Environmental analysis by electrochemical sensors and biosensors fundamentals

Nanostructure Science and Technology Series Editor: David J Lockwood Ligia Maria Moretto Kurt Kalcher Editors Environmental Analysis by Electrochemical Sensors and Biosensors Volume 1: Fundamentals Tai Lieu Chat Luong Nanostructure Science and Technology Series Editor: David J Lockwood, FRSC National Research Council of Canada Ottawa, Ontario, Canada More information about this series at http://www.springer.com/series/6331 Ligia Maria Moretto • Kurt Kalcher Editors Environmental Analysis by Electrochemical Sensors and Biosensors Fundamentals Volume Editors Ligia Maria Moretto Department of Molecular Sciences and Nanosystems University Ca’ Foscari of Venice Venice, Italy Kurt Kalcher Institute of Chemistry Karl-Franzens Universitaăt Graz, Austria ISSN 1571-5744 ISSN 2197-7976 (electronic) ISBN 978-1-4939-0675-8 ISBN 978-1-4939-0676-5 (eBook) DOI 10.1007/978-1-4939-0676-5 Springer New York Heidelberg Dordrecht London Library of Congress Control Number: 2014949384 © Springer Science+Business Media New York 2014 This work is subject to copyright All rights are reserved by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed Exempted from this legal reservation are brief excerpts in connection with reviews or scholarly analysis or material supplied specifically for the purpose of being entered and executed on a computer system, for exclusive use by the purchaser of the work Duplication of this publication or parts thereof is permitted only under the provisions of the Copyright Law of the Publisher’s location, in its current version, and permission for use must always be obtained from Springer Permissions for use may be obtained through RightsLink at the Copyright Clearance Center Violations are liable to prosecution under the respective Copyright Law The use of general descriptive names, registered names, trademarks, service marks, etc in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use While the advice and information in this book are believed to be true and accurate at the date of publication, neither the authors nor the editors nor the publisher can accept any legal responsibility for any errors or omissions that may be made The publisher makes no warranty, express or implied, with respect to the material contained herein Printed on acid-free paper Springer is part of Springer Science+Business Media (www.springer.com) Foreword Electrochemical sensors are transforming our lives From smoke detectors in our homes and workplaces to handheld self-care glucose meters these devices can offer sensitive, selective, reliable, and often cheap measurements for an ever increasing diversity of sensing requirements The detection and monitoring of environmental analytes is a particularly important and demanding area in which electrochemical sensors and biosensors find growing deployment and where new sensing opportunities and challenges are constantly emerging This manual provides up-to-date and highly authoritative overviews of electrochemical sensors and biosensors as applied to environmental targets The book surveys the entire field of such sensors and covers not only the principles of their design but their practical implementation and application Of particular value is the organizational structure The later chapters cover the full range of environmental analytes ensuring the book will be invaluable to environmental scientists as well as analytical chemists I predict the book will have a major impact in the area of environmental analysis by highlighting the strengths of existing sensor technology whilst at the same time stimulating further research Oxford University Oxford, UK Richard G Compton v Preface Dear Reader, We are pleased that you have decided to use Environmental Analysis by Electrochemical Sensors and Biosensors either as a monograph or as a handbook for your scientific work The manual comprises two volumes and represents an overview of an intersection of two scientific areas of essential importance: environmental chemistry and electrochemical sensing Since the invention of the glass electrode in 1906 by Max Cremer, electrochemical sensors represent the oldest type of chemical sensor and are ubiquitously present in all chemical labs, industries, as well as in many fields of our everyday life The development of electrochemical sensors exploiting new measuring technologies makes them useful for chemical analysis and characterization of analytes in practically all physical phases - gases, liquids and solids - and in different matrices in industrial, food, biomedical, and enviromental fields They have become indispensible tools in analytical chemistry for reliable, precise, and inexpensive determination of many compounds, as single shot, repetitive, continuous, or even permanent analytical devices Environmental analytical chemistry demands highly sensitive, robust, and reliable sensors, able to give fast responses even for analysis in the field and in real time, a requirement which can be fulfilled in many cases only by electrochemical sensing elements The idea for this manual was brought to us by Springer The intention was to build up an introduction and a concise but exhaustive description of the state of the art in scientific and practical work on environmental analysis, focused on electrochemical sensors To manage the enormous extent of the topic, the manual is split into two volumes The first one, covering the basic