The ability to tune the properties of semiconductor and semiconductor-metal hybrid nanoparticles for imaging, sensing and optical modulations of specific biological functions, at the molecular, cellular and tissue levels, can deepen our understanding of the corresponding biological processes, reveal the underlying mechanisms for different diseases and open new avenues for developing novel nano-tools and prosthetic devices for treatment and prevention modalities. In our group, we develop nanocrystals based systems for such applications. Recent examples, being the uses of nanocrystals for imaging of inflamed and/or cancerous tissues, for photodynamic therapy, enzymatic and neuronal stimulation in vitro and of blind retinas, development of quantum photoinitiators for 3D biomedical printing, etc.