## 2 Applications of Chiral Nanoparticles
### Biomedicine  
Chirality is ubiquitous in nature and plays many essential roles in biological processes through homochirality of its basic constituents, i.e., L-amino acids and D-sugars. As a consequence, many chiral biomaterials have been prepared and their influence on biological systems investigated [63]. Chiral NPs have also been shown to possess different behaviors when interacting with biological systems, with the main findings of these studies being summarized in Table 3.  
For example, selenium nanoparticles stabilized with arginine (L(D)-Arg@Se NPs) and additionally functionalized with a dinuclear ruthenium (II) complex, acting as gene carrier and anti-tumor drug, were employed to efficiently deliver short interfering RNA (siRNA) that targeted the multi-drug resistance-1 (MDR1) gene [64]. Remarkably, Ru-L-Arg@Se NPs revealed high tumor-targeted fluorescence, improved anti-tumor efficacy, and reduced systemic toxicity compared to the D-Arg-capped NPs, both in vitro and in vivo. Chiral interactions also allow for the obtaining of a more significant delivery of APIs. Mesoporous silica nanoparticles capped with 3-N-aminopropyl-L-tartaric acid were shown to be more effective in delivering doxorubicin compared to the corresponding achiral NPs, thus resulting in being more cytotoxic to MCF-7 cells [65]. Chiral interaction with biological systems was investigated by [PERSON] and colleagues who synthesized aptamer-driven chiral Ag@Au core shell nanoparticle assemblies that displayed marked \begin{table}
\begin{tabular}{c c c c} \hline \hline
**NPs** & **Surface Functionalization** & **Application** & **Reference** \\ \hline Se & Ru(II)-L-arginine & siRNA delivery & [64] \\ SiO2 & 3-\(N\)-aminopropyl-L-tartaric acid & doxorubicin delivery & [65] \\ Ag@Au & aptamers & tumor targeting & [66] \\ PNBC polypeptides & - & camptothecin delivery & [67] \\ PMO & poly-L-lysine & drug delivery & [68] \\ Se & D-penicillamine & A@ fibrilogenesis inhibition & [69] \\ Au & N-isobutyl-L-cysteine & amylin fibrillation inhibition & [70] \\ Au NCs and NOs & polyacrylamide1-L-valine & cellular uptake/cytotoxicity & [71] \\ Ag & (_R_)-imazethapyr & cellular uptake/cytotoxicity & [72] \\ Ag & cysteine & cellular uptake/cytotoxicity & [73] \\ SiO2 & \(N\)-palmityl-L-alanine & indomethacin delivery & [74] \\ SiO2 & D-tartaric acid & indomethacin delivery & [75] \\ SiO2 & L-tartaric acid & indomethacin delivery & [76] \\ SiO2 & \(N\)-myristyl-L(D)-alanine & ibuprofen delivery & [77] \\ CdS & L-cysteine & BSA binding & [78] \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Main applications of chiral NPs for biomedicine and their principal characteristics. and opposite chiral bisignate plasmonic peaks [66]. The authors showed that the chiral assemblies were able to discriminate circulating HER2 tumor cells from normal cells. Similarly, [PERSON] and colleagues showed that the chirality of poly(S-(o-nitrobenzyl)-L(D)-cysteine) (PNBC) polypeptides influenced their secondary structure and, as a further consequence, also the drug release and biological properties of the associated nanoparticles [67]. [PERSON] et al. also exploited the chirality-dependent cellular uptake of mesoporous silica nanoparticles (MSNs) but they showed that it can be influenced by the amount of organic molecules carried and by the chiral polymers covering periodic mesoporous organosilica (PMO) NPs [68]. As a result, the following release of different quantities of organic molecules to primary fibroblast cells also varied and the authors concluded that this behavior was caused and dominated by the formation of protein corona on the PMO surfaces. A characteristic of [PERSON]'s disease (AD) is the misfolding of amyloid-\(\beta\) (\(\Delta\beta\)) into fibrils and its accumulation into plaques [79]. Consequently, one of the approaches for the treatment of this pathology is to inhibit A\(\beta\) fibrillogenesis. With this aim, [PERSON] et al. prepared chiral penicillin-capped selenium (L(D)-Pen@Se) NPs that could perform as A\(\beta\) inhibitors [69].