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Atomically precise, ligand-protected gold nanoclusters (AuNCs) attract considerable attention as contrast agents in the biosensing field. However, the control of their optical properties and functionalization of surface ligands remain challenging. Here we report a strategy to tailor AuNCs for the precise detection of protein carbonylation-a causal biomarker of ageing. We produce Au 15 SG 13 (SG for glutathione) with atomic precision and functionalize it with a thiolated aminooxy moiety to impart protein carbonyl-binding properties. Mass spectrometry and molecular modelling reveal the key structural features of Au 15 SG 12 -Aminooxy and its reactivity towards carbonyls. Finally, we demonstrate that Au 15 SG 12 -Aminooxy detects protein carbonylation in gel-based 1D electrophoresis by one- and two-photon excited fluorescence. Importantly, to our knowledge, this is the first application of an AuNC that detects a post-translational modification as a nonlinear optical probe. The significance of post-translational modifications in life sciences may open avenues for the use of Au 15 SG 13 and other nanoclusters as contrast agents with tailored surface functionalization and optical properties., (© 2021. The Author(s).)

Atomically precise Au 25 (MBA) 18 nanoclusters were investigated by mass spectrometry and ion mobility spectrometry. We show that clusters sharing the same chemical composition and bearing the same net charge may display different structures and different charge repartition patterns, namely, the number of charges corresponding to deprotonation of the ligand moieties through carboxyl groups is not the same for all detected species. Part of the observed heterogeneity is a consequence of spontaneous electron loss occurring in the gas phase, which modifies the net charge of the clusters while maintaining the initial (de)protonation state.

Unique physicochemical features place gold nanoclusters at the forefront of nanotechnology for biological and biomedical applications. To date, information on the interactions of gold nanoclusters with biological macromolecules is limited and restricts their use in living cells. Methods : Our multidisciplinary study begins to fill the current knowledge gap by focusing on lysosomes and associated biological pathways in U251N human glioblastoma cells. We concentrated on lysosomes, because they are the intracellular destination for many nanoparticles, regulate cellular homeostasis and control cell survival. Results : Quantitative data presented here show that gold nanoclusters (with 15 and 25 gold atoms), surface-modified with glutathione or PEG, did not diminish cell viability at concentrations ≤1 µM. However, even at sublethal concentrations, gold nanoclusters modulated the abundance, positioning, pH and enzymatic activities of lysosomes. Gold nanoclusters also affected other aspects of cellular homeostasis. Specifically, they stimulated the transient nuclear accumulation of TFEB and Nrf2, transcription factors that promote lysosome biogenesis and stress responses. Moreover, gold nanoclusters also altered the formation of protein aggregates in the cytoplasm. The cellular responses elicited by gold nanoclusters were largely reversible within a 24-hour period. Conclusions : Taken together, this study explores the subcellular and molecular effects induced by gold nanoclusters and shows their effectiveness to regulate lysosome biology. Our results indicate that gold nanoclusters cause homeostatic perturbations without marked cell loss. Notably, cells adapt to the challenge inflicted by gold nanoclusters. These new insights provide a framework for the further development of gold nanocluster-based applications in biological sciences., Competing Interests: Competing Interests: The authors have declared that no competing interest exists., (© The author(s).)

Thiolate-protected metal nanoclusters have highly size- and structure-dependent physicochemical properties and are a promising class of nanomaterials. As a consequence, for the rationalization of their synthesis and for the design of new clusters with tailored properties, a precise characterization of their composition and structure at the atomic level is required. We report a combined ion mobility-mass spectrometry approach with density functional theory (DFT) calculations for determination of the structural and optical properties of ultra-small gold nanoclusters protected by thioglycolic acid (TGA) as ligand molecules, Au 10 (TGA) 10 . Collision cross-section (CCS) measurements are reported for two charge states. DFT optimized geometrical structures are used to compute CCSs. The comparison of the experimentally- and theoretically-determined CCSs allows concluding that such nanoclusters have catenane structures.

We report a simple size focusing, two-step "bottom-up" protocol to prepare water-soluble Au 25 (MBA) 18 nanoclusters, using the three isomers of mercaptobenzoic acids ( p / m / o -MBA) as capping ligands and Me 3 NBH 3 as a mild reducing agent. The relative stability of the gas-phase multiply deprotonated Au 25 (MBA) 18 ions was investigated by collision-induced dissociation. This permitted us to evaluate the possible isomeric effect on the Au-S interfacial bond stress. We also investigated their optical properties. The absorption spectra of Au 25 (MBA) 18 isomers were very similar and showed bands at 690, 470, and 430 nm. For all Au 25 (MBA) 18 isomeric clusters, no measurable one-photon excited fluorescence under UV-vis light was found, in neither solid- nor solution-state. The two-photon excited emission spectra and first hyperpolarizabilities of the clusters were also determined. The results are discussed in terms of the possible isomeric effect on excitations within the metal core and the possibility of charge transfer excitations from the ligands to the metal nanocluster., Competing Interests: The authors declare no competing financial interest.

We report the three-dimensional mapping of 150 nm gold metallic nanoparticles dispersed in a homogeneous transparent polyacrylamide matrix using second-harmonic generation. We demonstrate that the position of single nanoparticles can be well defined using only one incident fundamental beam and the harmonic photon detection performed at right angle. The fundamental laser beam properties are determined using its spatial autocorrelation function and used to prove that single nanoparticles are observed. Polarization resolved measurements are also performed allowing for a clear separation of the second-harmonic response of the single gold metallic nanoparticles from that of aggregates of such nanoparticles.