based Ag/GO nanocomposites plasmonic sensor

(1)

AIP Conference Proceedings 2203, 020002 (2020); https://doi.org/10.1063/1.5142094 2203, 020002

E-coli identification using Kretschmann- based Ag/GO nanocomposites plasmonic sensor

Cite as: AIP Conference Proceedings 2203, 020002 (2020); https://doi.org/10.1063/1.5142094 Published Online: 08 January 2020

Wan Maisarah Mukhtar

ARTICLES YOU MAY BE INTERESTED IN Automatic energy monitoring system

AIP Conference Proceedings 2203, 020001 (2020); https://doi.org/10.1063/1.5142093

Principles and characteristics of random lasers and their applications in medical, bioimaging and biosensing

AIP Conference Proceedings 2203, 020017 (2020); https://doi.org/10.1063/1.5142109 Sn doped ZnO thin film for formaldehyde detection

AIP Conference Proceedings 2203, 020027 (2020); https://doi.org/10.1063/1.5142119

(2)

E-coli Identification using Kretschmann-based Ag/GO Nanocomposites Plasmonic Sensor

Wan Maisarah Mukhtar

Faculty of Science and Technology, Universiti Sains Islam Malaysia (USIM), Bandar Baru Nilai, 71800 Nilai, Negeri Sembilan,Malaysia.

Corresponding author: [email protected]

Abstract. A low cost and highly efficient surface plasmon resonance (SPR) sensor for e-coli detection was developed by employing Kretschmann prism coupling technique. Silver thin film and graphene oxide were deposited on top of hypotenuse side of prism surface to excite surface plasmon polaritons (SPP). Their thicknesses were modulated between 43nm to 49nm and 1nm to 15nm respectively. The excitations of SPP were investigated by monitoring its minimum reflectance, Q-factor values and amount of angle shifting. Hybrid nanolayers of 1nm GO which was coated on top of 43nm- 45nm silver thin film exhibited excellent sensitivity resulting maximum angle shifting about 0.30º. As thicknesses of silver exceeded 45nm, the generation of SPR signals were less significant which led to the degradation of sensor’s sensing performance. In conclusion, the sensitivity of SPR sensors for the identification of e-coli can be optimized by introduced nanocomposites silver-GO with total thicknesses between 44nm and 46nm. Optimum sensitivity can only be achieved by employing maximum thickness of 1nm GO.

INTRODUCTION

Accessibility to quality clean water is basic essential in health, food production and economics. Drinking water has a potential to migrate microbial pathogens to great number of people which resulting the degradation of health quality [1-2]. The microbiological quality of drinking water can be monitored based on examination of indicator bacteria such as coliforms, Escherichia coli, and Pseudomonas aeruginosa [3-4]. Its presence in environmental samples usually indicates recent faecal contamination or poor sanitation practices in food-processing facilities [5]. The population of E. coli in these samples is influenced by the extent of faecal pollution, lack of hygienic practices, and storage conditions. Common techniques used for the analysis of e-coli pathogens include culturing methods, polymerase chain reaction (PCR), and enzyme linked immunosorbent assays (ELISA) [6-8].

The development of surface plasmon resonance (SPR) sensors are rapidly growth recently due to its high sensitivity and less complicated structure. SPR biosensors have been widely used for detection of urea, glucose, heavy ion metal etc [9-10]. The basic requirement to generate SPR is p-polarized laser, metal and light coupler such as prism and fiber optics. There are two types SPR sensors namely free space sensor and fiber optics-based sensors. SPR sensor is one of the favourable sensors for e-coli detection [11-12]. In developing an efficient sensor, the employment of noble metals either in a form of thin film or nanoparticles plays a significant role. Typically, there are few common methods in synthesizing metal nanoparticles namely seed-mediated growth, green synthesis etc [13-15]. Gold thin film is usually prepared by using sputtering and e-beam deposition techniques. Gold is preferable due to its stability which is oxidization resistance made it a suitable candidate for the long-term usage. The main drawback of gold is due to its high cost. Other noble metals namely silver, platinum and aluminium have been introduced to replace gold [16-19].

Nonetheless, oxidization issue became the main issue which limits the sensitivity ability of SPR sensor. Recently, graphene has received great attention due to its outstanding optical properties that can support either the TE modes or the TM modes [20]. It able to enhance the surface evanescent fields of the coated prism due to its high refractive index

(3)

[21]. Interestingly, graphene also has an extraordinary property due to its superior optical and mechanical properties [22].

