The NC State researchers, advised by Dr. Orlin Velev, assistant professor of chemical and biomolecular engineering, include undergraduate student Jeffrey R. Millman and graduate students Ketan H. Bhatt and Brian G. Prevo. They created different types of tiny particles that could eventually be used in everything from drug delivery to determinations of the presence or concentration of biological molecules.

Some types of new particles look like microscopic eyeballs, but are really made of tiny particles of gold and latex. Others look like billiard balls, but are slivers of gold, silica and colored latex beads.

The research is published in the January edition of Nature Materials.

“We’re looking at scaling down microfabrication by making special microfluidic chips that can serve as microscopic factories,” Velev says. “All sorts of particulate materials – electrically conductive, magnetic, polymer, metallic, fluorescent – can be combined for special high-tech applications.”

In 2003, Velev and his students published in the journal Nature a technique to control the movement of microscopic droplets of liquid freely floating across centimeter-sized chips packed with electrodes. The breakthrough came as the researchers learned how to circumvent friction by suspending the droplets of water inside fluorinated oil, and then applying electrical voltages to make the liquid hover over the electrical circuits of the chip. Switching the chip’s electrodes on and off – either manually or with the aid of a computer – lets researchers move the droplets across the oil surface to any location on the chip.

In the current research, the NC State scientists create anisotropic particles, or particles with different layers or properties, on the microfluidic chip. The droplets contain tiny amounts of different materials, like gold and latex, along with a small amount of water; the scientists combine them and allow them to dry. The dried particles take on the look of eyeballs, with the gold slivers making a dark dot inside the latex white of the eye.

In the billiard-ball particles, tiny pieces of gold, silica microspheres, yellow latex beads and water resemble something similar to a yellow-and-white striped nine-ball in billiards after drying, with the latex beads clustering at the top of the particle, the gold slivers forming a stripe of brown in the middle of the particle, and the silica microspheres congregating at the bottom of the particle. Similar striped particles were formed from tiny gold slivers, red latex beads and silica microspheres.

“The eyeball and striped particles could be used in electronic paper and as barcoded tags in biological and environmental research,” Velev says, “as well as in advanced drug delivery and targeted therapeutics.”

The research is funded by Velev’s National Science Foundation Career Award.

- kulikowski -

Notes The abstract of the paper follows.

“Anisotropic Particle Synthesis in Dielectrophoretically Controlled Microdroplet Reactors”
Authors: Jeffrey R. Millman, Ketan H. Bhatt, Brian T. Prevo and Dr. Orlin D. Velev, NC State University
Published: Jan. 2005, in Nature Materials

Abstract: The miniaturization of chemical and biological processes in microfluidic devices and bioarrays is a major technological achievement. Microchips performing multiphase material synthesis operations could be a future step in this trend of miniaturizing technology. Here we show how electrically controlled chips can be used for the synthesis and manipulation of new types of particles with advanced structure. The method is based on a technique that allows freely suspended droplets and particles to be entrapped and transported using electric fields. The fields that hold and guide the droplets and particles are applied through arrays of electrodes submerged in the oil. Each of the microdroplets suspended on the surface of fluorinated liquid serves as a microscopic reactor, where the particles are formed by solidification of the carrier droplets. Controlled on-chip assembly, drying, encapsulation and polymerization were used to make anisotropic ‘eyeball’ and striped particles, polymer capsules and semiconducting microbeads.