Integrated photonic biosensors for time domain measurements

点击翻译按钮获取中文摘要

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.******