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Raman image of cellulose structure in poplar. From a 2006 paper by Gierlinger and Schwanninger. Click to enlarge.

A researcher at the US Department of Energy’s Ames Laboratory is applying Raman imaging—a well-known technique—to analyze plant cell structure to determine which crops offer the right combination of cell wall composition and degradation to maximize the materials’ conversion to ethanol. 

Emily Smith, who is also an Iowa State University Assistant Professor of Chemistry, specifically plans to screen the lignin, hemicellulose and cellulose content of biofuel plant stocks, such as switchgrass, Miscanthus, corn, and poplar and willow trees.

Lignin interferes with enzymatic conversion of polysaccharides to ethanol, so Smith will use the imaging to help select plant stocks that have low lignin content.

If the research proves successful, a simplified version of the test could be used in the field to determine if plants were at the prime stage for harvest.

Just like vintners monitor and test the sugar content of their grapes in the field, biofuel producers could potentially use this technology to determine if their crop was at optimal development for conversion to ethanol.

—Emily Smith

The Raman technique employs an optical microscope. Specimens are illuminated with a laser beam.  As the laser light hits the sample, some of the light is scattered.  By analyzing the scattered light with a spectrometer, Smith can easily and quickly determine the chemical makeup of the plant material. A fiber optic bundle placed between the microscope and the spectrometer allows a direct measure of the chemical makeup at any location on the sample being viewed on the microscope.

The method requires little material, allowing for sampling from a growing plant without damaging the plant, according to Smith. Furthermore, because only very small pieces of plant material are needed and little time is required to prepare samples, multiple samples can be analyzed quickly, making the technique high-throughput.

Plant material for the project will be provided by collaborator Ken Moore, Iowa State University agronomy professor and expert in biomass crop systems.

We hope to find out if lignin content changes over time, with different growing conditions, or with different stock material so we can determine if there is an optimal time to harvest a particular crop.

—Emily Smith

Smith has been using the Raman imaging technology to study animal and insect proteins and said it wasn’t a “big leap” to study plant material.

Smith’s work is being jointly funded through a two-year grant from ISU’s Plant Science Institute and by the DOE’s Office of Basic Energy Sciences.




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