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A special issue of Sensors (ISSN 1424-8220). This special issue belongs to the section "Chemical Sensors".

Deadline for manuscript submissions: closed (31 October 2021) | Viewed by 39703

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Prof. Dr. Peter Kruse

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Department of Chemistry and Chemical Biology, McMaster University, 1280 Main Street West, Hamilton, ON L8S 4M1, Canada
Interests: surface science; 2D materials; surface analysis; interfacial doping; solid state sensors
Special Issues, Collections and Topics in MDPI journals

Dr. Lorena Parra

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Research Institute for Integrated Management of Coastal Areas (IGIC), Universitat Politècnica de València, 46730 Grau de Gandia, Spain
Interests: environmental monitoring; precision agriculture; image processing; crop management; smart cities; physical sensors
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Sensors for aqueous environments are needed in environmental monitoring, municipal drinking water and wastewater processing and distribution, agriculture, and industrial processes, including in the food and beverage industry. All aspects of life on this planet are predicated on access to clean water. In recent times, the strain on the water resources of our planet has increased substantially, requiring action in water management and purification. To quantify the magnitude of the problem and to verify the success of remedial actions, we need to develop reliable and affordable water quality sensors.

Relevant parameters include turbidity, color, temperature, conductivity, hardness, pH, disinfectant concentration, nutrients, heavy metals and other ion concentrations, organic pollutants, and pathogen counts. Sensor technologies need to be developed that can form the basis of robust, low-power, low-cost devices for continuous monitoring. A variety of sensor technologies have been considered, including mass-analytic (cantilever, quartz crystal microbalance, mass spectrometry), optical (colorimetry/absorbance, chemiluminescence, fluorescence, phosphorescence, Raman, surface plasmons, atomic emission), and solid state (electrochemical sensors, chemiresistive sensors, and field-effect devices) methods. Supporting infrastructure for sample conditioning, data transmission and analysis are also required.

This Special Issue aims to bring together researchers from academia and industry to share recent advances in materials, devices, and supporting infrastructure with applications in water quality sensing. Submissions of original research articles as well as critical reviews of recent progress are welcome. Special Issue topics include, but are not limited to, the following:

Sensor geometries and materials;
Mechanical, optical, electrochemical, or electrical sensors;
Spectrometric and spectroscopic methods;
Sample pre-treatment, filtration, preconcentration, etc.;
Stand-alone sensors and sensor networks;
Data transmission from remote sensors;
Data collection and processing from sensor networks;
Online sensors;
Off-line analytical methods for water quality determination;
Low-cost sensors and solutions for crowdsourcing and citizen science;
Redox and disinfectant sensors;
Aqueous ion sensors;
pH, temperature, conductivity, hardness, turbidity, color sensors;
Nutrient sensors;
Organic pollutant sensors;
Pathogen sensors.

Prof. Dr. Peter Kruse
Prof. Dr. Lorena Parra
Guest Editor

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Sensors is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Published Papers (10 papers)

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20 pages, 4317 KiB

Open AccessArticle

Development of a Low-Cost Optical Sensor to Detect Eutrophication in Irrigation Reservoirs

by Javier Rocher, Lorena Parra, Jose M. Jimenez, Jaime Lloret and Daniel A. Basterrechea

Sensors 2021, 21(22), 7637; https://0-doi-org.brum.beds.ac.uk/10.3390/s21227637 - 17 Nov 2021

Cited by 4 | Viewed by 2056

Abstract

In irrigation ponds, the excess of nutrients can cause eutrophication, a massive growth of microscopic algae. It might cause different problems in the irrigation infrastructure and should be monitored. In this paper, we present a low-cost sensor based on optical absorption in order to determine the concentration of algae in irrigation ponds. The sensor is composed of 5 LEDs with different wavelengths and light-dependent resistances as photoreceptors. Data are gathered for the calibration of the prototype, including two turbidity sources, sediment and algae, including pure samples and mixed samples. Samples were measured at a different concentration from 15 mg/L to 4000 mg/L. Multiple regression models and artificial neural networks, with a training and validation phase, are compared as two alternative methods to classify the tested samples. Our results indicate that using multiple regression models, it is possible to estimate the concentration of alga with an average absolute error of 32.0 mg/L and an average relative error of 11.0%. On the other hand, it is possible to classify up to 100% of the samples in the validation phase with the artificial neural network. Thus, a novel prototype capable of distinguishing turbidity sources and two classification methodologies, which can be adapted to different node features, are proposed for the operation of the developed prototype. Full article

(This article belongs to the Special Issue Water Quality Sensors)

