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CommunicationJournal of

Nanoscience and NanotechnologyVol. 14, 6786–6788, 2014

www.aspbs.com/jnn

Perylenetetracarboxylic Diimide (PTCDI) Nanowires forSensing Ethyl Acetate in Wine

Yashdeep Khopkar1, Arben Kojtari2, Dayne Swearer2, Sandra Zivanovic1�∗, and Hai-Feng Ji2�∗1Department of Electric Engineering, Louisiana Tech University, Ruston, LA 71272, USA

2Department of Chemistry, Drexel University, Philadelphia, PA 19104, USA

We report the application of perylenetetracarboxylic diimide (PTCDI) nanowires for sensing ethylacetate. The conductivity of the crystalline nano/microwires increases quickly and selectively in thepresence of ethyl acetate vapor, but not with water, acid and alcohol vapors, suggesting that thenanowires of PTCDI may be used for monitoring ethyl acetate during a wine manufacturing process.

Keywords: PTCDI, Nanowires, Conductivity, Ethyl Acetate Sensor, Thermal Evaporation.

In the wine industry, ethyl acetate is the most abundantester found within wine and it is mainly formed throughfermentation with yeast. The final concentration createdin this way is dependent on the species of yeast and theinitial constituents of the wine.1�2 A small amount of ethylacetate can add a depth of body, richness and sweetnessto a wine3 and becomes part of the pleasant bouquet ofwines.4 However, the presence of too much ethyl acetatein wine gives an unpleasant acetone aroma5�6 when theconcentration of ethyl acetate exceeds a threshold between100–200 mg/l.7�8 Furthermore, excessive concentration ofethyl acetate generally suppresses the formation of othercompounds contributing to a fruity aroma.9

A simple and cost-effective device that can quantify theamount of ethyl acetate in wine during the wine manu-facturing is of demand by wine producers since the tasteof the wine will determine its grade, and subsequentlythe price of the wine.10 Methods available for the anal-ysis of air samples of ethyl acetate, such as gas chro-matography and mass spectrometry,11 are expensive andpower consuming. Methods for detection of chemicals thatrely on the interaction of sensing materials with targetmolecules hold promise for detecting chemicals with real-time response, high sensitivity and selectivity, miniaturizedsize, low power requirements, and low cost.12 However,little work has been reported on ethyl acetate detectionbased on interaction of sensing materials with ethyl acetatevapor due to a lack of selectivity.

∗Authors to whom correspondence should be addressed.

It is recognized that sensors based on conductivitychanges are potentially advantageous in cost and con-venience than that based on other methods. To developconductivity-change based sensors, PTCDI (Scheme 1) isexpected to be a good candidate since PTCDI is a well-known semiconductive material13 that may be used forlight emitting diodes, photoconductive devices, and photo-voltaic cell.14–16

Recently, we synthesized and characterized one-dimensional (1D) nano/microwires of PTCDI.17 We alsoinvestigated its electrical properties.18 In this work, wedemonstrate our preliminary study on their potential appli-cation in detecting ethyl acetate. The conductivity of thePTCDI nanowires can be used for selective detection ofethyl acetate. It is expected that the concentration of ethylacetate can be readily quantified at any stage of wine man-ufacture by using this simple approach.PTCDI was purchased from Aldrich and was used as

received. The PTCDI nanowires were fabricated in a fur-nace according to a vapor deposition method reportedpreviously.16 In general, a 5 mg of PTCDI powder wasplaced in a 50-mL quartz tube (Fig. 1). The quartz tube,but not a glass tube was used because the quartz tubecan stand the high temperature needed for the nanowiregrowth. The tube was heated to 500 �C in vacuum for 1 h,and then the tube was allowed to be naturally cooled toroom temperature. A network film of PTCDI nanowires(or nanobelts) were self-assembled on a glass substrate inthe tube (Fig. 2 left). These nanowires have a diameter ofapproximately 100 nm.

6786 J. Nanosci. Nanotechnol. 2014, Vol. 14, No. 9 1533-4880/2014/14/6786/003 doi:10.1166/jnn.2014.9380

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Khopkar et al. Perylenetetracarboxylic Diimide (PTCDI) Nanowires for Sensing Ethyl Acetate in Wine

Scheme 1. Chemical structure of PTCDI.

Figure 1. Schematic diagram of the apparatus used in these work.

