Engineered nanoparticles are one of the leading nanomaterials currently under investigation due to their applicability in various fields, including drug and gene delivery, biosensors, cancer treatment and diagnostic tools. Moreover, the number of commercial products containing nanoparticles released on the market is rapidly increasing. Nanoparticles are already widely distributed in air, cosmetics, medicines and even in food. Therefore, the unintended adverse effect of nanoparticle exposure is a growing concern both academically and socially. In this context, the toxicity of nanoparticles has been extensively studied; however, several challenges are encountered due to the lack of standardized protocols. In order to improve the experimental conditions of nanoparticle toxicity studies, serious consideration is critical to obtain reliable and realistic data. The cell type must be selected considering the introduction route and target organ of the nanoparticle. In addition, the nanoparticle dose must reflect the realistic concentration of nanoparticles and must be loaded as a well-dispersed form to observe the accurate size- and shape-dependent effect. In deciding the cytotoxicity assay method, it is important to choose the appropriate method that could measure the toxicity of interest without the false-negative or -positive misinterpretation of the toxicity result.

Polyoxometalates (POMs), as inorganic ligands, can endow metal nanocrystals (NCs) with unique reactivities on account of their characteristic redox properties. In the present work, we present a facile POM-mediated one-pot aqueous synthesis method for the production of single-crystalline Pd NCs with controlled shapes and sizes. The POMs could function as both reducing and stabilizing agents in the formation of NCs, and thus gave a fine control over the nucleation and growth kinetics of NCs. The prepared POM-stabilized Pd NCs exhibited excellent catalytic activity and stability for electrocatalytic (formic acid oxidation) and catalytic (Suzuki coupling) reactions compared to Pd NCs prepared without the POMs. This shows that the POMs play a pivotal role in determining the catalytic performance, as well as the growth, of NCs. We envision that the present approach can offer a convenient way to develop efficient NC-based catalyst systems.

Pt-based bimetallic nanocrystals (NCs) are an important class of catalytic materials especially in the area of energy conversion due to their outstanding catalytic performance. The catalytic function of Pt-based bimetallic NCs toward a specific catalysis reaction can be optimized by tailoring their surface structure, which can be realized through the precise control of the NC morphology. In the present work, we developed a facile one-pot polyoxometalate (POM)-mediated synthesis approach for the synthesis of Pt-based bimetallic NCs with controlled morphologies and fine crystal structures, and investigated the influence of their morphology on their catalytic function. Pd@Pt core-shell NCs with well-defined morphologies and controlled surface structures could be prepared by the simultaneous reduction of Pt and Pd precursors in the presence of a typical Keggin-type POM (H3PMo12O40) and ascorbic acid (AA). During the formation of NCs, the POMs served not only as a stabilizing agent but also a reducing agent. Notably, the presence of the POMs as well as the relative concentration of AA to metal precursors could afford fine control over the growth mode of the Pt shells on the Pd cores, and thus the final morphology of the Pd@Pt NCs. The prepared POM-passivated Pd@Pt NCs outperformed Pd@Pt NCs synthesized without the POMs as well as a commercial Pt/C catalyst for the electrooxidation of methanol, and their catalytic activity and stability distinctly depended on their Pt shell structure. We envision that this strategy will pave the way for the rational design of NC-based catalyst systems.

Synthetic nanostructures, such as nanoparticles and nanowires, can serve as modular building blocks for integrated nanoscale systems. We demonstrate a microfluidic approach for positioning, orienting, and assembling such nanostructures into nanoassemblies. We use flow control combined with a cross-linking photoresist to position and immobilize nanostructures in desired positions and orientations. Immobilized nanostructures can serve as pivots, barriers, and guides for precise placement of subsequent nanostructures.

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