Nanomaterials Based Electrochemical Sensing Applications for Safety and Security

Nanomaterials Based Electrochemical Sensing Applications forSafety and Security

Sergio Mar�n,a Arben MerkoÅi*a, b

a Nanobioelectronics & Biosensors Group, CIN2, Institut Catal� de Nanotecnologia, Barcelona, Spainb ICREA, Barcelona, Spain*e-mail: [email protected]

Received: October 5, 2011;&Accepted: December 16, 2011

AbstractNanomaterials based sensing systems provide a new class of rapid and low cost detection alternatives with interestin the field of safety and security applications. In this review we report the recent trends in the use of various nano-materials such as nanoparticles, carbon nanotubes, nanowires and graphene to detect different safety and securityrelated analytes (i.e. microorganisms, toxins, pesticides and explosives). Nanomaterials are used either as modifiersof the electrochemical transducers or as labels with the objective to enhance the electrochemical signal, improvethe stability and in general the performance of the detection systems including their cost-efficiency. Most of the de-veloped systems are shown to bring excellent improvements while being used in the laboratory. Their application inreal sample and during in-field monitoring still needs a long way while issues such as the reproducibility, stability,mass production capability of the designed devices etc. shouldn�t still yet be resolved.

Keywords: Nanomaterials, Nanoparticles, Carbon nanotubes, Nanowires, Graphene, Safety, Security

DOI: 10.1002/elan.201100576

1 Introduction

Since the terrorist attacks in September 2001 the societyis being worried much more about safety and securityissues. Fast and easy in-field detection of compounds suchas explosives, pesticides, toxins and bacteria are gettingspecial importance. In this context the development ofnovel biosensing detection systems based on nanomateri-als seems to be an advantageous alternative in compari-son to classical devices.

Nanostructured materials or nanomaterials are a newclass of materials which provide a great potential for im-proving the performance of biosensing systems andextend their applications in various fields of material sci-ences and biomedical sciences [1,2] between others. Thestudy of nanomaterials involves creation, manipulationand use of materials, devices and systems usually with di-mensions smaller than 100 nm. Nanomaterials with di-mensions within this range display unique physical andchemical features because of effects such as the quantumsize effect (i.e. fluorescence), surface effect (i.e. catalysis)etc. Nanomaterials display physical properties such as ad-sorption, surface modification and catalytic featureswhich are different from bulk properties of the same ma-terials. Thanks to these properties nanomaterials are play-ing an important role in the advancement of nanoscienceand nanotechnology in applications such as in humanhealthcare [1–25] and security and safety [26–71] betweenother industries. Such progress in nanobiotechnology is

bringing novel alternatives in the development of biosen-sors and biosensing systems. This review provides recentresearch advances involving the use of nanomaterialssuch as nanoparticles, carbon nanotubes, nanowires andgraphene in the electrochemical detection of analyteswith interest in the field of safety and security.

2 Nanomaterials Applications

2.1 Nanoparticles

Nanoparticles (NPs) possess several distinctive physicaland chemical properties that make them promising mate-rials for the creation of novel chemical and biological de-tection systems [72].

Indeed, in the last few years nanostructured materials,such as noble metal nanoparticles, quantum dots, andmagnetic nanoparticles, have been employed in a broadspectrum of highly innovative approaches for assays ofmetal ions, small molecules, proteins and nucleic acids bi-omarkers, bacteria and other species [3,4,7,9,12,14]. In ad-dition to the large surface-to-volume ratio that favoursminiaturization, nanoparticles possess unique optical,electronic and magnetic properties depending on theircore materials [2].

