Thin Solid Films 519 (2010) 1122–1127

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Sol–gel derived cerium-oxide–silicon-oxide nanocomposite forcypermethrin detection

Akhilesh Gupta, Nirmal Prabhakar, Renu Singh, Ajeeet Kaushik, Bansi D. Malhotra ⁎DST Centre on Biomolecular Electronics, Biomedical Instrumentation Section, National Physical Laboratory, Dr. K. S. Krishnan Marg, New Delhi-110012, India

⁎ Corresponding author. Tel.: +91 11 45609152; fax:E-mail address: bansi.malhotra@gmail.com (B.D. Ma

0040-6090/$ – see front matter © 2010 Elsevier B.V. Adoi:10.1016/j.tsf.2010.08.055

a b s t r a c t

a r t i c l e i n f o

Available online 25 August 2010

Keywords:CypermethrinDNA biosensorSilicon-oxideNanocomposite

Cerium oxide (CeO2) nanoparticles have been self-assembled onto sol–gel derived silicon-oxide (SiO2) filmfabricated onto indium tin oxide (ITO) coated glass plate. These SiO2–CeO2 nanocomposite films have beenused to immobilize the double stranded calf thymus deoxy ribose nucleic acid (dsCT-DNA) by physicaladsorption to detect cypermethrin (CM). Both CeO2–SiO2/ITO electrode and dsCT-DNA/CeO2–SiO2/ITObioelectrodes have been characterized using Fourier transform infrared (FTIR) spectroscopy, scanningelectron microsopy (SEM) and differential pulse voltammetry (DPV) to confirm the formation of CeO2–SiO2

nanocomposite and binding of dsCT-DNA with CeO2–SiO2 nanocomposite. Electrochemical response studiesof dsCT-DNA/CeO2–SiO2/ITO bioelectrode carried out as a function of CM concentration using DPV techniqueexhibit detection limit up to 0.0025 ppm with response time of 30 s.

+91 11 45609310.lhotra).

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© 2010 Elsevier B.V. All rights reserved.

1. Introduction

Cypermethrin (CM), a synthetic pyrethroid synthetic compound isprimarily used as an insecticide that acts as a fast-acting neurotoxin ininsects such as fish, bees and aquatic insects. It easily degrades on soiland plants but can be effective for weeks when applied to indoor inertsurfaces. During 1988, pyrethroids amounted for about 40% of the salesfor insecticides for cotton treatment in theworld (CM8%) [1]. And CM isone of the most important insecticides for cereals and vegetables in theUK. There has been a dramatic increase in the use of CM for arable cropsin the UK: from approximately 216,000 ha in 1988 to 1,582,000 hasprayed in 1992, falling back to 863,000 ha in 1994 [2]. Besides this, it isused for impregnation of mosquito bed nets to prevent malaria, andextensively for indoor pests. And many people due to consumption ofpyrethroids expired between 1993 and 1996 [3].

Thus, the toxic effects of the CM provoke its detection in theenvironment up to 0.25–1.5 mg/kg bw/day limits. The most analyticaltechniques for CM detection are based on chromatography andenzyme-linked immunosorbent assays [4–7]. Jin andWebster in 1998have extracted the residues of CM isomers and their metabolites fromelm bark, litter, and soil, with liquid–liquid partitioning, andchromatography by GC–ECD. The average recoveries of CM isomerpairs are 82 to 112% with relative standard deviation (RSDs) of 2.3 to10% at the fortification levels of 2, 10, 100 μg/g in elm bark, 2, 15,150 μg/g in litter, and 0.2, 2, 20 μg/g in soil [8]. Saxena et al. haveinvestigated the effect of CM on root meristem cells of A. sativum and

A. cepa using ultraviolet (UV) and FTIR spectroscopy techniques,respectively [9]. Normal phase high performance liquid chromatog-raphy (HPLC) and FTIR techniques have been used to estimate CMupto 0.3 mg/mL in most mobile phases, and up to 0.1 mg/mL inacetonitrile/n-hexane [10]. Though these methods are specific theyhave a number of limitations such as need of bulky instrumentation,manpower expertise, longer response time, etc. Keeping these inview, DNA biosensors have recently been utilized to provideinformation on insecticides, pesticides, and toxic compounds inenvironmental and biological samples.

