Real-time detection of mercury ions in environmental water conditions by using a differential phase SPR system equipped with a repeatable SPR chip

Contamination with heavy metal ions is one of the most widespread and harmful sources of environmental pollution. In this work, we developed a rapid, reproducible, and highly sensitive biosensor based on the surface plasmon resonance (SPR) effect to detect mercury ions (Hg 2+ ) in DI water, tap water, and rainwater. A homemade differential phase SPR biosensor was designed and constructed, with phase shifts in the SPR interference spectrum extracted using a windowed Fourier transform (WFT) method. Custom software was developed to extract the phase shift values of the SPR system in real-time. The sensing surface of the SPR system is an Au film functionalized with thymine-1-acetic acid (T-COOH), where the thymine group specifically binds to Hg 2+ , forming a stable T-Hg 2+ -T structure. By integrating a microfluidic chip with the sensing surface, the SPR system achieves a detection limit for Hg 2+ of 8.59 × 10 −4  mg/L in DI water, 7.26 × 10 −4  mg/L in tap water, and 8.82 × 10 −4  mg/L in rainwater, with excellent specificity compared to ions like Ca 2+ , Cd 2+ , Co 2+ , Cu 2+ , Fe 2+ , Mg 2+ , and Pb 2+ . Additionally, L-cysteine is used for the regeneration of the SPR sensor, which shows no significant loss of sensitivity after 40 cycles. Therefore, the differential phase SPR biosensor holds great promise for future applications in environmental monitoring, drinking water safety, and healthcare.