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11 pages, 3469 KiB

Open AccessArticle

A Low-Cost Digital Colorimetry Setup to Investigate the Relationship between Water Color and Its Chemical Composition

by Ruosha Zeng, Chris M. Mannaerts and Zhehai Shang

Sensors 2021, 21(20), 6699; https://0-doi-org.brum.beds.ac.uk/10.3390/s21206699 - 09 Oct 2021

Cited by 3 | Viewed by 2126

Abstract

Developments in digital image acquisition technologies and citizen science lead to more water color observations and broader public participation in environmental monitoring. However, the implications of the use of these simple water color indices for water quality assessment have not yet been fully evaluated. In this paper, we build a low-cost digital camera colorimetry setup to investigate quantitative relationships between water color indices and concentrations of optically active constituents (OACs). As proxies for colored dissolved organic matter (CDOM) and phytoplankton, humic acid and algae pigments were used to investigate the relationship between water chromaticity and concentration. We found that the concentration fits an ascending relationship with xy chromaticity values and a descending relationship with hue angle. Our investigations permitted us to increase the information content of simple water color observations, by relating them to chemical constituent concentrations in observed waters. Full article

(This article belongs to the Special Issue Water Quality Sensors)

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22 pages, 5759 KiB

Open AccessArticle

Low-Cost System Based on Optical Sensor to Monitor Discharge of Industrial Oil in Irrigation Ditches

by Daniel A. Basterrechea, Javier Rocher, Lorena Parra and Jaime Lloret

Sensors 2021, 21(16), 5449; https://0-doi-org.brum.beds.ac.uk/10.3390/s21165449 - 12 Aug 2021

Cited by 3 | Viewed by 1782

Abstract

Uncontrolled dumping linked to agricultural vehicles causes an increase in the incorporation of oils into the irrigation system. In this paper, we propose a system based on an optical sensor to monitor oil concentration in the irrigation ditches. Our prototype is based on the absorption and dispersion of light. As a light source, we use Light Emitting Diodes (LEDs) with different colours (white, yellow, blue, green, and red) and a photodetector as a sensing element. To test the sensor’s performance, we incorporate industrial oils used by a diesel or gasoline engine, with a concentration from 0 to 0.20 mL_oil/cm². The experiment was carried out at different water column heights, 0 to 20 cm. According to our results, the sensor can differentiate between the presence or absence of diesel engine oil with any LED. For gasoline engine oil, the sensor quantifies its concentration using the red light source; concentrations greater than 0.1 mL_oil/cm² cannot be distinguished. The data gathered using the red LED has an average absolute error of 0.003 mL_oil/cm² (relative error of 15.8%) for the worst case, 15 cm. Finally, the blue LED generates different signals in the photodetector according to the type of oil. We developed an algorithm that combines (i) the white LED, to monitor the presence of oil; (ii) the blue LED, to identify if the oil comes from a gasoline or diesel engine; and (iii) the red LED, to monitor the concentration of oil used by a gasoline engine. Full article

(This article belongs to the Special Issue Water Quality Sensors)

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15 pages, 3071 KiB

Open AccessArticle

Fabrication, Potentiometric Characterization, and Application of Screen-Printed RuO₂ pH Electrodes for Water Quality Testing

by Kiranmai Uppuluri, Maryna Lazouskaya, Dorota Szwagierczak, Krzysztof Zaraska and Martti Tamm

Sensors 2021, 21(16), 5399; https://0-doi-org.brum.beds.ac.uk/10.3390/s21165399 - 10 Aug 2021

Cited by 18 | Viewed by 2872

Abstract

Screen-printed sensing electrodes attract much attention for water pollution monitoring due to their small size, physical and chemical durability, and low cost. This paper presents the fabrication and broad potentiometric characterization of RuO₂ pH sensing electrodes deposited by screen printing on alumina substrates and sintered in the 800–900 °C temperature range. All the fabricated electrodes showed close to Nernstian sensitivity, good linearity, fast response, small drift, low hysteresis, and low cross-sensitivity toward various interfering cations and anions. Furthermore, decreasing the sintering temperature led to better adhesion of the RuO₂ layer and a negligible response to interfering ions. The measurements in real-life samples from different water sources showed that the fabricated electrodes are on par with conventional glass electrodes with a maximum deviation of 0.11 pH units, thus indicating their potential for application in water quality monitoring. Full article

(This article belongs to the Special Issue Water Quality Sensors)

