SANTA BARBARA, Calif., May 5, 2015 — A research team at the University of California, Santa Barbara, has discovered how to create a programmed, tunable fluorescent array by cradling silver nanoclusters inside synthetic DNA.
Led by Beth Gwinn, a professor in UCSB’s physics department, the team worked with the precious metal to create nanoscale silver clusters with unique fluorescent properties. These properties are important for a variety of sensing applications, including biomedical imaging.
Most recently, the scientists positioned silver clusters at programmed sites on a nanoscale breadboard, which is a construction base used for prototyping photonics and electronics. According to the Stacy Copp, a physics graduate student and lead author on team’s latest research article, the breadboard was a nanotube with spaces programmed 7 nm apart.
DNA nanotubes decorated by silver clusters with DNA-programmed color. Courtesy of UCSB.
"Due to the strong interactions between DNA and metal atoms, it's quite challenging to design DNA breadboards that keep their desired structure when these new interactions are introduced," Gwinn said. She continued, "Stacy's work has shown that not only can the breadboard keep its shape when silver clusters are present, it can also position arrays of many hundreds of clusters containing identical numbers of silver atoms — a remarkable degree of control that is promising for realizing new types of nanoscale photonics."
The colors of the clusters largely are determined by the DNA sequence that wraps around them and controls their sizes. To create a positionable silver cluster with DNA-programmed color, the researchers engineered a piece of DNA with two parts: one that wraps around the cluster and one that attaches to the DNA nanotube. "Sticking out of the nanotube are short DNA strands that act as docking stations for the silver clusters' host strands," Copp said.
The group was able to tune the silver clusters to fluoresce in a wide range of colors — from blue-green all the way to the IR — an important achievement because tissues have windows of high transparency in the IR. Biologists always are looking for better dye molecules or other IR-emitting objects in order to image through tissue, Copp said.
The results of this novel DNA nanotechnology address the difficulty of achieving uniform particle sizes and shapes.
DNA controls the size, shape and fluorescent color of the silver clusters. Courtesy of UCSB.
"In order to make photonic arrays using a self-assembly process, you have to be able to program the positions of the clusters you are putting on the array," Copp said.
The research's overarching theme is to understand how DNA controls the size and shape of the silver clusters and then figure out how to use the fact that these silver clusters are stabilized by DNA in order to build nanoscale arrays. Additionally, this research uses a step-by-step process that can be generalized to silver clusters of different sizes and to many types of DNA scaffolds.
"People are already using similar silver cluster technologies to sense mercury ions, small pieces of DNA that are important for human diseases and a number of other biochemical molecules," Copp said. She said there is "a lot more you can learn by putting the silver clusters on a breadboard instead of doing experiments in a test tube. You get more information if you can see an array of different molecules all at the same time."
The research was published in ACS Nano (doi: 10.1021/nn506322q).
For more information, visit www.ucsb.edu.