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Sensors and Actuators B 137 (2009) 566–573

Contents lists available at ScienceDirect

Sensors and Actuators B: Chemical

journa l homepage: www.e lsev ier .com/ locate /snb

ffect of nanostructure on the urea sensing properties of sol–gel synthesized ZnO

.G. Ansari a,d, Rizwan Wahaba, Z.A. Ansari c, Young-Soon Kima, Gilson Khangb,. Al-Hajryd, Hyung-Shik Shina,∗

School of Chemical Engineering, Chonbuk National University, Jeonju 561-756, Republic of KoreaDepartment of Polymer Nano Science and Technology, Chonbuk National University, Jeonju 561-756, Republic of KoreaCenter for Interdisciplinary Research in Basic Sciences, Jamia Millia Islamia, Jamia Nagar, New Delhi 110025, IndiaDepartment of Physics, Faculty of Science, Najran University, Najran, Saudi Arabia

r t i c l e i n f o

rticle history:eceived 9 September 2008eceived in revised form 1 January 2009ccepted 9 January 2009vailable online 21 January 2009

a b s t r a c t

Urea sensing properties of zinc oxide in thick film form are presented here. Zinc oxide thick films wereprepared on Al-sheet by conventional doctor blade method using organic additives. Flower-like struc-ture and nanobelts of ZnO was synthesized by solution method using zinc acetate dihydrate and sodiumhydroxide. Structural morphology significantly changed with precursor concentration (0.3–0.5 M) froma belt to flower-like structure. Urease was covalently attached with zinc oxide (by soaking in urease solu-

eywords:inc oxideolution synthesisnzyme immobilizationrea sensor

tion containing 100 units for 3 h). In general, conductivity of film increases after urease immobilization.The urease immobilized films were found sensitive to urea concentration from 1 mM to 100 mM. Threedifferent sensitivity regions are observed viz. (i) lower concentrations (below 10 mM); (ii) linear regionup to 50 mM; and (iii) a saturation region above 50 mM. Sensors are extremely sensitive in region (i).Nanobelt structure of ZnO resulted in highest urea sensitivity. Sensors exhibited linear response when

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urface composition tested for different concereproducible, reliable, rev

. Introduction

The human senses are the best examples of specialized neu-al sensors. Enzymatic electrochemical biosensors have attractedesearcher’s attentions due to their potential applications andmprovement in performance with nano-technological approach.n last few decades, the development of enzyme-based biosensorsas been a topic of considerable interest due to their potential appli-ations, since the spectroscopic methods are laborious and oftenot useful in online monitoring system. The inconvenience wasvercome by the use of electrochemical methods for biosensing.

The most widespread example of a commercial biosensor (thirdeneration sensor) is the blood glucose biosensor, which uses annzyme to breakdown the blood glucose, breaking the sugar downnto its metabolites. Glucose oxidase (GOx) is a dimeric protein

hich catalyzes the oxidation of beta-d-glucose into d-glucono-,5-lactone which then hydrolyzes to gluconic acid. In this process,t transfers an electron to the electrode which is used as a measure

f the blood glucose concentration [1–7].

Among a large number of enzymes used for biosensor construc-ion, urease is an important part in most enzyme-based sensorevelopment to fulfill the growing demand for urea detection. Urea

∗ Corresponding author. Tel.: +82 63 2702438; fax: +82 63 2702306.E-mail address: hsshin@chonbuk.ac.kr (H.-S. Shin).

925-4005/$ – see front matter © 2009 Elsevier B.V. All rights reserved.oi:10.1016/j.snb.2009.01.018

on of human urine in buffer solution (1:9 to 4:6). The sensor responses arele and selective, with a response time of 6 s.

© 2009 Elsevier B.V. All rights reserved.

((NH2)2CO) is basically an organic compound of carbon, nitrogen,oxygen and hydrogen. Most organisms’ deal with the excretion ofnitrogen waste originating from protein and amino acid catabolism.The normal level of urea in serum is 3–7 mM (15–40 mg/dl). Inpatients suffering from the renal insufficiency, the urea concentra-tion in serum is from 30 mM to 80 mM (180–480 mg/dl) and at thelevel above 180 mg/dl, the hemodialysis is required. However, toohigh concentration in the blood can cause damage to body organs.Therefore, its analysis is of considerable importance.

