Plasmonic Sensor Based on Dielectric Nanoprisms
© The Author(s) 2017
Received: 17 July 2017
Accepted: 19 October 2017
Published: 3 November 2017
A periodic array of extruded nanoprisms is proposed to generate surface plasmon resonances for sensing applications. Nanoprisms guide and funnel light towards the metal-dielectric interface where the dielectric acts as the medium under test. The system works under normal incidence conditions and is spectrally interrogated. The performance is better than the classical Kretschmann configurations, and the values of sensitivity and figure of merit are competitive with other plasmonic sensor technologies. The geometry and the choice of materials have been made taking into account applicable fabrication constraints.
where n P is is the refractive index of the prism and β SP is the propagation constant of the surface plasmon generated at an angle of incidence θ r [12, 13]. The angle of incidence is typically quite large, and this fact sometimes limits the operational range and the operative easiness of the device. To overcome these constraints, several proposals for integrated SPR sensors have been analyzed in the literature. For example, very narrow grooves on thin metal films excite SPR under normal incidence conditions . However, the very narrow width of the grooves, in the range of 3 nm, may compromise the device fabrication. A similar approach that is achieved experimentally is the excitation of SPR using narrow metallic nanocavities . Another approach has been demonstrated theoretically using metallic gratings embedded in a glass substrate, obtaining spectral reflectances showing acute dips with widths or around 3 nm . These approaches allow normal incidence conditions, and the interrogation method is now based on the spectral variation of the reflected light. This is why sharp spectral features are very much appreciated to improve the performance of those sensors. We have chosen spectral reflectivity to allow reading the signal from the incidence side. Optical absorption enhancement produced by plasmonic nanostructures excited at normal incident conditions also provides an alternative to the Kretschmann configuration. This approach uses absorption as a sensing parameter for photo-detection [17, 18].
In this contribution, we propose to maintain normal incidence conditions for the incoming light and make use of funneling mechanisms in dielectric structures to direct light towards the locations where SPR are generated. High-aspect ratio dielectric gratings (HARDG) have been proposed to guide light into active layers of photovoltaic cells . The same concept is applicable to sensing devices redirecting light towards the metal-dielectric interface of interest. In this contribution, we propose the use of nanoprisms embedded on a dielectric substrate that is flat and adjacent to the metal-dielectric layer used for sensing through the excitation of SPR. This structure funnels the incoming radiation more efficiently, and therefore, plasmon resonances benefit from the increase in the energy reaching the plane of interest. The proposed devices perform better than similar structures and have geometrical and material arrangements that are feasible and fabricable with standard nanofabrication techniques.
The proposed material arrangement enhances the funneling effect already observed in some HARDG. The funneling and guiding effects in HARDG couples radiation towards the thin metal film where the SPR is generated.
A preliminary analysis considers a TM plane wave normally incident from the substrate side on the structure, without incorporating the metal layer. The amplitude of the incident electric field is 1 V/m. The results for this structure (see Fig. 1b) show how light is funneled and guided through the prism reaching the region where the metal-dielectric interface generates SPR. The field available at this region is stronger than that of the classical Kretschmann setup. This configuration shows a very strong plasmonic resonance at some specific wavelengths determined by the geometrical parameters of the structure. Additionally, the geometry of the device and the choice of materials are of great importance to properly operate the device. The geometry of the system is determined by the thicknesses of the buffer and metal layers, t BL and t M, and by the parameters defining the nanoprism (width and height, w G and H), and its spatial periodicity, P. The three-dimensional shape of the nanoprism is extruded from a two-dimensional design (see Fig. 1a). The prism region is divided into two portions, A and B, defining the groove array and the plane-parallel buffer layer. These two regions can be fabricated with the same material or using two materials. These two configurations will produce different spectral behaviors.
The analysis of the performance of this device is made by a computational electromagnetism package (COMSOL Multiphysics) based on a finite element method. The COMSOL model has been positively checked by evaluating the behavior of the classical Kretschmann configuration and comparing the numerical results against the analytical solution . The results obtained from the computation have been used to optimize the design with two main goals: to increase the field amplitude at the location where SPR are generated (metal-water interface) and to decrease the width of the reflectance dip associated with the resonance. This resonance is parameterized by the full-width-at-half-maximum (FWHM) of the reflectance.
This parameter is the ratio of sensitivity to the spectral width of the reflectance dip, and it is given as 1/RIU. This figure of merit already considers the capability of a given system to sense a given change in the location of the minimum of reflectance.
