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Sensors and Actuators B 206 (2015) 119–125

Contents lists available at ScienceDirect

Sensors and Actuators B: Chemical

jo ur nal home page: www.elsev ier .com/ locate /snb

ilver/graphene nanocomposite-modified optical fiber sensorlatform for ethanol detection in water medium

ziz A.a, Lim H.N.a,∗, Girei S.H.b, Yaacob M.H.c, Mahdi M.A.c, Huang N.M.d,∗∗,andikumar A.d,∗ ∗ ∗

Department of Chemistry, Faculty of Science, University Putra Malaysia, 43400 UPM Serdang, Selangor Darul Ehsan, MalaysiaDepartment of Computer and Communication Engineering, Faculty of Engineering, University Putra Malaysia, 43400 UPM Serdang, Selangor Darul Ehsan,alaysia

Wireless and Photonics Network Research Centre, University Putra Malaysia, 43400 UPM Serdang, Selangor Darul Ehsan, MalaysiaLow Dimensional Materials Research Centre (LDMRC), Physics Department, Faculty of Science, University of Malaya, 50603 Kuala Lumpur, Malaysia

r t i c l e i n f o

rticle history:eceived 25 May 2014eceived in revised form 26 August 2014ccepted 11 September 2014vailable online 20 September 2014

a b s t r a c t

A silver nanoparticle-incorporated reduced graphene oxide (Ag/rGO) nanocomposite-based tapered opti-cal fiber sensor was successfully fabricated for the sensing of ethanol in an aqueous medium. The sensorprobe was fabricated by using a drop-casting technique to coat Ag/rGO on a multimode tapered opticalfiber, and the dynamic response was investigated under an exposed condition for ethanol in an aqueousmedium. The operating principle of the sensor device was based on the spectral intensity interrogation

eywords:ilver nanoparticlesrapheneanocompositeptical fiber sensor

technique in the visible region. The visible region spectral intensity was found to vary linearly withthe ethanol content in the range of 1–100%. The high sensitivity, rapid response, and good stabilityof the Ag/rGO nanocomposite-based optical fiber sensor make it a potential candidate for monitoringenvironmental pollution and the safety requirements of industry and daily life.

© 2014 Elsevier B.V. All rights reserved.

thanol sensor

. Introduction

Drug addiction is a demoralizing affliction that affects manyeople and is currently a major burden on society. A Unitedations Office on Drugs and Crime (UNODC) survey states thatmong the 250 million people surveyed, 3–5% (aged between5 and 64 years) used illegal drugs at least once in 2008 [1,2].ome drugs can even change a person’s body and brain, whichan lead to violent crime. Drugs are chemicals. Because of theirhemical structures, they can affect the body in different ways,nd can enter the body by drinking, injection, inhalation, andngestion. Among these methods, the drinking of alcohol is veryangerous and harmful to human beings. Drinking has a vari-ty of negative consequences, including poor grades, risky sex,

lcohol addiction, and car crashes [3–6]. The most common alco-olic beverages (such as wine, beer, whiskey, and brandy) containthanol. Hence, the detection of ethanol in a liquid medium is

∗ Corresponding author. Tel.: +60163301609.∗∗ Corresponding author.

∗ ∗Corresponding author.E-mail addresses: janet limhn@yahoo.com (L. H.N.), huangnayming@gmail.com

H. N.M.), pandikumarinbox@gmail.com (P. A.).

ttp://dx.doi.org/10.1016/j.snb.2014.09.035925-4005/© 2014 Elsevier B.V. All rights reserved.

very essential to save lives and prevent violent crimes. Severalmethods have been used for the detection of ethanol, includinghigh-performance liquid chromatography (HPLC), mass spectrom-etry (MS), liquid chromatography/mass spectrometry (LC/MS), andinfrared spectroscopy (FT-IR) [7]. However, these traditional ana-lytical techniques are time-consuming and require large samples,complicated operations, and well-trained operators. Hence, a rapidand accurate method for the on-site detection of ethanol is anemerging need from the perspective of safety to monitor alcoholconsumers.

