According to the methods used for sampling contents from single cells, we classified ambient SCMS techniques into three categories: direct suction by microprobes, microextraction by probe with solid or liquid phase, and direct desorption and ionization . The first two categories primarily use probe-based approaches. Due to the small size of single cells, often only a few micrometers, traditional sampling and preparation techniques from bulk analyses are not applicable. Microprobes were introduced to meet the specific requirements of single-cell analysis .