Roadmap on optical sensors.

Optical sensors and sensing technologies are playing a more and more important role in our modern world. From micro-probes to large devices used in such diverse areas like medical diagnosis, defence, monitoring of industrial and environmental conditions, optics can be used in a variety of ways to achieve compact, low cost, stand-off sensing with extreme sensitivity and selectivity. Actually, the challenges to the design and functioning of an optical sensor for a particular application requires intimate knowledge of the optical, material, and environmental properties that can affect its performance.

ZIF-Induced d-Band Modification in a Bimetallic Nanocatalyst: Achieving Over 44 % Efficiency in the Ambient Nitrogen Reduction Reaction.

The electrochemical nitrogen reduction reaction (NRR) offers a sustainable solution towards ammonia production but suffers poor reaction performance owing to preferential catalyst-H formation and the consequential hydrogen evolution reaction (HER). Now, the Pt/Au electrocatalyst d-band structure is electronically modified using zeolitic imidazole framework (ZIF) to achieve a Faradaic efficiency (FE) of >44 % with high ammonia yield rate of >161 μg mg  h under ambient conditions. The strategy lowers electrocatalyst d-band position to weaken H adsorption and concurrently creates electron-deficient sites to kinetically drive NRR by promoting catalyst-N interaction.

Driving CO to a Quasi-Condensed Phase at the Interface between a Nanoparticle Surface and a Metal-Organic Framework at 1 bar and 298 K.

We demonstrate a molecular-level observation of driving CO molecules into a quasi-condensed phase on the solid surface of metal nanoparticles (NP) under ambient conditions of 1 bar and 298 K. This is achieved via a CO accumulation in the interface between a metal-organic framework (MOF) and a metal NP surface formed by coating NPs with a MOF. Using real-time surface-enhanced Raman scattering spectroscopy, a >18-fold enhancement of surface coverage of CO is observed at the interface.

Nanoporous Gold Bowls: A Kinetic Approach to Control Open Shell Structures and Size-Tunable Lattice Strain for Electrocatalytic Applications.

Controlling sub-10 nm ligament sizes and open-shell structure in nanoporous gold (NPG) to achieve strained lattice is critical in enhancing catalytic activity, but it remains a challenge due to poor control of reaction kinetics in conventional dealloying approach. Herein, a ligament size-controlled synthesis of open-shell NPG bowls (NPGB) through hetero-epitaxial growth of NPGB on AgCl is reported. The ligament size in NPGB is controlled from 6 to 46 nm by varying the hydroquinone to HAuCl4 ratio.

One-step synthesis of zero-dimensional hollow nanoporous gold nanoparticles with enhanced methanol electrooxidation performance.

Nanoporous gold with networks of interconnected ligaments and highly porous structure holds stimulating technological implications in fuel cell catalysis. Current syntheses of nanoporous gold mainly revolve around de-alloying approaches that are generally limited by stringent and harsh multistep protocols. Here we develop a one-step solution phase synthesis of zero-dimensional hollow nanoporous gold nanoparticles with tunable particle size (150-1,000 nm) and ligament thickness (21-54 nm).

Precision synthesis: designing hot spots over hot spots via selective gold deposition on silver octahedra edges.

A major challenge in plasmonic hot spot fabrication is to efficiently increase the hot spot volumes on single metal nanoparticles to generate stronger signals in plasmon-enhanced applications. Here, the synthesis of designer nanoparticles, where plasmonic-active Au nanodots are selectively deposited onto the edge/tip hot spot regions of Ag nanoparticles, is demonstrated using a two-step seed-mediated precision synthesis approach. Such a "hot spots over hot spots" strategy leads to an efficient enhancement of the plasmonic hot spot volumes on single Ag nanoparticles.

Understanding the synthetic pathway of a single-phase quarternary semiconductor using surface-enhanced Raman scattering: a case of wurtzite Cu₂ZnSnS₄ nanoparticles.

Single-phase Cu2ZnSnS4 (CZTS) is an essential prerequisite toward a high-efficiency thin-film solar cell device. Herein, the selective phase formation of single-phase CZTS nanoparticles by ligand control is reported. Surface-enhanced Raman scattering (SERS) spectroscopy is demonstrated for the first time as a characterization tool for nanoparticles to differentiate the mixed compositional phase (e.

Graphene oxide and shape-controlled silver nanoparticle hybrids for ultrasensitive single-particle surface-enhanced Raman scattering (SERS) sensing.

Graphene oxide (GO) is an emerging material for surface-enhanced Raman scattering (SERS) due to its strong chemical enhancement. Studying the SERS performance of plasmonic nanoparticle/GO hybrid materials at the single particle level is crucial for direct probing of the chemical effect of GO on plasmonic nanoparticles. In this work, we integrate GO and shape-controlled Ag nanoparticles to create hybrid nanomaterials, and the chemical enhancement arising from GO is investigated using single-particle SERS measurements.

Bimetallic platonic Janus nanocrystals.

We demonstrate the creation of Ag-based bimetallic platonic Janus nanostructures by confining galvanic replacement reaction at a nanoscale interface on highly symmetrical nanostructures such as Ag nanocubes and nanooctahedra using reactive microcontact printing (μCP). The extent of galvanic replacement reaction can be controlled kinetically to derive Janus nanostructures with Au nanodots deposited on either one or multiple facets of Ag nanocubes. The selective deposition of Au dots on a single facet of Ag nanocubes breaks the cubic symmetry and brings about unique and anisotropic plasmonic responses.

A chemical route to increase hot spots on silver nanowires for surface-enhanced Raman spectroscopy application.

The effective number of surface-enhanced Raman spectroscopy (SERS) active hot spots on plasmonic nanostructures is the most crucial factor in ensuring high sensitivity in SERS sensing platform. Here we demonstrate a chemical etching method to increase the surface roughness of one-dimensional Ag nanowires, targeted at creating more SERS active hot spots along Ag nanowire's longitudinal axis for increased SERS detection sensitivity. Silver nanowires were first synthesized by the conventional polyol method and then subjected to chemical etching by NH(4)OH and H(2)O(2) mixture.