Electrochemical DNA biosensors have been fabricated usingvarious matrices such as graphite, carbon electrode, self-assembledmonolayers, and conducting polymers for detection of varioustoxicants/pesticides. Solanki et al. in 2008 have developed a nucleicacid sensor based on polyaniline (PANI) by covalently immobilizingdouble stranded calf thymus (dsCT) DNA onto perchlorate (ClO4)-doped PANI film deposited onto indium tin oxide (ITO) glass plateusing 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochlo-ride (EDC)/N-hydroxysuccinimide (NHS) chemistry to detect cyper-methrin (0.005 ppm) and trichlorfon (0.01 ppm) in 30 and 60 s,respectively [11]. Recently, detection limit for cypermethrin has beenimproved by developing nucleic acid sensor with immobilization ofssCT-DNA onto chitosan (CH)-iron oxide (Fe3O4) nanoparticles basedhybrid nanobiocomposite film deposited ITO coated glass forpyrethroids like cypermethrin (CM) (0.0025–2 ppm) and permethrin(PM) (1–300 ppm) detection using DPV technique within 25 s and40 s, respectively [12].

To fabricate an electrochemical DNA biosensor, the immobilizationof DNA is a crucial step wherein DNA must retain its natural stateresulting in improved sensing properties. In this context,

1123A. Gupta et al. / Thin Solid Films 519 (2010) 1122–1127

nanomaterials are receiving a great deal of attention because of theirexceptional optical and electrical properties due to electron andphonon confinement, as alternative matrices for DNA immobilizationto improve the stability and sensitivity of biosensors [13,14].Nanomaterials exhibit interesting properties such as a large surface-to-volume ratio, high surface reaction activity, high catalytic efficiencyand strong adsorption ability that make them potential candidatematerials to play a catalytic role in the fabrication of a biosensor.

Among the various electro-active biocompatible nanomaterialssuch as zinc oxide, cerium oxide, titanium oxide, magnetite etc, silicananoparticles (SiO2) with controlled particle size, porousmorphology,biocompatibility, non-toxicity, high ionic conductivity and highsurface-to-volume ratio along with its chemical, thermal and easyfunctionalization properties have been used for biosensor applications[15]. Sol–gel derived nanostructured SiO2 film is known to haveseveral advantages such as low temperature processing, tunablephysical parameters, optical transparency, chemical inertness, ther-mal stability and negligible swelling in aqueous and nonaqueoussolutions for the immobilization of enzymes. The surface functiona-lization of SiO2 with organic moieties or another nanostructure mayresult in loading of the desired biomolecules and direct electrochem-istry of enzymes resulting in enhanced sensing characteristics.However, there is a considerable scope to improve the biosensingperformance of SiO2 by preparing nanocomposite of SiO2 with electro-active materials such as nanostructured CeO2 wherein the CeO2

nanoparticles increase the electro-active surface area of NanoSiO2 filmresulting in loading of desired biomolecules. CeO2 nanoparticles haveattracted much interest owing to their unique properties includinghigh mechanical strength, oxygen ion conductivity, high isoelectricpoint, biocompatibility and high adsorption capability and oxygenstorage capacity for the development of biosensors. Furthermore,non-toxicity, high chemical stability and high electron transfercapability make CeO2 a promising material for biosensor applications[16].

In this paper, we report results of the studies relating to theimmobilization of dsCT-DNA onto the CeO2–SiO2 nanocomposite filmdeposited onto indium tin oxide (ITO) coated glass substrate to detectCM.

