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Ultra-intense, ultra-fast X-ray free-electron lasers (XFELs) enable the imaging of single protein molecules under ambient temperature and pressure. A crucial aspect of structure reconstruction involves determining the relative orientations of each diffraction pattern and recovering the missing phase information. In this paper, we introduce a predicted model-aided algorithm for orientation determination and phase retrieval, which has been tested on various simulated datasets and has shown significant improvements in the success rate, accuracy and efficiency of XFEL data reconstruction.

Oxygenated organic molecules (OOMs) play an important role in the formation of secondary organic aerosols (SOAs), but the mixing states of OOMs are still unclear. This study investigates the mixing states of OOM-containing single particles from the measurements taken using a single particle aerosol mass spectrometer in Guangzhou, China in 2022. Generally, the particle counts of OOM particles and the mass concentration of secondary organic carbon (SOC) exhibited similar temporal trends throughout the entire year. The OOM particles were consistently enriched in secondary ions, including 16O−, 26CN−, 46NO2−, 62NO3−, and 97HSO4−. In contrast, the number fractions and diurnal patterns of OOM particles among the total detected particles showed similar distributions in August and October; however, the SOC ratios in fine particulate matter were quite different, suggesting that there were different mixing states of single-particle oxygenated organics. In addition, further classification results indicated that the OOM particles were more aged in October than August, even though the SOC ratios were higher in August. Furthermore, the distribution of hydrocarbon fragments exhibited a notable decrease from January to October, emphasizing the more aged state of the organics in October. In addition, the sharp increase in elemental carbon (EC)-OOM particles in the afternoon in October suggests the potential role of EC in the aging process of organics. Overall, in contrast to the bulk analysis of SOC mass concentration, the mixing states of the OOM particles provide insights into the formation process of SOAs in field studies. [ABSTRACT FROM AUTHOR]

• ON particles increased as NO x enhancement at night. • ON particles were mainly produced via heterogeneous reactions between NO x and organics. • The decrease of ON particles was associated with photo-bleaching effect. Organic nitrogen (ON) compounds play a significant role in the light absorption of brown carbon and the formation of organic aerosols, however, the mixing state, secondary formation processes, and influencing factors of ON compounds are still unclear. This paper reports on the mixing state of ON-containing particles based on measurements obtained using a high-performance single particle aerosol mass spectrometer in January 2020 in Guangzhou. The ON-containing particles accounted for 21% of the total detected single particles, and the particle count and number fraction of the ON-containing particles were two times higher at night than during the day. The prominent increase in the content of ON-containing particles with the enhancement of NO x mainly occurred at night, and accompanied by high relative humidity and nitrate, which were associated with heterogeneous reactions between organics and gaseous NO x and/or NO 3 radical. The synchronous decreases in ON-containing particles and the mass absorption coefficient of water-soluble extracts at 365 nm in the afternoon may be associated with photo-bleaching of the ON species in the particles. In addition, the positive matrix factorization analysis found five factors dominated the formation processes of ON particles, and the nitrate factor (33%) mainly contributed to the production of ON particles at night. The results of this study provide unique insights into the mixing states and secondary formation processes of the ON-containing particles. [Display omitted] [ABSTRACT FROM AUTHOR]

X-ray free-electron lasers (XFELs) can probe chemical and biological reactions as they unfold with unprecedented spatial and temporal resolution. A principal challenge in this pursuit involves the delivery of samples to the X-ray interaction point in such a way that produces data of the highest possible quality and with maximal efficiency. This is hampered by intrinsic constraints posed by the light source and operation within a beamline environment. For liquid samples, the solution typically involves some form of high-speed liquid jet, capable of keeping up with the rate of X-ray pulses. However, conventional jets are not ideal because of radiation-induced explosions of the jet, as well as their cylindrical geometry combined with the X-ray pointing instability of many beamlines which causes the interaction volume to differ for every pulse. This complicates data analysis and contributes to measurement errors. An alternative geometry is a liquid sheet jet which, with its constant thickness over large areas, eliminates the problems related to X-ray pointing. Since liquid sheets can be made very thin, the radiation-induced explosion is reduced, boosting their stability. These are especially attractive for experiments which benefit from small interaction volumes such as fluctuation X-ray scattering and several types of spectroscopy. Although their use has increased for soft X-ray applications in recent years, there has not yet been wide-scale adoption at XFELs. Here, gas-accelerated liquid sheet jet sample injection is demonstrated at the European XFEL SPB/SFX nano focus beamline. Its performance relative to a conventional liquid jet is evaluated and superior performance across several key factors has been found. This includes a thickness profile ranging from hundreds of nanometres to 60 nm, a fourfold increase in background stability and favorable radiation-induced explosion dynamics at high repetition rates up to 1.13 MHz. Its minute thickness also suggests that ultrafast single-particle solution scattering is a possibility.

Semi-quantum secret sharing is an important research issue in quantum cryptography. In this paper, we propose a (t, n) threshold semi-quantum secret sharing protocol, which combines the practicality of semi-quantum secret sharing protocols and the flexibility of (t, n) threshold quantum secret sharing protocols. Participants prepare and transmit single particles in a circular way, and then any t out of n participants can recover the secret according to Shamir’s secret sharing scheme. As quantum resources, single particles are easy to prepare. Furthermore, classical participants only need to possess the capability to prepare and insert particles. The security analysis shows our protocol has security against most attacks. Except decoy particles, all particles are useful to carry the secret message, so the efficiency of the proposed protocol can achieve 100%.

