Number Concentration Of Nanoparticles Research Articles

Individual Detection and Electrochemically Assisted Identification of Adsorbed Nanoparticles by Using Surface Plasmon Microscopy.

The increasing production and application of nanoparticles necessitates a highly sensitive analytical method for the quantification and identification of these potentially hazardous materials. We describe here an application of surface plasmon microscopy for the individual detection of each adsorbed nanoparticle and for visualization of its electrochemical conversion. Whereas the adsorption rate characterizes the number concentration of nanoparticles, the potential at which the adsorbed nanoparticles disappear during an anodic potential sweep characterizes the type of material. All the adsorbed nanoparticles are subjected to the potential sweep simultaneously; nevertheless, each of the up to a million adsorbed nanoparticles is identified individually by its electrochemical dissolution potential. The technique has been tested with silver and copper nanoparticles, but can be extended to many other electrochemically active nanomaterials.

Analysis of silver and gold nanoparticles in environmental water using single particle-inductively coupled plasma-mass spectrometry

The production and use of engineering nanomaterials (ENMs) leads to the release of manufactured or engineered nanoparticles into environment. The quantification and characterization of ENMs are crucial for the assessment of their environmental fate, transport behavior and health risks to humans. To analyze the size distribution and particle number concentration of AgNPs and AuNPs in environmental water and track their stability at low number concentration, a systematic study on SP-ICPMS was presented. The Poisson statistics was used to discuss the effect of dwell time and particle number concentration theoretically on the detection of NPs in solution by SP-ICPMS. The dynamic range of SP-ICPMS is approximately two orders of magnitude. The size detection limits for silver and gold nanoparticle in ultrapure water are 20 and 19nm respectively. The detection limit of nanoparticle number concentration is 8×104particlesL−1. Size distribution of commercial silver and gold nanoparticle dispersions is determined by SP-ICP-MS, which was in accordance with the TEM results. High particle concentration recoveries of spiked AgNPs and AuNPs are obtained (80–108% and 85–107% for AgNPs and AuNPs respectively in ultrapure and filtered natural water). It indicates that SP-ICPMS can be used to detect AgNPs and AuNPs. The filtration study with different membranes showed that filtration might be a problematic pre-treatment method for the detection of AgNPs and AuNPs in environmental water. Furthermore, the stability of citrate-coated AgNPs and tannic acid-coated AuNPs spiked into filtrated natural and waste water matrix was also studied at low concentration using SP-ICP-MS measurements. Dissolution of AgNPs was observed while AuNPs was stable during a ten day incubation period. Finally SP-ICPMS was used to analyze NPs in natural water and waste water. The results indicate that SP-ICPMS can be used to size metallic nanoparticles sensitively of low concentration under realistic environmental conditions.

Numerical study of natural convection characteristics of nanofluids in an enclosure using multiphase model

The natural convective heat transfer and flow characteristics of nanofluids in an enclosure are numerically simulated using the multiphase-flow model and single phase model respectively. The simulated results are compared with the experimental results from the published papers to investigate the applicability of these models for nanofluids from a macro standpoint. The effects of Rayleigh number, Grashof number and volume concentration of nanoparticles on the heat transfer and flow characteristics are investigated and discussed. Comparisons of the horizontal and vertical central dimensionless velocity profiles between nanofluid and water for various Grashof numbers are studied. In addition, both streamline contours and isotherms lines for different volume concentrations of nanofluids are analyzed as well. The study results show that a great deviation exists between the simulated result of the single phase model and the experimental data on the relation of Nusselt number and Rayleigh number, which indicates that the single phase model cannot reflect the heat transfer characteristic of nanofluid. While the simulated results using the multiphase-flow model show a good agreement with the experimental data of nanofluid, which means that the multiphase-flow model is more suitable for the numerical study of nanofluid. For the natural convection, the present study holds the point that using Grashof numbers as the benchmark would be more appropriate to describe the heat transfer characteristics of nanofluid. Moreover, the simulated results demonstrate that adding nanoparticles into the base fluid can enhance both the motion of fluid and convection in the enclosure significantly.

