Due to their exceptional optical properties and the vast opportunities provided by surface functionalization, Quantum Dots (QDs, i.e. semiconductor nanocrystals) are prime candidates for theranostics applications, which aim at combining diagnosis, targeting and therapy agents on a single nanoplatform. Ag2S-based QDs have recently emerged as promising nanoplatforms for in vivo imaging due to their ability to emit in the NIR spectral region, enabling for deep tissue imaging. In addition to their photophysical performance, these QDs are made of a highly stable and non-toxic material, Ag2S, paving the way for in vivo applications. However, as of today, clinical studies are precluded by the lack of knowledge about the nano-specific behavior of Ag2S-QDs in vivo. This thesis work focuses on further developing aqueous-based synthetic routes to produce NIR emitting Ag2S QDs, and fully characterise their photophysical and structural properties both in colloidal dispersions and in cellulo. Here, two aqueous phase synthetic approaches are explored yielding both NIR-I and NIR-II emitting Ag2S QDs. Conventional lab-based techniques are employed to characterise the photophysical and morphological properties of the QDs, and their dependence on the modulation of the reaction conditions studied (SyMMES, CEA Grenoble). Their biocompatibility is assessed through toxicity assays in human liver cancer cells to evaluate their suitability as in vivo imaging probes. Finally, in-depth X-ray Absorption Fine Structure spectroscopy, in collaboration with the European Synchrotron Radiation Facility (ESRF), is used to divulge the local chemical environment of the QDs and detect their fate in cellulo (CBM, CEA Grenoble). By integrating synthesis with advanced characterisation, this work contributes to the development of stable NIR emitting Ag2S QDs, which hold great promise for in vivo imaging. These results provide an exciting opportunity for the development of new non-toxic bio-probes, with the potential to conjugate to bioactive molecules, paving the way for a new generation of multi-modal QD-based probes for biomedical applications.[ ​​​​
​

​​
​