Quantum Dot-Based Hybrid Coacervate Nanodroplets for Ultrasensitive Detection of Hg2+

Multifunctional organic-inorganic hybrid materials with inherent optical, electrical, and/or magnetic properties find tremendous importance in various fields such as sensing, photovoltaics, therapeutics, bioimaging, and light-emitting devices. Herein, we have fabricated membrane-free organic-inorganic hybrid luminescent coacervate nanodroplets and utilized them toward ultrasensitive detection and efficient removal of mercuric ions (Hg2+) simultaneously. The self-assembly of negatively charged mercaptosuccinic acid (MSA) capped CdTe quantum dots (QDs) in the presence of positively charged poly(diallyl-dimethylammonium chloride) (PDADMAC) leads to the formation of luminescent nanodroplets with average size of 430 +/- 20 nm. Selective luminescence quenching of these nanodroplets has been observed only in the presence of Hg2+. It has also been observed that the presence of other metal ions does not interfere in the sensing process. Our findings reveal that Hg2+ ions specifically associate with the porous structure of these nanodroplets via electrostatic interactions with the free carboxylate groups of MSA ligands at the surface of CdTe QDs and undergo photoinduced electron transfer (PET) with photoexcited QDs. The limit of detection (LOD) for Hg2+ sensing with our present system is estimated to be 1.32 nM (0.26 ppb), which is significantly lower than most of the earlier reported self-assembled materials. Moreover, these hybrid nanodroplets efficiently sequester trace quantities of Hg2+ from contaminated water. The overall performance of our present system toward Hg2+ remediation is superior over most of the earlier reported hybrid nanocomposites in terms of fast uptake kinetics (within 15 min), ultrasensitive detection (LOD 0.26 ppb), and high sequestration efficiency (98.3%). With regard to our present findings in particular, the tailorability of surface ligands and inorganic nanoparticles in hybrid nanodroplets provide great advantage for the development of multifunctional nanomaterials for a diverse range of applications.