Electrochemical sensing and biosensing based on square wave voltammetry

AnalyticalMethods

CRITICAL REVIEW

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Electrochemical se

ACRUiUHabmta1

cles, �70 industrial technical reprecipient of the Lakehead UniveAward, the Canadian CatalysisSociety for the Promotion of Scienthe Keith Laidler Award of the C(CSC), the Lash Miller Award oCanadian Section, the Fred BeamOntario Premier's Research Exceelected as a Fellow of the Royal Soc

Department of Chemistry, Lakehead Univ

Ontario P7B 5E1, Canada. E-mail: aic

3467775; Tel: +1-807-343-8318

Cite this: Anal. Methods, 2013, 5, 2158

Received 26th January 2013Accepted 7th March 2013

DOI: 10.1039/c3ay40155c

www.rsc.org/methods

2158 | Anal. Methods, 2013, 5, 2158

nsing and biosensing based on squarewave voltammetry

Aicheng Chen* and Badal Shah

Square wave voltammetry (SWV) has been widely used in the development of electrochemical sensors and

biosensors in recent years due to its high selectivity and sensitivity. It is of great interest and importance to

rapidly and sensitively detect disease-related biomarkers, environmental pollutants (e.g., heavy metals and

other chemical contaminants), which are severely detrimental to human and animal life and the environment

as a whole. Further, efficacious sensing is required for the detection of food resident contaminants (e.g.,

bacteria, viruses and parasites) and for the verification of the therapeutic ingredients of dietary supplements.

Enzyme kinetics is another interesting domain that employs SWV as an effective analytical tool for the

mechanistic study of enzyme reactions. The aim of this paper is to provide a comprehensive review of the

electrochemical SWV method and its significant applications in sensing and biosensing spanning various

fields such as diagnosis, environmental and food analysis and enzyme kinetics. The development of novel and

improved electrode surfaces and nanomaterials introduces the possibility of sensors and biosensors that will

exhibit even higher sensitivity, with SWV serving as an ideal methodology for its optimization. Concurrent

with a better understanding of electrochemistry and life sciences, sensors and biosensors based on SWV

have the potential to serve as next generation point-of-care diagnostic devices, as well as highly sensitive

and selective detectors for food/environmental monitoring and enzyme studies.

icheng Chen is a Professor ofhemistry and Canadaesearch Chair at Lakeheadniversity. He received his PhDn electrochemistry at theniversity of Guelph in 1998.is research interests span thereas of electrochemistry,iosensor, green chemistry,aterials science and nano-echnology. He has authored/co-uthored six book chapters, over20 peer-reviewed journal arti-orts and two patents. He is arsity Distinguished ResearcherLectureship Award, the Japance (JSPS) Invitation Fellowship,anadian Society for Chemistryf The Electrochemical Societyish Award of the CSC, and thellence Award (PREA). He wasiety of Chemistry (UK) in 2011.

Badal Shah is a PhD student inthe Biotechnology program atLakehead University. Hereceived his Bachelor in Phar-macy from Shree DhanvantaryPharmacy College, Surat, Indiain 2009 and M. Sc in Biotech-nology from the PolytechnicInstitute of New York University,USA in 2011. His researchinterests are electrochemicalsensors/biosensors and nano-materials for drug delivery. He

was awarded the Ontario Trillium Scholarship (OTS) in 2011 andthe 2012 High Output and Publication Excellence (HOPE) Awardby Lakehead University. The OTS program is a signicant initiativeto attract the best qualied international students to Ontario forPhD studies.

ersity, 955 Oliver Road, Thunder Bay,

[email protected]; Fax: +1-807-

–2173 This journal is ª The Royal Society of Chemistry 2013

http://dx.doi.org/10.1039/c3ay40155c

http://pubs.rsc.org/en/journals/journal/AY

http://pubs.rsc.org/en/journals/journal/AY?issueid=AY005009

Critical Review Analytical Methods

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1 Introduction

Voltammetry has been practiced for a long time and has revo-lutionized analytical chemistry.1,2 Many electroanalytical tech-niques have inherent advantages and disadvantages withvariable purposes, and therefore may be utilized in a multitudeof different elds of study, encompassing enzyme catalysis,3 freeradical generation,4 solar energy conversion5 andmyriad others.The main advantages of using voltammetric methods overspectroscopy or chromatography include their high sensitivity,precision, accuracy and cost effectiveness. In the past, voltam-metric techniques were difficult to apply and were not nearly asuseful as they are today. Present techniques are largely availabledue to the advent of computers and their key role in the controland measurement of the potentials and currents of potentio-stats. Previous polargraphic techniques have advanced largelydue to better instrumentation and improved electrodematerials.

In recent years, the use of square wave voltammetry (SWV)has been a staple in the fabrication of sensitive electrochemicalsensors and biosensors. The effectiveness of a sensor is directlyproportional to how sensitive and selective it is as relates to itsanalyte.6 This responsiveness may be increased by applying amore sensitive electrochemical technique such as SWV. Othermethods for increasing sensitivity include the modication ordevelopment of more effective electrodes. Investigationsregarding the effect of electrodes on sensitivity and detectionlimits have been conducted using boron-doped diamond lmelectrodes,7 carbon paste electrodes,8 metal oxide based nano-wires/nanotubes,9 and carbon nanotubes.10 Each of thesestudies involved the utilization of modied or bare electrodes inwhich SWV was employed as the primary methodology.

A survey of relevant papers spanning the last ten years inwhich SWV was utilized as a methodology in sensor develop-ment reveals that the technique is increasing in popularity asshown in Fig. 1. The application of this technique for analytical

Fig. 1 Number of publications reporting the use of square wave voltammetry asan electroanalytical technique (2003–2012) based on Web of KnowledgeSM

(December 21, 2012).

This journal is ª The Royal Society of Chemistry 2013

purposes is gaining ground and becoming recognized as auseful methodology. This is evidenced by the doubling of thenumber of associated publications per year over the last tenyears.

This methodology has impacted multiple elds includingdiagnostics, environmental analysis, food sciences, enzymekinetics and pharmaceuticals. This review will examine each ofthese areas as derived from the literature mainly over the lastve years, but save for pharmaceutical applications, which havebeen extensively catalogued.11–15 Finally, the assessment andfuture prospects for the advancement of sensors and biosen-sors, which have evolved through the implementation of SWV,and unique electrode materials will be addressed.

Fig. 2 Waveforms for CV, DPV and SWV with the current sampling time.