Furthermore the properties of nanomaterials dependon their size and shape, and vary with their surroundingchemical environment. Additionally, nanoparticles can befashioned with a wide range of small organic ligands and

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Electroanalysis 2012, 24, No. 3, 459 – 469 � 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 459

Review

large biomacromolecules by using tools and techniques ofsurface modification. Each of these capabilities has al-lowed researchers to design novel diagnostic systems thatoffer significant advantages in terms of sensitivity, selec-tivity, reliability and practicality. [2]

2.1.1 Quantum Dots

Quantum dots (QDs) have unique intrinsic optical prop-erties (i.e. fluorescence) but in the last years have beenalso employed for their electrochemical properties (red-ox or electrocatalytic) showing interesting labelling capa-bilities [73,74] in biosensing systems. Electrochemical de-tection of QDs (i.e. stripping analysis) is related to lowcost instruments and mass production devices (i.e. screen-printed electrodes) that can be easily used in miniaturizedforms for rapid and in-field detections. QDs have beenused the detection of Epstein–Barr virus-derived latentmembrane protein 1 (LMP-1) [10]. The strategy consists

on signal amplification of LMP-1/cadmium telluride(CdTe) quantum dots (QDs) functionalized silica nano-sphere labels (Si/QD/Ab2). Si/QD/Ab2 was fabricated bycovalently binding LMP-1 antibody (denoted Ab2) toCdTe QDs, which have been previously coated onto thesurface of silica nanoparticles via EDC chemistry. The as-prepared Si/QD/Ab2 label can be brought to a modifiedgold slide by a “sandwiched” immunoreaction, which wasconfirmed by SEM images and detected by square wavevoltammetry (SWV) (see Figure 1).

2.1.2 Gold Nanoparticles

Gold nanoparticles (AuNPs) have been widely used andhave attracted considerable attention in analytical andbiomedical areas due to their easy chemical synthesis,their narrow size distribution and their convenient label-ling of biomolecules. As QDs, AuNPs are studied fortheir interesting electrochemical properties and have

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Fig. 1. Detection of a virus related protein using CdTe quantum dots-capped silica nanoparticle labels. (I) Schematic drawing of thepreparation of Si/QD/Ab2 labels. TEM images of silica nanospheres synthesized using the improved “seed-growth” route (A and D)before and (B) after coating with CdTe QDs. (C) shows the colour change of QDs coated silica nanosphere before (a) and after (b)coupling with Ab1. (II) (A) Records of anodic stripping voltammograms after the Ab1-modified gold slide were incubated in 3 ng/mLLMP-1 solution for 30 min (a), then in Si/QD/Ab2 solution (b) or in CdTe QD-labeled LMP-1 antibody (c) for 30 min, and finally dis-solved in 0.05 mol/l H2SO4 for 20 s; (B) Anodic stripping voltammograms of CdTe captured by Si/QD/Ab2-Ag-Ab1- MUA/MU-Au atLMP-1 concentrations of 0.01, 0.05, 0.1, 0.5, 1, 5, and 10 ng/mL, respectively. Square wave stripping detection was performed by 2 mindeposition at �1.4 V on a Bi film modified glassy carbon electrode (7 mm2) and scanning from �1.4 to �0.5 V at an amplitude of25 mV and a frequency of 15 Hz. Adapted from [10].

460 www.electroanalysis.wiley-vch.de � 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Electroanalysis 2012, 24, No. 3, 459 – 469

Review S. Mar�n, A. MerkoÅi

http://www.electroanalysis.wiley-vch.de

been used in several works, such as for bacteria [3–7,12],toxins [56,58] and pesticides [26,29–32,36,37] detections.One reported example is related to the modification ofEscherichia coli single-stranded DNA binding (SSB) pro-tein with gold nanoparticles for electrochemical detectionof DNA hybridization [4]. The SSB was attached onto aself-assembled monolayer (SAM) of single-stranded oli-gonucleotide modified Au nanoparticle, and the resultingAu-tagged SSB was used as the hybridization label.Changes in the Au oxidation signal were monitored uponbinding of Au tagged SSB to the probe and the hybridlinked onto the electrode surface (Figure 2) during thedetection step.

2.1.3 Other Nanoparticles

Other metal nanoparticles with electrochemical proper-ties have been used for the detection of microorganisms[8,9,13,14], toxins[55], pesticides [27,28,33–35] and explo-sives [62,63].

