Environmental analysis by electrochemical sensors and biosensors applications

A rotating ring-disc electrode RRDE was utilized for the determination ofchemical oxygen demand COD.3 A PbO2layer was deposited on the platinumdisc surface of the ring-disc electrode bec

Series Editor: David J Lockwood

Nanostructure Science and Technology

Ligia Maria Moretto

Kurt Kalcher Editors

Environmental Analysis by

Electrochemical Sensors and

Biosensors

Volume 2: Applications

Tai Lieu Chat Luong

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

Department of Molecular Sciences

and nanosystems

University Ca’ Foscari of Venice

Venice, Italy

Kurt KalcherInstitute of ChemistryUniversita¨t GrazGraz, Austria

ISSN 1571-5744 ISSN 2197-7976 (electronic)

ISBN 978-1-4939-1300-8 ISBN 978-1-4939-1301-5 (eBook)

DOI 10.1007/978-1-4939-1301-5

Springer New York Heidelberg Dordrecht London

Library of Congress Control Number: 2014949384

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Springer is part of Springer Science+Business Media (www.springer.com)

Electrochemical sensors are transforming our lives From smoke detectors in ourhomes and workplaces to handheld self-care glucose meters these devices can offersensitive, selective, reliable, and often cheap measurements for an ever increasingdiversity of sensing requirements The detection and monitoring of environmentalanalytes is a particularly important and demanding area in which electrochemicalsensors and biosensors find growing deployment and where new sensing opportu-nities and challenges are constantly emerging.

This manual provides up-to-date and highly authoritative overviews of chemical sensors and biosensors as applied to environmental targets The booksurveys the entire field of such sensors and covers not only the principles of theirdesign but their practical implementation and application Of particular value is theorganizational structure The later chapters cover the full range of environmentalanalytes ensuring the book will be invaluable to environmental scientists as well asanalytical chemists

electro-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 timestimulating further research

Oxford University

Oxford, UK

Richard G Compton

v

Dear Reader,

We are pleased that you have decided to useEnvironmental Analysis with chemical Sensors and Biosensors either as a monograph or as a handbook for yourscientific work The manual comprises two volumes and represents an overview of

Electro-an intersection of two scientific areas of essential importElectro-ance: environmentalchemistry and electrochemical sensing

Since the invention of the glass electrode in 1906 by Max Cremer, ical sensors represent the oldest type of chemical sensor and are ubiquitouslypresent in all chemical labs, industries, as well as in many fields of our everydaylife The development of electrochemical sensors exploiting new measuring tech-nologies makes them useful for chemical analysis and characterization of analytes

electrochem-in practically all physical phases - gases, liquids and solids - and electrochem-in differentmatrices in industrial, food, biomedical, and environmental fields They havebecome indispensible tools in analytical chemistry for reliable, precise, and inex-pensive determination of many compounds, as single shot, repetitive, continuous,

or even permanent analytical devices Environmental analytical chemistry demandshighly sensitive, robust, and reliable sensors, able to give fast responses even foranalysis in the field and in real time, a requirement which can be fulfilled in manycases only by electrochemical sensing elements

The idea for this manual was brought to us by Springer The intention was tobuild up an introduction and a concise but exhaustive description of the state of theart in scientific and practical work on environmental analysis, focused on electro-chemical sensors

To manage the enormous extent of the topic, the manual is split into twovolumes The first one, covering the basic concepts and fundamentals of bothenvironmental analysis and electrochemical sensors,

1 gives a short introduction and description of all environments which are subject

to monitoring by electrochemical sensors, including extraterrestrial ones, as aparticularly interesting and exciting topic;

vii

2 provides essential background information on electroanalytical techniques andfundamental as well as advanced sensor technology;

3 supplies numerous examples of applications along with the concepts and egies of environmental analysis in all the various spheres of the environment andwith the principles and strategies of electrochemical sensor design

strat-The second volume is more focused on practical applications, mostly mentary to the examples given in volume I, and

comple-1 overviews and critically comments on sensors proposed for the determination ofinorganic and organic analytes and pollutants, including emerging contaminants,

as well as for the measurement of global parameters of environmentalimportance;

2 reviews briefly the mathematical background of data evaluation

We hope that we have succeeded in fulfilling all these objectives by supplyinggeneral and specific data as well as thorough background knowledge to makeEnvironmental 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 differentspecialized areas in analytical and environmental chemistry requires the expertise

of many scientists Therefore, in the first place we would like to thank all thecontributors to this book for all the time and effort spent in compiling and criticallycommenting on research, and the data and conclusions derived from it

Of course, we would like to particularly acknowledge all the people fromSpringer who have been involved with the process of publication Our cordialthanks are addressed to Kenneth Howell, who accompanied us during all theprimary steps and, later during the process of revision and editing together withAbira Sengupta, was always available and supportive in the most professional andpleasant manner

Furthermore, we are indebted to a number of our collaborators, colleagues, andfriends for kindly providing us literature and ideas, and stimulating us with fruitfuldiscussions We would also like to thank all the coworkers who did researchtogether with us and under our supervision, as well as all the scientific communityworking 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 othersinterested in this book, since we are aware that some contributions or useful detailsmay have escaped our attention Such feedback is always welcome and will also bereflected in our future work

December 2013

Ligia Maria Moretto graduated in Chemical Engineering at the Federal University

of Rio Grande do Sul, Brazil, and received her Ph.D in 1994 from the UniversityCa’ Foscari of Venice with a thesis entitled “Ion-exchange voltammetry for thedetermination of copper and mercury Application to seawater.” Her academiccareer began at the University of Caxias do Sul, Brazil, and continued at theResearch Institute of Nuclear Energy, Sao Paulo, Brazil In 1996 she completedthe habilitation as researcher in analytical chemistry at the University Ca’ Foscari

of Venice Working at the Laboratory of Electrochemical Sensors, her researchfield has been the development of electrochemical sensor and biosensors based onmodified electrodes, the study of gold arrays and ensembles of nanoelectrodes, withparticular attention to environmental applications She has published more than

60 papers, several book chapters, and has presented about 90 contributions atinternational conferences, resulting in more than 1,100 citations Prof Morettocollaborates as invited professor and invited researcher with several institutions inBrazil, France, Argentina, Canada, and the USA

Kurt Kalcher completed his studies at the Karl-Franzens University (KFU) with adissertation in inorganic chemistry entitled “Contributions to the Chemistry ofCyantrichloride, CINCCI2”; he also received his Ph.D in 1980 from the sameinstitution In 1981 he then did postdoctoral work at the Nuclear Research Center inJu¨lich (Germany) under the supervision of Prof Nu¨rnberg and Dr Valenta, andconducted intensive electroanalytical research while he was there Prof Kalchercontinued his academic career at KFU with his habilitation on chemically modifiedcarbon paste electrodes in analytical chemistry in 1988 Since then, he has beenemployed there as an associate professor His research interests include the devel-opment of electrochemical sensors and biosensors for the determination of inor-ganic and biological analytes on the basis of carbon paste, screen-printed carbon,

ix

and boron-doped diamond electrodes, as well as design, automation, and datahandling with small analytical devices using microprocessors He has publishedaround 200 papers and has presented about 200 contributions at internationalconferences These activities have resulted in more than 3,100 citations.Prof Kalcher has received numerous guest professor position offers inBosnia-Herzegovina, Poland, Slovenia, and Thailand.

