Single-stranded RNA viruses co-assemble their capsid with the genome, and variations in capsid structures can have significant functional relevance. In particular, viruses need to respond to a dehydrating environment to prevent genomic degradation and remain active upon rehydration. Theoretical work has predicted low-energy buckling transitions in icosahedral capsids, which could protect the virus from further dehydration. However, there has been no direct experimental evidence, nor a molecular mechanism, for such behavior. Here, we observe this transition using X-ray single particle imaging of MS2 bacteriophages after aerosolization. Using a combination of machine learning tools, we classify hundreds of thousands of single-particle diffraction patterns to learn the structural landscape of the capsid morphology as a function of time spent in the aerosol phase. We found a previously unreported compact conformation as well as intermediate structures that suggest an incoherent buckling transition that does not preserve icosahedral symmetry. Finally, we propose a mechanism for this buckling, where a single 19-residue loop is destabilized, leading to the large observed morphological change. Our results provide experimental evidence for a mechanism by which viral capsids may protect themselves from dehydration upon aerosolization. In the process, these findings also demonstrate the power of single-particle X-ray imaging and machine learning methods in studying biomolecular structural dynamics.

Probing nanoscale transport in liquids under extreme thermodynamic conditions is essential for understanding soft matter and nanomaterials. However, accessing intrinsic microsecond dynamics of nanometre-sized objects remains challenging for synchrotron-based X-ray photon correlation spectroscopy (XPCS) because of limitations of coherent flux and detector repetition rates. Here, we investigate the diffusion of dilute polyethylene glycol (PEG)-coated gold nanoparticles dispersed in water over a wide temperature range, including water's supercooled regime using XPCS. The measured dynamics exhibit purely diffusive behaviour, with relaxation rates scaling as q2, and the extracted diffusion coefficients quantitatively follow the Stokes-Einstein relation with no slip boundary condition. Viscosity values derived from nanoparticle motion agree with established literature data, confirming that PEGylated nanoparticles act as reliable nanoscopic viscosity probes without evidence of ligand shell compression or structural changes. Using event-based XPCS with next-generation detectors, we access microsecond dynamics approaching the intrinsic Brownian timescale of nanometer-sized particles. These results establish PEGylated gold nanoparticles as robust probes of nanoscale transport and demonstrate the capability of advanced XPCS instrumentation to investigate fast dynamics in soft and nanoscale materials.

Dynamic properties of nanoparticles under high pressure are poorly understood due to experimental challenges. Here, we use X-ray photon correlation spectroscopy (XPCS) to investigate the diffusion dynamics of polyethylene glycol (PEG)-functionalized gold nanoparticles dispersed in water at pressures up to 6 kbar. Complementary small-angle X-ray scattering reveals no measurable pressure-induced changes in the gold core size, confirming structural stability across the studied pressure range. XPCS measurements show a systematic slowing down of nanoparticle dynamics with increasing pressure, with relaxation rates retaining the expected q2-dependence characteristic of Brownian motion. The extracted diffusion coefficients decrease continuously with pressure and align with predictions based on the pressure-dependent viscosity of water and the Stokes-Einstein relation, assuming a constant hydrodynamic particle size. Within experimental uncertainty, no additional contribution from pressure-induced ligand-shell modifications is observed in these dilute dispersions.

We report a facile centrifugation-based method for assembling polystyrene (PSSH)-functionalized gold nanoparticles (Au NPs) onto porous silicon (pSi) substrates in two distinct configurations: two- and three-dimensional (2D and 3D) assemblies. The 2D assemblies are densely packed monolayer coatings of the exposed Si-surfaces including the inner pore walls, whereas the 3D structures result from Au NPs clustering inside the pores. Remarkably, this shift from 2D to 3D architectures was achieved by minor modification of the PSSH coating thickness. Scanning electron microscopy (SEM) characterization confirmed the homogeneity and high packing density of these assemblies extending over several thousand square micrometers. This approach offers a straightforward and versatile route for the fabrication of well-ordered pSi-Au NP hybrid nanostructures with potential applications in catalysis, surface-enhanced spectroscopy and optical metamaterials.

