Wearable Platform for Real-time Monitoring of Sodium in Sweat.

A fully integrated and wearable platform for harvesting and analysing sweat sodium concentration in real time during exercise has been developed and tested. The platform was largely produced using 3D printing, which greatly simplifies fabrication and operation compared to previous versions generated with traditional production techniques. The 3D printed platform doubles the capacity of the sample storage reservoir to about 1.3 ml, reduces the assembly time and provides simple and precise component alignment and contact of the integrated solid-state ion-selective and reference electrodes with the sorbent material. The sampling flowrate in the device can be controlled by introducing threads to enhance wicking of sweat from the skin, across the electrodes to the storage area. The platform was characterised in the lab and in exercise trials over a period of about 60 minutes continuous monitoring. Sweat sodium concentration was found to rise initially to approximately 17 mM and decline gradually over the period of the trial to about 11-12 mM.

Combining Remote Temperature Sensing with in-Situ Sensing to Track Marine/Freshwater Mixing Dynamics.

The ability to track the dynamics of processes in natural water bodies on a global scale, and at a resolution that enables highly localised behaviour to be visualized, is an ideal scenario for understanding how local events can influence the global environment. While advances in in-situ chem/bio-sensing continue to be reported, costs and reliability issues still inhibit the implementation of large-scale deployments. In contrast, physical parameters like surface temperature can be tracked on a global scale using satellite remote sensing, and locally at high resolution via flyovers and drones using multi-spectral imaging. In this study, we show how a much more complete picture of submarine and intertidal groundwater discharge patterns in Kinvara Bay, Galway can be achieved using a fusion of data collected from the Earth Observation satellite (Landsat 8), small aircraft and in-situ sensors. Over the course of the four-day field campaign, over 65,000 in-situ temperatures, salinity and nutrient measurements were collected in parallel with high-resolution thermal imaging from aircraft flyovers. The processed in-situ data show highly correlated patterns between temperature and salinity at the southern end of the bay where freshwater springs can be identified at low tide. Salinity values range from 1 to 2 ppt at the southern end of the bay to 30 ppt at the mouth of the bay, indicating the presence of a freshwater wedge. The data clearly show that temperature differences can be used to track the dynamics of freshwater and seawater mixing in the inner bay region. This outcome suggests that combining the tremendous spatial density and wide geographical reach of remote temperature sensing (using drones, flyovers and satellites) with ground-truthing via appropriately located in-situ sensors (temperature, salinity, chemical, and biological) can produce a much more complete and accurate picture of the water dynamics than each modality used in isolation.

Normal-phase high-performance counter-current chromatography for the fractionation of dissolved organic matter from a freshwater source.

Normal-phase high-performance counter-current chromatography (HPCCC) is used to obtain a preliminary fractionation of components in dissolved organic matter (DOM) from a freshwater source. The HPCCC solvent system involved a normal-phase approach with water/methanol (1:1) as the lower stationary phase and hexane/ethyl acetate (1:1) as the upper mobile phase. The critical experiment parameters were optimised: revolution speed 1800 rpm and flow rate 0.15 mL/min. Under these conditions 50 µL of a 0.50 mg/mL DOM solution was loaded. The detection wavelength was monitored at 330 nm in order to isolate the main portion of DOM, which includes substances such as carboxyl-rich alicyclic molecules. By optimising this system it was possible to isolate materials that, according to GC-MS, can be related to molecules with an analogous structural background. Where fraction analysis was not suitable for GC-MS, RP-HPLC with UV absorbance detection was used, showing unique chromatograms for each fraction at both 210 and 330 nm.

Geochemical properties of blue carbon sediments through an elevation gradient: study of an anthropogenically impacted coastal lagoon.

