Integrated interferometer design for zero cross-sensitivity to matrix perturbations

Integrated photonic biosensors constitute an important technology for the growing point-of-care paradigm. Due to their high sensitivity and ample design freedom, interferometric sensors are an attractive embodiment for this application. In an effort to continuously lower the limit of detection and build ultra-precise devices, the sensitivity is steadily increased. Thereby, the limiting factors are optical loss, noise, and cross-sensitivities to external perturbations. We present a novel design method for integrated interferometers to inherently compensate for the cross-sensitivity to bulk perturbations in the matrix’s refractive index. We exploit that the analyte induces a localized effect when binding to the bioreceptors. By using different guided modes with engineered phase signals in the interferometer, we distinguish between analyte binding and bulk perturbations. To first order, their optical path may be designed such that the relative change due to bulk perturbations vanishes while sensitivity to the analyte is retained. We demonstrate this methodology via simulations of a Mach-Zehnder-interferometer for an immunosensor based on a silicon nitride platform. We show that this design may be easily incorporated in most conventional layouts, due to an excess of degrees of freedom, and could further be applied in fiber-based devices. In this manner, interferometers utilizing guided modes could compensate cross-talk for perturbations in the matrix’s temperature, pH, or general chemical composition. We believe that eliminating these limiting external impacts could help integrated photonic biosensors to overcome current issues with reliability and robustness.