Mechanistic insights and selected synthetic routes of atomically precise metal nanoclusters

Abstract During the last few decades, noble metal nanoclusters (NCs) have become an exciting building block in the field of nanoscience. With their ultrasmall size that ranges between 1 and 2 nm, NCs fill the gap between atoms and nanoparticles (NPs), and they show significantly different physicochemical properties compared to their bulk counterparts, such as molecule‐like HOMO‐LUMO discrete electronic transitions, photoluminescence, etc. These properties made NCs potential candidates in various applications, including catalysis, chemical/bioimaging, biomedicine, sensing, and energy conversion. Controlling the size of NPs, which usually exhibit a degree of polydispersity, has been a significant challenge for nano‐scientists. However, metal NCs with atomic precision pave the way to accurately fabricate NPs based on an atom‐by‐atom assembly. This Perspective is directed to the community of nano‐scientists interested in the field of NCs and summarizes the most commonly used synthetic routes of atomically precise metal NCs. Moreover, this Perspective provides an understanding of the different techniques used to control the size of metal NCs with insights on switching the surface ligands from phosphine to thiol. This Perspective also explains the role of physicochemical parameters in different synthetic routes such as high‐temperature route, CO‐directed route, solid‐state route, ligand‐exchange‐induced size/structure transformation (LEIST), etc. We finally give a brief outlook on future challenges of currently used synthetic routes with some suggestions to improve them

DIETARY ADMINISTRATION OF ETHANOL AND METHANOL EXTRACTS OF Withania somnifera ROOT STIMULATES INNATE IMMUNITY, PHYSIOLOGICAL PARAMETERS AND GROWTH IN NILE TILAPIA Oreochromis niloticus

U istraživanju je procijenjena učinkovitost etanola i metanolnih ekstrakata korijena ljekovite biljke Withania somnifera na imunostimulativna svojstva i rast Nilsketilapije Oreochromis niloticus. Korijeni Withanie ekstrahirani su vodom, etanolom, metanolom, metilenkloridom, heksanom i sukcesivnim metanolom. Izmjereni su sadržaji fenola i flavonoida te antiradikalna aktivnost svih ekstrakata. Nakon toga, izvršena je hranidba nilske tilapije (n=126) hranom koja je sadržavala različite koncentracije (0, 0,3, 0,5 i 0,7 g kg-1 hrane) etanola i metanolnih ekstrakata korijena W. somnifera tijekom 30 dana kroz 3 ponavljanja. Pri usporedbi s kontrolnom hranidbom, ribe hranjene hranom obogaćenom biljnim ekstraktom indicirale suznačajno bolje (P <0,05) imunološke, hematološke i biokemijske pokazatelje te parametre rasta. Riba hranjena hranom koja sadrži ekstrakt etanola u koncentraciji od 0,7g kg-1 imala je najveće imunološke (fagocitna aktivnost, aktivnost respiratornog praska, lizozim u serumu, ukupni protein, ukupni imunoglobulin), hematološke (ukupna crvena krvna zrnca, hemoglobin, hematokrit, ukupnobijelih krvnih zrnaca, limfocita) i biokemijske (smanjena aktivnost glutationa, glutation-reduktaza) pokazatelje te najviše parametre rasta (masa, prirast, specifičnu stopurasta). Prema rezultatima, istraživani biljni ekstrakt može djelovati kao sredstvo za uklanjanje slobodnih radikala u ribljim tkivima te posjeduje sposobnost zaštite tkiva,pritom povećavajući zdravlje riba.Efficacy of ethanol and methanol extracts of medicinal herb Withania somnifera roots was evaluated in Nile tilapia Oreochromis niloticus on immunostimulation and growth. Withania roots were extracted with water, ethanol, methanol, methylene chloride, hexane, successive methanol. Phenol, flavonoid content and antiradical activity of all the extracts weremeasured. Ethanol extract showed the highest phenol, flavonoid content and antiradical activity followed by methanol extract. Subsequently, Nile tilapia (n = 126) were fed diets containing different concentrations (0.0, 0.3, 0.5 and 0.7 g kg-1 feed) of ethanol and methanol extracts of W. somnifera roots for 30 days (3 replicates). Fish fed plant extract fortified diets showed significantly better (P<0.05) immunological, haematological, biochemical and growth parameters compared to the fish fed control diet. Fish fed dietcontaining ethanol extract at the concentration of 0.7 g kg-1 feed showed the highest immunological (phagocytotic activity, respiratory burst activity, serum lysozyme, total protein, total immunoglobulin), haematological (total red blood cells, haemoglobin, hematocrit, total white blood cells, lymphocyte), biochemical (reduced glutathione, glutathione reductase activity) and growth (final weight, weight gain, daily weight gain, specific growth rate) parameters. The plant extract might act as potent free radical scavenger in fish tissues and have tissue protecting ability, thus increasingfish health

