September 28, 2017
by Carol Lynn Alpert
All teams met by phone on Sept 6. The Communications Team announced the roll-out of the new Team Blog, previously hosted on qstormlegacy.com. All project team members will soon receive individual log-ins and instructions for direct posting.
The QDot Team described their latest moves in the ongoing struggle to get to QD-DNA conjugation. Abby went back to square one. She synthesized a new batch of CdSe cores, then added single layers of ZnS coating, seeking to optimize the purification steps between each layer. Success: she verified ZnS shell growth around the cores through TEM imaging, and demonstrated the corresponding red shift in peak absorbance. Finally, it was time to readdress the required transfer from organic to aqueous solution (DNA likes water). Abby applied the intermediate step, pyridine; and, quite suddenly, QD core/shell fluorescence plummeted. Big sigh.
Meanwhile, Abby's colleague, Kil Ho, has been running trials testing another route for transfer to aqueous solution.
This route uses 3-MPA ligands rather than pyridine and phytochelatin-3, and it's not working well either. The 3-MPA ligands are dissolved in aqueous solution and then energy is added to mix together the solution together with the oily solution containing the QDots. With mixing, the 3-MPA ligands are supposed to come into contact with the QDots in oil and yank them back over into the water. This time Kil Ho tested three alternative mixing procedures and three different starting core and core/shell combos. Of the various mixing procedures, the vortex method trumped the sonication and evaporation methods. Starting with TOPO and Oleic Acid coated CdSe cores succeeded better than starting with the TOP-coated cores. However, Kil Ho's subsequent attempts to add ZnS shell coating to the cores once they were transferred to the aqueous solution were unsuccessful. The QDots precipitated back out of solution and lost fluorescence.
Working with QDots in water is definitely still a challenge.
The Optics Team in Georgia is making steady progress toward building their new holographic STORM scope. Abhijit is modeling the mechanical design of every part in a computer CAD design program, and how they will fit together, before sending the specs out to the machine shop. (He is following the This Old House dictum "Measure twice, cut once.")
We'll meet again on October 26.