Part I Environmental Analysis

1 Introduction to Electroanalysis of Environmental Samples 3Ivan Sˇvancara and Kurt Kalcher

2 Soil 23Kenneth A Sudduth, Hak-Jin Kim, and Peter P Motavalli

3 Water 63Eduardo Pinilla Gil

4 Atmosphere 93Andrea Gambaro, Elena Gregoris, and Carlo Barbante

5 Biosphere 105Adela Maghear and Robert Sa˘ndulescu

6 Extraterrestrial 131Kyle M McElhoney, Glen D O’Neil, and Samuel P Kounaves

Part II Fundamental Concepts of Sensors and Biosensors

7 Electrochemical Sensor and Biosensors 155Cecilia Cristea, Veronica H^arceaga˘, and Robert Sa˘ndulescu

8 Electrochemical Sensors in Environmental Analysis 167Cecilia Cristea, Bogdan Feier, and Robert Sandulescu

9 Potentiometric Sensors 193Eric Bakker

10 Controlled Potential Techniques in Amperometric Sensing 239Ligia Maria Moretto and Renato Seeber

xi

11 Biosensors on Enzymes, Tissues, and Cells 283Xuefei Guo, Julia Kuhlmann, and William R Heineman

12 DNA Biosensors 313Filiz Kuralay and Arzum Erdem

13 Immunosensors 331Petr Skla´dal

14 Other Types of Sensors: Impedance-Based Sensors,

FET Sensors, Acoustic Sensors 351Christopher Brett

Part III Sensor Electrodes and Practical Concepts

15 From Macroelectrodes to Microelectrodes: Theory

and Electrode Properties 373Salvatore Daniele and Carlo Bragato

16 Electrode Materials (Bulk Materials and Modification) 403Alain Walcarius, Mathieu Etienne, Gre´goire Herzog,

Veronika Urbanova, and Neus Vila

17 Nanosized Materials in Amperometric Sensors 497Fabio Terzi and Chiara Zanardi

18 Electrochemical Sensors: Practical Approaches 529Anchalee Samphao and Kurt Kalcher

19 Gas Sensors 569Ulrich Guth, Wilfried Vonau, and Wolfram Oelßner

Part IV Sensors with Advanced Concepts

20 Sensor Arrays: Arrays of Micro- and Nanoelectrodes 583Michael Ongaro and Paolo Ugo

21 Sensors and Lab-on-a-Chip 615Alberto Escarpa and Miguel A Lo´pez

22 Electronic Noses 651Corrado Di Natale

23 Remote Sensing 667Tomer Noyhouzer and Daniel Mandler

Index 691

Part I Sensors for Measurement of Global Parameters

1 Chemical Oxygen Demand 719Usman Latif and Franz L Dickert

2 Biochemical Oxygen Demand (BOD) 729Usman Latif and Franz L Dickert

3 Dissolved Oxygen 735Usman Latif and Franz L Dickert

4 pH Measurements 751Usman Latif and Franz L Dickert

Part II Sensors and Biosensors for Inorganic Compounds

of Environmental Importance

5 Metals 781Ivan Sˇvancara and Zuzana Navra´tilova´

6 Non-metal Inorganic Ions and Molecules 827Ivan Sˇvancara and Zuzana Navra´tilova´

7 Electroanalysis and Chemical Speciation 841Zuzana Navra´tilova´ and Ivan Sˇvancara

8 Nanoparticles-Emerging Contaminants 855Emma J.E Stuart and Richard G Compton

xiii

Part III Sensors and Biosensors for Organic Compounds

of Environmental Importance

9 Pharmaceuticals and Personal Care Products 881Lu´cio Angnes

10 Surfactants 905Elmorsy Khaled and Hassan Y Aboul-Enein

11 Determination of Aromatic Hydrocarbons

and Their Derivatives 931

K Peckova-Schwarzova, J Zima, and J Barek

12 Explosives 965Jiri Barek, Jan Fischer, and Joseph Wang

13 Pesticides 981Elmorsy Khaled and Hassan Y Aboul-Enein

Part IV Electrochemical Sensors for Gases of Environmental

Importance

14 Volatile Organic Compounds 1023Tapan Sarkar and Ashok Mulchandani

15 Sulphur Compounds 1047Tjarda J Roberts

16 Nitrogen Compounds: Ammonia, Amines and NOx 1069Jonathan P Metters and Craig E Banks

17 Carbon Oxides 1111Nobuhito Imanaka and Shinji Tamura

Part V Data Treatment of Electrochemical Sensors and Biosensors

18 Data Treatment of Electrochemical Sensors and Biosensors 1137Elio Desimoni and Barbara Brunetti

Index 1153

Part I

Sensors for Measurement of Global

Parameters

Chemical Oxygen Demand

Usman Latif and Franz L Dickert

Organic pollution in water can be monitored by measuring an important indexcalled chemical oxygen demand (COD).1Different countries such as China andJapan set this parameter as a national standard to investigate the organic pollution inwater The conventional method to measure the COD is the determination of excessoxidizing agent such as dichromate or permanganate left in the sample.2Thus, COD

is defined as the number of oxygen equivalents required to oxidize organic rials in water In the conventional method, a strong oxidant such as dichromate isadded to the water sample to digest the organic matter whereas the remainingoxidant is determined titrimetrically by using FeSO4 as the titrant However,some drawbacks are associated with this procedure as it requires almost 2–4 h tocomplete the analysis.3,4Thus, rapid as well as automatic analysis is not possible byusing this method Moreover, skilled workers are required to produce reproducibleresults In addition, health issues and safety concerns also arise because of theconsumption of expensive (Ag2SO4), corrosive (concentrated H2SO4), and toxic(Cr2O7
) chemicals.5,6

mate-The problems associated with the conventional method can be prevented byutilizing electrochemical treatment of wastewater having organic pollutants.7,8Thebasic principle of this procedure is to electrochemically oxidize organic matter by

U Latif

Department of Analytical Chemistry, University of Vienna,

Waehringer Strasse 38, 1090 Vienna, Austria

Department of Chemistry, COMSATS Institute of Information Technology,

Tobe Camp, University Road, 22060 Abbottabad, Pakistan

F.L Dickert ( * )

Department of Analytical Chemistry, University of Vienna,

Waehringer Strasse 38, 1090 Vienna, Austria

e-mail: Franz.dickert@univie.ac.at

© Springer Science+Business Media New York 2015

L.M Moretto, K Kalcher (eds.), Environmental Analysis by Electrochemical

Sensors and Biosensors, DOI 10.1007/978-1-4939-1301-5_1

719

applying a high potential This method will degrade organic pollutants into waterand carbon dioxide whereas the amount of charge required for electrochemicaloxidation is directly proportional to the value of COD However, this method ispractically impossible by using ordinary electrodes because it requires very highpotentials to degrade organic pollutants which results in the oxidation of water Inorder to shorten the oxidation time, thin-layer electrochemical cells were alsofabricated for complete oxidation of organic pollutants.9,10 In these cells a thinlayer of the sample (2–100μm) was allowed to rest on the electrode surface Thisthin-layer electrochemical cell realizes time-effective electrolysis of sample layerswith a large ratio of electrode area to solution volume The coulometric analysis ofCOD via exhaustive oxidation of organic species is still difficult and requires a longtime of about 30 min even in the thin-layer electrochemical cell In order toovercome these problems, a number of electrodes were designed by coating withelectrocatalytic materials which lower the oxidation overpotential as well asshorten the reaction time The determination of COD in water samples is necessary

to evaluate its quality because normally in slightly contaminated water the value ofCOD is 20–25 mg/L of consumed oxygen11and in extremely contaminated indus-trial wastewater streams its value may increase to 100,000 mg/L.12

The reaction kinetics are very slow when oxidation of the COD pollutants is carriedout with oxygen, K2Cr2O7, KMnO4, and Ce (IV) which leads to an incomplete oreven non-occurring oxidation of some organic compounds even when employing atime-consuming refluxing process in the conventional method Moreover, inorganiccompounds such as (Cl
, Fe2+) may also be oxidized Thus, the COD values do notactually reflect the actual concentration of organics present in the sample In order

to overcome these problems, there should be such a species as part of a redoxsystem which should oxidize COD pollutants rapidly and selectively Moreover,this species should have enough lifetime to react with all the organic species present

in the sample The generation of hydroxyl radicals as an unstable intermediate inthe oxygen evolution reaction at the electrode is capable to address all the issuesconcerning COD values

