Integrated photonic biosensors for time domain measurements

光作为其环境的非接触和高精度探针的能力为光学传感器提供了许多有吸引力的功能。虽然各种光学传感技术已经广泛用于生物医学，环境和工业领域的许多不同应用，但该技术尚未充分发挥其潜力。光学微谐振器代表了已知的最灵敏的光学传感器类别。它们通常是由非常低损耗的材料制成的球体或环形。光以“回音壁”模式的形式在这些装置的内部传播。表面特性的任何变化都会影响谐振频率，这是可以测量的。通过在表面涂上一层化学物质，可以特异性地与我们想要检测的分子结合，我们就可以形成一个传感器。当前回音壁模式传感器的挑战在于，它们需要通过使用可调谐激光器或光谱分析仪来测量谐振频率的变化来询问。这增加了成本和复杂性，并且代表了使用的显著障碍。我们的目标是开发非常灵敏和集成的多通道光学传感器，这些传感器只需要低成本和宽带光源和光电探测器。在2012年，我们展示了时域技术的应用，即相移腔衰荡光谱（PSCRDS）在硅微环中的生物检测。这种方法利用了这样一个事实，即表面结合事件也会改变光子在腔内停留的时间长度。这可以通过检测正弦调制光注入腔体时的相移来测量，仅需要适度（<100 MHz）的调制速率和简单的光电探测器。PSCRDS方法还具有比波长感测方法大得多的抗噪性的优点。虽然上面的演示使用了可调谐激光器，但我们现在将其扩展到白色光PSCRDS。我们将使用宽带光学光源，其将发射跨越腔的频率响应的一个或多个谐振峰的光谱。我们将在集成光子波导平台中实现这一点，这将使我们能够将输入和输出波导与每个谐振器集成在一起。输出波导将只拾取耦合到谐振器中的光（不需要光学调谐）。为了实现这一目标，我们必须克服在器件设计，建模制造，信号处理和封装方面的重大挑战。我们将通过检测水中的军团菌来验证我们的传感器（与工业合作伙伴合作），并将其作为传感器阵列用于肝癌和前列腺癌的调查（与医学研究人员合作）。该计划将为18名研究生和本科生提供高质量的多学科培训。

The ability of light to act as a non-contact and high precision probe of its environment provides optical sensors with many attractive capabilities. Whilst various optical sensing technologies are already widely used for many different applications in the biomedical, environmental and industrial sector, this technology has not yet achieved its full potential. Optical micro-resonators represent the most sensitive class of optical sensors known. They are typically spheres or toroids made from a very low loss material. Light propagates around the inside of these devices in the form of `whispering gallery' modes. Any change to the surface properties will influence the resonant frequency, which can be measured. By coating the surface with a chemistry that will bind specifically to the molecules that we are seeking to detect we can form a sensor.****The challenge of current whispering gallery mode sensors is that they need to be interrogated by using either tunable lasers or optical spectrum analysers to measure the change of resonant frequency. This adds to cost and complexity and represent a significant barrier to use. Our objective is to develop very sensitive and integrated multi-channel optical sensors that require only low cost and broadband light sources and photodetectors.****In 2012 we demonstrated the application of a time-domain technique, namely phase shift cavity ring down spectroscopy (PSCRDS) to biodetection in silica microtoroids. This approach makes use of the fact that a surface binding event will also change the length of time that a photon remains in the cavity. This can be measured by detecting the phase shift when sinusoidally modulated light is injected into the cavity, requiring just a modest (<100 MHz) modulation rate and simple photodetector. The PSCRDS approach also has the advantage of much greater noise immunity than wavelength sensing approaches. While the above demonstration used a tunable laser, we will now extend this to white light PSCRDS. We will use a broadband optical light source which will emit a spectrum spanning one or more resonant peaks of the cavity's frequency response. We will implement this in an integrated photonic waveguide platform which will allow us to integrate an input and output waveguide with each resonator. The output waveguide will pick up only the light that couples into the resonator (no optical tuning required).****In order to achieve this we must overcome significant challenges in terms of device design, modeling fabrication, signal processing and packaging. We will validate our sensors by testing for the detection of the legionella-causing bacteria in water (in collaboration with an industrial partner) and implement them as a sensor array for the investigation of liver and prostate cancers (in collaboration with medical researchers). The program will provide high quality and multidisciplinary training to 18 graduate and undergraduate students.******