SiN integrated MZI for high sensitivity biosensing

This work presents the development of label-free biosensors based on silicon nitride (SiN) photonic integrated circuits (PICs), using Mach–Zehnder interferometers (MZIs) as the core sensing elements. Two SiN platforms were optimized for operation at telecom (1550 nm) and visible (780 nm) wavelengths to evaluate the impact of waveguide geometry and wavelength on sensitivity and optical losses. Experimental measurements indicate propagation losses of approximately 1.0 dB/cm at 780 nm and 0.6 dB/cm at 1550 nm in TE polarization. An active control system based on integrated Ti/TiN/Ti heaters provides precise phase tuning, with a π-shift power of 57 mW at 780 nm and 120 mW at 1550 nm when deep trenches are used for thermal isolation. At 1550 nm, this value can be further reduced to 13.3 mW by adopting suspended heaters. Preliminary biological validation was carried out at 1550 nm using a conventional passive readout approach based on monitoring the MZI spectral response during a sandwich assay for C-reactive protein (CRP), achieving detection down to 5 pM.