Experimental investigation on heat transfer characteristics and pressure drop of BPHE (brazed plate heat exchanger) using TiO2–water nanofluid

In this research, the effect of using TiO2–water nanofluid on heat transfer enhancement and pressure drop in a Brazed Plate Heat Exchanger used in domestic hot water system is investigated experimentally. TiO2 nanoparticles with 20nm diameter and 99+% purity are used for making the nanofluid at 0.3%, 0.8% and 1.5% weight concentration of suspended nanoparticles, in such experiments. This study is done on the brazed plate heat exchanger under turbulent flow condition. The effects of Reynolds number and weight concentration of nanoparticles on the heat transfer characteristics are investigated experimentally. This results in a significant increase in convective heat transfer coefficient through adding nanoparticles to distilled water. The results show that, the convective heat transfer coefficient and the overall heat transfer coefficient of TiO2–water nanofluid is increased with enhancement of Reynolds number and at a specified Reynolds number, heat transfer characteristics is enhanced by increasing weight concentration of nanoparticles in brazed plate heat exchanger. The maximum enhancement of the nanofluid convective heat transfer coefficient at 0.3%, 0.8% and 1.5% weight fraction of nanoparticles are about 6.6%, 13.5% and 23.7% respectively. Also the maximum enhancement of the nanofluid overall heat transfer coefficient at mentioned weight concentrations of nanoparticles are about 2.2%, 4.6% and 8.5% respectively. Finally, the nanofluid pressure drop at various levels of nanoparticles is measured experimentally. According to these results, increment in system pressure drop is negligible compared to the heat transfer improvement.

Characteristics of formation and growth of atmospheric nanoparticles observed at four regional background sites in Korea

Measurements of the number concentration and size distribution of atmospheric nanoparticles were conducted at four sites on the west coast of the Korean Peninsula by using identical scanning mobility particle sizers (SMPSs) in October 2012. The new particle formation and subsequent growth (NPF) of atmospheric nanoparticles, which were identified by the cyclostationary empirical orthogonal function (CSEOF) analysis technique, was observed on 11 out of 21days at the Baengnyeong-do Comprehensive Monitoring Observatory (BCMO); and on 10 out of 21days at the Korea Global Atmosphere Watch Center (KGAWC) from October 9 to 29, 2012. We also observed NPF events for 9 out of 21days at both the Gosan Climate Observatory (GCO) and the Jeju Comprehensive Monitoring Observatory (JCMO). During the study period, NPF was simultaneously observed for five days at all four sites, which indicates that the NPF event had a spatial extent of at least 540km.A cold, dry and cloud-free continental air mass originated from northern China, formed favorable environmental conditions (e.g., increasing solar insolation at the surface) on simultaneous NPF at the four sites. These synoptic weather patterns were closely associated with an extraordinary typhoon passing over the south of Japan. The mean values of particle formation rates at BCMO (1.26cm−3s−1) and KGAWC (1.49cm−3s−1) were relatively higher than those at GCO (0.39cm−3s−1) and JCMO (0.74cm−3s−1), however, the growth rate showed a similar level among four sites. An increase in the spatial homogeneity and inter-site correlation of atmospheric particles among the four sites was apparent for small particles (diameter<30nm) on simultaneous NPF event days.

Aerosol Emission Monitoring and Assessment of Potential Exposure to Multi-walled Carbon Nanotubes in the Manufacture of Polymer Nanocomposites.

