During cancer radiotherapy protocols, the early profile of energy deposition is decisive for the prediction and control of radiation-induced biomolecular and sub-cellular damage. A major challenge of spatio-temporal radiation biomedicine, a newly emerging interdisciplinary domain, concerns the complete understanding of biophysical events triggered by an initial energy deposition inside confined ionization clusters (tracks) and evolving over several orders of magnitude, typically from femtosecond (1 fs = 10-15 s) and sub-nanometer scales. The innovating advent of femtosecond laser sources providing ultra-short photon beam and relativistic electron bunches, in the eV and MeV domain respectively, open exciting opportunities for a real-time imaging of radiation-induced biomolecular alterations in nanoscopic tracks. Using a very short-lived quantum probe (2p-like excited electron) and high-time resolved laser spectroscopic methods in the near IR and the temporal window 500 – 5000 fs, we demonstrate that short-range coherent interactions between the quantum probe and a small biosensor of 20 atoms (disulfide molecule) are characterized by an effective reaction radius of 9.6 ± 0.2 angströms. For the first time, femtobioradical investigations performed with aqueous environments give correlated information on spatial and temporal biomolecular damages triggered by a very short lived quantum scalpel whose the gyration radius is around 6 angströms. This innovating approach would be applied to more complex biological architectures such as nucleosomes, healthy and tumour cells. In the framework of high-quality ultra-short penetrating radiation beams devoted to pulsed radiotherapy of cancers, this concept would foreshadow the development of real-time nanobiodosimetry combined to highly-selective targeted pro-drug activation.