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

Control of Vibronic Transition Rates by Resonant Single-Molecule-Nanoantenna Coupling

Plasmonic nanostructures dramatically alter the radiative and nonradiative properties of single molecules in their vicinity. This coupling-induced change in decay channels selectively enhances specific vibronic transitions, which can enable plasmonic control of molecular reactivity. Here, we report coupling-dependent spectral emission shaping of single Rhodamine 800 molecules in the vicinity of plasmonic gold nanorods. We show that the relative vibronic transition rates of the first two vibronic transitions of the spontaneous emission spectrum can be tuned in the weak coupling regime, by approximately 25-fold, on the single molecule level.Peer ReviewedPostprint (author's final draft

Isolating strong nanoantenna-molecule interactions by ensemble-level single-molecule detection

Traditionally, the nanoscale interaction between single photon emitters and plasmonic nanostructures is studied by relying on deterministic, near-perfect, nanoscale-control, either top-down or bottom-up. However, these approaches are ultra-low throughput thus rendering systematic studies difficult and time-consuming. Here, we show a highly parallelised far-field tactic, combining multiplexed super-resolution fluorescence localization microscopy and data-driven statistical analysis, to study near-field interactions between gold nanorods and single molecules, even at bulk concentrations. We demonstrate that ensemble-level single molecule detection allows separating individual emitters according to their coupling strength with tailored resonant structures, which ultimately permits the reconstruction of super-resolved 2D interaction maps around individual nanoantennas.Peer ReviewedPostprint (author's final draft

Surface-Enhanced Raman Scattering Holography

Nanometric probes based on surface-enhanced Raman scattering (SERS) are promising candidates for all-optical environmental, biological and technological sensing applications with intrinsic quantitative molecular specificity. However, the effectiveness of SERS probes depends on a delicate trade-off between particle size, stability and brightness that has so far hindered their wide application in SERS imaging methodologies. In this Article, we introduce holographic Raman microscopy, which allows single-shot three-dimensional single-particle localization. We validate our approach by simultaneously performing Fourier transform Raman spectroscopy of individual SERS nanoparticles and Raman holography, using shearing interferometry to extract both the phase and the amplitude of wide-field Raman images and ultimately localize and track single SERS nanoparticles inside living cells in three dimensions. Our results represent a step towards multiplexed single-shot three-dimensional concentration mapping in many different scenarios, including live cell and tissue interrogation and complex anti-counterfeiting applications.Peer ReviewedPostprint (author's final draft

Widefield phototransient imaging for visualizing 3D motion of resonant particles in scattering environments

: Identifying, visualising and ultimately tracking dynamically moving non-fluorescent nanoparticles in the presence of non-specific scattering is a long-standing challenge across the nano- and life-sciences. In this work we demonstrate that our recently developed ultrafast holographic transient (UHT) microscope is ideally suited for meeting this challenge. We show that UHT microscopy allows reliably distinguishing off-resonant, dielectric, from resonant, metallic, nanoparticles, based on the phototransient signal: a pre-requisite for single-particle tracking in scattering environments. We then demonstrate the capability of UHT microscopy to holographically localize in 3D single particles over large volumes of view. Ultimately, we combine the two concepts to simultaneously track several tens of freely diffusing gold nanoparticles, within a 110 × 110 × 110 μm volume of view at an integration time of 10 ms per frame, while simultaneously recording their phototransient signals. The combined experimental concepts outlined and validated in this work lay the foundation for background-free 3D single-particle tracking applications or spectroscopy in scattering environments and are immediately applicable to systems as diverse as live cells and tissues or supported heterogeneous catalysts

‘Sciencenet’—towards a global search and share engine for all scientific knowledge

Summary: Modern biological experiments create vast amounts of data which are geographically distributed. These datasets consist of petabytes of raw data and billions of documents. Yet to the best of our knowledge, a search engine technology that searches and cross-links all different data types in life sciences does not exist

Observation of giant and tunable thermal diffusivity of a Dirac fluid at room temperature

Conducting materials typically exhibit either diffusive or ballistic charge transport. When electron–electron interactions dominate, a hydrodynamic regime with viscous charge flow emerges. More stringent conditions eventually yield a quantum-critical Dirac-fluid regime, where electronic heat can flow more efficiently than charge. However, observing and controlling the flow of electronic heat in the hydrodynamic regime at room temperature has so far remained elusive. Here we observe heat transport in graphene in the diffusive and hydrodynamic regimes, and report a controllable transition to the Dirac-fluid regime at room temperature, using carrier temperature and carrier density as control knobs. We introduce the technique of spatiotemporal thermoelectric microscopy with femtosecond temporal and nanometre spatial resolution, which allows for tracking electronic heat spreading. In the diffusive regime, we find a thermal diffusivity of roughly 2,000 cm s, consistent with charge transport. Moreover, within the hydrodynamic time window before momentum relaxation, we observe heat spreading corresponding to a giant diffusivity up to 70,000 cm s, indicative of a Dirac fluid. Our results offer the possibility of further exploration of these interesting physical phenomena and their potential applications in nanoscale thermal management.We thank M. Polini and P. Piskunow for fruitful discussions, and H. Agarwal and K. Soundarapandian for help with sample fabrication. We acknowledge the following funding sources: European Union’s Horizon 2020 research and innovation programme under grant nos. 804349 (K.-J.T.), 873028 (A.P.), 785219 (F.H.L.K. and S.R.), 881603 (F.H.L.K. and S.R.) and 670949 (N.F.v.H.); Spanish MCIU/AEI under grant nos. RYC-2017-22330 (K.-J.T.), PID2019-111673GB-I00 (K.-J.T.), BES-2016-078727 (M.L.), RTI2018-099957-J-I00 (M.L.) and PGC2018-096875-B-I00 (M.L. and N.F.v.H.); the Government of Catalonia under grant nos. SGR1656 (F.H.L.K.) and 2017SGR1369 (N.F.v.H.) and the CERCA program (ICN2 and ICFO); Spanish MINECO under grant nos. SEV-2017-0706 (ICN2) and CEX-2019-000910-S (ICFO); the International PhD fellowship program ‘la Caixa’ (A.B.); Leverhulme Trust grant no. RPG-2019-363 (A.P.); the Elemental Strategy Initiative conducted by the MEXT, Japan, grant no. JPMXP0112101001 (K.W. and T.T.), JSPS KAKENHI grant no. JP20H00354 (K.W. and T.T.) and the CREST (grant no. JPMJCR15F3) and JST (K.W. and T.T.); Fundació Privada Cellex (ICFO) and Fundació Mir-Puig (ICFO)

Political activism across the life course

The study of political activism has neglected people’s personal and social relationships to time. Age, life course and generation have become increasing important experiences for understanding political participation and political outcomes (e.g. Brexit), and current policies of austerity across the world are affecting people of all ages. At a time when social science is struggling to understand the rapid and unexpected changes to the current political landscape, the essay argues that the study of political activism can be enriched by engaging with the temporal dimensions of people’s everyday social experiences because it enables the discovery of political activism in mundane activities as well as in banal spaces. The authors suggest that a values-based approach that focuses on people’s relationships of concern would be a suitable way to surface contemporary political sites and experiences of activism across the life course and for different generations