In the field of cellular biology, single-cell analysis refers to the study of individual cells isolated from tissues in multi-cellular organisms. Single cell analysis is a natural step in the reductionist approach to studying organisms. By studying one cell at a time, the results are certain to stem from that particular cell. A cell can for example be monitored as it migrates or divides into two cells, how many divisions that occur over time and the rate of cell division in a specific cell clone. Cell divisions are interesting in for example cancer, due to the uncontrolled rate of cell proliferation of a cancer cell as compared to a normal cell.
Genetic patterns and protein expression can explain cellular behavior to a large extent, but the dynamic study of living cells can increase the understanding of the interconnecting molecular events continually taking place in each cell . Each cell is more or less different from the other, even within the same cell type. Cellular heterogeneity is well known in bacteria and increasingly apparent in eukaryotic cells. For a long time it was desired as well as assumed that cell cultures were of a homogeneous nature, and that analyzing a collection of cells would give an accurate assessment of the behavior of the cells in that culture or tissue. The average response of the cells was, and often still is, interpreted as the response of all cells in that sample. Additionally, the effect of cell number (signaling, interactions, etc.) on cell behavior was, and is still often, neglected due to difficulties in monitoring such detailed phenomena. The attitude to ensemble measurements is starting to change; today's researchers are increasingly aware of, hence interested to study, the resulting effects of heterogeneity in cell samples, as mirrored in recent reviews on single-cell analysis.
The title term may also refer to chemical analysis of the contents of a cell. For example, fluorescent probes built around 15-crown-5 and 18-crown-6 have been used to follow intra-cellular sodium and potassium ions.