Synthesis and Surface Passivation of CuInS₂/MnS/ZnS Core–Multishell Nanocrystals, Their Optical, Structural, and Morphological Characterization, and Their Bioimaging Applications

Abstract

This article describes the design and characterization of CuInS2-based core–multishell nanocrystals with the appropriate architecture of MnS as the inner layer and ZnS as the outer layer. These are wider bandgap materials being used to develop the type-I core/shell structure. The designed CuInS2/MnS/ZnS colloidal nanocrystals were synthesized by a multistep hot-injection method. This material gains importance in view of its superior luminescence property. The existence of an efficient dual emission in both green and NIR regions, with high stability corresponding to 543 and 752 nm, highlights its utility as an efficient bioimaging probe, and its formation was confirmed with combined optical and structural characterization techniques. The photoluminscence study revealed that the optimum concentration of both shells was 0.1 mmol (by varying shell concentration from 0.1 to 0.5 mmol), since beyond this concentration the intensity of the shells was reduced gradually according to the concentration. The zinc blende structure was retained throughout the entire growth process with slight deviation in the diffraction peak positions. The oxidation states of the elements present in the system were confirmed by X-ray photoelectron spectroscopy studies. High resolution transmission electron microscopy observation confirmed multiple layers in the synthesized material. The prepared nanocrystals are made hydrophilic by encapsulation with F127 copolymer, and their cell viability studies revealed the material to be of negligible cytotoxicity. All together, the study strongly suggests that the green and NIR emitting CuInS2/MnS/ZnS core–multishell nanocrystal, designed and synthesized in this study, is an attractive candidate as a biological contrast agent.