One of the outstanding analytical problems in X-ray single-particle imaging (SPI) is the classification of structural heterogeneity, which is especially difficult given the low signal-to-noise ratios of individual patterns and the fact that even identical objects can yield patterns that vary greatly when orientation is taken into consideration. Proposed here are two methods which explicitly account for this orientation-induced variation and can robustly determine the structural landscape of a sample ensemble. The first, termed common-line principal component analysis (PCA), provides a rough classification which is essentially parameter free and can be run automatically on any SPI dataset. The second method, utilizing variation auto-encoders (VAEs), can generate 3D structures of the objects at any point in the structural landscape. Both these methods are implemented in combination with the noise-tolerant expand–maximize–compress (EMC) algorithm and its utility is demonstrated by applying it to an experimental dataset from gold nanoparticles with only a few thousand photons per pattern. Both discrete structural classes and continuous deformations are recovered. These developments diverge from previous approaches of extracting reproducible subsets of patterns from a dataset and open up the possibility of moving beyond the study of homogeneous sample sets to addressing open questions on topics such as nanocrystal growth and dynamics, as well as phase transitions which have not been externally triggered.

Serial diffraction data collected at the Linac Coherent Light Source from crystalline amyloid fibrils delivered in a liquid jet show that the fibrils are well oriented in the jet. At low fibril concentrations, diffraction patterns are recorded from single fibrils; these patterns are weak and contain only a few reflections. Methods are developed for determining the orientation of patterns in reciprocal space and merging them in three dimensions. This allows the individual structure amplitudes to be calculated, thus overcoming the limitations of orientation and cylindrical averaging in conventional fibre diffraction analysis. The advantages of this technique should allow structural studies of fibrous systems in biology that are inaccessible using existing techniques.

Single‐particle imaging with X‐ray free‐electron lasers depends crucially on algorithms that merge large numbers of weak diffraction patterns despite missing measurements of parameters such as particle orientations. The expand–maximize–compress (EMC) algorithm is highly effective at merging single‐particle diffraction patterns with missing orientation values, but most implementations exhaustively sample the space of missing parameters and may become computationally prohibitive as the number of degrees of freedom extends beyond orientation angles. This paper describes how the EMC algorithm can be modified to employ Metropolis Monte Carlo sampling rather than grid sampling, which may be favorable for reconstruction problems with more than three missing parameters. Using simulated data, this variant is compared with the standard EMC algorithm. [ABSTRACT FROM AUTHOR]

High efficiency and good security are two crucial factors to evaluate multiparty quantum key agreement (MQKA) protocols. An efficient MQKA protocol is put forward and characterized by block and complete-graph travelling mode. It employs combined strategies of mutually unbiased bases, asynchronous actions, delay-wait, random sorting and comparison. The detailed analysis shows that it can well defend outside attacks and participant attacks. In contrast to typical existing MQKA protocols, its overall performance about security and efficiency is preferable. Moreover, it is feasibly implemented by current technologies as its information carriers are single particles. [ABSTRACT FROM AUTHOR]

Free‐electron lasers could enable X‐ray imaging of single biological macromolecules and the study of protein dynamics, paving the way for a powerful new imaging tool in structural biology, but a low signal‐to‐noise ratio and missing regions in the detectors, colloquially termed 'masks', affect data collection and hamper real‐time evaluation of experimental data. In this article, the challenges posed by noise and masks are tackled by introducing a neural network pipeline that aims to restore diffraction intensities. For training and testing of the model, a data set of diffraction patterns was simulated from 10 900 different proteins with molecular weights within the range of 10–100 kDa and collected at a photon energy of 8 keV. The method is compared with a simple low‐pass filtering algorithm based on autocorrelation constraints. The results show an improvement in the mean‐squared error of roughly two orders of magnitude in the presence of masks compared with the noisy data. The algorithm was also tested at increasing mask width, leading to the conclusion that demasking can achieve good results when the mask is smaller than half of the central speckle of the pattern. The results highlight the competitiveness of this model for data processing and the feasibility of restoring diffraction intensities from unknown structures in real time using deep learning methods. Finally, an example is shown of this preprocessing making orientation recovery more reliable, especially for data sets containing very few patterns, using the expansion–maximization–compression algorithm. [ABSTRACT FROM AUTHOR]

Single‐particle X‐ray diffractive imaging (SPI) of small (bio‐)nanoparticles (NPs) requires optimized injectors to collect sufficient diffraction patterns to allow for the reconstruction of the NP structure with high resolution. Typically, aerodynamic lens‐stack injectors are used for NP injection. However, current injectors were developed for larger NPs (>100 nm), and their ability to generate high‐density NP beams suffers with decreasing NP size. Here, an aerodynamic lens‐stack injector with variable geometry and a geometry‐optimization procedure are presented. The optimization for 50 nm gold‐NP (AuNP) injection using a numerical‐simulation infrastructure capable of calculating the carrier‐gas flow and the particle trajectories through the injector is also introduced. The simulations were experimentally validated using spherical AuNPs and sucrose NPs. In addition, the optimized injector was compared with the standard‐installation 'Uppsala injector' for AuNPs. Results for these heavy particles showed a shift in the particle‐beam focus position rather than a change in beam size, which results in a lower gas background for the optimized injector. Optimized aerodynamic lens‐stack injectors will allow one to increase NP beam density, reduce the gas background, discover the limits of current injectors and contribute to structure determination of small NPs using SPI. [ABSTRACT FROM AUTHOR]

