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Aqueous synthesis of DNA-Functionalized Near-Infrared AgInS2/ZnS Core/Shell Quantum Dots.

Annette Delices,Davina Moodelly,Charlotte Hurot,Yanxia Hou,W. Ling,C. Saint-Pierre,D. Gasparutto,G. Nogues,P. Reiss,K. Kheng

Published 2020 in ACS Applied Materials and Interfaces

ABSTRACT

Biocompatibility, biofunctionality as well as chemical stability are essential criteria to be fulfilled by QD emitters for bio-imaging and -sensing applications. In addition to these criteria, achieving efficient near-infrared emission with non-toxic QDs remains very challenging. In this perspective, we developed water soluble near-infrared emitting AgInS2/ZnS core/shell (AIS/ZnS) QDs functionalized with DNA. The newly established aqueous route relying on a two-step hot-injection synthesis led to highly luminescent chalcopyrite-type AIS/ZnS core/shell QDs with an unprecedented photoluminescence quantum yield (PLQY) of 55% at 700 nm and a long photoluminescence decay time of 900 ns. Fast and slow hot-injection of the precursors were compared for the AIS core QDs synthesis, yielding a completely different behavior in terms of size, size distribution, stoichiometry and crystal structure. The PL peak positions of both types of core QDs were 710 (fast) and 760 nm (slow injection) with PLQYs of 36% and 8%, respectively. The slow and successive incorporation of the Zn and S precursors during the subsequent shell growth step on the stronger emitting cores promoted the formation of a three-monolayer thick ZnS shell, evidenced by the increase of the average QD size from 3.0 nm to 4.8 nm. Bioconjugation of the AIS/ZnS QDs with hexylthiol modified DNA was achieved during the ZnS shell growth, resulting in a grafting level of 5-6 DNA single strands per QD. The successful chemical conjugation of DNA was attested by UV-Vis spectroscopy and agarose gel electrophoresis. Importantly, surface plasmon resonance imaging (SPRi) experiments using complementary DNA strands further corroborated the successful coupling and the stability of the AIS/ZnS-DNA QD conjugates as well as the preservation of the biological activity of the anchored DNA. The strong NIR emission and biocompatibility of these AIS/ZnS-DNA QDs provide a high potential for their use in biomedical applications.

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