Carbon dots: Types, preparation, and their boosted antibacterial activity by photoactivation. Current status and future perspectives.

Carbon dots (CDs) correspond to carbon-based materials (CBM) with sizes usually below 10 nm. These nanomaterials exhibit attractive properties such us low toxicity, good stability, and high conductivity, which have promoted their thorough study over the past two decades. The current review describes four types of CDs: carbon quantum dots (CQDs), graphene quantum dots (GQDs), carbon nanodots (CNDs), and carbonized polymers dots (CPDs), together with the state of the art of the main routes for their preparation, either by "top-down" or "bottom-up" approaches. Moreover, among the various usages of CDs within biomedicine, we have focused on their application as a novel class of broad-spectrum antibacterial agents, concretely, owing their photoactivation capability that triggers an enhanced antibacterial property. Our work presents the recent advances in this field addressing CDs, their composites and hybrids, applied as photosensitizers (PS), and photothermal agents (PA) within antibacterial strategies such as photodynamic therapy (PDT), photothermal therapy (PTT), and synchronic PDT/PTT. Furthermore, we discuss the prospects for the possible future development of large-scale preparation of CDs, and the potential for these nanomaterials to be employed in applications to combat other pathogens harmful to human health. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Infectious Disease.

Curcumin/d-mannitol as photolarvicide: induced delay in larval development time, changes in sex ratio and reduced longevity of Aedes aegypti.

BACKGROUND: Resistant populations of Ae. aegypti have been a major problem in arboviruses epidemic areas, generating a strong demand for novel methods of vector control. In this regard, our group has demonstrated the use of curcumin as an efficient photoactive larvicide to eliminate Ae. aegypti larvae. This work was aimed to evaluate the Ae. aegypti (Rockefeller) development under sublethal conditions, using a curcumin/d-mannitol (DMC) formulation. The photolarvicidal efficacy under semi-field and field conditions (wild populations) was also analyzed, as well as the photobleaching and residual activity of DMC. RESULTS: A delay in development time when larvae were exposed to sublethal concentrations of DMC was observed, followed by significant changes in sex ratio and reduction in longevity. DMC also presented a low residual activity when compared to usual larvicides, and had a substantial photolarvicidal activity against wild populations in field trials, achieving 71.3% mortality after 48 h. CONCLUSIONS: Overall, these findings are of great biological importance for the process of enabling the implementation of DMC as a new product in the control of Ae. aegypti larvae, and contributes to the improvement of new plant-based larvicides. © 2021 Society of Chemical Industry.

Curcumin in formulations against Aedes aegypti: Mode of action, photolarvicidal and ovicidal activity.

Combating the Aedes aegypti vector is still the key to control the transmission of many arboviruses, such as Dengue, Zika, and Chikungunya. As few products are efficient for Aedes aegypti control, the search for new strategies have become pivotal., t Substances with photodynamic activity, such as curcumin and their formulations, are strongly encouraged, due to their multi-target mechanism of action. In this study, we evaluated the photolarvicidal and ovicidal activity of curcumin in the presence of sucrose (named SC) and d-mannitol (named DMC). To support the understanding of the larvicidal action of these formulations, Raman micro-spectroscopy was employed. We also studied the morphological changes in Danio rerio (Zebrafish) gills, a non-target organism, and demonstrate that this is an environmentally friendly approach. Both SC and DMC presented a high photo-larvicidal potential. DMC showed the highest larval mortality, with LC50-24h values between 0.01 and 0.02 mg.L-1. DMC also significantly decreased egg hatchability, reaching a hatching rate of 10 % at 100 mg.L-1. The analysis of molecular mechanisms via Raman micro-spectroscopy showed that DMC is highly permeable to the peritrophic membrane of the larva, causing irreversible damage to the simple columnar epithelium of the digestive tube. Histological changes found in the D. rerio gills were of minimal or moderate pathological importance, indicating an adaptive trait rather than detrimental characteristics. These findings indicate that curcumin in sugar formulations is highly efficient, especially DMC, proving it to be a promising and safe alternative to control Aedes mosquitoes. Moreover, Raman micro-spectroscopy demonstrated high potential as an analytical technique to understand the mechanism of action of larvicides.

Environmental safety and mode of action of a novel curcumin-based photolarvicide.

Aedes aegypti is the vector of important diseases like dengue, zika, chikungunya, and yellow fever. Vector control is pivotal in combating the spread of these mosquito-borne illnesses. Photoactivable larvicide curcumin obtained from Curcuma longa Linnaeus has shown high potential for Ae. aegypti larvae control. However, the toxicity of this photosensitizer (PS) might jeopardize non-target aquatic organisms. The aim of this study was to evaluate the toxicity of this PS to Daphnia magna and Danio rerio, besides assessing its mode of action through larvae biochemical and histological studies. Three PS formulations were tested: PS in ethanol+DMSO, PS in sucrose, and PS in D-mannitol. The LC50 of PS in ethanol+DMSO to D. rerio was 5.9 mg L-1, while in D. magna the solvents were extremely toxic, and LC50 was not estimated. The PS formulations in sugars were not toxic to neither of the organisms. Reactive oxygen species (ROS) were generated in D. magna exposed to 50 mg L-1 of PS in D-mannitol, and D. rerio did not elicit this kind of response. D. magna feeding rates were not affected by the PS in D-mannitol. Concerning Ae. aegypti larvae, there were changes in reduced glutathione and protein levels, while catalase activity remained stable after exposure to PS in D-mannitol and sunlight. Histological changes were observed in larvae exposed to PS in sucrose and D-mannitol, most of them irreversible and deleterious. Our results show the feasibility of this photolarvicide use in Ae. aegypti larvae control and its safety to non-target organisms. These data are crucial to this original vector control approach implementation in public health policies.