A rotating ring-disc electrode (RRDE) was utilized for the determination ofchemical oxygen demand (COD).3 A PbO2layer was deposited on the platinumdisc surface of the ring-disc electrode because lead oxide is a promising candidatefor the direct oxidation of carbohydrates and amino acids This device was fabri-cated in such a way to produce a strong oxidant by in situ formation of an aggressivespecies which oxidizes the compounds that contribute to COD The aggressivespecies which are left behind after oxidizing the compounds react with oxygen

which is monitored at the ring electrode In such type of COD sensor, a strongoxidant is electrochemically generated at the disc part of the rotating ring-discelectrode The COD pollutants are exposed to the RRDE, and some of the pollutantswill be directly converted to its elementary components (CO2and H2O) at the discsurface while others will be converted indirectly with the generated oxidant at thedisc surface Thus, organic compounds will be degraded via two different paths.Some organic compounds are directly oxidized at a potential where also the oxygenevolution occurs, and then hydroxyl radicals will be produced as an intermediate.These hydroxyl radicals will consume the rest of the organic compounds and excess

of hydroxyl will also be oxidized to oxygen The generation of a strongly oxidizingagent at the electrode surface has the advantage that it would keep the surface clean

by avoiding the adsorption of substances

In another approach the electrocatalytic activity of lead oxide was enhanced withfluoride doping The F-doped lead oxide-modified electrode leads to the fabrication

of an electrochemical detection system for flow injection analysis to detect thechemical oxygen demand (COD) in water samples.13 The combination of flowinjection analysis with electrochemical detection of COD results in the develop-ment of a low-cost, rapid, and easily automated detection system with minimumreagent consumption The basic principle of the F-doped lead oxide electrode is thegeneration of hydroxyl radicals which are subsequently utilized for the oxidation ofCOD pollutants in order to determine the COD value It is a multistep process: atfirst, hydroxyl radicals will be produced at the surface of the F-PbO2electrode bythe anodic discharge of water:

S½ þ H2O! S OH½  þ Hþþ e

These hydroxyl radicals will be adsorbed on the unoccupied surface sites(S[]) forming S[OH] which represents the adsorbed hydroxyl radicals Theelectrocatalytic activity of lead oxide is amplified with the doping with F
because

it increases the number of unoccupied surface sites.14 If the reverse dischargingreaction is ignored then the O-transfer step can be represented by the followingequation:

S OH½  þ R ! S½ þ RO þ Hþþ e

The COD pollutants are electrocatalytically oxidized by the surface sites and outputcurrent signals are produced which are proportional to the COD value R representsthe organic pollutants which are oxidized to RO by the hydroxyl radical However,the current efficiency of the O-transfer reaction will be decreased by the

consumption of hydroxyl radicals which results in the evolution of oxygen by thefollowing reaction:

S OH½  þ H2O! S½ þ O2þ 3Hþþ e

The higher the overpotential of materials for oxygen evolution, the better thereaction compels the physisorbed hydroxyl radicals to oxidize the organics ratherthan to turn into oxygen

Dimensionally stable anodes (DSAs) are usually fabricated by depositing metallicoxides on a metal substrate such as titanium In order to synthesize DSAs, aprecursor such as metallic chloride is decomposed in an oven or by electromagneticinduction heating However, this procedure is very complex and requires a lot oftime to complete These problems can be solved by using the laser as a heat sourcefor developing DSAs via calcination The designed DSA possesses very uniqueproperties of high corrosion resistance, robustness, and electrocatalytic abilities.The electrocatalytic activity of DSAs is attributed to the formation of hydroxylradicals at the electrode surface These physisorbed species, generated by theoxygen evolution reaction, has the ability to oxidize organic pollutants electro-chemically However, a severe side reaction occurs simultaneously which con-sumes hydroxyl radicals and results in the evolution of oxygen Thus, this sidereaction competes with the oxidative degradation of organic pollutants and lowersthe current efficiency The problem can be solved by using higher overpotentialmetal oxides for oxygen evolution which preferentially compel hydroxyl radicals toelectrocatalytically oxidize organic compounds rather than to release oxygen A

Rh2O3/Ti electrode was prepared by laser calcination to develop an amperometricsensor for the determination of COD.15 Electrocatalytic oxidation of organiccompounds could be monitored with this electrode in flow injection analysis Thecurrent responses from the oxidation of the organic contaminants at the electrodesurface were proportional to the COD values

Boron-doped diamond (BDD) possesses unique properties such as a wide-rangeworking potential, low background current, stable responses, environmental friend-liness, and robustness.16,17Thus, boron-doped diamond is an excellent material todesign a sensing electrode for electrochemical water treatment.18,19A BDD filmcan be deposited on a support electrode by microwave plasma chemical vapordeposition

The BDD electrode was employed as a detecting element for determining COD

in combination with flow injection analysis (FIA).20This continuous flow methodled to the development of an online amperometric COD monitoring system whichreduced the analysis time significantly The BDD electrode was deactivated if theapplied voltage was very low because of the electropolymerization of someorganics such as phenol on the surface of the electrode This inhibition of electrodecould be overcome if a high voltage was applied to hinder the polymerization oforganic compounds The COD values monitored by this rapid online system wereclosely related to the conventional method The electrode with BDD acts as agenerator for hydroxyl radicals due to its wide electrochemical potential window,and high oxygen evolution potential.21The electrochemical oxidation of organicpollutants in water samples by employing BDD electrode is a direct or a hydroxylradical-mediated process However, oxidative degradation of organics is mainlydominated by indirect hydroxyl radicals at high potential Moreover, the oxidativepotential of hydroxyl radicals decreases with an increase in pH At the same time,the overpotential for oxygen evolution will be lowered when the solution becomesmore alkaline which leads to oxygen bubbles at the electrode The excellentcorrelation of the BDD-detecting element with the conventional method supportsthe suitability of the proposed sensor for COD detection

The electrochemical deposition of Cu nanoparticles on a Cu disc electrode led to thefabrication of a sensor device for chemical oxygen demand (COD).22The modifi-cation of the Cu disc electrode with Cu nanoparticles by using controlled-potentialreduction greatly increased the oxidation current signals in comparison to thesimple Cu disc electrode The increase in sensitivity was attributed to the largesurface area, and enhanced active sites of nanomaterials in comparison to bulkmaterials Thus, nano-Cu exhibited high catalytic activity which resulted in adecrease of the oxidation overpotential and an enhancement of the current signals

of the oxidation of organic compounds present in water In this way, a very sensitiveand stable amperometric sensor was developed for the detection of COD

A special carbon material called glassy carbon is widely used as electrode material

in the field of electrochemistry The responsive behavior of a glassy carbonelectrode (GCE) can be greatly enhanced by means of electrochemical treatment.The GCE can be activated by cyclic sweeps23or constant potential oxidation.24Theactivation of glassy carbon electrode (GCE) by applying constant potential oxida-tion tailors its surface morphology, functional groups, and electrochemical activity

The oxidative activation method introduces thornlike nanostructures as well ashydroxyl groups on the surface of a GCE which will enhance its electrochemicalactivity.25This strategy develops a very sensitive, low-cost, and simply fabricatedamperometric COD detection system having better practical applicability andaccuracy.

The modification of a glassy carbon electrode with cobalt oxide led to an excellentsensor for chemical oxygen demand.26 The sensing film of cobalt oxide wasprepared on the surface of a glassy carbon electrode via constant potential oxida-tion Co(NO3)2was used as a precursor for the electrochemical deposition of a thinand homogeneous layer The electrocatalytic ability of the cobalt oxide film wasdirectly related to the potential applied to the electrochemical film deposition Thesensing film which was prepared at an optimized potential (1.3 V vs SCE) had ahigh surface roughness, which enhanced its response area and the number of activesites The high valence cobalt in the sensing film had the capability to catalyticallyoxidize reduced organic compounds which led to a decrease of the current signal at0.8 V vs SCE The cobalt oxide film was highly useful for COD determinations andthe results were reproducible as the response signal decreased sharply after theaddition of the wastewater

The physical and chemical properties of metal nanoparticles greatly differ fromtheir bulk materials because of their morphology Nanoparticles show excellentcatalytic activity and selectivity towards different analytes if their shape and sizesare properly controlled.27The convenient and most suitable way for synthesizingmetal nanoparticles is electrochemical deposition Nickel nanoparticles can bedeposited on the electrode surface via galvanic or potentiostatic deposition Aprocess of constant potential reduction was employed for electrochemically depos-iting nickel nanoparticles on the surface of a glassy carbon electrode by utilizingNiSO4as precursor The sensitive surface fabricated in this way exhibited highelectrochemical activity to oxidize reduced organic compounds which resulted in

an increase of the oxidation current signals The catalytic activity of Ninanoparticles could be enhanced by optimizing the preparation parameters such

as reduction potential, deposition time, pH value, and concentration of nickel ions

