In the last two decades, light responsive nano drug delivery systems (DDSs) have gained considerable importance, particularly in the area of biology and medicine. In general, light responsive nano DDSs are bicomponent and constructed using two ingredients, namely a nanocarrier and a phototrigger. The synthesis of these bicomponent nano DDSs requires multiple steps, which limits their applications. Hence, we have reported single component light responsive nano DDSs using fluorescent organic nanoparticles (FONPs) which acted both as a nanocarrier and a phototrigger. This feature article provides an overview of recently developed light responsive single component FONPs and their applications in the regulated release of anticancer drugs, gasotransmitters, antibacterial agents, and pesticides, and also as efficient PDT agents. We have summarised the synthesis, characterisation, and photophysical, photochemical, and in vitro behaviours of these light responsive FONPs. In addition, we also discussed the advantages of using FONPs as a nano DDS for cellular studies like: excellent biocompatibility, efficient cellular internalisation, real time monitoring of the drug release ability inside the cells, and enhanced cytotoxicity due to regulated release of bioactive molecules inside the cells.