In quantum key agreement (QKA), a shared key is established among two or more parties where each participant equally contributes its part to the shared key, and none of the participants can determine the shared key alone. Zhou et al. (Electron Lett 40(18):1149, 2004) gave the first QKA protocol based on quantum teleportation and since then quite a few variants and extensions have been proposed. However, none of the existing protocols are device-independent, i.e., all of them assume implicitly that the single-photon states or entangled states supplied to the participants are of certain form. In this work, we exploit the idea of the device-independent dimension witness for independent preparation and measurement devices proposed by Tavakoli (Phys Rev Lett 125:15050, 2020) and connect it with the QKA protocol (Chong and Hwang in Opt Commun 283:1192–1195, 2010) to present the concept of semi-device-independent QKA protocol for the first time. [ABSTRACT FROM AUTHOR]

Incoherent diffractive imaging (IDI) promises structural analysis with atomic resolution based on intensity interferometry of pulsed X‐ray fluorescence emission. However, its experimental realization is still pending and a comprehensive theory of contrast formation has not been established to date. Explicit expressions are derived for the equal‐pulse two‐point intensity correlations, as the principal measured quantity of IDI, with full control of the prefactors, based on a simple model of stochastic fluorescence emission. The model considers the photon detection statistics, the finite temporal coherence of the individual emissions, as well as the geometry of the scattering volume. The implications are interpreted in view of the most relevant quantities, including the fluorescence lifetime, the excitation pulse, as well as the extent of the scattering volume and pixel size. Importantly, the spatiotemporal overlap between any two emissions in the sample can be identified as a crucial factor limiting the contrast and its dependency on the sample size can be derived. The paper gives rigorous estimates for the optimum sample size, the maximum photon yield and the expected signal‐to‐noise ratio under optimal conditions. Based on these estimates, the feasibility of IDI experiments for plausible experimental parameters is discussed. It is shown in particular that the mean number of photons per detector pixel which can be achieved with X‐ray fluorescence is severely limited and as a consequence imposes restrictive constraints on possible applications. [ABSTRACT FROM AUTHOR]

With the emergence of X-ray free-electron lasers, it is possible to investigate the structure of nanoscale samples by employing coherent diffractive imaging in the X-ray spectral regime. In this work, we developed a refinement method for structure reconstruction applicable to low-quality coherent diffraction data. The method is based on the gradient search method and considers the missing region of a diffraction pattern and the small number of detected photons. We introduced an initial estimate of the structure in the method to improve the convergence. The present method is applied to an experimental diffraction pattern of an Xe cluster obtained in an X-ray scattering experiment at the SPring-8 Angstrom Compact free-electron LAser (SACLA) facility. It is found that the electron density is successfully reconstructed from the diffraction pattern with a large missing region, with a good initial estimate of the structure. The diffraction pattern calculated from the reconstructed electron density reproduced the observed diffraction pattern well, including the characteristic intensity modulation in each ring. Our refinement method enables structure reconstruction from diffraction patterns under difficulties such as missing areas and low diffraction intensity, and it is potentially applicable to the structure determination of samples that have low scattering power.

The routine atomic resolution structure determination of single particles is expected to have profound implications for probing structure–function relationships in systems ranging from energy-storage materials to biological molecules. Extremely bright ultrashort-pulse X-ray sources – X-ray free-electron lasers (XFELs) – provide X-rays that can be used to probe ensembles of nearly identical nanoscale particles. When combined with coherent diffractive imaging, these objects can be imaged; however, as the resolution of the images approaches the atomic scale, the measured data are increasingly difficult to obtain and, during an X-ray pulse, the number of photons incident on the 2D detector is much smaller than the number of pixels. This latter concern, the signal `sparsity', materially impedes the application of the method. An experimental analog using a conventional X-ray source is demonstrated and yields signal levels comparable with those expected from single biomolecules illuminated by focused XFEL pulses. The analog experiment provides an invaluable cross check on the fidelity of the reconstructed data that is not available during XFEL experiments. Using these experimental data, it is established that a sparsity of order 1.3 × 10−3 photons per pixel per frame can be overcome, lending vital insight to the solution of the atomic resolution XFEL single-particle imaging problem by experimentally demonstrating 3D coherent diffractive imaging from photon-sparse random projections.

An error in Fig. 3(c) of the article by Assalauova et al. [IUCrJ (2020), 7, 1102–1113] is corrected.