Anal. Methods, 2013, 5, 2158–2173 | 2159


Fig. 3 The effect of square wave frequency on the peak current (A) and peakpotential (B) of guanine. A linear increase in the square wave frequency showed alinear increase in the peak current, while a linear increase of peak potential wasseen with an increase in the log of f. Reproduced from ref. 19 with permission ofElsevier.

Analytical Methods Critical Review

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2 Principle

The most common voltammetric techniques are based on thecontinuous alteration of the potential that is applied to thesolution through the electrode, coupled with the measurementof the resulting current. The most popular continuous wavetechnique is cyclic voltammetry (CV), which is used to deter-mine the nature of the redox reactions that take place in asolution. This strategy, although not as sensitive as the pulsetechniques, has a multitude of uses beyond the trace determi-nation of an analyte. CV is most oen used as a tool for theacquisition of critical data such as oxidation/reduction mech-anisms, the determination of formal potentials, electrontransfer and electron transfer kinetics.16

Waveforms for different types of voltammetry and currentsampling time are depicted in Fig. 2. The waveform for CV islinear; therefore the potential is continuously modied as alinear function of time. Of all electroanalytical techniques, thepulse strategies tend to be the most sensitive. Procedures suchas differential pulse voltammetry (DPV), normal pulse voltam-metry (NPV) and square wave voltammetry (SWV) have beenrepeatedly shown to be some of the most useful electroanalyt-ical techniques. These methods alter the potential of a samplethrough pulsing from one potential to another rather thansweeping through varying potentials, as is the case with cyclicvoltammetry. For DPV, current is sampled at points S1 and S2.The typical value of T ranges from 0.5 to 5.0 s, while the value oftp is on the order of 50 ms. If we consider current at points S1and S2 as I1 and I2, respectively, the difference of I2 � I1 repre-sents the current due to the application of pulse. The waveformof SWV can be seen as a special case of DPV waveform, wherethe pre-electrolysis period (T) and pulse period (tp) are of equalduration. The waveform of SWV is a symmetrical square waveon a staircase; current is sampled twice per cycle, at the end ofeach pulse, as shown in Fig. 2. The forward sample S1 arisesfrom the rst pulse per cycle, while the reverse current issampled at the end of the second pulse. The difference iscalculated as forward current � reverse current (S1 � S2).

The core principle behind pulse techniques resides in thedifference in the decay rates of the charging and faradaiccurrents. The charging current decays much more rapidly thanthe faradaic current due to its decaying as an exponential func-tion, while the decomposition of the faradaic current is inverselyproportional to the square root of time.11,12 Therefore, at theconclusion of each pulse the capacitive current is negligiblecompared to that of the faradaic current.17This increased ratio offaradaic tonon-faradaic current allows for a lower detection limitas well as higher sensitivity, and is therefore ideal for analyticalpurposes. SWV can be applied for the analysis of reversible andirreversible reactions, reactionwith slow electron transfer aswellas for catalytic reactions. O'dea et al. have calculated experi-mentally measurable parameters such as peak shis, heights,and widths for different types of reactions and plotted them as afunction of the appropriate rate constants.2

SWV is oen utilized due to its ability to be operated at highfrequency.11 This means that square wave utilized experimentsmay be accomplished quickly and can conserve electroactive

2160 | Anal. Methods, 2013, 5, 2158–2173

species with respect to other pulse techniques.18 Since there is adecrease in the use of electroactive species, electrode surfacestend to be less hindered with non-electroactive products.Another advantage of SWV is that the exclusion of oxygen fromthe analyte solution may not be necessary due to the reductionof oxygen being included in the background current.12 This, ofcourse, is dependent on whether the applied potential is morecathodic than that for the reduction of oxygen. If the potential isindeed more cathodic, the magnitude of the forward andreverse currents will both include the current from the reduc-tion of oxygen and will be subtracted from the background.

The square wave frequency is a parameter that arises from theuse of the square wave on the staircase potential and is thefrequency at which the analyte is sampled. Each pulse results in asmall incrementofpotential andhence, should the frequencyof thepulses increase then an increase in the rate atwhich thepotential isscanned occurs. Similar to cyclic voltammetry, the increase in thesweep rate will also correspond to an increase in the peak current.However, this also involves an increase in the peak potential, andunlike inaCV, this shi inpeakpotentialwill beproportional to thelogarithm of the square wave frequency. Chatterjee and Chenshowed an increase in the peak current and potential with theincrease in square wave frequency as seen in Fig. 3.19

A comparison of the three main voltammetric techniques isdepicted in Fig. 4, which shows the voltammograms of a glasscarbon electrode (GCE) recorded in a 0.1 M pH 7.4 phosphatebuffer solution in the presence of (red curve) and in the absence(blue curve) of 50 mM of 4-nitrophenol. The characteristics ofthese voltammograms follow the trends that are expected ofthem, with the peak current of SWV being approximately fourtimes larger than that of DPV.11 The positive aspects of square



Fig. 4 The cyclic voltammogram (A), differential pulse voltammogram (B) andsquare wave voltammogram (C) before (blue) and after (red) a 50 mM injection of4-nitrophenol into pH 7.4, 0.1 M phosphate buffer solution.


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wave voltammetry far outweigh any negatives; thereby affordingfurther credence for its use as a dynamic and versatile tech-nique. SWV has been widely applied in medical diagnostics,environmental analysis, food sciences and toward the deter-mination of enzymatic kinetics.

3 Application of SWV in diagnosticbiosensors

It is of great interest and importance to rapidly and sensitivelydetect disease-related biomarkers, which can assist in diagnostic


applications as well as to assess pharmacological responses totreatment. In recent times various approaches have beenemployed in sensing/biosensing for various disease biomarkers.Primary approaches include immunoassay, antibody-function-alized magnetic beads and DNA decorated electrodes.

