AIP Conference Proceedings 1972, 030007 (2018); https://doi.org/10.1063/1.5041228 1972, 030007
© 2018 Author(s).
Study on plasmon absorption of hybrid Au- GO-GNP films for SPR sensing application
Cite as: AIP Conference Proceedings 1972, 030007 (2018); https://doi.org/10.1063/1.5041228 Published Online: 05 June 2018
Wan Maisarah Mukhtar, Farah Hayati Ahmad, Nurul Diyanah Samsuri, and Noor Faezah Murat
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Study on Plasmon Absorption of Hybrid Au-GO-GNP Films for SPR Sensing Application
Wan Maisarah Mukhtar
1,a), Farah Hayati Ahmad
1,b), Nurul Diyanah Samsuri
1,c)and Noor Faezah Murat
1,d)1Faculty of Science and Technology, Universiti Sains Islam Malaysia, Bandar Baru Nilai, 71800 Nilai, Negeri Sembilan, Malaysia
a)Corresponding author: [email protected]
Abstract. This study proposed the development of hybrid Au-GO-GNP films for the enhancement of plasmon absorption in SPR sensing. Several thicknesses of Au at t=40nm, t=50nm and t=300nm were sputtered on the glass substrate. The hybridization of bilayer and trilayer films were formed by depositing GO-GNP layers and GNP-GO layers on top of various thicknesses of Au coated substrates. UV-Vis spectra analysis was conducted to characterize the plasmon absorption for each configuration. The plasmon absorption was successfully amplified by employing hybrid trilayer Au- GO-GNP with the thickness of Au film was fixed at t=50nm. It is noteworthy to highlight that the employment of bilayer and trilayer configurations are the key success to enhance the SPP excitation. Au-GNP and Au-GNP-GO results no significant outcome in comparison with Au-GO and Au-GO-GNP. A redshift of the absorbance wavelength evinces the presence of GO on Au-GO sample and GNP on Au-GO-GNP sample due to the surface reconstruction. It is important to emphasize that not all bilayer and trilayer configurations able to enhance the plasmon absorption where no significant output was obtained with the hybridization order of Au-GNP and Au-GNP-GO.
INTRODUCTION
Water covers more than 70% of the surface of Earth and it is one of the purest symbol of health and nature. It is the most useful natural source that mainly influence our daily life routine. The importance of water covers many aspects of human lives such as in agriculture, transportation, lifestyle etc. [1]. As an essential source for survival, our body utilizes drinking water to facilitate digestion of food and adsorption of nutrients. Unfortunately, the quality of drinking water is threatened by pollution nowadays due to the contamination of harmful chemicals. The exposure of heavy ion metal to the human results many dangerous deceases such as kidney damage, hallucinations, reproductive effect, carcinogenicity and neurological effects [2]. Many scientific activities have been demonstrated to overcome this issue including the innovation of devices to absorb heavy metal ions and the introduction of portable sensor to detect the presence of plumbum (Pb) and its concentration in drinking water [3-6]. Early detection of Pb which is able to reduce the exposure risk of chronic deceases demands the development of a high sensitivity sensor. Until now, many studies have been conducted to enhance the performance of sensor for heavy ions metal detection by introducing various types of sensor such as optical sensor, electronic sensor and electrochemical sensor [7-9]. The advantage of optical sensor is the simplicity of its working principle which rely to the interaction between light and
medium to be detected. This sensor can be fabricated in a compact size which make it a suitable candidate for remote area application.
Surface plasmon resonance (SPR) sensor is one of the favorable optical sensor due to its simplicity. Its working principle is based on surface plasmon polaritons (SPP) excitation as an incident light strike the noble metal (i.e:
gold, silver, aluminium) resulting the presence of evanescent field due to the SPR phenomenon [10]. Recently, graphene attracts great attention in optical sensor due to its strength and high conductivity properties [11]. Many graphene based nanocomposites have been constructed towards applications in SPR sensor [12,13]. Graphene oxide (GO) is an atomically thin sheet of graphite that has commonly served as a precursor for graphene, but it excellent features has attracting researchers such as conductance changing as a function of extent of surface adsorption and large specific surface area make it a promising candidate in optical sensing field to detect variety of molecules ranging from gaseous to biomolecules [14,15].
