New Sensing Device Reads Chemical Makeup In Real-Time

Purdue University researchers are bringing this "Star Trek" technology down to Earth by developing a new tool that can be used to chemically analyze a wide variety of materials in real time.

A group of researchers led by chemistry Professor Dor Ben-Amotz has developed a Near-Infrared Raman Imaging Microscope, called NIRIM, which uses laser light to analyze composite materials thousands of times faster than current methods.

The instrument reads the color changes produced when a laser interacts with molecular vibrations, a process known as Raman scattering, to fingerprint a sample as it is being viewed under a microscope.

"It's like having a robot with eyes capable of seeing the chemical structure of what it is looking at," Ben-Amotz says. "Instead of saying this is a piece of plastic, it says this is a piece of plastic made of high-density polyethylene."

Potential applications of the new technology include real-time robotic vision systems, micro-chemical separation methods, medical diagnostics and automated manufacturing.

Details of the new device appear in the August issue of the Journal of Raman Spectroscopy.

The instrument, which was created with support from the National Science Foundation and Purdue, maps the distribution of chemical species present in a sample at unprecedented speed -- as fast as one second instead of hours-- using an optical fiber-bundle image compression technique developed at Purdue.

The method used by the Purdue team builds on recent advances that have given rise to new types of chemical imaging instruments. These new devices can be thought of as a cross between a microscope and an optical spectrometer, a tool that measures the wavelengths associated with different colors of light, Ben-Amotz says.

"An optical spectrometer measures the wavelengths of different colors of light, ranging from red to violet," he says. "In the case of Raman spectroscopy, the resulting colors come from the vibrations of molecules. Because each molecule has a unique pattern of vibration -- determined by its chemical structure -- we can use this method to fingerprint different types of chemicals."

Several scanning methods have previously been used to generate Raman images, but these methods, slowed by the need to collect data one wavelength at a time, cannot collect a complete Raman image in real time, Ben-Amotz says.

"All of these instruments, including ours, rely on a two-dimensional array detector to collect spectral data from various spatial locations, while a Raman image is a three-dimensional data cube," he says. "This means that a method for slicing sequentially through the cube, in order to read the data in two dimensions, is usually required, and that is very time-consuming."

The fiber-bundle image compression method used in the Purdue instrument speeds the process by compressing all the data from the three-dimensional data cube into a single detector frame, allowing all points on the sample to be read in a single pass.

"Our method is unusual in that it collects these images much faster and more efficiently than any other methods," Ben-Amotz says. "Data can be presented so that one read gives us a complete Raman spectrum at every point in the image."

The new method can be up to a thousand times faster than other methods -- completing in seconds or a few minutes analyses that used to take hours or even a day -- making it a good approach to developing applications such as real-time robotic vision or biomedical imaging, Ben-Amotz says.

"The delay of a day is almost like sending a sample out to a laboratory for analysis," he says. "That's where the strength of this technique is. It's a very efficient way of collecting this kind of data."

The ability to analyze chemical composition in real time opens doors to applications for use in manufacturing automation control or developing new types of medical diagnostics, Ben-Amotz says.

"That's not to say there are not limitations to this," he says. "Because our technique takes smaller images -- in the sense of fewer spatial points -- it's harder to acquire images with a large number of points. It can be done, but it takes longer and we become almost equivalent to the other methods."

For each sample, the Purdue instrument analyzes 100 spatial points, analyzing the chemical identify of a thousand different colors for each point. For large images, the detector uses a computer-controlled system to develop a composite image from several smaller images.

"Because it is computer controlled, and because the new method is inherently more efficient than the previous single-color scanning method, each frame is processed quickly, making the method as fast or faster than other high-resolution methods," Ben-Amotz says.

The chemical information content in an image also may be enhanced using sophisticated MultiSpec software originally developed at Purdue for space- and aircraft-based imaging of the Earth's surface.

"The idea is based on the same principle used in enhanced color satellite imaging, except we're focusing on microscopic information instead of cornfields, smokestacks or other surface features," Ben-Amotz says.

The new instrument is in Purdue's Chemistry Departmental Laser Facility and is being used by Purdue faculty members working on a wide variety of applications, including drug development, biological applications, combinatorial chemical imaging and nanoparticle surface chemical analysis.

The instrument was developed in collaboration with Ken Haber, director of the laser facility, Jiaying Ma, a postdoctoral fellow, and graduate students Brian McClain of Lincoln, Calif., and Alan Gift of Des Moines, Iowa.

Ben-Amotz and his group are now working to make the device capable of taking real-time movies so that it can analyze matter in motion. They have succeeded in using it to analyze a film of oil spreading over a surface of sapphire. Ultimately, the technology may someday be used to develop real-time identification methods to address manufacturing waste reduction and quality control issues or to develop tools for medical diagnostics and nanotechnology applications, Ben-Amotz says.

"We are only beginning to realize all of the potential uses for this technology, but the applications seem almost unlimited," he says.