Global research is showing that coastal blue carbon ecosystems are vulnerable to climate change driven threats including accelerated sea-level rise and prolonged periods of drought. Furthermore, direct anthropogenic impacts present immediate threats through deterioration of coastal water quality, land reclamation, long-term impact to sediment biogeochemical cycling. These threats will invariably alter the future efficacy of carbon (C) sequestration processes and it is imperative that currently existing blue carbon habitats be protected. Knowledge of underlying biogeochemical, physical and hydrological interactions occurring in functioning blue carbon habitats is essential for developing strategies to mitigate threats, and promote conditions to optimise C sequestration/storage. In this current work, we investigated how sediment geochemistry (0-10 cm depth) responds to elevation, an edaphic factor driven by long-term hydrological regimes consequently exerting control over particle sedimentation rates and vegetation succession. This study was performed in an anthropogenically impacted blue carbon habitat along a coastal ecotone encompassing an elevation gradient transect from intertidal sediments (un-vegetated and covered daily by tidal water), through vegetated salt marsh sediments (periodically covered by spring tides and flooding events), on Bull Island, Dublin Bay. We determined the quantity and distributions of bulk geochemical characteristics in sediments through the elevation gradient, including total organic carbon (TOC), total nitrogen (TN), total metals, silt, clay, and also, 16 individual polyaromatic hydrocarbon's (PAH's) as an indication of anthropogenic input. Elevation measurements for sample sites were determined on this gradient using a LiDAR scanner accompanied by an IGI inertial measurement unit (IMU) on board a light aircraft. Considering the gradient from the Tidal mud zone (T), through the low-mid marsh (M) to the most elevated upper marsh (H), there were significant differences between all zones for many measured environmental variables. The results of significance testing using Kruskal-Wallis analysis revealed, that %C, %N, PAH (µg/g), Mn (mg/kg), TOC:NH4 + and pH are significantly different between all zones on the elevation gradient. The highest values for all these variables exists (excluding pH which followed a reverse trend) in zone H, decreasing in zone M and lowest in the un-vegetated zone T. TC content is 16 fold higher overall in vegetated (3.43 -21.84%) than uninhabited (0.21-0.56%) sediments. TN was over 50 times higher (0.24-1.76%), more specifically increasing in % mass on approach to the upper salt marsh with distance from the tidal flats sediments zone T (0.002-0.05%). Clay and silt distributions were greatest in vegetated sediments, increasing in % content towards upper marsh zones The retention of water, metals, PAHs, mud, chloride ions, NH4 +, PO4 3- and SO4 2- increased with elevated C concentrations, concurrently where pH significantly decreased. Sediments were categorized with respect to PAH contamination where all SM samples were placed in the high polluted category. The results highlight the ability of Blue C sediments to immobilise increasing levels of C, N, and metals, and PAH with over time and with both lateral and vertical expansion. This study provides a valuable data set for an anthropogenically impacted blue carbon habitat predicted to suffer from sea-level rise and exponential urban development. Graphical abstract: Summarized results from this study demonstrating the geochemical changes through an elevation gradient, with a transect encompassing intertidal sediments through supratidal salt marsh sediments within Bull Island's blue carbon lagoon zones. Supplementary Information: The online version contains supplementary material available at 10.1007/s10533-022-00974-0.

Biogeochemical properties of blue carbon sediments influence the distribution and monomer composition of bacterial polyhydroxyalkanoates (PHA).

Coastal wetlands are highly efficient 'blue carbon' sinks which contribute to mitigating climate change through the long-term removal of atmospheric CO2 and capture of carbon (C). Microorganisms are integral to C sequestration in blue carbon sediments and face a myriad of natural and anthropogenic pressures yet their adaptive responses are poorly understood. One such response in bacteria is the alteration of biomass lipids, specifically through the accumulation of polyhydroxyalkanoates (PHAs) and alteration of membrane phospholipid fatty acids (PLFA). PHAs are highly reduced bacterial storage polymers that increase bacterial fitness in changing environments. In this study, we investigated the distribution of microbial PHA, PLFA profiles, community structure and response to changes in sediment geochemistry along an elevation gradient from intertidal to vegetated supratidal sediments. We found highest PHA accumulation, monomer diversity and expression of lipid stress indices in elevated and vegetated sediments where C, nitrogen (N), PAH and heavy metals increased, and pH was significantly lower. This was accompanied by a reduction in bacterial diversity and a shift to higher abundances of microbial community members favouring complex C degradation. Results presented here describe a connection between bacterial PHA accumulation, membrane lipid adaptation, microbial community composition and polluted C rich sediments. Graphical Abstract: Geochemical, microbiological and polyhydroxyalkanoate (PHA) gradient in a blue carbon zone. Supplementary Information: The online version contains supplementary material available at 10.1007/s10533-022-01008-5.

A wearable sensor for the detection of sodium and potassium in human sweat during exercise.