The evaluation of the field enhancement at the analyte location, and the reflectance FWHM at the peak, takes a quite long time using dedicated computers. This fact makes multidimensional optimization harder to solve. Besides, it would need the definition of a merit function combining properly the performance parameters. Then, we choose to take one parameter at the time to optimize the device. This strategy is well suited to understand how each geometrical parameter changes the overall performance of the device. Additionally, by monitoring and optimizing the field enhancement and the FWHM of the spectral reflectance, we also obtain higher values for the sensitivity and FOM. After optimization, we found that the geometrical parameters producing a better response are t BL = 100 nm, t M = 30 nm, w G = 325 nm, and H = 700 nm and a periodicity of P = 550 nm. These values have been obtained taking into account the fabrication constraints. This is why we have considered a step of 25 nm between successive values included in the optimization. We have also avoided the use of ultra-thin or ultra-thick layers that could compromise the feasibility of the device.
Results and Discussions
In the previous optimization process, we paid attention to the geometry of the device. Now, we analyze how a different choice of materials can improve the performance of the device. To do that, we distinguish between the nanoprism region and the plane-parallel layer separating the nanoprism from the metallic deposition (portions A and B in Fig. 1a). Then, the nanoprism material is still made of AZO to preserve the funneling characteristics and easiness of fabrication using spin-coating techniques. In region B, we replace AZO by GaP (optical constants obtained from ). This change solves the degradation of the sharpness of the reflectance peak when moving to a higher index (see Fig. 3a). When analyzing the final optimized design, we will resume this comparison. This behavior is well appreciated to improve the stability and reliability of the sensor.
For the optimum case of a bi-metal layer considered previously, we have plotted in Fig. 4b the spectral response for several values of the index of refraction. When comparing the spectral reflectances in Figs. 3a and 4b, we can also check how the sharpness of the spectral peak is maintained for a larger range in the index of refraction of the analyte. The reason for this improvement is the use of GaP in the fabrication of the buffer layer of the device. Figure 4c contains the values of sensitiviy and FOM for the optimized device that contains a bimetallic layer (25 nm silver/5 nm gold) and a GaP buffer layer. These values are higher than those presented in Fig. 3b where we had a single-metal gold layer and an AZO buffer layer. Figure 4c includes a vertical red line that signals the upper limit in the index of refraction where the design analyzed in Fig. 3 begins to degrade the sharpness of the spectral reflectance peak. The optimum structure has a maximum S B =450 nm/RIU, which is stable over a wide range of refractive index changes and corresponds to a FOM ranging from 160 to 220 1/RIU.
These values are better than some recent proposals that use graphene [28, 30, 35], silicon nanostructures , dielectric or metallic gratings [26, 29], oxide films , and metallic nanoprisms (gold coated over silver nanoprisms) . When not working at normal incident, some other plasmonic structures, as the gold mushrooms, show a higher sensitivity but a lower FOM .
This contribution presents a dielectric nanoprism extruded geometry that increases the available power to generate SPR at the sensing surface. Therefore, The SPR extends deeper within the analyte and, consequently, it increases its interaction volume. This characteristic should lower the limit of the detection of the system. The device works under normal incidence conditions. This makes possible an easier integration of the illumination and interrogation system, for example, placing the sensor at the tip of an optical fiber. The performance of the system is better than the previously reported results in this field. Sensitivity shows a plateau of around 450 nm/RIU for a large range in the index of refraction (from 1.33 to 1.39). The figure of merit, FOM, is also large and has a minimum value of 160 and a maximum of 220 1/RIU in the whole range of index of refraction between 1.33 and 1.43. To obtain these figures in performance, the design has been optimized by changing its geometrical parameters and the material choice. We have also considered materials that can be incorporated in a fabrication strategy involving spin coating. This allows the planarization of the device and does not interfere with the refraction index matching conditions. In this optimization, we have always keep in mind the feasibility of the fabrication, avoiding very narrow features that could compromise the device. The optimization in terms of the material choice has substituted AZO by GaP at the buffer layer to extend the range in the index of refraction from 1.40 to 1.43. Also, we have dimensioned a silver-gold bimetallic layer that takes advantage of the good plasmonic response of silver and the biocompatibility of gold. The nanoprism structure presented here improves operational easiness, allowing a normal incidence setup, and can be used for biomedical, environmental, or industrial applications involving liquids.
We would like to thank the Egyptian Cultural Office in Madrid, Spain.
This work was partially supported by the Egyptian Ministry of Higher Education missions section under Egyptian co-supervision grant at Univeristy Complutense of Madrid (Spain) and by the project TEC2013-40442 from the Spanish Ministerio of Economía and Competitividad.
