Nanocelluloses with native crystalline internal structures have attracted considerable interest due to their plant-based origin, high mechanical properties, modifiability, and chiral liquid crystallinity, which suggest novel functional sustainable materials. [1−27] In particular, cellulose nanocrystals (CNCs) are colloidal rods, having a typical lateral dimension of 5−10 nm and length of 50−300 nm. Above a critical aqueous concentration, they exhibit lefthanded chiral nematic (cholesteric) liquid crystallinity (LC) and optical iridescence, [4][5][6] which is preserved in dried films [4,28] . It allows templating for photonic materials using inorganics, nanoparticles, polymers, and pyrolyzed carbonized matter. [10,12,16,25,26] On the other hand, the CNCs have been suggested to possess a right-handed twist along their nanorod axis to explain the left-handed twist in their chiral LC. [6] Recently, the right-handed twist of individual CNCs and nanocelluloses of three different origins was observed by cryo-electron tomography (cryo-ET), and electron and atomic force microscopy [27,29] supported by molecular dynamics simulations [30−32] .Exploiting the twisting shape along the individual CNC nanorods could allow new optical functions in the nano/colloidal scale in dilute aqueous dispersions, i.e. not limited to the chiral LC based on the inter-rod assembly involving a larger length scale. Surprisingly, such optical findings have not been reported so far.Surface plasmons, i.e. collective oscillations of the conduction electrons on metal surfaces, allow physics and applications ranging from photonic devices, sensing, and solar cells to pharmacology. [33−37] In nanoparticles (NPs) the oscillations become coupled to allow a chiral plasmonic response, provided that they are sufficiently closely positioned and assembled in a chiral manner. This manifests in circular dichroism (CD) spectroscopy, which describes the difference in absorption between left-and right-handed circularly polarized light. The chiral coupling of surface plasmons induces a bisignated CD signal with a zerocrossing at the characteristic localized surface plasmon resonance wavelength of the isolated NPs. Such a Cotton effect is either dip−peak or peak−dip, depending on the handedness of chirality. [38−42] In chiral biological molecules, such as DNA, proteins and polypeptides, the CD signal is at ultraviolet wavelengths, whereas the CD signal of helical metal nanoparticle assemblies is at the visible wavelengths. This extends the applications to e.g. in biosensing. [37] Chiral nanoparticle assemblies have been shown using helical polymers, supramolecular fibers, and DNA-based constructs as templates. [40−42] In particular, a chiral plasmonic signal is obtained using DNA-origami to organize the nanoparticles in well-defined helices with tunable pitch, separation, and handedness. [40,41] Even if the above approaches are promising allowing in-depth tunable chiral plasmonic response, introducing rapid, scalable, and economic ways for producing chiral plas...

Material properties depend critically on the packing and order of constituent units throughout length scales. Beyond classically explored molecular self-assembly, structure formation in the nanoparticle and colloidal length scales have recently been actively explored for new functions. Structure of colloidal assemblies depends strongly on the assembly process, and higher structural control can be reliably achieved only if the process is deterministic. Here we show that self-assembly of cationic spherical metal nanoparticles and anionic rod-like viruses yields well-defined binary superlattice wires. The superlattice structures are explained by a cooperative assembly pathway that proceeds in a zipper-like manner after nucleation. Curiously, the formed superstructure shows right-handed helical twisting due to the right-handed structure of the virus. This leads to structure-dependent chiral plasmonic function of the material. The work highlights the importance of well-defined colloidal units when pursuing unforeseen and complex assemblies.

11Metal nanoclusters consist of a few to few hundreds of atoms, and exhibit attractive molecular 12 properties such as ultrasmall size, discrete energy levels and strong fluorescence. Although 13 patterning of these clusters down to the microscale or nanoscale could lead to 14 applications such as high-density data storage, it has been reported only for inorganic 15matrices. Here we demonstrate the first submicron-scale mask-free patterning of fluorescent 16 silver nanoclusters in an organic matrix. The nanoclusters were produced by direct 17 laser writing in poly(methacrylic acid) thin films, and exhibit a broadband emission at visible 18 wavelengths with photostability that is superior to Rhodamine 6G dye. This fabrication 19 method could open new opportunities for applications in nanophotonics like imaging, 20 labeling, and metal ion sensing. We foresee that this method can be further applied to prepare 21 other metal nanoclusters embedded in compositionally different polymer matrices. 22 KEYWORDS 24Optical lithography, metal nanoclusters, photoluminescence, photobleaching, photostability, 25 polymer 26

ABSTRACT:There is an urgent need for accessible purification and separation strategies of atomically precise metal clusters in order to promote the study their fundamental properties. Although the separation of mixtures of atomically precise gold clusters Au25L18, where L are thiolates, has been demonstrated by advanced separation techniques, we present here the first separation of metal clusters by thin layer chromatography (TLC), which is simple yet surprisingly efficient. This method was successfully applied to a binary mixture of Au25L18 with different ligands, as well as to a binary mixture of different cluster cores, Au25 and Au144, protected with the same ligand. Importantly, TLC even enabled the challenging separation of a multi-component mixture of mixedmonolayer-protected Au25 clusters with closely similar chemical ligand compositions. We anticipate that the realization of such simple yet efficient separation technique will progress the detailed investigation of cluster properties.