2. Experimental

2.1. Chemicals and reagents

Double stranded calf thymus DNA (dsCT-DNA) was obtained fromGenei Bangalore Pvt. Ltd., India. Tris base, ethylene diamine tetraaceticacid (EDTA), potassium monohydrogen phosphate and potassiumdihydrogen phosphate were procured from Sigma (Aldrich). Cyper-methrin was procured from Loba Chemie, India. Indium tin oxide(ITO) coated glass plates were obtained from Balzers UK. All chemicalsused were of molecular biology grade. Deionizedwater (Milli Q 10 TS)was used for the preparation of reagents and solutions. All glass wareswere autoclaved prior to being used.

2.2. Preparation of ssDNA/CeO2–SiO2/ITO electrodes

SiO2 sol was prepared by hydrolysis and polymerization reactionof tetramethyl orthosilicate (TMOS, Merck Chemicals) in the presenceof nitric acid catalyzer (HNO3, Merck Chemicals, 65%). TMOS:HNO3:H2O:EtOH was mixed in required amounts with a molar ratio of1:0.5:7.5:6.5. The mixture was stirred at 70 rpm and reflux used for5 h. The obtained sol, containing 10 wt.% SiO2, was diluted with EtOHin order to obtain 4 wt.% SiO2 sol. Thus obtained sol was used for dipcoating after an aging period of 24 h. SiO2 thin filmswere deposited onto ITO coated glass by dipping them into the SiO2 colloidal sol andwithdrawing at 20 cm/min speed. After drying in air at 100 °C, the

coated samples were baked at 450 °C for 2 h. These SiO2 sol–gel filmswere covered with the CeO2 nanoparticles.

The CeO2 nanoparticles solution was spread onto SiO2/ITOelectrode to prepare the CeO2–SiO2/ITO electrode. Firstly, 1 g ofcerium ammonium nitrate [(NH4)2Ce(NO3)6] was dissolved in 20 mLdeionised water. Then 5 mL (1 M) solution of ammonium hydroxide(NH4OH) was added drop wise in this solution with constant stirringfor 4 h at 25 °C to maintain pH 10. A pale yellow precipitate of Ce(OH)4 thus obtained was washed several times with deionized wateruntil a neutral pH was achieved. Thus obtained Ce(OH)4 was dried at400 °C for 8 h to obtain nanoparticles of CeO2 [17,18]. Preparednanostructured CeO2 nanoparticles were suspended in methanol(5 mg/mL) and sonicated for 4 h. 100 μL of this suspension wasdeposited onto the SiO2/ITO electrode and dried overnight. The CeO2–

SiO2/ITO electrode was washed with deionized water prior to DNAimmobilization.

10 μL of dsCT-DNA (1 mg/mL) was physisorbed onto preparedCeO2–SiO2/ITO electrode and these films were kept in a humidchamber overnight. dsCT-DNA binds with the CeO2 via electrostaticinteraction as CeO2 has high IEP (Isoelectric point i.e., positivelycharged) while DNA bears low IEP i.e., negatively charged. Prior tobeing used, these dsCT-DNA immobilized CeO2–SiO2/ITO electrodesare allowed to dry under desiccated conditions for a few minutes andthen washed with 2 mL phosphate buffer (0.05 M, pH 7.0) to removeany unabsorbed DNA. These dsCT-DNA/CeO2–SiO2/ITO bioelectrodesare stored in desiccators at 25 °C when not in use.

2.3. Characterization

CeO2–SiO2/ITO electrode and dsCT-DNA/CeO2–SiO2/ITO bioelec-trodes have been characterized using Fourier transform infrared(FTIR) spectrophotometer (Perkin-Elmer Spectrum, BX) and Scanningelectron microscope (LEO 440). The cyclic voltammetry (CV) anddifferential pulse voltammetry (CV) studies of CeO2–SiO2/ITO elec-trode and dsCT-DNA/CeO2–SiO2/ITO bioelectrodes have been con-ducted using Autolab, Potentiostat/Galvanostat electrochemicalanalyzer using three electrode systems. The response of thesedisposable dsCT-DNA/CeO2–SiO2/ITO bioelectrodes has been studiedusing DPV for the detection of CM.