concepts and fundamentals of both environmental analysis and electrochemcial sensors, gives a short introduction and description of all environments which are subject to monitoring by electrochemical sensors, including extraterrestrial ones, as a particularly interesting and exciting topic; vii viii Preface provides essential background information on electroanalytical techniques and fundamental as well as advanced sensor technology; supplies numerous examples of applications along with the concepts and strategies of environmental analysis in all the various spheres of the environment and with the principles and strategies of electrochemical sensor design The second volume is more focused on practical applications, mostly complementary to the examples given in volume I, and overviews and critically comments on sensors proposed for the determination of inorganic and organic analytes and pollutants, including emerging contaminants, as well as for the measurement of global parameters of environmental importance; reviews briefly the mathematical background of data evaluation We hope that we have succeeded in fulfilling all these objectives by supplying general and specific data as well as thorough background knowledge to make Environmental Analysis with Electrochemical Sensors and Biosensors more than a simple handbook but, rather, a desk reference manual It is obvious that a compilation of chapters dealing with so many different specialized areas in analytical and environmental chemistry requires the expertise of many scientists Therefore, in the first place we would like to thank all the contributors to this book for all the time and effort spent in compiling and critically commenting on research, and the data and conclusions derived from it Of course, we would like to particularly acknowledge all the people from Springer who have been involved with the process of publication Our cordial thanks are addressed to Kenneth Howell, who accompanied us during all the primary steps and, later during the process of revision and editing together with Abira Sengupta, was always available and supportive in the most professional and pleasant manner Furthermore, we are indebted to a number of our collaborators, colleagues, and friends for kindly providing us literature and ideas, and stimulating us with fruitful discussions We would also like to thank all the coworkers who did research together with us and under our supervision, as well as all the scientific community working in the field of environmental sensing In particular, we would like to express our gratitude to all the persons, especially to our families, who supported us in the period of the preparation of the book Last but not least, we will be glad for comments from readers and others interested in this book, since we are aware that some contributions or useful details may have escaped our attention Such feedback is always welcome and will also be reflected in our future work Venice, Italy Graz, Austria December 2013 Ligia Maria Moretto Kurt Kalcher About the Editors Ligia Maria Moretto graduated in Chemical Engineering at the Federal University of Rio Grande Sul, Brazil, and received her Ph.D in 1994 from the University Ca’ Foscari of Venice with a thesis entitled “Ion-exchange voltammetry for the determination of copper and mercury Application to seawater.” Her academic career began at the University of Caxias Sul, Brazil, and continued at the Research Institute of Nuclear Energy, Sao Paulo, Brazil In 1996 she completed the habilitation as researcher in analytical chemistry at the University Ca’ Foscari of Venice Working at the Laboratory of Electrochemical Sensors, her research field has been the development of electrochemical sensor and biosensors based on modified electrodes, the study of gold arrays and ensembles of nanoelectrodes, with particular attention to environmental applications She has published more than 60 papers, several book chapters, and has presented about 90 contributions at international conferences, resulting in more than 1,100 citations Prof Moretto collaborates as invited professor and invited researcher with several institutions in Brazil, France, Argentina, Canada, and the USA Kurt Kalcher completed his studies at the Karl-Franzens University (KFU) with a dissertation in inorganic chemistry entitled “Contributions to the Chemistry of Cyantrichloride, CINCCI2”; he also received his Ph.D in 1980 from the same institution In 1981 he then did postdoctoral work at the Nuclear Research Center in Juălich (Germany) under the supervision of Prof Nuărnberg and Dr Valenta, and conducted intensive electroanalytical research while he was there Prof Kalcher continued his academic career at KFU with his habilitation on chemically modified carbon paste electrodes in analytical chemistry in 1988 Since then, he has been employed there as an associate professor His research interests include the development of electrochemical sensors and biosensors for the determination of inorganic and biological analytes on the basis of carbon paste, screen-printed carbon, ix 23 Remote Sensing 675 Fig 23.8 (a) Illustration of monitoring station distribution in an aquatic environment (b) Buoys that are designed by Sound Ocean System Inc for deep, coastal, and protected water47 Furthermore, several of these heavy metals tend to bioaccumulate37 in various organisms, which complicates their monitoring significantly Automatic trace metal monitoring systems (ATMS)25 