Ultrasensitive Label-Free Nanosensing and High-Speed Tracking of Single Proteins

: Label-free detection, analysis, and rapid tracking of nanoparticles is crucial for future ultrasensitive sensing applications, ranging from understanding of biological interactions to the study of size-dependent classical-quantum transitions. Yet optical techniques to distinguish nanoparticles directly among their background remain challenging. Here we present amplified interferometric scattering microscopy (aiSCAT) as a new all-optical method capable of detecting individual nanoparticles as small as 15 kDa proteins that is equivalent to half a GFP. By balancing scattering and reflection amplitudes the interference contrast of the nanoparticle signal is amplified 1 to 2 orders of magnitude. Beyond high sensitivity, a-iSCAT allows high-speed image acquisition exceeding several hundreds of frames-per-second. We showcase the performance of our approach by detecting single Streptavidin binding events and by tracking single Ferritin proteins at 400 frames-per-second with 12 nm localization precision over seconds. Moreover, due to its extremely simple experimental realization, this advancement finally enables a cheap and routine implementation of label-free all-optical single nanoparticle detection platforms with sensitivity operating at the single protein level.Peer ReviewedPostprint (author's final draft

Demonstrating photoluminescence from Au is electronic inelastic light scattering of a plasmonic metal: the origin of SERS backgrounds.

Temperature-dependent surface-enhanced Raman scattering (SERS) is used to investigate the photoluminescence and background continuum always present in SERS but whose origin remains controversial. Both the Stokes and anti-Stokes background is found to be dominated by inelastic light scattering (ILS) from the electrons in the noble metal nanostructures supporting the plasmon modes. The anti-Stokes background is highly temperature dependent and is shown to be related to the thermal occupation of electronic states within the metal via a simple model. This suggests new routes to enhance SERS sensitivities, as well as providing ubiquitous and calibrated real-time temperature measurements of nanostructures.The authors would like to thank EPSRC (EP/K028510/1, EP/ G060649/1, EP/H007024/1, EP/L027151/1), ERC LINASS 320503, EU CUBiHOLE, and Renishaw Diagnostics Ltd. for funding and samples.This is the final published version. It first appeared at http://pubs.acs.org/doi/abs/10.1021/acs.nanolett.5b00146

On the nature of SERS from plasmonic nanostructures

The nature of surface-enhanced Raman scattering (SERS) on nanostructured surfaces is explored using both inorganic and organic-based systems and a variety of environmental perturbation mechanisms. Experimental optical characterisation systems are developed and existing systems extended to facilitate this exploration. SERS of inorganic semiconducting quantum dots (QDs) is observed for the first time, paving the way for their use as spatially well-defined SERS markers. Tuning of the Raman excitation wavelength allows comparison between resonance and nonresonance QD SERS and identifies enhancement due to the plasmonic nanostructure. A gentle mechano-chemical process (carbon dioxide snow jet) is used to rearrange adsorbed organic thiol monolayers on a gold plasmonic nanostructure. The necessity of nanoscale roughness to the large SERS enhancement on pit-like plasmonic nanostructures is shown and demonstrates a new method to boost SERS signals (> 500 %) on plasmonic nanostructures. A multiplexed time-varied exposure technique is developed to track this molecular movement over time and highlights the different origins of the SERS peak and its accompanying background continuum. Using low-temperature cryogenics (down to 10 K) the SERS peak and background continuum intensity are shown to increase as the plasmonic metal damping reduces with temperature. Temperature dependent measurements of QD (resonance) SERS are shown to have strong wavelength dependence due to the excitonic transitions in QDs. Changes to the QD fluorescence at low temperature allows striking comparison between the Raman and fluorescence processes. The role of charge transfer and electromagnetic enhancement in the SERS intensity of p-aminothiophenol (pATP) is investigated on nanostructured plasmonic surfaces coupled to metallic nanoparticles. The results support the importance of charge transfer effects to the SERS of pATP, and highlight the difference between those of electromagnetic origin. Addition of nanoparticles to the nanostructured surface was seen to enhance SERS signals by up to 100×.Funded by an EPSRC Industrial CASE studentship in collaboration with Renishaw Diagnostics Ltd