By optimizing these parameters the shape and sizes of particles were controlledwhich lead to the fabrication of a sensitive detection tool for the chemical oxygendemand but with poor reproducibility.28

1.2.9 Nickel-Copper Alloy Electrode

An environmentally friendly sensor was developed by fabricating a nickel-copper(NiCu) alloy electrode to determine the chemical oxygen demand.29 The NiCualloy film was applied to modify the surface of a glassy carbon electrode which led

to a very stable detecting element The surface morphology of NiCu alloy wasinvestigated by atomic force microscopy which confirmed its continuity and uni-form thickness over the entire electrode The chemical composition of the devel-oped NiCu film was evaluated by energy-dispersive X-ray spectrometry whichrevealed 69 % presence of Ni in the alloy

Nickel is widely used as an electrode material for electrochemical water ment as well as in many electrochemical analyses Moreover, it is an excellentelectrocatalyst for oxidizing different organic compounds on the basis of the Ni(OH)2/NiOOH redox couple Mixing of Ni with Cu enhances the electrocatalyticactivity as well as provides long-term stability to the structure In addition, a widerange of composition of NiCu alloys is possible because both metals have similarface-centered cubic structure.30The addition of Cu to the Ni(OH)2/NiOOH redoxcouple suppresses the formation of γ-NiOOH and enhances the formation ofβ-NiOOH which is an excellent electroactive substance The electrochemical activ-ity of NiCu alloy was evaluated by cyclic voltammetry where the electrochemicallyrelevant reactions were attributed to the Ni(II)/Ni(III) redox couple31:

treat-Niþ 2OH

2e
! Ni OHð Þ2

Ni OHð Þ2þ OH

e
$ NiOOH þ H2OThe formation of Ni(OH)2at the electrode leaves behind a Cu-enriched surfacewhich can be also oxidized to Cu2O and finally to Cu(OH)2 At the end, the surfacefilm will be a mixture of NiOOH and Cu(OH)2where the counterions are mobileenough to maintain electroneutrality at the electrode surface during the redoxprocess When a NiCu alloy-modified electrode comes in contact with organicpollutants present in the sample the Ni(III) species rapidly oxidize them and formNi(II) species, as follows:

Ni OHð Þ2þ OH
! NiOOH þ H2Oþ e

NiOOHþ organicsð reduced Þþ H2O! Ni OHð Þ2þ organicsð oxidized Þþ OH

The electrocatalytic activity of the NiCu alloy electrode is higher than of a Nielectrode because the Cu(OH)2 species enhance the formation of the β-NiOOHphase and suppress the formation ofγ-NiOOH The proposed sensor device based

on NiCu alloy is a promising tool for the determination of COD in water qualitycontrol and pollution evaluation

1.3 Total Organic Carbon (TOC)

Total organic carbon is considered as a parameter to assess the organic pollution of

a sample.32 In order to measure the TOC in aqueous solutions two digestionprocedures33 are employed such as high-temperature combustion34 and photo-oxidation35 to degrade organics The basic principle of the abovementionedmethods is the complete conversion of organic compounds to carbon dioxide.Then, the evolved carbon dioxide is detected by following traditional analyticaltechniques such as infrared spectrometry, coulometry, conductivity, flame ioniza-tion, or ion chromatography Both methods demand certain protocols, as oxidationvia combustion requires high temperature as well as expensive thermal catalysts.The second method needs UV light of shorter wavelengths in the presence ofperoxodisulfate in the sample to completely oxidize organic compounds at moder-ate temperature The inexpensive photo-oxidation method has an advantage ofmeasuring lower TOC concentrations in comparison to the combustion method

References

1 Zhang S, Li L, Zhao H (2009) A portable photoelectrochemical probe for rapid determination

of chemical oxygen demand in wastewaters Environ Sci Technol 43(20):7810–7815 doi:10 1021/es901320a

2 Moore WA, Kroner RC, Ruchhoft CC (1949) Dichromate reflux method for determination of oxygen consumed Anal Chem 21(8):953–957 doi:10.1021/ac60032a020

3 Westbroek P, Temmerman E (2001) In line measurement of chemical oxygen demand by means of multipulse amperometry at a rotating Pt ring—Pt/PbO2 disc electrode Anal Chim Acta 437(1):95–105 doi:10.1016/S0003-2670(01)00927-8

4 Kim Y-C, Sasaki S, Yano K, Ikebukuro K, Hashimoto K, Karube I (2002) A flow method with photocatalytic oxidation of dissolved organic matter using a solid-phase (TiO2) reactor followed by amperometric detection of consumed oxygen Anal Chem 74(15):3858–3864 doi:10.1021/ac015678r

5 Moore WA, Walker WW (1956) Determination of low chemical oxygen demands of surface waters by dichromate oxidation Anal Chem 28(2):164–167 doi:10.1021/ac60110a005

6 Zhao H, Jiang D, Zhang S, Catterall K, John R (2003) Development of a direct trochemical method for determination of chemical oxygen demand Anal Chem 76 (1):155–160 doi:10.1021/ac0302298

photoelec-7 Sire´s I, Oturan N, Oturan MA (2010) Electrochemical degradation of β-blockers Studies on single and multicomponent synthetic aqueous solutions Water Res 44(10):3109–3120 doi:10 1016/j.watres.2010.03.005

8 Y-h C, X-y L, Chen G (2009) Electrochemical degradation of bisphenol A on different anodes Water Res 43(7):1968–1976 doi:10.1016/j.watres.2009.01.026

9 Lee K-H, Ishikawa T, McNiven S, Nomura Y, Sasaki S, Arikawa Y, Karube I (1999) Chemical oxygen demand sensor employing a thin layer electrochemical cell Anal Chim Acta 386 (3):211–220 doi:10.1016/S0003-2670(99)00041-0

10 Lee K-H, Ishikawa T, Sasaki S, Arikawa Y, Karube I (1999) Chemical oxygen demand (COD) sensor using a stopped-flow thin layer electrochemical cell Electroanalysis 11 (16):1172–1179 doi:10.1002/(sici)1521-4109(199911)11:16 <1172::aid-elan1172>3.0.co;2-j

11 Charef A, Ghauch A, Baussand P, Martin-Bouyer M (2000) Water quality monitoring using a smart sensing system Measurement 28(3):219–224 doi:10.1016/S0263-2241(00)00015-4

12 Pun˜al A, Lorenzo A, Roca E, Herna´ndez C, Lema JM (1999) Advanced monitoring of an anaerobic pilot plant treating high strength wastewaters Water Sci Technol 40(8):237–244 doi:10.1016/S0273-1223(99)00631-9

13 Li J, Li L, Zheng L, Xian Y, Ai S, Jin L (2005) Amperometric determination of chemical oxygen demand with flow injection analysis using F-PbO2 modified electrode Anal Chim Acta 548(1–2):199–204 doi:10.1016/j.aca.2005.05.068

14 Amadelli R, Armelao L, Velichenko AB, Nikolenko NV, Girenko DV, Kovalyov SV, Danilov

FI (1999) Oxygen and ozone evolution at fluoride modified lead dioxide electrodes Electrochim Acta 45(4–5):713–720 doi:10.1016/S0013-4686(99)00250-9

15 Li J, Li L, Zheng L, Xian Y, Jin L (2006) Rh2O3/Ti electrode preparation using laser anneal and its application to the determination of chemical oxygen demand Meas Sci Technol 17 (7):1995–2000 doi:10.1088/0957-0233/17/7/044

16 Wang J, Farrell J (2004) Electrochemical inactivation of triclosan with boron doped diamond film electrodes Environ Sci Technol 38(19):5232–5237 doi:10.1021/es035277o

17 Jolley S, Koppang M, Jackson T, Swain GM (1997) Flow injection analysis with diamond film detectors Anal Chem 69(20):4099–4107 doi:10.1021/ac961269x

thin-18 Cabeza A, Urtiaga AM, Ortiz I (2007) Electrochemical treatment of landfill leachates using a boron-doped diamond anode Ind Eng Chem Res 46(5):1439–1446 doi:10.1021/ie061373x

