Imaging biofuels

Raman imaging is being used to help researchers determine which crops are best suited for conversion to ethanol.

Skyrocketing petrol prices and growing concern over global warming has spawned massive growth of the biofuel industry, particularly ethanol production.

While corn has been the major raw material for producing ethanol, producers are looking for other more cost effective and sustainable crops and researchers at the US Department of Energy’s Ames Laboratory are looking at a novel way to help them determine what type of plant material offers the best solution.

Analytical chemist Emily Smith plans to use Raman imaging to study plant cell structure to determine which crops offer the right combination of cell wall composition and degradation to maximise the materials’ conversion to ethanol.  If successful, a simplified version of the test could even 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,’ said Smith, who is also an Iowa State University assistant professor of chemistry.

The Raman technique Smith uses employs an optical microscope, and specimens are illuminated with a laser beam. As the laser light hits the sample, some of the light is scattered. By analysing the scattered light with a spectrometer, Smith can easily and quickly determine the chemical makeup of the plant material.  A fibre 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.

‘This method has several advantages over other analytical techniques,’ Smith explained. ‘First, analysis requires very little material so you can take small samples from a growing plant over time without damaging the plant.’

This also makes the technique high-throughput because only very small pieces of plant material are needed and little time is required to prepare samples, multiple samples can be analysed quickly.

Smith specifically plans to screen the lignin, hemicellulose and cellulose content of biofuel plant stocks, such as switchgrass, Miscanthus (a subtropical perennial grass that can grow 4m high), 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.

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

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

While the scope of this project will be used to study biofuel crops, Smith said the technology could also be used to study other plant materials, such as those used for pharmaceuticals.

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.