A JOEL JEM2100 operated at 120 keV was usedfor obtaining transmission electron microscopy (TEM)images. TEM experiments indicated that the PTCDInanowires (Fig. 3) have a crystalline structure. The cor-responding electron diffraction pattern (Fig. 3 insert)shows well-defined diffraction spots with 14 Å character-istic d-spacing in the perpendicular direction and 3.6 Åd-spacing in the longitudinal nanowire direction, suggest-ing that the molecules are oriented with their long axisperpendicular to the belt and the �–� stacking directionparallel to the belt.17

Conductive glue was applied on two ends of the glassside as two electrodes (Fig. 2 right). Gas sensing exper-iments were performed with a nanowire resistor deviceplaced in a glass tube with 20 cm in length and 1.5 cm indiameter. A targeted vapor was transferred to the tube toreach a concentration of 200 ppm. I–V curves were mea-sured before and after the device was exposed to the chem-ical vapors with a Keithley 2636A source meter. Since themajor components in the vapor of wine containers duringthe fermentation process are water vapor, ethanol, ethylacetate, acetic acid,19 we focus on the effects of thesevapors on the conductivity of the PTCDI network in thiswork. It is noteworthy that other flavor molecules, such aslactic acid, malic acid, glycerol, also exist in the vapor,

Figure 2. Left: SEM picture of network of self assembled PTCDI nanowires formed in the quartz tube. Right: Schematic of the sensing device setup.

Figure 3. TEM image of a PTCDI nanowire.

however, they vary from wine to wine, more importantly,the concentrations of these flavor molecules are generallymuch less than the target chemicals.Figure 4 Left shows the I–V curve of the network of

PTCDI nanowires. Figure 4 Right shows the electric cur-rent vs exposure time of the network of PTCDI nanowiresto 200 ppm ethyl acetate. The electric conductivity of thePTCDI nanowire network increases due to the exposureto ethyl acetate, and reaches a plateau of approximately6-fold increase after ~2 min exposure to ethyl acetate, sug-gesting that the network of the nanowires of PTCDI maybe used for in situ monitoring of ethyl acetate concen-tration in wine production since the fermentation processgenerally takes days to weeks.Figure 5 shows the conductivity change of the net-

work of PTCDI nanowires upon exposure to a variety ofchemicals at the same concentration. The conductivity ofthe nanowire network increases significantly on exposureto ethyl acetate, but does not change or change slightlyon exposure to a H2O, alcohol, and acetic acid. Thechange in conductivity when exposing to ethyl acetate maybe explained by creating more ‘holes’ when the diimdesection of PTCDI complexes with the electron withdraw-ing ester.20 The fact that acetic acid does not cause a sig-nificant change of the conductivity of the PTCDI networkmay be due to the hydrophilic character of the acid, whichhinders it from diffusing into the hydrophobic networkof PTCDI. These results suggest the conductivity of thePTCDI nanowire network may be used for monitoring the

J. Nanosci. Nanotechnol. 14, 6786–6788, 2014 6787

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Perylenetetracarboxylic Diimide (PTCDI) Nanowires for Sensing Ethyl Acetate in Wine Khopkar et al.

Voltage, V–15 –10 –5 0 5 10 15

Cur

rent

, A

–6e-7

–4e-7

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4e-7

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without ethyl acetatewith ethyl acetate

Time, min0 1 2 3 4 5

Cur

rent

, nA

0

50

100

150

200

250

300

Figure 4. Left: I–V curve of PTCDI nanowire network in N2 (solid line) and 200 ppm ethyl acetate vapor (dashed line). Right: Electric current verustime of the PTCDI nanowire network on exposure to 200 ppm ethyl acetate vapor.

Chemical vapors

(I-I

0)/I 0

0

200

400

600

800

Hex

ane

Tol

uene

Tet

rahy

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uran

Eth

er

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idin

e

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yl e

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Figure 5. Effect of chemical vapors on the conductivity of a PTCDInanowire network. (I-I0�/I0 is the % change of electric current of thedevice in the chemical vapors (I) to those in N2 (I0) at the same concen-tration (200 ppm).

level of ethyl acetate during the grape fermentation pro-cess. Figure 5 also shows the response of the sensor to avariety of other chemical vapors, for potential ethyl acetatesensing in other occasions.In conclusion, the PTCDI nanowire network has shown

a significant change in conductivity with the exposure toethyl acetate vapor, but not a variety of other chemicals.The conductive properties of PTCDI can be exploited foruse as selective chemical sensors for real-time monitor-ing of ethyl acetate concentrations during the fermentationprocess of wine-making by using facile electrical conduc-tance measurements.

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Received: 6 September 2013. Accepted: 30 September 2013.

6788 J. Nanosci. Nanotechnol. 14, 6786–6788, 2014