Optical strategies for ion sensing hold promise for portable and in situ analysis, yet their reliability is frequently limited by pH-dependent interferences that alter metal-ligand interactions. Herein, we present a multiprobe surface-enhanced resonance Raman scattering (SERRS) platform that enables simultaneous quantification of Fe(II) and direct in situ pH readout in aqueous media. The sensor is constructed from polystyrene beads (PS) densely coated with silver nanoparticles and functionalized with two probes: phenanthroline (Phen), a metal-selective dye, hydrophobically entrapped within a cetrimonium bromide (CTAB) bilayer to retain its Fe(II) binding activity, and 4-mercaptobenzoic acid (MBA), covalently anchored to the silver surface to provide a reliable pH response. Resonant excitation at 532 nm maximizes SERRS sensitivity, yielding Fe(II) detection down to 30 ppb with strong selectivity against competing metal ions. Crucially, the MBA readout decouples pH effects from Fe(II) quantification, avoiding false results at alkaline pH where iron hydroxide precipitates dominate. This dual-sensing strategy provides a robust concept to overcome pH interference in optical ion sensing and paves the way for portable, time-resolved monitoring of metal ions in biological and environmental systems.

Nanoparticle (NP) self-assembly is a promising tool for the straightforward preparation of complex materials without lithography. Self-assembly on liquid subphases is established for the preparation of thin NP films with quasicrystalline order on large scales. Small-angle X-ray scattering (SAXS) at synchrotron radiation sources is in particular advantageous to study self-assembly in situ, providing detailed structural information with high temporal resolution. Here we present a new experimental setup that allows measuring SAXS in a vertical geometry. This way it is possible to study the self-assembly of nanoparticles on liquid subphases in situ as demonstrated with gold nanoparticles. In contrast to measurements with grazing incidence (GISAXS), spatial resolution in the µm range and sampling of the volume material is possible. Integration of optical microscopy allows observing the measurement position and formation of supercrystal flakes. The setup can be used to study self-assembly of various nanoparticles on liquid subphases but is not limited to such studies. It was realized at the beamline P10 at PETRA III (Deutsches Elektronen-Synchrotron DESY, Hamburg, Germany).

Increasing spills in the environment with plastic nanoparticles causes unwanted contamination. A proof-of-concept study is presented in which mammalian cells are loaded with enzymes capable of degrading capsules, here poly(ethylene terephthalate) (PET) hydrolase. Loading into cells via endocytosis is achieved by polymeric encapsulation, which upon integration of poly(ethylenimine) also provides suitable local working conditions for the enzymes. In this way, the enzymatic activity of the PET hydrolase is also maintained in the acidic environment of endosomes/lysosomes. It is demonstrated that PET nanoparticles endocytosed by cells can be degraded by cells upon exposure to encapsulated PET hydrolase enzymes. For this first, a colocalization analysis of endocytosed PET nanoparticles and encapsulated PET hydrolase is described, showing qualitatively that enzymes can encounter the plastics nanoparticles. Second, degradation of fluorescence-labeled plastics nanoparticles via enzymatic degradation is monitored in terms of loss of intracellular fluorescence over time. Limitations and potential future applications perspectives of this concept are discussed. A roadmap is presented on how this semiquantitative study could be extended into obtaining quantitative data and first applications.

In addition to enhanced fields and possible charge transfer, the concentration of photothermal energy at the nanoscale is a central feature of plasmon-driven photochemistry. It is well known that light energy can be efficiently concentrated in metal nanoparticles to length scales far below the wavelength of light. Here we demonstrate that the energy absorbed by a gold nanoparticle can be further localized within a bimetallic gold-paladium nanoparticle system by the dissipation of energy into the attached palladium satellite nanoparticles. After pulsed excitation of the gold core, the satellites collect nearly all photothermal energy and heat up by 180 K while the light-absorbing gold core remains much colder. By comparing transient absorption dynamics of a series of bimetallic nanoparticles with a three-temperature model, we can precisely assess the temperatures of the electronic and vibrational subsystems. We find a strong inverted temperature gradient that opposes the direction of energy input and concentrates the light energy at the active catalytic nanosite.

