Schiff base and Lewis acid-base interaction-regulated aggregation/dispersion of gold nanoparticles for colorimetric recognition of rare-earth Sc3+ ions

The design and development of colorimetric sensors for recognition of rare-earth Sc3+ ions are very challenging and most of the reported methods are limited by poor sensitivity and serious interference. Herein, we unveiled a new colorimetric strategy for the sensitive and selective detection of Sc3+ based on the surface plasmon resonance properties of gold nanoparticles (GNPs). The key aspect of the proposed protocol is the selection of pyridoxal phosphate (PLP), an important biomolecule involved in many biological processes, both as an effective aggregation promoter of GNPs stabilized by cysteamine (Cyst-GNPs) and a strong chelator for the selective complexation of Sc3+. PLP can covalently bind to the Cyst-GNPs through the formation of a Schiff base, which neutralizes the positive surface charges, weakens the electrostatic repulsion force among the nanoparticles, thereby triggering the agglomeration of Cyst-GNPs. Owing to the intensive Lewis acid-base interactions, the introduced Sc3+ ions effectively compete with Cyst-GNPs to bind PLP, and the Cyst-GNPs tend to be dispersed in this case. A linear response from 0.1 to 3 mu M is achieved for Sc3+, and a detection limit down to 0.02 mu M is obtained. Negligible interfere from other ions is observed in this assay under identical experimental conditions.