Finite-Difference Time-Domain Simulation of Localized Surface Plasmon Resonance Adsorption by Gold Nanoparticles Wen-Chi Lin1, Wen-Chen Lin1, Cheng-Lun Tsai2, and Kang-Ping Lin1,* 1 2
Department of Electrical Engineering, Chung Yuan Christian University, Chung Li, Taiwan Department of Biomedical Engineering, Chung Yuan Christian University, Chung Li, Taiwan
[email protected]
Abstract— Using optical sensors to transform light-matter interaction into optical signal has become more and more popular. This is especially true for the fields that require ultrafast responsibility and remote sensing, such as environmental monitoring, food analysis and medical diagnosis. Among numerous optical sensors, plasmonic nanosensors are of great promise due to their spectral tunability and good adaptability to modern nanobiotechnologies. Localized surface plasmon resonance (LSPR) is the electromagnetic resonance of conducting electrons on metal surface, and it is very sensitive to the variation of environmental refractive index. The LSPR is considered as a useful sensing parameter that provides very good biochemical information. The SPR absorption peak also can be adjusted by changing the nano structure on the LSPR biological sensor chip. In this study, Finite-Difference TimeDomain (FDTD) was applied to simulate the LSPR absorption peak. Four model parameters were modified to study the LSPR sensing sensitivity: (a) the incident light wavelength, (b) the diameter of nanoparticle, (c) the spacing among nanoparticles, and (d) the height of nanoparticle. The simulation results show that 860nm is the best wavelength for the LSPR adsorption measurement. The optimal diameter of nanoparticle is 150nm, and the nanoparticle spacing is 90nm. Higher nanoparticle height provides higher sensitivity, but it also depends on the process capability. The FDTD simulation can be a useful tool to design a LSPR nanoparticle biosensor. Keywords—Localized Surface Plasmon Resonance (LSPR); Biosensor; nanoparticles; Finite-Difference Time-Domain (FDTD) I. INTRODUCTION
Spectroscopy is applied in the fields of Biophysics / Biochemistry basic research, new medical diagnostic methods development, disease treatment control and structure characteristics identification which monitor the core effect of molecular structure change in Biophysical / Biochemical spectrum. Therefore, a lot of sensing technologies are applied in biological sense such as (Surface Enhanced Raman Scattering; SERS)[1-4] and (Surface Plasmon Resonance; SPR)[5-7], which is a good technology to provide biological sense information.
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When a metal layer changes into metal nanostructure, very strong electric field amplification effect will appear between metal nanoparticles that is Localized Surface Plasmon Resonance (LSPR) [8]. The LSPR absorption wavelength positions change with the particle sizes because the metal nanoparticles are disturbed by visible light source to disturb the electron inside particles while instant polarization appeared. The polarized electrons cause harmonic oscillation inside the nanoparticles. When the nanoparticle size is smaller, the oscillation frequency is faster and this means that the range of visible optical wavelength absorption is shorter. When the nanoparticle size is bigger, the oscillation frequency is slower and this means that the range of visible optical wavelength absorption is longer. In addition, the LSPR absorption wavelength are sensitive to the particle shape and surrounded environment such as the temperature [7], particle size and particle space [6] and so on. In recent years, a lot of metal particle arrays have been used to enhance the SPR sensitivity and there are a lot of methods to produce metal nanoparticles such as e-beam lithography (EBL) [10], nanoimprint lithography (NIL) , anodic aluminum oxide (AAO) [12], nanosphere lithography (NSL) [1-4] and oblique angle deposition (OAD)[6, 13],etc. However, how to find the optimal condition to increase the biosensor sensitivity is important. The FDTD simulation technology was applied to change 4 different conditions, which are incident wavelength, nanoparticle diameter, nanoparticle space and height that the optimal condition could be found to apply in biological sensing. II. SIMULATION
In this study, Rsoft was applied for simulation. The FDTD simulation parameters with incident light wavelength of 300~900 nm and the CW excitation light source. The metal was setting to gold. The combination of both the Drude model and two Lorentz poles was used in the FDTD calculation. The uniaxial perfectly matching layer was applied as an adsorbing boundary. Fig. 1 showed the LSPR simulation conditions diagram. The LSPR absorption peak
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© Springer International Publishing Switzerland 2015 J. Goh and C.T. Lim (eds.), 7th World Congress on Bioengineering 2015 IFMBE Proceedings 52, DOI: 10.1007/978-3-319-19452-3_37
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Finite-Difference Time-Domain Simulation of Localized Surface Plasmon Resonance Adsorption by Gold Nanoparticles
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was w different ddue to change the nanopaarticle shape, size, sp pace and heighht. Where D is the nanopartiicle diameter and s is the sspace beetween nanoparticles, t is nanoparticles n height h andȪiis the wavelength w of iincident light source. The optimal o condiitions were w simulatedd as the follow wings. 1. Changees of the waveelength of incident light souurce. 2. Changees of the gold nanoparticle diameters. 3. Changees of the gold nanoparticle space. 4. Changees of the gold nanoparticle heights.
