Highly Photostable and Two-Photon Active Quantum Dot–Polymer Multicolor Hybrid Coacervate Droplets

Abstract

Fabrication and precise control of the physicochemical properties of multifunctional organic–inorganic hybrid nanocomposites find great importance in various research fields. Herein, we report the fabrication of a new class of luminescent hybrid coacervate droplets from CdTe quantum dots (QDs) and a poly­(di­allyl­di­methyl­am­monium chloride) (PDADMAC) aqueous mixture. The colloidal stability of these droplets has been explored over wide ranges of composition, pH, and ionic strength. Although these hybrid droplets are quite stable in a low-ionic-strength medium (<100 mM NaCl) and neutral/basic pH (pH >6.5), they are unstable in a higher-ionic-strength medium (>100 mM NaCl) and acidic pH (pH <5.5). Our findings indicate specific electrostatic interactions between negatively charged QDs and positively charged PDADMAC behind the observed coacervation. They exhibit the preferential sequestration of organic dyes and serum albumins. The intrinsic luminescent properties of these hybrid droplets have been explored using confocal laser scanning microscopy (CLSM) and epifluorescence microscopy. CLSM reveals the formation of intrinsically luminescent hybrid droplets. In addition, mixed two-color luminescent droplets have been fabricated by simultaneously mixing green- and red-emitting QDs with PDADMAC aqueous solution. Epifluorescence imaging reveals highly photostable and nonbleaching photoluminescence (PL) from individual droplets as a consequence of efficient surface passivation by polymeric chains of PDADMAC. Moreover, using two-photon (2P) confocal imaging we have shown that these hybrid droplets are ideal candidates for 2P confocal imaging applications. The present study can be easily extended to fabricate a wide range of hybrid droplets with various inorganic counterparts having unique optoelectronic properties, which will further expand their applicability in nanocatalysis, bioimaging, and biosensing.

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

“…The SEM image of this equilibrated binary mixture shows the formation of well-dispersed spherical coacervates in the size range between 50 and 1500 nm with a mean size of 430 ± 20 nm (Figure E). The estimated ξ potential of these nanodroplets is +8.1 mV . Notably, no nanodroplet formation has been observed in the absence of either QDs or PDADMAC, indicating the essential role of both the constituents in the nanodroplet formation.…”

“…Two different-sized MSA-capped CdTe QDs were synthesized and characterized using various spectroscopic and microscopic techniques. , The synthesized QDs exhibit excitonic peak positions at 482 and 614 nm, while the corresponding PL peaks appear at 523 (QD 523 ) and 666 nm (QD 666 ), respectively (Figure A). The estimated PL QYs of QD 523 and QD 666 are 0.27 and 0.57, respectively.…”

“…The estimated mean sizes of QD 523 and QD 666 are 2.3 and 3.1 nm, respectively (Figure S1). The covalent attachment of MSA ligands on the surface of QDs has been established by FTIR spectroscopy. , The estimated ξ potentials for QD 523 and QD 666 are −25.4 ± 1.1 and −11.1 ± 0.4 mV, respectively. The powder XRD pattern of QD 523 reveals peaks at 2θ values of 24.8, 41.4, and 47.3°, corresponding to the (111), (220), and (311) crystalline planes, respectively (Figure C) …”

“…These findings unambiguously indicate the presence of self-assembled QDs inside these coacervates. The colloidal stability of these hybrid nanodroplets has been recently explored by our group in a wide range of composition, pH, and ionic strength of the solution . While these nanodroplets are quite stable in neutral to basic pH (>7), they disassembled in lower acidic pH (<5).…”

“…These physicochemical properties make coacervate nanodroplets promising candidates for bioreactors and biosensors. Recently, our group has illustrated the fabrication of a new class of hybrid coacervate nanodroplets with unique physicochemical properties in a wide range of composition, pH, and ionic strength . These hybrid nanodroplets exhibit unique photoluminescence (PL) properties such as high photostability and two-photon (2P) active PL.…”