Nanomaterials have received great interests in the field of biosensors due to their exquisite sensitivity in chemical and biological sensing [16]. Gold nanoparticles (GNP) are more favorable among the nanomaterials due to its stability, light scattering properties and large enhancement ability of the local electromagnetic field [17,18]. To amplified the SPR signal excitation, hybrid layers compose of noble metal and GO have been introduced recently [19,20]. However, it very important to monitor the thicknesses of gold and GO to avoid the diminishment of SPP excitation. Here, we proposed a hybrid trilayer configuration consisting of Au-GO-GNP to maximize the plasmon absorption. Throughout this work, various configurations have been developed to study the influence of materials’
order in enhancing the SPR signal. The effect of gold film thicknesses ranging from thin film to thick film are varied
at 40nm, 50nm and 300nm is also investigated.
MATERIALS AND METHODS
The chemicals used in this experiment are graphene oxide water dispersion 250 ml (0.05 wt% concentration, 0.125 g GO content) and commercial gold nanoparticles (gold colloid) with diameter of 50nm (stabilized suspension in citrate). All chemicals were used without further purification. Distilled water was used in experiments. Firstly, gold thin film with thicknesses of 40nm, 50nm and 300nm were deposited on top of borosilicate glass slide (Brand:
Corning, size 22mm x 15mm, refractive index, b=1.51) by using a magnetron sputtering machine (Brand: NSC 3000 Sputter Coater Nano Master Inc). Variation of gold thin film thicknesses were obtained by controlling the sputtering time within 5 minutes to 37 minutes at 5 x 10-3 atm. The percentage of oxygen was kept constant at 1%, meanwhile the distance between sample holder and target was maintained at 17cm during the sputtering process. Table 1 shows the control parameters of gold thin film sputtering process. Gold film thicknesses was then characterized by using reflectometer spectroscopy (Brand: Filmetrics (model: F50)). The operation of this instrument is based on light reflectance concept. A curve fitting technique utilizing the FILMapper software was then applied to measure the thicknesses of films.
TABLE 1. Control parameters for deposition of gold thin film with various thicknesses on glass substrate by using sputtering technique.
Film thicknesses,
t(nm)
Sputtering time, t (min)
Percentage of oxygen
(%)
Rotational direction of
sample holder
Power (W)
Distance between sample holder and target (cm)
Pressure (atm)
40 5
1 CW 50W 17 5.00E-03
50 7
300 37
Two types of hybrid bilayer configurations were developed by deposited thin layer of Graphene Oxide (Brand:
Graphenea) (Au-GO) and gold nanoparticles with diameter of d=50nm (Au-GNP) (Brand: Sigma Aldrich) respectively by applying drop-off technique on top of gold thin films with various thicknesses ranging from 40nm, 50nm and 300nm (Fig. 1(a)(ii) & (b)(ii)). After each drop of GO and GNP, the samples were dried at 70°C and 60°
C respectively. The development of hybrid trilayer configurations were performed by deposited one layer of GNP (Au-GO-GNP) and GO (Au-GNP-GO on top of bilayer films as illustrated in Fig. 1(a)(iii) and Fig. 1(b)(iii). All samples were characterized by using UV-Vis spectrometer (Brand: Jasco V-650) to study the plasmon absorption properties.
(a) Hybrid Au-GO-GNP
(b) Hybrid Au-GNP-GO
FIGURE 1. Various configurations of thin film structure (a) (i) single layer Au (a) (ii) hybrid bilayer Au-GO (a) (iii) hybrid trilayer Au-GO-GNP; (b)(i) single Au (b)(ii) hybrid bilayer Au-GNP (b)(iii) hybrid trilayer Au-GNP-GO.
RESULTS AND DISCUSSIONS
The thicknesses of gold thin films were controlled by monitoring the sputtering time. To ensure the deposition of gold thin film with thickness t1 = 40 nm, the sputtering time was tuned at ts1=5 min. Note that the actual thickness obtained was obtained as t1 = 40.56 nm with ±1.38% of accuracy from the expected thickness. At ts2=7 min and ts3 = 36 min, the thicknesses were resulted as t2 = 51.46 nm and t3 = 298.46 nm with ±2.83 % and ±0.52 % accuracies, respectively. For the simplification purpose, the values of thicknesses were rounded to the zero decimal places such as t1 = 40 nm, t2 = 50 nm and t3 = 300 nm. Based on UV-Vis characterization, it was found that value of absorbance became greater with the increment of gold thin film thicknesses from t1=40nm to t3=300nm as illustrated in Fig.
