Sub-ppm photonic biosensor for water quality control: feasibility study on zinc and lead detection

We evaluate the performance of a lab-on-chip optoelectronic device made with a polymeric waveguide and a hydrogenated amorphous silicon (a-Si:H) photodetector. Both components are integrated onto a compact BK7 glass substrate with a small surface area. The device is designed to measure the analyte concentration in a sample by detecting changes in light power caused by the interaction between the solution droplet and the guided radiation. This power variation is related to the sample's refractive index and is detected by an a-Si:H photosensor. Through numerical simulations in the red spectrum (632.8 nm), we assess the device's efficiency for detecting zinc (Zn) and lead (Pb). We analyze the interaction between the sample and the chip in various conditions and combine these findings with experimental data on the a-Si:H detector's performance. Our results indicate that the sensor exhibits a sensitivity down to 16.6 pA/ppm for Zn and 16.2 pA/ppm for Pb, with detection limits of 9.8 ppb for Zn and 10 ppb for Pb. This compact, cost-effective, and user-friendly chip demonstrates promising performance for applications in health and environmental monitoring, particularly in detecting heavy metals in water in real-time.