Grating and waveguide plasmonic sensors

飞秒激光产生的光脉冲非常短，同时又非常强大。当这样的激光向下聚焦时，可用的强度能够改变透明材料的结构，甚至可以从表面烧蚀材料。我们已经对激光脉冲与光学玻璃的相互作用有了一定的了解，因此，根据脉冲参数，我们可以制造光波导、耦合器、弯曲和光栅结构，甚至可以在微米尺度上加工表面以改变其拓扑结构。在这个项目中，我们希望把这些能力结合起来，创造一种通用的等离子体传感技术。表面等离子体激元是金属薄膜中自由电子的振荡，它们可以利用光在靠近金属薄膜的波导中传播的能量产生。重要的是，从光到等离子体激元的能量转移只发生在一个明确的波长上，这在很大程度上取决于等离子体激元电场延伸的金属膜上方一微米厚区域的折射率。通过向金属薄膜附近的波导发射一束广谱的光，并注意到设备吸收的波长，就可以非常准确地测量金属上面的折射率。如果在金属膜上涂上特定的化学或生物化学涂层，则传感器可以检测到特定的物种。在本提案中，我们计划研究适体在这方面的使用。适配体是一种寡核苷酸序列，可以设计成与特定分子、蛋白质、DNA序列甚至细胞结合，提供了一种高度灵活的传感技术。该技术的另一个应用是作为监测细胞运动和生长的手段。细胞在特定的点接触表面，如果细胞被放置在支撑等离子体的金属薄膜上，光将从接触点的等离子体场散射出去。这种光可以用显微镜观察，这将允许随着时间的推移跟踪细胞的运动。细胞对不同表面拓扑的反应不同，fs激光可用于修改传感器表面，以研究不同表面拓扑对细胞运动和生长的影响。

Femtosecond lasers produce pulses of light which are extremely short and at the same time extremely powerful. The intensities available when light from such a laser is focussed down are capable of modifying the structure of transparent materials or even ablating material from the surface. We have developed an understanding of the interaction of fs laser pulses with optical glasses so that, depending on the pulse parameters, we can create light waveguides, couplers, bends and grating structures or even machine the surface to alter its topology on a micron scale.In this project we wish to bring these capabilities together to create a generic plasmonic sensing technology. Surface plasmons are oscillations of the free electrons in a thin metal film and these can be generated using the energy from light travelling in a waveguide close to the metal film. Importantly, the transfer of energy from the light to the plasmon only occurs at a well defined wavelength which depends strongly on the refractive index in a micron thick region above the metal film where the electric field of the plasmon extends. By sending a broad spectrum of light though the waveguide near the metal film and noting which wavelength is absorbed by the device it is possible to measure the refractive index above the metal very accurately.If chemical or biochemical specific coatings are applied to the metal film then the sensor can detect specific species. In this proposal we plan to investigate the use of aptamers in this regard. Aptamers are oligonucleotide sequences, which can be designed to bind to specific molecules, proteins, DNA sequences or even cells, providing a highly flexible sensing technology.An additional application for the technology is as a means of monitoring cell movement and growth. Cells contact a surface at specific points and if a cell is placed on the plasmon supporting metal film, light will be scattered from the plasmon field at the points of contact. This light may be viewed using a microscope which will allow the movement of the cells to be tracked over time. Cells respond differently depending on surface topology and the fs laser can be used to modify the sensor surface to enable studies of the effect of different surface topologies on cell movement and growth.