There are numerous studies related to electrochemicalsensing/biosensing of various analytes for diagnostic purposesusing SWV. Various papers relating to diagnostic electro-chemical sensors or biosensors based on SWV are listed inTable 1. For instance, Reisberg et al. have developed an elec-trochemical DNA hybridization sensor that has the remarkablecapacity for detection down to the resolution of a single pointmutation (Single Nucleotide Polymorphism (SNP)).39 Thissensor is based on a peptide nucleic acid (PNA) probe that isattached to a quinone-derived electroactive polymer, poly(JUG-co-JUGA). As shown in Fig. 5, upon the hybridization of the PNAprobe with a complementary target DNA strand, changes in theexibility of the PNA probe strand generate electrochemicalchanges at the polymer–solution interface. An increase in thepeak current of quinone was observed by SWV; whereas nochange was observed with a non-complementary sequence. Thissensor has very strong potential to be used in the geneticdiagnosis of various diseases that are caused by SNP. An elec-trochemical genosensor was developed by Liao et al. for thedetection of Escherichia coli O157:H7, a verocytotoxin (VT1/2)-producing pathogen, which causes hemorrhagic colitis andsevere haemolytic-uremic syndrome.55 It is commonly found inground beef, unpasteurized or raw milk, cold sandwiches,vegetables, apple cider and drinking water. In this paper, elec-trodeposited gold nanoparticle screen-printed electrodes weredeveloped and modied with a self-assembled monolayer ofthiol-capped single-stranded DNA (capture probe) for thedetection of the rE gene, which is specic for E. coli O157:H7.As depicted in Fig. 6A, this genosensor functions on the prin-ciple of competitive assay; competition between the target genein E. coli (complementary to the DNA capture probe) and theDNA-tagged reporter hexaammineruthenium(III) chloride-encapsulated liposomes for hybridization. As shown in Fig. 6B,when the reporter DNA binds with the capture probe, thecurrent signal is increased via the released liposomalRu(NH3)6

3+. When both the target DNA in E. coli and reporterDNA are present, the intensity of the current is contingent onthe amount E. coli present. Liu et al. have developed animmunosensor for interferon gamma (INF-g), which is a cyto-kine produced by T cells and NK cells.48 It is used in the treat-ment of chronic granulomatous disease (CGD) and severemalignant osteopetrosis. An electrode was fabricated byimmobilizing a thiolated DNA hairpin containing an IFN-gbinding aptamer that was conjugated with a methylene blue(MB) redox tag on a gold electrode via self-assembly. As pre-sented in Fig. 7, when IFN-g combines with its binding site onthe aptamer it unfolds and pushes the MB away from the elec-trode, which in turn decreases the electron transfer efficiency.Changes in the redox current due to this process were observedby SWV. Ho and Liao have developed an immunosensor for thedetection of immunogenic tumor-associated antigen a-Enolase(ENO1), which is associated with small cell lung cancers,

Anal. Methods, 2013, 5, 2158–2173 | 2161


Table 1 Electrochemical sensors and biosensors based on SWV for diagnostic applications

Analyte Electrode Analytical parameters Ref.

Acute myocardial infarction (cardiacmyoglobin and troponin I as biomarkers)

Didodecyldimethylammonium bromidemodied SPCE

Qualitative analysis 20

Adenine in the presence of adenosinemonophosphate (AMP)

SWCNT modied EPPGE Linear range: 5–100 nM 21LOD: 37 � 10�10 M

Adenosine MB attached to adenosine and SWCNTmodiedGCE aptamer

LOD: 0.2 nM 22

Adenosine monophosphate in thepresence of adenine

SWCNT modied EPPGE Linear range: 10–100 nM 21LOD: 76 � 10�10 M

Albumin Antibody labeled AuNP and PVA modiedscreen printed carbon electrode

Linear range: 2.5–200 mg mL�1 23LOD: 25 ng mL�1

Amplication process of inuenza virusDNA

Screen printed electrode using USB poweredpotentiostat. (DNA was amplied by reversetranscription loop-mediated isothermalamplication (RT LAMP.)) Amplied DNA wasattached to MB, which was used for theelectrochemical study


Angiogenin Anti-angiogenin aptamermodied Au electrode.Redox couple ferro/ferricyanide was used as adetection probe

Linear range: 0.01–30 nM 25LOD: 1 pM

Apoferritin encapsulated silver(I) ions MWCNT modied CPE LOD: 5 nM 26Calf thymus DNA Zr(IV) and mercaptopropionic acid self-

assembled monolayer modied gold electrodeLinear range: 1.0 � 10�4 to 5.0 �10�7 g mL�1

27

LOD: 9.5 � 10�8 g mL�1

Carcinoembryonic antigen (CEA) Gold nanoparticles and anti-CEA antibodymodied GCE. DNA, Methylene Blue (MB) andanti-CEA antibody modied gold nanoparticleswere used as detection probes

0.10–2.0 pg mL�1 28LOD: 0.05 pg mL�1

Carcinoembryonic antigen (CEA) ZnO nanoparticles, Au nanoparticles and anti-CEA antibody modied gold electrode

Linear range: 0.1–200 ng mL�1 29LOD: 0.01 ng mL�1

Carcinoembryonic antigen (CEA) insaliva and serum

Monoclonal anti-CEA antibodies immobilizedon polyethyleneimine wrapped multi-walledcarbon nanotube screen-printed electrode. Anti-CEA antibodies tagged with ferrocene carboxylicacid were used for sandwich immunoassay

Linear range: 5 � 10�12 to 5 �10�7 gm L�1

30

LOD: 1 � 10�12 gm L�1

Cell-secreted TNF-a and IFN-g Electroactive aptamer (anti-INF-a DNA aptamerand anti-TNF-a RNA aptamer), and MB redoxreporter modied micropatterned goldelectrodes

LOD: 0.06 nM IFN-g 0.58 nMTNF-a

31

Linear range: 10–100 ng mL�1

Changes in protein structures (based onoxidizability of tyrosine and tryptophanresidues)

Edge plane pyrolytic graphite electrode (EPPGE) Qualitative analysis 32

DNA (SNP) Carbon nanotubes, self-assembledmonolayer ofcysteamine, a quinone derivative 3-[(2-aminoethyl)sulfanyl-5-hydroxy-1,4-naphthoquinone], and ssDNA modied Auelectrode


DNA damage SWCNT, chitosan and dsDNA modied SPE Qualitative analysis 34DNA damage DNA modied GCE Co(bpy)3

3+ was used as anelectroactive indicator


DNA damage and antioxidant capacity ofSericin

dsDNA immobilized dendrimer-encapsulatedbimetallic nanoparticles (Au–Pd) in a chitosancomposite modied GCE


DNA damage and antioxidant properties DNA and glucose oxidase modied GCECo(bpy)3

3+ were used as electroactive indicatorsQualitative analysis 37

DNA damage and repair withepigallocatechin gallate, chlorogenic acidand ascorbic acid

DNA modied PGE Quantitative analysis 38

DNA mismatch (single point mutation) Peptide nucleic acid and quinone-basedelectroactive polymer [5-hydroxy-1,4-naphthoquinone, (JUG)-co-5-hydroxy-3-thioacetic acid-1,4-naphthoquinone (JUGA)]modied GCE

Detection limit: 10 nM 39Detection of single point mutationin DNA

DNA Nucleic acid MB attached to ssDNA and SWCNT modiedGCE

Linear range: 0.01–5.0 nM 22LOD: 1 pM

2162 | Anal. Methods, 2013, 5, 2158–2173 This journal is ª The Royal Society of Chemistry 2013


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Table 1 (Contd. )

Analyte Electrode Analytical parameters Ref.