Recent animal studies have shown that carbon nanotubes (CNTs) may pose a significant health risk to those exposed in the workplace. To further understand this potential risk, effort must be taken to measure the occupational exposure to CNTs. Results from an assessment of potential exposure to multi-walled carbon nanotubes (MWCNTs) conducted at an industrial facility where polymer nanocomposites were manufactured by an extrusion process are presented. Exposure to MWCNTs was quantified by the thermal-optical analysis for elemental carbon (EC) of respirable dust collected by personal sampling. All personal respirable samples collected (n = 8) had estimated 8-h time weighted average (TWA) EC concentrations below the limit of detection for the analysis which was about one-half of the recommended exposure limit for CNTs, 1 µg EC/m(3) as an 8-h TWA respirable mass concentration. Potential exposure sources were identified and characterized by direct-reading instruments and area sampling. Area samples analyzed for EC yielded quantifiable mass concentrations inside an enclosure where unbound MWCNTs were handled and near a pelletizer where nanocomposite was cut, while those analyzed by electron microscopy detected the presence of MWCNTs at six locations throughout the facility. Through size selective area sampling it was identified that the airborne MWCNTs present in the workplace were in the form of large agglomerates. This was confirmed by electron microscopy where most of the MWCNT structures observed were in the form of micrometer-sized ropey agglomerates. However, a small fraction of single, free MWCNTs was also observed. It was found that the high number concentrations of nanoparticles, ~200000 particles/cm(3), present in the manufacturing facility were likely attributable to polymer fumes produced in the extrusion process.

Determination of nanoscale particles in the air of working zone at the metallurgical production

The results of studies of the air of working zone at the metallurgical production on the example of Avisma OJSC (Berezniki, the Perm Territory) for the content of nanoscale particles are specified. The maximum nanoparticles concentration in the range of 13523–28609 mln./m3 is determined at the working place of the titanium production smelter with the maximum size of particles of 10–15 nm. At the working place in the administrative building (reference working place) the maximum concentration is determined within the range of 524–1000 mln./m3; the maximum size of nanoparticles is 20 nm. It was established that the number concentration of nanoparticles at the reference working places (administration of Avisma OJSC) is significantly lower than at the working places of main production processes. The presented studies can be used as the additional factors in the assessment of labor conditions and occupational risk during the manufacture and use of materials containing nanoparticles as well as the production processes with the nanoparticles formation.

Relationships between number, surface area, and mass concentrations of different nanoparticles in workplaces

No consistent metric for measuring exposure to nanoparticles has yet been agreed upon internationally. This study seeks to examine the relationship between the number concentration (NC), surface area concentration (SAC), and mass concentration (MC) of nanoparticles in workplaces. Real-time NC20-1000 nm, SAC10-1000 nm, and respirable MC100-1000 nm were determined for different nanoparticles. Concentration ratio (CR, activity: background), exposure ranking (ER), and between-metric correlation coefficients (R) were used to analyze the relationships between the three metrics. The ratio of cumulative percentage by number (APN) and cumulative percentage by mass (APM) was used to analyze whether the nanoparticle number is predominant, as compared with the nanoparticle mass. The CRs of NC20-1000 nm and SAC10-1000 nm for different nanoparticles at the corresponding work sites were higher than those of respirable MC100-1000 nm. The ERs of NC20-1000 nm for nano-Fe2O3 and nano-Al2O3 were the same as those of SAC10-1000 nm, but were inconsistent with those of respirable MC100-1000 nm. The order of correlation coefficients between NC20-1000 nm, SAC10-1000 nm, and respirable MC100-1000 nm was: RSAC and NC > RSAC and MC > RNC and MC. The ratios of APN and APM for nano-Al2O3 and grinding-wheel particles (less than 100 nm) at the same work site were 2.03 and 1.65, respectively. NC and SAC metrics are significantly distinct from the MC in characterizing exposure to airborne nanoparticles. Simultaneous measurements of the NC, SAC, and MC should be conducted as part of nanoparticle exposure assessment strategies and epidemiological studies.

