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A surface-enhanced Raman spectroscopy-based in situ analytical tool for the sensitive and rapid monitoring of hydrogen transport through graphene was developed.

The intrinsic correlation between an enhancement of catalytic activity and the flow of hot electrons generated at metal–oxide interfaces suggests an intriguing way to control catalytic reactions and is a significant subject in heterogeneous catalysis. Here, we show surface plasmon-induced catalytic enhancement by the peculiar nanocatalyst design of hexoctahedral (HOH) Au nanocrystals (NCs) with Cu2O clusters. We found that this inverse catalyst comprising a reactive oxide for the catalytic portion and a metal as the source of electrons by localized surface plasmon resonance (localized SPR) exhibits a change in catalytic activity by direct hot electron transfer or plasmon-induced resonance energy transfer (PIRET) when exposed to light. We prepared two types of inverse catalysts, Cu2O at the vertex sites of HOH Au NCs (Cu2O/Au vertex site) and a HOH Au NC–Cu2O core–shell structure (HOH Au@Cu2O), to test the structural effect on surface plasmons. Under broadband light illumination, the Cu2O/Au vertex site catalyst showed 30–90% higher catalytic activity and the HOH Au@Cu2O catalyst showed 10–30% higher catalytic activity than when in the dark. Embedding thin SiO2 layers between the HOH Au NCs and the Cu2O verified that the dominant mechanism for the catalytic enhancement is direct hot electron transfer from the HOH Au to the Cu2O. Finite-difference time domain calculations show that a much stronger electric field was formed on the vertex sites after growing the Cu2O on the HOH Au NCs. These results imply that the catalytic activity is enhanced when hot electrons, created from photon absorption on the HOH Au metal and amplified by the presence of surface plasmons, are transferred to the reactive Cu2O.

The intrinsic correlation between an enhancement of catalytic activity and the flow of hot electrons generated at metal-oxide interfaces suggests an intriguing way to control catalytic reactions and is a significant subject in heterogeneous catalysis. Here, we show surface plasmon-induced catalytic enhancement by the peculiar nanocatalyst design of hexoctahedral (HOH) Au nanocrystals (NCs) with Cu2O clusters. We found that this inverse catalyst comprising a reactive oxide for the catalytic portion and a metal as the source of electrons by localized surface plasmon resonance (localized SPR) exhibits a change in catalytic activity by direct hot electron transfer or plasmon-induced resonance energy transfer (PIRET) when exposed to light. We prepared two types of inverse catalysts, Cu2O at the vertex sites of HOH Au NCs (Cu2O/Au vertex site) and a HOH Au NC-Cu2O core-shell structure (HOH Au@Cu2O), to test the structural effect on surface plasmons. Under broadband light illumination, the Cu2O/Au vertex site catalyst showed 30-90% higher catalytic activity and the HOH Au@Cu2O catalyst showed 10-30% higher catalytic activity than when in the dark. Embedding thin SiO2 layers between the HOH Au NCs and the Cu2O verified that the dominant mechanism for the catalytic enhancement is direct hot electron transfer from the HOH Au to the Cu2O. Finite-difference time domain calculations show that a much stronger electric field was formed on the vertex sites after growing the Cu2O on the HOH Au NCs. These results imply that the catalytic activity is enhanced when hot electrons, created from photon absorption on the HOH Au metal and amplified by the presence of surface plasmons, are transferred to the reactive Cu2O.

To achieve a reliable formation of a surface-enhanced Raman scattering (SERS) sensor with evenly distributed hot spots on a wafer scale substrate, we propose a hybrid approach combining physical nanolithography for preparing Au nanodisks and chemical Au reduction for growing them. During the chemical growth, the interstitial distance between the nanodisks decreased from 60 nm to sub-5 nm. The resulting patterns of the nanogap-rich Au nanodisks successfully enhance the SERS signal, and its intensity map shows only a 5% or less signal variation on the entire sample.

Nucleic acid-based technologies have been applied to numerous biomedical applications. As a novel material for target detection, DNA has been used to construct a barcode system with a range of structures. This paper reports multi-functionalized DNA nanospheres (DNANSs) by rolling circle amplification (RCA) with several functionalized nucleotides. DNANSs with a barcode system were designed to exhibit fluorescence for coding enhanced signals and contain biotin for more functionalities, including targeting through the biotin-streptavidin (biotin-STA) interaction. Functionalized deoxynucleotide triphosphates (dNTPs) were mixed in the RCA process and functional moieties can be expressed on the DNANSs. The anti-epidermal growth factor receptor antibodies (anti-EGFR Abs) can be conjugated on DNANSs for targeting cancer cells specifically. As a proof of concept, the potential of the multi-functional DNANS barcode was demonstrated by direct cell detection as a simple detection method. The DNANS barcode provides a new route for the simple and rapid selective recognition of cancer cells.

We report an analysis method to identify conjugated ligands and their binding states on semiconductor nanocrystals based on their molecular information. Surface science techniques, such as time-of-flight secondary-ion mass spectrometry (ToF-SIMS) and FT-IR spectroscopy, are adopted based on the micro-aggregated sampling method. Typical trioctylphosphine oxide-based synthesis methods of CdSe/ZnS quantum dots (QDs) have been criticized because of the peculiar effects of impurities on the synthesis processes. Because the ToF-SIMS technique provides molecular composition evidence on the existence of certain ligands, we were able to clearly identify n-octylphosphonic acid (OPA) as a surface ligand on CdSe/ZnS QDs. Furthermore, the complementary use of the ToF-SIMS technique with the FT-IR technique could reveal the OPA ligands’ binding state as bidentate complexes.

We report a facile method for the synthesis of Pd nanostructures with highly open structure and huge surface area by reducing Na2PdCl4 with ascorbic acid and using cetylpyridinium chloride (CPC) as a surfactant in an aqueous solution. The prepared Pd nanostructures had an average overall size of 70 nm and were composed of dozens of needle-like thin arms, originating from the same core, with an average thickness of 2.3 nm; the arms looked like chestnut-burs. Time evolution of Pd nanostructures implied that small Pd particles generated at the early stage of the reaction by fast reduction grew via the particle attachment growth mechanism. The morphology and size of the Pd nanostructures could be readily controlled by varying the concentration of CPC; depending on the amount of CPC, the reduction rates varied the morphology of the Pd nanostructures. Because of the huge surface area and possible catalytically active sites, the prepared chestnut-bur-like Pd nanostructures exhibited greater electrocatalytic activity toward ethanol electrooxidation compared to other Pd nanocatalysts, including cubic and octahedral Pd nanocrystals, and even commercial Pd/C.

Bimetallic nanocrystals (NCs) enclosed by high-surface energy facets have been of enormous interest due to their pronounced catalytic performance in numerous chemical and electrochemical reactions. However, it remains a significant challenge to develop a facile method to synthesize bimetallic NCs with high-surface energy facets in the form of finely tuned structures due to the difficulties in manipulating the nucleation and growth kinetics of NCs in the presence of multiple metal precursors. In the present work, a facile one-pot aqueous synthesis method is developed for the production of bimetallic Au@Pd core-shell NCs with an unusual truncated hexoctahedral (THOH) shape without pre-synthesized seeds. The THOH Au@Pd NCs are bound by multiple high- and low-index facets. The formation of this unique structure is realized through co-reduction of Au and Pd precursors under precisely controlled kinetic conditions. The prepared THOH NCs exhibit a prominent electrocatalytic performance for ethanol oxidation, which is attributed to their characteristic structural features. This study significantly expands the understanding of NC growth and will lead to fabricating novel nanomaterials with desired morphologies and functions.