One of examples is the quantification of phosphorylat-ed acetylcholinesterase pesticide that consists in the de-velopment of a new sandwich type electrochemical immu-nosensor – for quantification of organophosphorylatedacetylcholinesterase (OP-AChE), an exposure biomarkerof organophosphate pesticides and nerve agents using zir-conia nanoparticles (ZrO2 NPs) (used due to the advan-tages such as lack of toxicity as well as the strong affinityfor the phosphoric group) [27]. ZrO2 NPswere anchoredon a screen printed electrode (SPE) to preferably captureOP-AChE adducts by metal chelation with phospho-moi-eties, which was selectively recognized by lead phosphate-apoferritin labeled anti-AChE antibody (LPA–anti-AChE). The sandwich-like immunoreactions were per-formed among ZrO2 NPs, OP-AChE and LPA–anti-AChE to form ZrO2/OP-AChE/LPA–anti-AChE complexand the released lead ions were detected using a disposa-ble SPE. The binding affinity was investigated by squarewave voltammetry (SWV). (Figure 3)

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Fig. 2. Detection of bacteria DNA using gold nanoparticles modification. (I) Schematic illustration of the hybridization detectionprotocol. Au-tagged SSB can bind to the single-stranded probe, thus amplify the Au oxidation signal. However, only a low Au signalcan be obtained from the double-stranded hybrid after interaction with SSB (II) Calibration plot for the dependence of Au oxidationsignal upon increasing the concentration of probe at bare biotin-modified carbon paste electrodes (BCPE) in the presence of50 gmL�1 SSB in PBS (A). Histograms for Au oxidation signal by using Au-tagged SSB (Au-SSB) and only probe-modified Au nano-particles (Au) with the mean and the standard deviation of the signal values obtained with five different replicates of the electrode(n=5) (B). Adapted from [4].

Electroanalysis 2012, 24, No. 3, 459 – 469 � 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim www.electroanalysis.wiley-vch.de 461

Nanomaterials Based Electrochemical Sensing Applications for Safety and Security


2.2 Carbon Nanotubes

Carbon nanotubes (CNTs) combine in a unique way highelectrical conductivity, high chemical stability and ex-tremely high mechanical strength. These special proper-ties of both single-wall (SW) and multi-wall (MW) CNTshave attracted the interest of many researchers in thefield of electrochemical sensors. The latest advances andfuture trends in producing, modifying, characterizing andintegrating CNTs into electrochemical sensing systemsare already demonstrated [75].

CNTs have either been used as single probes after in-situ formation or even individually attached onto aproper transducing surface after synthesis. Both SWCNTs

and MWCNTs can be used to modify several electrodesurfaces in either vertically oriented ��nanotube forests��or even a non-oriented way.

CNTs have been used as electrochemical platforms forseveral applications such as for microbiological [18–22,25], toxins [59,60], pesticides [31,38–52] and explosives[64–66] detections.

CNT have been used for electrochemical biosensing ofmethyl parathion and chlorpyrifos pesticides [43], two ofthe most commonly used organophosphorous insecticidesin vegetable crops. The self-assembled monolayers(SAMs) of SWCNT wrapped by thiol terminated singlestrand oligonucleotide (ssDNA) on gold were utilized toprepare nano size polyaniline matrix for acetylcholines-

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Fig. 3. Detection of pesticides using a nanoparticle based system. (I) (A) TEM image of lead phosphate-apoferritin nanoparticles.(B) FTIR spectrums of paraoxon (a), AChE (b) and OP-AChE adduct (c). (C) QCM responses of f during the whole sandwich-likeimmunoreaction process. (D) SWV responses of the immunosensor for 1.0 nM OP-AChE (a), 1.0 nM OP-AChE (b), 5.0 nM nonpho-phorylated AChE (c), 5.0 nM OP (d) and 1% BSA (e). (II) Schematic illustration of sandwich-like immunoassay of OP-AChE ad-ducts. Adapted from [27].




terase (AChE) enzyme immobilization. The key step ofthis biosensor was AChE acetylcholine enzymatic reac-tion which causes the small changes of local pH in the vi-cinity of an electrode surface. The pesticides were deter-mined through inhibition of enzyme reaction (Figure 4).

2.3 Nanowires

Nanowires are a part of the group of the one dimensional(1-D) nanostructures that have become the focus of in-tensive research due to their unique properties and theirpotential for fabrication into high density nanoscale devi-ces including sensors, electronics, and optoelectronics.