Performance and emission characteristics of a vehicle fueled with enriched biogas and natural gases

This study aimed to investigate the characteristics of exhaust emissions and the fuel economy of a compressed natural gas (CNG) vehicle fueled with biogas and natural gases. A large CNG vehicle currently used as a city bus in Korea was tested on a chassis dynamometer under the European Transient Cycle (ETC) and the National Institute of Environmental Research (NIER) 06 cycles. One CH4-enriched biogas (97.6% CH4) and 5 natural gases with different CH4 contents (81.6–94.0% CH4) were used as test fuels. Total hydrocarbons (THC), CO, NOx and CO2 emissions in the NIER 06 cycle were higher than those in the ETC cycle for all tested fuels, while the fuel economy in the NIER 06 cycle was 43.7–51.5% lower than that in the ETC cycle. Total VOC emissions increased with increasing CH4 content in the fuel, with toluene being the highest proportion of the BTEX emissions in both the ETC cycle (72–80%) and the NIER 06 cycle (73–78%). Emissions of elemental/organic carbon exhibited a similar trend to that of nanoparticle emissions. Total organic carbon was mainly comprised of organic compounds at 97–99% (ETC cycle) and 95–99% (NIER 06 cycle). Polycyclic aromatic hydrocarbon emissions in the NIER 06 cycle were 133.3–577.8% higher than in the ETC cycle because of incomplete combustion and an increase in unburned fuel in the NIER 06 cycle, which is a low-speed driving mode. Nanoparticle number concentrations were lowest for M91 among the 6 tested fuels; the total number of particles in the NIER 06 cycle was 33.2–123.8% higher than in the ETC cycle.

Nanoparticle tracking analysis characterisation and parts-per-quadrillion determination of fullerenes in river samples from Barcelona catchment area.

In the present work, the analysis of seven fullerenes (C60 and C70 fullerenes and five functionalised fullerenes) has been performed in river samples collected in the vicinities of Barcelona (Catalonia, NE of Spain). The results of 48 samples (25 river waters, 12 river sediments and 11 wastewater effluents) are presented. Extracts of river water, river sediments and wastewater effluents were analysed by liquid chromatography (LC), using a pyrenylpropyl group bonded silica based column, coupled to a high-resolution mass spectrometer (HRMS), using a dual ion source, atmospheric pressure photoionisation/atmospheric pressure chemical ionisation source (APPI/APCI). The novel methodology presents good chromatographic separation, excellent selectivity and instrumental limits of quantification (ILOQ) in the femtogram order. Method limits of quantification (MLOQ) ranged from 2.9 to 17 pg/l and from 3.2 to 31 pg/l in surface waters and wastewaters, respectively. In wastewater effluents, the sums of C60 and C70 ranged from 0.5 to 9.3 ng/l. In surface waters, C60 fullerene was the most ubiquitous compound, being detected in 100% of the samples in concentrations from 31 pg/l to 4.5 ng/l, while C70 concentrations ranged from less than the method limits of detection (MLOD) to 1.5 ng/l. The presence of fullerenes in both the large particulate (diameter Ø > 450 nm) and the colloidal (Ø < 450 nm) fractions of surface waters should be noticed. In sediments, the concentrations of fullerenes were between the MLOD and 34.4 pg/g. In addition, nanoparticle tracking analysis (NTA) was used for the characterisation of water samples in terms of nanoparticle number concentration and size distribution. As far as our knowledge is concerned, this is the first time that NTA has been used for the characterisation of complex river waters with an environmental focus.

