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  • Microscope Offers Portable Raman

Photonics Spectra
Nov 2001
Gary Boas

Raman imaging just got a little easier. For the past couple of years, the department of chemistry at Purdue University in West Lafayette, Ind., has offered chemists, pharmacists and engineers the use of its near-infrared Raman imaging microscopy system. But the range of viable applications was limited by the fact that samples had to be brought to the university's laser facility.

techMicroscopeResearchers at Purdue University have developed a portable Raman imaging microscope. Here, laser facility director Hartmut G. Hedderich analyzes a sample of Tylenol. Courtesy of Purdue University.

"There were many requests for a portable system that can be moved easily into a laboratory environment, to follow reactions as they advance in a reaction vessel, or that can be used for field experiments to quickly analyze samples," said Hartmut G. Hedderich, director of the facility. In response, chemists at the university have developed the portable Raman imaging microscope, or Prim.

Weighing approximately 30 lb, Prim features a 1-W, 799-nm laser diode, a Roper Scientific Inc. SpectraPro 150 spectrograph and a Santa Barbara Instrument Group CCD detector. The laser is fiber coupled through a 7-m-long bundle of 19 200-µm-diameter fibers to an optical rail on a damped mounting post and X-Y-Z stage. The optical rail also contains a Sony Corp. camera board connected to a Snappy 4.0 video snapshot module from Play Inc., which obtains white-light images of the sample. Raman radiation is collected along the same optical path and directed through the spectrograph to the CCD. A laptop computer running KestrelSpec software controls the system.

Prim is similar to conventional systems, but with two significant differences. First, the sample need not be transported into the lab to be imaged. In fact, it need not be moved at all. Prim can image samples that cannot be placed on a microscope stage -- mixtures in a vat, for example -- and can collect data through glass or plastic packaging. Second, the system uses Raman scattering to collect the chemical fingerprints of whatever is on the sample surface. Other Raman microscopes do this, but they require that the sample be on the stage for alignment and focus.

Raman shift to 4000 cm-1

Prim's developers foresee a wide variety of applications for the imaging system, from academic research into catalysts, nanomaterials and micromachines to industrial areas such as quality assurance and control in manufacturing.

"One of the most exciting applications that we are currently pursuing is the use of Prim for skin-cancer screening," said Dor Ben-Amotz, a professor of chemistry at the university and co-creator of the system. The portability of the system could result in more widely available screenings and thus a greater opportunity to detect cancer early.

The portable Raman imaging microscope is available commercially through SpectraCode Inc. of West Lafayette. A second system is under development because the current setup is limited by low resolution resulting from the diode laser linewidth and by an observable Raman shift of approximately 100 to 1900 cm-1. The next system will use a HeNe laser at 633 nm as an excitation source, which should enable higher resolution and a Raman shift of up to 4000 cm-1.

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