Toward DNA-embedded Quantum Dots II

February 20, 2018

by Kil Ho Lee

CdSe/ZnS with 3-mercaptopropionic acid (3-MPA) ligand is soluble in aqueous environment. DNA embedding procedure involves the additional ZnS shell formation, which the ssDNA molecules are physically entrapped within ZnS layers. Previously, the success of DNA embedding procedure was questioned because of the negligible change in size distribution. In addition, the loss of QDs in between each steps toward DNA embedding caused the difficulty tuning the ratio of QDs to additional Zn monomers, and the ratio of QDs to ssDNA.


Figure 1. Schematic of DNA embedding Set up


First, the aggregation/precipitation of QDs were not observed. The purification was done to remove excess Zn2+ and ssDNA using 100kDa centrifugal filter device. Purified QDs were retrieved and diluted in water. Second, TEM results showed the increased in ferret length (Figure 2A and 2B). Compared to QDs prior to the additional ZnS coating, the particle shape became more irregular and the size distribution clearly indicated the increase in the particle size; the mode size for QDs post additional ZnS shell coating with DNA increased to ~ 12 nm from ~ 7 nm. Third, the surface charges of QDs before and after ZnS shell coating/DNA embedding were determined using the Zeta potential measurement device. The average Zeta potential for QDs in water was - 0.023 mV, whereas the average Zeta potential for QDs after ZnS shell coating/DNA embedding was -7.18 mV.

Work in progress

The presence of ssDNA on QD surface can be further verified by incubating QDs with DNA origami hinges. Castro’s group (OSU Mechanical engineering) will provide DNA hinges equipped with the complementary DNA sequences at the nanoparticle binding site. TEM and fluorescence microscopy will be done this coming week to verify if DNA embedded QDs will bind to DNA hinges.

Figure 2. TEM images of QDs in water: (A) after Ligand exchange, (B) after additional ZnS coating/DNA embedding, and (C) size distirbutions: QD size increase after ZnS coating/DNA embedding