Improvement of On-Site Sensor for Simultaneous Determination of Phosphate, Silicic Acid, Nitrate plus Nitrite in Seawater

Microfluidics for macrofluidics: addressing marine-ecosystem challenges in an era of climate change

Climate change presents a mounting challenge with profound impacts on ocean and marine ecosystems, leading to significant environmental, health, and economic consequences. Microfluidic technologies, with their unique capabilities, play a crucial role in understanding and addressing the marine aspects of the climate crisis. These technologies leverage quantitative, precise, and miniaturized formats that enhance the capabilities of sensing, imaging, and molecular tools. Such advancements are critical for monitoring marine systems under the stress of climate change and elucidating their response mechanisms. This review explores microfluidic technologies employed both in laboratory settings for testing and in the field for monitoring purposes. We delve into the application of miniaturized tools in evaluating ocean-based solutions to climate change, thus offering fresh perspectives from the solution-oriented end of the spectrum. We further aim to synthesize recent developments in technology around critical questions concerning the ocean environment and marine ecosystems, while discussing the potential for future innovations in microfluidic technology. The purpose of this review is to enhance understanding of current capabilities and assist researchers interested in mitigating the effects of climate change to identify new avenues for tackling the pressing issues posed by climate change in marine ecosystems.

An impedimetric approach for determination of ammonium using silver/poly-1-aminoanthraquinone/carbon paste electrode

Here, we present the electrochemical determination of ammonium in water samples, emphasizing the importance of accurate and precise assessment of its concentration. The modified electrode used in this study was fabricated through the anodic polymerization of 1-aminoanthraquinone (1-AAQ) and deposition of silver particles into a carbon paste electrode. The fabrication process involved cyclic voltammetry in a 0.1 M HCl solution, followed by the application of a potential of 0.2 V for 75 s. The resulting Ag/poly-1-AAQ/CPE exhibited remarkable electrochemical properties, as confirmed by scanning electron spectroscopy (SEM), energy-dispersive X-ray analysis (EDX), and elemental mapping. The successful deposition of silver at percentages of 12.07% on Ag/CPE and 0.75% on Ag/poly-1-AAQ/CPE was observed. The Ag/poly-1-AAQ/CPE was employed for impedimetric determination of ammonium in a solution of 0.1 M Na2SO4. The charge transfer resistance) output from the fitting of the experimental impedimetric data of ammonium determination exhibited good linearity over a concentration range of 5 µM to 200 µM NH4+, with a detection limit of 3.3 µM NH4+. The precision of the modified electrode over ten replicate measurements were conducted at three concentration levels (a low of 5 µM NH4+, a medium of 50 µM NH4+, and a high of 200 µM NH4+). The obtained relative standard deviation (RSD) values of 18%, 12% and 7%, respectively, indicating good precision.

AutoGIS processing for site selection for solar pond development as efficient water treatment plants in Egypt

The increasing demand for renewable and environmentally friendly energy sources is a top priority for many countries around the world. It is obvious that renewable solar energy will help to meet most of the energy demand in the coming years. A solar pond is a huge Salt artificial Lake that serves as a solar energy collection system. However, site selection is a critical factor that affects the effectiveness and lifetime of a solar pond. Here, we present an innovative methodology for site selection based on three environmental factors, including direct solar irradiance (DNI), temperature, and wind speed. Our approach uses Python programming and clustering analysis with several libraries, including Pandas, Geopandas, Rasterio, Osgeo, and Sklearn, to analyse and process data collected over a 30-year period from NASA power. This method was applied to the geographic boundaries of Egypt, but the methods can be applied to any spatial context if the same dataset is available. The results show that Egypt has a potential land area of 500 km2 suitable for solar ponds construction along the border with Sudan throughout the year, including 2000 km2 in winter (between January and March), 800 km2 in spring (between April and June), 900 km2 in summer (between July and September), and the largest area of 3700 km2 (between October and December), most of which is located in the south of the Eastern Desert and around the Nile River. Notably, the northwestern region, close to the Mediterranean Sea on the border with Libya, exhibits suitability for solar pond development, with consistent performance throughout the year. Our results provide an efficient way for GIS and data processing and could be useful for implementing new software to find the best location for solar ponds development. This could be beneficial for those interested in investing in renewable energy and using solar ponds as an efficient water treatment plant.