1-D nanostructures, this smallest dimension structures,can be used for both efficient transport of electrons and

optical excitation making these structures of great interestfor nanoscale devices. Because of their high surface-to-volume ratio and tuneable electron transport propertiesdue to quantum confinement effect, their electrical prop-erties are strongly influenced by minor perturbations.Compared to 2-D thin films where binding to the surfaceleads to depletion or accumulation of charge carriers onlyon the surface of a planar device, the charge accumula-tion or depletion in the 1-D nanostructure takes place inthe “bulk” of the structure thus giving rise to largechanges in the electrical properties that potentially ena-bles the detection of even a single molecule. 1-D nano-structures thus avoid the reduction in signal intensitiesthat are inherent in 2-D thin films as a result lateral cur-rent shunting. This property of the 1-D nanostructures

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Fig. 4. Detection of pesticides using a carbon nanotube based system. (I) Schematic representation of biosensor fabrication and itsfunctions. Step 1 – SWCNT wrapping with thiol terminated ssDNA; Step 2 – ssDNA wrapped SWCNT self-assembled on gold elec-trode; Step 3 – controlled electrochemical polymerization of aniline on the Au/ssDNA–SWCNT layers; Step 4 – immobilization ofAChE enzyme by glutaraldehyde; Step 5 – pesticide sensing mechanism of Au/ssDNA–SWCNT/PANI/AChE. (II) (A) Typical AFMimages of ssDNA wrapped SWCNT SAMs on Au surface. (B) Calibration curve for methyl parathion and chlorpyrifos (0.6<SD<3.5). Inset: SWV net current responses of biosensor after 15 min incubation with different concentrations of methyl parathion in0.002 M PBS (pH 7.0) containing 1 mM AChCl and 0.1 M NaCl; SWV measuring conditions. Adapted from [43].




provides a sensing modality for label-free and direct elec-trical readout when the nanostructure is used as a semi-conducting channel of a chemiresistor or field-effect tran-sistor [24,76].

Electrical and electrochemical sensors based on nano-wires for bacterial [23,24], toxin [61] and pesticide [54]detections have been reported. For cyanide detection ahydroxyapatite nanoarray-based biosensor formed bydeposition of hydroxyapatite nanowires array (HANWA)onto a glassy carbon electrode surface has been reported[61]. This electrochemical biosensor determines cyanidethrough its inhibitory effect on horseradish peroxidase(HRP) encapsulated by chitosan (CHIT) onto theHANWA platform. The current organic–inorganic hybridnanostructure provides excellent enzyme–substrate con-tact with enzyme activity well maintained within the de-veloped matrix. The densely distributed HANWA withlarge surface area and abundant adsorbing sites can pro-vide a favourable electrochemical interface for the con-struction of electrochemical biosensor (Figure 5).

2.4 Graphene

Although graphene was shown to exist in 2004 a hugeand increasing number of papers dealing with this materi-al can be found in the literature. Kostya S. Novoselov andAndre K. Geim, the 2010 Nobel Laureates in Physics,demonstrated that single layers of graphene could be iso-lated from graphite and definitively identified by micros-copy [77] (although a similar fabrication method was pub-lished five years earlier by Ruoff�s group [78]). Novoselovand the team measured the electrical properties of few-layer graphene and found some remarkable behaviour,such as the fact that graphene behaved as a zero-gap sem-iconductor with ballistic transport of charge carriers,which could be electrons or holes, depending on the signof the applied gate voltage. These and other intriguingproperties were considered to offer exciting prospects forgraphene to be used in creating nanometer-scale metallictransistors and other devices.

