## 2 Applications of Chiral Nanoparticles
### Biomedicine
They observed that D-Pen@Se NPs were more efficient inhibitors and they improved both understanding and memory impairments. Furthermore, D-Pen@Se NPs also decreased Zn\({}^{2+}\)-induced intracellular A\(\beta\)\({}_{40}\) fibrillation in PC12 cells, while L-Pen@Se NPs did not, suggesting a potential biomedical application of chiral D-Pen@Se NPs (Figure 6). [PERSON] et al. used Au NPs (diameter of \(\approx\)4 nm) functionalized with \(N\)-isobutyl-L(D)-cysteine (L(D)-NIBC) as a prototype to exemplify the chiral effect on the amylin fibrillation at nano-bio interface [70]. The authors stated that both enantiomers were able to inhibit amylin fibrillation in a dose-dependent way but the inhibition obtained with the L-functionalized NPs was higher than that with the D-functionalized NPs. In situ real time CD spectra evidenced that L-NIBC-Au NPs were able to inhibit the conformational change of amylin from random coils to \(\alpha\)-helix, while the D enantiomer could only delay but not avoid the construction of the \(\alpha\)-helix. These encouraging results shed some light on the mechanism of formation of amyloid peptides from a chiral point of view and could help in designing novel therapeutic inhibitors for anti-amyloidosis formation in neurodegenerative diseases. Chirality has also been shown to impact cellular internalization and cytotoxicity. [PERSON] and colleagues reported that gold nanocubes (Au NCs) and nanooctahedras (Au NOs) covered with polyacryl-L(D)-valine (L(D)-PAV) exhibited different cytotoxicity to A549 cells despite having the same size, morphology, and ligand density [71]. The L-PAV-capped Au NCs and Au NOs exhibited  
Figure 6: Inhibition effects of chiral penicillin-capped NPs both in vitro and in vivo. Reprinted with permission from [69], Copyright Elsevier, 2017.  
higher cytotoxicity than the D-PAV coated forms, and the PAV-Au NOs were more cytotoxic than PAV-Au NCs when capped with the same type of enantiomers, respectively. Their cytotoxicity was associated with the internalized amount and the subsequent production of intracellular reactive oxygen species (ROS). Silver NPs, well known for their antibacterial activity, were functionalized with chiral molecules. For example, [PERSON] and colleagues conjugated the herbicide imazethapyr (IM), usually employed as racemic mixture although just the (\(R\)) enantiomer is active, to Ag NPs and investigated their cytotoxic effect on _Arabidopsis thaliana_[72]. They showed that exposure of IM-Ag NPs to _A. thaliana_ could intensify the enantioselective ecotoxicity. They found that the silver effectiveness in roots was 1.40-fold higher when bound to the herbicially active (\(R\))-IM than when capped to the (\(S\)) enantiomer. Similarly, Ag\({}^{+}\) concentration was 77.78% higher in sprouts when (\(R\))-IM-Ag NPs were used instead of (\(S\))-IM ones, suggesting a preferential uptake of the silver when bound to the (R) enantiomer. Silver toxicity in chiral nanoparticles was also studied by [PERSON] and colleagues, who functionalized them with cysteine and investigated their enantioselective phytotoxic effect [73]. Freshwater microalgae _Scenedesmus obliquus_ and terrestrial plant _Arabidopsis thaliana_ were used as a model and they behaved differently to exposure to the chiral system. The authors observed that Ag NPs exerted their toxicity to _S. obliquus_ by exploiting Ag\({}^{+}\), produced in higher quantities by D-Cys-Ag NPs; on the other hand, _A. thaliana_ was more susceptible to L-Cys-Ag NPs, which produced more ROS and oxidative stress. [PERSON] et al. exploited mesoporous silica nano-cocoons (A-CMSNs) functionalized with a chiral anionic surfactant, \(N\)-palmity-L-alanine, for the drug delivery of indomethacin (IMC), a poorly water-soluble drug [74]. The use of chiral surfactants influenced the 2D hexagonal morphology of the A-CMSN with curled channels on its surface, differently from typical 2D hexagonal mesoporous silica nanoparticles with straightaway channels, thus also enhancing the drug loading and its release profile.