Cation-Induced Assembly Confers Aqueous Stability on Magic-Sized Clusters for Enhanced Electrochemiluminescence

Magic-sized semiconductor clusters (MSCs) synthesized in organic solvents typically exhibit poor compatibility with aqueous media, which hampers electron transfer and leads to weak electrochemiluminescence (ECL), thereby limiting their biological and environmental applications. Here we report that cation-induced assembly confers aqueous stability on Cd₁₅Se₁₂ MSCs and simultaneously boosts their ECL efficiency. Using cysteine (Cys) as a stabilizing ligand, we prepared water-dispersible Cd₁₅Se₁₂-Cys MSCs and introduced multivalent metal cations (Mⁿ⁺=Zn²⁺, Cd²⁺, K⁺, Na⁺, Al³⁺) to electrostatically bind the surface carboxylate groups, thereby driving spontaneous intercluster assembly. The assembled Cd₁₅Se₁₂-Cys-Mⁿ⁺ MSCs exhibited a 10-fold enhancement in ECL intensity compared to unassembled counterparts, along with excellent signal stability over 1000 s of continuous operation. Mechanistic studies revealed that the cation valence critically dictates the assembly mode and ECL efficiency. Notably, Zn²⁺-modified assemblies functioned as highly efficient ECL emitters in a biosensing platform, enabling sensitive lactate detection in sweat with a broad linear range (0.01-50 mM). This work establishes cation-induced assembly as a general strategy to achieve aqueous-stable MSCs with enhanced ECL performance, opening new opportunities for their application in biosensing and environmental monitoring.