紅外局部表面電漿光學感測器對A549癌細胞之遷移

Abstract

基本上，一個感測器應該針對於至少一種目標物做出反應，此機制常被應用在污染物感測、藥物開發、科學研究以及醫療等用途上。一般而言，對目標做出快速的反應在感測器表現上是被需要的，有鑑於此，光學感測器在速度的表現上具有優勢。 在眾多種類的光學感測器中，表面電漿感測器在生物感測的相關應用上具高靈敏度，因該類感測器透過將光場集中於偵測用的表面，並以此光場來偵測目標物。幾十年來，表面電漿共振感測器因為其本身具備的高靈敏度而被廣泛應用於生物感測，直至今日該感測器被認定為最具代表性的光學感測器之一。另一方面，局部表面電漿感測器因製程技術的進步而在這幾年開始發展，而其結構通常以三維金屬為主，有別於表面電漿感測器的平面結構。局部表面電漿感測器在結構設計上的高自由性有利於其光學性質的調整，此外，其靈敏度在生物感測上幾乎不亞於表面電漿感測器。 因局部表面電漿共振的波長是由金屬結構的尺度來決定，不同尺度的金屬結構陣列亦產生不同的局部表面電漿共振。根據此特性，我們決定用不同尺度的金屬結構來製作局部表面電漿感測器，並將其中相同的金屬結構視作一感測單元。最終我們希望從頻譜中不同的局部表面電漿共振來同時執行複數感測單元的量測。 為了在感測過程得到高強度的光學訊號，我們採取金屬／絕緣體／金屬的結構於感測器，因為該結構所產生的局部表面電漿共振具有高效率的光吸收。藉由模擬工具的輔助，我們首先藉由模擬探討了結構上的調整如何影響感測特性，並且發現靈敏度可以兩種方式提升，分別為將圓結構替換為橢圓結構以及將該結構同時構築於上層金屬以及中間之絕緣體。 實驗中，我們首先製作能產生複數局部表面電漿共振之感測器，其中每個共振對應至感測器表面之特定感測區。接著我們藉由正光阻來局部地覆蓋感測器，這個動作是為了改變感測器表面之折射率，因為折射率變化為光學生物感測之要素。實驗結果指出，局部表面電漿共振之頻譜紅移與光阻於感測器表面之局部覆蓋狀況吻合，此階段實驗的成功次使我們接著執行預定的生物感測實驗。 在生物感測實驗中，A549癌細胞在一開始時被設置於感測器的一側，因次其遷移會朝向感測器的另一側，該細胞於感測器上的遷移會導致局部的折射率變化。在感測器方面，我們採用兩種不同尺寸的結構，因此感測器會在近紅外波段產生兩個不同的局部表面電漿共振。在細胞遷移的過程中，我們在量測頻譜上觀察到有序的局部表面電漿共振紅移，根據紅移的方式，我們推得細胞在感測器表面的遷移狀況，此推測在與實際的細胞與感測器影像比對後得到一致的結果。因次，我們亦在實驗上證實此局部表面電漿感測器可同時於複數感測區執行生物感測。

Basically, a sensor should specifically respond to at least one type of targets, being useful in applications such as pollutant detection, drug discovery, scientific research, medical care, etc. Generally speaking, fast response to the presence of targets is preferable when considering a sensor’s performance; regarding this, the sensors using light as probing signal, which is known as optical sensors, are advantageous for the purpose of fast speed. Among various types of optical sensors, plasmonic sensors are sensitive in biosensing applications through concentrating light near the target-specified surfaces, so adhesions of targets onto the surface can be easily detected by the concentrated light. Over decades, surface plasmon resonance (SPR) sensors have been widely utilized in biosensing due to their high sensitivity, regarded as one of the most typical optical sensors for the time being. On the other hand, localized surface plasmon resonance (LSPR) sensors start to grow in recent years due to the advance of fabrication methods. In contrast to the planar structures of SPR sensors, LSPR sensors are commonly characterized by metal structures finite in three dimensions. The great degree of freedom in designing the geometry of a LSPR sensor results in high tunability for controlling the optical properties of the LSPR sensor. Beside, LSPR sensors are as nearly sensitive as SPR sensors in biosensing applications. Since LSPR wavelengths are determined by the dimensions of metal structures, arrays of metal structures of different dimensions will also have their LSPRs different. Exploiting this unique characteristic of LSPR, we decided to make a LSPR sensor which includes metal structures of different dimensions, and structures with the same dimension would be regarded as a sensing unit. Hopefully, we want perform simultaneous measurements on multiple sensing units by their corresponding LSPRs by the spectrum measured. To create strong optical signals from the LSPR sensor, we adopted metal-insulator-metal (MIM) structure which is known for its efficient optical absorption based on LSPR. The effect of modifying the MIM structure on its sensing properties was also investigated by simulation, and we thereby found that sensitivity can be improved by replacing circular disk by elliptic disk and making disk structures in both the top metal layer and the middle insulator layer. Afterwards, we fabricated the LSPR sensor with multiple LSPR peaks in absorption spectrum, of which each LSPR corresponds to a distinct sensing region. Then we tested the LSPR sensor by coating PMMA masks over part of the sensor patterns in order to cause the refractive index change which is essential in optical biosensing. According to the measured results, we observed that spectral redshifts of LSPRs were in accord with the conditions of the LSPR sensors partly covered by the PMMA masks. The success in the test gave us the green light to proceed toward biosensing measurement with the LSPR sensor. The biosensing experiment incorporated A549 cancer cells, which were set to migrate from one side of the LSPR sensor. The migration of cells would cause the refractive index change on the sensor. The LSPR sensors were made of dual-sized patterns which corresponded to two distinct LSPRs in measure NIR spectra. As the cells migration preceded, orderly redshifts of LSPRs were observed. Based on order of LSPR redshifts, we derived the patterns of cell migration over the LSPR sensors. The derived cell migration was found consistent with the optical images of cells situated around the LSPR sensors, proving that the simultaneous optical sensing in at least two distinct sensing regions was feasible by a LSPR sensor.