An important part for biosensors construction is to immobilizebiomolecules on the transducer without changing their structuralconformation and their activity. The immobilization feature cangovern the performance and reliability of the obtained biosen-sor. The host material generally used for biosensor developmentincludes clays, layered double hydroxides (e.g. ZnAl), nanoporousalumina membranes, polymers, tin oxide, etc. [8–16]. Researchersare putting extensive effort in exploring/understanding the bio-compatibility of inorganic (especially metal oxide) nanomaterialssynthesized by various techniques. There are few reports that haveshown the promising development of the third generation biosen-sors using such materials [17–20]. Nanomaterials offer unique

advantages in immobilizing enzymes due to increase surface reac-tivity, preserving enzyme activity due to the microenvironment.

Zinc oxide; a versatile semiconductor, which has attracted atten-tion for its wide range application in the field of solar cells,luminescent, electro-acoustic devices, etc. Being a nanoporous

d Actuators B 137 (2009) 566–573 567

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aterial from the family of the richest nanostructure, it can alsoe used as a matrix for immobilization of biomolecules. ZnO hasreat potential for biosensing due to its biomimetic and fast elec-ron transfer properties. High isoelectric point of ZnO (IEP ∼9.5)

akes it suitable for adsorption low IEP proteins such as uricaseith IEP ∼4.3, urease with IEP ∼5.9, etc. Liu et al. [18] synthesizedower-like structure hydrothermally and used it as a matrix fororseradish peroxidase immobilization. Zhao et al. [19] used cross-

inking method to immobilize GOx on nanoclustors of ZnO:Co films.imilarly, Zhang et al. [20] immobilized uricase on ZnO nanorodsor uric acid sensing. However, in these reports, a complicated

ethod was used to immobilize the protein. Here, we report aimple method to immobilize the protein on the nanostructuredinc oxide and construction of sensor in a thick film form. The sug-ested test method is simple and can be easily adopted to fabricate arobe.

A systematic study on the detection of urea and diluted-urinesing urease immobilized zinc oxide is presented here. ZnO thicklms were prepared on Al-sheet using doctor blade technique.ffect of urea/urine on the electrical properties of urease immo-ilized ZnO films were studied by varying potential across the filmnd measuring the corresponding current.

. Experimental

.1. Materials and methods

Zinc acetate dihydrate [Zn(CH3COO)2·2H2O] was used as arecursor with sodium hydroxide (NaOH) solution. Aluminum99.999%, Goodfellows, size: 1 × 1.5 × 0.1 cm3) was used as sub-trate. Urease (EC 3.5.1.5, from jack bean, 50 U/mg) and Urea (ACSeagent, 99.0–100.5%) were purchased from Sigma–Aldrich. Deion-zed (DI) water (resistivity of 18 M�, Milli-Q system, Millipore Inc.)as used for rinsing and preparing all aqueous solutions.

.2. ZnO synthesis, thick film preparation and characterization

For synthesis of nano-structured ZnO, the solution methodas used, wherein zinc acetate dihydrate (0.3–0.5 M) and 3 M

odium hydroxide was dissolved in 100 ml DI water, stirred wellnd refluxed at 90 ◦C for 1 h each. After refluxing, the precipitatewhite powder) was neutralized with methanol and dried at roomemperature.

A thick film paste was prepared mixing ZnO (70%) and organicdditives (30%, ethyl cellulose (Biochemica) and Carbetole acetateAldrich) in agate-mortal and pastel. This paste was partiallypplied on electropolished Al-sheet (1 cm × 1.5 cm), using doctorlade method. Films (area: 1 cm2) were allowed to settle at roomemperature and then dried under IR-lamp (250 W). Film area wasept constant for all the samples prepared for the measurement.he substrates were degreased with acetone and electropolishedrior to film deposition [21].

Morphological observations of powder and thick film samplesere carried out by field emission scanning electron microscopy

FESEM, Hitachi S4700). Elemental and compositional analysis wasarried out using X-ray diffraction spectrometry (XRD, Rigaku, Cu�). Urease immobilization was confirmed by obtaining surfacetate information using X-ray photoelectron spectroscopy (XPS, VGicrotech, U.K.), with Al K� (15 kV, 20 mA) as X-ray source.