Recently, ultraviolet–visible absorption spectroscopy-basedoptical fiber sensors have received much attention in relationto ethanol sensing because of their high sensitivity, real-timeand onsite detection capability, and rapid response and recoverytime [8–11]. A surface plasmon resonance-based Au nanoparticle-coated fiber optic sensor was developed for detecting small watercontent in ethanol using a wavelength interrogation method [8].However, the cost of gold will hinder its commercial application. Aevanescent wave absorption fiber optic sensor was developed andused for detecting a low water content in ethanol [9,10]. Recently,

a graphene-based optical multimode fiber tip was developed, andit showed a dynamic response toward ethanol detection due to thegraphene modification on the sensor surface of the fiber tip [11].Graphene has a two-dimensional (2-D) layer of carbon ordered

120 A. A. et al. / Sensors and Actuators B 206 (2015) 119–125

de tap

imawtocp

trtwmeis

2

2

pmpAtA(sshAwcd

2

i(fs

Fig. 1. Experimental setup for multimo

nto a honeycomb crystalline structure, and it has a high electronicobility, surface area, chemical stability, good dispersion perform-

nces, inherently low electrical noise, and high sensitivity to aide range of analytes at room temperature [12–15]. The modifica-

ion of metal nanoparticles significantly influences the propertiesf graphene. In particular, the incorporation of metal nanoparti-les into the graphene sheets concurrently enhances the sensingerformances for several analytes [13–15].

Herein, we report the successful fabrication of a multimodeapered optical fiber sensor based on silver nanoparticles incorpo-ated into a reduced graphene oxide (Ag/rGO) nanocomposite forhe detection of ethanol in an aqueous medium. The sensor probeas fabricated by drop-casting the Ag/rGO nanocomposite onto theultimode tapered optical fiber, and its dynamic response toward

thanol was investigated in an aqueous medium. The character-stic features of this ethanol sensor in terms of its sensing range,ensitivity, and response and recovery times were also determined.

. Experimental methods

.1. Synthesis of Ag/rGO nanocomposite

The Ag/rGO nanocomposite was synthesized using the followingrocedure. Initially, GO was prepared using a simplified Hum-er’s method [16]. A silver–ammonia (Ag(NH3)2OH) complex was

repared separately by adding ammonia (1 v/v%) to 50 mM ofgNO3 solution until complete precipitates with a 40 mM concen-

ration of Ag(NH3)2OH were obtained. Further, a freshly preparedg(NH3)2OH complex was mixed with the aqueous solution of GO

1.0 mg/mL) at a volume ratio of 8:1 for GO:Ag(NH3)2OH and thentirred for 5 min to ensure homogeneous mixing. The resultingolution was subjected to acoustic cavitation using an ultrasonicorn (Misonix Sonicator S-4000, USA, 20 kHz). Finally, the obtainedg/rGO nanocomposite was centrifuged and washed with distilledater three times and then redispersed into the distilled water. For

omparison, rGO was also prepared by following the same proce-ure without adding the Ag(NH3)2OH complex.

.2. Setup for optical fiber-based ethanol sensor

The multimode tapered optical fiber was prepared accord-

ng to the reported procedure [9]. The Ag/rGO nanocomposite0.2 mg/mL) was redispersed into the distilled water and usedor sensor fabrication. The Ag/rGO nanocomposite coating on theurface of the multimode tapered optical fiber (with a diameter

ered optical fiber detection of ethanol.

of 30 �m) was carried out using a drop-casting technique (Fig.S1). The liquid sensing experimental setup is schematically shownin Fig. 1. A tungsten-halogen lamp (Ocean optics HL 2000) wasused as a light source. An Ocean optics USB-4000 absorption spec-trophotometer was used as the light detector, and a computer withthe SpectraSuite software was used for spectral data processing.Different concentrations of ethanol (1–100%) were prepared bymixing different ratios of distilled water with pure ethanol andused for the sensing studies.

2.3. Characterization techniques

The crystal phase of the Ag/rGO nanocomposite was studiedusing a Philips X’pert system X-ray powder diffractometer with CuK� radiation (� = 1.5418 A), and a Raman analysis was carried outusing a Renishaw inVia Raman microscope with laser excitationat � = 514 nm. The morphology and elemental compositions wereanalyzed using an FEI Nova Nano-SEM 400 field emission scanningelectron microscope fitted with an EDAX accessory.