Endoscopic Repair of Spontaneous CSF Rhinorrhoea: Results from 21 Cases

Introduction Surgery to close the skull base defect is the treatment of choice in persistent spontaneous cerebrospinal fluid rhinorrhoea with endoscopic endonasal repair being the method of choice.  This study analysed the demographics of presentation, optimal diagnostic and localisation strategies and the effectiveness of transnasal endoscopic treatment strategies  with post-operative follow-up of CSF rhinorrhoea patients in a tertiary care institution   . Materials and Methods  A prospective longitudinal study was conducted on 21 CSF rhinorrhoea patients operated on between August 2014 and August 2018 and results documented. Results CSF rhinorrhoea was found most commonly in middle aged female patients in our study. HRCT PNS was capable of identifying a leak site in 66% of the cases. All patients were operated endoscopically with no major intra-operative or post-operative complications. Resolution of CSF leak occurred in 85% of cases. Conclusion CSF rhinorrhoea can be diagnosed and endoscopic repair can be effectively performed in our existing tertiary care set-ups with good results

Toward Diffusion Measurements of Colloidal Nanoparticles in Biological Environments by Nuclear Magnetic Resonance

Protein corona formation on the surface of nanoparticles (NPs) is observed in situ by measuring diffusion coefficients of the NPs under the presence of proteins with a F-19 nuclear magnetic resonance (NMR) based methodology. Formation of a protein corona reduces the diffusion coefficient of the NPs, based on an increase in their effective hydrodynamic radii. With this methodology it is demonstrated that the apparent dissociation constant of protein-NP complexes may vary over at least nine orders of magnitude for different types of proteins, in line with the Vroman effect. Using this methodology, the interaction between one type of protein and one type of nanoparticle can be studied quantitatively. Due to the NMR-based detection, this methodology has no interference by absorption/scattering effects, by which optical detection schemes are affected. By using the potential of the NMR chemical shift, the detection of multiple F-19 signals simultaneously opens the possibility to study the diffusion of several NPs at the same time. The F-19 labeling of the NPs has negligible effect on their acute toxicity and moderate effect on NPs uptake by cells.This work was supported by the Cluster of Excellence "Advanced Imaging of Matter" of the Deutsche Forschungsgemeinschaft (DFG) EXC 2056 - project ID 390715994, by the Basque Government (project IT1196-19) and by the Fundacion Biofisica Bizkaia and the Basque Excellence Research Centre (BERC) program of the Basque Government. This work was performed under the Maria de Maeztu Units of Excellence Programme-Grant No. MDM-2017-0720 Ministry of Science, Innovation and Universities. The help of Marta Gallego in the surface tension and TEM measurements is acknowledged. Parts of the ICP-MS measurements were done at the ICP-MS facility of CIC biomaGUNE by Javier Calvo

Strong and Elastic Membranes via Hydrogen Bonding Directed Self-Assembly of Atomically Precise Nanoclusters

2D nanomaterials have provided an extraordinary palette of mechanical, electrical, optical, and catalytic properties. Ultrathin 2D nanomaterials are classically produced via exfoliation, delamination, deposition, or advanced synthesis methods using a handful of starting materials. Thus, there is a need to explore more generic avenues to expand the feasibility to the next generation 2D materials beyond atomic and molecular-level covalent networks. In this context, self-assembly of atomically precise noble nanoclusters can, in principle, suggest modular approaches for new generation 2D materials, provided that the ligand engineering allows symmetry breaking and directional internanoparticle interactions. Here the self-assembly of silver nanoclusters (NCs) capped with p-mercaptobenzoic acid ligands (Na4Ag44-pMBA30) into large-area freestanding membranes by trapping the NCs in a transient solvent layer at air–solvent interfaces is demonstrated. The patchy distribution of ligand bundles facilitates symmetry breaking and preferential intralayer hydrogen bondings resulting in strong and elastic membranes. The membranes with Young's modulus of 14.5 ± 0.2 GPa can readily be transferred to different substrates. The assemblies allow detection of Raman active antibiotic molecules with high reproducibility without any need for substrate pretreatment.publishedVersionPeer reviewe

Strong and Elastic Membranes via Hydrogen Bonding Directed Self-Assembly of Atomically Precise Nanoclusters

