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Integrating W[O.sub.3] nanostructure on IDE for ethylene detection feasibility.

INTRODUCTION

Ethylene had attracted research area particularly in precision agriculture area due to their numerous effects on the growth, development and storage life of many fresh commodities at molecular concentration [1,2].This colourless and odourless gas is responsible for the changes in texture, softening, colour and other process involved in ripening especially for climacteric fruits includes apples, bananas, melons, apricots and tomatoes [3].By accurately measuring the ethylene gas level, the food supply chain management is in better control to determine the correct time for harvesting as well as in controlling the logistic of the food itself. In recent review by Cristescu et al. [4], he suggest that there are three main categories of methods can be used to detect ethylene; gas chromatography (GC), optical and electromechanical sensing. Among them, electrochemical technologies shows better advantage in lower p.p.m level capability, good repeatability and accuracy, smaller in dimension and consume relatively low power consumption. Under this technology domain, state of the chemoresistive sensor utilizing nanotechnology sensing material starts to emerged. Esser at al [5] mixed single-wall carbon nanotubes (SWNTs) with copper complex to detect the present of ethylene through the change of resistance. While the success of this sensor is proven, the processes of producing SWNTs require high temperature and high power process. Therefore, a much simple yet effective process such as hydrothermal should be explored towards producing fast response, sensitive and selective at lower production cost which matches with economic of scale required for mass sensor production [6].

Methodology:

W[O.sub.3] nanostructure was grown on micro IDE via facile hydrothermal synthesis process following similar setup by Feng et al. [7]. The aqueous solutions were prepared by dissolving 8.25g of sodium tungstate dehydrate powder ([Na.sub.2]W[O.sub.4]-2[H.sub.2]O) in de-ionized (DI) water. The pH value was modified to 2.4 by adding oxalic acid ([H.sub.2][C.sub.2][O.sub.4]). After 30 min stirring at ambient temperature, the IDE sensor package was immersed in the salt solution inside 100 ml Teflon lined autoclave reactor. The reactor was heat up to 130[degrees] C for 8 hours. The sensor were dried at 60[degrees] C for about 5 minuntes. For morphology analysis. scanning electron microscopy (JEOL, JSM7500 F) with 5 kV voltage acceleration was used to examine the W[O.sub.3] nanostructure morphology grown on IDE.

To investigate ethylene detection capability, the sensor was connected to LCR meter and initial resistance in air reading (Ra) was recorded. Subsequently, the sensor was located horizontally inside the chamber which contains specific p.p.m level of ethylene which was measured by industrial grade commercial Ethylene sensor (Detcon , USA) earlier. Once the resistance reading was stable, the value (Rg)was recorded and the sensitivity of the as-synthesize nanostructure on IDE was calculated. The gas sensitivity (S) of the sensor toward Ethylene gas is defined as the ratio of the stationary electrical resistance of the sensing materials in the test gas (Rg) to the resistance in air (Rg) or initial resistance; that is S = Rg/ Ra. The plot of sensitivity versus ethylene p.p.m level was plotted accordingly.

RESULTS AND DISCUSSION

Figure 1 shows the SEM of WO3 nanostructure layered on IDE surface. In general it can be seen that the nanostructure was sporadically distributed in between the IDE (Figure 1 (a)). At higher magnification, the nanostructure actually contains multidimensional structure which consist of 1D (nanorods) 2D (thick film slab) and 3D (nanoflower like).

[FIGURE 1 OMITTED]

The resistance measurement of such integrated IDE was perform folowing the electrical connection illustrated in Figure 2. The sensor was connected with voltage sources of 1 V at 100 kHz and the LCR meter will shows in-situ resistance reading on air as well as when the sensor located inside the testing chamber. The resistance value versus the p.p.m level of ethylene was plotted in Figure 3. Base on 3 point measurement, the resistance of the sensore increased linearly with the increased of ethylene p.p.m. More points of measurement was needed to confirm the actual resistance behaviour of the sensor.

In this feasibility study, the testing was done at ambient condition. On top of that, the ethylene was measured not in continuous manner because the sensor was removed from the chamber while the p.p.m level being adjusted. It is proposed to conduct continuous monitoring to avoid any resistance variation due to taking in and out of the sensor because it may have reacted with surrounding during that time. At this point of time, the sensitivity of the sensor towards 3 different p.p.m level as tabulated in Table 1.

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

Conclusion:

This paper reports the initial development of chemoresistive sensor to detect low concentration ethylene. W[O.sub.3] with multidimensional nanostructure was successfully integrated with silicon IDE platform via facile hydrothermal process. Despite the non-homogenous nanostructure observed on the device, the fabricated sensor shows a good response towards different ethylene concentration. Further characteristic study can venture base on this preliminary work towards fabrication of ultra sensisitive, selective and sustainable ethylene sensor in the future.

ARTICLE INFO

Article history:

Received 28 February 2014

Received in revised form 25 May 2014

Accepted 6 June 2014

Available online 20 June 2014

ACKNOWLEDGEMENTS

The authors wish to thank MIMOS Berhad, Universiti Teknologi MARA (UiTM) and Ministry of Higher Education Malaysia (MOE) for the financial support under ERGS grant (File No : 600-RMI/ERGS 5/3 (18/2013)).

REFERENCES

[1] Ruiz-Garcia, Luis, et al. 2009. "A review of wireless sensor technologies and applications in agriculture and food industry: state of the art and current trends." Sensors, 9.6: 4728-4750.

[2] Abeles, Frederick, B. Page W. Morgan, and Mikal E. Saltveit Jr, 1992. Ethylene in plant biology. Academic press.

[3] Bapat, Vishwas A., et al. 2010. "Ripening of fleshy fruit: molecular insight and the role of ethylene." Biotechnology advances, 28.1: 94-107.

[4] Cristescu, Simona M., et al. 2013. "Current methods for detecting ethylene in plants." Annals of botany, 111.3: 347-360.

[5] Esser, Birgit, Jan, M. Schnorr and Timothy M. Swager. 2012. "Selective Detection of Ethylene Gas Using Carbon Nanotube-based Devices: Utility in Determination of Fruit Ripeness." Angewandte Chemie International Edition, 51.23: 5752-5756.

[6] Rashid, Amirul Abd, et al. 2013. "Preliminary Study of W[O.sub.3] Nanostructures Produced via Facile Hydrothermal Synthesis Process for CO2 Sensing. "Applied Mechanics and Materials, 431: 37-41.

[7] Feng, Z., G. Min and Z. Mei 2013. CrystEngComm., 15: 277.

(1,2) Amirul Abd Rashid, (2) Nor Hayati Saad, (1) Daniel Bien Chia Sheng

(1) MIMOS Berhad, Technology Park Malaysia, Kuala Lumpur, 57000, Malaysia

(2) Micronanoelectro Mechanical System Laboratory (MINEMS), Faculty of Mechanical Engineering, Universiti Teknologi MARA, 40450 Shah Alam, Selangor, Malaysia

Corresponding Author: Amirul Abd Rashid, MIMOS Berhad, Technology Park Malaysia, Kuala Lumpur, 57000, Malaysia
Table 1: Sensitivity of WO3 nanostrucutred IDE sensor
to different ethylene concentration.

Ethylene Concentration    2        7        16
(p.p.m)

Ra                       260      220      246
Rg                       366      715      1250
Sensitivity              1.4      3.25     5.08
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Author:Rashid, Amirul Abd; Saad, Nor Hayati; Sheng, Daniel Bien Chia
Publication:Advances in Environmental Biology
Article Type:Report
Date:Jun 5, 2014
Words:1183
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