The response times of the dsCT-DNA/CeO2–SiO2/ITO bioelectrodeshave been optimized with different duration times (10 s to 2 min)using DPV technique in triplet sets of experiment. It has been foundthat 25 s is sufficient for detection of CM for obtaining maximumreduction in magnitude of current for CM. The effect of CM onto dsCT-DNA/CeO2–SiO2/ITO bioelectrodes has been studied by percentagereduction in the guanine oxidation current on interaction with CM.Experiments have been carried out using several dsCT-DNA/CeO2–

SiO2/ITO electrodes with DPV techniques under identical experimen-tal conditions. It is observed that bioelectrodes yield reproducibleresults within 0.1% and the electrochemical response is reproduciblewithin 0.2%

3. Results and discussion

3.1. Fourier transforms infrared (FTIR) spectroscopic studies

FTIR spectra of SiO2/ITO (Curve a) electrode, CeO2–SiO2/ITO (Curveb) electrode and dsCT-DNA/CeO2–SiO2/ITO (Curve c) bioelectrode areshown in Fig. 1. FTIR spectra of SiO2 shows characteristic IR bands at1040 cm−1 and 790 cm−1 corresponding to Si–0–Si symmetric andsymmetric stretching vibration modes and band at 500 cm−1 which isdue to Si–O–Si bending vibration in SiO2 reveals the formation of SiO2

film [19–22]. The FTIR spectra of CeO2–SiO2 nanocomposite showscharacteristic bandof SiO2 and a band at ~533 cm−1 is assigned to Ce–Ostretching vibration mode indicating the presence of CeO2 nanoparti-cles. CeO2–SiO2/ITO electrode shows a broad band at 3404 cm−1 and a

Fig. 2. SEM images of CeO2–SiO2/ITO electrode (image A) and dsCT-DNA/CeO2–SiO2/ITObioelectrode (image B).

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sharp band at 1010 cm−1 corresponding to O–H stretching and bendingvibrations of absorbedwater on thefilm surface [14]. The FTIR spectra ofthe dsCT-DNA/CeO2–SiO2/ITO bioelectrode (Curve c) exhibits charac-teristic bands at 1550 and 1400 cm−1 assigned to the nitrogenous basesof dsCT-DNA [23]. The presence of bands corresponding to phosphategroup of DNA seen at about 1225 cm−1 in dsCT-DNA/CeO2–SiO2/ITObioelectrode indicates the immobilization of DNA.

3.2. Scanning electron microscopic studies

Surface morphological studies of CeO2–SiO2/ITO electrode (imagea) and ds-DNA/CeO2–SiO2/ITO bioelectrodes (image b) have beenstudied using scanning electron microscopy (SEM, Fig. 2.). The twophase appearance of CeO2–SiO2/ITO electrode (image a) reveals thatCeO2 nanoparticles have been incorporated within the sol–gel derivedSiO2/ITO film. However, the appearance of clusters in CeO2–SiO2

nanocomposite may perhaps be due to interaction between surfacecharged CeO2 and SiO2 nanoparticles. The rough porous morphologyof CeO2–SiO2 changes into a regular porousmorphology revealing thatCeO2–SiO2 nanocomposite provides a favourable environment fordsCT-DNA immobilization via electrostatic interaction betweenmultifunctional CeO2–SiO2 nanocomposite and dsCT-DNA.

