Although fear is known to serve essential purposes in protecting individuals from dangerous situations and threats, dysfunction of fear response can lead to neuropsychiatric disorders – such as pathological anxiety and post-traumatic stress disorder. The understanding of the neuropathophysiology of those disorders is still limited, and therapeutic options (psychotherapy or medication) remain in some cases ineffective. Works investigating the function of neuronal networks helped highlight the implication of the dorsomedial prefrontal cortex (dmPFC) in fear response. Moreover studies on mice have shown, using fear conditioning and dmPFC optogenetic stimulation, that fear behavior can be precisely manipulated. As with several other pathophysiological contexts, neuromodulation could be considered as a potential therapeutic solution for fear-linked psychiatric disorders. In particular optogenetic stimulation, with its unmatched precision (down to the cellular subtype) and versatility (ion and kinetic tunability), offers new possibilities for cell-stimulation based strategies. Recent works attempt to use near-infrared light (NIR) to perform optogenetics, potentially overcoming the need for a light-delivery implant that can harm the tissue, either by using red shifted opsins, or through NIR to visible photoconversion with UpConversion NanoParticles (UCNP). These works present the development and use of a Fluorescent Organic Nanoparticles (FONs) toolbox, and their application to dmPFC stimulation for fear behavior manipulation in mice. These FONs could be a solution for the application of optogenetic stimulation to stimulate the brain (which is biologically highly protected) without an invasive implant, but also apply light-based stimulation to mobile organs and eventually new preclinical applications.