Since then, the number of experimental and theoreticalstudies of graphene has skyrocketed. Some of these sworks have been generated by condensed-matter physi-

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Fig. 5. Detection of toxins using nanowire system (I) Typical SEM images of the HANWA modified GCE: (A) low-magnificationimage; (B) high-magnification image. The electrodeposition was obtained under a constant cathode current of 0.005 mAmm�2 for5 min. (II) (A) CVs of the CHIT–HRP/HANWA biosensor in the following: (a) 10 mM PBS; (b) the same as curve �a� with 2 mMH2O2; (c) the same as curve b with 20 ngmL�1 cyanide standing 15 min before measurement for sufficient enzyme inhibition. Scanrate: 100 mV s�1. (B) Dynamic response of the CHIT–HRP/HANWA biosensor to 0.6 mM H2O2 and the successive addition of specif-ic concentrations of cyanide in 10 mM PBS at a potential of �0.1 V. Adapted from [61].




cists who finally have a material that had long been mod-elled, but had not been believed to exist in a free state[79]. The application of the graphene as a transducerplatform are really interesting in several fields such as mi-crobiological detection [15–17], detection of pesticides[33,53] and explosive detection [67–71]. Graphene havebeen used as transducer platform for bacteria detection[15]. It consists on functionalized graphene oxide (GO)sheets coupled with a signal amplification method basedon the nanomaterial-promoted reduction of silver ions forthe sensitive and selective detection of bacteria. This re-ported work aims to develop an electrochemical routecombined with GO sheet-mediated Ag enhancement forbiological/chemical analyte detection (Figure 6).

3 Conclusions and Future Perspectives

Table 1 summarizes the results obtained with some of thereported nanomaterials based electrochemical sensors al-ready applied or with special interest for safety and secur-ity applications. Most of the applications of the nanoma-terials in electrochemical sensors are related to their useas substrate/transducer (or immobilization platform). Ofspecial importance for such a use are CNT and graphenealthough the application of nanoparticles to build/modifytransducers surfaces have been also shown to be effectivealternative for the improvement of the sensor perfor-

mance. Between the various nanomaterials used for trans-ducers modification CNT have shown to be the most re-ported [75,80].

The use of gold nanoparticles so as to connect/immobi-lize biological material have been of great interest forDNA or protein detection.

Usually the achieved detection limits although most ofthem reported for synthetic matrix while using nanomate-rials (using synthetic or real/spiked samples) seem to besometimes better in comparison to the cases without theirpresence. Although the large variety of the nanomaterialsused have shown clear advantages for electrochemicalsensing considering the importance of safety and securityissue (between other fields) a careful and extensive studyis still required so as to bring the developed devices tousers.

Beside the various nanomaterials and electrochemicalmethods already described in this review the applicationof hybrid materials (i.e. TiO2 decorated graphene – TiO2-G nanohybrid) and electrochemical impedance analysis(EIA) applied recently for organophosphate compounds(OPs) detection based on acetylcholinesterase (AChE)inhibition can also be considered. [81] EIA in relation tothe use of nanomaterials and toxic/safety related applica-tion is mostly applied as a characterisation tool (i.e. fordetection of methyl paraoxon, carbofuran and phoxim[82]. Its application in real sample analysis would need

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Fig. 6. Detection of bacteria using graphene as support. (I) Schematic Representation of This New Detection Method for Sulphate-Reducing Bacteria (SRB) Based on the GO Sheet-Amplified Immunoassay Combined with the Silver Enhancement. (II) Typical PSAspectra (A) based on GO-mediated immunosensor for antibody immobilization and sample detection, calibration relationship (B) be-tween the PSA responses and concentrations of SRB with (9) and without (0) GO-mediated immunosensor, and detection of SRBbased on immunoassay dot blot analysis (C) using the GO sheets as deposition substrate for Ag enhancement. Adapted from [15].




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R Table 1. Nanomaterials applications in electrochemical biosensing systems applied in safety and security related issues. AuNP: goldnanoparticles; Amp.: amperometry; CV: cyclic voltammetry; EIS: electrochemical impedance spectroscopy; DPV: differential pulsevoltammetry; SWV: square wave voltammetry; PX: paraoxon; PT: parathion; ASV: anodic stripping voltammetry; CAmp: chronoam-perometry; DPSV: differential pulse stripping voltammetry; LSV: linear sweep voltammetry; PSA: potentiometric stripping analysis;LSSV: linear sweep stripping voltammetry; 2,4-DNT: 2,4-dinitrotoluene; TNT: trinitrotoluene; 1,3,5-TNB: 1,3,5-trinitrobenzene; 1,3-DNB: 1,3-dinitrobenzene.