E. coli MWCNT modied GCE Linear range: 2 � 102 to 2 � 108

cell per mL40

LOD: 2 � 102 cell per mLGlucose Photo-sensitive polymermodied gold electrode Linear range: 5.0–120 mM 41

LOD: 0.2 mg L�1

Guanine Electrodeposited nanostructured platinum thinlm modied GCE

Linear range 0.1–500 mM 42LOD: 3.1 � 10�8 M

Hepatitis B surface antigen (HBsAg) Anti-HBsAg antibody modied SPE.Horseradish peroxidase attached anti-HBsAgantibody was used as a detector probe

Linear range: 1–500 ng mL�1 43LOD: 0.3 ng mL�1

Homocysteine Gold electrodeposited MECNT modied CPE — 44Human immunodeciency virus type 1Reverse Transcriptase (RT) enzyme

Self-assembled monolayer (SAM) of asynthesized ferrocene labeled lipoic acidattached with RT specic peptide modied goldelectrode

Linear range: 100–500 pg mL�1

(equivalent to 85.5–427.4 fM)45

LOD: 50 pg mL�1 (42.7 fM).

Human growth hormone (hGH) Monoclonal anti-hGH antibody attached to syl-activated magnetic microparticles, poly-anti-hGH antibody and anti-IgG antibody labelledwith alkaline phosphate (AP) were used forimmunoassay. Aer immunoreactions, theprepared conjugate was analysed on the SPEelectrode, using 4-aminophenyl phosphate as asubstrate for AP enzyme

Linear range: 0.01–100 ng mL�1 46LOD: 0.005 ng mL�1

Human luteinizing hormone (LH) Colloidal gold and monoclonal mouse anti-LHantibody modied Au electrode. Polyclonalrabbit anti-LH antibody modied cadmium ion-doped magnetic poly(styrene-acrylic acid)nanosphere was used as a detection probe

Linear range: 0.25–240 mIU mL�1 47LOD: 0.08 mIU mL�1

Interferon (IFN)-g Self-assembled thiolated DNA hairpincontaining IFN-g binding aptamer, conjugatedwith methylene blue modied gold electrode

LOD: 0.06 nM. 48Linear response: 0.06–10 nM

Lignin peroxidase (lip) genes by anelectrochemical DNA sensor

Thiolated capture probe (ssDNA) modied goldelectrode. For sandwich immunoassay thedetection probe specic to P. chrysosporium lipgenes was modied with the streptavidin–horseradish peroxidase (HRP) conjugate

Linear range: 0.6–30 nM 49LOD: 0.03 nM

Metabolic activity of human cells and celldeath

Carbon nanotube modied GCE Qualitative analysis 50

Methylglyoxal (as biomarker for diabetes) SWCNT modied GCE Linear range: 0.1–100 mM 51Myoglobin (myocardial infarctionbiomarker)

Gold nanoparticles,didodecyldimethylammonium bromide andanti-myoglobin antibody-modied screenprinted graphite electrode

Linear range: 10–1780 ng mL�1

(0.56–100 nM)52

LOD: 10 ng mL�1 (0.56 nM)

Nickel ion release from stainless steelcrowns in articial saliva

Dimethylglyoxime modied mercury electrode The author was able to detectnickel in ppm range.

53

Nitric oxide Trans[Ru(NH3)4(Ist)SO4]+ electropolymerized on

gold electrodeLinear range: 2.85 � 10�6 to2.82 � 10�5 mol dm�3

54

LOD: 7.73 � 10�8 mol dm�3

rE gene (Escherichia coli O157) Gold nanoparticle electrodeposited screen-printed electrodes modied with a self-assembled monolayer of thiol-capped single-stranded DNA. For competitive immunoassayhexaammineruthenium(III) chlorideencapsulated liposome tagged reporter DNA(complementary to the capture probe DNA) wasused as a detection probe

Linear range: 1–106 fmol 55LOD: 0.75 amol (Equivalent to theamount present in 5 mL of a 0.15pM solution).

a-Enolase (ENO1) (human lung cancer-associated antigen)

Anti-ENO1 monoclonal antibody onpolyethylene glycol-modied disposable screen-printed electrode. A polyclonal secondary anti-ENO1-tagged, gold nanoparticle was used as adetection probe

LOD: 11.9 fg (equivalent to 5 mL ofa 2.38 pg mL�1 solution)

56

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Fig. 5 Polymer structure, hybridization reaction and transduction processes of the proposed sensor. Reproduced from ref. 39 with permission of Elsevier.

Fig. 6 (A) Flow diagram depicting the concept behind the competitive assay-based performance of the developed genosensor. (B) Cartoon representations of theanalyses of (I) the control group in the absence of target DNA and (II) the experimental group with addition of 2 � 105 fmol of target DNA. Reproduced from ref. 55with permission of Elsevier.


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non-small cell lung cancers and head and neck cancers. Thusthe detection of ENO1 may be employed as a potential diag-nostic test for lung cancer.56 As is shown in Fig. 8, the electrodewas fabricated by immobilizing anti-ENO1 monoclonal anti-bodies on a disposable polyethylene glycol-modied screen-printed electrode. Gold nanoparticles were tagged with poly-clonal secondary anti-ENO1 antibodies and used as detection

2164 | Anal. Methods, 2013, 5, 2158–2173

probes. Subsequent to binding with ENO1, electrochemicalsignals from the bound nanoparticles were obtained followingtheir oxidation in 0.1 M HCl at 1.2 V for 120 s, followed by thereduction of AuCl4

� by square wave voltammetry. Li et al. havedeveloped a biosensor based on aptamers for the detection ofangiogenin, one of the most potent angiogenic factors, which isinvolved with angiogenesis (formation of new blood vessels) in



Fig. 7 Schematic of an aptamer-based electrochemical sensor for IFN-g. (A) The aptamer hairpin was thiolated at the 50 end, allowing self-assembly on gold elec-trodes. The redox label was attached at the 30 end of the hairpin and was in close proximity to the electrode surface. (B) Upon addition of the IFN-g aptamer, the hairpinchanged conformation and the redox label moved further away from the electrode, lowering the electron-transfer efficiency. (C) The differences in faradaic currentbefore and after the addition of IFN-g were quantified by SWV. Reproduced from ref. 48 with permission of Elsevier.

