THE USE OF LIQUID MICROJUNCTIONS AS AN ANALYTICAL TOOL IN BIOLOGICAL SURFACE ANALYSIS

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Authors
McEwen, Rory
Keyword
microfluidics , analytical chemistry , strawberries , tissue imaging , mass spectrometry , ambient soft ionization , LMJ-SSP , MALDI , ESI , electrospray ionization , Imaging Mass Spectrometry
Abstract
Imaging mass spectrometry (IMS) typically requires extensive sample preparation involving formalin fixation, staining, matrix deposition and embedding (e.g. optimum cutting temperature polymer, OCT) to enable microtomy. The sample preparation steps add considerable time to the analysis and risk altering analyte distribution. Herein we investigate the use of liquid microjunctions as a tool in imaging mass spectrometry to mitigate sample handling steps. First, we describe a new liquid tissue stamping method, Poly-Synchronous Surface Extraction (PSSE), that utilizes an omniphobic substrate patterned with hydrophilic surface energy traps, which when wetted with solvent, form a dense microdroplet array. When contacted with a tissue sample, each droplet locally extracts analytes from the tissue surface, which subsequentially can be analyzed with MALDI-MS or ambient ionization-MS techniques (LMJ-SSP). Optimization of the patterned surface (droplet size and spacing) and its comparison to established imaging techniques is examined. The PSSE method showed good alignment with direct analysis and demonstrated potential to increase the speed of ambient MS tissue imaging techniques. Secondly, the different properties associated with liquid microjunction surface sampling probe imaging mass spectrometry were investigated to determine their effect on the overall image quality. Extraction tests examined the extraction efficiencies of eight different solvents/mixtures. Four of the solvents from the extraction test and one additional mixture were then used as the LMJ-SSP solvent to directly image 10μm thick strawberry slices. After concluding the best imaging solvent (50/50 Water/Methanol), the dependency of sample thickness on signal intensity was investigated. In addition, an absolute quantitative imaging run was conducted using a pseudo internal standard and at external calibration curve. The use of liquid microjunction methods for direct and indirect analysis showed great potential for increasing sensitivity and versatility, while also decreasing sample handing steps.
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