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Nanoscale Thermometer Has Potential to Boost Temperature Sensing and Other Applications

January 1, 2006 By: Peter Adrian

This content is excerpted from Sensor Technology Alert and Newsletter, a sensor intelligence service published by the Technical Insights unit of Frost & Sullivan.


A nanoscale thermometer nanoparticle assembly, created in the process of research mainly funded by the National Science Foundation and the Defense Advanced Research Projects Agency, has potential for very accurately measuring temperature and for facilitating such applications as more accurate medical testing devices, as well as applications in homeland security, and micro- and nano-electromechanical system technologies. The technology, which is well-suited for use with microfludic devices, could potentially help facilitate a new family of nanotechnology-based sensing and optoelectronic devices.

"The accurate temperature regime is critical for medical applications," stated Nicholas Kotov, associate professor of chemical engineering at the University of Michigan. "All of the biological systems are temperature sensitive. 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. 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."

Moreover, in contrast to existing devices, the nanothermometer is potentially capable of measuring temperature in micro- and nanoscale volumes of water because the spaces are in some cases thousands of times smaller than the commas on a page.

The nanothermometer was made by attaching a core gold nanoparticle (about 20 nm in diameter) and a cadmium telluride nanoparticle (about 3.7 nm in diameter) to opposite ends of a flexible polymer, which acts as a spring. The particles interact optically. The nanothermometer's underlying microscopic detection mechanism involves plasmon resonance and excitonplasmon interaction. When excited by laser light, the cadmium telluride glows. When many polymers connect to the gold core, they fan out and form a corona shape.

The polymer spring functions in the fashion of 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 or farther apart. At low temperature, the cadmium telluride glows more brightly, since the spring is tighter and the cadmium telluride is closer to the gold. As temperature increases, and the spring stretches, the glow is less pronounced. With the molecular spring, scientists can detect temperature changes down to one or two degrees.

Kotov has noted that the nano device's responses are not limited to temperature. "In terms of applications, this stimulus response system is actually just the beginning of many other, similar structures of sensing devices," he stated. Researchers could design the particle to respond to varied 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," he stated.

'Nanoparticle assemblies with molecular springs: A nanoscale thermometer,' by Jaeboom Lee, Alexander Govorov, and Nicholas Kotov, published in the journal Angewandte Chemie International Edition (2005; vol: 44; pp: 7439-7442) notes that: "Compared to other approaches to sensing with nanocolloides, the expansion and contraction of molecular springs represents a very sensitive transduction mechanism for clinical detection: Any change in the dimensions of the superstructure results in a shift of the plasmon resonance with respect to the exciton energy and, subsequently, in a reduction of the enhancement factor."

Kotov told Sensor Technology that some particularly promising applications for the nanoscale assembly technology include testing and monitoring of nano- and microfluidic devices. He noted that the researchers have already demonstrated the ability to design the device to measure parameters other than temperature. Future enhancements to the technology depend on the particular application of interest.

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