Fig. 8 Schematic representation of the operation of the electrochemical immunosensor for the detection of ENO1. Reproduced from ref. 56 with permission of ACSpublications.


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tumors.25 The electrode was fabricated by immobilizing anti-angiogenin aptamers on a bare gold electrode, while ferro/ferricyanide couples were employed as redox couples. Thebinding of analytes with the aptamers on the surface of theelectrode makes them less available for the redox couples,resulting in a decrease in current that may be observed by SWV.Labib et al. developed an ultrasensitive electrochemicalbiosensor for the detection of HIV-1 virus reverse transcriptase(HIV1 RT).45 The HIV virus is responsible for causing AIDS andits early detection can be very useful in the diagnosis of thedisease. This biosensor was based on the formation of a self-assembled monolayer (SAM), comprised of a synthesizedferrocene (Fc) labeled lipoic acid on a gold electrode. For thedetection of HIV-1 RT, a short RT-specic peptide (VEAIIR-ILQQLLFIH) was covalently attached to the Fc labeled lipoicacid. When the RT was bound to its specic peptide, the anodicshi and reduction of current density of the Fc redox wereobserved by SWV. This biosensor has a very sensitive (50 pgmL�1) limit of detection, and a rapid (20 s) response time,compared with other methods such as ELISA and western blot.


More examples related to diagnostic electrochemical sensors orbiosensors based on SWV can be found in Table 1.

4 Application of SWV in environmentalmonitoring

Environmental pollution is a serious global issue. It is wellunderstood that increasingly pervasive chemical contaminantsin the atmosphere and waterways are severely detrimental tohuman and animal life and the environment as a whole.Various techniques such as HPLC, GC, FT-IR and other wetchemistry methods are being used for the detection of variouspollutants such as phenolic compounds, heavy metals andorganophosphate pesticides. All of these techniques suffer fromvarious drawbacks, while electrochemical methods offeradvantages, including rapid and sensitive detection and costeffectiveness. In Table 2, various electrochemical sensors/biosensors for environmental purpose applications are listed.

Alizadeh et al. developed a sensor for the detection of 2,4,6-trinitrotoluene (TNT) in ambient water and soil samples. A TNT

Anal. Methods, 2013, 5, 2158–2173 | 2165


Table 2 Electrochemical sensors and biosensors based on SWV for environmental applications

Analyte Electrode Linear range LOD Ref.

4-Aminobiphenyl b Cyclodextrin modied gold electrode 1 � 10�5 to 1 � 10�4

mol L�18.9 � 10�6 mol L�1 57

4-Nitrophenol Prussian blue, polyazulene, poly(3,4-ethylenedioxythiophene) and poly(3-[(E-2-azulene-1-yl)vinyl]thiophene) modiedPt electrode

30–90 mM 8.23 mM 58

Ag(I) Metallothionein (MT) and anti-MTantibody modied CPE

15.6–500 mM 0.5 nM 59

Arsenic trioxide Cytochrome c modied BDDE 0–10 mM 22.02 mM 60Atrazine (ATZ) Poly(JUG-HATZ) and anti-ATZ antibody

modied GCE0.1 pM to 10 mM 1 pM 61

Benzaldehyde in air Pt electrode — 8.66 ppm 62Benzaldehyde in air Pt electrode — 10.33 ppm 62Cadmium Algerian humic acid and polyaniline

emeraldine base composite modiedcavity microelectrode

0–1 � 10�5 mol L�1 11.9 nM 63

Cadmium Bismuth oxide screen printed electrode 10–150 mg L�1 30 mg L�1 64Carbaryl MWCNT and cobalt phthalocyanine

modied GCE0.33–6.61 mmol L�1 5.46 nmol L�1 65

Choline Fe3O4 magnetic nanoparticles andcholine oxidase modied gold electrode

10�9 to 10�2 M 0.1 nM 66

Copper ion Carboxyl end capped over oxidizedpolypyrrole nanowire and tripeptide (Gly-Gly-His) modied gold electrode

20–300 nM — 67

Cu(II) Polyluteolin modied GCE 1.0 � 10�11 to 1.0 �10�6 M

0.6 � 10�11 M 68

Cu(II) Polykaempferol modied GCE 1.0 � 10�11 to 1.0 �10�6 M

0.3 � 10�11 M 68

Cu(II) 4-Formylphenylboronic acid and 4-amino-6-hydroxy-2-mercaptopyrimidinemonohydrate modied gold electrode

1.0 � 10�10 to 1.0 �10�4 M

5 � 10�12 M 69

Cu(II) Functionalized polypyrrole nanotubearrays, ZnO nanowire and tripeptide (Gly-Gly-His) modied ITO coated glass

0.1–30 mM 46 nM 70

Cyanide in wastewater Silver hexacyanoferrate nanoparticlesimmobilized on MWCNT modied GCE

40 nM to 150 mM 8.3 nM 71

Diuron Prussian blue-gold nanoparticles, haptenprotein conjugate and anti-diuronantibody modied laser ablated goldelectrodes. Alkaline phosphatase labelledantirabbit IgG antibody was used as adetection probe

1 ppt to 10 ppm 1 ppt 72

Endosulfan SWCNT, endosulfan hapten and anti-endosulfan IgG antibody modied GCE

0.01–20 ppb 0.01 ppb 73

Esculetin Gold nanoparticles dispersed in ionicliquid [1-butyl-3-methylimidazoliumhexauorophosphate] and polyphenoloxidase modied CPE

0.40–9.86 mM 0.11 mM 74

Fenitrothion in forestsamples

Molecularly imprinted polymer modiedSPE

3 � 10�6 to 10�4

mol L�18 � 10�7 M 75

Formaldehyde in air Gold electrode — 9.66 ppm 62Formaldehyde in air Gold electrode — 13.33 ppm 62Hydrogen peroxide Horseradish peroxidase induced

deposition of polyaniline on the designedgraphene–carbon nanotube–naon/gold–platinum alloy nanoparticlemodied GCE

5.0 � 10�7 to1.0 � 10�4 M

1.7 � 10�7 M 76

Hydroxylamine TiO2 nanoparticles and quinizarinemodied CPE

1–400 mM 0.173 mM 77

Indole-3-acetic acid BDDE 5–50.0 mM 1.22 mM 78Lead Bismuth oxide screen printed electrode 10–150 mg L�1 10 mg L�1 64

2166 | Anal. Methods, 2013, 5, 2158–2173 This journal is ª The Royal Society of Chemistry 2013


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Table 2 (Contd. )

Analyte Electrode Linear range LOD Ref.