are one example of an important tool in monitoring these elements using a stationary remote sensing device ATMS, are a family of systems that can be placed in different locations and provide continuous (time dependent) monitoring.1,38–40 Billon and coworkers applied the ATMS for voltammetric detection of Cu, Fe, Pb, Mn, and Zn in the De^ule River (France).41 They showed, using differential pulse anodic stripping voltammetry (DP-ASV) that the concentrations of Zn, Cu and Fe vary, and is a function of the pH and turbidity.25,29 ATMS can also be used as part of a sensor network.42 The information that is collected by such network can be utilized in order to obtain a 2D or 3D models of the contaminant distribution in the environment.24,43,44 The sensor network offers a powerful combination of distributed sensing capacity, computational tools together with internet or satellite communication, which are applicable in numerous research fields, such as ecological studies Moreover, new designs of sensor networks allow for the observation of systems in near real-time, based on incoming data not only from local sources, but also from nearby networks, and from remote sensing data streams.24,45 These advances are providing new and better understanding of our ecological systems by revealing previously unobservable phenomena and also raising questions and insights.46 Figure 23.8a shows a schematic distribution of a sensor network The ATMS (which are marked by the red dots) are placed in strategically points that are determined by a previous geological survey, simulations, or a potential contamination source The ATMS are placed not only in the estuaries (entering or exiting the water body) but can also be positioned along the river or lake in order to provide a better insight on the measured parameters Buoys are used in order to position a station and acquire information regarding phenomenon that occurs not near the shore, but also in the middle of the water body Buoys can also be used to supply power to the sensor via solar panels and make an ideal platform for numerous sensors for monitoring atmospheric and hydrodynamic environments as well as for speciation Figure 23.8b shows three 676 T Noyhouzer and D Mandler types of buoys that are manufactured by Sound System Ocean Inc (SOSI).47 These buoys are designed for different conditions, i.e., deep, costal, and protected waters During the last decades there has been an extensive use of aquatic sensors and monitoring stations for monitoring basic water parameters, such as temperature and conductivity (salinity) Physical sensors are very often used for monitoring aquatic systems They are usually very robust and reliable and can be used for long time without or with minimal maintenance Mead et al used a network of gas sensors for measuring ppb levels of toxic gases (CO, NO, and NO2) in urban environments.48 Coloso and coworkers used a sensor network to measure temperature and dissolved oxygen (DO) in various habitats and at multiple depths for a more complete estimate of whole lake metabolism and better understanding of the spatial and temporal complexity of lakes.49 Other chemical aquatic sensors such as used for measuring total suspended solids (TSS), nutrients (N, P), and dissolved organic matter, are constantly developed and improved Yet, depending on local biofouling, they require very frequent maintenance, that is, after a period of weeks up to month a cleaning procedure or other services are crucial for their reliable operation Electrochemical sensors for monitoring the oxidation–reduction potential (ORP) or ion selective electrodes (ISEs) had been considered the most problematic for long-term autonomous deployment within networks, as their response tended to drift excessively over time in the absence of frequent servicing However, major developments in sensor technology, such as better LOD or stability due to new membrane materials, especially in electrochemical sensors50–52 enable the long term use of sensors in remote locations as part of a sensor network.41 Evidently, as more aquatic sensors are becoming accessible, models can be readily examined and refined 23.2.2 Mobile Remote Electrochemical Sensing In the period between 1975 and 1977 three scientists from the San-Diego Naval Ocean Systems Center went on a sampling campaign in the San-Diego bay The sampling and measurements were conducted from a small vessel This was not the first off-shore sampling campaign, but it was the first one that utilized an automated electrochemical system for the measurement of heavy metals.53 In the previous sections we described the aspects of remote environmental monitoring using different technologies We emphasized the advantages of placing the sensor at a remote or unreachable location These sensors are usually deployed at a stationary location, which can be by river estuaries, factories, or even in the middle of the water body positioned inside a special buoy (Fig 23.8b) The use of stationary sensors are very common for monitoring fresh water sources, such as ground and surface water, however monitoring a marine environment is more challenging Positioning of a permanent sensor at the estuary can monitor the diversity and speciation flowing into the bay, but not the entire large area of the bay or the ocean Furthermore, one needs to consider the fact that some water bodies exhibit complex 23 Remote Sensing 677 currents and coastal systems Tides, for example, influence the