Comparing the Fundamental Limit of Detection for Interferometric and Resonant Biosensors with Coherent Phase Read-Out

Integrated photonic biosensors are capable of detecting trace amounts of biochemical substances without time-consuming labeling steps [1]. Ring resonators and Mach-Zehnder interferometers (MZI) are among the most widely used sensor architectures. The latter can operate with a simple, fixed-wavelength source and have recently shown state-of-the-art limit of detections (LOD) (10−7–10−8 RIU) [2] by using the coherent phase read-out illustrated in Fig. 1(a), overcoming sensitivity fading and directional ambiguity [3]. Sensors using resonant structures often require a wavelength-swept source or broadband source combined with a spectrum analyzer [4]. However, they can also be interrogated with a coherent detection scheme and a fixed wavelength source, shown in Fig. 1(b), making them especially suited for cost sensitive point-of-care devices.