19 Bensalah G, Can˜izares P, Sa´ez C, Lobato J, Rodrigo MA (2005) Electrochemical oxidation of hydroquinone, resorcinol, and catechol on boron-doped diamond anodes Environ Sci Technol 39(18):7234–7239 doi:10.1021/es0500660

20 Yu H, Ma C, Quan X, Chen S, Zhao H (2009) Flow injection analysis of chemical oxygen demand (cod) by using a boron-doped diamond (BDD) electrode Environ Sci Technol 43 (6):1935–1939 doi:10.1021/es8033878

21 Wang J, Li K, Zhang H, Wang Q, Wang Y, Yang C, Guo Q, Jia J (2012) Condition optimization of amperometric determination of chemical oxygen demand using boron-doped diamond sensor Res Chem Intermed 38(9):2285–2294 doi:10.1007/s11164-012-0545-6

22 Yang J, Chen J, Zhou Y, Wu K (2011) A nano-copper electrochemical sensor for sensitive detection of chemical oxygen demand Sens Actuators B 153(1):78–82 doi:10.1016/j.snb 2010.10.015

23 Du M, Han X, Zhou Z, Wu S (2007) Determination of Sudan I in hot chili powder by using an activated glassy carbon electrode Food Chem 105(2):883–888 doi:10.1016/j.foodchem.2006 12.039

24 Ahammad AJS, Sarker S, Rahman MA, Lee J-J (2010) Simultaneous determination of hydroquinone and catechol at an activated glassy carbon electrode Electroanalysis 22 (6):694–700 doi:10.1002/elan.200900449

25 Wu C, Yu S, Lin B, Cheng Q, Wu K (2012) Sensitive and rapid monitoring of water pollution level based on the signal enhancement of an activated glassy carbon electrode Anal Methods 4 (9):2715–2720 doi:10.1039/c2ay25523e

26 Wang J, Wu C, Wu K, Cheng Q, Zhou Y (2012) Electrochemical sensing chemical oxygen demand based on the catalytic activity of cobalt oxide film Anal Chim Acta 736:55–61 doi:10.1016/j.aca.2012.05.046

27 Zhou X, Xu W, Liu G, Panda D, Chen P (2009) Size-dependent catalytic activity and dynamics

of gold nanoparticles at the single-molecule level J Am Chem Soc 132(1):138–146 doi:10 1021/ja904307n

28 Cheng Q, Wu C, Chen J, Zhou Y, Wu K (2011) Electrochemical tuning the activity of nickel nanoparticle and application in sensitive detection of chemical oxygen demand J Phys Chem

C 115(46):22845–22850 doi:10.1021/jp207442u

29 Zhou Y, Jing T, Hao Q, Zhou Y, Mei S (2012) A sensitive and environmentally friendly method for determination of chemical oxygen demand using NiCu alloy electrode Electrochim Acta 74:165–170 doi:10.1016/j.electacta.2012.04.048

30 Jafarian M, Forouzandeh F, Danaee I, Gobal F, Mahjani MG (2009) Electrocatalytic oxidation

of glucose on Ni and NiCu alloy modified glassy carbon electrode J Solid State Electrochem 13(8):1171–1179 doi:10.1007/s10008-008-0632-1

31 Jing T, Zhou Y, Hao Q, Zhou Y, Mei S (2012) A nano-nickel electrochemical sensor for sensitive determination of chemical oxygen demand Anal Methods 4(4):1155–1159 doi:10 1039/c2ay05631c

32 Canals A, del Remedio HM (2002) Ultrasound-assisted method for determination of chemical oxygen demand Anal Bioanal Chem 374(6):1132–1140 doi:10.1007/s00216-002-1578-2

33 Thomas O, El Khorassani H, Touraud E, Bitar H (1999) TOC versus UV spectrophotometry for wastewater quality monitoring Talanta 50(4):743–749 doi:10.1016/S0039-9140(99) 00202-7

34 Jin B, He Y, Shen J, Zhuang Z, Wang X, Lee FSC (2004) Measurement of chemical oxygen demand (COD) in natural water samples by flow injection ozonation chemiluminescence (FI-CL) technique J Environ Monit 6(8):673–678 doi:10.1039/b404034c

35 Lev O, Tsionsky M, Rabinovich L, Glezer V, Sampath S, Pankratov I, Gun J (1995) ically modified sol-gel sensors Anal Chem 67(1):22A–30A doi:10.1021/ac00097a001

Organ-Biochemical Oxygen Demand (BOD)

Usman Latif and Franz L Dickert

to BOD estimates (obtained in 5 days)

U Latif

Department of Analytical Chemistry, University of Vienna,

Waehringer Strasse 38, 1090 Vienna, Austria

Department of Chemistry, COMSATS Institute of Information Technology,

Tobe Camp, University Road, 22060 Abbottabad, Pakistan

F.L Dickert ( * )

Department of Analytical Chemistry, University of Vienna,

Waehringer Strasse 38, 1090 Vienna, Austria

e-mail: Franz.dickert@univie.ac.at

© Springer Science+Business Media New York 2015

L.M Moretto, K Kalcher (eds.), Environmental Analysis by Electrochemical

Sensors and Biosensors, DOI 10.1007/978-1-4939-1301-5_2

729

2.2 Sensors for the Determination of BOD

2.2.1 Ferricyanide-Mediated BOD Sensor

The bacterial catabolism can be monitored with redox mediators These redoxmediators are the species which are able to trap electrons from the redox moleculesinvolved in the electron transport chain.3,4By gaining electrons from the reducedelectron transfer chain molecule, the oxidized mediators are reduced This reduc-tion of mediators is subsequently monitored electrochemically A biochemicaloxygen demand (BOD) sensing method was developed by employing ferricyanide(FC) as a mediator.5 This mediator was anchored on an ion-exchangeablepolysiloxane The polysiloxane was synthesized from 3-(aminopropyl)trimethoxysilane by a sol–gel process and ferricyanide was immobilized by ionassociation and subsequently utilized for electrode modification Ferricyanide(FC) acts as an efficient mediator for shuttling electrons between the redox centers

of reduced bacterial enzymes and the electrode surface.6In the presence of FC as amediator, electrons derived from the oxidation of organic substrates in aerobiccatabolism are transferred to the FC ion which is reduced from ferricyanide toferrocyanide,7 as shown in Eq (2.1) The reduced form is then re-oxidized toferricyanide at the working electrode (anode):

2.2.2 Hybrid Material for BOD Sensor

An electrochemical biochemical oxygen demand (BOD) sensor was fabricated byusing an organic–inorganic hybrid material.8The hybrid material was synthesizedfrom silica and co-polymerized with poly(vinyl alcohol) and 4-vinylpyridine(PVA-g-P(4-VP)) Afterwards, Trichosporon cutaneum strain 2.570 cells wereimmobilized on the hybrid material The entrapment of cell strains in extracellularmaterials provides considerable advantage over free cells such as enhanced meta-bolic properties and stability The hybrid materials also protect them from environ-mental stress and toxicity The organic–inorganic material provides a biocompatiblemicroenvironment toT cutaneum cells which ensures the long-term viability of

cells proven by confocal laser scanning microscopy (CLSM) The viability of thecells is due to arthroconidia (the state ofTrichosporon cutaneum when stored) which

is produced in the extracellular material.9The arthroconidia state has the ability toresist against environmental stress and toxicity The proposed sensor by utilizingbiocompatible hybrid material could be applied for BOD determinations afteractivating the arthroconidia in appropriate conditions

2.2.3 Mediated BOD Sensor

A flow injection biochemical oxygen demand (BOD) analysis system was oped by utilizing a microbial approach.10The flow injection technique has advan-tage over batch analysis due to the ease of rapid and repetitive measurements Ayeast strain was isolated from an activated sludge and was utilized as biologicalrecognition element This strain was anchored on the substrate made of silica gelparticles and packed into a fixed bed reactor A redox mediator was employed fortransporting the electrons from the microbes to the electrode surface The redoxmediators act as electron acceptors from microbes instead of oxygen when organicsubstrates are decomposed by microbes Then, these mediators transport the elec-trons to the electrode surface such as hexacyanoferrate.5The mediators are reducedafter accepting the electrons and later are re-oxidized at the electrode surface Thecurrent produced via re-oxidation of the reduced mediator can be related with theconcentration of organic contents Potassium hexacyanoferrate(III) was employed

devel-as a mediator Thus, the mediated BOD sensor device in flow injection mode wdevel-asfabricated by immobilizing microbes in a reactor which was further coupled to anelectrochemical flow cell The designed detection tool was employed to monitorBOD ofshochu distillery wastewater (SDW)

