Irish, a Mechanical Engineer, Part of Nanotech Revolution
As a graduate student in Professor Anne Lazarides lab, Elizabeth Irish is learning how to play with the tiniest of building blocks. Her ultimate goal: to assemble nanosize squares of gold or silver on silicon surrounded by soft matter made entirely of DNA molecules.
Such diminutive objects ultimately aim to take advantage of the ability of some metal nanoparticles, including gold and silver, to emit light in the visible spectrum, a field known as plasmonics. Such particles could provide a simple method for monitoring processes much too small to see. Irish said the structures she is working to produce could serve as tiny biosensors for detecting macromolecules in the blood system. Plasmonic particles could also monitor the assembly of DNA into precise, molecular-scale structures, among other applications.
The truth is, however, that the potential applications for such nanomaterials remains wide open, Irish added. Before they can figure out what they can do, scientists have to focus on how to reliably manipulate the tiny ingredients and how to fuse hard elements, such as metal and glass, to soft biomaterials like DNA.
Whats neat is that this field is still so unknown, Irish said. As Richard Feynman said, Theres plenty of room at the bottom for discovery of ways to manipulate molecules down to the nanoscale.
There are lots of things not known about proteins and biomaterials. Its incredible to see it evolve and be part of the evolution of nanotechnology.
As a first step, Irish had to master the skills of electron-beam lithography, a process that relies on electrons to pattern surfaces. The very short wavelengths of an electron beam allow patterning on a very fine scale.
Irishs goal was to create a pattern on silicon of evenly spaced, tiny squares, just one micron in size. By comparison, the period at the end of a sentence is equal to about 615 microns. She then evaporates the gold onto the surface, she said.
The e-beam vaporizes the gold, which then deposits on the silicon surface, she explained.
The gold doesnt stick where the surface was exposed to the e-beam, Irish said. After a lift off process, youre left with the metal only on the surfaces where you wrote the pattern.
Next, she will merge her precise gold-patterned silicon structures with self-assembled DNA produced earlier by electrical and computer engineering professor Chris Dwyer and computer science professor Thom LaBean. DNA allows the mass-production of infinitesimally small patterns at least 10-fold smaller than that possible with lithography.
In theory, the merging of the gold and DNA grids isnt necessarily a big challenge, Irish said. The negatively charged DNA backbone attracts the positively charged metal. In fact, gold and DNA structures have been made before, but obtaining the particular plasmonic properties Irish is aiming for requires their alignment to be even more precise.
And producing the structures is only the beginning.
Its knowing exactly what you have that is harder than doing it, she said. Proving it is the real challenge.
Visualizing the structures requires atomic force microscopy (AFM), specialized microscopes that allow scientists to see down to the molecular level. She will additionally employ scanning electron microscopy, a type of imaging capable of producing high resolution images with a characteristic three-dimensional appearance.
The optical characteristics of the actual structures will also be compared to simulated versions of their expected plasmonic properties.
Irish plans to make several versions of the structures, each with its own distinctive plasmonic behavior. In place of the grids, she will also use nanotracks, very finely patterned arrays of self-assembled DNA that look something like railroad tracks. Some of the structures planned will also include tiny bits of silver attached to the DNA in addition to the gold squares.
You can increase the precision of the optical properties with the addition of other metal components, Irish said. Adding the silver would give you a different peak. It changes the resonance condition. To an observer such a difference would mean a more distinct, or different, color to provide information about the contents of a blood sample, for example.
While growing up in Rocky River, Ohio, Irish always liked the sciences, but she didnt initially set out to be an engineer. On her college applications, she checked off her interests: math, biology and physics. The acceptance letters she got back placed her in engineering.
She enrolled as an engineering student at the University of Pennsylvania in Philadelphia and quickly realized that it was just the place for her.
While an undergraduate, she gained early research experience, working with a material scientist and anesthesiologist to make synthetic blood vessels. The vessels were intended for use in testing drugs, particularly those intended to prevent or break up blood clots, Irish said.
That experience was the stepping stone for my interest in the possibility of research, Irish said. I found out that I liked it.
Her work at the intersection of biology and materials science made Lazarides lab within the Duke Center for Biologically Inspired Materials and Material Systems a perfect fit. Irish was also familiar with Duke, where both her father and sister had completed their undergraduate education.
In addition to her primary research, Irish is also working on a side project to examine the thermodynamics of melting DNA assemblies. She is involved with the Graduate and Professional Student Council and organizes a graduate student lunch seminar series. She also works as a volunteer for Hospice through Duke Health Community Care.