3. Results and discussion

3.1. Characterization of Ag/rGO nanocomposite

The Ag/rGO nanocomposite was prepared by a sonicationmethod using an aqueous solution of AgNO3, NH3, and GO as a pre-cursor. In the typical preparation method, the AgNO3 was mixedwith an NH3 solution and formed a Ag(NH3)2OH complex. Thiscould be confirmed from the absorption spectrum of the AgNO3,which showed a characteristic peak at approximately 280 nm.Then, after forming the complex with NH3, Ag(NH3)2OH, theabsorbance maximum was red shifted to 300 nm (Fig. 2(a and b)).Further, this Ag(NH3)2OH complex was mixed with the GO solutionand formed Ag(NH3)2OH–GO. For the GO, the absorbance peakobserved at 231 nm with a shoulder at around 300 nm (Fig. 2(c))could be assigned to the � → �* transitions of the aromatic C Cbonds and n → �* transitions of the C O bonds, respectively [17].While mixing the Ag(NH3)2OH complex with GO, the disappear-ance of the characteristic peaks for Ag(NH3)2OH at 300 nm and GOfor 231 nm was observed (Fig. 2(d)). The dispersed GO sheets inwater are negatively-charged due to the ionization of carboxyl and

hydroxyl groups on the surface of GO. This causes the positively-charged [Ag(NH3)2]+ ions to be adsorbed on the negatively-chargedGO sheets by electrostatic attraction [18,19]. Upon subject to soni-cation, the GO is converted to rGO and simultaneously it reduced to

A. A. et al. / Sensors and Actuators B 206 (2015) 119–125 121

Fig. 2. UV–visible absorption spectra for aqueous solutions of (a) AgNO3, (b andi(t

ffsffab

wiAuaGfFmaa[tp

np

100 0 150 0 2000 25 00 30 00

G

Inte

nsity

(a.u

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Raman Shift (cm-1

)

D A

1000 150 0 200 0 250 0 300 0Raman Shift (cm-1 )

GD

b

Inte

nsity

(a.u

.)

a

B

nset) Ag(NH3)2OH, (c) GO, (d) Ag(NH3)2OH-GO, and (e) Ag/rGO nanocomposite.Inset) photographs of the Ag(NH3)2OH-GO solution (A) before and (B) after sonica-ion.

orm Ag nanoparticles. As a consequence, the GO acted as a supportor Ag nanoparticles during the sonication process, and the GO wasimultaneously converted to rGO (Fig. 2(inset photograph)). Theormation of new peaks at 400–500 nm confirmed the successfulormation of Ag nanoparticles on the rGO sheets (Fig. 2(e)) and thebsorption features raised from the surface plasmon resonanceand of the Ag nanoparticles [18,19].

Phase analyses of the prepared rGO and Ag/rGO nanocompositeere carried out using XRD measurements, and their correspond-

ng diffraction patterns are shown in Fig. 3. Both the rGO andg/rGO nanocomposite exhibited typical diffraction peaks at 2� val-es between 23◦ and 26◦ due to the (0 0 2) plane of the rGO withn interlayer d-spacing of 0.38 nm. This clearly indicated that theO was greatly reduced to rGO, and most of the oxygen-containing

unctional groups were removed during the sonication process [20].or the Ag/rGO nanocomposite, in addition to rGO diffraction, fourore peaks were observed at the 2� values of 38.1◦, 44.3◦, 64.5◦,

nd 77.5◦, which are corresponded to the (1 1 1), (2 0 0), (2 2 0),nd (3 1 1) crystalline planes of the Ag nanoparticles, respectively21]. The sharp, intense diffraction peak observed at 38.1◦ due tohe (1 1 1) plane confirmed the formation of highly crystalline Agarticles in the nanocomposite [22].

Fig. 4 shows the Raman spectra of the GO, rGO, and Ag/rGOanocomposite. It can be seen that all three samples exhibit strongrominent peaks at 1350 and 1598 cm−1 corresponding to the D

20 30 40 50 60 70 80

rGO

(002)

Inte

nsity

(a.u

.)

2 Theta (Degree)

b

(111)

(200)

(220) (311)

(002)

a

Fig. 3. XRD patterns obtained for (a) rGO and (b) Ag/rGO nanocomposite.

