Comparative Study of Properties and Cytotoxicity of Eco-Friendly AgInS2, CuInS2, and ZnIn2S4 Quantum Dots under a Unified Experimental Framework

Abstract

Ternary quantum dots (TQDs) are promising cadmium-free nanomaterials for optoelectronic and biomedical applications; however, systematic comparisons among AgInS2 (AIS), CuInS2 (CIS), and ZnIn2S4 (ZIS) quantum dots remain limited because these materials are typically investigated using different synthetic protocols and characterization methodologies. Herein, we present a systematic comparative study of aqueously synthesized AIS, CIS, and ZIS quantum dots, enabling direct comparison of their optical, electrochemical, surface, and biological properties within a unified comparative framework. The nanocrystals exhibited similar sizes (4–6 nm), ensuring that the observed differences primarily reflected composition. Combined optical and electrochemical analyses revealed consistent trends in bandgap energies that were in good agreement with Mulliken electronegativity-based predictions. Despite their structural similarity, AIS showed long lifetimes and moderate emission efficiency, CIS exhibits suppressed photoluminescence due to dominant nonradiative recombination, whereas ZIS exhibited fast recombination dynamics associated with surface-dominated states. X-ray photoelectron spectroscopy established a direct relationship between composition, defect states, and electronic structure, while all QDs exhibited high cell viability (>90%), confirming their cytocompatibility. Overall, this unified comparative approach demonstrates that cation identity governs band alignment, recombination pathways, and cytocompatibility, providing practical guidance for the rational design of cadmium-free quantum dots for photocatalytic, optoelectronic, and biomedical applications.