3.3. Electrochemical studies

The stepwise formation of SiO2/ITO electrode (curve a), CeO2–

SiO2/ITO electrode (Curve b) and dsCT-DNA/CeO2–SiO2/ITO bioelec-trode (curve c) have been studied using differential pulse voltam-metry (DPV, Fig. 3A) technique in phosphate buffer saline solution[PBS, 50 mM, pH 7.0, 0.9% NaCl] containing 5 mM [Fe(CN)6]−3/−4. TheSiO2/ITO electrode (Curve a) shows DPV response arising due tocationic characteristics of SiO2 that accept electrons from the redoxprobe [Fe(III)/Fe(IV)] and transfer these to the electrode. Themagnitude of the peak current response increase for the CeO2–SiO2/ITO electrode suggesting that CeO2 nanoparticles inceases the electro-active surface area of CeO2–SiO2 nanocomposite resulting in highadsorption of redox probe leading to enhanced electron transfer fromthemedium to electrode. Moreover, the cationic characteristic of CeO2

nanoparticles (IEP ~9.2) and its uniform dispersion in sol–gel derivedSiO2 network at the electrode result in improved electronic and ionictransport due to its three-dimensional conductive network extendedthroughout the electrode [16]. The magnitude of current response

Fig. 1. FTIR spectra of SiO2/ITO electrode (Curve a), CeO2–SiO2/ITO electrode and dsCT-DNA/CeO2–SiO2/ITO bioelectrode (Curve c).

decreases after the dsCT-DNA immobilization for the dsCT-DNA/CeO2–SiO2/ITO bioelectrode. This may be attributed to the covering ofdsCT-DNA onto the surface of the CeO2–SiO2/ITO electrode becauseDNA has less conductivity as compared to that of CeO2–SiO2

nanocomposite that hinder the electronic transport between mediumand electrode leading to reduced magnitude of current.

The results of cyclic voltammertic (CV, data not shown) studies asobtained from DPV studies are similar to those wherein themagnitude of current for CeO2–SiO2/ITO nanocomposite electrode ishigher than that of SiO2/ITO electrode and the magnitude of currentdecreases after the immobilization of dsCT-DNA onto CeO2–SiO2/ITOnanocomposite electrode. This suggests the CeO2–SiO2 nanocompo-site matrix provides a favourable microenvironment for DNA withhigher affinity and it retains its biological activity resulting inimproved biosensing performance.

Fig. 3B and C shows CV studies of CeO2–SiO2/ITO electrode anddsCT-DNA/ CeO2–SiO2/ITO bioelectrode, respectively as a function ofscan rate (10–100 mV/s). It can be seen that magnitudes of cathodic(Ip) and anodic (Ic) current response exhibit a linear relationship withthe square root of scan rate (inset, Fig. 3B and C), suggesting that theelectrochemical reaction is a diffusion-controlled process and followsEqs. (1)–(4)

Ιp CeO2−SiO2 = ITOð Þ= ITOÞ A½ �= 5:804 × 10−5 Α½ � + 1:156 × 10−4 Αs=mV½ �*scanrate mV=sð Þ1=2

withR2 = 0:988

ð1Þ

Ιc CeO2−SiO2 = ITOð Þ= ITOÞ A½ �= −1:4 × 10−4 Α½ �−9:33 × 10−5 Αs=mV½ �Tscanrate mV=sð Þ1=2

withR2 = 0:995

ð2Þ

Fig. 3. A) Differential pulse voltammogram (DPV) studies of SiO2/ITO electrode (Curve a), CeO2–SiO2/ITO electrode and dsCT-DNA/CeO2–SiO2/ITO bioelectrode (Curve c). B) Cyclicvoltammetry (CV) studies of CeO2–SiO2/ITO electrode obtained as a function of scan rate (10–100 mV/s). C) CV studies of dsCT-DNA/CeO2–SiO2/ITO electrode obtained as a functionof scan rate (10–100 mV/s) in PBS(50 mM, pH 7.0, 0.9% NaCl) containing 5 mM [Fe(CN)6]−3/−4.

