Bum Chul Park

The fabrication of 3D hollow nanostructures not only allows the tactical provision of specific physicochemical properties but also broadens the application scope of such materials in various fields. The synthesis of 3D hollow nanocoils (HNCs), however, is limited by the lack of an appropriate template or synthesis method, thereby restricting the wide‐scale application of HNCs. Herein, a strategy for preparing HNCs by harnessing a single sacrificial template to modulate the interfacial reaction at a solid–liquid interface that allows the shape‐regulated transition is studied. Furthermore, the triggering of the Kirkendall effect in 3D HNCs is demonstrated. Depending on the final state of the transition metal ions reduced during the electrochemical preparation of HNCs, the surface states of the binding anions and the composition of the HNCs can be tuned. In a single‐component CrPO₄ HNC with a clean surface, the Kirkendall effect of the coil shape is analyzed at various points throughout the reaction. The rough‐surface multicomponent MnO_xP_0.21 HNCs are complexed with ligand‐modified BF₄‐Mn₃O₄ nanoparticles. The fabricated nanocomposite exhibits an overpotential decrease of 25 mV at neutral pH compared to pure BF₄‐Mn₃O₄ nanoparticles because of the increased active surface area.

The artificial construction of nature‐mimic inorganic–organic heterostructures is an emerging technological interest for protective surface applications. Mimicking the spikiness of sea urchin spicules for their protective function, here, the synthesis of zinc oxide (ZnO) nanometer‐scale spicules grown from micrometer‐scale polylactic acid (PLA) beads and fibers as super‐hydrophilic and bactericidal surfaces is reported. The thermodynamic mechanism behind the interfacial assembly of pre‐entrapped ZnO nanoparticles right at the PLA–water interfaces above the glass transition temperature of PLA, allowing for the follow‐up growth of nano‐spicules on the PLA templates is uncovered. This sea urchin‐like topography of ZnO nano‐spicules induces super‐hydrophilicity while generating reactive oxygen species as well as allowing the stabbing action of nano‐spicules. All of the above help enhance the bactericidal activity against both gram‐positive and gram‐negative bacteria in an unprecedentedly effective way. The findings conceptualize a new strategy to spontaneously assemble nanoparticles at the polymer–liquid interfaces, enabling various heterostructures with topography‐induced functions.

Cell microenvironment is an essential factor in determining cell growth and cell fate. Many studies have been carried out to understand the functions and mechanisms of small molecules or growth factors/cytokines; however, the effects of the physical environment on cells are relatively unknown. Changes in the cell's physical microenvironment affect cell adhesion and modify intracellular signaling controlled by adhesion properties, resulting in altering the cytoskeletal structure and cellular properties. Herein, it is demonstrated that the changes in cell adhesion can affect the epithelial‐mesenchymal transition (EMT) of epithelial cells by implementing a cell microenvironment with a gold (Au) nanowire array to influence cell adhesion. A forcible decrease in cell adhesion leads to the downregulation of epithelial biomarkers and the upregulation of mesenchymal biomarkers. The results of force‐distance experiments using atomic force microscopy showed that the overall stiffness of epithelial cells declined similarly to the case for mesenchymal‐like cells. With this comprehensive analysis of cellular properties, a physical microenvironment for cell adhesion alteration is suggested, that can induce mesenchymal characteristics in both epithelial and mesenchymal cells through partial EMT.

Mesocrystals, consisting of small subunits, have gained research interests owing to their ability to simultaneously modify material‐specific properties and interactions among subunits. However, despite these unique characteristics, most mesocrystals are composed of a single material, and there is a disjunction between academic discovery and practical application. In this study, the synthesis of multi‐component mesocrystalline nanoparticles composed of Fe₃O₄, ZnFe₂O₄, and ZnO subunits using a polymerization induced heterogeneous nucleation method is reported. The structure has small ZnFe₂O₄ and ZnO nanocrystals covering the Fe₃O₄ crystallites. It exhibits not only magnetic and catalytic properties determined by the size of each subunit nanocrystal, but also enhances photocatalytic and colloidal properties that originates because of its crowded arrangement. The magnetically recoverable catalysts exhibit remarkable photodegradation of organic molecules under the irradiation of visible light for 1 h; thus, improving its applicability in purifying a large amount of wastewater during the daytime.

Magnetic‐plasmonic nanoparticles have received considerable attention for widespread applications. These nanoparticles (NPs) exhibiting surface‐enhanced Raman scattering (SERS) activities are developed due to their potential in bio‐sensing applicable in non‐destructive and sensitive analysis with target‐specific separation. However, it is challenging to synthesize these NPs that simultaneously exhibit low remanence, maximized magnetic content, plasmonic coverage with abundant hotspots, and structural uniformity. Here, a method that involves the conjugation of a magnetic template with gold seeds via chemical binding and seed‐mediated growth is proposed, with the objective of obtaining plasmonic nanostructures with abundant hotspots on a magnetic template. To obtain a clean surface for directly functionalizing ligands and enhancing the Raman intensity, an additional growth step of gold (Au) and/or silver (Ag) atoms is proposed after modifying the Raman molecules on the as‐prepared magnetic‐plasmonic nanoparticles. Importantly, one‐sided silver growth occurred in an environment where gold facets are blocked by Raman molecules; otherwise, the gold growth is layer‐by‐layer. Moreover, simultaneous reduction by gold and silver ions allowed for the formation of a uniform bimetallic layer. The enhancement factor of the nanoparticles with a bimetallic layer is approximately 10⁷. The SERS probes functionalized cyclic peptides are employed for targeted cancer‐cell imaging and separation.

Zinc oxide (ZnO)-based nanocomposites have shown promising potential for various biomedical applications, including vaccine development, owing to their multifunctionality and biocompatibility. Here, we synthesized radially grown ZnO nanowires (NWs) on poly-L-lactic acid (PLLA) microfibers with unique 3-dimensional structure and applied them as therapeutic cancer vaccines. This inorganic–organic hybrid nanocomposite has mild cellular toxicity but efficiently delivers a tumor antigen into dendritic cells, cellular bridges between innate and adaptive immunity, to stimulate them to express inflammatory cytokines and activation surface markers. We also demonstrated that the hybrid nanocomposites successfully induce tumor antigen-specific cellular immunity and significantly inhibit tumor growth in vivo. ZnO NWs on PLLA fibers systemically reduced immune suppressive T_Reg cells and enhanced the infiltration of T cells into tumor tissues, compared to mice immunized with PLLA fibers coated with the antigen. Our current findings open a new avenue in extending the biomedical application of inorganic metal oxide-inert organic hybrid nanocomposites as a novel vaccine platform.

Recently, polymer‐coated magnetite (Fe₃O₄) nanoparticles (NPs) are extensively studied for applications in therapeutics or diagnostics using photothermal effect. Therefore, it is essential to understand the interactions between Fe₃O₄ NPs and polymers when optical stimuli are applied. Herein, the photonic reactions of Fe₃O₄ NPs and polymer composites upon application of a 780 nm multiphoton laser are analyzed. The photonic reactions produce unique results including fluorescence from conformationally changed polymer and low‐temperature phase transformation of Fe₃O₄ NPs. Typically, π‐conjugated chains are formed, inducing fluorescence through a series of main and side‐chain cleavage reactions of polymers with the aliphatic chain. In addition, fluorescence is detected in the cellular system by photonic reactions between Fe₃O₄ NPs and biomolecules. After multiphoton laser irradiation, light emission is detected near the intracellular Fe₃O₄ NPs, and a stronger intensity is observed in large‐sized NPs.