Size Dependent Plasmonic Effect on BiVO4 Photoanodes for Solar Water Splitting.

Plasmonic nanostructures show great promise in enhancing the solar water splitting efficiency due to their ability to confine light to extremely small volumes inside semiconductors. While size plays a critical role in the plasmonic performance of Au nanoparticles (AuNPs), its influence on plasmon-assisted water splitting is still not fully understood. This holds especially true for low band gap semiconductors, for which interband excitations occur in wavelength regions that overlap with plasmonic resonances. Here, BiVO4 films are modified with AuNPs of diameters varying from 10 to 80 nm to study the size dependence of the plasmonic effect. Plasmon resonance energy transfer (PRET) is found to be the dominant effect in enhancing the water splitting efficiency of BiVO4. "Hot electron" injection effect is weak in the case of BiVO4/AuNP. This is attributed to the interband excitation of BiVO4, which is unfavourable for the hot electrons accumulation in BiVO4 conduction band. The resonant scattering effect also contributes to the enhanced water splitting efficiency for the larger diameter AuNPs. It is also for the first time found that higher PRET effect can be achieved at larger off-normal irradiation angle

Nanoimprint lithography of Al nanovoids for deep-UV SERS.

Deep-ultraviolet surface-enhanced Raman scattering (UV-SERS) is a promising technique for bioimaging and detection because many biological molecules possess UV absorption lines leading to strongly resonant Raman scattering. Here, Al nanovoid substrates are developed by combining nanoimprint lithography of etched polymer/silica opal films with electron beam evaporation, to give a high-performance sensing platform for UV-SERS. Enhancement by more than 3 orders of magnitude in the UV-SERS performance was obtained from the DNA base adenine, matching well the UV plasmonic optical signatures and simulations, demonstrating its suitability for biodetection.We acknowledge financial support from EPSRC grant EP/G060649/1, EP/I012060/1, EP/J007552/1, ERC grant LINASS 320503.This is the final version of the article. It first appeared from ACS via http://dx.doi.org/10.1021/am505511

Self-aligned colloidal lithography for controllable and tuneable plasmonic nanogaps.

Au nanoparticles (NPs) deposited on a substrate function as ring shaped colloidal shadow masks. Using e-beam evaporation of gold, nanometer sized gaps are formed as a result. The size of these gaps can be accurately tuned by controlling the thickness of the gold deposition, thereby tuning the plasmonic coupling of the NPs with the substrate. The clean cavity produced between the Au NPs and the Au film provides an excellent SERS platform for trace molecule detection.The authors acknowledge the fi nancial support of this research from EPSRC grant EP/G060649/1, EP/I012060/1, and ERC grant LINASS 320503. FB acknowledges support from the Winton Pro-gramme for the Physics of Sustainability.This article was originally published in Small, 2015, DOI: 10.1002/smll.201402639

Facile Fabrication of Spherical Nanoparticle-Tipped AFM Probes for Plasmonic Applications.

We wish to acknowledge the support of grants UK EPSRC EP/G060649/1, EP/H007024/1, a Marie Curie Intra-European Fellowship (FP7-PEOPLE-2011-IEF 298012 to L.Z.), ERC LINASS 320503, and Royal Society IE120879. R.W.B. thanks Queens’ College, Cambridge for financial support.This is the final published version. It originally appeared in Particle & Particle Systems Characterization and is available in http://onlinelibrary.wiley.com/doi/10.1002/ppsc.201400104/abstract

Monitoring morphological changes in 2D monolayer semiconductors using atom-thick plasmonic nanocavities

This is an open access article published under a Creative Commons Attribution (CC-BY) License.-- et al.Nanometer-sized gaps between plasmonically coupled adjacent metal nanoparticles enclose extremely localized optical fields, which are strongly enhanced. This enables the dynamic investigation of nanoscopic amounts of material in the gap using optical interrogation. Here we use impinging light to directly tune the optical resonances inside the plasmonic nanocavity formed between single gold nanoparticles and a gold surface, filled with only yoctograms of semiconductor. The gold faces are separated by either monolayers of molybdenum disulfide (MoS2) or two-unit-cell thick cadmium selenide (CdSe) nanoplatelets. This extreme confinement produces modes with 100-fold compressed wavelength, which are exquisitely sensitive to morphology. Infrared scattering spectroscopy reveals how such nanoparticle-on-mirror modes directly trace atomic-scale changes in real time. Instabilities observed in the facets are crucial for applications such as heat-assisted magnetic recording that demand long-lifetime nanoscale plasmonic structures, but the spectral sensitivity also allows directly tracking photochemical reactions in these 2-dimensional solids.This work was supported by the UK EPSRC grants EP/G060649/1, EP/L027151/1, Defence Science and Technology Laboratory (DSTL), and ERC grant 320503 LINASS. C.T. and J.A. acknowledge financial support from Project FIS2013-41184-P from MINECO, ETORTEK 2014-15 of the Basque Department of Industry and IT756-13 from the Basque consolidated groups.Peer Reviewe

Quantitative multiplexing with nano-self-assemblies in SERS.