Fig. 4. (A) Raman spectrum of GO and (B) Raman spectra of (a) rGO and (b) Ag/rGOnanocomposite.

band and G band, respectively. The observed intense peak for the Dband (sp3 carbon) at 1350 cm−1 originated from the out-of-planebreathing mode of the sp2 carbons, which could be attributed tothe existence of defects upon the oxidization and reduction process[23]. The observed G band at 1598 cm−1 was caused by the vibrationof sp2-bonded carbon atoms in the 2D hexagonal lattice. Moreover,the D band could be attributed to the breathing mode of k-pointphonons with A1g symmetry, whereas the G band was assigned tothe first-order scattering of the E2g phonons of sp2 carbon atoms[24]. The G band of the Ag/rGO nanocomposite (1602 cm−1) wasobviously upshifted by 4 cm−1 with respect to rGO (1598 cm−1).This was consistent with the existing literature and showed thatthe incorporation of Ag in the rGO sheets caused an upshift of the Gband due to the electron–phonon coupling and the doping effectsimposed by the Ag nanoparticles [18,20,22].

Fig. 5(A–D) shows typical FESEM images of the sonochemicallyprepared rGO and Ag/rGO nanocomposite-coated tapered opticalfibers. As can be seen from Fig. 5(A and B), the rGO and Ag/rGOnanocomposite were successfully deposited on the surface of theoptical fiber. Fig. 5(C and D) shows some wrinkles on the surface,which can be attributed to the edges of the rGO nanosheets [25].The rGO and Ag/rGO nanocomposite surfaces of the tapered opti-cal fibers are relatively smooth, and no obvious physical damage

(pores or cracks) was observed. As can be seen from Fig. 5(D), Agnanoparticles with a size range of 220–350 nm were successfullyincorporated into the surface of the rGO sheets. The uneven sizes

122 A. A. et al. / Sensors and Actuators B 206 (2015) 119–125

F ) rGO

n

oAcbwfiAsiEAs

3e

twwsstI

ig. 5. FESEM images of multimode tapered optical fibers coated with (A and Canocomposite-coated multimode tapered optical fibers.

f the Ag nanoparticles were due to the wide aggregation of theg(NH3)2OH particles on the rGO sheets [26]. The Ag nanoparti-les on the translucent rGO sheets could be readily differentiatedy their clear white and gray contrast. The chemical compositionsere determined using an EDX analysis (Fig. 5(E and F), which con-rmed the existence of C and O in the rGO sample and C, O, andg in the Ag/rGO nanocomposite sample. Both samples showed aignal for the Si element, which was due to the presence of the sil-ca wafer (SiO2) substrate where the samples were deposited. TheDAX mapping further confirmed the attachment of the rGO andg/rGO nanocomposite on the surfaces of the tapered optical fiberensors (Fig. S2).

.2. Performance of Ag/rGO-modified tapered optical fiber forthanol sensing

The optical responses of the Ag/rGO nanocomposite-coatedapered optical fiber sensor with different ethanol concentrationsere studied to evaluate the sensing performance when ethanolas introduced into the liquid chamber where the tapered sen-

or was placed. The ethanol caused a change in the absorbancepectra, which could be evaluated and better understood based onhe dynamic responses for the different concentrations of ethanol.n the optical sensor, the analyte was allowed to interact with

and (B and D) Ag/rGO nanocomposite. EDAX spectra of (E) rGO and (F) Ag/rGO

the receptor, and the light passing through it caused changesin the absorbance spectra and dynamic response of the sensor.The absorption spectra of the rGO and Ag/rGO nanocomposite-coated tapered optical fiber sensors with different concentrationsof ethanol were recorded and are shown in Fig. S3(A and B). As canbe seen from the absorption spectra, a change in the ethanol con-centration led to a change in the absorbance intensity in the range of350–800 nm. As the ethanol concentrations were varied from 1% to100%, the absorption spectrum showed a linear increase in its inten-sity. Further, the peak increased at around 650 nm, which indicatedthe presence of water absorption on the rGO [27]. However, theAg/rGO nanocomposite-based sensor showed improved intensitychanges compared to the rGO-based sensor. This improved per-formance of the Ag/rGO nanocomposite was due to the presenceof optical and catalytically active Ag nanoparticles on the surfaceof the rGO. Moreover, the Ag nanoparticles were extremely sensi-tive to changes in the local refractive index induced by the analytebinding on the nanoparticle surface [28].