2(a). The single absorbance peak in the range of 500 – 520 nm is due to the characteristic surface plasmon absorption band of the gold thin films [21]. At t3=300nm, strong noise was observed probably due to the large thickness of film which was beyond the properties of thin films which behave as a bulk metal [22]. At t1=40nm, the plasmon absorption of gold thin film appeared at λ=510.9963nm with minimum absorbance of 0.57126 a.u. in the UV-Vis spectrum. The plasmon absorption shows an increment about 42.89 % (Absmin= 0.8163 a.u) as gold thin film’s thickness was raised to t2 = 50 nm. The absorption wavelength was blue-shifted to λ=506.0043nm, which is about 0.9769 % from the previous thickness. The appointment of bulk film, t3 = 300 nm witnessed a strong absorption, Absmin=3.2088 a.u without any changes on the absorbance wavelength. The employment of bilayer
hybrid configuration consists of Au-GO with numerous thicknesses of gold films affects the plasmon absorption properties as depicted in Fig. 2(b). When a very thin layer of GO was deposited on top gold thin film thickness, t1 = 40 nm (Aut=40nm-GO); the plasmon absorption occurred at λ = 514.0192 nm (red-shifting in comparison with single layer Aut=40nm) with minimum absorbance Absmin=0.5790 a.u. The absorption was occurred at λ=510.9963nm using the Aut=50nm-GO, resulting the increment of absorbance peak about 40.66% to Absmin= 0.8144 a.u. No significant changes were observed as the Aut=300nm-GO configuration was introduced where the Absmin was obtained as Absmin=3.2084 a.u at λ = 506.0043 nm.
In order to demonstrate the plasmon absorption of trilayer hybrid configuration (Au-GO-GNP), gold nanoparticles (GNP) with diameter of d = 50 nm was deposited on top of the Au-GO bilayer configuration as illustrated in Fig. 2(c). The optical properties of Aut=40nm-GO-GNP exhibits the same behaviour as single layer Au, where the value of Absmin and plasmon absorption wavelength are similar suggesting the probability of GO thin film layer was detached during the deposition process of GNP. As the thickness of gold thin film was increased to t2 = 50 nm forming a trilayer of Aut=50nm-GO-GNP, the plasmon absorption appeared at λ=512.9614nm with Absmin= 0.8215 a.u. For Aut=300nm-GO-GNP configuration, both optical properties (Absmin and absorption wavelength) remain similar with the bilayer hybrid of Aut=300nm-GO.
FIGURE 2. UV-Vis spectra for several types of thin film configurations (a) gold (Au) thin films (b) Au-GO (c) Au-GO-GNP
Figure 3 shows the UV-Vis spectra for several types of thin film configurations such as single gold (Au) layer only (Fig. 3(a)), hybrid bilayer of Au-GNP (Fig. 3(b)) and hybrid trilayer of Au-GNP-GO (Fig. 3(c)). The optical properties of single layer Au portrays the same behavior as per discuss in previous paragraph. When GNP was deposited on top of gold thin film with t1 = 40 nm producing hybrid bilayer Aut=40nm-GNP configuration, no significant changes were seen where the plasmon absorption remain as Absmin= 0.8163 a.u at λ = 510.9963 nm. The absorption wavelength was blue-shifted about 0.28 % to λ = 509.5378 nm experiencing the same amount of plasmon absorption as previous configuration when gold thin film thickness was raised to Aut=50nm-GNP. Note that for each configuration consisting 300 nm gold film, the minimum absorbance and wavelength were constant at 3.2084 a.u and 506.0043 nm respectively. The employment of hybrid trilayer Aut=50nm-GNP-GO exhibits slightly change on
0.00.5 1.01.5 2.02.5 3.03.5 4.04.5 5.05.5 6.0
300 350 400 450 500 550 600 650 700 750 800 Au
t=50nm t=40nm t=300nm
Absorbance, Abs (a.u) Absorbance, Abs (a.u)
Absorbance, Abs (a.u)
Wavelength, λ(nm) Wavelength, λ(nm)
Wavelength, λ(nm)
(a) (b)
(c) 0.00.5 1.01.5 2.02.5 3.03.5 4.04.5 5.05.5 6.0
300 350 400 450 500 550 600 650 700 750 800 Au-GO
t=40nm t=50nm t=300nm
0.00.5 1.01.5 2.02.5 3.03.5 4.04.5 5.05.5 6.0
300 350 400 450 500 550 600 650 700 750 800 Au-GO-GNP
t=40nm t=50nm t=300nm
plasmon absorption where the value of minimum absorbance (Absmin) decreased to 0.31 % resulting Absmin= 0.8132 a.u in comparison with the hybrid bilayer (Aut=50nm-GNP). For other thicknesses under this configuration, the properties are the same with hybrid bilayer Au-GNP.