2.2.4 Multi-Species-Based BOD Sensor

A BOD detection system containing single-strain microbes shows good stability aswell as long lifetime The single-strain sensors have disadvantages regardingaccuracy due to their limited detection capacity for a wide spectrum of substrates.BOD sensors based on multi-species microbes, however, show high detectioncapacity for a wide spectrum of substrates; but their stability is compromised due

to the interference among immobilized multi-species In the multi-species assaymicrobial cells are immobilized on a polymer or hydrogel for BOD monitoringsystems If the microbes are immobilized by physical adsorption only, then theactivation of the biofilm is very easy but with the disadvantage of limited stabilityand reproducibility because microorganisms may leak Proper immobilization ofmicrobes prevents the microorganisms from leaking which provides long-termstability; however, the cross-linked matrix of the hydrogel which entraps the

microbes acts as a barrier for the transfer of substrate and oxygen to microbes Thus,these surfaces required a long activation process.11The biofilms prepared for theBOD system must be activated12before use and this process takes from hours toseveral days, which is liming its applicability.

A stable BOD sensor was designed by immobilizing a multi-species BOD seedfor wastewater monitoring in a flow system.13The biofilm was synthesized with theBOD seed in an organic–inorganic hybrid material by which the activation time isgreatly reduced The hybrid material was based on a silica sol andco-polymerization was carried out with poly(vinyl alcohol) and 4-vinylpyridine.This organic–inorganic hybrid eliminated problems like cracking and swelling andprovided a stable biofilm after immobilizing microbes The multi-species seed was

a commercially available microbial community which was entrapped in the hybridmatrix The species comprised seven kinds of microbes which were isolated fromactivated sludge Thus, immobilizing such multi-species on a hybrid matrix led to areproducible, long-term stable BOD sensor

2.2.5 Miniaturized Electrochemical Respirometer

The miniaturization of electrochemical systems is very promising in detecting theanalyte of interest A miniaturized electrochemical respirometer was designed toanalyze the organic contents in water samples.14This miniaturized device has theability to monitor the analyte semicontinuously in comparison to other BODsensors Thus, the developed sensing tool is based on the concept of a microfluidicrespirometer, a microbial fuel cell in an amperometric mode.15Thus, it is called abioreactor—not strictly a biosensor The BOD detection device contains two twinelectrochemical oxygen sensors located in parallel chambers The protection ofelectrodes is done by coating with a silicone membrane, and one of them issubsequently modified by an agarose layer containingTrichosporon cutaneum, ayeast The whole system is fabricated by standard microfabrication techniqueswhile the electrochemical oxygen sensors are used to monitor the BOD Themicrosystem geometry as well as the coating membranes are optimized to maxi-mize the system output

The microorganisms consume oxygen in an aerobic process while metabolizingthe organic matter present in the sample In order to understand the function of theminiaturized device, we may assume that the medium is homogeneous The processcan be explained in two steps: At first, bacteria reach an uptake equilibrium withorganic matter present in the sample (Eq.2.2) Then, in a second step they willconsume oxygen to metabolize that matter into CO2and water (Eq.2.3):

bact-orgþ O2! bact þ CO2þ H2O ð2:3Þ

In the abovementioned equations, bact represents microbial cells without reducedorganic matter in their cytosol The amount of organic matter is represented byorganics which will be degraded by microbes by utilizing oxygen Thus, the amount

of oxygen consumed is directly related to the organic contents present in thesample The term bact-org represents the microbes having reduced organic matter

in their cytosol The respiration of microbial cells is explained by the secondequation in which bacteria consume organic matter by utilizing oxygen and produce

CO2and H2O The last part of this miniaturized BOD detection tool is monitoringthe amount of oxygen at an electrode expressed in simplified form by Eq (2.4):

The above mechanism of oxygen detection is rather complex16,17and involves twoseparate two-electron steps in order to detect the oxygen content by the electro-chemical sensor

Bioactivity sensors (BAS) are related to sensors for the estimation of the BOD, butthey are more general in their working concept.18–20They rely on the detection ofelectroactive metabolites from cultivated biologically active organisms (rather thanoxygen in the case of BOD) and may be, therefore, employed under aerobic as well

as anaerobic conditions Bioactivity sensors are useful in quality assessments ofwastewaters and may detect the activity of aerobic auto- and heterotrophic biomass,anoxic denitrificants, and anaerobic microorganisms The working principle isbased on a biofuel cell where the electron transfer from the biological component

to the anode is the analytically exploitable parameter

Another assay of bioactivity sensors exploits microorganisms immobilized onelectrode surfaces and monitors their activity in dependence on the surroundingconditions.21

4 Ertl P, Mikkelsen SR (2001) Electrochemical biosensor array for the identification of organisms based on lectin lipopolysaccharide recognition Anal Chem 73(17):4241–4248 doi:10.1021/ac010324l

micro-5 Chen H, Ye T, Qiu B, Chen G, Chen X (2008) A novel approach based on mediator immobilized in an ion-exchangeable biosensing film for the determination of bio- chemical oxygen demand Anal Chim Acta 612(1):75–82 doi:10.1016/j.aca.2008.02.006

ferricyanide-6 Morris K, Zhao H, John R (2005) Ferricyanide-mediated microbial reactions for tal monitoring Aust J Chem 58(4):237–245 doi:10.1071/CH05038

environmen-7 Catterall K, Zhao H, Pasco N, John R (2003) Development of a rapid ferricyanide-mediated assay for biochemical oxygen demand using a mixed microbial consortium Anal Chem 75 (11):2584–2590 doi:10.1021/ac0206420

8 Liu L, Shang L, Guo S, Li D, Liu C, Qi L, Dong S (2009) Organic–inorganic hybrid material for the cells immobilization: long-term viability mechanism and application in BOD sensors Biosens Bioelectron 25(2):523–526 doi:10.1016/j.bios.2009.08.004

9 Li H-M, Du H-T, Liu W, Wan Z, Li R-Y (2005) Microbiological characteristics of medically important Trichosporon species Mycopathologia 160(3):217–225 doi:10.1007/s11046-005- 0112-4

10 Oota S, Hatae Y, Amada K, Koya H, Kawakami M (2010) Development of mediated BOD biosensor system of flow injection mode for shochu distillery wastewater Biosens Bioelectron 26(1):262–266 doi:10.1016/j.bios.2010.06.040

11 Chan C, Lehmann M, Chan K, Chan P, Chan C, Gruendig B, Kunze G, Renneberg R (2000) Designing an amperometric thick-film microbial BOD sensor Biosens Bioelectron 15 (7–8):343–353 doi:10.1016/S0956-5663(00)00090-7

12 Tan TC, Lim EWC (2005) Thermally killed cells of complex microbial culture for biosensor measurement of BOD of wastewater Sensors Actuators B Chem 107(2):546–551 doi:10 1016/j.snb.2004.11.013

13 Liu C, Ma C, Yu D, Jia J, Liu L, Zhang B, Dong S (2011) Immobilized multi-species based biosensor for rapid biochemical oxygen demand measurement Biosens Bioelectron 26 (5):2074–2079 doi:10.1016/j.bios.2010.09.004

14 Torrents A, Mas J, Mun˜oz FX, del Campo FJ (2012) Design of a microfluidic respirometer for semi-continuous amperometric short time biochemical oxygen demand (BODst) analysis Biochem Eng J 66:27–37 doi:10.1016/j.bej.2012.04.014

15 Chang IS, Jang JK, Gil GC, Kim M, Kim HJ, Cho BW, Byung BH (2004) Continuous determination of biochemical oxygen demand using microbial fuel cell type biosensor Biosens Bioelectron 19(6):607–613 doi:10.1016/S0956-5663(03)00272-0

