Single-cell capillary electrophoresis mass spectrometry (CE-MS) is a promising platform to analyze cellular contents and probe cell heterogeneity. However, current single-cell CE-MS methods often rely on offline microsampling processes and may demonstrate low sampling precision and accuracy. We have recently developed an electrospray-assisted device, spray-capillary, for low-volume sample extraction. With the spray-capillary, low-volume samples (pL−nL) are drawn into the sampling end of the device, which can be used directly for CE separation and online MS detection. Here, we redesigned the spray-capillary by utilizing a capillary with a <15 μm tapered tip so that it can be directly inserted into single cells for sample collection and on-capillary CE-MS analysis. We evaluated the performance of the modified spray-capillary by performing single-cell microsampling on single onion cells with varying sample injection times and direct MS analysis or online CE-MS analysis. We have demonstrated, for the first time, online sample collection and CE-MS for the analysis of single cells. This application of the modified spray-capillary device facilitates the characterization and relative quantification of hundreds of metabolites in single cells.
The analysis of low-volume samples provides valuable
insight into
complex biological systems. However, the proteomic and metabolomic
analysis of low-volume samples remains challenging due to the lack
of simple, efficient, and reproducible microsampling techniques. We
have developed an electrospray-assisted device for quantitative low-volume
sample extraction, referred to here as “Spray-Capillary”.
Stable electrospray was achieved through a chemically etched tip from
a long (e.g., 50 cm) capillary with a conductive sheath flow. This
electrospray provided the driving force to quantitatively draw low-volume
samples into the capillary. We evaluated the precision and accuracy
of sample injection volumes using our spray-capillary as the electrospray
voltage, capillary ID, and column length were varied. Our results
demonstrate that spray-capillary allows for reproducible and quantitative
microsampling with low injection flow rates (as low as 15 pL/s). Furthermore,
spray-capillary can be directly coupled with capillary zone electrophoresis
(CZE) for separation. Overall, spray-capillary is a simple microsampling
device that holds great potential for high-throughput quantitative
omics analysis of ultralow-volume samples.
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