Available online at www.sciencedirect.com
ScienceDirect Procedia Engineering 120 (2015) 865 – 869
EUROSENSORS 2015
A theoretical design of a biosensor device based on split ring resonators for operation in the microwave regime
Markus Wellenzohna,b, Martin Brandla,* a
Donau-Universität Krems, Center for Integrated Sensor Systems, 3500 Krems, Austria b FH Campus Wien, University of Applied Sciences, 1100 Wien, Austria
Abstract
In this theoretical study a biosensor device based on microwave split-ring resonators (SRRs) was developed and optimized for operation in the ultra-high frequency regime, by means of extensive finite element method (FEM) simulations. For sensor applications, the metallic surface will be bio functionalized and since SRRs are highly sensitive to the change in dielectric material the resonant frequencies shift proportional to the load of biomolecules. Our simulation results indicate a frequency shift of about 100.9 MHz for a hydrogel based bio-functionalization with a layer thickness of 3 μm. © 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license © 2015 The Authors. Published by Elsevier Ltd. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility the organizing committee of EUROSENSORS 2015. Peer-review under responsibility of theof organizing committee of EUROSENSORS 2015
Keywords:split ring resonator; metamaterials; microwave biosensor; finite element method simulation; microwave resonator;
1. Introduction In 1968 V. G. Veselago described a theoretical material in which the dielectric permittivity (ε) and the magnetic permeability (μ) are negative [1]. From a physical point of view such materials have a negative refractive index and form a left-handed system between the electric and magnetic field vectors and the wave-vector. Such theoretical materials produce several unusual exciting effects like an inversed refraction, an inversed Doppler and an inversed
*
Corresponding author. E-mail address:
[email protected]
1877-7058 © 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of EUROSENSORS 2015
doi:10.1016/j.proeng.2015.08.737
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Cherenkov effect. Therefore this class of materials are called metamaterials. At that time the generally accepted opinion was that nature does not provide materials including such unusual behaviours and thus the realization of metamaterials became a very challenging task over several decades. In 1999 Pendry et al. published a study where split ring resonator structures were investigated which reveal a negative magnetic permeability (μ< 0) [2]. Therefore a first milestone towards the realization of a metamaterial with a negative refractive index was achieved. A few years later Shelby et al. investigated a compound material which consist of a two-dimensional array of repeated unit cells of copper strips which produce a negative dielectric permittivity (ε < 0) and split ring resonator structures with a negative magnetic permeability [3]. Therefore the authors demonstrated the first experimental realization of a metamaterial by an experimental verification of the negative refraction index. In 2007 Pimenov et al. experimentally demonstrated that in nature also ferromagnetic materials with a negative refraction index exist and therefore they verified that nature does provide metamaterials [4], in contrast to the generally accepted opinion at that time. During the last years the research field of metamaterials has become very popular and a huge effort took place e.g. applications like cloaking devices [5] and super-lenses [6] which have the potential to overcome the diffraction limit of light, were intensively investigated. Additional metamaterials used in antenna systems or in sensor device applications were designed for operation in higher frequency regimes by a significant reduction of the structure sizes up to the limits of the fabrication processes. Microwave sensors based on metamaterials have also become very attractive in the field of chemical analytics and medical diagnostics due to a wide range of beneficial properties and to their multitude of applications, especially for development and realization of compact and high-sensitive devices. In particular, split-ring resonators designed for operation in the microwave regime combine the best features of microwave-resonators and metamaterials and therefore open the road for the development of compact and costefficient sensing devices e.g. [7-12]. For real sensor applications like the detection of diverse biomolecules and biomarkers, small parts of the metallic SRR surface will be bio-functionalized where only specific molecules can bind e.g. [13-15]. Proportional to the load of biomolecules the electric permittivity of the SRR gets changed and the resonant frequency is shifted. In a real bio-functionalization process the metallic surfaces of the biosensor devices are typically covered with a hydrogel where thicknesses of 100 nm up to 3 μm were usual used. Such a biofunctionalization process is also taken into account in our simulation models by the integration of a hydrogel layer on the top surface of the metallic SRR structures. To guarantee precise and correct simulation outcomes all simulation were performed with a state of the art finite element simulation method (FEM). The main focus of our study lies on the development of a theoretical biosensor device based on split ring resonator structures operating in the microwave regime. In order to assess the sensor functionality of our theoretical SRR devices we computed the scattering parameters depended on the frequency for several different hydrogel thicknesses (dhyd). In addition we calculated the resonant frequencies and the corresponding resonant frequency shift (Δfres) dependent on the hydrogel thickness. As final result we find that the resonant frequency shift strongly depends on the used hydrogel thicknesses and in the case of a hydrogel thickness of about 3 μm we fond a frequency shift of about 100.9 MHz which indicate a high sensor functionality of our SRR devices. 2. Sensor design and working principle Biosensor devices based on microwave resonator technology, such as SRRs, have the potential to be a key element for a rapid and cost-efficient direct molecule detection in pharmaceutical and clinical applications, due to
Fig. 1 A schematic diagram of a single, double and triple split ring resonator device with a five-layer composition (Cu/FR4/Cu/Ni/Au).
