Recent Advances in Hybrid Materials of Metal Nanoparticles and Polyoxometalates

Polyoxometalates (POMs), anionic metal-oxygen nanoclusters that possess various composition-dependent properties, are widely used to modify the existing properties of metal nanoparticles and to endow them with new ones. Herein, we present an overview of recent advances in hybrid materials that consist of metal nanoparticles and POMs. Following a brief introduction on the inception of this area and its development, representative properties and applications of these materials in various fields such as electrochemistry, photochemistry, and catalysis are introduced. We discuss how the combination of two classic inorganic materials facilitates cooperative and synergistic behavior, and we also give personal perspectives on the future development of this field.

Metal-metal bonds in polyoxometalate chemistry

Half a century ago, F. Albert Cotton emphasized the relevance of metal-metal bonding in the constitution of cluster materials. Based on his description, nanoscale polyoxometalates (POMs) normally would not be regarded as cluster materials. One reason is that metal-metal bonding is typically associated with inorganic systems featuring metal centres in low oxidation states, a feature that is not common for POMs. However, over the past decades, there have been increasing reports on POMs integrating different types of metal-metal bonding. This article conceptualises and reviews the area of metal-metal bonded POMs, and their preparation and physicochemical properties. Attention is given to the changes in the electronic structure of POMs, the emergence of covalent dynamics and its impact on the development of applications in catalysis, nanoswitches, donor-acceptor systems, electron storage materials and nanoelectronics (i.e., "POMtronics").

Hybrid Gold Nanoparticle-Polyoxovanadate Matrices: A Novel Surface Enhanced Raman/Surface Enhanced Infrared Spectroscopy Substrate

Bare gold nanoparticles were embedded into an iron-polyoxovanadate matrix and used to enhance both the infrared and Raman signatures of a model analyte. A detailed characterization of the matrix-embedded nanoparticles revealed that they retained a plasmon resonance at 564 nm. The enhancement of vibrational signatures of the model analyte crystal violet using bare and embedded gold nanoparticles was compared for both surface enhanced infrared (SEIRA) spectroscopy and surface enhanced Raman spectroscopy (SERS) yielding enhancement factors of 2.2 for SEIRA and 77 for SERS. In contrast, the bare gold nanoparticles revealed significantly lower enhancements (1.6 for SEIRA; 20 for SERS). Hence, it was shown that embedding nanoparticles within an inorganic polyoxometalate-based matrix is an innovative strategy to amplify their signal enhancement properties in vibrational spectroscopies.

Sonochemical synthesis of polyoxometalate-stabilized gold nanoparticles for point-of-care determination of acetaminophen levels: preclinical study in an animal model

The aim of this study is the accurate and rapid detection of acetaminophen (AP) for point-of-care (POC) clinical diagnosis. Acetaminophen overdose causes acute liver failure and currently there is a lack of rapid quantitative detection methods for this drug in the emergency room. Here, low-frequency sonication (20 kHz) in the presence of phosphomolybdic acid (PMo₁₂) was used to reduce Au³⁺ to Au⁰ and stabilize the resulting spherical Au⁰ nanoparticles (herein AuNPs). These AuNPs@PMo₁₂ were used as nano-probes for the selective detection of acetaminophen in the presence of other commercial drugs. The optical sensing method we describe is based on the aggregation of AuNPs@PMo₁₂ in the presence of acetaminophen, which produces a red-shift in the absorption spectrum of the AuNPs@PMo₁₂, which is characterised by a color change from red to purple that is visible to the naked eye. Furthermore, the quantitative determination of acetaminophen concentrations can be carried out using the eyedropper function in Microsoft's PowerPoint or open access ImageJ software, using RGB (red, green, and blue) values. To prove the feasibility of this novel nanosensor, the concentration of acetaminophen was measured in over-the-counter pharmaceutical tablets and in serum samples taken from mice. This simple sensing approach offers high stability, selectivity, rapid detection time, and cost saving compared to other detection methods, which therefore opens the way for the development of quantitative POC acetaminophen detection using polyoxometalate-stabilized metal nanoparticles.

The aim of this study is the accurate detection of acetaminophen (AP) for point-of-care (POC) clinical diagnosis. The concentration of acetaminophen was measured in over-the-counter pharmaceutical tablets and in serum samples taken from mice.

In vitro cell cytotoxicity profile and morphological response to polyoxometalate-stabilised gold nanoparticles

Polyoxometalate-stabilised gold nanoparticles internalise in vast quantities into kidney epithelial and skin melanoma cell lines causing antiproliferative action on tumoural cells.

Proton switching as a driving force for the metal–organic complex-mediated growth of gold colloids

A mono-protonated (bis(4′-(4-pyridyl)-2,2′:6′,2′′-terpyridine)iron(ii)) complex [[Fe(ptpy)(Hptpy)](PF₆)₃] acts as a structure directing agent for larger gold colloids in the present investigation.