# Solvent-Dispersible Nanostructured MIMI: An Experimental and Computational Study
## 4 Conclusions  
This paper presents the first example of a nanomaterial with MIMI architecture dispersed in an aqueous environment. The nanomaterial was designed and synthesized according to a seed-mediated growth approach, starting from CTAB-coated gold nanorods, gave shape, step by step, to a hybrid hierarchical structure consisting of the alternation of gold and silica shells, recalling the structure of a matryoshka. The same protocol was applied to any shape of the nanoparticles, and the final plasmonic properties of the nano-matryoshka depended on the shape of the metal core. All the intermediates were characterized, both from a morphological point of view, by TEM, and optically, by UV-Vis spectroscopy. When the matryoshka took shape, the spectrum of both samples changed drastically: the longitudinal band of the nanorods widened substantially until reaching wavelengths in the NIR range, the band of the AuNP@CTAB-derived nanosystems continued to fall into the visible range, but a shoulder around 700 nm was impressive. The computational results, based on an FEM analysis, confirmed the experimental ones, highlighting that the final plasmonic properties of the nano-matryoshka depended on the shape of the metal core and on the refractive index of the surrounding media and could be suitably tuned to the NIR spectrum region. Furthermore, the comparison between the experimental and the calculated spectra allowed estimating the mutual contribution of scattering and absorption to the optical properties of the nanosystems. The computational effort represents a practical tool for the development of matryoshka with specific plasmonic features. These findings could have application in various fields; in particular, the construction of metamaterials in aqueous solution is an exceptional goal, considering the possibility to properly functionalize the nanoparticle surface, obtaining a biocompatible nano-matryoshka that, by exploiting the sensitivity of a metamaterial, could be used for in vivo biopsies. Figure 5: Experimental spectra: extinction spectra of the aqueous colloidal dispersions: AuNP@CTAB (**a**’, blue line); AuNP@SiO\({}_{2}\) (**b**’, red line); AuNP@SiO\({}_{2}\)@seed (**c**’, green line); AuNP@SiO\({}_{2}\)@Au (**d**’, violet line) overlapping with AuNP@SiO\({}_{2}\)@Au@SiO\({}_{2}\) (**e**’, orange dotted line). **Supplementary Materials:** The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app13052982/s1](https://www.mdpi.com/article/10.3390/app13052982/s1)]([https://www.mdpi.com/article/10.3390/app13052982/s1](https://www.mdpi.com/article/10.3390/app13052982/s1)); Figure S1: TEM images and Uv-Vis spectra of AuNS@NaCit; Cross section calculations; Figure S2: Calculated extinction, absorption and scattering cross sections of (a) AuNR, (b) AuNR@SiO2, (c) AuNR@SiO2@Au and (d) AuNR@SiO2@Au@SiO2; Figure S3: EDX measurement of AuNR@SiO2@Au@SiO2; Table S1: Parameters used in the numerical modelling of the nanostructures. [PERSON] synthesized and characterized the samples, wrote the draft of the manuscript, prepared the figures; [PERSON] reviewed the manuscript; [PERSON], [PERSON] and [PERSON], conducted the theoretical study; [PERSON] supervised all steps, wrote the main manuscript text, reviewed and validated the manuscript. All authors have read and agreed to the published version of the manuscript. This research received no external funding. Not applicable. We encourage all authors of articles published in MDPI journals to share their research data. In this section, please provide details regarding where data supporting reported results can be found, including links to publicly archived datasets analyzed or generated during the study. Where no new data were created, or where data is unavailable due to privacy or ethical restrictions, a statement is still required.