Plasmonic Nanocavity Coupling

The large losses of plasmonic nanocavities, orders of magnitude beyond those of photonic dielectric cavities, places them, perhaps surprisingly, as exceptional enhancers of single emitter light‐matter interactions. The ultra‐confined, sub‐diffraction limited, mode volumes of plasmonic systems offer huge coupling strengths (in the 1‐100 meV range) to single quantum emitters. Such strengths far outshine the lower coupling strengths of dielectric microcavities, which nonetheless easily achieve single emitter ‘strong coupling’ due to the low loss rates of dielectric cavities. In fact, it is the much higher loss rate of plasmonic cavities that make them desirable for applications requiring bright, fastemitting photon sources. Here we provide a simple method to reformulate lifetime measurements of single emitters in terms of coupling strengths to allow a useful comparison of the literature of plasmonic cavities with that of cavity‐QED, typically more closely associated with dielectric cavities. Using this approach, we observe that the theoretical limit of coupling strength in plasmonic structures has almost been experimentally achieved with even single molecule strong coupling now observed in plasmonic systems. However, key problems remain to maximise the potential of plasmonic cavities, including precise and deterministic nanopositioning of the emitter in the nanosized plasmonic mode volumes, understanding the best geometry for the plasmonic cavity, separating useful photons from background photons and dealing with the fluorescence quenching problems of metals. Here we attempt to raise awareness of the benefits of plasmonic nanocavities for cavity‐QED and tackle some of the potential pitfalls. We observe that there is increasing evidence, that using correct geometries, and improving emitter placement abilities, significant quenching can be avoided and photon output maximised towards the extraordinary limit provided by the high radiative rates of plasmonic nanocavitiesPeer ReviewedPostprint (author's final draft

Nanoscale mapping and control of antenna-coupling strength for bright single photon sources

Cavity QED is the art of enhancing light-matter interaction of photon emitters in cavities, with opportunities for sensing, quantum information and energy capture technologies. To boost emitter-cavity interaction, i.e. coupling strength , ultrahigh quality cavities have been concocted yielding photon trapping times of µs to ms. However, such high-Q cavities give poor photon output, hindering applications. To preserve high photon output it is advantageous to strive for highly localised electric fields in radiatively lossy cavities. Nanophotonic antennas are ideal candidates combining low-Q factors with deeply localised mode volumes, allowing large , provided the emitter is positioned exactly right inside the nanoscale mode volume. Here, with nanometre resolution, we map and tune the coupling strength between a dipole nanoantenna-cavity and a single molecule, obtaining a coupling rate of max ~ 200 GHz. Together with accelerated single photon output, this provides ideal conditions for fast and pure non-classical single photon emission with brightness exceeding 10E9 photons/sec. Clearly, nanoantennas acting as “bad” cavities offer an optimal regime for strong coupling , to deliver bright on-demand and ultrafast single photon nanosources for quantum technologies.Peer ReviewedPostprint (author's final draft

Probing confined phonon modes in individual CdSe nanoplatelets using surface-enhanced Raman scattering.

The phonon modes of individual ultrathin CdSe nanoplatelets are investigated using surface-enhanced Raman scattering in a tightly confined plasmonic geometry. The surface-enhanced Raman scattering spectra, taken on single nanoplatelets sandwiched between a gold nanoparticle and a gold surface, reveal a phonon doublet arising from oscillations perpendicular to and within the platelet plane. The out-of-plane mode cannot be observed with conventional Raman spectroscopy. The resulting strong electric field enhancements and the field vector reorientation within such nanometer-sized plasmonic gaps reveal otherwise hidden information deep into the Brillouin zone illuminating the vibrational properties of ultrathin materials.EPSRCThis is the Author Accepted Manuscript of Daniel O. Sigle, James T. Hugall, Sandrine Ithurria, Benoit Dubertret, and Jeremy J. Baumberg which was published in Physical review letters (https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.113.087402). "Copyright 2014 by the American Physical Society.

Monitoring Early-Stage Nanoparticle Assembly in Microdroplets by Optical Spectroscopy and SERS.