Mercury(II) Poly(1,8-diaminonaphthalene) andcarbon nanotube modied interdigitatedarrays

0.05–10 mM _ 79

Methomyl Platinum nanoparticles in ionic liquidphase supported in montmorillonite andenzyme laccase modied CPE

9.8 � 10�7 to 9.0 � 10�6

mol L�12.35 � 10�7 mol L�1 81

Methomyl Laccase modied carbon ceramicelectrode

0.5–12.2 mM 0.2 mM 80

Methyl parathion MWCNT modied GCE 0.05–2.0 mg mL�1 0.005 mg mL�1 82Methyl parathion ZrO2 nanoparticle modied CPE 5–3000 ng mL�1 2 ng mL�1 83Methyl parathion Gold nanoparticle modied naon lm

coated GCE5.0 � 10�7 to1.2 � 10�4 M

1.0 � 10�7 M 84

Methyl parathion Zirconia nanoparticle decoratedgraphene hybrid nanosheets

0.002–0.9 mg mL�1 0.6 ng mL�1 85

Nickel Algerian humic acid and polyanilineemeraldine base composite modiedcavity microelectrode

0–9 � 10�6 mol L�1 12.7 nM 63

Nitrobenzene Bismuth-lm modied CPE 1.0 � 10�6 to1.0 � 10�4 M

8.3 � 10�6 M 86

O-Nitrophenol Generation 2 poly(propyleneimine)dendrimer and gold nanoparticlemodied GCE

6.1 � 10�7 to 6.25 �10�4 mol L�1

4.5 � 10�7 mol L�1 87

Organophosphorylatedacetylcholinesterase (OP-AChE)

Zirconia nanoparticles, lead phosphateapoferritin and anti-AChE antibodymodied screen printed electrode (SPE)

0.05–10 nM 0.02 nM 88

Parathion Nanocomposite ZrO2 modied Au lmelectrode

20–140 ng mL 3 ng mL 89

Parathion Self-assembled mercaptoethanesulfonicacid sodium and zirconia nanoparticlemodied gold electrode

0.005–1.0 mg mL 0.8 ng mL 90

Phenol Boron-doped nanocrystalline diamondelectrode

30–130 mmol L�1 0.1 mg L�1 91

Phenolic compounds MWCNT and cobalt phthalocyaninemodied GCE

0.99–8.30 mmol L�1 1,4-Benzoquinone:13.75 mg L�1

92

Catechol: 15.62 mg L�1

Hydroquinone:17.91 mg L�1

Resorcinol: 46.12 mg L�1

Phenol: 58.83 mg L�1

p-Nitrophenol (PNP) inestuarine and surfacewaters

C/p-NiTSPc coated carbon bermicroelectrode

— 0.1 mg L�1 93

Potassium cyanide Cytochrome c modied BDDE 0–10 mM 9.08 mM 60Prussian blue Cytochrome c modied BDDE 0–6 mM 37.49 mM 60Sudan I SWCNT and iron(III) porphyrin modied

GCE5.03 � 10�8 to 2.01 �10�6 mol L�1

1 � 10�8 mol L�1 94

Zinc Bismuth oxide screen printed electrode 10–150 mg L�1 5 mg L�1 64


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selective, molecularly imprinted polymer (MIP) modiedcarbon paste electrode was used for the sensitive detection/recognition unit. The LOD and linear range for this sensor were1.5 � 10�9 mol L�1 and 5 � 10�9 to 1 � 10�6 mol L�1, respec-tively.95 Mazloum-Ardakani et al. proposed a sensor that wasbased on a TiO2 nanoparticle and quinizarine modied carbonpaste electrode for the sensitive determination of hydroxyl-amine. The anodic oxidation of hydroxylamine at the electrodesurface was observed by SWV, and the LOD and linear range forthis sensor were 0.173 mM and 1.0–400 mM, respectively.77 Asensor for the detection of the extremely toxic insecticide


fenitrothion was developed by Pellicer et al. using a portabledevice, which was based on a molecularly imprinted polymermodied screen-printed electrode. The selectivity of this sensorwas tested via the detection of fenitrothion while in the pres-ence of some potential interfering compounds, such as meta-mitron, fenitrothion-oxon and methyl-parathion. The LOD andlinear range for this sensor were 8 � 10�7 M and 3 � 10�6 to10�4 mol L�1, respectively.75 Noroozifar et al. proposed a sensorfor the detection of cyanide in wastewater samples. This sensorwas fabricated through the modication of a glassy carbonelectrode with silver hexacyanoferrate nanoparticle (SHCFNP)

Anal. Methods, 2013, 5, 2158–2173 | 2167


Fig. 9 Schematic illustration of sandwich like immunoassay of OP-AChE adducts.Reproduced from ref. 88 with permission of Elsevier.


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doped MWCNTs. The cyanide reacted with the SHCFNPs toproduce Ag(CN)2� complexes, which may be reduced to Ag in anelectrochemical reaction. The LOD and linear range for thissensor were found to be 8.3 nM and 40 nM–150 mM, respec-tively.71 Du et al. developed a biosensor for the detection oforganophosphorylated acetylcholinesterase (OP-AChE), whichis a biomarker that indicates exposure to organophosphatepesticides. This biosensor works on the principle of a sandwichimmunoassay. As shown in Fig. 9, zirconia nanoparticles wereimmobilized on a screen printed electrode to capture the OP-AChE via metal chelation with phosphomoieties in an enzyme.This AChE enzyme was detected via a lead phosphate apo-ferritin labeled anti-AChE antibody. Subsequent to theseimmunoreactions, the released lead ions were detected by SWV.This biosensor can be employed to screen for organophosphatepesticide exposure in humans because of its low limit ofdetection (0.02 nM) and wide linear range (0.05–10 nM).88

Fig. 10 Strategy for the electrochemical detection of atrazine based on the changepoly(JUG-HATZ)-modified electrode; (2) after complexation with a-ATZ, poly(JUG-Hduced from ref. 61 with permission of Elsevier.

2168 | Anal. Methods, 2013, 5, 2158–2173

Atrazine (ATZ) is a highly toxic, mutagenic and teratogenicherbicide that is in wide use. Tran et al. proposed an immu-nosensor for the highly selective determination of atrazine,based on a poly(JUG-HATZ) and anti-ATZ modied glassycarbon electrode. The polymer contains a hydroxyatrazinefunctional group, which serves as a bio-recognition element.The changes in current prior to and following the addition ofatrazine serve as an indicator, as shown in Fig. 10.61 Moreexamples associated with the broad application of SWV forenvironmental monitoring are summarized in Table 2.

