February 20, 2018
by Kil Ho Lee
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.
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.