We investigate the adsorption of hexavalent uranium, U(VI), on phosphorylated cellulose nanofibers (PHO-CNF) and compare the results with those for native and TEMPO-oxidized nanocelluloses. Batch adsorption experiments in aqueous media show that PHO-CNF is highly efficient in removing U(VI) in the pH range between 3 and 6. Gelling of nanofiber hydrogels is observed at U(VI) concentration of 500 mg/L. Structural changes in the nanofiber network (scanning and transmission electron microscopies) and the surface chemical composition (X-ray photoelectron spectroscopy) gave insights on the mechanism of adsorption. The results from batch adsorption experiments are fitted to Langmuir, Freundlich, and Sips isotherm models, which indicate a maximum adsorption capacity of 1550 mg/g, the highest value reported so far for any bioadsorbent. Compared to other metals (Zn, Mn, and Cu) and typical ions present in natural aqueous matrices the phosphorylated nanofibers are shown to be remarkably selective to U(VI). The results suggest a solution for the capture of uranium, which is of interest given its health and toxic impacts when present in aqueous matrices.

No abstract

Although various complex, bulky ligands have been used to functionalize plasmonic gold nanoparticles, introducing them to small, atomically precise gold clusters is not trivial. Here we demonstrate a simple one-pot procedure to synthesize fluorescent magic number Au25 clusters carrying controlled amounts of bulky calix [4]arene functionalities. These clusters are obtained from a synthesis feed containing binary mixtures of tetrathiolated calix [4]arene and 1-butanethiol. By systematic variation of the molar ratio of ligands, clusters carrying one to eight calixarene moieties were obtained. Structural characterization reveals unexpected binding of the calix [4]arenes to the Au25 cluster surface with two or four thiolates per moiety. TOC GRAPHICS KEYWORDS: Chart 1. Structures of Thiol LigandsAu25 clusters passivated with mixtures of Calix-4SH and BuSH were synthesized by modifying the method by Qian et al. 10 Details of the synthetic procedure can be found in the Supporting Information. Briefly, a mixture of Calix-4SH and BuSH was added to a solution containing HAuCl4 and tetraoctylammonium bromide (TOAB) in tetrahydrofuran (THF). After the formation of colorless Au-thiolates, NaBH4 was added in aqueous solution to obtain a polydisperse cluster mixture. This polydisperse cluster mixture was size-focused by allowing it to react until Au25 cluster absorption features became prominent. The clusters were purified by repeated centrifugal washing with methanol followed by size-exclusion chromatography (SEC) to ensure removal of free Calix-4SH from the final cluster product. SEC served well to separate free Calix-4SH as well as a minor portion of larger cluster species from the final product ( Figure 1, inset). The Au25 cluster yields were typically 12−20 %.6 Figure 1. UV-vis absorption spectra of Au25 clusters with varying Calix-4SH concentration (spectra are vertically shifted for clarity). The inset shows spectra before and after size-exclusion chromatography.Absorption spectroscopy was initially used to get information about the core size of the clusters. Prominent absorption features were observed from all cluster samples at 680 nm, 442 nm, 400 nm and 320 nm which are well-known features of Au25(SR)18 cluster core (Figure 1). In addition, details in the absorption spectrum revealed the charge state of the cluster. It has beenshown that a broad absorption at 800 nm is an indication of a negatively charged, reduced gold core as well as a ratio of 1.2 between ~400 nm and ~440 nm absorptions. 29,30 All Calix-4S functionalized cluster samples showed these features thereby indicating a majority of negatively charged cluster cores as observed also in previous reports from similar syntheses. 10,29,30 The counter-ion of these negatively charged clusters was TOA + which was detected in the nuclear magnetic resonance (NMR) spectra of all Au25(Calix-4S)x(BuS)y clusters.To further analyze the structure of the clusters, the ligand compositions were probed by electrospray ionization mass spectrometry (ESI-MS) and N...

Cationic gold nanoparticles offer intriguing opportunities as drug carriers and building blocks for self‐assembled systems. Despite major progress on gold nanoparticle research in general, the synthesis of cationic gold particles larger than 5 nm remains a major challenge, although these species would give a significantly larger plasmonic response compared to smaller cationic gold nanoparticles. Herein we present the first reported synthesis of cationic gold nanoparticles with tunable sizes between 8–20 nm, prepared by a rapid two‐step phase‐transfer protocol starting from simple citrate‐capped particles. These cationic particles form ordered self‐assembled structures with negatively charged biological components through electrostatic interactions.