Improve crystal engineering with DNA


May 08, 2023

(Nanowerk News) Northwestern researchers have demonstrated that fine-tuning DNA interaction strengths can enhance the engineering of colloidal crystals to enhance their use in creating a variety of functional nanomaterials, according to a study recently published in ACS nano (“Programming Nucleation and Growth in Colloidal Crystals Using DNA”).

Chad Mirkin, PhD, professor of Medicine in the Division of Hematology and Oncology, George B. Rathmann Professor of Chemistry at Northwestern Weinberg College of Arts and Sciences, and director of the International Institute for Nanotechnology, is the study’s senior author.

Engineering colloidal crystals with DNA involves modifying nanoparticles into programmable atomic equivalents, or “PAEs”, which are used to form colloidal crystals which can then be used to design synthetic programmable DNA sequences.

Recently, these processes have focused on controlling crystal size and shape, however, even with well-established methods, it is difficult to separate crystal formation, or nucleation, and growth. Image showing a schematic view of a core-shell crystal A drawing showing a schematic view of a crystal core-shell; the red region contains gold nanoparticles with “seed” DNA and the yellow shell region contains silver nanoparticles with “growth” DNA. (Image: Mirkin’s lab)

“New crystals can be nucleated throughout the process while existing ones grow throughout the process, so you can have some very small crystals that may be forming at the end of the process and large ones that are growing over time, and you’ll end up with really populations that don’t exist. uniform in terms of crystal size. So trying to separate those two events, growth from initial crystal formation, is a problem we wanted to tackle,” said Kaitlin Landy, a PhD student in the Department of Chemistry at the Weinberg College of Arts and Sciences and co-lead author of the study.

In the study, Mirkin’s team explored how DNA interaction forces could be used to separate nucleation and growth in colloid crystallization.

To do this, the team created two groups of complementary nanoparticles: one batch contained complementary base pairs, called “seed” PAEs, and the other contained mismatched base pairs to make “growth” PAEs.

“So you have early crystals (‘seed’ particles) that make up the solution, and then your weaker crystals (‘growth’ particles) you can grow on top of what’s already there,” says Kyle Gibson, a postdoctoral fellow in Mirkin’s lab. and one of the lead authors of the study.

Using this method, the researchers were able to increase the uniformity of the crystals. They can also independently select nanoparticle and DNA shell sequences and essentially mix and match them, allowing them to incorporate a wide variety of materials into crystals.

“One thing we think is really powerful moving forward is thinking about how we can track this (crystallization) process using different particle nuclei,” added Gibson.

“This method can be used to fabricate these interesting core-shell structures in a single step, which previously required several steps with post-synthetic stabilization of the first crystal before the second growth step,” said Landy. “Given these two different DNA interaction strengths, if we can basically label where different types of particles are going in the final structure, it would be useful for investigating those fundamental questions.”


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