16 Godino N, Da´vila D, Vigue´s N, Ordeig O, del Campo FJ, Mas J, Mun˜oz FX (2008) Measuring acute toxicity using a solid-state microrespirometer: Part II A theoretical framework for the elucidation of metabolic parameters Sensors Actuators B: Chem 135(1):13–20 doi:10.1016/j snb.2008.06.056

17 Lavacchi A, Bardi U, Borri C, Caporali S, Fossati A, Perissi I (2009) Cyclic voltammetry simulation at microelectrode arrays with COMSOL Multiphysics ® J Appl Electrochem 39 (11):2159–2163 doi:10.1007/s10800-009-9797-2

18 Holtmann D, Schrader J, Sell D (2006) Quantitative Comparison of the Signals of an chemical Bioactivity Sensor During the Cultivation of Different Microorganisms Biotechnol Lett 28:889–896

Electro-19 Holtmann D, Sell D (2002) Detection of the microbial activity of aerobic heterotrophic, anoxic heterotrophic and aerobic autotrophic activated sludge organisms with an electrochemical sensor Biotechnol Lett 24:1313–1318

20 Holtmann D (2005) Elektrochemisches Monitoring biologischer Aktivita¨t Doctoral thesis, University Magdeburg (Germany) 229

21 Leifheit M, Mohr KH (1997) PTS-Manuskript (PTS-MS 66, PTS-Analytik-Tage: Aktuelle Analyseverfahren) 4/1-4/9

A number of chemical and biological reactions in water also depend on theamount of dissolved oxygen Monitoring the oxygen in ground or wastewater is animportant test in water quality and waste treatment.6,7The quality of water caneasily be assessed by the concentration of dissolved oxygen since the metabolicactivity and growth rate of microorganisms and aerobic cells depend on theiroxygen consumption.8

The oxygen present in water systems is due to atmospheric aeration and synthetic activity These common sources maintain an adequate level of oxygen inthe aqueous environment which is necessary for the existence and growth of all

photo-U Latif

Department of Analytical Chemistry, University of Vienna,

Waehringer Strasse 38, 1090 Vienna, Austria

Department of Chemistry, COMSATS Institute of Information Technology,

Tobe Camp, University Road, 22060 Abbottabad, Pakistan

F.L Dickert ( * )

Department of Analytical Chemistry, University of Vienna,

Waehringer Strasse 38, 1090 Vienna, Austria

e-mail: Franz.dickert@univie.ac.at

© Springer Science+Business Media New York 2015

L.M Moretto, K Kalcher (eds.), Environmental Analysis by Electrochemical

Sensors and Biosensors, DOI 10.1007/978-1-4939-1301-5_3

735

forms of life in water If the concentration of oxygen in aquatic systems falls below

2 mg/L for some time then it can cause the dying of large fish.9Thus, the amount ofdissolved oxygen is a vital parameter to assess water quality

The DO level should be kept high in order to maintain freshwater streams forswimming or fishing If the oxygen level drops too low then fish will suffocate andthe aqueous environment will be quite favorable for harmful bacteria There shouldalso be an optimum level of dissolved oxygen in the wastewater treatment processcontrol because the solids in wastewater are allowed to settle and bacteria are added

to decompose this solid If the concentration of oxygen is quite higher than theoptimum level more energy is required for aeration and processes will becomeexpensive If the dissolved oxygen level is low the aerobic bacteria will die anddecomposition ceases

Selectivity can be introduced to an electrode by covering it with a membrane Thismembrane helps the specific analyte in reaching the electrode surface and leavesother substances behind In addition, these membranes also eliminate the problem

of electrode poisoning The best known example is the Clark electrode which iscovered with a polytetrafluoroethylene (PTFE) membrane This porous membraneassists the diffusion of oxygen only A platinum or gold electrode is first coveredwith a thin layer of electrolyte Then, a PTFE porous membrane is placed over itwhich hinders other species except oxygen to permeate to the electrode, thusavoiding its poisoning A potential is applied to the working electrode to reduceoxygen A silver disc serves as a reference electrode

Leland C Clark developed this well-known oxygen sensor in 1956 which is widelyused for physiological, industrial, and environmental analysis It is an amperomet-ric sensor which consists of a working electrode, a reference electrode, and theelectrolyte as shown in Fig.3.1

The working electrode (cathode) is made of noble metals such as platinum orgold, so the cathode material does not take part in the chemical reaction, whereasthe anode is Ag in KCl A negative potential is applied to cathode relative to theanode (reference electrode) in order to reduce the dissolved oxygen present in thesolution by the following reaction:

O2þ 2H2Oþ 2e! H2O2þ 2OH

HO þ 2e! 2OH

The electrode surface is isolated by the oxygen-permeable polymeric membrane inorder to avoid the interference of any electroactive species present in the solutionalong with DO As a result, only dissolved oxygen present in the sample will diffusethrough the membrane and be reduced at the cathode surface due to a negativeexternal potential which will produce an electric current At a specific value ofpolarization potential which depends on the cathode material the current is linearlyproportional to the oxygen concentration.

Xingbo and co-workers designed a device to determine the DO content10 with

a sensor based on metal insulator semiconductor field effect (MISFET) structure

A LaF3 crystal exhibits extraordinary sensing capability towards oxygen whichmakes it an attractive material for researchers.11In order to fabricate the device,carbon paste with a Pt-LaF3mixture film was used as a sensing membrane Thesensor was assessed with different oxygen concentrations (5–12 ppm) and outputvoltage signals were obtained at different temperatures and different biases Thedevice with Pt-LaF3sensor film exhibited excellent sensitivity towards DO con-centrations The sensor responded to a change in oxygen concentration producing a

Fig 3.1 Clark oxygen

sensor

gate voltage shift of the MISFET which was used to measure DO concentrations.The gate of the sensor device was developed by following N-type metal oxidesemiconductor (NMOS) technology Then, the sensing film of Pt-LaF3was pre-pared by a carbon paste film Paraffin wax was used as an adhesive and by melting it

at 60C it was spread equally on the surface of the gate which helped in preparing

the film with the sensing mixture after drying

The device was operated at a constant drain-source current and voltage Themeasurement was carried out with a feedback loop by regulating the referencevoltage.12The sensor output signals in terms of gate voltage shift were measured as

a function of the DO concentration by a digital voltmeter

LaF3was also employed as solid electrolyte while using Pt as a sensing electrode

to develop a potentiometric oxygen sensor.13

A potentiometric sensor was developed by Martinez-Manez and co-workers inthick film technology.14RuO2was used as sensitive material whereas this activeelectrode surface was covered with a semipermeable polymeric (poly-isophthalamide diphenylsulfone, PIDS) or ceramic-based (TiO2) membrane Themeasurement of DO could only be carried out effectively if other redox processeswere excluded except the desired reaction which was produced by oxygen.15Thiswas achieved by covering the active electrode with a semipermeable polymeric orceramic membrane which allowed to pass DO and excluded any other redox-activespecies present in solution A schematic view of the DO potentiometric sensor isdisplayed in Fig.3.2

This DO electrode consisted of (1) a substrate made of isolating material, (2) alayer of conductive material with (2a) as the terminal side of this material, (3) alayer of sensitive material (RuO2), (4) a layer of a polymer or ceramic as oxygen-permeable membrane, and (5) an isolating layer exposing the active and terminalsides and covering the rest The response of the TiO2-coated RuO2electrode wasmonitored in the presence of oxygen in an aqueous environment Variations in the

Fig 3.2 Schematic representation of MISFET for dissolved oxygen electrode: (1) substrate, (2) layer of conductive material, (2a) terminal area, (3) layer of material sensible to oxygen, (4) layer consisting of a membrane ideally permeable to oxygen and non-permeable to ions, and (5) isolating layer, adapted from reference [14]

emf of the active electrode versus an Ag/AgCl reference electrode as a function of

DO concentrations in water were obtained A linear response with a Nernstian slope

of 59.4 mV per decade was observed in 0.5–8 ppm DO concentration range Thisreaction involved only one electron per oxygen molecule in the reduction processindicating that superoxide (O2) was produced by the reaction O2+ 1e¼ O2 .

