Single-Cell Lipidomics:
Characterizing and Imaging
Lipids on the Surface of Individual Aplysia californica Neurons with Cluster Secondary Ion Mass Spectrometry
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Abstract
Neurons isolated from Aplysia californica, an organism with a well-defined neural network, were imaged with
secondary ion mass spectrometry, C<sub>60</sub>-SIMS. A major lipid
component of the neuronal membrane was identified as 1-hexadecyl-2-octadecenoyl-<i>sn</i>-glycero-3-phosphocholine [PC(16:0e/18:1)] using tandem
mass spectrometry (MS/MS). The assignment was made directly off the
sample surface using a C<sub>60</sub>-QSTAR instrument, a prototype
instrument that combines an ion source with a commercial electrospray
ionization/matrix-assisted laser desorption ionization (ESI/MALDI)
mass spectrometer. Normal phase liquid chromatography mass spectrometry
(NP-LC–MS) was used to confirm the assignment. Cholesterol
and vitamin E were also identified with in situ tandem MS analyses
that were compared to reference spectra obtained from purified compounds.
In order to improve sensitivity on the single-cell level, the tandem
MS spectrum of vitamin E reference material was used to extract and
compile all the vitamin E related peaks from the cell image. The mass
spectrometry images reveal heterogeneous distributions of intact lipid
species, PC(16:0e/18:1), vitamin E, and cholesterol on the surface
of a single neuron. The ability to detect these molecules and determine
their relative distribution on the single-cell level shows that the
C<sub>60</sub>-QSTAR is a potential platform for studying important
biochemical processes, such as neuron degeneration