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the fact that they exhibit very sharp resonances at microwave frequencies with high quality factors above 1000, and on the basis of their circular shapes and rectangular wire structures (with dimension in the mm regime) PCB technology can be used for the device manufacture. In figure 1 a schematic diagram of three different split ring resonator devices are pictured. All different SRR devices investigated in this study are designed with a five-layer composition (Cu/FR4/Cu/Ni/Au) with layer thicknesses of (35μm/1.55mm/35μm/5μm/0.1μm).The sensor devices include two main components, the micro strip-line with an input and output port for the propagation of TEM modes, and the split ring resonator structures which consists of one or several metallic rectangular loops including a split at one side of each loop. At the input port a TEM mode in the microwave regime enters the sensor device and
Fig. 2 The S-parameter depended on the frequency for a SRR biosensor device with and without a bio-functionalization as well as the corresponding resonant frequencies and the expected resonant frequency shift (Δfres).
propagates along the micro strip-line where the mode can couple into the metallic loop of the SRR device. The fundamental mode can be easily understood in terms of a simple RLC circuit model where the ohmic resistance takes into account the material losses, the gap of the rectangular ring act as a capacitance and the loop is responsible for the inductance e.g. [9] and for further details of the coupling mechanism between the metamaterial elements of the split ring resonator devices see [16]. The working principle of the SRR biosensors can be easily demonstrated by analyzing the scattering parameters of the device. In a first step the transmission spectra S21 and the reflectance spectra S11 which both strongly depend on the frequency were computed. In a second step, the expected resonant frequency shift (Δfres), which is defined as the absolute value of the difference between the resonant frequencies in the case with and without a bio-functionalization Δfres=|fres,o-fres,w|, were calculated. Form a physical point of view the calculated resonant frequency shift is the most important indicator for the evaluation of the sensor functionality. Figure 2 plots a schematic diagram of the frequency dependent scattering parameter S for a SRR biosensor device with (blue curve) and without (red curve) a bio-functionalization and also illustrates the expected resonant frequency shift.
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3. Simulation results The major focus of our study is on the simulation and development of multi-functional biosensor operating in the microwave regime at ultra-high frequencies nearby 3 GHz, e.g. for the detection of diverse biomolecules and
Fig. 3 (a) FEM simulation results of the reflectance spectra S11 for a single rectangular SRR by the use of a hydrogel based biofunctionalization process with a hydrogel thickness of 500 nm (black curve) and without bio-functionalization (red curve), the resonant frequency is shifted about 8.9 MHz (from 3.5087 GHz to 3.4998 GHz); (b) absolute value of the resonant frequency shift (Δfres) dependent on the hydrogel thickness (dhyd).
biomarkers in human blood, saliva or urine. The final goal lies on the development of biosensor design were SRRs with different resonance frequencies are aligned along one waveguide for the detection of diverse biomolecules at one single sensor platform. In this study we modelled and designed single SRRs as well as double and triple split ring resonators with resonant frequencies in the ultra-high frequency regime (0.3 GHz - 4 GHz). All simulations within this study were performed by the use of the finite element method (FEM). For the bio-functionalization of split ring resonators typically hydrogels with refractive indexes of 1.45-1.5 and layer thicknesses of about 100 nm up to 3 μm were used. Figure 3(a) plots the calculated reflectance spectra S11 dependent on the frequency for the single SRR sensor device with a hydrogel based bio-functionalization (black curve), where a hydrogel layer thickness of 500 nm was investigated, and without bio-functionalization (red curve). As result we found that the resonant frequency is shifted about 8.9 MHz. In figure 3(b) the absolute value of the resonant frequency shift is plotted dependent on the hydrogel thickness. As major result we find that a hydrogel thickness of 3 μm on the top surface of our split ring resonator devices will lead to a frequency shift of about 100.9 MHz. Such huge frequency shifts easily can be measured and therefore our simulation outcomes indicate a high sensor functionality of the SRR biosensor devices.