The Sichuan Basin has experienced serious air pollution from fine particulate matter (PM 2.5) in the past few years with biomass burning has been identified as a major source of PM 2.5 in this region. We used single particle aerosol mass spectrometer to investigate the characteristics of biomass burning particles in three interacting cities representing different types of urban environment in the Sichuan Basin. A total of 739,794, 279,610, and 380,636 biomass burning particles were detected at Ya'an, Guang'an, and Chengdu, which represented 42%, 69%, and 61%, respectively, of the total number of particles. We analyzed the chemical composition, transportation, and evolution of biomass burning particles. The contribution of K-elemental carbon and K-secondary inorganic particles was highest in Ya'an (36%) and Guang'an (47%), respectively, reflecting the important role of fresh biomass burning particles and long-distance transport in these two cities. Air masses originating from different directions corresponded to different levels of PM 2.5 and the contributions of polluted clusters increased significantly on polluted days. Fresh and secondary inorganic biomass burning particles increased pollution at Ya'an and Guang'an, respectively, but dominated different stages of pollution in Chengdu. K-nitrate particles were formed by photochemical reactions, whereas K-sulfate particles were formed by both photochemical and liquid-phase reactions. Investigation of the degree of particle aging showed that there were more fresh particles at Ya'an and more aged particles at Guang'an. These results are useful in helping our understanding of the characteristics of biomass burning particles and evaluating their role in PM 2.5 pollution in the Sichuan Basin. Image 1 [ABSTRACT FROM AUTHOR]

To understand the characteristics of haze in Chengdu—one of the cities in China typically suffering from this form of pollution—the chemical composition, sources, morphology, and evolution of fine particulate matter (PM 2.5) were analyzed in the most polluted winter by filter sampling and transmission electron microscopy with energy-dispersive X-ray spectroscopy. It was found that the average mass concentration of PM 2.5 during the whole observation period was 97.5 ± 40.4 μg m−3, and the contributions of major PM 2.5 components were: OM (31.7 %), NO 3 − (19.3 %), NH 4 + (11.1 %), and SO 4 2− (7.9 %). All single particles were divided into five types: OM, S-rich, mineral, soot, and fly ash/metal particles, most of which existed in the form of internally mixed. PM 2.5 sources included combustion (16.9 %), secondary aerosols (44.1 %), traffic emissions (33.2 %), and dust (5.8 %). Based on the PM 2.5 chemical composition, single particle analysis, and source apportionment results, we were able to conclude that traffic emissions and secondary aerosols jointly led to the evolution from non-polluted to moderately polluted days, while the evolution from moderately to heavily polluted days was mainly dominated by secondary aerosols. The internal mixing of particles increased significantly during the evolution from non-polluted to polluted days. The air masses originated from eastern Sichuan corresponded to the lowest pollution level and the highest contribution of carbonaceous components, while the air masses originated from the west corresponded to the highest pollution level and contribution of secondary inorganic species. Long-distance transmission was closely related to the evolution of pollution in Chengdu. [Display omitted] • Integrating filter sampling and TEM-EDS methods to study air pollution in Chengdu. • Secondary aerosols and traffic emissions caused the aggravation of pollution. • Enhanced internal mixing of particulate matter during the aggravation of pollution. • Regional transmission was closely related to the pollution characteristics of Chengdu. [ABSTRACT FROM AUTHOR]

Serial diffraction data collected at the Linac Coherent Light Source from crystalline amyloid fibrils delivered in a liquid jet show that the fibrils are well oriented in the jet. At low fibril concentrations, diffraction patterns are recorded from single fibrils; these patterns are weak and contain only a few reflections. Methods are developed for determining the orientation of patterns in reciprocal space and merging them in three dimensions. This allows the individual structure amplitudes to be calculated, thus overcoming the limitations of orientation and cylindrical averaging in conventional fibre diffraction analysis. The advantages of this technique should allow structural studies of fibrous systems in biology that are inaccessible using existing techniques.

Multi-elemental analysis of particulate matters is highly desirable for the identification of their emission sources. However, the traditional techniques for single particle analysis usually require time-consuming sample preparation procedures. We report here a system that combines bright-field microscopy with laser induced breakdown spectroscopy (LIBS), allowing rapid and multi-elemental analysis of single particles. The improved throughput of the system was benefited from the use of ultra-thin polyethylene films for particle immobilization such that their spectra were collected successively. The simple composition of the films avoided their interferences in the particles' LIBS spectra. Moreover, the small thickness of the films allowed their rapid vaporization during laser ablation such that the plasma emissions from the particles were not quenched by their substrates. The performances of the system were demonstrated by studying the heterogeneity in particles' compositions and discriminating dust particles with very similar chemicals, suggesting that it is a promising tool for environmental risk assessment. Image 1 • Use of films for particle immobilization mitigated shockwave effects. • Simple composition of polyethylene film avoided substrate interferences. • Small thickness of the film prevented the quenching of LIBS signals by the film. • Multivariate analysis was used to discriminate particles with very close constituents. • Particle mixtures with various ratios can be well predicted by their spectra. [ABSTRACT FROM AUTHOR]