.3. Enzyme immobilization

Urease was immobilized by soaking the samples in ureaseolution. Initially samples were immersed in a phosphate bufferolution (PBS, 0.1 M, pH 7.2) containing 0.2 mg of urease per ml forh at 25 ◦C. Total 10 ml of solution was prepared containing 100

Fig. 1. Schematic of the cell constructed for urea sensing measurement; consists ofgold wire (1 mm diameter, 5 cm length) as one electrode and urease immobilizedfilms as another electrode.

units of urease. The samples were then washed and kept in PBSuntil use. Amount of enzyme immobilized on these samples wasnot calculated or estimated.

2.4. Determination of enzyme activity after immobilization

After urease immobilization, the electrical property of ZnO thickfilms was studied to determine the enzyme activity. For this, poten-tial from 0 V to 1 V was applied to the film and the correspondingcurrent was measured using computer interfaced Keithely 6517/Aelectrometer. For each sample, five sets of measurement were car-ried out. A sample to sample (in a batch) was studied to understandthe reliability of the sensors. All the measurements were carriedout at room temperature (25 ◦C).

For this measurement, a cell, schemated as Fig. 1, was con-structed consisting of gold wire (1 mm diameter, 5 cm length) as oneelectrode and urease immobilized ZnO films were used as anotherelectrode. Urea solution prepared in PBS was used as an electrolyte.Amount of electrolyte was kept constant as 10 ml for all measure-ment. Solution was prepared with various concentrations of ureasuch as 1 mM, 3 mM, 5 mM, 10 mM, 20 mM, 50 mM and 100 mM(6–600 mg/dl). For this solution preparation, the amount of PBS waskept constant as 10 ml while the molar concentration of urea wascalculated with reference to 10 ml of PBS. The respective amountof urea was added in separate beakers. Since the amount of ureawith respect to PBS has changed with increasing molar concentra-tion, this effect would reflect in the sensitivity curves indicating thevariation due to urea, as presented below. Solution pH was neithermeasured nor controlled. The ratio of current to voltage is used asa measure of enzyme activity.

Human urine sample diluted with buffer solution from 1:9 to4:6 (i.e. a total 10 ml of solution was prepared where urine concen-

tration was varied from 1 ml to 4 ml).

Electrochemical properties were studied with WonAtech Poten-tiostat (WPG-100) at room temperature in a conventionalthree-electrode system. ZnO thick films were used as working elec-trode, platinum wire (1 mm dia) was used as auxiliary electrode

5 d Actuators B 137 (2009) 566–573

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nd Ag/AgCl as a reference electrode. Solution with various ureaoncentrations was used electrolyte.

. Results and discussion

.1. ZnO powder and film characterization

Fig. 2a–c shows the FESEM images of ZnO powder synthesizedith 0.3 M, 0.4 M and 0.5 M of zinc acetate dihydrate, respectively,here a change from nanobelt to flower-like structure is observed.s the structure has varied, the corresponding surface has alsoeduced thereby affecting the adsorption on the film, and effectiveensing area even though the deposited film area is same.

The X-ray diffraction peaks match well with the d-values ofexagonal zinc oxide with lattice constants a = 3.249 and c = 5.206 ÅJCPDS 36-1451), presented as Fig. 3. Increase in the peak intensitiesndicates increase in crystallinity with concentration.

.2. Enzyme immobilization on ZnO thick films

Fig. 4 shows typical I–V curves, for the film, with ZnO powderynthesized using 0.3 M zinc acetate dihyrate, before (solid curves)nd after (dotted curves) urease immobilization, at various ureaoncentrations (1–100 mM (6–600 mg/dl)). A wide range of ureaoncentration was chosen to study the possible detection limit.

bout 2% error is observed. Similar measurements were carried outt various human urine:buffer concentration (1:9, 2:8, 3:7, and 4:6,–V data not shown here).

