October 26, 2017
by Carol Lynn Alpert
All teams met by phone on October 28 and delivered updates.
Alas, the QDot Team is still seeing progressive loss of fluorescence during the hexane-to-water transfer steps required to bring the QDots into conjugation with DNA. Fluorescence declines during Steps 2 and 3, and disappears completely after the Step 4 transfer to water.
Even though the QDots were not fluorescing, they WERE in aqueous solution, so Abby just decided to just go ahead and see if she could get them to conjugate with DNA. In the Transmission Electron Microscope (TEM) below. Visible QDot particles are circled in yellow; in reality, there are many more, but this is not zoomed in enough. The red circles denote where the QDots are properly conjugated to the DNA origami hinges, but there are so few, that Abby thinks this may have happened by chance. She is going back to the literature to find a way to fix this.
In the past few months, Kil Ho has synthesized CdSe cores with several initial coating options and several methods of performing the 3-MPA ligand exchange as well. Some of these worked with moderate levels of success, but all resulted in some loss of fluorescence. This month, he decided to try to narrow down the variables by using commercially available red CdSe/ZnS QDots from Ocean Nanotechnology, which are very stable. This worked, but only if he used commercial 3-MPA ligands and commercial DMF solution, instead of making his own from powder. You can see that the fluorescence is coming from the aqueous layer, indicating successful transfer. Now the question is if Kil Ho will be able to repeat this success using the smaller (and less stable) green QDots available from Ocean Nano. The green wavelength is required for working with the gold quenching.
Down in Georgia, the Optics Team began constructing the new microscope. The stage is connected to the computer and is working properly using the controller and the software provided by the company (SmarAct). Abhijit would prefer to use an open-source microscopy software called Micromanager to control the stage. It is customized for use with microscopes so it would save a lot of coding steps. Abhijit got Micromanager to recognize the stage, but there were still some conflicts with the SmarAct proprietary software. He has contacted the company for assistance. In the meantime, he is using a less capable program, LabView, to control stage. The specs for the aluminium plate (on which the the z-piezo positioner will sit) were sent to the machine shop. Above, the microscope platform awaits its plate.
In Boston, the Communication Team's website designer finished up her work, providing documentation and a video recording explaining how to make entries in the team blogs. She sent these out to all QSTORM team members and provided individual log-ins and passwords. We would like each participant to try making a blog post in the coming month and perhaps work on background sections for the team pages.
We meet again on December 7.