Multiplexed or simultaneous detection of multiple analytes is a valuable tool in many analytical applications. However, complications caused by the presence of interfering compounds in a sample form a major drawback in existing molecular sensor technologies, particularly in multi-analyte systems. Although separating analytes through extraction or chromatography can partially address the problem of interferents, there remains a need for developing direct observational tools capable of multiplexing that can be applied in situ. Surface-enhanced Raman Spectroscopy (SERS) is an optical molecular finger-printing technique that has the ability to resolve analytes from within mixtures. SERS has attracted much attention for its potential in multiplexed sensing but it has been limited in its quantitative abilities. Here, we report a facile supramolecular SERS-based method for quantitative multiplex analysis of small organic molecules in aqueous environments such as human urine.The authors thank Ms. Anna Andreou for the 1H-NMR measurements and acknowledge funding from Walters-Kundert Trust, EPSRC (EP/K028510/1, EP/G060649/1, EP/H007024/1, ERC LINASS 320503), an ERC starting investigator grant (ASPiRe 240629), EU CUBiHOLE grant. S.K. thanks Krebs Memorial Scholarship (The Biochemical Society) and Cambridge Commonwealth Trust for funding.This is the final version of the article. It first appeared from NPG via http://dx.doi.org/10.1038/srep0678

Threading plasmonic nanoparticle strings with light

This work is licensed under a Creative Commons Attribution 4.0 International License.-- et al.Nanomaterials find increasing application in communications, renewable energies, electronics and sensing. Because of its unsurpassed speed and highly tuneable interaction with matter, using light to guide the self-assembly of nanomaterials can open up novel technological frontiers. However, large-scale light-induced assembly remains challenging. Here we demonstrate an efficient route to nano-assembly through plasmon-induced laser threading of gold nanoparticle strings, producing conducting threads 12±2nm wide. This precision is achieved because the nanoparticles are first chemically assembled into chains with rigidly controlled separations of 0.9nm primed for re-sculpting. Laser-induced threading occurs on a large scale in water, tracked via a new optical resonance in the near-infrared corresponding to a hybrid chain/rod-like charge transfer plasmon. The nano-thread width depends on the chain mode resonances, the nanoparticle size, the chain length and the peak laser power, enabling nanometre-scale tuning of the optical and conducting properties of such nanomaterials.We acknowledge financial support from EPSRC grants EP/G060649/1, EP/K028510/1 and EP/L027151/1, ERC grants LINASS 320503 and ASPiRe 240629, and project FIS2010-19609-C02-01 from the Spanish Ministry of Science and Innovation. J.S.B. acknowledges the School of Physical Science, University of Cambridge, for the funding of the transmission electron microscope. S.K. acknowledges funding from the Biochemical Society (Krebs Memorial Scholarship) and the Cambridge Commonwealth Trust.Peer Reviewe

DNA origami based assembly of gold nanoparticle dimers for surface-enhanced Raman scattering.

Plasmonic sensors are extremely promising candidates for label-free single-molecule analysis but require exquisite control over the physical arrangement of metallic nanostructures. Here we employ self-assembly based on the DNA origami technique for accurate positioning of individual gold nanoparticles. Our innovative design leads to strong plasmonic coupling between two 40 nm gold nanoparticles reproducibly held with gaps of 3.3 ± 1 nm. This is confirmed through far field scattering measurements on individual dimers which reveal a significant red shift in the plasmonic resonance peaks, consistent with the high dielectric environment due to the surrounding DNA. We use surface-enhanced Raman scattering (SERS) to demonstrate local field enhancements of several orders of magnitude through detection of a small number of dye molecules as well as short single-stranded DNA oligonucleotides. This demonstrates that DNA origami is a powerful tool for the high-yield creation of SERS-active nanoparticle assemblies with reliable sub-5 nm gap sizes

Observing Single Molecules Complexing with Cucurbit[7]uril through Nanogap Surface-Enhanced Raman Spectroscopy.

In recent years, single-molecule sensitivity achievable by surface-enhanced Raman spectroscopy (SERS) has been widely reported. We use this to investigate supramolecular host-guest chemistry with the macrocyclic host cucurbit[7]uril, on a few-to-single-molecule level. A nanogap geometry, comprising individual gold nanoparticles on a planar gold surface spaced by a single layer of molecules, gives intense SERS signals. Plasmonic coupling between the particle and the surface leads to strongly enhanced optical fields in the gap between them, with single-molecule sensitivity established using a modification of the well-known bianalyte method. Changes in the Raman modes of the host molecule are observed when single guests included inside its cavity internally stretch it. Anisotropic intermolecular interactions with the guest are found which show additional distinct features in the Raman modes of the host molecule.The authors acknowledge funding from Walters-Kundert Trust, EPSRC (EP/K028510/1, EP/G060649/1, EP/ H007024/1, ERC LINASS 320503), an ERC starting investigator grant (ASPiRe 240629), EU CUBiHOLE grant and the Defence Science and Technology Laboratory (DSTL). S.K. thanks Krebs Memorial Scholarship (The Biochemical Society) and Cambridge Commonwealth Trust for funding.This is the author accepted manuscript. The final version is available from ACS via http://dx.doi.org/10.1021/acs.jpclett.5b0253

Threading plasmonic nanoparticle strings with light.

Nanomaterials find increasing application in communications, renewable energies, electronics and sensing. Because of its unsurpassed speed and highly tuneable interaction with matter, using light to guide the self-assembly of nanomaterials can open up novel technological frontiers. However, large-scale light-induced assembly remains challenging. Here we demonstrate an efficient route to nano-assembly through plasmon-induced laser threading of gold nanoparticle strings, producing conducting threads 12±2 nm wide. This precision is achieved because the nanoparticles are first chemically assembled into chains with rigidly controlled separations of 0.9 nm primed for re-sculpting. Laser-induced threading occurs on a large scale in water, tracked via a new optical resonance in the near-infrared corresponding to a hybrid chain/rod-like charge transfer plasmon. The nano-thread width depends on the chain mode resonances, the nanoparticle size, the chain length and the peak laser power, enabling nanometre-scale tuning of the optical and conducting properties of such nanomaterials.This is the published version of the article. It was published by NPG in Nature Communications and can be found on the journal website here: http://www.nature.com/ncomms/2014/140728/ncomms5568/full/ncomms5568.html