A monotonous increase in the current with applied voltage islearly evident. The solid curves indicate the response of the film

Fig. 2. FESEM images of ZnO powder as a function of c

Fig. 3. X-ray diffraction spectra of ZnO powder synthesized at various concentra-tions of zinc acetate dihydrate.

before urease immobilization and the dotted lines are the responseafter urease immobilization. Significant increase in the samplecurrent is evident after immobilization i.e. the film conductivityincreased after immobilization. The role of urease in the electrode

system is very clear, as can be seen in Fig. 3. This is the clear evidencethat the change in response is due to the urease immobilization. It isknown that urea can react directly with ZnO but the extent of reac-tion may not be same as that after urease immobilization, since theurease–urea reaction kinetics (catalytic reaction) are different than

oncentrations (a) 0.3 M; (b) 0.4 M; and (c) 0.5 M.

S.G. Ansari et al. / Sensors and Actuators B 137 (2009) 566–573 569

Fig. 4. Typical I–V curves showing the effect of urease immobilization on ZnOfiri

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lms (0.3 M concentration) with increasing urea concentration. Dotted lines are theesponse after urease immobilization and solid lines are the response before ureasemmobilization.

hat of ZnO–urea. This increase is attributed to the catalytic reactionf urea–urease as below;

H2CONH2 + 2H2OUrease−→ 2NH4

+ + CO32− (1)

This reaction results in the production of three ions i.e. two NH4+

nd CO3− from uncharged urea which increases the conductivity of

he host material by providing excess electron to the conductionand of the material.

Similar curves were plotted for the films with 0.4 M and 0.5 Moncentrations and the slope of these curves (dI/dV) is used as theeasure of enzyme activity. This slope is plotted as a function of

ncreasing urea concentration and presented as Fig. 5a (for 0.3 M,.4 M and 0.5 M concentrations). These curves are used as the sen-itivity curves for urea sensitivity estimation. The effect of ureaoncentration and nanostructure variation is clearly evident fromhese curves.

Increasing enzyme activity is observed, for all the samples, withncreasing urea concentration. In general, the sensitivity curvesepict three different sensitivity regions; (i) region at lower con-entrations (below 10 mM. presented as Fig. 5b); (ii) linear regionp to 50 mM and (iii) saturation region above 50 mM. The curveresents an interesting data with three regions. The first regionFig. 5b) appears to be the most sensitive region for urea detection.he developed sensors would be useful at lower urea concentra-ion, since the normal level of urea is below 10 mM. The secondegion indicates that developed sensor can be used to sense higheroncentration of urea (<50 mM, 300 mg/dl). The saturation regionthird region) at higher concentration might be due to the unavail-bility of free urease sites for urea catalysis. The appearance of threeegions indicates that the surface reactions are different at differentoncentrations. At lower concentration, physisorption would playajor role, while at higher concentration, chemisorption processould be dominant resulting in saturation of the sensor perfor-ance. Analogous to this, there regions were obtained in our earlierork using tin oxide thin film [16], however, the sensitivity of

hese sensors is higher due to higher surface area (nanostructuredaterial). Jha et al. reported urea sensing using composite poly-

er membrane over a wide range 1–100 mM [22]. They also found

hree regions of different sensitivity. They reported response timef 120 s with lower sensitivity values (8.3 V/M up to 40 mM ofrea). Zhang et al. immobilized uricase on ZnO nanorods and usedor uric acid sensing (from 5.0 �M/l to 1.0 �M/l) [20]. However, it

Fig. 5. (a and b) Sensitivity (dI/dV, calibration curves) as a function of urea concen-tration and precursor concentrations (0.3 M, 0.4 M, and 0.5 M).

is difficult to compare the response with these reported sensorssince the materials and methods are different. We believe that thepresent method is simple to use and can be easily adopted for probefabrication.

It is interesting to see the effect of surface area (nanostructure

variation) on the sensing. The powder synthesized with 0.3 M con-centration, exhibits highest sensitivity, estimated in region (i). Thisindicates that the nanobelts are more suitable for sensor as theyoffer higher surface area in comparison with flower-like morphol-

570 S.G. Ansari et al. / Sensors and Actuators B 137 (2009) 566–573

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Fig. 8. (a) Cyclic voltammogram of the ZnO thick film (0.3 M concentration) as aworking electrode in phosphate buffer solution (PBS), 1 mM, and 5 mM urea solution,

ig. 6. A cycle to cycle variation (of a sample) tested after a week. The results wereeproducible within 3% of the measurement values.

gy. The powder synthesized with 0.5 M concentration, exhibitedoor sensitivity, indicating that immobilization was not good dueo the structural morphology and lesser surface area. Since theanostructure has varied from belt to flower-like structure, the spe-ific surface area has also changed, thereby affecting the amount ofmmobilized enzyme. As the concentration increase, the sensitiv-ty reduces indicating reduction in the surface area available fordsorption of the protein/enzyme.

