January 17, 2019
by Carol Lynn Alpert
Participating: Jessica, Abhijit, Abhilasha, Kil Ho, Faiz, Carol Lynn. Happy new year!
Abhijit led us off with his quest to eliminate the “twin image” problem. He solved it by placing the curved mirror on a “linear piezo-electric translational stage” that allowed phase-stepping. He also improved the interferometric set up by using dual diffractive lenses (two spherical waves) rather than one spherical and one plane wave. This allows him to control the size of the hologram being produced. With the amount of light constant, spreading it over a smaller area gives a stronger signal. He has to balance that benefit against the risk of making it so small the camera won’t be able to resolve the concentric rings. It’s basically a trade-off, and he’s now working on finding the exact sweet spot for the mirror’s optical focal length. Then he’s got to get Peter to order it for the lab. He’s currently able to image 100 nm fluorescent beads.
Meanwhile, in Ohio, Kil Ho acquired 680 wavelength quantum dots to match the Georgia lasers. They’re not easy to find, but Kil Ho tested them in Ohio and found them good. He then encapsulated them in micelles and sent them to Abhijit in Georgia. But, at about 40 nm, they’re too small for the new microscope, motivating Peter and Abhijit to tackle the noise problem once again. They did it by a reverse process of elimination. They completely darkened the room and covered the camera and began adding one essential element at a time. No noise was introduced until the moment they put in the glass slide, and then the noise shot up from 0 to two. The most the system can tolerate is .5. The glass slide and cover slip are autofluorescencing. Peter and Abhijit have put in an order for new slides and coverslips that are supposedly guaranteed against autofluorescence. We’re all keeping our fingers crossed.
Meanwhile, back in Ohio, Kil Ho and Abhilasha are still slogging through the swamp of chemical and physical obstacles that are making the synthesis of switchable QD-DNA-gold nanoparticle composites a heroic effort. Abby succeeded in switching to a technique that gave her 39% more coverage of single DNA strands on the gold nanoparticles, which she thinks will help improve her yield of QDot – gold nanoparticle composites, but her attempts to test successful conjugation with electrophoresis were inconclusive. She will try TEM imaging next.
Kil Ho sought to improve his yield of DNA-embedded QDots by improving the purification process. Too many single strand DNAs are remaining in solution after centrifugal filtration. They could not only inhibit the hybridization of QDots with gold nanoparticles but also cause stray fluorescence signaling. Abby suggested Kil Ho try using a buffer solution saltier than water (pH 7.2). This turned out to be more successful at washing out the excess single-stranded DNA, but on the other hand, it was so effective it also washed out the much needed QDots conjugated to DNA. The team thinks the DNA strands are pulling in and balling up around the QDots, reducing the size of the QD-DNA conjugates and washing through the filter pores. The next step is to try growing larger QD-ZnS-DNA composite particles and reducing the filter pore size. Kil Ho also tried to confirm his embedding procedure using electrophoresis, and found that he still needs to increase the number of DNA strands embedded on the QD surface. And then, folks, after solving the current batch of problems, both Kil Ho and Abby will have to go through many of these same steps again with azobenzene molecules attached to the DNA strands. The azobenzene molecules are the switching mechanisms key to using QDots for STORM imaging. More next month.
In Boston, the communications team is getting ready to launch the first national edition of the Quantum Matters™ Science Communication Competition. Here’s our new logo. NSF is providing support to fly in Finalists from other areas of the country. We’re also adding another competition track, for Hands-on Activities related to quantum science and technology. Can’t wait to see what comes in!
Our next meeting will be February 22 at 1 pm.