Nanomaterial Analyte Application mode Technique Detection limit Range of response Ref.

AuNP Microorganism Substrate Amp. 50 CFU/mL(milk) 102 to 107 CFU/mL [5]6 CFU/mL (PBS)

CV MP: 3 pM MP: 5 to 300 pM [12]LP:5 pM LP: 5 to 750 pMCP:8 pM CP: 10 to 750 pMSP:9 pM SP: 10 pM to 1 nM

Signal amplification EIS 0.825 ng/mL(1.2 fM) 27.5 to 0.825 mg/mL [3]DPV 1.7 pM for T1-DNA 0.044 to 2.0 nM [7]

1.55 pM for T2-DNALabel SWV 2.17 pM 0.030 to 9.550 nM [4]

Toxins Label CV 30 pg/mL 0.1 to 20 ng/mL [56]Signal amplification EIS 12 ppt 15 to 1000 ppt [58]

Pesticides Substrate Amp. 33 nM 10 to 135 nM [29]PX: 0.5 ng/L PX: 10�10 to 10�2 g/L [30]PT: 1 ng/L PT: 10�9 to 10�2 g/L0.1 pM 0.1 pM to 5 nM [32]0.03 ng/mL (0.1 nM) 0.1 to 20 ng/mL [36]

CV 10 mM 50 to 100 mM [26]10 nM 0.1 to 10 mM [31]

Label ASV 30 CFU/mL 50 to 5.0 �104 CFU/mL [6]Nanoparticles Microorganism Substrate CV 5 cfu/mL of E. coli 103 to 5� 105 cfu/mL [14]

EIS 103 CFU/mL 103 to 107 CFU/mL [8]DPV 0.38 mg/L [55]

Label CV 1.0 fM 1.0 fM to 10 pM [9]ASV 0.001 ng/mL 0.001 to 10 ng/mL [10]

98.9 CFU/mL 1.30� 102 to 2.6 �103 CFU/mL [13]Pesticide Substrate DPV 0.5 ng/mL 1.0 ng/mL to 7.0 mg/mL [37]

SWV 0.02 nM 0.05 to 10 nM [27]2.0 ng/mL 5.0 to 3000.0 ng/mL [33]0.8 ng/mL 0.005 to 1.0 mg/mL [34]3 ng/mL 20 to 140 ng/mL [35]

Signal amplification CV 0.01 mM 0.05 to10 mM [28]Explosive Substrate CV 2 ppm 2 to 4 ppm [62]

Labels SWV 0.5 ng/mL 0.01 ng/mL to 1.0mg/mL [63]CNT Microorganism Substrate CAmp 1.37 U/L laccase 1.37 to 33.79 U/L laccase [18]

DPV 1,76 pM 0.01 nM to 1.0 mM [19]11 nM 79.4 nM to 1.58 mM [20]100 pM 10 pM to 100 nM [22]

CV 0.62 U/mL 0.62 to 1.8 U/mL [21]10 pg/mL 0.05 to 15 ng/mL [25]

Toxin Substrate DPV 98.6 nM 600 nM to 66 mM [59]CV 562 pg/mL 0.625 to 25 ng/mL [60]

Pesticide Substrate Amp. 0.04 ppb 0.04 to 0.1 ppb [38]1.08 mM 0.95 mM to 1.9 mM [40]4 nM 10 nM to 1 mM [44]

CV 10 mM 10 to 60 mM [39]0.005 mM 0.02 to 1 mM [49]

DPSV 10 ng/mL 10 ng/L to 50 mg/L [41]0.8 mg/L 0.05 to 100 mg/L [45]0.1 mg/L 0.01 to 100 mg/L [51]

SWV 0.12 mg/mL 0.41 to 83.30 mg/mL [42]1 pM 10 pM to 1 mM [43]0.005 mg/mL 0.05 to 2.0 mg/mL [47]5.46 nM (1.09 mg/L) 0.33 to 6.61 mM [52]

DPV 12.2 nM (2.02 mg/L) 0.83 to 9.90 mM [46]CAmp 1.15 mM 4.5 to 20 mM [48]LSW 9 nM 200 nM to 10 mM [50]

Explosive Substract SWV 1.5 nM 45 nM to 8.5 mM [65]




overcoming of problems related to sensitivity as well asthe requested analysis time.

