Meet the Researchers: Zack Urbach

Zack Urbach is a graduate student in the group of CBES senior investigator Chad Mirkin studying the effect of DNA and magnetic coupling interactions on nanoparticles. In this Q&A, Urbach discusses the two papers he has published on this topic, his post-graduation plans and his experience mentoring middle school students in Chicago.

When did you develop an interest in science and what pushed you toward a path in materials chemistry?

My dad was a geologist so he always talked about science and looking at the world through a scientific, questioning lens. Also, my grandpa was a chemistry professor, so growing up I was inspired from a lot of different avenues — either through being taught actual chemistry or geology or even just questioning the world like a scientist.

When I attended Carnegie Mellon for undergrad, I took a really great introductory honors chemistry course and stuck with chemistry from there. The combination of disciplines was why I gravitated toward materials chemistry. It involved chemistry but on a larger scale to solve materials-based problems rather than atomic-level problems.

How would you describe your current CBES research interests to non-scientists?

I take really small pieces of materials that act as magnets and can be attracted together or repel each other, similar to regular magnets that we can see. But at the nanometer level, they interact in some strange ways. 

One way to control these interactions is by putting a sticky layer of DNA on the surface of the magnets to have them bind together in a controlled manner. By combining DNA bonding between particles and magnetic bonding between particles, we can form custom crystals of magnetic nanoparticles with long rod shapes that could not be formed through either magnetic bonding or DNA bonding alone.

Is this mostly fundamental research at this stage or are there some near-term applications for this work? What is the ultimate goal for this research?

What I’ve focused on in these studies is pretty fundamental, looking at the combination of the DNA and magnetic coupling interactions.

I think long-term, there could be some more investigation into how these assembled, fibrous structures behave in solution under the presence of a magnetic field. Scientists are working to create reconfigurable microswarms of tiny “microrobots” that can change and shift shape in a magnetic field. By potentially using a DNA-coated surface, not only can you manipulate the structure with the field, but you can also change the structure by changing the DNA bonding. In other words, you could change the length between particles and their preferred symmetry. 

By adding this DNA layer, you could potentially apply some sort of robotic swimmer into biological materials, transport cargo or perform other biologically relevant applications. But that’s way down the line; I haven’t gotten close to that point.

Can you summarize the main findings of the two CBES papers you’ve authored, the 2019 Advanced Materials paper and the recent paper in Angewandte Chemie?

The Advanced Materials paper was the first study looking at spherical magnetic iron oxide nanoparticles with layered DNA, and how those assemble in the presence of a magnetic field. What we found is that DNA interactions dominate at the nanoscale level, so they lead to a nucleation and clustering of the particles. But once those clusters or particles grow to a certain critical size, they begin to magnetically align because there is an overall cluster dipole.

Once those reach critical size, they start to form these elongated, high-aspect ratio rods of particles. By changing the nanoparticle core diameter, by changing the field strength, by changing the DNA lengths — or the distance between the particles — we can control the point at which these nanoparticles start to cluster together. We did this through a lot of electron microscopy studies and we collaborated with Monica Olvera de la Cruz’s group to come up with some theoretical explanations for the system. It laid a solid groundwork for how this combination of interactions behaved.

For the second work in Angewandte Chemie, we sought to change out the spherical core for a cubic nanoparticle core to test what effect that shape would have on the assembly and orientation of the particles. The key takeaway was that we could functionalize cubic iron oxide particles with a spherical shell DNA, and they behave similarly to how spherical magnetic particles cluster and assemble in a field with these high-aspect ratio structures. But, by having a cubic iron oxide core, the preferred orientation of the crystal then changes compared to using a spherical core.

We worked a lot with people at Argonne National Laboratory to develop the right setups we needed for X-ray scattering analyses, and I think this a good way of setting up to investigate new shapes and crystal symmetries in the future.

I know Professor Mirkin has a huge group. What has it been like to work in that environment?

He has set it up so there are mentors assigned to certain projects, just so there’s a sort of home base for new members in the group. Older grad students or postdocs work in pairs or groups with the less-experienced researchers, but there’s so much expertise that you can just go to whoever you need to for help or advice about a problem. Because it’s all in-house and it’s all within the group, it makes those conversations really fast and really easy.

I’ve worked with several postdocs over the years who are basically pseudo-advisors. Sarah Park, who I coauthored the two papers with, was really great. We really clicked and pushed each other, and Chad responds well to a good team and sees a lot of value in that. So, there are a lot of core teams in the lab, either duos or groups of people that really push projects forward.

What do you enjoy doing outside of the lab?

Prior to the pandemic, I played percussion in a community band in Chicago called Windy City Winds. We play the classic wind ensemble kind of stuff. That was really fun and something I did to get out of my head a little bit.

Also, I volunteered as part of Science Club through Science in Society at Northwestern. We would go to a Boys & Girls Club in Uptown and mentor two or three students a week and get to know them. I did that for three years and it was a really great experience.

Science is part of why we’re there, but you’re communicating to middle schoolers and you realize that you’re not always going to talk about science the whole time. You’re getting to know them, and then you can try to fit science in there every once in a while. It’s really rewarding to see their growth.

Your expected graduation date is coming up this month. What are your post-PhD plans?

I recently accepted a postdoc position at UC Irvine to study conductive peptide assembly. It’s part of a new MRSEC (Materials Research Science and Engineering Center) that they started there.

I’m really excited to continue this collaborative spirit that CBES has sparked in my projects and my research. Translating from DNA to peptides will be a fun transition.

Because I’ll be looking at the conductive properties of these materials, it will still be relevant to energy science. I can’t go into too many details because I’m still new to it, but it’s also in the vein of biologically inspired assembly formations. Peptide assemblies are very dynamic so it will likely involve using that to our advantage to design functional conductive materials.