This paper reports on improved techniques to create and characterize nanometre‐sized droplets from dilute aqueous solutions by using a gas dynamic virtual nozzle (GDVN). It describes a method to measure the size distribution of uncharged droplets, using an environmental scanning electron microscope, and provides theoretical models for the droplet sizes created. The results show that droplet sizes can be tuned by adjusting the gas and liquid flow rates in the GDVN, and at the lowest liquid flow rates, the size of the water droplets peaks at about 120 nm. This droplet size is similar to droplet sizes produced by electrospray ionization but requires neither electrolytes nor charging of the solution. The results presented here identify a new operational regime for GDVNs and show that predictable droplet sizes, comparable to those obtained by electrospray ionization, can be produced by purely mechanical means in GDVNs. [ABSTRACT FROM AUTHOR]

Chengdu, the capital city of Sichuan Province, is one of the most polluted cities in China. We used single-particle aerosol mass spectrometer to monitor particulate matter pollution in an urban area of Chengdu from December 9, 2015 to January 4, 2016 to determine the characteristics of air pollution during the winter months. The mass concentrations of particulate matter were high during the whole observation period, with mean values for PM2.5 and PM10 of 101 ± 60 and 162 ± 99 μg m−3, respectively. The particles were clustered into nine distinct particle types: dust (3%), potassium-elemental carbon (KEC) (24%), organic carbon (OC) (12%), combined OC and EC (OCEC) (6%), K-organic nitrogen (KCN) (10%), K-nitrate (KNO3) (12%), K-sulfate (KSO4) (18%), K-sulfate and nitrate (KSN) (12%), and metal (3%) particles. Analysis on different types of day showed that: (1) from "excellent" (days with PM2.5 lower than 35 μg m−3) to "light pollution" (PM2.5 between 75 and 115 μg m−3) days, local/regional combustion was the major contributor, whereas the aggravation of pollution from light pollution to "heavy pollution" (PM2.5 higher than 150 μg m−3) days was mainly determined by the combined effect of local/regional combustion and long-distance transport; (2) as the air quality deteriorated, the mixing of sulfate and nitrate in particles increased sharply, especially sulfate; and (3) the relative aerosols acidity increased from excellent to light pollution days, while decreased significantly from light pollution to heavy pollution days. Backward trajectory analysis showed that there were significant differences in PM2.5 concentrations and particle compositions between clusters of trajectories, which affected the level and evolution of PM2.5 pollution in Chengdu. These results give a deeper understanding of PM2.5 pollution in Chengdu and the Sichuan Basin. [ABSTRACT FROM AUTHOR]

Abstract To investigate the formation of haze during the cold season, continuous ambient air measurements were taken at an urban site in Zhengzhou from October 10, 2016 through December 31, 2016 using a single particle aerosol mass spectrometer. In total, 4,099,800 particles were analyzed and classified into eight major particle types: elemental carbon (EC, 36.7%), organic carbon (OC, 30.0%), ECOC (8.6%), K-rich (13.0%), levoglucosan (1.2%), metal (2.2%), NH 4 -K (2.1%), and dust (6.2%). By combining these measurements with correlation analysis and wind data, particle sources were determined to be vehicles, industrial emissions, coal combustion, biomass burning, secondary aerosols, agriculture, and dust. Additionally, analysis of mixing states indicated that particles underwent substantial aging and secondary OC particles were dominant OC species. Temporal profiles of meteorological parameters, mixing states, and particle types during a typical haze episode revealed that EC and OC particles were dominant components during haze formation, and a northeastern transport route (Anyang-Zhengzhou and Puyang-Xuchang) for OC particles was identified by potential source contribution function and concentration weighted trajectory analysis. Relatively higher humidity and lower temperature favored the formation of secondary inorganic aerosol. Wind direction and speed determined the transport, formation, and elimination of stagnant weather conditions. In sum, heavy haze during the cold season in Zhengzhou was observed due to extensive aerosol aging under adverse weather conditions (i.e., northeastern wind direction, wind speed <2 m s−1, temperature < 10 °C, relative humidity >60%, temperature inversion, and uniform pressure field). Graphical abstract Unlabelled Image Highlights • Studying chemical compositions of individual particles in Zhengzhou; • Identifying possible sources based on three month data of single particles; • Investigating mixing state of particles; • Observing the effects of particle types and meteorological conditions on haze. [ABSTRACT FROM AUTHOR]

Luminescent properties of Er3+- and Yb3+- co-doped CaF2 upconversion nanoparticles (UCNPs) were investigated in single particle and densely-packed states with a custom-built microscope. The single UCNPs exhibit linear dependency of luminescent intensity on excitation power while the densely-packed UCNPs exhibit a 2-order power law-dependency indicating a two-photon absorption process. Time-domain luminescence intensity measurements were performed and the curves were fitted to excitation∖emission rate functions based on a simplified three-state model. The results indicate that the intermediates in single particles are much less and saturated in a short time, and there are strong couplings of the ground states and intermediate states between neighboring UCNPs in densely packed UCNPs.