Availability of Data and Materials
The optical constants used in this paper to characterize the materials have been extracted from reliable sources that are referred in the text.
Ethics Approval and Consent to Participate
Consent for Publication
The authors declare that they have no competing interests.
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.
- Stockman MI (2011) Nanoplasmonics: past, present, and glimpse into future. Opt Express 19(22):22029–22106.View ArticleGoogle Scholar
- Oh Y, Kim K, Hwang S, Ahn H, Oh JW, Choi Jr (2016) Recent advances of nanostructure implemented spectroscopic sensors–A brief overview. Appl Spectrosc Rev 51(7-9):656–68.View ArticleGoogle Scholar
- Langer J, Novikov SM, Liz-Marzán LM (2015) Sensing using plasmonic nanostructures and nanoparticles. Nanotechnology 26(32):322001.View ArticleGoogle Scholar
- Izquierdo-Lorenzo I, Alda I, Sanchez-Cortes S, Garcia-Ramos JV (2012) Adsorption and Detection of Sport Doping Drugs on Metallic Plasmonic Nanoparticles of Different Morphology. Langmuir 28(24):8891–901.View ArticleGoogle Scholar
- Esteban O, Alonso R, Navarrete MC, Gonzàlez-Cano A, Lightwave J (2012) Surface Plasmon Excitation in Fiber-Optics Sensors: A Novel Theoretical Approach. J. Lightwave Technol. 20(3):448.View ArticleGoogle Scholar
- King NS, Liu L, Yang X, Cerjan B, Everitt HO, Nordlander P, Halas NJ (2015) Fano resonant aluminum nanoclusters for plasmonic colorimetric sensing. ACS Nano 9(11):10628–0636.View ArticleGoogle Scholar
- Zhang Y, McKelvie ID, Cattrall RW, Kolev SD (2016) Colorimetric detection based on localised surface plasmon resonance of gold nanoparticles: merits, inherent shortcomings and future prospects. Talanta 152:410–22.View ArticleGoogle Scholar
- Kretschmann E (1971) Die Bestimmung optischer Konstanten von Metallen durch Anregung von Oberflächenplasmaschwingungen. Zeitschrift für Physik A Hadrons and nuclei 241(4):313–24.View ArticleGoogle Scholar
- Homola J (2003) Present and future of surface plasmon resonance biosensors. Anal Bioanal Chem 377(3):528–39.View ArticleGoogle Scholar
- Akowuah EK, Gorman T, Haxha S (2009) Design and optimization of a novel surface plasmon resonance biosensor based on Otto configuration. Opt Express 17(26):23511–3521.View ArticleGoogle Scholar
- Byun KM, Kim SJ, Kim D (2007) Grating-coupled transmission-type surface plasmon resonance sensors based on dielectric and metallic gratings. Applied optics 46(23):5703–708.View ArticleGoogle Scholar
- Maier SA (2007) Plasmonics: fundamentals and applications. Springer Science & Business Media LCC, New York.Google Scholar
- Huang DW, Ma YF, Sung MJ, Huang CP (2010) Approach the angular sensitivity limit in surface plasmon resonance sensors with low index prism and large resonant angle. Opt Eng 49(5):054403–54403.View ArticleGoogle Scholar
- Dhawan A, Canva M, Vo-Dinh T (2011) Narrow groove plasmonic nano-gratings for surface plasmon resonance sensing. Opt Express 19(2):787–813.View ArticleGoogle Scholar
- Polyakov A, Thompson K, Dhuey S, Olynick D, Cabrini S, Schuck P, Padmore H (2012) Plasmon resonance tuning in metallic nanocavities. Sci Rep 2:933.View ArticleGoogle Scholar
- Lee TW, Gray SK (2010) Remote grating-assisted excitation of narrow-band surface plasmons. Opt Express 18(23):23857–3864.View ArticleGoogle Scholar
- Liu N, Mesch M, Weiss T, Hentschel M, Giessen H (2010) Infrared perfect absorber and its application as plasmonic sensor. Nano Lett 10(7):2342–348.View ArticleGoogle Scholar
- Yu P, Wu J, Ashalley E, Govorov A, Wang Z (2016) Dual-band absorber for multispectral plasmon-enhanced infrared photodetection. J Phys D Appl Phys 49(36):365101.View ArticleGoogle Scholar
- Elshorbagy MH, Alda J (2017) Funneling and guiding effects in ultrathin aSi-H solar cells using one-dimensional dielectric subwavelength gratings. J Photonics Energy 7(1):017002.View ArticleGoogle Scholar