Another analyte, with interest to be considered insafety and security applications, commonly used as explo-sive is 2,4,6-trinitrotoluene (TNT). The importance ofTNT analysis is related not only to security issues but alsoto environment problems due to the contamination it cancause to soil and water. To achieve real sample/in-fieldapplications of sensors for TNT or other explosives sever-al requisites must be fulfilled. Considering the vapor pres-sure of TNT at room temperature the sensors must bevery sensitive and at the same time selective enough so asto eliminate both false positive and negative results. Inaddition the sensing devices must be robust, not prone todrift, able for in-field and real-time high-throughput anal-ysis. Following the mentioned requisites the use of nano-sensors (nanowire-based field-effect transistors, NW-FETs) for an easy and rapid detection of TNT vapours(TNT molecules can strongly bind to the surface of thenanowires through an acid–base pairing interaction withamino ligands on the sensor surface) may play an impor-tant role. [83] Metal oxide semiconductor (MOS) gassensor as a class of the electronic noses and usually re-ported as detectors for VOCs (volatile organic com-pounds) in general and explosives [84] particularly wouldbe also interesting tools for future development of sensi-tive, low-cost and easy manufacturing explosive detectors.

The application of nanomaterials for heavy metal sens-ing although not mentioned in this review are of great im-portance for safety and security too [85]

The results obtained so far, although almost since onedecade only, show clear advantages of nanomaterialscompared to other conventional materials. Advantagessuch as the low cost, stability and reproducibility com-bined with high sensitivity and multidetection capabilityof nanomaterials based electrochemical sensors are evi-dent. Nevertheless we still need to push forward our ef-forts to get inside and explain the response mechanisms

related to such improvements [86] and make possible thereal safety and security issues solving using nanomaterialsbased electrochemical sensors. In addition the applicationof the mentioned methods in real samples is still in pre-liminary steps and more efforts are necessary to solveproblems related to the whole integration/miniaturizationof the biosensing systems in simple and easy to use plat-forms (i.e. lateral flow) where sample pre-treatment/incu-bation steps are already integrated into the same platformwhere the detection/signalling of the analyte occurs.

Acknowledgements

The financial support from the Spanish Ministry of Sci-ence and Innovation through Project MAT2011-25870 andthe NATO Science for Peace and Security Programme�ssupport under the Project SfP 983807 are acknowledged.A. M. thanks the support given by A. Puig for the manu-script revision.

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Table 1. (Continued)

Nanomaterial Analyte Application mode Technique Detection limit Range of response Ref.

CV 25 nM 0.6 to 20.0 mM [66]Nanowire Microorganism Label EIS 48 cells/mL 48 to 2000 cells/mL [23]

Substrate EIS 10 fM 10 to 35 fM [24]Toxin Substrate Amp. 0.6 ng/mL 2 to 20 ng/mL [61]Pesticide Substrate Amp. 4.8 mM 59 mM to 12 mM [54]

Graphene Microorganism Amplification PSA 50 CFU/mL 1.8 � 102 to 1.8� 108 CFU/mL [15]Substrate EIS 180 CFU/mL 180 to 1.8 � 107 CFU/mL [16]

100 fM 10 fM to 1 mM [17]Pesticide Substrate DPV 2 nM 5 nM to 0.45 mM [53]Explosives Substrate DPV 1 mg/mL 1 to 19 mg/mL [67]

Substrate Amp. 0.6 nM 2.0 nM to 0.23 mM [68]Substrate ASV 4 ppb 0.03 to 1.5 ppm [69]Substrate 2,4-DNT: 1 ppb 50 to 250 ppb [71]

TNT: 0.5 ppb1,3,5-TNB:1 ppb1,3-DNB:2 ppb

Substrate LSSV 42 nM 0.549 to 11 mM [70]




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Nanomaterials Based Electrochemical Sensing Applications for Safety and Security

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