Here, the investigation on optimization of SPR signal with an employment of silver and graphene nanocomposite films has been theoretically conducted. Many works verified that thickness of noble metals plays a crucial role in generating strong SPR signal [25-26]. In this work, we manipulated the thickness of silver within 43nm to 49nm for excellent excitation of surface plasmons. To enhance the excitation, a very thin layer of graphene oxide was deposited on top of silver thin films. We successfully proved that an ideal graphene plasmonic sensor for detection of e-coli can be developed by controlling the thickness of silver and GO within 43-44nm and 1nm respectively. This research

proposed a high sensitivity and low cost SPR sensor for biosensing application.

METHODS

This study was conducted by using Winspall 3.02 simulation software based on Fresnel equation [25-27]. Two layers on nanocomposite materials were deposited on top the triangular prism via Kretschmann configuration as illustrated in Fig. 1. Silver thin film with various thicknesses ranging from 43nm to 49nm was coated on the hypothenuse surface of prism. To enhance the strength on plasmon excitation and reduce the environmental impact due to oxidization issue, a very thin layer of graphene oxide (GO) was deposited on top of the silver layer. The thicknesses of GO were modulated between 1nm to 5nm. The excitation of SPP was created by applying a p-polarized incident laser with wavelength of 633nm on the coated prism. The strength of SPR signal was investigated by studying the characteristics of resulted curves such as value of minimum reflectance (Rmin), Q-factor (SPR curve depth) and location of SPR angle. Throughout this study, the thicknesses of silver and GO were manipulated by controlling the incident angle from 38° to 50° with an increment of 0.30° per reading. The presence of evanescent field due to the surface plasmons excitation indicated the sensing ability of the sensor. E-coli bacteria with refractive index of 1.38 [28] was then introduced on top of the coated prism. Similar procedure was repeated with the presence of e-coli. The sensitivity of the sensor was investigated by calculating the amount of angle shifting. The larger the amount of shifting, the better the sensitivity of sensor.

FIGURE 1. SPR experimental setup (a) nanocomposites consisted of silver and GO (b) detection of sample contained e-coli bacteria using SPR sensor

RESULTS AND DISCUSSIONS

Fig. 2 illustrates the SPR curves for several thicknesses of nanocomposites thin films consisted of silver and GO.

The strength of SPR signals were evaluated based on the curve depth. The deeper the depth, the stronger the SPP excitations [29]. Fig. 2(a) depicts the generation of SPR when thickness of silver was set at 43nm meanwhile the thicknesses of graphene oxide (GO) layer were varied between 1nm to 5nm. Minimum thickness (t=1nm) of GO resulted maximum plasmon absorption as the incident light was located at θi=θSPR=42.26° in which the value of minimum reflectance was obtained as Rmin=0.0120 a.u. At tGO=2nm, value of Rmin increased to 0.0445 a.u indicated the reduction of SPR strength about 3.25% where the SPR angle was red-shifted to 42.56°. The weakest SPR signal

(4)

FIGURE 2. SPR curves for various thicknesses of nanocomposites thin films Ag and GO (a) tAg =43nm; tGO=1-5nm (b) tAg

=43nm; tGO=1-5nm (c) tAg =43nm; tGO=1-5nm (d) tAg =43nm ; tGO=1-5nm (e) tAg =43nm; tGO=1-5nm (f) tAg =43nm;

tGO=1-5nm (g) tAg=43nm; tGO=1-5nm

was obtained as the GO thickness was set at maximum value, t=5nm. Overall, it was found that the strength of SPR signal was dropped about 25.78% with the increment of GO layers from 1nm to 5nm. Similar behaviour of plasmon excitations were observed as the thicknesses of silver were raised from 44nm to 49nm as displays in Fig. 2(b)-Fig.

2(g). The SPR signal was excellently enhanced when silver and GO nanocomposites with thicknesses of 45nm and 1nm respectively were deposited on the glass prism as portrayed in Fig. 2(c)). Value of Rmin was obtained as 0.0055 a.u. As thickness of silver was raised to t=46nm with tGO=1nm as shown in Fig. 2(d), amount plasmon excitations was started to slightly decrease about 0.42% where Rmin value was resulted as 0.0097 a.u. Note that the maximum SPR excitations were resulted as thickness of GO was set at 1nm. The employment of silver with t=47nm as displayed

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

38 39 40 41 42 43 44 45 46 47 48 49 50 Ag 43nm

43nm : 1nm 43nm: 2nm 43nm : 3nm 43nm : 4nm 43nm : 5nm

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

38 39 40 41 42 43 44 45 46 47 48 49 50 Ag 44nm

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

38 39 40 41 42 43 44 45 46 47 48 49 50 Ag 45nm

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

38 39 40 41 42 43 44 45 46 47 48 49 50 Ag 46nm

Reflectance, R (a.u) Reflectance, R (a.u)

