Understanding the Role of AgNO3 Concentration and Seed Morphology to Achieve Tunable Shape Control in Gold Nanostars

Gold nanostars are one of the most fascinating anisotropic nanoparticles. Nanostar morphology can be controlled by changing various synthetic parameters; however, the detailedgrowth mechanisms are not fully understood. Herein, we investigate this process in six-branched nanostars, focusing first on the properties of the single crystalline seed, which evolves to include penta-twinned defects as the gateway to anisotropic growth into 6-branched nanostars. In particular, we report on a high-yield seed-mediated protocol for the synthesis of these particles with high monodispersity in the presence of Triton-X, ascorbic acid, and AgNO3. Detailedspectroscopic and microscopic analyses have allowed the identification of several key intermediates in the growth process, revealing that it proceeds via penta-twinned intermediate seeds. Importantly, we report the first experimental evidence tracking the location of silver withsub-nanometer resolution and prove its role as stabilizing agent in these highly branched nanostructures. Our results indicate that metallic silver on the spikes stabilizes the nanostar morphology, and that the remaining silver, present when AgNO3 is added at high concentration, deposits on the core and between the base of neighboring spikes. Importantly, we also demonstrate the possibility to achieve monodispersity, reproducibility, and tunability in colloidal gold nanostars that are substantially higher than previously reported, which could be leveraged to carry out holistic computational-experimental studies to understand, predict, and tailor their plasmonic response.</div

Shaping Gold Nanostar Electric Fields for Surface-Enhanced Raman Spectroscopy Enhancement via Silica Coating and Selective Etching

The application of gold nanostars in direct and indirect surface-enhanced raman spectroscopy (SERS) sensing has significantly grown in the past few years, mainly because of the particles’ excellent field enhancement properties. However, experimental demonstrations correlating SERS signal enhancements to specific morphology features of the nanostars are still scarce, primarily because of the complexity of the nanostar morphology itself. Herein, we have addressed this fundamental issue by synthesizing surfactant-free gold nanostars, coating them with a uniform silica layer, and then etching the silica away selectively with NaBH₄ to expose increasing amounts of the metallic surface. We have then functionalized the nanoparticles with a Raman active molecule, aminothiophenol (ATP), and compared the resulting SERS spectra with those obtained on surfactant-free stars functionalized with ATP. Through comparison of the experimental results with the electric field intensities and distributions calculated via finite element simulations, we have observed a strong correlation between the Raman signal enhancements obtained experimentally and the heat losses calculated on three-dimensional representations of the same nanostructures. We believe that our model could be used to predict the effectiveness of nanostars at enhancing SERS signals based on their overall morphology, even when thorough experimental characterization is lacking

The number cutaneous and visceral leishmaniasis cases reported in the Eastern Mediterranean Region, 2012–2019, Global Health Observatory data repository (https://apps.who.int/gho/data/node.main.A1638?lang=en).

The number cutaneous and visceral leishmaniasis cases reported in the Eastern Mediterranean Region, 2012–2019, Global Health Observatory data repository (https://apps.who.int/gho/data/node.main.A1638?lang=en).</p

The number of leprosy cases registered for treatment per 10,000 population (prevalence) in the Eastern Mediterranean Region, 2012–2019, Global Health Observatory data repository (https://apps.who.int/gho/data/node.main.A1638?lang=en).

The number of leprosy cases registered for treatment per 10,000 population (prevalence) in the Eastern Mediterranean Region, 2012–2019, Global Health Observatory data repository (https://apps.who.int/gho/data/node.main.A1638?lang=en).</p

The number of rabies deaths reported in EMR by country, 2012–2017, Global Health Observatory.

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Percentage populations with access to safe water and appropriate sanitation, Global Indicator Data Platform for Sustainable Development Goals, 2017.

Percentage populations with access to safe water and appropriate sanitation, Global Indicator Data Platform for Sustainable Development Goals, 2017.</p

WHO interventions for neglected tropical diseases endemic in the Eastern Mediterranean Region.

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The number of reported cases of mycetoma reported in EMR by country, 2016–2018, EMR Regional Health Observatory (2020).

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List of NTDs with targets extracted from WHO Roadmap for 2012–2020 with priority public health approaches (intensified disease management or PC) and criteria for RAG status.

List of NTDs with targets extracted from WHO Roadmap for 2012–2020 with priority public health approaches (intensified disease management or PC) and criteria for RAG status.</p

Geographical, program, and national coverage of drug treatment for lymphatic filariasis in the Eastern Mediterranean Region, 2016–2019, Preventive Chemotherapy Data Portal.

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