Amphiphilic copolymers can be effectively used to encapsulate a broad range of nanomaterials. Since the surface charge and charge distribution can strongly affect relevant effects like protein adsorption, effective routes are required to tune it. Herein, a straightforward strategy is presented to tune the formal charge of poly (isobutylene‐alt‐maleic anhydride), converting it into an amphiphilic polymer with negative charge, zwitterionic character, or positive charge. This is a route of surface modification in which impact on other colloidal parameters apart for surface charge is minimized. The encapsulation of quantum dots are tested with the resulting polymers and confirm their robust stabilization over a range of pH values and ionic strengths.

Gold nanoclusters of around 1.7 nm diameter were encapsulated in a matrix of the biodegradable polymer polyL-arginine (PLAG), leading to nanoparticles (NPs) of around 70 nm diameter. It was shown that in order to achieve the same amount of endocytosed Au after 24 h exposure of HeLa cells to the NPs, for the encapsulated nanoclusters around 3 times less Au needed to be added to the cells, minimizing the necessary exposure concentration. On the other hand, due to the degradability of the PLAG, the intracellular Au could be exocytosed by around 3.5 times faster than for non-degradable Au NPs of similar initial size. This study thus quantified the effect of size-variable NPs on endo- and exocytosis. Aggregation of small NPs to bigger NPs in biodegradable matrices allows for improved endocytosis. De-aggregation of endocytosed aggregated NPs upon degradation of the biodegradable matrix allows for improved exocytosis, which is an important prerequisite for NPs clearance from cells, avoiding long-term toxicity.

Silver-based metal organic frameworks (MOFs) have recently acquired considerable interest due to their potential applications in sensing and detection, bioimaging, and light-emitting devices. Incorporating specific linkers or functional groups into the MOF structure can tailor their fluorescence characteristics and thus can selectively respond to target analytes. Herein, we report the synthesis of novel luminescent silver-based MOFs (SOF1) derived from 2,3-dihydroxyterephthalic acid (2,3-DHBDC). The formation of SOF1 was established via Fourier transform infrared spectroscopy (FTIR), powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS) and elemental analysis. The synthesis conditions i.e. molar ratio of Ag+ to 2,3-DHBDC and temperature played a crucial role in the formation of clean SOF with no formation of silver nanoparticles (NPs). High-resolution transmission electron microscopy (HRTEM) revealed various shapes depending on the synthesis conditions. Mostly, octahedrons and hexagons were observed for SOFs obtained utilizing molar ratio of 1:1 and 1:2, respectively. Furthermore, the selected area electron diffraction (SAED) pattern revealed high crystallinity. The synthesized SOF1 showed a distinct and strong fluorescent signal that is much higher than that produced from SOF2 based on the isomeric ligand; 2,5-dihydroxyterephthalic acid (2,5DHBDC). The designed sensor was utilized for the sensitive detection of trifluralin (TRF) pesticide in river water samples. The achieved limit of detection of TRF was found to be 8 mu g/L. The fluorescence quenching was experimentally and mathematically confirmed to primarily occur through the mechanisms of inner-filter effect (IFE), static quenching (SQ) and photoinduced electron transfer (PET). Moreover, a thin film of SOF1 was synthesized for selective visualization of TRF.

Understanding the thermal properties of nanocrystal solids is important for their implementation. However, probing the intrinsic properties of monolayer to few‐layer supercrystals where non‐diffusive effects can emerge has remained elusive. Here, spatiotemporally resolved thermoreflectance microscopy and correlative atomic force microscopy are used to locally access lateral thermal transport in gold nanocrystal supercrystals with long polymer ligands from the monolayer up to eight layers. In contrast to the thermal size effect of typical thin film materials, it is demonstrated that above a few supercrystal layers the thermal diffusivity is nearly constant with increasing thickness. Notably, the mono‐to‐few layer range moreover experiences an inverted thickness dependence wherein the lateral thermal diffusivity increases when approaching the monolayer to a value 30–60% larger than the bulk. Simulations of quasi‐ballistic thermal transport successfully model the experimental trend, indicating the need to account for the phonon mean free path in the ligand matrix and the geometry of scattering interfaces. Phonons responsible for heat transport within the nanocrystalline composite have mean free paths shorter than the thickness of single supercrystal layers. This leads to behavior distinct from typical thickness‐dependent phonon–boundary scattering. These unusual behaviors present important considerations and opportunities for thermal management in applications of nanocrystal solids.