5 Application of SWV in food analysis

The novel use and successful integration of electrochemicalfood quality sensors/biosensors holds tremendous potential inthe detection of food resident contaminants as well as thetherapeutic ingredients of dietary supplements. The contami-nation of food stuffs with bacteria, viruses and parasitescomprises the major source of foodborne diseases. The highresolution detection of these agents may signicantly facilitatethe prevention of these illnesses. The detection of food aller-gens/pathogens and the recognition and quantication oftherapeutically valuable ingredients in dietary supplementshold equivalent importance. Recent advances in the eld ofSWV-based sensors/biosensors for food analysis are summa-rized in Table 3.

Medeiros et al. proposed a sensor for the simultaneousdetection of aspartame and cyclamate in dairy products. Both ofthese compounds are in wide use as articial sweeteners invariety of products. In a number of countries such as Canada,the USA and several European countries, cyclamate is pro-hibited as an articial sweetener due to its possible conversionto cyclohexylamine, a potent carcinogen. A boron doped dia-mond electrode and SWV were utilized in this sensor, whereanodic peak potentials of 1.5 V (aspartame) and 1.9 V

in electroactivity of the polymer film, poly(JUG-HATZ). SWV recorded with (1) theATZ/a-ATZ)-modified electrode; and (3) after addition of ATZ in solution. Repro-



Table 3 Electrochemical sensors and biosensors based on SWV for food analysis applications

Analyte Electrode LOD Linear range Ref.

Aspartame (in the presenceof Cyclamate) in dairyproducts

BDDE 3.5 � 10�7 mol L�1 5.0 � 10�6 to 4.0 � 10�5

mol L�196

Biotin in food stuffs Streptavidin attachedmagnetic microbeadmodied magneto graphite–epoxy composite electrodes

20 mg L�1 1.4 � 10�8 to 3.57 � 10�7

mol L�197

Brilliant Blue (BB) MWCNT modied CPE 5.0 nM L�1 0.05 to 25 nM L�1 98Butylated hydroxyanisole(BHA) in the presence ofbutylated hydroxytoluene(BHT)

BDDE 0.14 0.6–10 mM 99

Butylated hydroxyanisole(BHA) in the presence ofbutylated hydroxytoluene(BHT)

Cu3(PO4)2 immobilized inpolyester resin modiedcarbon composite electrode

7.2 � 10�8 mol L�1 3.4 � 10�7 to 4.1 � 10�5

mol L�1100

Butylated hydroxytoluene(BHT) in the presence ofbutylated hydroxyanisole(BHA)

BDDE 0.25 0.6–10 mM 99

Butylated hydroxytoluene(BHT) in the presence ofbutylated hydroxyanisole(BHA)

Cu3(PO4)2 immobilized inpolyester resin modiedcarbon composite electrode

9.3 � 10�8 mol L�1 3.4 � 10�7 to 4.1 � 10�5

mol L�1100

Caffeine in coffee 4-Amino-3-hydroxynaphthalenesulfonic acid modied GCE

1.37 � 10�7 mol L�1 6 � 10�8 to 4 � 10�5 mol L�1 101

Catechins in green and blackteas

GCE 0.04 and 2.48 mM for EGCGand EGC, respectively

— 102

Ceiofur (antibiotic) milk HMDE 1.86 ng mL�1 52.4 to 524 ng mL�1 103Cyclamate (in the presenceof aspartame) in dairyproducts

BDDE 4.5 � 10�6 mol L�1 5.0 � 10�5 to 4.0 � 10�4

mol L�196

Ellagic acid in food stuffs GCE 1.0 � 10�8 mol L�1 1.0 � 10�7 to 1.5 � 10�6

mol L�1104

Lipoic acid in dietarysupplements

Fluorine-doped tin oxideelectrodes

3.68 mmol L�1 5–200 mmol L�1 105

Luteolin Ag nanoparticles dispersedin ionic liquid (1-butyl-3-methylimidazoliumhexauorophosphate) andlaccase immobilized inchitosan chemically cross-linked with cyanuricchloride

0.054 � mM 0.099–5.825 mM 106

Luteolin Au nanoparticles dispersedin ionic liquid (1-butyl-3-methylimidazoliumhexauorophosphate) andlaccase immobilized inchitosan chemically cross-linked with cyanuricchloride

0.028 � mM 0.099–5.825 mM 106

Methylglyoxal in wine andbeer

Platinum electrodepositedSWCNT modied GCE

2.8 � 10�9 M 0.1 � 10�6 to 100 � 10�6 M 107

Ochratoxin A (OTA) in redwine

OTA monoclonal antibodyattached magnetic beadmodied carbon screenprinted electrodes

0.008 ppb 0.01–20 ppb 108

Ochratoxin A (OTA) in winegrapes

Anti-OTA antibody attachedmagnetic particle modiedGCE

0.02 mg kg�1 0.5–50 mg kg�1 109

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Table 3 (Contd. )

Analyte Electrode LOD Linear range Ref.

Ochratoxin A mycotoxin inred wine samples

Cysteamine self-assembledmonolayer modied goldelectrodes

0.004 mg L�1 0.02 to 2.0 mg L�1 110

Total antioxidant capacity ofvarious antioxidantstandards, avours andavoured waters

Guanine modied GCE Ascorbic acid: 0.77 mg L�1 Ascorbic acid: 1.00–5.00mg L�1

111

Gallic acid: 0.10 mg L�1 Gallic acid: 0.10–1.00 mg L�1

Caffeic acid: 0.10 mg L�1 Caffeic acid: 0.1–1.00 mg L�1

Coumaric acid: 0.08 mg L�1 Coumaric acid: 0.50–1.00mg L�1

Resveratrol: 0.06 mg L�1 Resveratrol: 0.10–0.50mg L�1

Total antioxidant propertiesof metallothionein intransgenic tobacco plants

CPE Qualitative analysis Qualitative analysis 112

Ziram (zinc-dimethyldithiocarbamate) invegetables

HMDE 0.0072 mg mL�1 0.01–0.19 mg mL�1 113


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(cyclamate) were observed for analytical purposes. This sensorexhibited good selectivity and sensitivity with a LOD and linearrange for aspartame of 3.5 � 10�7 mol L�1 and 5.0 � 10�6 to 4.0� 10�5 mol L�1, respectively. For cyclamate, the LOD and linearrange were 4.5 � 10�6 mol L�1 and 5.0 � 10�5 to 4.0 � 10�4 molL�1, respectively.96 A sensor proposed by Barbosa et al. was usedto detect trace quantities of the antibiotic ceiofur in milk. Ahanging mercury drop electrode was used for analysis and aLOD of 1.86 ng mL�1 was obtained, which is ve times lowerthan the LOD obtained from HPLC analysis (9.70 ng mL�1).103