The ethanol-sensing properties of the rGO and Ag/rGOnanocomposite-coated optical fiber sensors with different concen-

trations of ethanol (%) were also investigated, and it was found thatthe Ag/rGO nanocomposite exhibited a higher response to differ-ent concentrations of ethanol (1–100%) than the rGO-coated opticalfiber because the ethanol could be easily catalyzed on the surface of

A. A. et al. / Sensors and Actuators B 206 (2015) 119–125 123

0 500 1000 1500

0

10

20

30

40

100 %80 %

60 %40 %

20 %

10 %5 %

1 %

Nor

mal

ized

Abs

orba

nce

(%)

Time (sec)

A

0 30 0 60 0 90 0 12 00 150 0

0

20

40

60

80

100

100 %

80 %60 %

40 %

20 %

10 %5 %

Nor

mal

ized

Abs

orba

nce

(%)

Time (sec)

1 % B

0 20 40 60 80 1000

20

40

60

80

100C

b

ΔΔab

s (%

)

Ethanol (%)

a

F nanoe ) againn

tMbhttbiitte1httemctmc

iagfrO

on the surface of rGO sheets significantly influences the sensingresponse toward ethanol.

ig. 6. Dynamic response–recovery curves obtained for (A) rGO and (B) Ag/rGOthanol (%). (C) The sensor responses as a function of the ethanol concentration (%anocomposite-coated tapered optical fiber ethanol sensors.

he Ag nanoparticles present in the rGO sheets of the sensing layer.oreover, the Ag/rGO nanocomposite-based sensor (Fig. 6(B)) had

etter ethanol sensing properties, with a shorter response time andigher response, than the rGO-based sensor (Fig. 6(A)). In addition,he responses of both sensors increased when the ethanol concen-ration increased from 1% to 100%. According to the relationshipetween the response and the ethanol concentration (Fig. 6(C)),

t can be seen that the difference in the absorbance (�abs) (%)ncreased with a linear increase in the ethanol content from 1%o 20%. Beyond 20%, �abs (%) slowly attained saturation. Initially,he sensors showed very poor response and recovery times for 1%thanol, with a maximum response in absorbance. In contrast, at00% ethanol, they showed rapid response and recovery times. At aigh concentration, more ethanol molecules easily interacted withhe adsorbed oxygen ions, providing a fast response [29]. Althoughhe absorption spectra for the rGO-based sensor showed a lin-ar increase with an increase in the ethanol concentration, theagnitude for this sensor showed quite a large gap increase at

oncentrations of 80 and 100% ethanol. For other ethanol concen-rations, a slight increase in the absorption was observed, which

ay have been due to the saturation of the sensor at an ethanoloncentration above 80% [30].

The ethanol sensing mechanism of the Ag/rGO nanocompos-te is shown in Fig. 7. The oxygen molecules present in the air getdsorbed on the surface of the Ag/rGO nanocomposite. These oxy-

en molecules transfer electrons to the Ag nanoparticles, and thusorm O2

−, and the Ag nanoparticles rapidly transfer electrons to theGO sheets. Instantaneously, ethanol comes into contact with the2

− species to form CO2 and H2O. The O2− acquires electrons from

composite-coated tapered optical fiber sensors with different concentrations ofst the difference in the normalized absorbance (%) for the (a) rGO and (b) Ag/rGO

the ethanol and is regenerated as O2 [31]. The Ag nanoparticlesact as an electron sink, which facilitates the electron transfer fromthe O2 to rGO sheets, leading to a rapid and enhanced sensitivitytoward ethanol.

The dynamic response and recovery of the Ag/rGOnanocomposite-coated tapered optical fiber were examinedusing 10% ethanol and are shown in Fig. 8. It can be seen that,upon the introduction of 10% ethanol, the sensor showed a relativeabsorbance of 74% within 11 s. After the sensor was removed andexposed to the air, it showed a rapid recovery response within 6 s.The response and recovery times for the Ag/rGO nanocompositewere quite low compared to the rGO-based ethanol sensor due tothe Ag nanoparticles incorporated on the surface of the rGO sheets.Hence, it was proven that the incorporation of Ag nanoparticles

Fig. 7. Schematic representation of ethanol sensing at surface of Ag/rGO nanocom-posite.

124 A. A. et al. / Sensors and Actuators B 206 (2015) 119–125

Table 1Comparison of various nanomaterials sensing performance toward ethanol.

Sensor materials Operating temperature Ethanol content Sensitivity Ref.