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15 pages, 4498 KiB

Open AccessArticle

All Silica Micro-Fluidic Flow Injection Sensor System for Colorimetric Chemical Sensing

by Vedran Budinski and Denis Donlagic

Sensors 2021, 21(12), 4082; https://0-doi-org.brum.beds.ac.uk/10.3390/s21124082 - 14 Jun 2021

Cited by 8 | Viewed by 2746

Abstract

This paper presents a miniature, all-silica, flow-injection sensor. The sensor consists of an optical fiber-coupled microcell for spectral absorption measurements and a microfluidic reagent injection system. The proposed sensor operates in back reflection mode and, with its compact dimensions, (no more than 200 µm in diameter) enables operation in small spaces and at very low flow rates of analyte and reagent, thus allowing for on-line or in-line colorimetric chemical sensing. Full article

(This article belongs to the Special Issue Water Quality Sensors)

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16 pages, 44088 KiB

Open AccessArticle

Water Nitrate Remote Monitoring System with Self-Diagnostic Function for Ion-Selective Electrodes

by Dae-Hyun Jung, Hak-Jin Kim, Joon Yong Kim, Soo Hyun Park and Woo Jae Cho

Sensors 2021, 21(8), 2703; https://0-doi-org.brum.beds.ac.uk/10.3390/s21082703 - 12 Apr 2021

Cited by 1 | Viewed by 6143

Abstract

The detection of nitrate pollutants is a widely used strategy for protecting water sources. Although ion-selective electrodes (ISEs) have been considered for the determination of ion concentrations in water, the accuracy of ISE technology decreases owing to the signal drift and decreasing sensitivity over time. The objectives of the present study were: (1) to develop an online water monitoring system mainly consisting of an Arduino board-based Internet-of-Things (IoT) device and nitrate ISEs; and (2) to propose a self-diagnostic function for monitoring and reporting the condition of the ISEs. The developed system communicates with the cloud server by using the message queuing telemetry transport (MQTT) protocol and provides monitoring information through the developed cloud-based webpage. In addition, the online monitoring system provides information on the electrode status, which is determined based on a self-diagnostic index (SDI, with a range of 0–100) of the electrode drift and sensitivity. The diagnostic method for monitoring and reporting the electrode status was validated in a one-month-long laboratory test followed by a field test in a stream near an agricultural facility. Moreover, a self-diagnostic index (SDI) was applied in the final field experiments with an accuracy of 0.77. Full article

(This article belongs to the Special Issue Water Quality Sensors)

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22 pages, 11057 KiB

Open AccessArticle

A Co-Nanoparticles Modified Electrode for On-Site and Rapid Phosphate Detection in Hydroponic Solutions

by Feng Xu, Peng Wang, Shiyuan Bian, Yuliang Wei, Deyi Kong and Huanqin Wang

Sensors 2021, 21(1), 299; https://0-doi-org.brum.beds.ac.uk/10.3390/s21010299 - 05 Jan 2021

Cited by 7 | Viewed by 3264

Abstract

Conventional strategies for determining phosphate concentration is limited in efficiency due to the cost, time, and labor that is required in laboratory analysis. Therefore, an on-site and rapid detection sensor for phosphate is urgently needed to characterize phosphate variability in a hydroponic system. Cobalt (Co) is a highly sensitive metal that has shown a selectivity towards phosphate to a certain extent. A disposable phosphate sensor based on the screen-printed electrode (SPE) was developed to exploit the advantages of Co-nanoparticles. A support vector machine regression model was established to predict the concentration of phosphate in the hydroponic solutions. The results showed that Co-nanoparticles improve the detection limit of the sensor in the initial state. Meanwhile, the corrosion of Co-nanoparticles leads to a serious time-drift and instability of the electrodes. On the other hand, the coefficient of variation of the disposable phosphate detection chip is 0.4992%, the sensitivity is 33 mV/decade, and the linear range is 10⁻¹–10^−4.56 mol/L. The R² and mean square error of the buffer-free sensor in the hydroponic solution are 0.9792 and 0.4936, respectively. In summary, the SPE modified by the Co-nanoparticles is a promising low-cost sensor for on-site and rapid measurement of the phosphate concentration in hydroponic solutions. Full article

(This article belongs to the Special Issue Water Quality Sensors)

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13 pages, 3594 KiB

Open AccessArticle

Photometric Sensing of Active Chlorine, Total Chlorine, and pH on a Microfluidic Chip for Online Swimming Pool Monitoring

by Sait Elmas, Aneta Pospisilova, Aneta Anna Sekulska, Vasil Vasilev, Thomas Nann, Stephen Thornton and Craig Priest