Incident angle,θ (°)

Incident angle,θ (°) Incident angle,θ (°)

(a) (b)

(c) (d)

Reflectance, R (a.u)

Incident angle,θ (°) 0

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

38 39 40 41 42 43 44 45 46 47 48 49 50

Ag 47nm

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

38 39 40 41 42 43 44 45 46 47 48 49 50

Ag 48nm

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

38 39 40 41 42 43 44 45 46 47 48 49 50

Ag 49nm

(e) (f)

(g)

(5)

FIGURE 3. Effect of graphene oxide thicknesses on the location of SPR angles

FIGURE 4. (a) Relationship between maximum Q-factor and silver thin film thicknesses as glass prism was deposited with GO (a) numerous thicknesses of GO ranging from 1nm to 5nm; (b) thickness of GO = 1nm

FIGURE 5. SPR excitations became lesser as thickness of GO increased

in Fig. 2(e) witnessed the decrement of SPR strength where value of Rmin was resulted as 0.0187 a.u. Rmin became larger with the increment of silver thicknesses to 48nm and 49nm resulting its value as 0.0322 a.u and 0.0500 a.u respectively (Fig. 2(f) and 2(g)). Throughout this work, we noticed that the location of resonant angle was red-shifted from 42.56° to 43.77° as the thickness of GO were modulated between 1nm to 5nm as illustrated in Fig. 3.

Interestingly, the thickness of silver was not significantly influenced the shifting phenomena. We believed that the occurrence of this phenomena was due to the presence of dielectric on the surface of noble metal. Noble metal plays a vital role in the intensities of plasmons excitations, yet the angle shifting indicated the detection of dielectric on top of metal coated prism. Fig. 4 shows the relationship between silver thickness and SPR excitations (represented by Q- factor) as the thickness of GO were varied. Instead of the investigation on Rmin values, Q-factor analysis is more

42.0 42.2 42.4 42.6 42.8 43.0 43.2 43.4 43.6 43.8 44.0

1 2 3 4 5

SPRangle,θSPR(°)

Thickness of graphene oxide (GO) , t (nm)

0.45 0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.95

43 44 45 46 47 48 49

1nm 2nm 3nm

4nm 5nm

0.85 0.86 0.86 0.87 0.87 0.88 0.88 0.89 0.89 0.90 0.90

43 44 45 46 47 48 49

1nm GO

Maximum Q-factor(a.u) Maximum Q-factor(a.u)

Thickness of silver thin film, t (nm) Thickness of silver thin film, t (nm)

(a) (b)

0.4 0.5 0.6 0.7 0.8 0.9

1 2 3 4 5

43nm 44nm 45nm

46nm 47nm 48nm

49nm

Maximum Q-factor (a.u)

Thickness of graphene oxide (GO) , t (nm)

(6)

transparent because this analysis is dedicated to the determination of SPR curve depth which solely represented the percentage of plasmons excitation. It was clearly seen that for all thicknesses of silver in combination with 1nm layer of GO able to produce the highest Q-factor. The increment of GO layer to 2nm witnessed the decrement of Q-factor indicated that the plasmons excitations became poorer. The SPR strength decreased with the increment of silver thicknesses from 43nm to 49nm. Similar patterns were noticed for several thicknesses GO from 3nm to 5nm in which SPR became less significant due to increment thicknesses of metals which led to the absorption of plasmons polaritons.

We noticed an interesting phenomenon as nanocomposite metals and 1nm of GO were deployed in the SPR optical setup as illustrated in Fig. 4(b). The Q-factor did not exhibit similar patterns as others (i.e. Q-factor was linearly decreased with the increment of metal thicknesses) where the Q-factor was maximum at t=45nm with 89.77% of incident light was successfully excited as SPP. 89.73% of incident light was converted into SPP when thickness was

FIGURE 6. Numerous SPR angle shifting due to the presence of e-coli bacteria (represents by dotted line) on top of SPR sensor by varying silver thin films between 43nm to 49nm and maintaining GO thickness at 1nm

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

39 39.5 40 40.5 41 41.5 42 42.5 43 43.5 44 44.5 45 45.5 46 44nm

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

39 39.5 40 40.5 41 41.5 42 42.5 43 43.5 44 44.5 45 45.5 46 43nm

∆θSPR=0.30° ∆θSPR=0.30°

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

39 39.5 40 40.5 41 41.5 42 42.5 43 43.5 44 44.5 45 45.5 46 45nm

∆θSPR=0.12°

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

39 39.5 40 40.5 41 41.5 42 42.5 43 43.5 44 44.5 45 45.5 46 46nm

∆θSPR=0.10°

(a) (b)

