利用共振型超材料實踐多功性感測，細胞成像，及光調變

Toward multiplex sensing, intracellular imaging, and light manipulating via resonant-type metamaterials

陳政光(Cheng-Kuang Chen)

指導教授 ： 嚴大任

國立清華大學/工學院/材料科學工程學系/博士(2014年)

https://doi.org/10.6843/NTHU.2014.00347

摘要

超材料為一種人造材料，利用單位尺寸小於波長的結構製造等效性質改變整體電磁特性。因此，金屬超材料在最近得到矚目，因為金屬在光學頻率下的自由電子集體震盪，使得金屬表面產生表面電漿共振。由於表面電漿共振通常取決於金屬幾何形狀及光學常數。相對於其他偵測器適合感測表面環境的改變。在本論文中，我們設計了一種電漿子超材料可共振於近紅外頻段下，並感測其周圍環境的折射率變化。再利用陣列化的電漿子超材料，得到免耦合，免標定，可量化的折射率影像。最後，利用超保水高分子(羧甲基纖維素)及poly-l-lysine 混合物增加該超材料保水度及增加表面對於細胞的親和力，進而量測活體細胞折射率影像。另外，我們也設計一個多共振頻段的多功性超材料可同時用於折射率量測及表面增強震動光譜。同樣地，該陣列化的電漿子超材料也可用於影像上的觀測，並同時得到待測物的多功性影像。我們發現，利用低共振模數的光譜，適用於接近表面的淺層觀測，如觀測官能基訊號；而高共振模數的光譜則適合用於深層的觀測，如細胞內部折射率平均值。這些特性可以幫助未來電漿子超材料用於快速生化檢測及活體細胞影像應用。
接下來，為了增強共振強度，我們嘗試利用介電質超材料作為研究主題。不同於金屬的自由電子形成表面電漿共振；介電質的表面增強效應來自於電磁場共振模的能量侷限作用。因此，我們設計一種Fano共振形式的介電質超材料，分別利用耦合相同/不同介電常數的介電質共振體對(dielectric resonator dimer)，得到了Fano共振，表面電磁場增強效應，以及慢光效應。這個結論可以使我們在未來利用介電質超材料應用於表面增強光譜。最後，為了研究介電質內部於中紅外下的的共振行為，我們將介電質超材料放置於二氧化釩表面上。利用溫度控制二氧化釩的介電常數，我們控制了介電質超材料的共振反應，並發現其共振反應會隨著二氧化釩的導電率增加而改變，類似一個RLC共振模型。利用這個方式，我們可以應用於光學感測，人造磁共振，負折率材料及隱形斗篷。

關鍵字

電漿子共振 ； 介電質共振器 ； 超材料 ； 細胞影像 ； 二氧化釩 ； 耦合 ； 表面增強光譜 ； 慢光效應

並列摘要

Metamaterials are artificial structures made of the repetition of subwavelength elements, often used in controlling and engineering the electromagnetic behavior of light as effective media due to quasi-static approximation. Metallic metamaterials are objects of high interest due to their ability to show resonances in the optical response given by the collective behavior of the conduction electrons near the surface of the metal, the so-called surface plasmons. These resonances depend strongly on the optical properties and geometry of the structures, providing a versatile tool to sensing surrounding information beyond conventional sensors. In this dissertation, we design a four-cut split ring resonator (4CSRR) performing plasmonic resonance in near infrared (NIR) region, supporting the capability in detecting their surrounding refractive index changes. A 4CSRR array is further utilized in refractive-index imaging application with quantitative, label-free ability and coupler-free measurements. By modifying a hydrogel (Carboxymethyl Cellulose)-poly-l-lysine mixture on 4CSRR-array to increase the surface adhesion and water retention for culturing cell, an in vivo intracellular observation is demonstrated due to the extension of cellular survival time. In addition, a compact multi-resonant plasmonic split ring resonator (MPSRR) array that is designed, for utilizing in both multi-band plasmonic resonance-enhanced vibrational spectroscopy and refractive index probing within a bandwidth of several octaves. Such a single-element plasmonic metamaterial can be used as a multifunctional sensing pixel that enables mapping the distribution of targets in thin films and biological specimens by enhancing the signals of vibrational signatures and sensing refractive index contrast. The low-order resonant modes in MPSRR present short-range detecting depth but high localized field for demonstrating plasmon-enhanced vibrational spectroscopy on the interface between target and MPSRR; in contrast, the high-order resonant modes exhibit long-range detecting ability with refractive index sensitive for realizing intracellular refractive index contrast observation. These unique features enable the plasmonic metamaterials to function as a rapid and accurate diagnosis, facilitating bio-sensing and imaging capabilities.
Next, to improve the resonant performance for the development in sensors, we apply dielectric-based metamaterial to provide control of the far-field radiation properties of nearby emitters due to the properties of coherent radiation of electric and magnetic modes. Unlike resonating plasmonic metamaterials are producing the oscillations of the free electron plasma, dielectric-based metamaterials rely on the fields and displacement currents induced in the resonator structure. In addition, we develop a Fano-resonant metamaterial by using dielectric-resonator dimers. By hybridizing two types of dielectric resonators, identical-dielectric-constant resonator dimer (IDR) and distinct-dielectric-constant resonator (DDR) dimer, respectively, we demonstrate Fano-resonance phenomena associated with a large group index (ng~354) and significant enhanced electromagnetic fields. Along this analysis, a comparison with metallic dimers has been carried out. This study opens new possibilities to perform field-enhanced spectroscopy and sensing with nanostructures made of suitable dielectric materials. Last, to control and investigate the resonant behaviors in dielectric-based metamaterial in mid infrared region, a highly symmetric dielectric metamtaterial is designed by germanium-based resonators array embedded with thermal-controlled functionality (vanadium dioxide, VO2). There are two distinct resonances respectively excited from particle and particle-substrate coupling. An enhanced reflectance change of resonant spectra occurs while raising temperature upto the VO2 phase-transition region, realizing the tunable resonances in mid infrared region. The tunibility significantly depends on the conductivity of vanadium dioxide layer, which agrees well to the simulation results. These results match to the model of an equivalent parallel RLC circuit, opening the feasibilities of optical sensing, artificial magnetism, perfect absorber and invisible cloak.

並列關鍵字

Plamonic resonance ； Dielectric resonator ； Metamaterial ； Intracelluar imaging ； Vanadium dioxide ； Coupling mode ； Surfaced enhanced spectroscopy ； Slow light effect

參考文獻

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