Porous ZnO nanosolid 370 ◦C 3000 ppm ∼21 [32]SnO2 nanoparticles 250 ◦C 1000 ppm 2565 [33]Brush-like hierarchical ZnO 265 ◦C 50 ppm ∼10 [34]Pt@SnO2 nanorods 300 ◦C 10 ppm 3.7 [35]Cu-doped SnO2 nanofibers 300 ◦C 100 ppm 13 [36]SnO2:CuO nanoparticles Room temperature 100 ppm 41 [31]Graphene oxide Room temperature

Graphene oxide Room temperature

Ag/rGO Room temperature

50 10 0 15 0 20 0 25 0100

80

60

40

20

0AirAir

Recovery time( 6 sec)

Response time (11 sec)

Stady state

Ethanol out

Nor

mol

ized

Abs

orba

nce

(%)

Time (sec)

Ethanol in

Fc

attecrrisstt

b

Ffi

ig. 8. Dynamic response–recovery curve obtained for Ag/rGO nanocomposite-oated tapered optical fiber sensor for 10% ethanol.

The sustainability of an ethanol sensor is very crucial, and plays role in its commercialization. In this respect, we also investigatedhe reversibility of the rGO and Ag/rGO nanocomposite-coatedapered optical fiber sensors in the absence and presence of 10%thanol for repeated cycles of exposure in air and ethanol (Fig. 9). Itan be seen that the fabricated ethanol sensor showed a very goodesponse and recovery, with good stability. The rapid response,ecovery, and high reversibility of the optical fiber sensor will allowt to be used for practical applications. Furthermore, the long-termtability of the Ag/rGO nanocomposite-based tapered optical fiberensor was examined over a two-week period and it was stored inhe refrigerator at 4 ◦C, it lost only 6% of the initial response after

wo weeks thus indicating good stability of the fabricated sensor.

The ethanol sensing performance of Ag/rGO nanocomposite-ased tapered optical fiber sensor is compared with the reported

10008006004002000

0

20

40

60

80

100

Ethan ol i n

a

Nor

mal

ized

Abs

orba

nce

(%)

Time (Sec )

bEthanol ou t

ig. 9. Reversibility of (a) rGO and (b) Ag/rGO nanocomposite-coated tapered opticalber sensors in absence and presence of 10% ethanol.

5% 98.2 [37]5% 37 [11]1% Present work

literatures and are summarized in Table 1. As can see from Table 1,most of the reported sensors showed high performance at higheroperating temperature [32–36] and very few reports demonstratesthe ethanol sensitivity at room temperature [31,37]. In the presentinvestigation, the Ag/rGO nanocomposite-based tapered opticalfiber sensor showed good performance toward ethanol at roomtemperature.

4. Conclusions

Herein, we report the successful fabrication of a Ag/rGOnanocomposite-based tapered optical fiber sensor for the sensingof ethanol in a water medium. The Ag/rGO nanocomposite was pre-pared by a sonication method using an aqueous solution of AgNO3,NH3, and GO as a precursor, and characterized using suitabletechniques. The sensor probe was fabricated by using a drop-casting technique to coat the prepared Ag/rGO nanocomposite ona multimode tapered optical fiber, and the dynamic response wasinvestigated under an exposure condition of ethanol in an aqueousmedium. The visible region spectral intensity was found to varylinearly with the ethanol content in the range of 1–100%. The highsensitive, rapid response and recovery, and good stability towardethanol sensing demonstrated by the Ag/rGO nanocomposite-based optical fiber sensor could make it a suitable candidate toapply in practical applications for environmental monitoring andsafety requirements in industries.

Acknowledgement

The authors gratefully acknowledge the financial support of theFundamental Research Grant Scheme (FRGS/1/2012/ST05/UPM/02/3) and High Impact Research Grant (UM.C/625/1/HIR/MOHE/SC/21) from the Ministry of Higher Education of Malaysia, and theResearch University Grant Scheme (05-02-12-2015RU) from Uni-versiti Putra Malaysia.

Appendix A. Supplementary data

Supplementary data associated with this article can be found, inthe online version, at http://dx.doi.org/10.1016/j.snb.2014.09.035.

References

[1] UNODC, World drug report, United Nations Publication, Sales No. E.10.XI.13,2010.

[2] L.B. Snyder, F.F. Milici, M. Slater, H. Sun, Y. Strizhakova, Arch. Pediatr. Adolesc.Med. 160 (2006) 18–24.