(c) (d)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

39 39.5 40 40.5 41 41.5 42 42.5 43 43.5 44 44.5 45 45.5 46 48nm

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

39 39.5 40 40.5 41 41.5 42 42.5 43 43.5 44 44.5 45 45.5 46 49nm

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

39 39.5 40 40.5 41 41.5 42 42.5 43 43.5 44 44.5 45 45.5 46 47nm

∆θSPR=0.08° ∆θSPR=0.04°

∆θSPR=0.04°

(e) (f)

(g)

(7)

FIGURE 7. Amount of angle shifting as silver thin films were modulated between 43nm to 49nm and GO thickness was fixed at 1nm

fixed at 44nm. Fig. 5 exhibits the characteristics of SPR with increment of GO thicknesses. Obviously, the optimum SPR signal able to be generated by employing 1nm of GO. The shifting of SPR angle was observed as e-coli bacteria with refractive index of 1.38 was introduced on top of the nanocomposite silver-GO sensor. Since the strongest SPR signal was resulted with the additional layer of 1nm GO, we decided to focus on the sensitivity of nanocomposite plasmonic sensor consisted of various thicknesses of silver (43nm until 49nm) and 1 nm GO as portrays in Fig. 6. The solid line and dashed line represent the response of SPR sensor with and without the presence of e-coli respectively.

The resonant angle was red-shifted about 0.30°from 42.26° to 42.56° as the sensor consisted of 43nm silver and 1nm GO was exposed to the e-coli bacteria (Fig. 6(a)). Similar shifting characteristics was resulted as the thickness of silver was increased to 44nm as illustrated in Fig. 6(b). Amount of shifting was decreased to 0.12° with the increment of silver film thickness to 45nm where the location of SPR angle was changed from 42.26° to 42.38°. About 0.10° of shifting was resulted as thickness of silver was raised to 46nm. The sensitivity of sensor became weaker as noble metal thickness was increased to 47nm where only small shifting about 0.08° was observed. The weakest sensitivity was resulted with the appointment of 48nm and 49nm silver thin films where the resonant angle for both was only shifted about 0.04°.

Fig. 7 simplifies the sensing properties of nanocomposite SPR sensor during its interaction with e-coli bacteria. High sensitivity of SPR sensor was successfully developed by employing nanocomposite silver with thicknesses of 43nm or 44nm and 1nm of GO. The sensing properties were reduced about 18% as the thickness was increased to 45nm. Its sensitivity dropped almost 75% when silver’s thicknesses were raised to 48nm and 49nm.

Surprisingly, it was found that the intensities of plasmon excitations were quite contradicted with the sensing properties of SPR sensors. If we recap on the properties of plasmon polaritons excitation as discussed in Fig. 4, it is noteworthy to highlight that strong SPR signals was not a transparent indicator for a high sensitivity sensor. Although thickness of silver at 45nm by maintaining GO at 1nm yield to the strongest excitation of plasmons about 89.78%, the sensitivity of sensor did not reach the optimum stage. Contradictory, sensitivity of SPR sensor was effectively enhanced by introducing 43nm or 44nm silver in which the percentage of excited plasmons were 89.18% and 89.73%

respectively. By considering environmental issue during metal thin film deposition such as oxidization, it is quite challenging to determine the best thicknesses with difference of 1nm between each value.

CONCLUSIONS

A high sensitivity and low cost SPR sensor for detection of e-coli bacteria was successfully developed by introducing nanocomposite silver with range of thicknesses between 43nm-45nm and 1nm GO. As thicknesses of silver exceeded 45nm, the generation of SPR signals were less significant which led to the less sensing performance of the sensor. The role of additional layer of GO is important to avoid the oxidization issue and to enhance the sensing properties. It is noteworthy to highlight that the excitation of plasmons were diminished when thickness of GO was more than 1nm.

(8)

ACKNOWLEDGMENTS

The authors would like to acknowledge the support of Malaysian Ministry of Higher Education (MOHE) through Universiti Sains Islam Malaysia (USIM) under grant USIM/FRGS/FST/32/51514 and Knoll Group from Max Planck Institute Research for the Winspall 3.02 simulation software.

REFERENCES

1. N.J. Ashbolt, Current Environmental Health Reports, 2, 95-106 (2015).

2. A.B. Hoyer, S. G. Schladow, F. J. Rueda, Water Research, 83, 227-236 (2015).

3. D.N. King, M. J. Donohue, S. J. Vesper, E. N. Villegas, M. W. Ware, M. E. Vogel, E. F. Furlong, D. W. Kolpin,, S.T. Glassmeyer, S. Pfaller, Science of the Total Environment, 562, 987-995 (2016).