Modified electrode decorated with silver as a novel non-enzymatic sensor for the determination of ammonium in water

Ammonium is an essential component of the nitrogen cycle, which is essential for nitrogen cycling in ecosystems. On the other hand, ammonium pollution in water poses a great threat to the ecosystem and human health. Accurate and timely determination of ammonium content is of great importance for environmental management and ensuring the safety of water supply. Here we report a highly sensitive electrochemical sensor for ammonium in water samples. The modified electrode is based on the incorporation of silver nitrate (AgNO3) into a carbon paste embedded with 1-aminoanthraquinone and supported by multi-walled carbon nanotubes, which are commercially available. A potential of 0.75 V is applied to the modified electrode, followed by activation in hydrochloric acid. The modified electrode was used for square wave voltammetry of ammonium in water in the potential range of - 0.4-0.2 V. The performance of ammonium analysis was determined in terms of square wave frequency, square wave amplitude and concentration of electrolyte solution (sodium sulphate). The calculation of the surface area according to the Randles-Sevcik equation resulted in the largest surface area for the Ag/pAAQ/MWCNTs/CPE. The modified electrode exhibited a linear range of 5-100 µM NH4+ in 0.1 M Na2SO4 with a detection limit of 0.03 µM NH4+ (3σ). In addition, the modified electrode showed high precision with an RSD value of 9.93% for 10 repeated measurements. No interfering effect was observed at twofold and tenfold additive concentrations of foreign ions. Good recoveries were obtained in the analysis of tap and mineral water after spiking with a concentration of ammonium ions.

A new approach for determination of orthophosphate based on mixed valent molybdenum oxide/poly 1,2-diaminoanthraquinone in seawater

Orthophosphate is an essential macronutrient in natural water that controls primary production and strongly influences the global ocean carbon cycle. Electrochemical determination of orthophosphate is highly recommended because electrochemistry provides the simplest means of determination. Here the determination of orthophosphate based on the formation of a phosphomolybdate complex is reported. Mixed-valent molybdenum oxide (MoxOy) was prepared by cyclic voltammetry on poly-1,2-diaminoanthraquinone (1,2-DAAQ), which was performed by cyclic voltammetry on the surface of a glassy carbon electrode under pre-optimized conditions for the thickness of the modified electrode layers. The proposed modified electrode was used for square-wave voltammetry of orthophosphate ions under pre-optimized square-wave parameters (i.e., frequency and amplitude) in strongly acidic medium (pH < 1). The linear range was 0.05-4 µM with a limit of quantification (LOD) of 0.0093 µM with no effect on two peaks due to cross interference from silicate. Furthermore, MoxOy/PDAAQ shows good reproducibility with a relative standard deviation (RSD) of 2.17% for the peak at 0.035 V and 3.56% for the peak at 0.2 V. Real seawater samples were also analyzed for PO43- analysis by UV spectrophotometry and the results were compared with the measurement results of our proposed electrode, with good recoveries obtained.

The Use of Bi-Potentiostat as a Simple and Accurate Electrochemical Approach for the Determination of Orthophosphate in Seawater

Autonomous on-site monitoring of orthophosphate (PO₄^3-), an important nutrient for primary production in natural waters, is urgently needed. Here, we report on the development and validation of an on-site autonomous electrochemical analyzer for PO₄^3- in seawater. The approach is based on the use of flow injection analysis in conjunction with a dual electrochemical cell (i.e., a bi-potentiostat detector (FIA-DECD) that uses two working electrodes sharing the same reference and counter electrode. The two working electrodes are used (molybdate/carbon paste electrode (CPE) and CPE) to correct for matrix effects. Optimization of squarewave voltammetry parameters (including step potential, amplitude, and frequency) was undertaken to enhance analytical sensitivity. Possible interferences from non-ionic surfactants and humic acid were investigated. The limit of quantification in artificial seawater (30 g/L NaCl, pH 0.8) was 0.014 µM for a linear concentration range of 0.02-3 µM. The system used a Python script for operation and data processing. The analyzer was tested for ship-board PO₄^3- determination during a four-day research cruise in the North Sea. The analyzer successfully measured 34 samples and achieved a good correlation (Pearson' R = 0.91) with discretely collected water samples analyzed using a laboratory-based colorimetric reference analyzer.

A Parametric Study on a Paper-Based Bi-Material Cantilever Valve

The novel paper-based Bi-Material Cantilever (B-MaC) valve allows the autonomous loading and control of multiple fluid reagents which contributes to the accurate operation of paper-based microfluidic devices utilized for biological and chemical sensing applications. In this paper, an extensive parametric study is presented to evaluate the effects of key geometric parameters of the valve, such as paper direction, cantilever width, paper type, tape type, and sample volume, in addition to the effects of relative humidity and temperature on the functionality of the B-MaC and to provide a better understanding of the rate of fluid flow and resulting deflection of the cantilever. Machine direction, cantilever width, paper type, and tape type were found to be important parameters that affect the B-MAC's activation time. It was also observed that the rate of fluid imbibition in the B-MaC is considerably affected by change in humidity for high (55 °C) and low (25 °C) temperatures, while humidity levels have no significant effect during imbibition in the B-MaC at an ambient temperature of 45 °C. It was also found that a minimum distance of 4 mm is required between the B-MaC and the stationary component to prevent accidental activation of the B-MaC prior to sample insertion when relative humidity is higher than 90% and temperature is lower than 35 °C. The rate of fluid imbibition that determines the wetted length of the B-MaC and the final deflection of the cantilever are critical in designing and fabricating point-of-care microfluidic paper-based devices. The B-MaC valve can be utilized in a fluidic circuit to sequentially load several reagents, in addition to the sample to the detection area.