Sensors 2020, 20(11), 3099; https://0-doi-org.brum.beds.ac.uk/10.3390/s20113099 - 30 May 2020

Cited by 18 | Viewed by 8725

Abstract

A microfluidic sensor was studied for the photometric detection of active chlorine, total chlorine, and pH in swimming pool samples. The sensor consisted of a four-layer borosilicate glass chip, containing a microchannel network and a 2.2 mm path length, 1.7 mL optical cell. The chip was optimised to measure the bleaching of methyl orange and spectral changes in phenol red for quantitative chlorine (active and total) and pH measurements that were suited to swimming pool monitoring. Reagent consumption (60 mL per measurement) was minimised to allow for maintenance-free operation over a nominal summer season (3 months) with minimal waste. The chip was tested using samples from 12 domestic, public, and commercial swimming pools (indoor and outdoor), with results that compare favourably with commercial products (test strips and the N,N’-diethyl-p-phenylenediamine (DPD) method), precision pH electrodes, and iodometric titration. Full article

(This article belongs to the Special Issue Water Quality Sensors)

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16 pages, 3027 KiB

Open AccessArticle

Development of a Solar-Powered IoT-Based Instrument for Automatic Measurement of Water Clarity

by Tuan Ngoc Pham, Anh Pham Huy Ho, Tuong Van Nguyen, Ha Minh Nguyen, Nhu Huynh Truong, Nguyen Duc Huynh, Tung Huy Nguyen and Le The Dung

Sensors 2020, 20(7), 2051; https://0-doi-org.brum.beds.ac.uk/10.3390/s20072051 - 06 Apr 2020

Cited by 5 | Viewed by 3975

Abstract

Water clarity is the most common indicator of water quality. The purpose of the study was to develop an instrument which can automatically measure water clarity in place of manual measurement by Secchi disk. The instrument is suspended by buoys at the water surface and uses solar energy to measure the light intensity of LED bulbs after passing through a water column; the result is then converted to Secchi depth by using a regression function. Measurement data are stored in a cloud server so that mobile users can access via an Internet connection. Three experiments were conducted to examine the instrument performance: (i) to ensure light intensity of the LED bulbs is strong enough to pass through the water column; (ii) to determine the regression relationship between the measured light intensity of the instrument and Secchi depth; and (iii) to evaluate the coefficient of variation (CV) of the measured water clarity when using our instrument and a conventional Secchi disk. Experiment results show that the measured values of light intensity are stable with the average CV = 5.25%. Moreover, although there are slight differences between the Secchi depth measured by our instrument and those measured by Secchi disk, the measurements by our instrument can efficiently replace the measurements by conventional Secchi disk, which can be affected by weather conditions as well as by human subjectivity. Full article

(This article belongs to the Special Issue Water Quality Sensors)

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14 pages, 2919 KiB

Open AccessTechnical Note

A Colorimetric Dip Strip Assay for Detection of Low Concentrations of Phosphate in Seawater

by Hojat Heidari-Bafroui, Amer Charbaji, Constantine Anagnostopoulos and Mohammad Faghri

Sensors 2021, 21(9), 3125; https://0-doi-org.brum.beds.ac.uk/10.3390/s21093125 - 30 Apr 2021

Cited by 8 | Viewed by 4265

Abstract

Nutrient pollution remains one of the greatest threats to water quality and imposes numerous public health and ecological concerns. Phosphate, the most common form of phosphorus, is one of the key nutrients necessary for plant growth. However, phosphate concentration in water should be carefully monitored for environmental protection requirements. Hence, an easy-to-use, field-deployable, and reliable device is needed to measure phosphate concentrations in the field. In this study, an inexpensive dip strip is developed for the detection of low concentrations of phosphate in water and seawater. In this device, ascorbic acid/antimony reagent was dried on blotting paper, which served as the detection zone, and was followed by a wet chemistry protocol using the molybdenum method. Ammonium molybdate and sulfuric acid were separately stored in liquid form to significantly improve the lifetime of the device and enhance the reproducibility of its performance. The device was tested with deionized water and Sargasso Sea seawater. The limits of detection and quantification for the optimized device using a desktop scanner were 0.134 ppm and 0.472 ppm for phosphate in water and 0.438 ppm and 1.961 ppm in seawater, respectively. The use of the portable infrared lightbox previously developed at our lab improved the limits of detection and quantification by a factor of three and were 0.156 ppm and 0.769 ppm for the Sargasso Sea seawater. The device’s shelf life, storage conditions, and limit of detection are superior to what was previously reported for the paper-based phosphate detection devices. Full article

(This article belongs to the Special Issue Water Quality Sensors)

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