Innovative SPR Sensing Method Based on Self-Assembled Porphyrin Structure for Hypersensitive Detection of Mercury Ion

Porphyrins are typical macrocyclic conjugated compounds widely utilized for designing high-sensitivity and high-selectivity chemical sensors. Porphyrin macrocycles can self-assemble into uniform two-dimensional (2D) nanostructures on gold films via π-π stacking, which extend horizontally along the X-Y plane and possess nanoscale thickness in the vertical Z-direction. The inherent electron-rich conjugated skeleton, 2D nanostructure-induced signal enhancement, and specific molecular recognition ability of porphyrins jointly satisfy the two core requirements of surface plasmon resonance (SPR) trace detection, namely target-specific recognition and signal amplification. This study leverages the integrated superiorities of porphyrin architectures to develop a high-sensitivity SPR strategy for heavy metal ion detection. Three key research contents are systematically explored herein: (1) sensitive layer fabrication, focusing on the optimization of preparation protocols for 2D porphyrin nanostructures on gold films, including the screening of material concentrations and solvents as well as the precise regulation of porphyrin aggregation; (2) detection performance evaluation, covering critical analytical parameters such as limit of detection (LOD), linear concentration range, and linear response property; and (3) practical performance assessment, involving the fabrication success rate, the detection repeatability and the storage stability of the sensitive layer, as well as the definition of application constraints including storage conditions, service life and standard operating procedures. The proposed porphyrin self-assembled structure achieves an ultra-low LOD of 1 pM for target detection, which is about 250-fold lower than the Class I limit for mercury in surface water (50 ng/L, GB 3838-2002).