetric analyzers making in situ nitrate and phosphate measurements from the surface ocean to the deep sea (>4800 m). This new technology gives users a new low-cost, high-performance tool for measuring chemistry in hyperbaric environments. Using a combination of laboratory verification and field-based tests, we demonstrate that the analyzers are capable of in situ measurements during profiling that are comparable to laboratory-based analyses. The sensors feature a novel and efficient inertial-flow mixer that increases the mixing efficiency and reduces the back pressure and flushing time compared to a previously used serpentine mixing channel. Four separate replicate units of the nitrate and phosphate sensor were calibrated in the laboratory and showed an average limit of detection of 0.03 μM for nitrate and 0.016 μM for phosphate. Three on-chip optical absorption cell lengths provide a large linear range (to >750 μM (10.5 mg/L-N) for nitrate and >15 μM (0.47 mg/L-P) for phosphate), making the instruments suitable for typical concentrations in both ocean and freshwater aquatic environments. The LOC systems automatically collected a series of deep-sea nitrate and phosphate profiles in the northeast Atlantic while attached to a conductivity temperature depth (CTD) rosette, and the LOC nitrate sensor was attached to a PROVOR profiling float to conduct automated nitrate profiles in the Mediterranean Sea

Greenland melt drives continuous export of methane from the ice-sheet bed

Ice sheets are currently ignored in global methane budgets1,2. Although ice sheets have been proposed to contain large reserves of methane that may contribute to a rise in atmospheric methane concentration if released during periods of rapid ice retreat3,4, no data exist on the current methane footprint of ice sheets. Here we find that subglacially produced methane is rapidly driven to the ice margin by the efficient drainage system of a subglacial catchment of the Greenland ice sheet. We report the continuous export of methane-supersaturated waters (CH4(aq)) from the ice-sheet bed during the melt season. Pulses of high CH4(aq) concentration coincide with supraglacially forced subglacial flushing events, confirming a subglacial source and highlighting the influence of melt on methane export. Sustained methane fluxes over the melt season are indicative of subglacial methane reserves that exceed methane export, with an estimated 6.3 tonnes (discharge-weighted mean; range from 2.4 to 11 tonnes) of CH4(aq) transported laterally from the ice-sheet bed. Stable-isotope analyses reveal a microbial origin for methane, probably from a mixture of inorganic and ancient organic carbon buried beneath the ice. We show that subglacial hydrology is crucial for controlling methane fluxes from the ice sheet, with efficient drainage limiting the extent of methane oxidation5 to about 17 per cent of methane exported. Atmospheric evasion is the main methane sink once runoff reaches the ice margin, with estimated diffusive fluxes (4.4 to 28 millimoles of CH4 per square metre per day) rivalling that of major world rivers6. Overall, our results indicate that ice sheets overlie extensive, biologically active methanogenic wetlands and that high rates of methane export to the atmosphere can occur via efficient subglacial drainage pathways. Our findings suggest that such environments have been previously underappreciated and should be considered in Earth’s methane budget

Assuring the integrity of offshore carbon dioxide storage

Carbon capture and storage is a key mitigation strategy proposed for keeping the global temperature rise below 1.5 °C. Offshore storage can provide up to 13% of the global CO2 reduction required to achieve the Intergovernmental Panel on Climate Change goals. The public must be assured that potential leakages from storage reservoirs can be detected and that therefore the CO2 is safely contained. We conducted a controlled release of 675 kg CO2 within sediments at 120 m water depth, to simulate a leak and test novel detection, quantification and attribution approaches. We show that even at a very low release rate (6 kg day−1), CO2 can be detected within sediments and in the water column. Alongside detection we show the fluxes of both dissolved and gaseous CO2 can be quantified. The CO2 source was verified using natural and added tracers. The experiment demonstrates that existing technologies and techniques can detect, attribute and quantify any escape of CO2 from sub-seabed reservoirs as required for public assurance, regulatory oversight and emissions trading schemes

