Programmed pH-Responsive Microcapsules for the Controlled Release of CdSe/ZnS Quantum Dots

Two methods for the preparation of pH-responsive all-DNA microcapsules loaded with CdSe/ZnS quantum dots (QDs) are discussed. One approach involves the construction of DNA microcapsules composed of nucleic acid layers that include, at pH 7.2, “dormant” C–G·C⁺ triplex sequences. The formation of the C–G·C⁺ triplex structures at pH 5.0 leads to the cleavage of the microcapsules and to the release of the QDs. A second approach involves the synthesis of CdSe/ZnS QD-loaded DNA microcapsules, stabilized at pH 7.2 by T–A·T interlayer triplex bridges. The dissociation of the bridges at pH 9.0 separates the bridging triplex units, resulting in the degradation of the microcapsules and to the release of the QDs. The programmed pH-stimulated release of luminescent QDs, emitting at 620 and 560 nm, from the C–G·C⁺ or T–A·T triplex-responsive microcapsules is demonstrated by subjecting the QD-loaded microcapsule mixtures to pH 5.0 or pH 9.0, respectively.