# The unbinding probability

Another quantity related to the number of molecule present on the surface is the unbinding probability P_{unb}i_{nding} that is usually defined as a ratio between the number of curves with the unbinding events to the total number of the recorded force curves:

Its value corresponds directly to the number of molecules present on a surface of living cells, which can vary depending on the complex or cell types [53] (see also Table 5.2).

Table 5.2 The unbinding probability determined for non-malignant HCV29 and malignant T24 bladder cells [53]

Cells |
Lectin-glycan complex |
Number of force curves |
Number of unbinding events |
Unbinding probability |

HCV29 |
ConA |
3982 |
438 |
0.110 |

HCV29 |
SNA |
4057 |
215 |
0.053 |

T24 |
ConA-mannose |
3983 |
111 |
0.028 |

T24 |
SNA-sialic acid |
4095 |
344 |
0.084 |

^{1}ConA-lectin from *Canavalia ensiformis. *^{2}SNA-lectin from *Sambucus nigra.*

The determination of the unbinding probability gives only the robust estimation of the number of receptors present on the investigated cellsâ€™ surfaces. This parameter does not describe the receptor distribution over the cell surface. The same unbinding probability value can be obtained for receptors randomly distributed over a certain area as well as in the case when receptors are grouped around one place in the same area.