Microextraction by probe with solid or liquid phase. These methods for single-cell analysis are divided into solid-liquid and liquid-liquid microextractions . In solid-liquid microextraction , a surface-treated metal needle is introduced into a single cell to extract and enrich analytes, which are subsequently analyzed by mass spectrometry under ambient conditions. Techniques such as probe electrospray ionization , direct sampling probes , and surface-coated probe nanoESI-MS are examples of solid-liquid microextraction developed for single-cell analysis. On the other hand, liquid-liquid microextraction employs organic solvents (e.g., methanol and acetonitrile) for extraction. These methods generally do not require additional solvents for MS analysis, leading to a higher throughput compared to solid-liquid techniques. In liquid-liquid extraction, a capillary is typically used to introduce the solvent, which then carries dissolved analytes to the mass spectrometer.