Active Coordination Sensitization via Thermo- and pH-Regulated Molecular Recognition for Ultrasensitive SERS Quantification of Cu2+ and Zn2+

Accurate quantification of trace metal ions in complex biological matrices remains challenging because of severe matrix interference and sluggish metal–ligand coordination at ultralow concentrations. Herein, we report an active coordination sensitization strategy for surface-enhanced Raman scattering (SERS)-based metal-ion analysis by modulating molecular recognition kinetics and interfacial chemical equilibria. Unlike conventional approaches relying primarily on plasmonic substrate engineering, this strategy directly tunes coordination chemistry through temperature and pH control. For Cu2+ detection, thermal activation at 50 °C accelerates tetrakis(4-carboxyphenyl) porphyrin (TCPP) metalation, yielding limits of detection (LODs) of 2.94 × 10−11 M in water and 2.01 × 10−10 M in serum, representing 28- and 12-fold improvements, respectively. For Zn2+ sensing, pH regulation promotes thiol-functionalized terpyridine (TPY)–Zn2+ coordination, giving LODs of 2.86 × 10−13 M in water and 1.0 × 10−11 M in serum, with 35- and 18-fold improvements, respectively. Density functional theory (DFT) calculations provide insights into temperature- and protonation-dependent coordination behaviors. Integrated with a microfluidic SERS platform, the method achieved serum recoveries of 97.9–102.1% with relative standard deviations (RSDs) below 4.20%, demonstrating accurate and reproducible analysis while advancing SERS sensing from passive plasmonic signal amplification toward active regulation of molecular recognition chemistry.