The SwEatch platform, a wearable sensor for sampling and measuring the concentration of electrolytes in human sweat in real time, has been improved in order to allow the sensing of two analytes. The solid contact ion-sensitive electrodes (ISEs) for the detection of Na+ and K+ have been developed in two alternative formulations, containing either poly(3,4-ethylenedioxythiophene) (PEDOT) or poly(3-octylthiophene-2,5-diyl) (POT) as a conductive polymer transducing component. The solution-processable POT formulation simplifies the fabrication process, and sensor to sensor reproducibility has been improved via partial automation using an Opentron® automated pipetting robot. The resulting electrodes showed good sensitivity (52.4 ± 6.3 mV/decade (PEDOT) and 56.4 ± 2.2 mV/decade (POT) for Na+ ISEs, and 45.7 ± 7.4 mV/decade (PEDOT) and 54.3 ± 1.5 mV/decade (POT) for K+) and excellent selectivity towards potential interferents present in human sweat (H+, Na+, K+, Mg2+, Ca2+). The 3D printed SwEatch platform has been redesigned to incorporate a double, mirrored fluidic unit which is capable of drawing sweat from the skin through passive capillary action and bring it in contact with two independent electrodes. The potentiometric signal generated by the electrodes is measured by an integrated electronics board, digitised and transmitted via Bluetooth to a laptop. The results obtained from on-body trials on athletes during cycling show a relatively small increase in sodium (1.89 mM-2.97 mM) and potassium (3.31 mM-7.25 mM) concentrations during the exercise period of up to 90 min.

Fabrication of Rugged and Reliable Fluidic Chips for Autonomous Environmental Analyzers Using Combined Thermal and Pressure Bonding of Polymethyl Methacrylate Layers.

The fabrication of highly reliable and rugged fluidic chips designed for use in autonomous analyses for nutrient monitoring is described. The chips are based on a two-layer configuration with the fluidic channels produced in one layer using precision micromilling. The second capping layer contains through holes for sample/standard and reagent addition and waste removal post-analysis. Two optically clear polymethyl methacrylate (PMMA) windows are integrated into the opaque PMMA chip, orthogonal to a 22.5 mm-long section of the channel downstream from a serpentine reagent and sample/standard mixing region. An LED source is coupled into the channel through one of the windows, and the light intensity is monitored with a photodiode located at the distal end of the channel outside the second optically clear window. Efficient coupling of the source through the channel to the detector is achieved using custom-designed alignment units produced using 3D printing. In contrast to fluidic chips produced using solvent adhesion, the thermal-/pressure-bonded simplified method presented removes the need for surface treatment. Optimization of the thermal/pressure conditions leads to very strong adhesion between the PMMA layers, requiring forces in the region of 2000 N to separate them, which is necessary for the use in long-term deployments. Profilometry imaging shows minimal evidence of channel distortion after bonding. Finally, we show the potential of these techniques for environmental applications. The fluidic chips were integrated into prototype nutrient analyzers that display no evidence of leakage in extensive lab tests involving 2500 phosphate measurements using the yellow (vanadomolybdophosphoric acid) method. Similarly, excellent analytical performance (LOD is 0.09 µM) is reported for a 28-day field trial comprising 188 in situ autonomous phosphate measurements (564 measurements) in total including calibration.

Low cost 235 nm ultra-violet light-emitting diode-based absorbance detector for application in a portable ion chromatography system for nitrite and nitrate monitoring.

A low cost, UV absorbance detector incorporating a 235 nm light emitting diode (LED) for portable ion chromatography has been designed and fabricated to achieve rapid, selective detection of nitrite and nitrate in natural waters. The optical cell was fabricated through micromilling and solvent vapour bonding of two layers of poly (methyl methacrylate) (PMMA). The cell was fitted within a 3D printed housing and the LED and photodiode were aligned using 3D printed holders. Isocratic separation and selective detection of nitrite and nitrate was achieved in under 2.5 min using the 235 nm LED based detector and custom electronics. The design of the new detector assembly allowed for effective and sustained operation of the deep UV LED source at a low current (<10 mA), maintaining consistent and low LED temperatures during operation, eliminating the need for a heat sink. The detector cell was produced at a fraction of the cost of commercial optical cells and demonstrated very low stray light (0.01%). For retention time and peak area repeatability, RSD values ranged from 0.75 to 1.10 % and 3.06-4.19 %, respectively. Broad dynamic linear ranges were obtained for nitrite and nitrate, with limits of detection at ppb levels. The analytical performance of the IC set up with optical cell was compared to that of an ISO-accredited IC through the analysis of five various water samples. Relative errors not exceeding 6.86% were obtained for all samples. The detector was also coupled to a low pressure, low cost syringe pump to assess the potential for use within a portable analytical system. RSD values for retention time and peak area using this simple configuration were <1.15% and <3.57% respectively, highlighting repeatability values comparable to those in which a commercial HPLC pump was used.