Figurre 2. Diameter Ch hange in Differennt Nanoparticle Sizes S and the LSPR PR Absorrption Wavelengtth Change Diagraam.
Figgure 1. LSPR Sim mulation Condition n Diagram
IIII. RESULTS AND A DISCUSSIOON
This study,, initially invvestigated the wavelength positio on of the LS SPR absorptioon peak when n the nanopar article sizzes were diffferent. In Figgure 2, it shows that the L LSPR ab bsorption peakk appeared inn the wave baand of 800~9000nm when w the nanopparticle sizes changed c from m 100nm to 50 0nm. In n reality, LED D incident lighht source is difficult d to be captu ured when thee wavelength is i lower than 400nm; thereefore, th he LSPR absoorption wavelengths between 800nm~9000nm were w simulatedd and the inciddent waveleng gth changed eevery 10 0nm displayedd in Figure 3. In Figure 3, it shows thhat the absorp ption could rreach 12 2.5% when tthe nanopartiicle diameter was 150nm m and prroduce 860nm m LSPR resonnance waveleength which ccause th he maximum aabsorption. Inn addition, wh hen the nanopparticle diameter chhanged to 1000nm, the LSP PR would movve to sh hort wavelenggth with absoorption wavelength of 84 0nm, which w showed tthat the LSPR R absorption wavelengths w w would ch hange with thee nanoparticlee sizes and were sensitive.
Figurre 3. Diameter Ch hange in Differennt Nanoparticle Sizes S and the LSPR PR Absorrption Wavelengtth Change Diagraam and the wavelength change is 10nm m.
When W the LSPR absorpttion wavelen ngth closed to 800~ ~900nm was confirmed, thhe nanoparticle diameter sizzes and the changes of o LSPR absoorption wavellength were furfu ther discussed. From F Figure 44, it shows th hat when the nan nopaarticle diametters changed w with 10nm an nd the diameeter was 150nm, the LSPR L absorptiion was the op ptimal; therefoore, the nanoparticle n diameter d of 1550nm was optiimal.
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Fig gure4, Diameter Change in Differrent Nanoparticlee Sizes and the LSSPR Ab bsorption Waveleength Change Diaagram when the Nanoparticle N diam meter sizzes are 100nm~2000nm and the chaange space is 10n nm.
Figurre6. Different golld Nanoparticle Sp Space and the LSP PR Absorption Waveelength Change Diagram D when thee Nanoparticle diiameter is 150nm m and the t thickness is 50 0nm
As A mentioned ppreviously, thhe LSPR abso orption waveleength po osition and thhe space betw ween particles changed withh the paarticle size. Inn Figure 5, when w the gold nanoparticle n sspace ch hanged with 110nm and thee space was 90nm, 9 the opttimal LS SPR absorpttion appearedd when the wavelength was 86 60nm that shoows the optim mal result app peared on the gold naanoparticle wiith space of 90nm. 9 In add dition, to applyy the LS SPR absorptioon peak dada with the wav velength of 8660nm from Figure 5 tto Figure 6 thhat shows wheen the nanopar article diiameter was 150nm, thickneess was 50nm m and space waas 90 nm m, the optimiized LSPR abbsorption peak k appeared onn the wavelength w of 8860nm.
Finaally, to changee the nanopartticle height, itt was found thhat the higher h the gold nanoparticcle height wass, the higher the t LSP PR absorption was. Howev ever, on accou unt of the Naano proccess, the higheer the height oof the gold naanoparticle was, w the higher h the Nao o process insta tability was that was the ressult of sh hadow effect which limiteed the height during the baack end process to deposit the meetal on the chip surface [3]. Therrefore, the hig ghest height to produce thee biochip duriing proccess was consiidered. IV. CONCL LUSIONS
By B the applicaation of FDT TD simulation n technology,, it was found that th he optimal abssorption peak k appeared whhen the LSPR L wavelength was 8600nm with nano oparticle diam meter of o 150nm and space of 90nm m. In addition n, the higher the t gold d nanoparticle was, the betteer the result was w that depennds on th he process cap pability. Its Inndex of refracction was diffferent with differen nt detected taarget. The siimulation ressult nce to design rrelevant chip format f when the t coulld be a referen LSP PR detected tarrget and chip structure chan nged.
ACKNOWLEEDGMENT Fig gure5. Differentt gold Nanopartticle Space and the LSPR Absoorption Wavelength Wa Changge Diagram whenn the Nanoparticlle size is 50nm~2250nm an nd the space channge between 50nm m~150nm is 10nm m.
The T authors arre grateful foor the financial support froom the Hsinchu Scieence Park, Miinistry of Sciience and Tecchnolo ogy under graant number 1103MG15, an nd the Southeern Taiw wan Science Park, P Ministryy of Science and a Technoloogy undeer grant numb ber BY-23-08--54-103.
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Finite-Difference Time-Domain Simulation of Localized Surface Plasmon Resonance Adsorption by Gold Nanoparticles
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Use macro [author address] to enter the address of the corresponding author: Author: KangƮPing Lin Institute: Department of Electrical Engineering, Chung Yuan Christian University, Street: 200 Chung Pei Road City: Chung Li Country: Taiwan Email:
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