Microfluidic microdroplets have increasingly found application in biomolecular sensing as well as nanomaterials growth. More recently the synthesis of plasmonic nanostructures in microdroplets has led to surface-enhanced Raman spectroscopy (SERS)-based sensing applications. However, the study of nanoassembly in microdroplets has previously been hindered by the lack of on-chip characterization tools, particularly at early timescales. Enabled by a refractive index matching microdroplet formulation, dark-field spectroscopy is exploited to directly track the formation of nanometer-spaced gold nanoparticle assemblies in microdroplets. Measurements in flow provide millisecond time resolution through the assembly process, allowing identification of a regime where dimer formation dominates the dark-field scattering and SERS. Furthermore, it is shown that small numbers of nanoparticles can be isolated in microdroplets, paving the way for simple high-yield assembly, isolation, and sorting of few nanoparticle structures.J. J. Baumberg and A. Salmon acknowledge the support of the European Research Council (LINASS 320503), the UK Engineering and Physical Sciences Research Council EP/K028510/1, EP/G037221/1, EP/G060649/1, EP/L027151/1, and the Nano Science and Technology Doctoral Training Centre (NanoDTC) of the University of Cambridge. J. Aizpurua and R. Esteban acknowledge the Spanish Ministry of Economy and Competitiveness (FIS2013-41184-P). R. Esteban acknowledges the Fellow Gipuzkoa Program of the Gipuzkoako Foru Aldundia through FEDER “Una Manera de hacer Europa”.This is the final version of the article. It first appeared from Wiley via https://doi.org/10.1002/smll.20150351

Evolutionary history of Serpulaceae (Basidiomycota): molecular phylogeny, historical biogeography and evidence for a single transition of nutritional mode

<p>Abstract</p> <p>Background</p> <p>The fungal genus <it>Serpula </it>(Serpulaceae, Boletales) comprises several saprotrophic (brown rot) taxa, including the aggressive house-infecting dry rot fungus <it>Serpula lacrymans</it>. Recent phylogenetic analyses have indicated that the ectomycorrhiza forming genera <it>Austropaxillus </it>and <it>Gymnopaxillus </it>cluster within <it>Serpula</it>. In this study we use DNA sequence data to investigate phylogenetic relationships, historical biogeography of, and nutritional mode transitions in Serpulaceae.</p> <p>Results</p> <p>Our results corroborate that the two ectomycorrhiza-forming genera, <it>Austropaxillus </it>and <it>Gymnopaxillus</it>, form a monophyletic group nested within the saprotrophic genus <it>Serpula</it>, and that the <it>Serpula </it>species <it>S. lacrymans </it>and <it>S. himantioides </it>constitute the sister group to the <it>Austropaxillus</it>-<it>Gymnopaxillus </it>clade. We found that both vicariance (Beringian) and long distance dispersal events are needed to explain the phylogeny and current distributions of taxa within Serpulaceae. Our results also show that the transition from brown rot to mycorrhiza has happened only once in a monophyletic Serpulaceae, probably between 50 and 22 million years before present.</p> <p>Conclusions</p> <p>This study supports the growing understanding that the same geographical barriers that limit plant- and animal dispersal also limit the spread of fungi, as a combination of vicariance and long distance dispersal events are needed to explain the present patterns of distribution in Serpulaceae. Our results verify the transition from brown rot to ECM within Serpulaceae between 50 and 22 MyBP.</p

Surface-enhanced Raman spectroscopy of CdSe quantum dots on nanostructured plasmonic surfaces

Although quantum dots (QDs) are widely used as fluorophores they have not so far been used as Raman labels. Here we demonstrate (resonant) surface-enhanced Raman scattering (SERS) of CdSe QDs attached to nanostructured plasmonic surfaces. The 208?cm?1 CdSe longitudinal optical phonon mode is observed for laser excitation at 514, 633, and 785 nm. Tuning the SERS signal into resonance with the localized surface plasmon reveals the effects of optical absorption and emission on QD SERS. Equivalent tuning of the localized plasmons on graded nanovoid samples shows strong resonant SERS enhancements. These results pave the way for exploiting QDs as SERS markers