Hee-Jeong Jang

Fabrication of 2D Au Nanorings with Pt Framework

Surface plasmonics of nanomaterials has been one of the main research themes in nanoscience. Spherical and elongated nanoparticles show their corresponding unique optical features mainly depending on the physical dimensions. Here we successfully synthesized Au nanorings having Pt framework (Pt@Au nanorings) with high uniformity through wet-chemistry. The synthetic strategy consisted of serial reactions involving site-selective growth of Pt on the rim of Au nanoplates, subsequent etching of Au nanoplates, followed by regrowth of Au on the Pt rim. In this synthetic method, Au(3+) ions exhibited dual functionality as an etchant and a metal precursor. The resultant product, Pt@Au nanorings, exhibited unique localized surface plasmon resonance (LSPR) bands originating from the Au shell. The inner Pt skeleton turns out to be important to hold structural stability.

Shape-controlled synthesis of Pt nanoframes

Plate-like Pt nanoframes were synthesized using Au nanoplates as a template, followed by formation of a Ag layer coating on the Au template, and selective chemical etching of Au and Ag leaving the Pt structure intact. Circular, triangular, and hexagonal Au nanoplates successfully served as templates for fabrication of various Pt nanoframe shapes, which resembled the original Au nanoplate shape. A thin Ag layer was found to play a critical role as an electron-transfer mediator in the galvanic replacement reaction between the thin Ag layer on Au nanoplates and Pt precursors. During the replacement reaction, the Pt layer grew faster at the {112} edges than at the {111} terraces of Au nanoplates. The thicker periphery of the nanoplates survived the chemical etching step, while the thinner center was etched, leading to formation of Pt nanoframes in high yield and good homogeneity.

Octahedral and Cubic Gold Nanoframes with Platinum Framework.

Herein, we report a general synthetic pathway to various shapes of three-dimensional (3D) gold nanoframes (NFs) embedded with a Pt skeleton for structural rigidity. The synthetic route comprises three steps: site-specific (edge and vertex) deposition of Pt, etching of inner Au, and regrowth of Au on the Pt framework. Site-specific reduction of Pt on Au nanoparticles (NPs) led to the high-quality of 3D Au NFs with good structural rigidity, which allowed the detailed characterization of the corresponding 3D metal NFs. The synthetic method described here will open new avenues toward many new kinds of 3D metal NFs.

Influence of iodide ions on morphology of silver growth on gold hexagonal nanoplates.

Different morphologies of Au@Ag nanocrystals have been successfully synthesized using iodide ions in growth solutions consisting of ascorbic acid, NaOH, and CTAB. Without I(-) ions in growth solution, there were unnoticeable changes in morphology. On the other hand, with addition of I(-) ions, remarkable changes were observed including formation of hexagonal bipyramidal nanocrystals. Ag(+) ions were reduced and deposited on {111} facets of gold hexagonal nanoplates (GHNs), and hexagonal bipyramidal nanoparticles were formed more quickly in the presence of I(-) ions than without I(-) ions. Our studies reveal that I(-) ion affects the selective growth of Ag onto GHNs. This can be explained by the decrease in the surface redox potential of nanocrystals that occurs by combining with the AgI complex on the metallic surface. These results were confirmed by FESEM images, UV-vis-NIR spectra, and TEM images.

Interfacial double layer mediated electrochemical growth of thin-walled platinum nanotubes

This work demonstrates that thin-walled platinum nanotubes can be readily synthesized by controlling the interfacial double layer in alumina nanochannels. The gradient distribution of ions in nanochannels enables the creation of Pt nanotubes with walls as thin as 5 nm at the top end when using a solution containing polyvinylpyrrolidone (PVP) and chloroplatinic acid (H2PtCl6) under the influence of an electric potential in nanochannels. The highly efficient formation of thin-walled Pt nanotubes is a result of the concentration gradient of [Formula: see text] and a thick double layer, which was caused by the low concentration of Pt precursors and the enhanced surface charge density induced by protonated PVP steric adsorption. This well-controlled synthesis reveals that the interfacial double layer is a useful tool to tailor the structure of nanomaterials in a nanoscale space, and holds promise in the construction of more complex functional nanostructures.

Fourier Transform Surface Plasmon Resonance (FTSPR) with Gyromagnetic Plasmonic Nanorods

An unprecedented active and dynamic sensing platform based on a LSPR configuration that is modulated by using an external magnetic field is reported. Electrochemically synthesized Au/Fe/Au nanorods exhibited plasmonically active behavior through plasmonic coupling, and the middle ferromagnetic Fe block responded to a magnetic impetus, allowing the nanorods to be modulated. The shear force variation induced by the specific binding events between antigens and antibodies on the nanorod surface is used to enhance the sensitivity of detection of antigens in the plasmonics-based sensor application. As a proof-of-concept, influenza A virus (HA1) was used as a target protein. The limit of detection was enhanced by two orders of magnitude compared to that of traditional LSPR sensing.

Synthesis of octahedral gold tip-blobbed nanoparticles and their dielectric sensing properties

Site-selective synthesis of nanostructures is an important topic in the nanoscience community. Normally, the difference between seeds and deposition atoms in terms of crystallinity triggers the deposition atoms to grow initially at the specific site of nucleation. It is more challenging to control the deposition site of atoms that have the same composition as the seeds because the atoms tend to grow epitaxially, covering the whole surface of the seed nanoparticles. Gold (Au) nano-octahedrons used as seeds in this study possess obvious hierarchical surface energies depending on whether they are at vertices, edges, or terraces. Although vertices of Au nano-octahedrons have the highest surface energy, it remains a challenge to selectively deposit Au atoms at the vertices but not at the edges and faces; this selectivity is required to meet the ever-increasing demands of engineered nanomaterial properties. This work demonstrates an easy and robust method to precisely deposit Au nanoparticles at the vertices of Au nano-octahedrons via wet-chemical seed-mediated growth. The successful synthesis of octahedral Au tip-blobbed nanoparticles (Oh Au TBPs) benefited from the cooperative use of thin silver (Ag) layers at the surface of Au nano-octahedron seeds and iodide ions in the Au growth solution. As-synthesized Au nanostructures (i.e., Au TBPs) gave rise to hybrid optical properties, as evidenced from the UV-vis-NIR extinction spectra, in which a new extinction peak appeared after Au nanoparticles were formed at the vertices of Au nano-octahedrons. A sensitivity evaluation toward dielectric media of a mixture of dimethyl sulfoxide and water suggested that Au TBPs were more optically sensitive compared to the original Au nano-octahedrons. The method demonstrated in this work is promising in the synthesis of advanced Au nanostructures with hybrid optical properties for versatile applications, by engineering the surface energy of vertex-bearing Au nanostructures to trigger site-selective overgrowth of congener Au atoms.