We demonstrate element-specific incoherent diffractive imaging (IDI) of single copper nanocubes using intensity correlations of Kα fluorescence at a hard X-ray free-electron laser. Combining single particle diffraction classification with IDI, we retrieve the form factor of 88 nm cubes with 20 nm resolution, extending IDI to the destructive single-particle regime with a large gain in resolution. IDI visibility drops sharply above a fluence of 10^2 J/cm^2, consistent with the assumption of amplified spontaneous emission. Our results reveal fundamental limits for high-fluence nanoimaging towards future single-particle X-ray imaging.

The structure and dynamics of concentrated silica-PNIPAm (poly-N-iso-prop-yl-acrylamide) nanogels are studied as a function of hydrostatic pressure up to 3500 bar. A combination of X-ray photon correlation spectroscopy and small-angle X-ray scattering shows similar characteristics of the dynamics for both temperature- and pressure-induced volume phase transitions of PNIPAm nanogels. Upon increasing the pressure and depending on the initial particle volume fraction, a transition from a liquid or glass state to a colloidal gel is observed for pressures p ≃ 1500 bar at a temperature of 293 K. Time-dependent analysis of the dynamics shows aging in glass and gel samples which is absent in the liquid state. This indicates stress-dominated dynamics upon pressure changes that equilibrate after a few hundred seconds.

Materials exposed to intense femtosecond X-ray pulses with energies above their K-shell absorption edge can enter an extremely ionized state, which could give rise to nonlinear phenomena, such as saturable absorption and reverse saturable absorption. In this work, we investigate these effects on single copper nanoparticles irradiated by an X-ray free-electron laser pulse. We study the properties of the Kα fluorescence for two different short pulse durations and three X-ray incident energies below and above the K-shell absorption edge, and correlate these with incident fluence estimates based on coherent diffraction. We observe that the incident fluence of the pulse and not its duration, is the main factor that modulates the non-linear response, which leads to an effective shortening of the fluorescence emission. Our findings have implications for fluorescence-based methods for imaging single particles using transiently coherent fluorescence, or diffractive imaging through transient resonances.

Thin‐film plasmonic supercrystals of pentagonal gold nanobipyramids (AuBP) exhibit a diverse range of packing structures that influence the near‐field distribution of the enhanced electric field and the far‐field response. By varying the molecular weight of the coating ligands, the softness of the anisotropic building blocks is changed. A thorough structural characterization reveals that this affects the resulting superstructures from self‐assembly more intricately than with isotropic building blocks. Softer coatings lead to smaller aligned domains in monolayers, while bilayers exhibit more crystalline domains with dominant interlayer twist angles near 0° and 90°. The far‐field distribution and near‐field response are measured using micro‐absorbance and electron energy loss spectroscopy (EELS). Correlating these data with high‐resolution transmission electron microscopy (HR‐TEM) structural analysis enabled the identification of the longitudinal and transverse individual and collective plasmonic modes. Notably, for large crystalline bilayer domains, a strong polarization‐dependent optical response is observed. These features underline the potential of these superstructures for applications in surface‐enhanced spectroscopies, plasmonic photocatalysis, and advanced optical manipulation in switchable optical metamaterials.

The penetration of nanoparticle (NP)-based drugs into tissue is essential for their use as nanomedicines. Systematic studies about how different NP properties, such as size, influence NP penetration are helpful for the development of NP-based drugs. An overview of how NPs of different sizes may penetrate three-dimensional cell spheroids is given. In particular different techniques for experimental analysis are compared, including mass spectrometry, flow cytometry, optical fluorescence microscopy, X-ray fluorescence microscopy, and transmission electron microscopy. An experimental data set is supplemented exclusively made for this review, in which the results of different techniques are visualized. Limitations of the analysis techniques for different types of NPs, including carbon-based materials, are discussed.