Miranda et al. developed a sensor for the detection of lipoic acidin dietary supplements. Lipoic acid is utilized in the treatmentof diabetes and various other diseases. A uorine doped tinoxide electrode was used to observe an anodic peak at about0.95 V. The proposed sensor was highly sensitive, with a LOD of3.68 mmol L�1 and a linear range of 5–200 mmol L�1 (ref. 105).Perotta et al. proposed an immunosensor for the sensitivedetection of ochratoxin A (OTA) in red wine. OTA is a secondaryfungal metabolite produced primarily by several Aspergillus andPenicillium genera. OTA is typically found in improperly storedfood including cereals, dried fruits, nuts and beverages, such asbeers and wines. OTA is a powerful nephrotoxic, teratogenic andimmunosuppressive agent. The proposed sensor was based onthe competitive immunoreactions between monoclonal anti-OTA antibodies that are attached to magnetic beads, and OTAand HRP attached to an anti-OTA antibody. H2O2 was used as a

Fig. 11 Schematic representation of an electrochemical peptide-based biosensor foinhibitor. The relative current response is proportional to the concentration of a sm

2170 | Anal. Methods, 2013, 5, 2158–2173

substrate for the HRP enzyme and a screen printed electrodewas used for SWV analysis.108 Chatterjee et al. have developed asensor based on the platinum electrodeposited SWCNT modi-ed GCE for determination of an a-dicarbonyl compound:methylglyoxal in wine and beer. This compound is of interest asit is associated with the pathophysiology of diabetes, and isbeing utilized as an indicator of complete fermentation in wineand beer. The proposed sensor exhibits a LOD of 2.8 � 10�9 Mwith the linear range from 0.1 � 10�6 to 100 � 10�6 M.107 Moreexamples of SWV-based sensors/biosensors for food analyticscan be found in Table 3.

6 Application of SWV in biosensors for thestudy of enzyme kinetics

A novel and effective use of electrochemical biosensors residesin the realm of enzymatic kinetics studies. In addition to theirserving as integral elements in various industrial processes,enzymes also play a vital role in the pathogenesis of variousdiseases. A biosensor that is endowed with the capacity todetermine enzymatic activity may impart multiple benets.Martic et al. developed a biosensor to determine the activity andinhibition of an enzyme sarcoma (src)-related protein kinase.The overexpression of protein kinase is associated with thepathophysiology of various diseases, including cancer; there-fore it is a viable target for cancer treatment. Some of the

r protein kinase-catalyzed phosphorylation reactions in the presence or absence ofall molecule inhibitor. Reproduced from ref. 115 with permission of Elsevier.



Table 4 Electrochemical sensors and biosensors based on SWV for the study of enzyme kinetics

Enzyme Electrode Analytical parameters Ref.

Cytochrome P450 17A1 Didodecyldimethylammoniumbromide (surfactant) and goldnanoparticle modied graphiteelectrode with immobilizedhemoprotein

Km (pregnenolone): 5.0 � 0.7 mM 114

Sarcoma related protein kinase Peptide (EGIYDVP) modied goldrod electrode

Km: 200 mM Vmax: 115 mA cm�2

min�1115

Sarcoma related kinase,extracellular signal-regulated kinase1 and cyclin A-dependent kinase 2

Peptide modied sputtered Au (onsilicon chip) electrode

— 116

Trypsin Gelatin coated screen printedelectrodes

Linear range: 0.75–7500 U mL�1

LOD: 0.075 U mL�1117


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important protein kinase inhibitors currently used in cancertreatment are getinib, desatinib and imatanib. This biosensorcan be utilized in high throughput screening for protein kinaseinhibitors. For analytical purposes, protein kinase was observedto catalyze phosphorylation reactions in the presence of aden-osine 50-g-ferrocenoyl triphosphate (FcATP). As shown inFig. 11, the sensor platform is based on a highly specic aminoacid sequence Glu-Gly-Ile-Tyr-Asp-Val-Pro (EGIYDVP), to whicha FcPO2 moiety may be transferred from FcATP via the action ofthe src related protein kinase. The kinetic parameters Km andVmax were determined for src related protein kinase with respectto the FcATP co-substrate, and were found to be 200 mM and115 mA cm�2 min. for the phosphorylation of the EGIYDVPpeptide substrate.115 Recent advances in sensors/biosensors forthe determination of enzyme kinetics are summarized inTable 4.

7 Conclusions and future outlooks

This review has endeavoured to highlight the differencesbetween three primary electrochemical techniques and hasshown that SWV reigns as the most sensitive of the conven-tional electrochemical techniques that are in use today. Thesensitivity of SWV coupled with its high frequency wasdemonstrated as an ideal technique for the development ofrapid response and reliable sensors. The usefulness of thistechnique was elucidated for applications in diagnostics,environmental analysis, the food industry and the measure-ment of enzymatic activity. The development of novel andimproved electrode surfaces and nanomaterials introducesthe possibility of sensors that will exhibit even higher sensi-tivity, with SWV serving as an ideal methodology for itsoptimization. Concurrent with the greater knowledge ofelectrochemistry and a better understanding of electrodesynthesis and modication, sensors will improve considerablyin terms of both sensitivity and detection limits. Micro- andnano-sensors will likely constitute the next disruptive para-digm in the eld of sensing and biosensing, and SWV willsurely play a critical role in their development. Advances inthese areas will be sure to spark innovations in industry andsociety as a whole.


Abbreviations

BDDE
Boron Doped Diamond Electrode CPE Carbon Paste Electrode dsDNA Double stranded DNA EPPGE Edge Plane Pyrolytic Graphite Electrode GCE Glassy Carbon Electrode HMDE Hanging Mercury Drop Electrode JUG-HATZ [N-(6-(4-hydroxy-6-isopropylamino-1,3,5-triazin-
2-ylamino)hexyl)-5-hydroxy 1,4-naphthoquinone-3-propionamide]

MB
Methylene Blue MWCNT Multi-Walled Carbon Nanotubes SWCNT Single Walled Carbon Nanotubes PGE Pyrolytic Graphite Electrode.
Acknowledgements

This work was supported by a Discovery Grant from the NaturalSciences and Engineering Research Council of Canada(NSERC). B. Shah appreciates the Ontario Trillium Scholarship.A. Chen acknowledges NSERC and the Canada Foundation ofInnovation (CFI) for the Canada Research Chair Award inMaterial and Environmental Chemistry.

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