4. I. Tryland, F.E. Eregno, H. Braathen, G. Khalaf, I. Sjølander, M. Fossum, International Journal of Environmental Research and Public Health, 12, 1788-1802 (2015).

5. R. Bain, R. Cronk, R. Hossain, S. Bonjour, K. Onda, J. Wright, H. Yang, T. Slaymaker, P. Hunter, A. Prüss‐

Ustün, J. Bartram, Tropical Medicine & International Health, 19, 917-927 (2014).

6. K.E. Motato, C. Milani, M. Ventura, F.E. Valencia, P. Ruas-Madiedo, S. Delgado, Food microbiology, 68, 129- 136 (2017).

7. B. Suo, Y. He, S.I. Tu, X. Shi, Foodborne Pathogens and Disease, 7, 619-628 (2010).

8. S.Tatineni, G. Sarath, D. Seifers, R. French, Journal of Virological Methods, 189,196-203 (2013).

9. R. Verma and B.D. Gupta, Food chemistry, 166, 568-575 (2015).

10. W.M. Mukhtar, R. M. Halim, K.A. Dasuki, A.R.A Rashid, N.A.M. Taib, Malaysian Journal of Fundamental and Applied Sciences, 13, 619-622 (2017).

11. N. Tawil, E. Sacher, R. Mandeville, M. Meunier, Biosensors and Bioelectronics, 37, 24-29 (2012) 12. Y. Wang, Z. Ye, C. Si, Y. Ying, Sensors, 11, 2728-2739 (2011).

13. W. M. Mukhtar, S. Shaari, P.S. Menon, Advanced Science Letters, 19, 1412-1415 (2013).

14. S. Pandey, G.K. Goswami, K.K. Nanda, International Journal of Biological Macromolecules, 51, 583-589 (2012).

15. N.D. Samsuri, W.M. Mukhtar, A.R.A. Rashid, K.A. Dasuki, A.A.R.A. Yussuf,. In EPJ Web of Conferences (162, 01002). EDP Sciences (2017).

16. L. Novotny, B. Hecht, Principles of Nano-Optics. Cambridge University Press, (2012).

17. W. M. Mukhtar, S. Shaari, P.S. Menon, Optoelectron Adv. Mat., 7, 9-13 (2013).

18. S. Shukla, M. Rani, N.K. Sharma, V. Sajal, Optik-International Journal for Light and Electron Optics, 126, 4636- 4639 (2015).

19. D. Barchiesi, Optics Express, 20, 9064-9078 (2012).

20. L. Wu, H.S. Chu, W.S. Koh, and E.P. Li, Optics Express, 18,14395-14400 (2010).

21. Y. Wu, B. Yao, A. Zhang, Y. Rao, Z. Wang, Y. Cheng, Y. Gong, W. Zhang, Y. Chen, K.S. Chiang, Optics Letters, 39, 1235-1237 (2014).

22. F.H. Koppens, D. E. Chang, F. J. Garcia de Abajo, Nano Letters, 11, 3370-3377 (2011).

23. N. F. Murat, W. M. Mukhtar, A.R.A Rashid, K.A. Dasuki, A.A.R.A. Yussuf, In Semiconductor Electronics (ICSE), 2016 IEEE International Conference on (pp. 244-247). IEEE. 2016-August.

24. Y. Zhang, P. Liang, Y. Wang, Y. Zhang, Z. Liu, Y. Wei, Z. Zhu, E. Zhao, J. Yang, L. Yuan, Sensors and Actuators A: Physical, 267, 526-531 (2017).

25. P. Subramanian, A. Lesniewski, I. Kaminska, A. Vlandas, A. Vasilescu, J. Niedziolka-Jonsson, E. Pichonat, H.

Happy, R. Boukherroub, S. Szunerits, Biosensors and Bioelectronics, 50, 239-243 (2013)..

26. H. Q. A. Lê, H. Sauriat-Dorizon, H. Korri-Youssoufi, H., Analytica Chimica Acta, 674, 1-8 (2010).

27. W. M. Mukhtar, R. M. Halim, H. Hassan, H., In EPJ Web of Conferences (Vol. 162, p. 01001). EDP Sciences (2017).

28. P. Y. Liu, L. K. Chin, W. Ser, T. C. Ayi, P. H. Yap, T. Bourouina, Y. Leprince-Wang, Procedia Engineering, 87, 356-359 (2014).

29. W.M. Mukhtar, S. Shaari, P.S. Menon, Advanced Science Letters, 19, 66-69 (2013).