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  • Novel nanoparticles change color

Photonics Spectra
Jun 2011
Compiled by Photonics Spectra staff

COLUMBUS, Ohio – Tiny polymeric containers stuffed with red and green quantum dots promise to provide continuous light for biomedical imaging.

Engineers at Ohio State University have invented nanoparticles that, somewhat unusually, glow red, green or yellow depending upon the state of the quantum dots contained within.

This series of photos depicts a novel nanoparticle changing from red to green to yellow over the course of 2 min. Courtesy of G. Ruan, Ohio State University.

Researchers routinely tag molecules with fluorescent materials to see them under the microscope. Unlike the more common fluorescent molecules, quantum dots shine brightly and could illuminate chemical reactions especially well, allowing researchers to see the inner workings of living cells. The new nanoparticles could be a useful addition to the arsenal of biomedical engineers trying to find the roots of diseases, scientists said.

“This work could be groundbreaking for the field of nanotechnology as a whole because it solves two seemingly irreconcilable problems with using quantum dots,” said research scientist Gang Ruan.

Because of their quantum mechanical effects, quantum dots “twinkle”: They randomly blink on and off. When many dots come together, however, the blinking becomes less noticeable – and when large clusters form, they appear to glow with a steady light. Researchers have found the blinking in quantum dots to be troublesome because it interrupts a tagged molecule’s trajectory when they are trying to follow it. But blinking is beneficial too because, when dots come together and the blinking disappears, they know that tagged molecules have aggregated.

The scientists discovered that they could use the “good” and avoid the “bad” aspects of blinking by grouping together a few quantum dots of different colors inside a micelle – a nanosize spherical container found in household detergents. Ruan and his team created micelles from polymers, with various combinations of red and green quantum dots inside.

Experiments confirmed that the micelles appeared to glow steadily. Those stuffed with only red quantum dots glowed red, and those stuffed with green glowed green. However, those stuffed with red and green dots changed from red to green to yellow. The color changes occurred when one dot or another blinked inside the micelle. Much as with the single-color-stuffed micelles, the dual-color-stuffed micelles could blink solely red or green – but if both lit up simultaneously, the micelle glowed yellow from the additive effect.

It’s not possible to control when color changes happen inside individual micelles, but the continuous glow allows uninterrupted tracking of tagged molecules, and color changes indicate when molecules have come together. The particles also could be used in fluid mechanics research, the scientists said.

The team also is working on developing magnetic particles to enhance medical imaging of cancer, which, combined with the quantum dot technology, could enable various types of imaging methods. Before the particles could be safe to use in the body, however, they would have to be made of biocompatible materials.

In the future, the scientists hope to introduce another color – blue – into the mix to see what happens.

An instrument consisting essentially of a tube 160 mm long, with an objective lens at the distant end and an eyepiece at the near end. The objective forms a real aerial image of the object in the focal plane of the eyepiece where it is observed by the eye. The overall magnifying power is equal to the linear magnification of the objective multiplied by the magnifying power of the eyepiece. The eyepiece can be replaced by a film to photograph the primary image, or a positive or negative relay...
The use of atoms, molecules and molecular-scale structures to enhance existing technology and develop new materials and devices. The goal of this technology is to manipulate atomic and molecular particles to create devices that are thousands of times smaller and faster than those of the current microtechnologies.
quantum dots
Also known as QDs. Nanocrystals of semiconductor materials that fluoresce when excited by external light sources, primarily in narrow visible and near-infrared regions; they are commonly used as alternatives to organic dyes.  
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