local measured concentrations and may also cause salinity shifts.54 From a biological point of view, heavy metals will undergo dilution when entering a large water body and appear very low but may still be of biologically significance Hence, it is evident that monitoring must allow time as well as space dependence of the target analytes The application of an automated-mobile system that is controlled from a boat or the shore can solve some of these issues The sensors can travel to a required area and perform the measurements and continue to their next location A major limitation of the traditional sensor network is the generally fixed sampling locations The fact that the sensor is not permanent like a station or a buoy gives the user more flexibility in planning the monitoring strategy This type of sensing can help covering a large area with a small number of sensors In fact, one sensor can perform as an entire network and produce results from several locations, thus contributing valuable insight on the entire system Another advantage is the ability of the sensor to access problematic areas in complex environments, for example under arctic ice sheets.55 Nevertheless, assembling an autonomous-mobile device has numerous demands spanning from power supply to a wireless control unit Several approaches have been considered in order to fulfill all the requirements from such robotic device also referred to as a robotic fish or “robofish”.56 One of the first devices was the “RoboTuna” project.57 A group from MIT demonstrated that a long robotic fish that mimics the motion of a fish can be used for aquatic monitoring Several versions of this prototype were made; the latest was developed in order to monitor the 2010 oil spill in the gulf oil Mexico The robot was equipped with an on-board crude oil sensor to detect and track oil plumes and a salinity sensor based on conductometry Monitoring and tracking these two elements was critical for clean-up effort, the protection of sensitive areas and understanding the spill’s environmental and ecological impacts There were a number of attempts to construct robotic fish for oceanographic investigations; most of them were battery-powered equipped with a CTD (Conductivity, Temperature, and Depth) detector leading to relatively short operation time This was a major set-back for the early systems such as Remus (remote environmental monitoring units)58 and AutoSub59 which could operate for and 12 h, respectively The use of solar-powered robots was just a matter of time, and led to the next anticipated progress in this field RiverNet was the first project aimed to develop a sensors network for water monitoring based on a solar-powered underwater robot (SAUV or solar-powered autonomous underwater vehicle).60 A production version of the robot is now commercially available from Falmouth Scientific, Inc., the “SAUV II” (see Fig 23.9) The SAUV is equipped with a standard CTD sensor as well as dissolved oxygen and pH sensors The SAUV can also be used as a platform for other environmental sensors such as nitrate, heavy metals, etc.61,62 Robotic and autonomous underwater vehicles (AUVs) are playing a crucial role in improving our understanding of the oceans Oceanographers are employing an increasing number (and variety) of in situ autonomous sensing systems.63 One example of a widely used system is the autonomous underwater gliders that are 678 T Noyhouzer and D Mandler Fig 23.9 SAUV II a solar-powered robot Reproduced with permission from Falmouth Scientific Inc sent to sample and monitor specific phenomena The gliders are equipped with wings that are designed for steering the vehicles horizontally while a buoyancy engine is used to conduct the vertical profiles.64 Although a mobile system has some advantages compared to a fixed system such as a buoy, it still suffers from some drawbacks The mobile sensor has a larger power consumption that cannot always be solved by using solar energy leading to a shorter operation time Radical changes in the flow or environment can cause damage to the mobile sensor or change the models it is programmed to follow, leading to a reduced functionality of the sensor A typical environmental change that can disrupt the operation of the sensor is the blossoming of algae on the water surface Commonwealth Scientific and Industrial Research Organization (CSIRO)65 tried to exploit all the advantages of the autonomous mobile sensor while using a network of fixed sensors to overcome the disadvantages The main interest was monitoring pathogens and pesticides especially organophosphates and carbamates In order to monitor these substances, the inventors used the enzyme, acetylcholinesterase (AChE) as a biomarker The measurement was based on the amperometric detection using carbon nanotubes (CNT) modified electrodes.66 They constructed two types of mobile robots; an AUV (autonomous underwater vehicles or autonomous Unmanned Vehicle) for shallow waters or small reservoirs and a Catamaran-based vehicle equipped with solar panels for other scenarios To reduce the power consumption the inventors used cellular communication and added an option whereby the robots change their operation and reduce the amount or type of sampling/sensing based on the amount of the energy power that is left They also constructed a large sensor network based on stationary sensors that were reinforced with mobile sensors This network could produce online information and utilizes 23 Remote Sensing 