Characterization and Determination of Silver Nanoparticle Using Single Particle-Inductively Coupled Plasma-Mass Spectrometry

Abstract A single particle-inductively coupled plasma mass spectrometry (SP-ICP-MS) method was established to detect the size distribution and number concentrations of silver nanoparticles (AgNPs) in dilute aqueous solution. The optimal dwell time was 3 ms to reduce possibility of two or more particles entering simultaneously into detector. An iterative algorithm was applied to distinguish AgNPs as outliers from baseline and dissolved metal ion signal if measured intensity was beyond five time standard deviation of whole data. The size distribution and number concentration of three commercial silver nanoparticle dispersions (nominal diameters of 30, 50 and 100 nm) were determined by SP-ICP-MS. The result of SP-ICP-MS was accurately similar to that of TEM, indicating that SP-ICPMS could be used to detect silver nanoparticles. The particle size detection limit was 25 nm and the limit of number concentration was 8 × 104 particles L−1 in dilute solution. Tap water being added with silver nanoparticles was tested to obtain a similar size distribution and number concentration. This method was simple, fast and highly sensitive, and quite feasible to investigate the risk assessment of silver nanoparticles in aqueous environment and monitor silver nanoparticles in drinking water.

Friction factor and heat transfer of nanofluids containing cylindrical nanoparticles in laminar pipe flow

Numerical simulations of polyalphaolefins-Al2O3 nanofluids containing cylindrical nanoparticles in a laminar pipe flow are performed by solving the Navier-Stokes equation with term of cylindrical nanoparticles, the general dynamic equation for cylindrical nanoparticles, and equation for nanoparticle orientation. The distributions of particle number and volume concentration, the friction factor, and heat transfer are obtained and analyzed. The results show that distributions of nanoparticle number and volume concentration are non-uniform across the section, with larger and smaller values in the region near the pipe center and near the wall, respectively. The non-uniformity becomes significant with the increase in the axial distance from the inlet. The friction factor decreases with increasing Reynolds number. The relationships between the friction factor and the nanoparticle volume concentration as well as particle aspect ratio are dependent on the Reynolds number. The Nusselt number of nanofluids, directly proportional to the Reynolds number, particle volume concentration, and particle aspect ratio, is higher near the pipe entrance than at the downstream locations. The rate of increase in Nusselt number at lower particle volume concentration is more than that at higher concentration. Finally, the expressions of friction factor and Nusselt number as a function of particle volume concentration, particle aspect ratio, and Reynolds number are derived based on the numerical data.

On-road chasing measurement of exhaust particle emissions from diesel, CNG, LPG, and DME-fueled vehicles using a mobile emission laboratory

We designed and applied a mobile emission laboratory for on-road measurements of exhaust particles emitted from conventional diesel, compressed natural gas (CNG), liquefied petroleum gas (LPG), and dimethyl ether (DME)-fueled vehicles. Fuel type and vehicle driving conditions significantly affected the particle size distribution and the number concentrations of the nucleation mode. For all buses, the size distributions of particles in the exhaust under idling conditions had larger mode diameters than at constant speed conditions of 50 km/h or 80 km/h. The nucleation mode (< 50 nm) fraction of diesel, CNG, LPG, and DME at a constant speed of 50 km/h was 53%, 63%, 79%, and 99%, respectively, indicating that the DME-fueled bus emitted the most nanoparticles. As the vehicle speed increased from 50 km/h to 80 km/h, the nucleation mode fraction of diesel, CNG, LPG, and DME changed to 43%, 99%, 99%, and 99%, representing a significant increase in the number concentrations of nanoparticles in the CNG and LPG-fueled vehicles. The particle size distributions in the exhaust of diesel, CNG, LPG, and DME-fueled vehicles were not affected by increase in the chasing distance.

A simple spectroscopic method for the quantification of gold nanoparticle number concentration in water and fetal bovine serum solutions

In this work, we developed a facile and low-cost method with sufficient sensitivity for the quantitative determination of gold nanoparticles (GNPs) number concentration in water and fetal bovine serum solutions. The Au(III) digested from GNPs was reduced to Au(I) presumably by the thiol group of 2-mercaptobenzimidazole, then the Au(I)–thiolate complex was formed, the concentration of which is determined by absorbance at 300 nm. The number concentration of GNPs can be converted using microscopic images and simple calculations. The interference of serum can be avoided in this method. The limit of detection (LOD) of GNPs was calculated as 2.1 × 10−12 mol/L in water solution and 1.3 × 10−11 mol/L in fetal bovine serum (FBS) solution. This method provides a simple and fast way to determine the concentration of GNPs, which can be in carried out in the routine laboratory practice.

