Nanothermometer could lead to new class of nanodevices

A nanoscale thermometer that responds to temperature represents a new class of nanoscale assemblies that could lead to more accurate medical testing devices, in addition to applications in homeland security, and micro- and nano-electromechanical system technologies, a U-M researcher says.

"The accurate temperature regime is critical for medical applications. All of the biological systems are temperature sensitive," says Nicholas Kotov, associate professor of chemical engineering. "We are designed to operate at 37 degrees [Celsius]. If the temperature gets higher or lower that makes a tremendous change in our feeling of health."

Similarly large differences occur with biomedical measurements based on protein reactions, Kotov says. "For example a microfluidics diagnostic device that is becoming more common now may show you that you have cancer when you don't, when temperature of the process is slightly off."

But there's no convenient way to measure temperature in micro- and nano-scale volumes of water because the spaces are in some cases thousands of times smaller than the commas on a page, says Kotov, who also has appointments in biomedical engineering and materials science and engineering.

The particular nanothermometer was made by attaching a core gold particle and a semiconductor particle to opposite ends of flexible polymer, which acts as the so-called spring. The particles interact optically, and when many polymers connect to the gold core they fan out and form a corona shape.

The polymer spring acts like a coiled garden hose that contracts and tightens in the cold and relaxes in the heat. As the polymer responds to heat or cold, the particles attached to the ends move closer together or farther apart. With the molecular spring, scientists can detect temperature changes down to one or two degrees.

But the responses aren't limited to temperature, Kotov says. "In terms of applications, this stimulus-response system is actually just the beginning of many other, similar structures of sensing devices," he says.

Researchers can design the particle to respond to any number of stimuli, such as a biological pathogen or an explosive. "The fact that they are different materials but interact make them a member of a class of metamaterials. These hold great promise because you can combine the properties of two types of solids."

A paper on the topic, "Nanoparticle Assemblies with Molecular Springs: A Nanoscale Thermometer," is available online at the Journal Angewandte Chemie International Edition. The paper was written by Kotov and collaborators J. Lee, a postdoctoral associate in the Chemical Engineering Department, and A.O. Govorov, a professor in the Department of Physics and Astronomy at Ohio University.

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