- Zhu P, Jin P, Shi H, Guo LJ (2013) Funneling light into subwavelength grooves in metal/dielectric multilayer films. Opt Express 21(3):3595.View ArticleGoogle Scholar
- Hailes RL, Oliver AM, Gwyther J, Whittell GR, Manners I (2016) Polyferrocenylsilanes: synthesis, properties, and applications. Chem Soc Rev 45(19):5358–407.View ArticleGoogle Scholar
- Dodge MJ (1984) Refractive properties of magnesium fluoride. Appl Opt 23(12):1980–85.View ArticleGoogle Scholar
- Treharne R, Seymour-Pierce A, Durose K, Hutchings K, Roncallo S, Lane D (2011) Optical Design and Fabrication of Fully Sputtered CdTe/CdS Solar Cells In: Journal of Physics: Conference Series, vol. 286., 012038.. IOP Publishing.Google Scholar
- Johnson PB, Christy RW (1972) Optical constants of the noble metals. Phys Rev B 6(12):4370.View ArticleGoogle Scholar
- Springer T, Ermini ML, Spackova B, Jablonku J, Homola J (2014) Enhancing sensitivity of surface plasmon resonance biosensors by functionalized gold nanoparticles: size matters. Anal Chem 86(20):10350–356.View ArticleGoogle Scholar
- Su W, Zheng G, Li X (2012) Design of a highly sensitive surface plasmon resonance sensor using aluminum-based diffraction grating. Opt Commun 285(21):4603–607.View ArticleGoogle Scholar
- Ouyang Q, Zeng S, Jiang L, Hong L, Xu G, Dinh XQ, Qian J, He S, Qu J, Coquet P, et al. (2016) Sensitivity enhancement of transition metal dichalcogenides/silicon nanostructure-based surface plasmon resonance biosensor. Sci Rep:6.Google Scholar
- Meshginqalam B, Ahmadi MT, Ismail R, Sabatyan A (2016) Graphene/Graphene Oxide-Based Ultrasensitive Surface Plasmon Resonance Biosensor. Plasmonics:1–7.Google Scholar
- Sun M, Sun T, Liu Y, Zhu L, Liu F, Huang Y, Chang-Hasnain C, (2016) Integrated plasmonic refractive index sensor based on grating/metal film resonant structure In: SPIE OPTO, 97570Q–7570Q.Google Scholar
- Wu L, Guo J, Dai X, Xiang Y, Fan D (2017) Sensitivity Enhanced by MoS2ŰGraphene Hybrid Structure in Guided-Wave Surface Plasmon Resonance Biosensor. Plasmonics:1–5.Google Scholar
- Luan N, Yao J (2016) High refractive index surface plasmon resonance sensor based on a silver wire filled hollow fiber. IEEE Photonics J 8(1):1–9.Google Scholar
- Mishra AK, Mishra SK, Gupta BD (2015) SPR based fiber optic sensor for refractive index sensing with enhanced detection accuracy and figure of merit in visible region. Opt Commun 344:86–91.View ArticleGoogle Scholar
- Liu BH, Jiang YX, Zhu XS, Tang XL, Shi YW (2013) Hollow fiber surface plasmon resonance sensor for the detection of liquid with high refractive index. Opt Express 21(26):32349–357.View ArticleGoogle Scholar
- Aspnes D, Studna A (1983) Dielectric functions and optical parameters of si, ge, gap, gaas, gasb, inp, inas, and insb from 1.5 to 6.0 ev. Phys Rev B 27(2):985.View ArticleGoogle Scholar
- Maurya J, Prajapati Y (2016) A comparative study of different metal and prism in the surface plasmon resonance biosensor having MoS2-graphene. Opt Quant Electron 48(5):1–12.View ArticleGoogle Scholar
- Paliwal A, Tomar M, Gupta V (2016) Table top surface plasmon resonance measurement system for efficient urea biosensing using ZnO thin film matrix. J Biomed Opt 21(8):087006–7006.View ArticleGoogle Scholar
- Martinsson E, Shahjamali MM, Enander K, Boey F, Xue C, Aili D, Liedberg B (2013) Local refractive index sensing based on edge goldcoated silver nanoprisms. J Phys Chem C 117(44):23148–154.View ArticleGoogle Scholar
- Shen Y, Zhou J, Liu T, Tao Y, Jiang R, Liu M, Xiao G, Zhu J, Zhou Z-k, Wang X, Jin C, Wang J (2013) Plasmonic gold mushroom arrays with refractive index sensing figures of merit approaching the theoretical limit. Nat Commun 4:2381.Google Scholar