A patent-pending method developed and tested at Purdue University can eliminate sample preparation and support spatial analysis using liquid chromatography-tandem mass spectrometry (LC-MS/MS)
The surface touch extraction imaging (STEi) method could benefit food scientists, toxicologists, and other laboratory scientists by enabling spatial analysis of samples with irregular surfaces for metabolites, lipids, environmental compounds and proteins using diverse instrumentation to generate multiomics data.
Christina Ferreira, research assistant professor at Purdue’s Bindley Bioscience Centre with a courtesy appointment in the Department of Food Science, and Ryan Hilger, assistant director of the Jonathan Amy Facility for Chemical Instrumentation in the James Tarpo Jr. and Margaret Tarpo Department of Chemistry, led the team that created STEi.
Ferreira said sample preparation for traditional LC-MS/MS analysis requires several steps, including mixing, centrifuging, transferring, and drying.
She said, “That destroys the sample and throws away spatial information about where a chemical was found in the sample. Also, if scientists want to spatially analyse an irregular surface such as a piece of liver tissue or a fish fillet, they must section it and make it flat to be able to extract the chemicals before the analysis.”
How STEi works
Ferreira said, “The STEi concept workflow essentially allows the user to load a sample, press ‘Run’, and create a spatially resolved chemical portrait of their sample based on an instrumentation input, without ever having to cut, grind or destroy it.”
The workflow starts with the user placing an intact, unprocessed sample, such as a tissue biopsy, food item, or piece of packaging, on the instrument stage. No flattening or grinding is required.
The instrument’s integrated camera/imaging module then scans the sample’s surface, enabling the software to compute a path across the surface to determine where the extraction probe should touch and in what sequence.
A fine probe tip descends into each programming point on the surface, making contact between the sample and the solvent, which could be water, acetonitrile, or a mixture. The force/pressure sensor helps the probe maintain consistent, controlled contact regardless of surface shape.
Ferreira said the pressure-controlled probe’s ability to sample uneven surfaces is a critical differentiator over flat-surface methods.
The software then registers the molecular data back to the original surface coordinates, generating spatial heat maps showing where specific lipids, contaminants, proteins or metabolites are concentrated across the sample.
STEi benefits
How the STEi improves traditional workflows:
- The process is quicker. Sampling takes 5-15 seconds by contacting a pressure-sensitive probe with the sample surface, facilitating extraction via a liquid bridge.
- Different instruments can analyse the collected samples. This enables surface imaging with a high-performance liquid chromatography autosampler and imaging experiments with liquid chromatography coupled to tandem mass spectrometry.
- As only the surface is sampled, samples remain largely intact, so resampling the same piece of food or tissue can be repeated over time.
- Spatial context is preserved. The scientist receives a chemical heat map showing, for example, where a contaminant is concentrated in the sample using the analytical method of choice.
- No expertise in sample preparation is required. STEi is automated and pressure-controlled; less experienced staff members can reliably run samples through the process.
STEi applications
STEi’s applications begin with food safety. Ferreira said, “The technology was designed to detect contaminants on food surfaces and packaging, and food quality and lipid profiling, such as cattle-breed lipid fingerprinting. It also could be used to monitor food spoilage by repeated nondestructive sampling of fresh produce, poultry, dairy and fish over time to track molecular changes. That’s a capability gap, not just an improvement on existing methods.”
Other applications are drug development and the life sciences.
Ferreira added, “In the preclinical toxicology arena, STEi coupled to mass spectrometry tools could map the metabolic impact of drugs, chemicals and proteins across liver, kidney, brain and intestinal tissues from animal models. It would show tissue-specific accumulation patterns and also sample proteins, as these can be extracted.”
The team are searching for partners to test STEi across several applications. The team is evaluating lipid and protein recovery using different probe configurations.
Besides lipids, about 2,000 different proteins have been recovered from bovine muscle using manual STEi, Thirumalaikumar shared. The proteins were functionally classified across contractile, metabolic, antioxidant, and structural categories.
Funding milestones and next development steps
Ferreira and the team received funding from Purdue Innovates’ Trask Innovation Fund to develop STEi.
Ferreira said the team is seeking partners to work on hardware optimisation, software integration for 3D path planning, and additional validation experiments, such as food spoilage monitoring, food packaging contamination detection, and other toxicology applications.
She said, “We also will explore regulatory alignment with the U.S. Food and Drug Administration and the U.S. Environmental Protection Agency analytical frameworks for selected applications.”
Industry partners interested in developing or commercialising STEi should contact Dipak Narula, lead technology development liaison and assistant director of business development and licensing — physical sciences, at [email protected].
