## 4 Discussion  
Synthesized CNSs have been tested for various applications, such as electrode materials for energy storage devices and electrochemical sensors [37; 42], in photomechanical actuators [43], and as materials for CO\({}_{2}\) adsorption [44], owing to the very high surface area and porosity. Such varied and increased use of nanoparticles leads to the exposure of humans to nanoparticles. Therefore, it is highly necessary to investigate the toxic effects elicited by such nanoparticles and various other nanomaterials and to determine the non-toxic dose for practical or safe applications. There are many studies investigating the toxic effect of carbon nanoparticles on the biological system [45; 46; 47]. In the present study, the toxicity of mesoporous CNSs synthesized from waste onion peel was evaluated using _Drosophila melanogaster_ as an in vivo animal model. The mesoporous CNSs used in the current analysis have not been evaluated previously for their toxic effects using an in vivo model system. The present study's overall results highlight the non-toxic nature and beneficial impacts of mesoporous carbon nanoparticles at 1, 10, and 100 \(\mu\)L/mL doses. The feeding of oral magnetite nanoparticles in _Drosophila_ caused developmental changes, with a delay in egg to pupae and pupae to adult transformations [48]. Therefore, to assess the effect of mesoporous CNSs on the development of _Drosophila_, all the developmental stages were carefully analyzed. The larvae from the control and the treated groups at different concentrations reached different developmental stages such as larva, pupa, and adult on the same day. Thus, the oral administration of mesoporous carbon nanoparticles does not elicit any developmental delay in _Drosophila_. The negative geotaxis or climbing assay was performed to assess the physiological impact of carbon nanoparticles on the motor system. Normally, flies tend to climb upwards when they are offered freedom to move vertically, and this can also be used to assess the neurodegeneration phenotype [26; 49; 50]. In the current analysis, the absence of significant changes in the climbing activity in CNS-nanoparticle-treated flies compared to control flies suggests that the oral administration of CNSs for 25 days did not cause any physiological/motor or neurodegenerative defects. Neurotoxicity refers to the structural and functional changes in the neurons and glial cells in the central and peripheral nervous systems. The AChE assay is used to evaluate the activity of AChE, an enzyme that hydrolyzes acetylcholine to choline and acetic acid, and this analysis has been previously used to assess the neurotoxic potential of NPs in _Drosophila_[51; 52]. The current results of the AChE analysis upon oral exposure to CNSs for 25 days did not reveal any significant changes in the activity of the enzyme. This suggests the absence of neurotoxicity upon dietary administration of CNSs at different concentrations. The effect of CNS ingestion on the metabolic activities in _Drosophila_ was studied. It was previously reported that the ingestion of silver NPs at higher concentrations affected the energy reserves in flies, such as glycogen and protein. It also altered the feeding behavior in flies [41]. To test whether oral ingestion of CNSs for 25 days affected the energy reserves and feeding behavior in flies, the glucose, protein, and triglyceride levels in flies. The results suggest that CNSs can be used to obtain beneficial effects in animals. The non-toxic nature of the synthesized mesoporous carbon nanomaterials in low concentrations could be due to their highly porous nature. Earlier research on functionalized CNTs has indicated a reduction in the toxicity of nanomaterials upon functionalization. This has been attributed to the formation of more defects within the system during the preparation of functionalized CNTs [20].