This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: A patent-pending method developed and tested for multiple applications at Purdue University eliminates sample preparation, a bottleneck that currently dominates a laboratory scientist's time and budget, and enables 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 when spatially analyzing 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 Center 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, lead the team that created STEi. Ferreira said sample preparation for traditional LC-MS/MS analysis requires several steps, including mixing, centrifuging, transferring and drying. "That destroys the sample and throws away spatial information about where a chemical was found in the sample," she said.
"Also, if scientists want to spatially analyze 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." Ferreira disclosed the STEi innovation to the Purdue Innovates Office of Technology Commercialization, which applied for a patent to protect the intellectual property. "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," Ferreira said. The workflow begins 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 and imaging module scan the sample's surface. Software computes a path across the surface to determine where the extraction probe should touch and in what sequence.
A fine probe tip descends to each programmed point on the surface, making contact between the sample and the solvent, which could be water, acetonitrile or a mixture. The force/pressure sensor ensures the probe makes 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. Ferreira said STEi improves upon traditional workflows in several ways. "Sampling takes a few seconds (usually 5–15 seconds) through the contact of a pressure-sensitive probe and the surface of the sample, allowing extraction through a liquid bridge," she said.
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