Isabel Díez

Fluorescent silver nanoclusters

Silver nanoclusters are a class of fluorophores with attractive features, including brightness, photostability and subnanometer size. In this review we overview the different scaffolds that are used as stabilizer for silver nanoclusters (e.g. polymers, dendrimers, DNA oligomers, cryogenic noble gas matrixes, inorganic glasses, zeolites and nanoparticles), and we briefly discuss the recent advances.

Color Tunability and Electrochemiluminescence of Silver Nanoclusters

Colorful clusters: Silver nanoclusters consisting of only a few atoms exhibit large chemical-environment-responsive shifts of their optical absorption and emission bands, that is, large solvatochromism (see picture). The photophysical characteristics and electrochemiluminescence of the Ag clusters give them remarkable advantages over larger nanoparticles in applications such as molecular sensing.

Multifunctional High-Performance Biofibers Based on Wet-Extrusion of Renewable Native Cellulose Nanofibrils

Fibrous architectures are among the most abundant loadcarrying materials in nature, encompassing molecular level peptide assemblies (e.g., amyloids), supramolecular protein materials (e.g., collagen), colloidal level native cellulose nanofi brils (nanofi brillated cellulose, NFC), through to macroscale spider silk. [ 1 , 2 ] NFC, also denoted as microfi brillated cellulose (MFC), exhibits diameters in the nanometer range and lengths up to several micrometers. These nanofi brils are composed of aligned β D -(1 → 4)glucopyranose polysaccharide chains, which form native cellulose I crystals where the parallel chains are strongly intermolecularly hydrogen bonded. NFC materials can be isolated by chemical/enzymatic and homogenization treatments [ 3 , 4 ] from the cell walls of wood and plants, where they are responsible for structural strength. NFC forms a remarkable emerging class of nature-derived nanomaterials because of its extraordinary mechanical properties, combining high stiffness of up to ca. 140 GPa and expected strength in the GPa range with a lightweight character (density ca. 1.5 g mL − 1 ). These properties rank NFC at the top end of high-performance natural materials, where the stiffness of cellulose I is 2–3 times higher than that of glass fi bers (50–80 GPa) and approaches that of steel (200 GPa). Since NFC is derived from wood or plant sources, it is globally abundant and renewable, and represents a resource that does not interfere with the food chain or require petrochemical components. In addition, related nanofi brils known as bacterial cellulose can be produced biotechnologically. [ 5 ] Consequently, NFC is emerging as one of the most promising sustainable building blocks for future advanced materials. So far the main interest in NFC has been to generate strong and tough nanopapers, nanocomposites upon adding small contents to polymeric matrices, or robust foams and aerogels. [ 4 , 6–16 ]

Functionalization of Nanofibrillated Cellulose with Silver Nanoclusters: Fluorescence and Antibacterial Activity

Native cellulose nanofibers are functionalized using luminescent metal nanoclusters to form a novel type of functional nanocellulose/nanocluster composite. Previously, various types of cellulose fibers have been functionalized with large, non-luminescent metal nanoparticles. Here, mechanically strong native cellulose nanofibers, also called nanofibrillatedcellulose (NFC), microfibrillatedcellulose (MFC) ornanocellulose, disintegrated from macroscopic cellulose pulp fibers are used as support for small and fluorescent silver nanoclusters. The functionalization occurs in a supramolecular manner, mediated by poly(methacrylic acid) that protects nanoclusters while it allows hydrogen bonding with cellulose, leading to composites with fluorescence and antibacterial activity.

Enhanced emission of silver nanoclusters through quantitative phase transfer.

Silver nanoclusters composed of only a few metal atoms present appealing properties such as fluorescence. We have previously reported on aqueous solutions of this fluorophore using poly(methacrylic acid) as scaffold and their sensing properties. Here we report on the preparation of organic solutions of fluorescent silver nanoclusters by quantitative transfer from aqueous solution to an immiscible organic solvent. The fluorescent silver nanoclusters in the organic phase present enhanced emission properties and increased purity, which may expand the range of applications of this promising fluorophore.

Few-Atom Silver Clusters as Fluorescent Reporters

Silver clusters, composed of only a few silver atoms, have remarkable optical properties based on electronic transitions between quantized energy levels. They have large absorption coefficients and fluorescence quantum yields, in com- mon with conventional fluorescent markers. But importantly, silver clusters have an attractive set of features, including subnanometer size, nontoxicity and photo- stability, which makes them competitive as fluorescent markers compared with organic dye molecules and semiconductor quantum dots. In this chapter, we review the synthesis and properties of fluorescent silver clusters, and their application as bio-labels and molecular sensors. Silver clusters may have a bright future as luminescent probes for labeling and sensing applications.

Aspects of Morphology Control during the Oxidative Synthesis of Electrically Conducting Polymers

The formation of micro- and nanostructures during the oxidative polymerization of polypyrrole and polyaniline is investigated using different sulfonic acid dopants. Rod- or tube-like structures are found in polypyrrole as well as in polyaniline without addition of further compounds to the initial reaction mixture of monomer, dopant and oxidant. In these cases, always a crystalline precursor complex composed of a dopand molecule and the pure monomer (aniline) or a trimeric moiety (pyrrole) serves as in-situ template. In most cases the surface of the growing polymer is covered by secondary structures with much smaller sizes so that a hierarchical order of structures at different length scales results. Corresponding model considerations for the polymerization process are outlined. Additionally, unusual structures like platelets, frames, rings, or ribbons are observed in the polypyrrole synthesis in the presence of fluorosurfactants.