A cycle to cycle variation (of a sample) was tested after a weeknd the corresponding data is presented Fig. 6. The results wereeproducible within 3% of the measurement values.

Typical current–response time of the sensor (for 0.3 M concen-ration) on successive step changes of typical urea concentrationup to 3 mM) was studied and presented as Fig. 7. A rapid and sen-itive response to the changes in solution concentration is observed.

steady-state (95%) current was observed after ∼6 s, which isuch faster than the sensor reported by Jha et al. [22]. The quick

esponse indicates that porous structure of ZnO matrix yields aery low mass transport barrier and results in a rapid diffusionrom solution to the enzyme and retains the bioactivity. This also

ndicates that ZnO matrix not only provide a friendly microenviron-

ent for negatively charge urease (IEP ∼5.9) to retain its activityut also promote fast electron transfer. A slight un-stability (wavi-ess in the curves) is noticed from the current–response response

ig. 7. Typical current–time response curve for successive addition of urea in phos-hate buffer solution at an applied voltage of 0.5 V.

before (dotted lines) and after (solid line) urease immobilization. (b) Variation in theanodic and cathodic current as a function of increasing urea concentration for theurease immobilized ZnO thick film (0.3 M concentration).

over the period of measurement. We believe that this un-stabilityis probably due to turbulence caused by the successive additionof the solution. One can see that the stability is much better incase of the 1 mM solution which reduced with addition of solu-tion.

Fig. 8a shows the difference in the typical cyclic voltammetericbehaviour of, ZnO thick films before and after urease immobiliza-tion, at a scan rate of 100 mV/s. For simplicity, data is presentedonly for the PBS, 1 mM and 5 mM solutions. Since this measure-ment was carried out just to understand the oxidation/reductionbehaviour in order to support the I–V characteristic, hence thescan rates were not varied. In case of PBS (0.1 M, pH 7.2), the elec-trochemical response did not show any current peak related tooxidation/reduction process. Addition of urea resulted in a typicalelectrochemical response with roughly symmetrical peak. The for-mal potential ((Eo = Epa + Epc)/2) of 0.72–0.75 V and a slight shift inthe cathodic and anodic current peaks are observed with increasingurea concentration. Fig. 8b, presents anodic and cathodic current (ofimmobilized films) variation with increasing urea concentration. Itis very clear that process is redox-dominated process. Initially redoxcurrent increases and then saturates. The current variation is analo-gous to that of the sensitivity curves derived from I–V characteristic

(Figs. 4 and 5). The cyclic voltammetric studies clearly indicates thatthe process is a reversible process and confirms the urea–ureaseinteraction as a function of applied potential i.e. a enzymatic catal-ysis.

S.G. Ansari et al. / Sensors and Actu

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buffer solution (pH 7.2), and the results were within the error limits(Fig. 5). For all the samples, the applied voltage was increased tomaximum value in 50 s to avoid the variation in response due todifferent reaction or adsorption time.

ig. 9. Sensitivity (dI/dV curves) as a function of diluted-urine concentration for thenO thick film (0.3 M concentration), before and after urease immobilization.

From cyclic voltammeteric studies and cycle-to-cycle studies, its confirmed that the developed sensors can be re-used. Howeverong-term stability need to be investigated in details.

The developed sensors were tested for diluted-urine samplesefore and after immobilization. Fig. 9 presents variation in theensitivity with increasing concentration of urine. Urine was dilutedith buffer solution from 1:9 to 4:6. Increase in sensitivity is noticedith increasing urine concentration. Immobilization results in an

ncrease in the current with applied voltage, analogous to that ofrea sensing. Such response supports the suggested mechanism.