Luminescent properties of Er 3 + - and Yb 3 + - co-doped CaF2 upconversion nanoparticles (UCNPs) were investigated in single particle and densely-packed states with a custom-built microscope. The single UCNPs exhibit linear dependency of luminescent intensity on excitation power while the densely-packed UCNPs exhibit a 2-order power law-dependency indicating a two-photon absorption process. Time-domain luminescence intensity measurements were performed and the curves were fitted to excitation ∖ emission rate functions based on a simplified three-state model. The results indicate that the intermediates in single particles are much less and saturated in a short time, and there are strong couplings of the ground states and intermediate states between neighboring UCNPs in densely packed UCNPs. [ABSTRACT FROM AUTHOR]

Optical excitation of nanostructures is known to induce local heating, a phenomenon that has been intensely exploited for drug release, gene delivery, cancer thermotherapy, and energy harvesting. However, the effect is typically small requiring collective heating of a large concentration or aggregates of particles. Herein, we show that optical excitation of individual semiconducting single-walled carbon nanotubes triggers strongly localized heating adequate to melt non-covalently attached double-stranded oligonucleotides in solution. In contrast to conventional thermal dehybridization, this optically triggered DNA melting occurs at a solution temperature that is 22 °C lower than the DNA melting temperature. This unexpectedly large localized optical heating effect provides important new insights to design selective optical nanoheaters at the single particle level. [ABSTRACT FROM AUTHOR]

Chengdu, the capital of Sichuan Province and the main city in Sichuan basin, is one of the heavily polluted cities in China. The characteristics of single particles in the atmosphere over Chengdu are critical for the in-depth understanding of their sources, formation mechanisms, and effects. In this study, a continuous ambient aerosol measurement was performed in summer in Chengdu with a single particle aerosol mass spectrometer (SPAMS) and other monitoring instruments. The particulate matter (PM) mass concentrations were low during our study period: PM 2.5 and PM 10 (aerosol particles with an aerodynamic diameter of less than 2.5 or 10 μm) were 40.5 ± 23.6 μg m −3 and 67.0 ± 38.1 μg m −3 , respectively. This was mainly caused by the favorable meteorological conditions during the summer season. Twelve particle types were identified and classified as dust particles (Dust), four types of carbonaceous particles, organic nitrogen and potassium containing particles (KCN), four types of secondary particles, Na-K-containing particles (NaK), and metal-containing particles (Metal). The highest contribution of particles was from potassium with elemental carbon (KEC; 23.0%), and the lowest from elemental carbon (EC; 0.2%). All types of particles showed different diurnal variations and size distributions, which were closely related to their sources and reactions in the atmosphere. The eastern and southern air masses corresponded with high PM 2.5 mass concentrations. The contributions of KEC and K-sulfate (KSO 4 ) particles to PM 2.5 were clearly higher than those in air masses from the southeast. During polluted days, the contributions of KEC and KSO 4 particles increased, while the contributions of organic carbon (OC), combined OC and EC particles (OCEC), and K-nitrate (KNO 3 ) particles decreased. This shows the importance of biomass burning and industrial emissions for the PM 2.5 pollution in Chengdu. These results will be useful for the in-depth understanding of the PM 2.5 pollution in Chengdu, even in Sichuan basin. [ABSTRACT FROM AUTHOR]

A new efficient quantum key agreement protocol without entanglement is proposed. In this protocol, each user encodes his secret key into the traveling particles by performing one of four rotation operations that one cannot perfectly distinguish. In the end, all users can simultaneously obtain the final shared key. The security of the presented protocol against some common attacks is discussed. It is shown that this protocol can effectively protect the privacy of each user and satisfy the requirement of fairness in theory. Moreover, the quantum carriers and the encoding operations used in the protocol can be achieved in realistic physical devices. Therefore, the presented protocol is feasible with current technology. [ABSTRACT FROM AUTHOR]

The formation of a protein corona, where proteins spontaneously adhere to the surface of nanomaterials in biological environments, leads to changes in their physicochemical properties and subsequently affects their intended biomedical functionalities. Most current methods to study protein corona formation are ensemble-averaging and either require fluorescent labeling, washing steps, or are only applicable to specific types of particles. Here we introduce real-time all-optical nanoparticle analysis by scattering microscopy (RONAS) to track the formation of protein corona in full serum, at the single-particle level, without any labeling. RONAS uses optical scattering microscopy and enables real-time and in situ tracking of protein adsorption on metallic and dielectric nanoparticles with different geometries directly in blood serum. We analyzed the adsorbed protein mass, the affinity, and the kinetics of the protein adsorption at the single particle level. While there is a high degree of heterogeneity from particle to particle, the predominant factor in protein adsorption is surface chemistry rather than the underlying nanoparticle material or size. RONAS offers an in-depth understanding of the mechanisms related to protein coronas and, thus, enables the development of strategies to engineer efficient bionanomaterials.

