Researchers have published a cellular delivery method of nanoparticles called quantum dots which could be used as molecular probes for simultaneous imaging and manipulation of single biomolecules in the nucleus and for observation of subnuclear structures and events in the Oct. 4 edition of Small.
With their bright fluorescence, photostability and nanoscale size, quantum dots have emerged as an alternative probe that complements fluorescent dyes and proteins. One of the most promising applications of quantum dots is molecular imaging in living cells, according to Min-Feng Yu, PhD, associate professor of mechanical science and engineering, University of Illinois at Urbana-Champaign, and colleagues.
"Lots of people rely on quantum dots to monitor biological processes and gain information about the cellular environment. But getting quantum dots into a cell for advanced applications is a problem," said Yu.
Yu worked with fellow mechanical science and engineering professor Ning Wang, PhD, and postdoctoral researcher Kyungsuk Yum, PhD, to develop a controlled delivery and release method that uses a cargo-carrying nanoneedle (serving also as a nanoscale electrode) to penetrate into the nucleus of a living cell.
To rapidly release the attached cargo inside the nucleus, the researchers applied a small external electrical potential through the nanoneedle. "Now we can use electrical potential to control the release of the molecules attached on the probe," Yu said. "We can insert the nanoneedle in a specific location and wait for a specific point in a biologic process, and then release the quantum dots. Previous techniques cannot do that."
The group coated a single boron nitride nanotube, only 50 nanometers wide, with a very thin layer of gold (10 to 20 nm in thickness), creating a nanoscale electrode probe. They then loaded the needle with streptavidin-conjugated quantum dots with overall diameter of 15 to 20 nm. A small electrical charge released the quantum dots from the needle.
The researchers demonstrated the method by delivering quantum dots into the nucleus of living HeLa cells and imaged the target cell using fluorescence microscopy. Yu and colleagues detected both slow and fast moving quantum dots within the boundary of the nucleus, showing that they were confined to the nucleus.
"Location is very important in cellular functions," Wang said. "Using the nanoneedle approach you can get to a very specific location within the nucleus. That's a key advantage of this method."
The technique opens up new avenues for study. The team hopes to continue to refine the nanoneedle, both as an electrode and as a molecular delivery system. They hope to explore using the needle to deliver other types of molecules as well – DNA fragments, proteins, enzymes and others – that could be used to study a myriad of cellular processes.
"It's an all-in-one tool," Wang said. "There are three main types of processes in the cell: chemical, electrical, and mechanical. This has all three: It's a mechanical probe, an electrode, and a chemical delivery system."