Low-Cost Grating-Based SPR Sensor for Detecting Waterborne Toxins

Overview

Over two billion people lack access to safe drinking water every year, exposing them to heavy metals, pesticides, and microbial toxins that cause cancer and developmental disorders. Biosensing—the detection of molecular interactions at the nanoscale—enables early toxin detection before concentrations become dangerous. However, traditional biosensors rely on fluorescent "labels" to signal binding, adding difficult preparation steps and preventing real-time monitoring, limiting their use for continuous water testing. Surface plasmon resonance (SPR) is a label-free optical sensing technology that identifies molecular binding by detecting refractive index changes at a metal-dielectric interface. This allows real-time measurements of biomolecular binding by tracking small changes in reflected light, making it possible to detect extremely low concentrations of pollutants. However, current SPR systems rely on prism- or grating-based sensors that need costly nanofabrication tools to etch nanoscale features, making them expensive and hard to reproduce outside of specialized labs. To address this, a novel low-cost grating-based SPR sensor was developed using DVD-R discs, which are affordable and already contain nanoscale grooves that diffract light. To create an optimal metal coating, silver and copper were tested for their strong plasmonic signals and to compare accuracy versus affordability. Each DVD-R disc was sputtered with Ag or Cu films of varying thicknesses (40-130 nm) to enable precise optical detection. A PLA microfluidic cell was designed in OnShape and 3D-printed to allow sample delivery across the surface, and reflectance spectra were measured at incident angles from 30° to 70° using an Avantes spectrometer. Results showed that (1) silver produced sharper SPR dips than copper, confirming system reliability and establishing silver as the baseline for further optimization, and (2) front-side illumination provided clearer resonance peaks, while back-side illumination gave weaker signals due to light scattering through the substrate. Thus, front-side illumination with silver coatings produced the most consistent and precise results. Using Ag-coated DVD-R discs for SPR sensors offers a rapid, reliable, and portable method for monitoring toxins in aquatic environments—especially in developing countries where chronic illnesses and developmental delays stem from the lack of pollutant testing equipment. Future studies will focus on stabilizing metal coatings, functionalizing surfaces to detect lead and Escherichia coli, and adding portability for on-site testing.

Competition history

• AJAS 2026 Category not listed

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