Sub-ppm Photonic Sensor for Detecting Heavy Metal Ions in Water

We assess the performance of a lab-on-chip optoelectronic device consisting of a polymeric waveguide and a hydrogenated amorphous silicon (a-Si:H) photodetector. These components are integrated onto a compact BK7 glass substrate with a small surface area. The device can measure the analyte concentration in a sample by detecting variations in light power resulting from the interaction between the solution droplet and guided radiation. This power change corresponds to shifts in the sample's complex refractive index and is detected by an a-Si:H photodiode. Leveraging on numerical simulations in the red spectrum (632.8 nm), we evaluate the device's efficiency in detecting four different heavy metals, zinc (Zn), lead (Pb), copper (Cu) and mercury (Hg). We examine the interaction between the sample and the chip under diverse conditions and combine these results with experimental data on the a-Si:H detector's performance. Our study evaluates a sensor’s sensitivity up to 16.6 pA/ppm for Zn, 16.2 pA/ppm for Pb, 25 pA/ppm for Cu and 17 pA/ppm for Hg with limits of detection of 9.8 ppb for Zn, 10 ppb for Pb, 6 ppb for Cu and 9 ppb for Hg. This compact, cost-effective, and userfriendly chip shows, therefore, promising performance for applications in health and environmental monitoring, particularly in real-time detection of heavy metals in water.