679 the mobile sensors in case further data are needed in a certain area or for monitoring special phenomenon There are numerous groups that develop AUVs and other robotic platforms most of them are aimed at increasing the data collection efficiencies, particularly in unreachable and hostile environments Despite the fast growing interest and demand for remote sensing for both regulatory and scientific purposes, more efforts that will contribute directly to the quality of remote environmental monitoring are required For example, underwater communication, biomimetics (robotics that mimics the function or structure of a biological system) and other propulsion mechanism, power sources, sensing, autonomous navigation , artificial intelligence and hydrodynamic.56 The technology is progressing rapidly and it is evident that autonomous robotic sensing is the future of oceanography and pollution monitoring 23.2.3 Submersible Remote Electrochemical Sensing Automatic monitoring is essential for recording large sets of temporal and spatial information from a water body (river, lake, lagoon, and even ocean), and is also required for rigorous biogeochemical interpretation.67 In the previous section we described the general concept of a remote station for environmental monitoring These systems are usually based on a sampling system that can withdraw the water from different depths and a flow system that can transfer it to the electrochemical measuring cell (detector) Another type of measurement is the submersible electrode (sensor), which is also known as an on-cable electrode This is a different concept were instead of using a sampling system and bringing the sample to the electrode, the electrode is brought to the sample The basic idea of the submersible electrode is shown in Fig 23.10 The electrode which comprises of a complete three-electrode cell is connected by a long shielded cable to a potentiostat and a recording device Fig 23.10 Schematics of the remote electrochemical sensor for remote sensing Reproduced with permission from reference (68) 680 T Noyhouzer and D Mandler Fig 23.11 Schematic diagram of a submersible electrode that can serve as a complete system A, cable connection; B, micropump; C, reservoirs for reagent and waste solutions; D, microdialysis sampling tube and an electrochemical flow detector; E and F, working and reference electrodes, respectively Reproduced with permission from reference (77) The first submersible device was designed by Trecier and Zirino in the early 1990s.69 They designed a submersible flow trough cell that was based on either a mercury film or a mercury drop electrode Since this early development, most of the work in this filed was carried out by Wang and his coworkers.70 They developed electrodes for monitoring different species from heavy metals71–73 to organic compounds, such as phenols, peroxides and explosives.68,74–76 The approach was usually similar and involved a submersible stripping sensor for in situ monitoring of the “total” content of dissolved species They also successfully integrated the submersible voltammetric TNT electrode with the Remus AUV creating an autonomous submersible electrode.68 In the beginning of the twenty-first century there have been a few major advancements in this field including the first step in the incorporation of all the protocol steps of the measuring system: sampling, sample pretreatment, calibration, measurement, and cleaning, into one sealed electrode.40,77,78 A schematic diagram of a submersible electrode that can serve as complete system or a lab-on cable system can be seen in Fig 23.11 Although the vast progress in this field and the clear advantages, there are only few commercially available submersible electrochemical sensors for marinespecification Most of the sensors that are developed in the lab show a lesser 23 Remote Sensing 681 Fig 23.12 Standard version of the VIP system for in-situ monitoring and profiling (a) Voltammetric probe, (b) multiparameter probe, and (c) online O2 removal system Reproduced with permission from reference (54) sensitivity in the field There are a few examples of submersible electrodes, which showed good results in the lab as well as under real conditions These electrodes were tested not only for sensitivity and accuracy but also for their reproducibility and stability as a function of time The major setback in the validation of the electrode is the fact that the electrodes are exposed to various species (organic and inorganic) that can cause fouling even in the presence of an automated cleaning protocol Even electrodes that pass all of these strict tests such as the electrodes developed for nitrate50 or trace metals79 not always succeed in the transition to the next step One of the very few commercially available systems is the voltammetric in situ profiling system (VIP) The first prototype of the VIP system was developed by Tracier in collaboration with Idronaut in 1998.1 This system later underwent further improvements and was commercialized by Idronaut (Fig 23.12) The VIP is made of several units, such as on-line oxygen removal module, a multiparameter probe, and a calibration unit The system has the capability of monitoring trace metals down to a depth of 500 m with a subnanomolar sensitivity.80,78 VIP systems may demonstrate the next step in the evolution of the submersible electrode In 2009 the VIP system was tested by four of the leading labs in aquatic metal speciation in Europe.78 