[3] L. Chassin, C. DeLucia, Alcohol Health Res. World (1996) 20175–20180.[4] P.M. O’Malley, L.D. Johnston, J.G. Bachman, Alcohol Health Res. World (1998)

2285–2294.[5] M.L. Cooper, R.S. Peirce, R.F. Huselid, Health Psychol. (1994) 13251–13262.

[6] M. Windle, C. Miller-Tutzauer, D. Domenico, Am. J. Public Health (1992)

74673–74681.[7] P.L. Jia, H.S. Wang, Sens. Actuators B: Chem. 177 (2013) 1035–1042.[8] S.K. Srivastava, R. Verma, B.D. Gupta, Sens. Actuators B: Chem. 153 (2011)

194–198.

ctuato

[[

[[[[[

[

[[[[[[[

[[[

[

[[

[

[[

[

[

[[

B

Aap

A. A. et al. / Sensors and A

[9] S.H. Girei, A.A. Shabaneh, P.T. Arasu, S. Painam, M.H. Yaacob, IEEE 4th Int. Conf.Photonics (ICP) (2013) 275–277.

10] F.B. Xiong, D. Sisler, Opt. Commun. 283 (2010) 1326–1330.11] A.A. Shabaneh, P.T. Arasu, S.H. Girei, S. Paiman, M.A. Mahdi, M.H. Yaacob, N.M.

Huang, IEEE 4th Int. Conf. Photonics (ICP) (2013) 272–274.12] S. Guo, S. Dong, Chem. Soc. Rev. 40 (2011) 2644–2672.13] C. Tan, X. Huang, H. Zhang, Nanoscale 5 (2013) 10765–10775.14] I.V. Lightcap, P.V. Kamat, Acc. Chem. Res. 46 (2013) 2235–2243.15] H. Ma, D. Wu, Z. Cui, Y. Li, Y. Zhang, B. Du, Q. Wei, Anal. Lett. 46 (2013) 1–17.16] N.M. Huang, H.N. Lim, C.H. Chia, M.A. Yarmo, M.R. Muhamad, Int. J. Nanomed.

6 (2011) 3443–3448.17] J.I. Parades, S. Villar-Rodil, A. Martinez-Alonso, J.M.D. Tascon, Langmuir 24

(2008) 10560–10564.18] Y. He, H. Cui, J. Mater. Chem. 22 (2012) 9086–9091.19] H.L. Jun, W.Y. Xin, W.H. Min, W. Yao, J. Electrochem. Sci. (2012) 11068–11075.20] R. Pasricha, S. Gupta, A.K. Srivastava, Small 5 (2009) 2253–2259.21] Y. Chen, X. Zhang, D.C. Zhang, P. Yu, Y.W. Ma, Carbon 49 (2011) 573–580.22] Y.M. Zhang, X. Yuan, Y. Wang, Y. Chen, J. Mater. Chem. 22 (2012) 7245–7251.23] Y. Geng, S.J. Wang, J.K. Kim, J. Colloid Interface Sci. 336 (2009) 592–598.24] Z.J. Fan, W. Kai, J. Yan, T. Wei, L.J. Zhi, J. Feng, Y.M. Ren, L.P. Song, F. Wei, ACS

Nano 5 (2010) 191–198.25] X.W. Liu, J.J. Mao, P.D. Liu, X.W. Wei, Carbon 49 (2011) 477–483.26] S. Wang, W. Zhang, H.L. Ma, Q. Zhang, W. Xu, Carbon 55 (2013) 245–255.27] J.C. Meyer, A.K. Geim, M.I. Katsnelson, K.S. Novoselov, T.J. Booth, S. Roth, Nature

446 (2007) 60–63.28] M.R. Das, R.K. Sarma, R. Saikia, V.S. Kale, M.V. Shelke, P. Sengupta, Colloid Surf.

