Synthesis of Ternary I-III-VI Quantum Dots for Biomedical Applications

Colloidal semiconductor nanocrystals, also known as quantum dots (QDs), have become a topic of extensive scientific research in recent decades, due to their unique optical and electronic properties, with applications ranging from solar cells to nanomedicine. Over many years, QD research was dominated by cadmium-based binary II-VI type systems. While these materials display excellent photoelectronic properties, the toxic nature of the heavy metals presents a major drawback, particularly for use in biomedical applications. Recently, ternary I-III-VI systems, e.g. AgInS₂ (AIS) and CuInS₂ (CIS), have emerged as promising alternatives to these toxic heavy-metal containing systems. These systems also offer several distinct advantages compared to II-VI based systems, such as greater tunability, large Stokes shifts and enhanced stability, though as of yet, their synthesis, properties and biocompatibility have been much less studied than those of their II-VI counterparts.
Herein we present the synthesis of various AIS and CIS based QDs, with varying chemical compositions, synthesised via both organic and aqueous approaches. Organic QDs were synthesised via a hot injection approach, and a post synthetic aqueous phase transfer method was developed. QDs were also synthesised directly in aqueous media, resulting in new chiroptically active QDs. Quaternary zinc shelled QDs were also produced, as well as QDs with differing Cu/Ag:In ratios. All particles showed photoluminescence (PL) in the visible-NIR region, corresponding to the optical window of biological tissue. AIS QDs showed high PL quantum yields of up to 40%, while the PL of CIS QDs exhibited high thermal sensitivity. The cellular uptake capability and cytotoxicity of the QDs was tested by in vitro cell studies, using various cell types, including both healthy and cancerous human and animal cell lines. The potential of the AIS QDs as fluorescent probes in biomedical imaging was demonstrated by in vitro cell imaging with fluorescence microscopy, while CIS QDs were tested for use as colloidal luminescent nanothermometers.