Balanced plasmonic-augmented silicon photonic interferometric sensor for biosensing applications

We demonstrate a self-referenced plasmonic augmented photonic Mach-Zehnder interferometer (MZI) for biosensing applications, incorporating a 70 µm long aluminum plasmonic waveguide in both arms of a silicon nitride (Si₃N₄) MZI. Experimental results matched well with numerical simulations, showing extinction ratio (ER) values that exceed 55 dB and bulk sensitivity of 2322 nm/RIU. Wavelength stability measurements revealed 5×10^-3 nm thermal dependance for an ambient temperature fluctuation of 1-degree Celsius which is 50 times better than a conventional hybrid plasmo-photonic asymmetric MZI (aMZI) configuration, highlighting the robustness of the proposed balanced sensor scheme to ambient temperature fluctuations. Moreover, the experimental results show that the proposed sensor has a limit of detection up to 2.6 ×10^-6 RIU. Surface sensitivity of the proposed sensing transducer was evaluated through a C-reactive protein (CRP) surface saturation measurements and found equal to 10.45 nm/RIU for protein binding. Our validated simulation model was then benchmarked against a diverse set of target bio-analytes (proteins, viruses, bacteria, fungi) with surface sensitivity values reaching up to 2306 nm/RIU, indicating the sensor's heterogeneous detection capabilities. The presented self-referencing sensor configuration offers a cost-effective yet scalable and highly sensitive approach for multiplexed on-chip detection of diverse target analytes.