The system was simultaneously tested in Sweden, Italy, Switzerland, and the UK They preformed measurements of Cu(II), Pb(II), and Cd(II) in natural waters at a frequency of 2–3 analyses per hour The results were compared to the standard methods: inductively coupled plasma mass spectrometry (ICP-MS) and voltammetry using mercury electrodes The results were almost 682 T Noyhouzer and D Mandler identical to those obtained by the standard methods and showed that the VIP system is a reliable solution for remote environmental sensing The system can provide information about the different geochemical behavior of dissolved metals and enables to distinguish between a variety of metal fractions To show a the possible use of the VIP system as part of a sensor network, two systems were placed a few meters apart and preformed sampling at a depth of 1.5 m every 50 for a couple of days The systems successfully measured dynamic concentrations of Cd and Pb as well as the salinity of the sampling site While this and similarly developed systems hold a great promise for possible sensor networks they still suffer from a few fundamental problems These systems require skilled operators, preferably with good background in electrochemistry Unlike the ISE, the VIP system can measure the open circuit potential (OCP) for a period of up to weeks without constant maintenance It is also worth mentioning that the VIP system has a size and weight limitation, which is not ideal for an autonomous remote device In summary, the most significant advantage of the submersible electrode is the fact that no sampling system is needed, which is also its biggest disadvantage A sampling system makes the remote system more complicated in terms of weight, size, and power supply but can also be used to filter the water and protect the electrode surface from fouling Although some submersible electrode can utilize a special filter it can also be fouled and requires maintenance Another type of a mobile environmental sensor, which does not utilize a flow system is the hybrid robot developed by the Brazilian oil company Petrobras S.A.81 This hybrid robot was developed not only to replace manual sampling but also to conduct continuous monitoring of water quality and gas emission near oil pipe lines The robot is designed to operate on a wide variety of terrains, including water, land, marshes, swamps, and sand 23.3 Environmentally Monitoring Platforms The previous sections described the different parameters involved in the fabrication of a remote environmental sensor and the different types of sensor, which were developed This section focuses on some of the more ambitious projects, which attempted to construct an environmentally monitoring platform The idea behind a platform is a combination of several sensors from the same or different types in order to obtain a complete prospective of the inspected area During the last decade several projects were mostly funded by the European Union (EU) or the US, but despite several successful trials, so far they all have remained as scientific projects and to the best of our knowledge none of them has been commercialized or is constantly operating HydroNet was a project funded by the EU framework 7th program The project began in 2008 and ended in the beginning of 2012 Partners from ten countries participated in the project It was aimed at designing, developing, and testing a new technological platform for improving the monitoring of water bodies based on a network of sensors and autonomous, floating, and sensorized robots, embedded in an Ambient Intelligence infrastructure A network of sensors was designed to 23 Remote Sensing 683 Fig 23.13 Schematics of the HydroNet robot All the sensors are connected to the main sampling system Fig 23.14 The HydroNet robots that were developed for: (a) costal water, (b) rivers sample and analyze several chemical and physical parameters in water in real-time and continuously monitor the well-being status of water bodies (Electro)chemical,52,82,83 optical and biological66 sensors were developed and used for monitoring of physical parameters and pollutants in water such as chromate, cadmium, mercury, oil, and chlorophyll Enhanced mathematical models were also developed for simulating the pollutants transport and processes in rivers, lakes, and coastal waters The sensors were planned also to be embedded into fixed stations (buoys) and mobile robots that are able to navigate, as part of a network, in diverse water scenarios, from coastal sea waters, to creeks and rivers (both at the head and mouth of the rivers) to natural and artificial lakes and lagoons The scheme of the Hydronet robot is shown in Fig 23.13, while Fig 23.14 shows the actual Hydronet robot that was developed 684 T Noyhouzer and D Mandler Fig 23.15 (a) Prototype of SHOAL-1 that was shown in the London Science Museum (b) The prototype of SHOAL-2 during a live test The robot and sensors were part of an Ambient Intelligence platform, which integrated not only sensors for water monitoring and robot tasks execution, but also communication backhaul systems, databases technologies, and knowledge discovery in databases (KDD) processes for extracting and increasing knowledge on water management From a scientific point of view the project was a big success, new technologies were developed and a significant contribution was made is several fields Yet, the project did not result in a prototype that could be easily commercialized