Nanoparticle Method for Rapid Detection of Pathogens

A new diagnostic method based on DNA-coated nanometer-sized gold particles and Raman spectroscopy has been developed to detect infectious disease agents. The technique was described in the August 30, 2002, issue of Science.

Researchers from Northwestern University (Evanston, IL, USA; www. northwestern.edu) have produced detection probes consisting of unique DNA subunits attached to 13 nm gold particles. These probes are used in conjunction with a chip spotted with strands of DNA designed to recognize different pathogenic organisms. If the pathogen is present in the sample being tested, it binds to the appropriate spot on the chip. Corresponding nanoparticle probes then bind to the organism. The chip is washed and then treated with ordinary photographic developing solution. Silver from the developer coats the gold nanoparticles where a match has taken place. The chip is then examined by Raman spectroscopy, and the signals for the probes are recorded. In this fashion a unique fingerprint can be designed for each biologic agent.

Raman spectroscopy is the measurement of the wavelength and intensity of inelastically scattered light from molecules. The Raman scattered light occurs at wavelengths that are shifted from the incident light by the energies of molecular vibrations. The mechanism of Raman scattering is different from that of infrared absorption, and Raman and infrared (IR) spectra provide complementary information. Typical applications are in structure determination, multicomponent qualitative analysis, and quantitative analysis.

"The silver enhances the signal by many orders of magnitude, creating a highly sensitive method for detecting DNA,” explained senior author Dr. Chad A. Mirkin, director of Northwestern University's Institute for Nanotechnology. "By providing a near infinite number of signals, this advance allows researchers to quickly and accurately screen a sample for an extraordinarily large number of diseases simultaneously. Our technique seems to surpass conventional fluorescence-based methods in almost every category -- sensitivity, selectivity, ease of use and speed -- and has the potential to be very inexpensive.”



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