1125A. Gupta et al. / Thin Solid Films 519 (2010) 1122–1127

1126 A. Gupta et al. / Thin Solid Films 519 (2010) 1122–1127

Ιp dsCT−DNA= CeO2−SiO2 = ITOð Þ A½ �= 3:66 × 10−5 Α½ � + 6:25 × 10−5 Αs=mV½ �Tscanrate mV=sð Þ1=2

withR2 = 0:998

ð3Þ

Ιc dsCT−DNA= CeO2−SiO2 = ITOð Þ= ITOÞ A½ �= −9:09 × 10−5 Α½ �−5:02 × 10−5 Αs=mV½ �Tscanrate mV=sð Þ1=2

withR2 = 0:991

ð4Þ

It has been shown that dsCT-DNA adsorbed onto CeO2–SiO2/ITOnanocomposite electrode undergoes reversible electron transfer withnanobiocomposite film. It is found that peak-to-peak separation [ΔE(V)=cathodic (Ep) and anodic (Ec)] potential increases linearly as thefunction of scan rate revealing that the facile electron transferphenomenon and obey Eqs. (5) and (6).

ΔΕp CH−NanoCeO2 = ITOð Þ V½ � = 0:157 V½ � + 0:00196 E s=m½ �T scanrate mV= sð ÞwithR2 = 0:9913

ð5Þ

ΔΕp r−IgGs= CH−NanoCeO2 = ITOð Þ V½ � = 0:153 V½ � + 0:0017 E s=m½ �T scan rate mV= sð ÞwithR2 = 0:9897

ð6Þ

The surface concentrations of ionic redox species on the SiO2/ITOand CeO2–SiO2/ITO nanocomposite electrodes, dsCT-DNA/CeO2–SiO2/ITO have been estimated using Eq. (7).

ip = 0:227nFAC04k0 exp

−αnaFRT

Ep−E′0� �� �

ð7Þ

where, ip is the anodic peak current, n is the number of electronstransferred (1), F is the Faraday constant (96485.34 C mol−1), A issurface area (0.25 cm2), R is the gas constant (8.314 J mol−1 K−1), C0*

is the surface concentration of the ionic species of film surface(mol cm−3), Ep is the peak potential and E0′ is the formal potential. The–αnaF/RT and k0 (rate constant) correspond to the slope and interceptof ln (ip) verses Ep–E0′ curve at different scan rates [23]. It may benoted that surface concentration of CeO2–SiO2/ITO nanocompositeelectrode (2×10−6 mol cm−3) is higher than that of SiO2/ITO(1.4×10−6 mol cm−3). The higher surface concentration of CeO2–

SiO2/ITO nanocomposite electrodes suggests that loading ofNanoCeO2 results in increased electron transport between mediumand electrode. The surface concentration of redox species onto dsCT-

Fig. 4. Response studies of dsCT-DNA/CeO2–SiO2/ITO electrode obtained usingdifferential pulse voltammetry as a function of CM concentration (0.00125–2.0 ppm)in PBS(50 mM, pH 7.0, 0.9% NaCl) containing 5 mM [Fe(CN)6]−3/−4. Inset: curvebetween magnitude of current response and CM concentration (0.00125–2.0 ppm).

DNA/CeO2–SiO2/ITO bioelectrodes decreases to 1.8×10−6 mol cm−3

due to hindrance in electron transport between medium andelectrode.

The effect of pH on dsCT-DNA/CeO2–SiO2/ITO bioelectrode hasbeen carried out using DPV technique and the magnitude of currentresponse is found to be maximum at pH 7.0 (data not shown). This isthe optimum value of pH for the catalytic activity of biomolecules andreveals that dsCT-DNA/CeO2–SiO2/ITO bioelectrodes bioelectrodeshows maximum activity at pH 7.0 at which DNA retains its naturalstructure and is responsible for low detection limit and highsensitivity for CM detection.