4. Conclusion Sensors based on microwave split-ring resonators combine the best features of microwave-resonators and metamaterials and therefore open the road for the development of compact and cost-efficient sensing devices. In this study a SRR biosensor device was developed and optimized, by means of extensive finite element method (FEM) simulations. For sensor applications, the metallic surface will be bio functionalized and since SRRs are highly sensitive to the change in dielectric material the resonant frequencies shift proportional to the load of biomolecules. The obtained simulation results show that the resonant frequency shift strongly depends on the hydrogel thickness. In addition our simulation outcomes show huge frequency shifts of a few MHz up to about 100 MHz for SRR biosensors including a bio-functionalization. Therefore the simulation outcomes indicate a high sensor functionality of our biosensor devices.
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Acknowledgements This work was supported by the NFB project under the contract ID: LSC13-023. The work of Markus Wellenzohn was partly supported by the MA 23 (FH-Call 16) under the project “Photonik - Stiftungsprofessur für Lehre” as well as the NFB project under the contract ID: LSC13-023. References [1] V. G. Veselago, The electrodynamics of substances with simultaneously negative values of ε and μ, Sov. Phys. Usp. Vol. 10, No. 4 (1968) 509-514. [2] J. B. Pendry, A. J. Holden, D. J. Robbins, W. J. Stewart, Magnetism from Conductors and Enhanced Nonlinear Phenomena, IEEE Trans. Microwave Theory and Techniques, Vol 47, No 11 (1999) 2075-2084. [3] R. A. Shelby, D. R. Smith, S. Schultz, Experimental Verification of a Negative Index of Refraction, Science 292 (2001) 77-79. [4] A. Pimenov, A. Loidl, K. Gehrke, V. Moshnyaga, K. Samwer, Negative Refraction Observed in a Metallic Ferromagnet in the Gigahertz Frequency Range, Phys. Rev. Lett. 98, (2007) 197401. [5] J. B. Pendry, D. Schurig, D. R. Smith, Controlling Electromagnetic Fields, Science 312(2006) 1780-1782. [6] J. B. Pendry, Negative Refraction Makes a Perfect Lens, Phys. Rev. Lett. 85, 18 (2000). [7] H. J. Lee, J. G. Yook, Biosensing using split-ring resonators at the microwave regime, Appl. Phys. Lett.92, (2008) 254103-1 - 254103-3. [8] T. Chen, S. Li, H. Sun, Metamaterials Application in Sensing, Sensors 12 (2012) 2742-2765. [9] W. Withayachumnankul, K. Jaruwongrungsee, A. Tuantranont, C. Fumeaux, D. Abbott, Metamaterial-based microfluidic sensor for dielectric characterization, Sensors and Actuators A 189 (2013) 233– 237. [10] H. Torun, F. Cagri Top, G. Dundar, and A. D. Yalcinkaya, An antenna-coupled split-ring resonator for biosensing, Jour. of Appl. Phys. 116 (2014) 124701-1 - 124701-6. [11] V.Rawat, S. Dhobale, S. N. Kalea, Ultra-fast selective sensing of ethanol and petrol using microwave-range metamaterial complementary split-ring resonators, Jour. of Appl. Phys. 116 (2014) 164106 -1 - 164106-5. [12] J. Sun, M. Huang, J.J. Yang et al., A Microring Resonator Based Negative Permeability Metamaterial Sensor, Sensors 11, (2011) 8060-8071. [13] H.J. Lee, J.G.Yook, Biosensing using split-ring resonators at microwave regime, Appl. Phys. Lett. 92 (2008) 254103-1 - 254103-3. [14] H. J. Lee, H.S. Lee, K.H. Yoo, J.G. Yook, DNA sensing using split-ring resonator alone at microwave regime, Jour. of Appl. Phys. 108 (2010) 014908-1 - 014908-6. [15] H.J. Lee, J.H. Lee, S. Choi, I.S. Jang, J.S. Choi, H.I. Jung, Asymmetric split-ring resonator-based biosensor for detection of label-free stress biomarkers, Appl. Phys. Lett. 103 (2013) 053702 -1 - 053702-5. [16] F. Hesmer et al., Coupling mechanism for split ring resonators: Theory and experiment, Phys. Stat. Sol. (b) 244, No. 4 (2007) 1170-1175.
