May 17, 2019
by Carol Lynn Alpert
Participating: Jessica, Peter, Abhijit, Abhilasha, Kil Ho, Faiz, Carol Lynn
Status update: Carol Lynn has submitted the MOS annual report and no-cost extension request; Peter has submitted a no-cost extension request; Jessica will be submitting a final report. The QDot team will continue working with us through the summer and beyond, and Faiz (their newest team member) will take over for Kil Ho and Abby when they graduate this summer. Welcome Faiz! Jessica has applied for an NIH grant to continue exploring DNA and QDot composites for labeling molecules; the review scores were high. She may continue with one of our current conjugation techniques, but will also investigate the molecular cage method of modulating QDot fluorescence.
After solving the setback of QDot dispersion last month, Abby has had a major success. She synthesized gold nanoparticle – DNA – QDot composites and demonstrated the quenching effect of the gold nanoparticle on the QDot. She was able to reliably reproduce these results multiple times. She calculated an effective decrease of 90% in QDot fluorescence compared to free QDots, an on/off ratio of 10, getting much closer to the target ratio of 20-1 required for STORM. She also showed that the effect is reversible when the gold nanoparticles dehybridize from the QDots. She did that using heating and cooling in this experiment, but next time will attempt to demonstrate it using the azobenzene cis-trans shifting mechanism. She is also going to try to optimize the quenching mechanism further by reducing the number of DNA base pairs from 16 to 12, tying the gold nanoparticles a nanometer closer to the QDots. Exciting news!
Kil Ho is defending his Ph.D. dissertation in June! He handed over his blog post writing duties to incoming grad student Faiz Khan. We asked Faiz to send us materials so that we can add him to the team pages. Kil Ho and Saiz have been working together on the DNA embedding technique for QDots; Saiz reminded us that the DNA gets embedded as a zinc sulfide shell grows around a CdSe core. They have been plagued by persistent problems with QDot aggregation and precipitation out of aqueous solution. From now on, they are sticking to NN Labs as a source of QDots; the Ocean Nanotech QDot batches have proved unreliable. Next they’ll try to increase the stability of the MPA-coated NN Labs QDots, adjusting MPA levels and dilution ratios.
Another stunning picture from the Kner Lab using the new STORM scope that Ahbijit built: this one shows details of the growth cone of a nerve cell attaching to muscle tissue in a fruit fly at depth inside a full embryo. Peter and Abhijit are working with neuroscientist Daichi Kamiyama to better understand these critical connections, and currently they’re seeking to sort out the best combination of fluorescent labels to use. Here the growth cone is stained with CF 568; the muscle is not labelled. Daichi prefers to use a protein called EOS for staining the growth cone, but the CF 568 will work if he cannot get the EOS to label properly.
Microscopy Update: Holography is working! The team is now able to image a 40nm microsphere using incoherent holography to optimize the emitted light. Excess noise is visible in the reconstructed image of a 40 nm microsphere on the right, but the signal to noise ratio has increased enough that they don’t need to see the diffraction rings visible in previous experiments.
To reduce noise from stray light, Abhijit and Peter have surrounded the set up with dark curtains and placed a dark box over the imaging table. But light from the excitation laser is still bouncing off everything in its path, the objective, slide, cover slip, optics elements, etc. The solution is to not send light through the objective, and the way to do that is to install the light sheet set-up. That’s the plan for this summer, along with introducing two-color capacity.
With the holographic technique working, it may not be necessary to add in an adaptive-optics deformable mirror as they had in their previous STORM scope.
We didn’t have time to brief the group on our efforts this month in Boston, but we had a triple success on April 6 with the launch of the first NanoDays with a Quantum Leap, the Finals of the national 2019 Quantum Matters™ Science Communication Competition, and the unveiling of Look Inside a Quantum Computer, a temporary exhibit on quantum computing produced in collaboration with IBM Q. The first place award of the QMC went to quantum dot researcher Sue Shi, a graduating senior at Mount Holyoke College. Karine Thate, emcee of the event, has now moved on to a new position at Harvard Business School. We wish her well!
Our next meeting is set for June 19 at 11 am.