FIGURE 3. UV-Vis spectra for several types of thin film configurations (a) gold (Au) thin films (b) Au-GNP (c) Au-GNP-GO.
The thickness of the gold films for various plasmonic applications may vary from a few tens to hundreds of nanometers due to differences in optical properties [22]. Figure 4 illustrates the analysis on the effects of gold thin film thicknesses with various configurations on plasmon absorption. At t1 = 40 nm, hybrid bilayer Aut=40nm-GO exhibits slightly greater plasmon absorption about 1.40 % in comparison with the single layer Au. As gold thin film thickness was increased to t = 50 nm, the Aut=50nm-GO-GNP indicates better absorption with 0.64 % of increment resulting the plasmon absorption of 0.8215 a.u. In contrary, the hybrid bilayer Aut=50nm-GO and trilayer Aut=50nm- GNP-GO experienced low absorption with the decrement of 0.40% probably due to the small part of Au layer which was detached from the substrate during the deposition process of the second and third layers. Strong absorptions (Abs = 3.2084 a.u) were observed for all configurations which consist of t3 = 300 nm gold thin film. This is because of the gold film’s physical properties that can be considered as bulk metal structure, allowing the visible spectrum at λ = 506.0043 nm to be absorbed. Higher absorbance results the diminished of evanescent wave where the surface plasmon resonance (SPR) will no longer took place [23].
Plasmon absorption is mainly affected by the properties of noble metal such as thicknesses and size of nanoparticle [24]. The development of hybrid layer is believed able to enhance the plasmon absorption which leads to the greater excitation of surface plasmon polaritons [25]. Absorption wavelength shifting is one of the important parameter to indicate the formation of hybrid layer as shown in Fig. 5. By setting the properties of single Au as reference, the comparison has been made. The employment of hybrid bilayer Aut=40nm, t=50nm-GO which forms a composite structure exhibits red-shifted of absorption wavelength proving that the GO layer are successfully deposited on top of gold coated substrates as illustrated in Fig. 5(a). The shifting is not occurred as the hybrid trilayer of Aut1=40nm-GO-GNP introduced indicating the possibility of two layers consisting of GO and GNP are eliminated from the gold coated substrate. However, with the increment of gold thin film thicknesses which
0.00.5 1.01.5 2.02.5 3.03.5 4.04.5 5.05.5 6.0
300 350 400 450 500 550 600 650 700 750 800 Au
t=50nm t=40nm t=300nm
0.00.5 1.01.5 2.02.5 3.03.5 4.04.5 5.05.5 6.0
300 350 400 450 500 550 600 650 700 750 800 Au-GNP
t=40nm t=50nm t=300nm
Absorbance, Abs (a.u) Absorbance, Abs (a.u)
Absorbance, Abs (a.u)
Wavelength, λ(nm) Wavelength, λ(nm)
(a) (b)
(c) Wavelength, λ(nm) 0.00.5
1.01.5 2.02.5 3.03.5 4.04.5 5.05.5 6.0
300 350 400 450 500 550 600 650 700 750 800 Au-GNP-GO
t=40nm t=50nm t=300nm
producing Aut=50nm-GO-GNP, the wavelength experiences red-shifting about 1.37 %. In comparison between hybrid Au-GO and Au-GO-GNP, the bilayer Au-GO configurations shows better stability due to the ability of GO to perfectly attach on the gold coated substrate. The appointment of hybrid Au-GNP and Au-GNP-GO witnessed the absence of wavelength shifting at t1 = 40 nm (Fig. 5(b)). However, hybrid bilayer configurations show better plasmon absorption than trilayer configurations (Au-GNP-GO) where the wavelength shifting is occurred at t2 = 50 nm. The Au-GNP absorb visible light due to SPR effect, resulting the enhancement of local electro-magnetic fields near the Au film [26]. According to these analyses, it can be concluded that the plasmon absorption can be optimized by using bilayer Au-GO due to the hydrophilic properties of GO [27]. Meanwhile, bilayer Au-GNP is not a suitable candidate for the enhancement of plasmonic signal which results the difficulty of the attachment between the two layers. To increase the stability between these two layers, an additional layer of polymer such as poly-L- lysine (amino-group) can be coated on top of gold layer before depositing the GNP to make the GNP adsorb to the surface of Au thin film [28].