Toward the Integrated Marine Debris Observing System

Plastics and other artificial materials pose new risks to the health of the ocean. Anthropogenic debris travels across large distances and is ubiquitous in the water and on shorelines, yet, observations of its sources, composition, pathways, and distributions in the ocean are very sparse and inaccurate. Total amounts of plastics and other man-made debris in the ocean and on the shore, temporal trends in these amounts under exponentially increasing production, as well as degradation processes, vertical fluxes, and time scales are largely unknown. Present ocean circulation models are not able to accurately simulate drift of debris because of its complex hydrodynamics. In this paper we discuss the structure of the future integrated marine debris observing system (IMDOS)thatisrequiredtoprovidelong-termmonitoringofthestateofthisanthropogenic pollution and support operational activities to mitigate impacts on the ecosystem and on the safety of maritime activity. The proposed observing system integrates remote sensing and in situ observations. Also, models are used to optimize the design of the system and, in turn, they will be gradually improved using the products of the system. Remote sensing technologies will provide spatially coherent coverage and consistent surveying time series at local to global scale. Optical sensors, including high-resolution imaging, multi- and hyperspectral, fluorescence, and Raman technologies, as well as SAR will be used to measure different types of debris. They will be implemented in a variety of platforms, from hand-held tools to ship-, buoy-, aircraft-, and satellite-based sensors. A network of in situ observations, including reports from volunteers, citizen scientists and ships of opportunity, will be developed to provide data for calibration/validation of remote sensors and to monitor the spread of plastic pollution and other marine debris. IMDOS will interact with other observing systems monitoring physical, chemical, and biological processes in the ocean and on shorelines as well as the state of the ecosystem, maritime activities and safety, drift of sea ice, etc. The synthesized data will support innovative multi-disciplinary research and serve a diverse community of users

Randomised controlled trial of the short-term effects of OROS-methylphenidate on ADHD symptoms and behavioural outcomes in young male prisoners with attention-deficit/hyperactivity disorder (CIAO-II)

Background Attention-deficit/hyperactivity disorder (ADHD) is a highly prevalent disorder, seen in 20–30% of young adult prisoners. Pharmacoepidemiological studies, a small randomised controlled trial and open trial data of methylphenidate suggest clinically significant reductions in ADHD symptoms, emotional dysregulation, disruptive behaviour and increased engagement with educational activities. Yet, routine treatment of ADHD in offenders is not yet established clinical practice. There is continued uncertainty about the clinical response to methylphenidate (MPH), a first-line treatment for ADHD, in offenders, who often present with an array of complex mental health problems that may be better explained by states of inattentive, overactive, restless and impulsive behaviours. To address this problem, we will conduct an efficacy trial to establish the short-term effects of osmotic-controlled release oral delivery system (OROS)-methylphenidate (Concerta XL), an extended release formulation of MPH, on ADHD symptoms, emotional dysregulation and behaviour. Methods This study is a parallel-arm, randomised, placebo-controlled trial of OROS-MPH on ADHD symptoms, behaviour and functional outcomes in young male prisoners aged 16–25, meeting Diagnostic and Statistical Manual of Mental Disorders, fifth edition criteria for ADHD. Participants are randomised to 8 weeks of treatment with OROS-MPH or placebo, titrated over 5 weeks to balance ADHD symptom improvement against side effects. Two hundred participants will be recruited with a 1:1 ratio of drug to placebo. The primary outcome is change in level of ADHD symptoms after 8 weeks of trial medication. Discussion Potential benefits include improvement in ADHD symptoms, emotional dysregulation, attitudes towards violence and critical incidents and increased engagement with educational and rehabilitation programmes. Demonstrating the efficacy and safety of MPH on ADHD symptoms and associated impairments may provide the data needed to develop effective healthcare pathways for a significant group of young offenders. Establishing efficacy of MPH in this population will provide the foundation needed to establish long-term effectiveness studies with the potential for demonstrating significant reductions in criminal behaviour and improved health-economic outcomes