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Proteins can template the heterogeneous nucleation and growth of size-confined nanocrystals. However, protein-templated mineralization often leads to particles that exhibit low colloidal stability, poor crystal quality, and/or diminished photoluminescence. Here, we report protein cage–spherical nucleic acids (SNAs) that can be used as nanoreactors for quantum dot (QD) synthesis and subsequent intracellular delivery. The resulting QD-SNA structures are monodisperse, colloidally stable, and photoluminescent in aqueous solution. The nanoreactors were prepared using two different proteins (~10 and 12 nanometers in diameter), and CdS, CdSe, and PbSe nanocrystals were synthesized. Moreover, the extent of surface defects and crystallinity depends on the relative concentrations of ionic precursors, which control the growth rate and the number of ionic vacancies. By optimizing conditions, CdS-SNAs that exhibit near-zero reabsorption loss were synthesized. Last, QD-SNAs exhibit enhanced cellular uptake and minimal cytotoxicity when compared to commercial QD-protein conjugates, making them potentially useful in bioimaging and diagnostic applications. 

Molecular strain can be introduced to influence the outcome of chemical reactions. Once a thermodynamic product is formed, however, reversing the course of a strain-promoted reaction is challenging. Here, a reversible, strain-promoted polymerization in cyclic DNA is reported. The use of nonhybridizing, single-stranded spacers as short as a single nucleotide in length can promote DNA cyclization. Molecular strain is generated by duplexing the spacers, leading to ring opening and subsequent polymerization. Then, removal of the strain-generating duplexers triggers depolymerization and cyclic dimer recovery via enthalpy-driven cyclization and entropy-mediated ring contraction. This reversibility is retained even when a protein is conjugated to the DNA strands, and the architecture of the protein assemblies can be modulated between bivalent and polyvalent states. This work underscores the utility of using DNA not only as a programmable ligand for assembly but also as a route to access restorable bonds, thus providing a molecular basis for DNA-based materials with shape-memory, self-healing, and stimuli-responsive properties.