A wearable patch for continuous monitoring of sweat electrolytes during exertion.

Implementation of wearable sweat sensors for continuous measurement of fluid based biomarkers (including electrolytes, metabolites and proteins) is an attractive alternative to common, yet intrusive and invasive, practices such as urine or blood analysis. Recent years have witnessed several key demonstrations of sweat based electrochemical sensing in wearable formats, however, there are still significant challenges and opportunities in this space for clinical acceptance, and thus mass implementation of these devices. For instance, there are inherent challenges in establishing direct correlations between sweat-based and gold-standard plasma-based biomarker concentrations for clinical decision-making. In addition, the wearable sweat monitoring devices themselves may exacerbate these challenges, as they can significantly alter sweat physiology (example, sweat rate and composition). Reported here is the demonstration of a fully integrated, wireless, wearable and flexible sweat sensing device for non-obtrusive and continuous monitoring of electrolytes during moderate to intense exertion as a metric for hydration status. The focus of this work is twofold: 1- design of a conformable fluidics systems to suit conditions of operation for sweat collection (to minimize sensor lag) with rapid removal of sweat from the sensing site (to minimize effects on sweat physiology). 2- integration of Na+ and K+ ion-selective electrodes (ISEs) with flexible microfluidics and low noise small footprint electronics components to enable wireless, wearable sweat monitoring. While this device is specific to electrolyte analysis during intense perspiration, the lessons in microfluidics and overall system design are likely applicable across a broad range of analytes.

The occurrence of PAHs and faecal sterols in Dublin Bay and their influence on sedimentary microbial communities.

The source, concentration, and potential impact of sewage discharge and incomplete organic matter (OM) combustion on sedimentary microbial populations were assessed in Dublin Bay, Ireland. Polycyclic aromatic hydrocarbons (PAHs) and faecal steroids were investigated in 30 surface sediment stations in the bay. Phospholipid fatty acid (PLFA) content at each station was used to identify and quantify the broad microbial groups present and the impact of particle size, total organic carbon (%TOC), total hydrogen (%H) and total nitrogen (%N) was also considered. Faecal sterols were found to be highest in areas with historical point sources of sewage discharge. PAH distribution was more strongly associated with areas of deposition containing high %silt and %clay content, suggesting that PAHs are from diffuse sources such as rainwater run-off and atmospheric deposition. The PAHs ranged from 12 to 3072ng/g, with 10 stations exceeding the suggested effect range low (ERL) for PAHs in marine sediments. PAH isomer pair ratios and sterol ratios were used to determine the source and extent of pollution. PLFAs were not impacted by sediment type or water depth but were strongly correlated to, and influenced by PAH and sewage levels. Certain biomarkers such as 10Me16:0, i17:0 and a17:0 were closely associated with PAH polluted sediments, while 16:1ω9, 16:1ω7c, Cy17:0, 18:1ω6, i16:0 and 15:0 all have strong positive correlations with faecal sterols. Overall, the results show that sedimentary microbial communities are impacted by anthropogenic pollution.

Online high-performance size exclusion chromatography-nuclear magnetic resonance for the characterization of dissolved organic matter.

The substantial heterogeneity of dissolved organic matter (DOM) inhibits detailed chromatographic analysis with conventional detectors as little structural information can be obtained in the presence of extensive coelution. Here we examine the direct hyphenation of high-performance size exclusion chromatography (HPSEC) with nuclear magnetic resonance (NMR) spectroscopy to determine how size-distinguished fractions differ in composition. The results support the applicability of using HPSEC to generate more homogeneous fractions of DOM prior to NMR analysis and demonstrate that structure is significantly altered with size. The largest fractions are enriched in carbohydrate- and aromatic-type structures. The midsized material is substantial and is representative of carboxyl-rich alicyclic molecules (CRAMs). The smallest material has strong signatures of material derived from linear terpenoids (MDLT). Both CRAMs and MDLT have been recently hypothesized as major components of DOM, and detection by HPSEC-NMR confirms their existence as unique and separable entities. This preliminary work focuses on NMR hyphenation to HPSEC due to widespread use of HPSEC to characterize DOM. Online hyphenation is useful not only for time-efficient analysis of DOM but also for that of other highly complex samples such as those found in many environmental analyses.