B 83 (2011) 16–22.29] S. Liu, J.Q. Tian, L. Wang, X.P. Sun, Carbon 49 (2011) 3158–3164.30] J.Q. Hu, Q. Chen, Z.X. Xie, G.B. Han, R.H. Wang, B. Ren, Adv. Funct. Mater. 14

(2004) 183–189.31] R.N. Mariammal, K. Ramachandran, B. Renganathan, D. Sastikumar, Sens. Actu-

ators B 169 (2012) 199–207.32] H. Xu, X. Liu, D. Cui, M. Li, M. Jiang, Sens. Actuators B 114 (2006) 301–307.33] B.M. Matin, Y. Mortazavi, A.A. Khodadadi, A. Abbasi, A.A. Firooz, Sens. Actuators

B (2010) 140–145.34] Y. Zhang, J. Xu, Q. Xiang, H. Li, Q. Pan, P. Xu, J. Phys. Chem. C 113 (2009)

3430–3435.35] X. Xue, Z. Chen, C. Ma, L. Xing, Y. Chen, Y. Wang, T. Wang, J. Phys. Chem. C 114

(2010) 3968–3972.36] L. Liu, T. Zhang, L. Wang, S. Li, Mater. Lett. 63 (2009) 2041–2043.37] A.A. Shabaneh, S.H. Girei, P.T. Arasu, W.B.W.A. Rahman, A.A.A. Bakar, A.Z. Sadek,

H.N. Lim, N.M. Huang, M.H. Yaacob, Opt. Commun. 331 (2014) 320–324.

iographies

ziz A. is currently an undergraduate student pursuing a B.Sc. in Industrial Chemistryt Universiti Putra Malaysia. Her research interests are graphene/metal nanocom-osite for optical fiber sensor for organic solvents.

rs B 206 (2015) 119–125 125

Dr. Lim H.N. received her B.Sc. and M.Sc. degrees from Universiti KebangsaanMalaysia in 2002 and 2004, respectively. She was awarded a Ph.D. degree in Chem-istry from Universiti Putra Malaysia in 2010. She was an Assistant Professor at theNottingham University Malaysia Campus and a Senior Lecturer at the University ofMalaysia before joining Universiti Putra Malaysia as a Senior lecturer. Since 2009,she has been actively involved in graphene-related research, encompassing thesynthesis of graphene-based nanomaterials and their applications.

Girei S.H. received his B.Eng. degree in Electrical/Electronic Engineering from theFederal University of Technology, Yola, Nigeria in 2007. He is currently an M.Sc. stu-dent in photonics and fiber optics system engineering at Universiti Putra Malaysia.His main research interests are fiber optic sensors, nanomaterials, and optical com-munications.

Dr. Yaacob M.H. received his Bachelor of Engineering (Electronic Computer Sys-tems) and Master of Science (Communication and Network Engineering) degreesfrom Salford University, UK (1999) and Universiti Putra Malaysia, Malaysia(2002), respectively. He did his Ph.D. research at RMIT University, Melbourne,Australia (2012) in the area of optical sensors based on nanomaterials forchemical sensing applications. His research interests are optical sensors, opticalcommunication systems, and nanotechnology. Currently, he is a lecturer at theDepartment of Computer and Communication Systems Engineering and a principalresearcher at the Wireless and Photonic Network Research Center, Universiti PutraMalaysia.

Prof. Dr. Mahdi M.A. received his B.Eng. degree from the Universiti KebangsaanMalaysia, and M.Sc. and Ph.D. degrees from the Universiti Malaya in 1996, 1999, and2002 respectively. He joined the Faculty of Engineering, Universiti Putra Malaysia in2003. Since 1996, he has been involved in photonics research specializing in opticalamplifiers and lasers. He has authored or coauthored over 250 journal papers and185 conference papers. His research interests include optical communications andnonlinear optics.

Dr. Huang N.M. received his B.Sc., M.Sc., and Ph.D. degrees from UniversitiKebangsaan Malaysia. He joined the University of Malaya in 2009 as a SeniorLecturer in the Department of Physics, Faculty of Science. He started workingon graphene and graphene-related materials in the same year and has appliedgraphene in various fields such as solar energy conversion, energy storage, andsensors.

Dr. Pandikumar A. received his B.Sc. and M.Sc. degrees from Gandhigram RuralUniversity in the years 2004 and 2006, respectively. He received his Ph.D.(2014) in Chemistry from Madurai Kamaraj University. Currently, he is workingas a Post-Doctoral Research Fellow in Universiti Malaya. His research interests

are graphene/semiconductor/metal nanocomposite materials based energy andenvironmental remediation via photocatalysis, photoelectrochemical cells, and dye-sensitized solar cells. Currently, he is working on graphene-based metal and metaloxide nanocomposites for electrochemical sensor, optical sensor, and electrochem-ical energy conversion and storage applications.