Single Cell Metabolite Detection Using Inertial Microfluidics-Assisted Ion Mobility Mass Spectrometry

Single-cell metabolite measurement
remains highly challenging due
to difficulties related to single cell isolation, metabolite detection,
and identification of low levels of metabolites. Here, as a first
step of the technological development, we propose a novel strategy
integrating spiral inertial microfluidics and ion mobility mass spectrometry
(IM-MS) for single-cell metabolite detection and identification. Cells
in methanol suspension are inertially focused into a single stream
in the spiral microchannel. This stream of separated cells is delivered
to the nanoelectrospray needle to be lysed and ionized and subsequently
analyzed in real time by IM-MS. This analytical system enables six
to eight single-cell metabolic fingerprints to be collected per minute,
including gas-phase collisional cross section (CCS) measurements as
an additional molecular descriptor, giving increased confidence in
metabolite identification. As a proof of concept, the metabolic profiles
of three types of cancer cells (U2OS, HepG2, and HepG2.215) were successfully
screened, and 19 distinct lipids species were identified with CCS
value filtering. Furthermore, principal component analysis (PCA) showed
differentiation of the three cancer cell lines, mainly due to cellular
surface phospholipids. Taken together, our technology platform offers
a simple and efficient method for single-cell lipid profiling, with
additional ion mobility separation of lipids significantly improving
the confidence toward identification of metabolites.