FIGURE 4. Effect of gold thin film thicknesses and various thin film’s configurations on plasmon absorption.
FIGURE 5. Effect of gold thin film thicknesses and various thin film’s configurations on plasmon absorption wavelength (a) hybrid Au-GO-GNP (b) hybrid Au-GNP-GO.
Au Au-GNP
Au-GNP-GO Au-GO
Au-GO-GNP
0 0.5 1 1.5 2 2.5 3 3.5
1 2 3
0.57126 0.8163
3.20844
0.57126 0.8163
3.20844
0.57126 0.81318
3.20844
0.579 0.814393
3.20844
0.57126 0.82152
3.20844
Plasmon Absorption, Abs (a.u)
Gold thin film thicknesses, t (nm)
40 50 300
506 508 510 512 514
40 50
300
510.9963
506.0043 506.0043 514.019165
510.9963
506.0043 510.9963
512.96136
506.0043 Au Au-GO Au-GO-GNP
506 508 510 512 514
40 50
300
510.9963
506.0043 506.0043 510.9963
509.93783
506.0043 510.9963
506.0043 506.0043
Au Au-GNP Au-GNP-GO
(a) (b)
This experiment shows an excellent agreement with our previous works [29,30] where the optimum thickness for the excitation of SPP is occurred at t = 50 nm. Bear in mind that the SPP will be damped because of radiation damping into the glass if the metal is too thin. Meanwhile, the SPP will not efficiently excited due to absorption in the metal if it is too thick [23]. As illustrated in Fig. 6, the stability of plasmon absorption is demonstrated where the optical absorbance exhibits an enhancement as the hybrid bilayer and trilayer were introduced. This result proves the possibility of applying hybrid trilayer Au-GO-GNP in SPR sensor for the improvement of SPP excitation.
Nonetheless, the efficient hybrid trilayer sensor can only be achieved by maintain the film thickness at t = 50 nm using Au-GO-GNP configurations. It is noteworthy to highlight that the employment of bilayer and trilayer configurations are the key success to enhance the SPP excitation. Au-GNP and Au-GNP-GO results no significant outcome in comparison with Au-GO and Au-GO-GNP (Fig. 5). A redshift of the absorbance wavelength evinces the presence of GO on Au-GO sample and GNP on Au-GO-GNP sample probably due to the surface reconstruction [31].
FIGURE 6. Optimization of plasmon absorption and absorbance wavelength for single gold layer (Aut=50nm), hybrid composite bilayer (Aut=50nm-GO) and hybrid composite trilayer (Aut=50nm-GO-GNP).
CONCLUSIONS
This study demonstrates the significant of hybrid configuration using Au thin film based to optimize the plasmon absorption. The order of the composite materials in hybrid bilayer and trilayer greatly influenced the excitation of SPP. We successfully verify that the appointment of Au-GO-GNP by using a simple and low cost drop-off technique for the material deposition on Au film able to maximize the SPR signal by specify the Au thickness at t = 50 nm. It is important to emphasize that not all bilayer and trilayer configurations able to enhance the plasmon absorption where no significant output was obtained with the hybridization order of Au-GNP and Au-GNP-GO. For future work, polymer such as poly-L-lysine will be coated on top of Au film to enhance the attachment stability between Au film and GNP leading to the optimization of the SPR signal.
ACKNOWLEDGMENTS
The work was supported by Universiti Sains Islam Malaysia (USIM) and Ministry of Higher Education (MOHE) under grant FRGS/2/2014/SG02/USIM/03/1. Advanced Materials Research Centre (AMREC), Kedah, Malaysia is acknowledged for the research facilities.
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