.3. Expected sensing mechanism

The mechanism of sensing can be explained based on the toweactions viz. (i) catalytic reaction and (ii) oxidation/reduction ofetal oxides; same as that of solid state gas sensors. The catalytic

eaction of urea–urease is well known which produces three ions.e. two NH4

+ and CO3− from uncharged urea. These produced ions

ncrease the conductivity of the host material by providing excesslectron to the conduction band of the material.

The second process for the oxidation/reduction of metal oxides,hich occurs due to the adsorbed oxygen and the catalytically pro-uced excess ions, can be explained as below. W. Henry and M. Peter,ere amongst the first few to report the microscopic model for the

peration of SnO2 based carbon mono-oxide (CO) sensor [23]. Thehysical basis of the model they presented is on the oxidation of COn sensor surface by chemisorbed oxygen and subsequent emissionf an electron from the chemisorbed species into the conductionand of the sensor. Based on this model, many reports explain thehange in the electrical conductance of a highly porous semicon-ucting thick or thin film sensor in the presence of toxic gases dueo the two below mentioned reactions occurring on the surface15–16,24–26].

In the first reaction atmospheric oxygen molecules arehysisorbed on the surface sites, which while moving from siteo site, get ionized by extracting an electron from the conductionand and are thus ionosorbed on the surface as Oads

− (O− or O2−

epending on the energy available). This leads to a decrease in theonductance of sensor and increase in potential barrier at the grainoundaries. The resulting equation is;

2 + 2e− → 2Oads− (2)

As indicated in Eq. (1), urea–urease catalytic reaction of resultsn the production of NH4

+ and CO3−. This ammonium ion reacts

ators B 137 (2009) 566–573 571

with the surface adsorbed oxygen (Oads−) and releases the trapped

electron to the conduction band of ZnO.In the second step, when reducing gas (R) molecules (ammo-

nia in the present case) reacts with pre-adsorbed negativelycharged oxygen adsorbates, the trapped electrons are given backto conduction band of the material. The energy released duringdecomposition of adsorbed ammonia molecules would be suffi-cient for electrons to jump up into the conduction causing onincrease in the conductivity of the sensor.

R + Oads− → RO + e− (3)

Desorption of RO depends basically on the left-over time (recov-ery time) or temperature of the sensor. A cyclic voltammeteric resultsupports the above-mentioned sensing mechanism, which clearlyindicates an oxidation and reduction process.

The reaction occurring on the surface of the immobilized sampleis rate determining, affecting the response time of the sensor. Theperformance of the sensor can be further enhanced by the use ofproper catalyst, where the catalyst may help in further splitting theammonia and then spill over on the surface. This will enhance thereaction with pre-adsorbed surface oxygen of host material therebyincreasing the conductance further and enhancing the response.

3.4. Corroboration of enzyme immobilization

In order to confirm the urease immobilization on the ZnO thickfilm (0.3 M concentration, typical example), it was characterizedfor surface bonded states using X-ray photoelectron spectroscopy.Fig. 10 shows the narrow scan spectra of N 1 s peak before and afterurease immobilization. It is clear from these spectrums that ureasehas immobilized on ZnO and resulted in a clear N 1 s peak. Thischange after immobilization clearly indicates that the urease hasimmobilized forming a covalent bond.

For operational and storage stability of the biosensors, the twosets of the samples were prepared and measured repeatedly. Forevery sample five times measurement was carried out and about±2% error was observed. To check the reliability, measurementswere repeated after one week of storage at room temperature in

Fig. 10. Narrow scan N 1 s spectra before and after urease immobilization. Theappearance of N 1 s peak after urease immobilization indicates the covalent bondingof the enzyme with zinc oxide.

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. Conclusion

A feasibility study is presented for the use of nanostructured zincxide in the form of a thick film for urea sensing at room tempera-ure. Structural and elemental measurement validated that ureaseas covalently attached with ZnO. The present study extended

he application of such organic–inorganic hybrid matrix to ureaensing which were found highly sensitive at lower urea con-entration (<10 mM). Urea concentration above 50 mM results inaturation. It is reconfirmed that the structure with highest surfacerea is better to biosensing. These results were found reproducibleith ±3% variation in sensitivity values. The detection range of

he studied sensor is wide (1–100 mM, 6–600 mg/dl), response areeproducible, reliable, reversible and selective. A portable instru-ent can be designed with proper electronics that will make

he device economical, portable and low power consuming. Theethod presented here can be implemented to other semiconduct-

ng oxide materials.

cknowledgement

S.G. Ansari acknowledges the Korean Federation of Science andechnology (KOFST) and KRF for Brain-Pool fellowship. Supportrom KOSEF research grant no. R01-2007-000-20810-0 and KMOSTesearch grant No. 2004-01352 is fully acknowledged. We alsoould like to acknowledge KBSI, Korea, Jeonju branch for access

o their FESEM setup.

