Customized Surface Design to Increase Throughput of Ambient Ionization Mass Spectrometry Lipidomics

Increased access to cheap and rapid mass spectrometry
testing of
biofluids is desirable for the analysis of disorders and diseases
that may be linked to alterations in metabolite or lipid levels. The
objective of this study is to establish an easily customized high-throughput
workflow for the analysis of biological samples using desorption electrospray
ionization-mass spectrometry (DESI-MS). The guiding principles of
this workflow are the use of low-cost, open-source, and readily accessible
materials with high-throughput and reproducibility. The design consists
of 3 steps: (1) PARAFILM surface customization of size, shape, and
depth of features on PARAFILM via 3D printed molds; (2) sample spotting
via high-throughput robotics using the relatively inexpensive and
open-source Opentrons platform to reduce variability and increase
reliability of sample spotting; and (3) an open-source point-and-click
graphical user interface (MSI.EAGLE) for data analysis via the R statistical
language building on the Cardinal package. Here we
describe this workflow and test optimal surface ionization characteristics
by comparison of serum extracts spotted on PARAFILM and on PTFE (porous
and nonporous). Untargeted analysis across three surfaces suggests
that they are all suitable for ionization of a wide range of metabolites
and lipids, with 3983 m/z features
detected. Differential analysis of polar vs nonpolar serum extracts
suggests that ∼80% of ions are desorbed preferentially from
different surfaces. PARAFILM is less impacted by the interference
of background ions derived from the surface. The developed system
allows for a wide range of researchers to access custom surface design
workflows and high-throughput analyses in a highly cost-effective
manner.