3.4. Electrochemical response studies

Fig. 4 shows electrochemical response of dsCT-DNA/CeO2–SiO2/ITO bioelectrode as a function of CM concentration (0.00125–2 ppm)using differential pulse voltammetry (DPV) in PBS (50 mM, pH 7.0)containing 5 mM [Fe(CN)6]−3/−4. It has been observed that magni-tude of the peak current of dsCT-DNA/CeO2–SiO2/ITO bioeletrodedecreases with increase in the concentration of CM (inset Fig. 4)[15,16]. It may be noted that maximum decrease in the current peak isobserved at 2.0 ppm of CM. And there is a minimum decrease in thecurrent peak at 0.00125 ppm concentration of CM indicating it as thedetection limit. The dsCT-DNA/CeO2–SiO2/ITO bioelectrode shows lowdetection limit of 0.00125 ppm, detection range from 0.00125–2 ppmof CM concentration, high sensitivity of 25A/Mcm–2 and responsetime of 25 s.

The improved detection limit of dsCT-DNA/CeO2–SiO2/ITO bioe-lectrode for CM may be attributed to the presence of CeO2

(responsible for fast conductivity) (Table 1). The observed decreasein the magnitude of current may be attributed to strong interaction ofCM with dsCT-DNA–CeO2–SiO2/ITO bioelectrode. It has been foundthat CM inhibits oxidation of nitrogenous bases of purine and resultsin decreased current response. It may be remarked that structures ofpyrethroid molecules exhibit two types of configurations: firstly theflexible part that has two negatively charged chloride ions, one estergroup and active dimethyl group. Among these, carbonium ionpredominantly interacts with the –NH2 terminal group of purinebases (adenine and guanine) due to polarization. Secondly, rigid partof the molecule provides support for this interaction. It appears thatCM interacts with dsCT-DNAmoietymore strongly than PMdue to theavailability of more electronegative groups on CM molecule that maybind more strongly with dsCT-DNA. The formation of a reactivecarbonium ion through hydroxylation and acetylation binding withdsCT-DNA has been proposed as a possible explanation for mutagenicand carcinogenic activity. The binding of CM with dsCT-DNA viapolarization may cause destabilization of dsCT-DNA structure andunwinding of the DNA helix, inducing chromosomal damage [15].

4. Conclusions

dsCT-DNA has been immobilized onto CeO2–SiO2 nanocompositefilm prepared onto ITO substrate to fabricate disposable electrochem-ical DNA biosensor for cypermethirn (CM) detection. The developed

Table 1Response characteristics of dsCT-DNA/CeO2–SiO2/ITO for detection of cypermethrin.

S.no.

Electrode Immobilization Detectionlimit

Responsetime

References

1. dsCT-DNA-PANI-ClO4/ITO

Covalentimmobilization

0.005 ppm 30 s [11]

2. ssCT-DNA- Electrostaticadsorption

0.0025 ppm 30 s [12]

3. dsCT-DNA/CeO2–

SiO2/ITOElectrostaticadsorption

0.00125 ppm 30 s Presentwork

1127A. Gupta et al. / Thin Solid Films 519 (2010) 1122–1127

nucleic acid biosensor exhibits fast response time of about 25 s andcan be used to detect CM from 0.00125 to 2.0 ppm. The presence ofinorganic salts as Ca2+, Mg2+, Cl−, and Na+ does not affect theobserved electrochemical response of the dsCT-DNA/CeO2–SiO2/ITObioelectrodes for CM detection. These electrodes are disposable innature and hence can be utilized for rapid and initial screening ofgenotoxicants/pesticides in industrial toxic waste, various food andbeverages.

Acknowledgements

We thank Dr. R. C. Budhani, Director, National Physical Laboratory,New Delhi, for providing the facilities. We acknowledge the financialsupport received from the Department of Science and Technology(DST), the Department of Biotechnology, Govt. of India (DBT/GAP070832).

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