Excellent emf variations were observed if the active electrode was covered with

an oxygen-permeable membrane because the typical interfering species was theproton Non-coated active electrodes gave a linear response against proton concen-trations in comparison to the oxygen-permeable membrane-coated electrode whichshowed a much lower variation of the potential against pH The PIDS-coated RuO2also exhibited a linear response as a function of DO concentrations in the range from0.8 to 8 ppm and showed negligible influence from pH, but the only drawback wasthe inferior adherence of the PIDS membrane in comparison to the titaniamembrane

Aside from covering their surface with a membrane, electrodes can be modifiedwith an electroactive species These modifiers act as mediators which help with theelectron transfer between the analyte and the electrode Moreover, this modificationalso helps in lowering the potential needed to reduce oxygen at the electrodesurface The modified electrodes can be prepared by direct adsorption ofelectroactive species or by physically covering the electrode surface In somecases, linkers are also employed in order to immobilize the mediators to theelectrode surface Chapter 16.2 of the volume 1 is dedicated to the many differentaspects of modified electrodes

Electrodes modified with electroactive polymers exhibit considerable sensitivityand may lower the reduction potential for the detection of oxygen.16Actually, thedirect reduction of oxygen at solid electrodes requires a highly negative potential.Electroactive metal complexes such as metal-porphyrins or metal-free organiccompounds can act as electron transfer mediators and are suitable for electrodemodification to determine oxygen.17Nile blue is a well-known electroactive medi-ator for electron transfer Poly(nile blue) film can easily be immobilized on a glassycarbon electrode by electropolymerization The resulting layer is very stable which

is attributed to the presence of conjugated aromatic rings in the dye The poly(nileblue) layer possesses significant affinity for dissolved oxygen By theelectrocatalytic activity of this compound oxygen is reduced in a two-electron-two-proton process at a lower potential as shown in Fig.3.3.18

3.3.2 Metalloporphyrin-Modified Electrode

Porphyrins and metalloporphyrins possess distinct properties which make themattractive as a class of material suitable for modifying electrodes.19These proper-ties include electrocatalytic activity, or photoreactivity Hydrolysis and subsequentcondensation of silanes with metalloporphyrins create a silica matrix in whichmetalloporphyrins are covalently bound The iron(III)-tetra-o-ureaphenyl-porphyrino silica matrix ((o)-FeTUPPS) is an excellent mediator for electrontransfer; it is obtained by anchoring iron porphyrin tetraurea to a silica matrix20;the resulting layer is highly stable due to the covalent attachment of the porphyrin tothe silica backbone.21

Modification of the electrode surface with (o)-FeTUPPS leads to the formation

of active sites available for the reduction of oxygen which occurs at a less negativepotential in comparison to the unmodified graphite electrode If metalloporphyrinsare used for electrode modification, then the reduction of dissolved oxygen canoccur via two mechanisms: reduction of oxygen to hydrogen peroxide by a transfer

of two electrons, or direct reduction to water when four electrons take part in theprocess (o)-FeTUPPS as a modifier catalyzes the two-electron process which leads

to the formation of H2O2which is determined by a rotating disk electrode

(CoTSPc)-Modified Electrode

In another approach, a DO sensor was proposed by modifying a glassy carbon(GC) electrode with cobalt tetrasulfonate phthalocyanine (CoTSPc).22The directreduction of oxygen at a solid electrode is a slow process and also requires a highnegative potential which can be lowered by electron transfer mediators that canshuttle the electrons between oxygen and electrode Among these mediators,phthalocyanines acquired a lot of attention because of their catalytic ability and

Fig 3.3 Electrocatalytic action of poly(nile blue) for the reduction of oxygen, adapted from reference [ 18 ]

stability.23,24CoTSPc was immobilized by using a poly-L-lysine (PLL) film whichacted as an excellent stabilizer for CoTSPc modifier.25This polyelectrolyte avoidsleaching of the electrocatalyst due to ion-pair attraction between the amino group ofPLL and the sulfonic acid group of CoTSPc The PLL film alone does not create anyeffect in reducing dissolved oxygen; the catalytic effect is solely attributed to [Co(II)TSPc]4as the active site present in the PLL film.

The influence of CoTSPc and PLL amount in the sensor response was analyzedand best results were obtained when using 0.8 mmol L1 of CoTSPc and0.12 mmol L1of PLL The measurements were carried out by differential pulsevoltammetry (DPV) and chronoamperometry With the latter technique a linearresponse was observed for 0.2–8 mg L1DO in solution

In the DPV measurements, the peak current increased with scan rates from 0.005

to 0.02 V s1 but accompanied by a broadening of peaks Best sensitivity wasachieved with a pulse amplitude of 0.075 V and a scan rate of 0.02 V s1 The DPVmeasurements showed a linear response at optimized conditions for concentrationsfrom 0.2 to 8 mg L1oxygen in solution The device with modified GC exhibitedexcellent catalytic activity and shifted the reduction potential of DO by 200 mVtowards less negative value

Cobalt-based macrocyclic complexes are some of the catalysts that exhibit icant catalytic activity against DO.26Vitamin B12 is a cobalt-based complex andinherits excellent electrocatalytic properties.27 It can be easily screen printed tomodify the electrode providing DO sensors better than the Clark-type electrode.The latter should be covered with a permeable membrane and must be properlymaintained Modifying the electrode with vitamin B12creates a membrane-free DOsensor Tedious maintenance is not required with this kind of sensor Moreover,poisoning of the membrane is not an issue anymore The electrochemical behavior

signif-of the vitamin B12-modified electrode involved in the reduction of oxygen can beexplained by the following equations28:

Electrode-vitamin B12 CoIII

þ e! Electrode-vitamin B12 CoII
Vitamin B12 CoII

þ O2þ 2Hþ! Vitamin B12 CoIII

þ H2O2Vitamin B12 CoII

þ H2O2þ 2Hþ! Vitamin B12 CoIII

þ 2H2OThese equations clearly show the electrocatalytic properties of vitamin B12 Theelectrocatalytic reduction of oxygen leads to the formation of hydrogen peroxide bythe electrode; H2O2is then further reduced to water molecules by vitamin B12

3.3.5 Manganese Phthalocyanine-Modified Electrode

A mixed oxide matrix comprises a porous framework which makes it a perfectsubstrate for the immobilization of electroactive species.29The surface of the mixedoxide network is covered with hydroxyl (-OH) groups which allow functiona-lization with electroactive species The electrochemical properties, electrical con-ductivity, as well as stability of transition metal complexes make them a promisingcandidate for designing an electrochemical sensor for dissolved oxygen.30Theseproperties are associated with the electrons of conjugated bonds and on the centralmetal atom as well The manganese phthalocyanine (MnPc) complex can beimmobilized on a porous network of a mixed oxide matrix consisting of SiO2/SnO231to which the mechanical stability of the film is attributed Chemical stabilityresults from the strong confinement of electroactive species in the pores of the oxideframework which prevents its leaching over a long time when being in contact withthe solution Moreover, the confinement of metal complexes in the pores ensures ahomogeneous layer of electroactive species over the whole-electrode surface.The reduction of oxygen can occur in two different ways, either involving twoelectrons yielding H2O2or through reduction to water with four electrons:

O2þ 2Hþþ 2e! H2O2

O2þ 4Hþþ 4e! 2H2OThe estimation of the number of electrons involved in oxygen reduction and theproduct obtained can be assessed by rotating ring-disk electrode experiments Thistechnique proved the involvement of four electrons when MnPc complex was usedfor the modification of electrodes

Some organic dyes show high electroactivity which makes them useful electronmediators.32The electrochemical activity of dyes, such as methylene blue, meth-ylene green, neutral red, and pyronin B, is attributed to their conjugated ringstructure.33 Modification of electrodes with these electroactive compounds (e.g.,methylene blue) for the detection of dissolved oxygen yields excellent results.However, problems are associated with their anchoring on the electrode surfacebecause they will leach if they are not properly attached Many organic dyes can beimmobilized on the electrode surface by carbon nanotubes, zeolite, Nafion, silane,

or electropolymerization

Electrodes which are modified with a dye-polymer exhibit usually good stability,conductivity, and enhanced electrochemical sensing behavior Among a lot of othersignificant properties silica nanoparticles possess a large surface area and openspace for the immobilization of organic dyes without affecting their inherent