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Biographies

S.G. Ansari was born in 1967. Received his Ph.D. degree, on thick film gas sensors,from the university of Pune, India, in 1997. He worked as deputy manager (R&D) atWIE pvt. Ltd., Pune, India. He was a visiting researcher at Chonbuk National Univer-sity, Korea and Japan Advanced Institute of Science and Technology, Japan. Presently,he is associate professor at Department of Physics, Najran University, Najran, KSA.His current research interest is immobilization of bio-materials on metal oxide,biosensing, nanopattering using AAO.

Rizwan Wahab was born in 1979. He got his Ph.D. degree in chemical engineer-ing on nano-biotechnological applications of metal oxides from Chonbuk NationalUniversity, Korea in 2008. His current research interest is on the synthesis of metaloxides using sol–gel technique and their interaction with bio-materials as well asbiosensing.

Z.A. Ansari was born in 1968. She received the Ph.D. degree on optical waveguidesensors from the University of Pune, India, in 1998. She was a Lecturer at Depart-ment of Physics and Department of Electronic Science, University of Pune, visitingprofessor at Inha University, Chonbuk National University, Korea and Japan AdvancedInstitute of Science and Technology, Japan. Presently, she is reader at Jamia MilliaIslamia, New Delhi, India. Her current research interest is surface studies of immo-bilized bio-organic/inorganic composites using SPM.

Young-Soon Kim was born in 1968. She received the Ph.D. degree on YBCO super-conductors from the Chonbuk National University, Korea, in 2000. She was a visitingresearcher at KBSI, Korea and RPI, USA. Presently, she is a visiting professor at e-Rest,Chonbuk National University, Korea. Her current research interest is in electro-chemistry for ULSI, renewable energy sources, solar/fuel cells, nano-patterning ofmaterials using AAO and bio-related applications.

Gilson Khang was born in 1961. He received Ph.D. degree from the University ofIowa, 1995 on polysulfone porous catheter tubes. He has been an active researcherand visited many universities as visiting professor worldwide. He is known for hiscontribution in the field of bio-mimetic materials, drug delivery systems, stem cellengineering, etc. He is member for various societies for tissue engineering, regen-erative medicine and biomaterials. Presently he is a professor at s BiomaterialsLaboratory, Chonbuk National University, Korea. Recently, he is twice awarded as an“excellent professor” of Chonbuk National University. His current research interest isin biomaterials, stem cell engineering, biosensors, bio-energy sources, bio-mimeticmaterials, etc.

Ali Al-Hajry is a Professor of Physics in the College of Science, and Vice President for

Graduate Studies and Research at Najran University, Saudi Arabia. He received hisPh.D. in Solid State Physics (in ‘neutron diffraction studies of disordered materials’)from the University of Sheffield, UK, in 1991.He holds the Directors position of theSaudi Physical Society (SPS). His research interests are in the field of structural andthermal studies of crystalline, nanocrystalline and amorphous materials, hydrogenstorage, chemical and biosensors.

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S.G. Ansari et al. / Sensors an

yung-Shik Shin was born in 1955. He received the Ph.D. degree on the kineticsf initial oxidation of Al(1 1 1) surface from the Cornell university, USA, in 1984. Heas been an active researcher and visited many universities as visiting professororldwide. He was the program director of KOSEF, Korea. He is an active executiveember of various programs/committee such KiChE, copy right protection, KAERI,

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etc. Presently he is a professor of school of chemical engineering and NURI, Chon-buk National University, Korea. His current research interest is in electrochemistry,renewable energy sources, solar/fuel cells, DSSC, bio-sensors, CNTs, diamond andnano-patterning of materials using AAO.