Engineering a Graphene Quantum Dot-Enhanced Surface Plasmon Resonance Sensor for Ultra-Sensitive Detection of Hg2⁺ Ions

The contamination of soil and water by heavy metals poses a significant environmental and public health concern worldwide. To address this issue, a novel graphene quantum dot (GQD)-based surface plasmon resonance (SPR) sensor is developed for the detection of mercury ions (Hg²⁺), a notorious heavy metal pollutant. The thiol and amine-functionalized GQDs (S,N-GQDs), synthesized via pyrolysis of citric acid and L-cysteine, are directly immobilized onto the SPR chip surface without prior pretreatment, demonstrating their potential as efficient sensing materials. The SPR sensor exhibits high sensitivity and selectivity toward Hg²⁺ ions, as confirmed by kinetic binding analysis and isotherm modeling. The Langmuir isotherm model, which accurately describes the interactions between Hg²⁺ and S,N-GQDs, provides insights into the sensor's mechanism of action. Furthermore, the sensor demonstrates robustness and reusability, with recoveries ranging from 98% to 104% over multiple cycles of analysis. Given the presence of contaminants in tap water, the developed sensor system holds significant importance for environmental monitoring and public health protection, offering a rapid, accurate, and cost-effective solution for detecting Hg²⁺ ions in such samples. Overall, this study represents a significant advancement in the field of heavy metal detection, with potential implications for addressing environmental pollution and ensuring water quality.