Serpentine and amphibole asbestos occur naturally in certain geologic settings worldwide, most commonly in association with ultramafic rocks, along associated faults. Ultramafic rocks have been used in Piên County, Southern Brazil for decades for the purpose of road paving in rural and urban areas, but without the awareness of their adverse environmental and health impact. The aim of this study was the chemical characterization of aerosols re-suspended in two rural roads of Piên, paved with ultramafic rocks and to estimate the pulmonary deposition of asbestos aerosols. Bulk aerosol samples were analyzed by means of X-ray fluorescence spectrometry and X-ray diffraction analysis, in order to characterize elemental composition and crystallinity. Single-particle compositions of aerosols were analyzed by computer-controlled electron-probe microanalysis, indicating the presence of a few percentages of serpentine and amphibole. Given the chemical composition and size distribution of aerosol particles, the deposition efficiency of chrysotile, a sub-group of serpentine, in two principal segments of the human respiratory system was estimated using a lung deposition model. As an important finding, almost half of the inhaled particles were calculated to be deposited in the respiratory system. Asbestos depositions were significant (∼25 %) in the lower airways, even though the selected breathing conditions (rest situation, nose breathing) implied the lowest rate of respiratory deposition. Considering the fraction of inhalable suspended chrysotile near local roads, and the long-term exposure of humans to these aerosols, chrysotile may represent a hazard, regarding more frequent development of lung cancer in the population of the exposed region. [ABSTRACT FROM AUTHOR]

Brake dust particles were characterised using an Aerosol Time-of-Flight Mass Spectrometer (ATOFMS) operated using two inlet configurations, namely the aerodynamic lens (AFL) inlet and countersunk nozzle inlet. Laboratory studies show that dust particles are characterised by mass spectra containing ions deriving from Fe and Ba and although highly correlated to each other, the Fe and Ba signals were mostly detected using the nozzle inlet with relatively high laser desorption energies. When using the AFL, only [ 56 Fe] and [ −88 FeO 2 ] ions were observed in brake dust spectra generated using lower laser desorption pulse energies, and only above 0.75 mJ was the [ 138 Ba] ion detected. When used with the preferred nozzle inlet configuration, the [ −88 FeO 2 ] peak was considered to be the more reliable tracer peak, because it is not present in other types of dust (mineral, tyre, Saharan etc). As shown by the comparison with ambient data from a number of locations, the aerodynamic lens is not as efficient in detecting brake wear particles, with less than 1% of sampled particles attributed to brake wear. Five field campaigns within Birmingham (background, roadside (3) and road tunnel) used the nozzle inlet and showed that dust particles (crustal and road) accounted for between 3.1 and 65.9% of the particles detected, with the remaining particles being made up from varying percentages of other constituents. [ABSTRACT FROM AUTHOR]

We have developed a novel system for real-time measurement of the mixing state of aerosol particles using a tandem combination of laser-induced fluorescence (LIF) and incandescence (LII) techniques. The tandem analysis system comprises two chambers connected in series; particles are analyzed with LIF in the first chamber and LII in the second chamber. We analyzed identical particles using the two methods as judged by the time intervals of detection in the two chambers. This system provides information on the mixing state of fluorescent compounds and black carbon in single particles. Ground-based measurements of ambient particles were performed in Tokyo during October 26–29, 2012. We analyzed 43,881 particles with optical diameters greater than 0.4 μm. The fractions of particles with fluorescent composition, black carbon, and both were 14.2%, 2.3%, and 0.3%, respectively, which indicates the presence of internal mixtures of black carbon and fluorescent species in the ambient air for the first time. Mixtures of biological materials (estimated from fluorescence patterns) and black carbon were also detected. The fluorescence patterns of single particles with and without black carbon were almost identical, suggesting that particles with both black carbon and fluorescent composition might be formed by aggregation in ambient air. [ABSTRACT FROM AUTHOR]

Here, an ultrasensitive electrochemiluminescence (ECL) biosensor was developed to detect exosomes down to single particles based on multiple signal amplification. In this strategy, NiFe-tris(2,2′-bipyridyl) ruthenium(II) (Ru(bpy) 3 2+) on the electrode exhibited an excellent catalytic effect on the ECL reaction, significantly enhancing the ECL signal by approximately six-fold. In addition, the high affinity between the aptamer and CD 63 protein on the exosome surface released the RNA assembled into the DNA-RNA heteroduplex on the electrode. Duplex-specific nucleases activated DNA cleavage on DNA-RNA heteroduplex and initiated RNA recycling. Consequently, massive ferrocene (Fc)-DNA was detached from the electrode surface to recover the ECL emission of the NiFe-Ru(bpy) 3 2+ emitter. Benefiting from the multiple signal amplification, the fabricated ECL biosensor achieved a limit of detection for exosomes as low as 5 particles/μL and was successfully used for exosomes determination in serum. This sensor fabrication strategy will provide a universal and sensitive nano-platform for exosomes detection and enable the early diagnosis of related diseases. • An ultrasensitive electrochemiluminescence (ECL) biosensor is developed for detection of exosomes down to single particles. • NiFe-Ru(bpy) 3 2+ on electrode exhibits good catalytic effect in ECL system, effectively increasing the ECL signal by approx. 6 fold. • Due to the multiple signal amplification, a small amount of RNA can detach abundant Fc-DNA, leading to high sensitivity and low detection limit. [ABSTRACT FROM AUTHOR]

The photoreactivity of single particles with atmospheric interest was studied by using an acoustic levitation system coupled to Raman microspectrometry. Both, inorganic and organic single particle phototransformation has been investigated without any surface contact. The Raman microspectrometry has suitably provided the identification, the chemical heterogeneity as well as the formation rates of products. Complex surface limited processes are demonstrated for photolysis of both nitrate-rich and sulfur-rich droplets. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A novel triaxial apparatus employing overlapping rigid boundaries has been designed and constructed for experimental measurement of contact forces under confined compression of single granules in the mm-scale. The performance of the apparatus was evaluated by performing uniaxial and triaxial compression experiments on ideal elastic–plastic materials. Compression curves were compared with the fully plastic Abbott–Firestone contact model and with results from FEM simulations. The increase in contact force associated with confined conditions was observed in the compression curves from triaxial compression experiments, as supported by predictions from simulations using single particle contact models. Hence, a new method for the assessment of mechanical behaviour of single particles under confined compression can be considered as established. [ABSTRACT FROM AUTHOR]