2D nanomaterials have provided an extraordinary palette of mechanical, electrical, optical, and catalytic properties. Ultrathin 2D nanomaterials are classically produced via exfoliation, delamination, deposition, or advanced synthesis methods using a handful of starting materials. Thus, there is a need to explore more generic avenues to expand the feasibility to the next generation 2D materials beyond atomic and molecular-level covalent networks. In this context, self-assembly of atomically precise noble nanoclusters can, in principle, suggest modular approaches for new generation 2D materials, provided that the ligand engineering allows symmetry breaking and directional internanoparticle interactions. Here the self-assembly of silver nanoclusters (NCs) capped with p-mercaptobenzoic acid ligands (Na4Ag44-pMBA30) into large-area freestanding membranes by trapping the NCs in a transient solvent layer at air–solvent interfaces is demonstrated. The patchy distribution of ligand bundles facilitates symmetry breaking and preferential intralayer hydrogen bondings resulting in strong and elastic membranes. The membranes with Young's modulus of 14.5 ± 0.2 GPa can readily be transferred to different substrates. The assemblies allow detection of Raman active antibiotic molecules with high reproducibility without any need for substrate pretreatment.publishedVersionPeer reviewe

Luminescent silver nanoclusters decorated on ZnO tetrapods: a detailed understanding of their role in photoluminescence features

Optical spectroscopic measurements are conducted on luminescent silver nanocluster (AgNC) decorated ZnO tetrapods (ZnO Tp), AgNC@ZnO Tp, synthesized via a colloidal route. Their properties are compared with those of the corresponding AgNC and ZnO Tp to understand their impact on the photoluminescence (PL). Raman spectroscopy reveals the high structural integrity of the ZnO structure in the AgNC@ZnO Tp. PL analysis of the ZnO Tp shows a well-resolved near band edge emission and a green band comprised by the overlapping of at least three emitting optical centres. The addition of AgNC to ZnO Tp in the hybrid material enhances the emission from ZnO surface states. The recombination of the AgNC in water solution is dominated by a red emission band peaking at ∼1.9 eV and the PL excitation spectra monitored at the band maximum reveal that the red PL of AgNC is preferentially populated by well-defined excitation bands corresponding to discrete electronic transitions of the NCs. Yet, a shift to lower energies of the AgNC emission occurs in the AgNC@ZnO Tp hybrid when excited with energies below the ZnO bandgap, while for energies above this value no emission from the AgNC was observed, with the ZnO-related recombination dominating the spectra. A gradual loss in the PL intensity of the AgNC is observed in the hybrid with increasing time, which is consistent with their coalescence to transform into larger Ag nanoparticles (NPs) on the tetrapod surface, as revealed by confocal microscopy.publishe

Variations in Biodistribution and Acute Response of Differently Shaped Titania Nanoparticles in Healthy Rodents

Titanium dioxide nanoparticles (TiO NPs) are one of the main sources of the nanoparticulate matter exposure to humans. Although several studies have demonstrated their potential toxic effects, the real nature of the correlation between NP properties and their interaction with biological targets is still far from being fully elucidated. Here, engineered TiO NPs with various geometries (bipyramids, plates, and rods) have been prepared, characterized and intravenously administered in healthy mice. Parameters such as biodistribution, accumulation, and toxicity have been assessed in the lungs and liver. Our data show that the organ accumulation of TiO NPs, measured by ICP-MS, is quite low, and this is only partially and transiently affected by the NP geometries. The long-lasting permanence is exclusively restricted to the lungs. Here, bipyramids and plates show a higher accumulation, and interestingly, rod-shaped NPs are the most toxic, leading to histopathological pulmonary alterations. In addition, they are also able to induce a transient increase in serum markers related to hepatocellular injury. These results indicate that rods, more than bipyramidal and spherical geometries, lead to a stronger and more severe biological effect. Overall, small physico-chemical differences can dramatically modify both accumulation and safety

Photoluminescence quenching of dye molecules near a resonant silicon nanoparticle

Luminescent molecules attached to resonant colloidal particles are an important tool to study light-matter interaction. A traditional approach to enhance the photoluminescence intensity of the luminescent molecules in such conjugates is to incorporate spacer-coated plasmonic nanoantennas, where the spacer prevents intense non-radiative decay of the luminescent molecules. Here, we explore the capabilities of an alternative platform for photoluminescence enhancement, which is based on low-loss Mie-resonant colloidal silicon particles. We demonstrate that resonant silicon particles of spherical shape are more efficient for photoluminescence enhancement than their plasmonic counterparts in spacer-free configuration. Our theoretical calculations show that significant enhancement originates from larger quantum yields supported by silicon particles and their resonant features. Our results prove the potential of high-index dielectric particles for spacer-free enhancement of photoluminescence, which potentially could be a future platform for bioimaging and nanolasers