Infrared Localized Surface Plasmon Optical Sensor for A549 Cancer Cells Migration
|關鍵字:||表面電漿共振;感測器;細胞;surface plasmon resonance;sensor;cells|
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.
|Appears in Collections:||Thesis|