SHOAL84 is another example of an ambitious project that was developed under the EU 7th framework program The SHOAL project began in 2009 and involved partners from France, UK, Spain, and Ireland SHOAL aimed to develop a number of robotic fish that will operate together in order to monitor and search for pollution in ports and other aquatic areas The swarms of autonomously controlled robots were equipped with an array of chemical sensors that were able to locate pollution and identify its source The robot was equipped with various sensors for phenols, dissolved oxygen (DO), nutrients, and heavy metals (Cu and Pb) The chemical sensors were based on an array of microelectrodes Moreover, the robots were also given intelligence so that in case that significant amount of pollution is detected, the robots operate together communicating via ultrasonic communications to find the source of the pollution In other words, the fleet of sensors aimed to provide early alarms and to determine the source of the pollution The data from the robots were to be used for creating a real-time map of the pollutants present in the water and their concentration and location on a 3D map of the port The robots were constructed to mimic real fish so as not to alarm other marine inhabitants Two prototypes were constructed SHOAL-1 (Fig 23.15a) and SHOAL-2 (Fig 23.15b) The project officially ended in may 2012 after a successful test in port of Gijon, Spain SHOAL was not the first project to develop a robot that mimics the behavior of fish Unlike the other projects, which are based on a sophisticated robotic platform, the Bayen group from UC Berkley designed a simpler system (see Fig 23.16) They based their system on a mobile floating sensor network.85 The sensors were put into a floating device equipped with a cellular device (smart-phone) which served as the microprocessor The devices were then scattered in estuarine environments and rivers and were carried by the current trough the area of interest The data from the 23 Remote Sensing 685 Fig 23.16 The two main types of floating sensors On the left, the passive sensors that are driven by the flow On the right, the sensors that have a propeller to maneuver them when encountering obstacles Reproduced with permission from reference (85) sensors were transmitted via the cellular phone network using a special application or a short-range wireless radio The movement of the sensors was tracked by GPS providing a virtual map of the current and the different measured parameters This information helped to track the movement of the contaminants in real time Since they used a large number of these sensors, and recorded the combined data, they gathered enough information to get a reliable picture about how contaminated the area was This approach is characterized by its simplicity and low-power consumption; on the other hand, the devices lack any real navigational abilities Although there was developed a more advanced model that has a propeller, which can assist the sensor to avoid obstacles once the sensors are deployed, no route adjustment can be made, and it is hard to repeat a measurement To solve this issue a large number of sensors must be deployed Furthermore since the device cannot navigate back to its base, a collection mechanism needs to be established Today the researches are waiting at the end of the route to collect each device These projects are just the tip of the iceberg Organization such as GEOTRACES86 which are interested in the distribution of the different elements in the environment under different conditions, as well as environmental agencies such as EPA, which are more interested in mapping and preventing pollution, are pushing all the time for more sophisticated platforms and more accurate sensors These demands help to push science into its limits and beyond We believe that with time more collaborations will lead to significant improvements making an autonomous remote sensing a common daily routine 23.4 Conclusions and Perspectives Clearly remote environmental sensing is going to play an increasing role in our attempts to understand anthropogenic and natural processes The ability to monitor the environment in space and time in not only crucial for understanding processes but also as a measure of protection, that could serve as early alarm in cases of sudden pollution or environmental changes Surveying the development of remote 686 T Noyhouzer and D Mandler environmental monitoring is fascinating and reveals tremendous efforts usually funded by governmental and legislation agencies Clearly, the progress in this area lags behind the need At the same time, the lack of commercial systems also inhibits legislation, which has also an effect on commercialization of new products Remote environmental sensing systems, which will be able to eventually make it to the market, require the development of an entire platform, which includes an autonomous vehicle and miniaturized sensors This, in fact, requires assembling many subunits such as power, control, and navigation systems as well as sampling and flow systems for the sensors Recently and mostly by the support of the EU we have witnessed such efforts to bring together under one umbrella the various expertise and skills that are needed to develop such systems A major challenge still lies in constructing the sensors There is a very large gap between a prototype that is developed in the 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