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Rapid and reliable characterization of heterogeneous nanoparticle suspensions is a key technology across the nanosciences. Although approaches exist for homogeneous samples, they are often unsuitable for polydisperse suspensions, as particles of different sizes and compositions can lead to indistinguishable signals at the detector. Here, we introduce holographic nanoparticle tracking analysis, holoNTA, as a straightforward methodology that decouples size and material refractive index contributions. HoloNTA is applicable to any heterogeneous nanoparticle sample and has the sensitivity to measure the intrinsic heterogeneity of the sample. Specifically, we combined high dynamic range k-space imaging with holographic 3D single-particle tracking. This strategy enables long-term tracking by extending the imaging volume and delivers precise and accurate estimates of both scattering amplitude and diffusion coefficient of individual nanoparticles, from which particle refractive index and hydrodynamic size are determined. We specifically demonstrate, by simulations and experiments, that irrespective of localization uncertainty and size, the sizing sensitivity is improved as our extended detection volume yields considerably longer particle trajectories than previously reported by comparable technologies. As validation, we measured both homogeneous and heterogeneous suspensions of nanoparticles in the 40–250 nm size range and further monitored protein corona formation, where we identified subtle differences between the nanoparticle–protein complexes derived from avidin, bovine serum albumin, and streptavidin. We foresee that our approach will find many applications of both fundamental and applied nature where routine quantification and sizing of nanoparticles are required., ACS Nano, 17 (1), ISSN:1936-0851, ISSN:1936-086X

The quantum ground state of a massive mechanical system is a stepping stone for investigating macroscopic quantum states and building high fidelity sensors. With the recent achievement of ground-state cooling of a single motional mode, levitated nanoparticles have entered the quantum domain. To overcome detrimental cross-coupling and decoherence effects, quantum control needs to be expanded to more system dimensions, but the effect of a decoupled dark mode has so far hindered cavity-based ground-state cooling of multiple mechanical modes. Here, we demonstrate two-dimensional ground-state cooling of an optically levitated nanoparticle. Utilizing coherent scattering into an optical cavity mode, we reduce the occupation numbers of two separate centre-of-mass modes to 0.83 and 0.81, respectively. By controlling the frequency separation and the cavity coupling strengths of the nanoparticle’s mechanical modes, we show the transition from 1D to 2D ground-state cooling. This 2D control lays the foundations for quantum-limited orbital angular momentum states for rotation sensing and, combined with ground-state cooling along the third motional axis shown previously, may allow full 3D ground-state cooling of a massive object., Nature Physics, ISSN:1745-2473, ISSN:1745-2481

Reconfigurable metasurfaces offer great promises to enhance photonics technology by combining integration with improved functionalities. Recently, reconfigurability in otherwise static metasurfaces has been achieved by modifying the electric permittivity of the meta-atoms themselves or their immediate surrounding. Yet, it remains challenging to achieve significant and fast tunability without increasing bulkiness. Here, we demonstrate an ultrathin tunable metalens whose focal distance can be changed through optomechanical control with moderate continuous wave intensities. We achieve fast focal length changes of more than 5% with response time of the order of 10 μs., Nano Letters, 23 (7), ISSN:1530-6984, ISSN:1530-6992

In plasmonic photothermal therapy (PPTT), illuminated gold nanoparticles are locally heated to produce selective damage in cells. While PPTT is expected to strongly depend on the cell line, available data are sparse and critical parameters remain unclear. To elucidate this pivotal aspect, we present a systematic study of diseased and nondiseased cells from different tissues to evaluate cytotoxicity, uptake of gold nanorods (AuNRs), and viability after PPTT. We identified differences in uptake and toxicity between cell types, linking AuNR concentrations to toxicity. Furthermore, the cell death mechanism is shown to depend on the intensity of the irradiated light and hence the temperature increase. Importantly, the data also underline the need to monitor cell death at different time points. Our work contributes to the definition of systematic protocols with appropriate controls to fully comprehend the effects of PPTT and build meaningful and reproducible data sets, key to translate PPTT to clinical settings., ACS Nanoscience Au, 2 (6), ISSN:2694-2496

A single levitated nanoparticle is used as a nano-reactor for studying surface chemistry at the nanoscale. Optical levitation under controlled pressure, surrounding gas composition, and humidity provides extreme control over the nanoparticle, including dynamics, charge, and surface chemistry. Using a single nanoparticle avoids ensemble averages and allows to study how the presence of silanol groups at its surface affects the adsorption and desorption of water from the background gas with unprecedented real time, spatial, and temporal resolution. Here, we demonstrate the unique potential of this versatile platform by studying the Zhuravlev model in silica particles. In contrast to standard methods, our system allowed the first observation of an abrupt and irreversible change in scattering cross section, mass, and mechanical eigenfrequency during the dehydroxylation process, indicating changes in density, refractive index and volume.

Optical tweezers are tools made of light that enable contactless pushing, trapping, and manipulation of objects ranging from atoms to space light sails. Since the pioneering work by Arthur Ashkin in the 1970s, optical tweezers have evolved into sophisticated instruments and have been employed in a broad range of applications in life sciences, physics, and engineering. These include accurate force and torque measurement at the femtonewton level, microrheology of complex fluids, single micro- and nanoparticle spectroscopy, single-cell analysis, and statistical-physics experiments. This roadmap provides insights into current investigations involving optical forces and optical tweezers from their theoretical foundations to designs and setups. It also offers perspectives for applications to a wide range of research fields, from biophysics to space exploration., Comment: 181 pages, 61 figures