Inductively coupled plasma optical emission spectroscopy (ICP-OES) and mass spectrometry (ICP-MS) can be considered as the most important tools in inorganic analytical chemistry. Huge progress has been made since the first analytical applications of the ICP. More stable RF generators, improved spectrometers and detection systems were designed along with the achievements gained from advanced microelectronics, leading to overall greatly improved analytical performance of such instruments. In contrast, for the vast majority of cases liquid sample introduction is still based on the pneumatic principle as described in the late 19th century. High flow pneumatic nebulizers typically demand the use of spray chambers as “aerosol filters” in order to match the prerequisites of an ICP. By this, only a small fraction of the nebulized sample actually contributes to the measured signal. Hence, the development of micronebulizers was brought forward. Those systems produce fine aerosols at low sample uptake rates, but they are even more prone for blocking or clogging than conventional systems in the case of solutions containing a significant amount of total dissolved solids (TDS). Despite the high number of publications devoted to liquid sample introduction, it is still considered the Achilles' heel of atomic spectrometry and it is well accepted, that the technology used for liquid sample introduction is still far from ideal, even when applying state-of-the-art systems. Therefore, this review is devoted to offer an update on developments in the field liquid sample introduction that had been reported until the year 2013. The most recent and noteworthy contributions to this field are discussed, trends are highlighted and future directions are outlined. The first part of this review provides a brief overview on theoretical considerations regarding conventional pneumatic nebulization, the fundamentals on aerosol generation and discusses characteristics of aerosols ideally suited for introduction into the ICP. In the following chapters, novel developments and applications in the field of low flow sample introduction are summarized with special focus on hyphenated techniques and multi-mode sample introduction systems. Issues associated with continuous or pulsed non-pneumatic aerosol generation systems, which has also been a major trend over the past couple of years, are also discussed in the final sections. [ABSTRACT FROM AUTHOR]

Beijing suffered from serious air pollution in October, 2011 with the occurrence of three continuous episodes. Here we analyze the pollution status of particulate matter, the relationship between the gaseous pollutants, physical and chemical properties of single particles, and the profile of water-soluble ions in PM 2.5 during the three episodes. Regional and photochemically aged air masses, which were characterized as having high values of O 3 and SO 2 , were hypothesized to have played a dominant role in the first episode. After mixing local air masses with freshly-emitted primary pollutants, the concentration of NO x continued to increase and the size of SO 4 2– NO 3 − and NH 4 + in the particle population continued to become smaller. The amount of elemental carbon-rich and organic carbon-rich particles in the scaled single particles (0.2–2 μm) and water-soluble K + in PM 2.5 also increased in the episodes. All the available information suggests that the biomass or fuel burning sources in or around Beijing may have had a huge impact on the last two episodes. [ABSTRACT FROM AUTHOR]

Single scattering particles, especially noble metal (plasmonic) nanoparticles, based analytical techniques are attractive recently and becoming the research focus of the light scattering analytical techniques. In this mini review, we summarize the single scattering particles based analytical techniques in the past decade including single scattering particles counting, single plasmonic nanoparticles sensing, and single plasmonic nanoparticles tracking/imaging. We emphasize the discussion on the single plasmonic nanoparticles sensing that combines with dark-field microscopy and resonant Rayleigh scattering spectroscopy. [ABSTRACT FROM AUTHOR]

Data evaluation is a crucial step when it comes to the determination of accurate and precise isotope ratios computed from transient signals measured by multi-collector-inductively coupled plasma mass spectrometry (MC-ICPMS) coupled to, for example, laser ablation (LA). In the present study, the applicability of different data evaluation strategies (i.e. 'point-by-point', 'integration' and 'linear regression slope' method) for the computation of U/U isotope ratios measured in single particles by LA-MC-ICPMS was investigated. The analyzed uranium oxide particles (i.e. 9073-01-B, CRM U010 and NUSIMEP-7 test samples), having sizes down to the sub-micrometre range, are certified with respect to their U/U isotopic signature, which enabled evaluation of the applied strategies with respect to precision and accuracy. The different strategies were also compared with respect to their expanded uncertainties. Even though the 'point-by-point' method proved to be superior, the other methods are advantageous, as they take weighted signal intensities into account. For the first time, the use of a 'finite mixture model' is presented for the determination of an unknown number of different U isotopic compositions of single particles present on the same planchet. The model uses an algorithm that determines the number of isotopic signatures by attributing individual data points to computed clusters. The U/U isotope ratios are then determined by means of the slopes of linear regressions estimated for each cluster. The model was successfully applied for the accurate determination of different U/U isotope ratios of particles deposited on the NUSIMEP-7 test samples. [ABSTRACT FROM AUTHOR]