Assessment of a Cylindrical and a Rectangular Plate Differential Mobility Analyzer for Size Fractionation of Nanoparticles at High-Aerosol Flow Rates

An existing differential mobility analyzer (DMA) of cylindrical electrodes and a novel DMA of rectangular plate electrodes are demonstrated for size fractionation of nanoparticles at high-aerosol flow rates in this work. The two DMAs are capable of delivering monodisperse size selected nanoparticles (SMPS σg < 1.1) at gas flow rates ranging from 200 slm to 500 slm. At an aerosol flow rate of 200 slm, the maximum attainable particle mean size is of about 20 nm for the cylindrical DMA and of nearly 50 nm for the rectangular plate DMA. The number concentration of the monodisperse nanoparticles delivered by the high-flow DMAs spans from 104 cm−3 to 106 cm−3 depending upon the particle mean size and particle size dispersion. Copyright 2014 American Association for Aerosol Research

Improving the accuracy of single particle ICPMS for measurement of size distributions and number concentrations of nanoparticles by determining analyte partitioning during nebulisation

The analyte is redistributed between the waste and plasma flows. These analyte partitioning effects need to be corrected to obtain the most accurate size calibration of spICPMS.

Quantitative measurement of the nanoparticle size and number concentration from liquid suspensions by atomic force microscopy

Microscopy techniques are indispensable to the nanoanalytical toolbox and can provide accurate information on the number size distribution and number concentration of nanoparticles (NPs) at low concentrations (ca. ppt to ppb range) and small sizes (ca. <20 nm). However, the high capabilities of microscopy techniques are limited by the traditional sample preparation based on drying a small volume of suspension of NPs on a microscopy substrate. This method is limited by low recovery of NPs (ca. <10%), formation of aggregates during the drying process, and thus, the complete misrepresentation of the NP suspensions under consideration. This paper presents a validated quantitative sampling technique for atomic force microscopy (AFM) that overcomes the above-mentioned shortcomings and allows full recovery and representativeness of the NPs under consideration by forcing the NPs into the substrate via ultracentrifugation and strongly attaches the NPs to the substrate by surface functionalization of the substrate or by adding cations to the NP suspension. The high efficiency of the analysis is demonstrated by the uniformity of the NP distribution on the substrate (that is low variability between the number of NPs counted on different images on different areas of the substrate), the high recovery of the NPs up to 71%) and the good correlation (R > 0.95) between the mass and number concentrations. Therefore, for the first time, we developed a validated quantitative sampling technique that enables the use of the full capabilities of microscopy tools to quantitatively and accurately determine the number size distribution and number concentration of NPs at environmentally relevant low concentrations (i.e. 0.34-100 ppb). This approach is of high environmental relevance and can be applied widely in environmental nanoscience and nanotoxicology for (i) measuring the number concentration dose in nanotoxicological studies and (ii) accurately measuring the number size distribution of NPs; both are key requirements for the implementation of the European Commission recommendation for definition of nanomaterials.

An Occupational Exposure Assessment for Engineered Nanoparticles Used in Semiconductor Fabrication

Engineered nanoparticles of alumina, amorphous silica, and ceria are used in semiconductor device fabrication during wafer polishing steps referred to as 'chemical mechanical planarization' (CMP). Some metal oxide nanoparticles can impact the biological response of cells and organ systems and may cause adverse health effects; additional research is necessary to better understand potential risks from nanomaterial applications and occupational exposure scenarios. This study was conducted to assess potential airborne exposures to nanoparticles and agglomerates using direct-reading instruments and filter-based samples to characterize workplace aerosols by particle number, mass, size, composition, and morphology. Sampling was repeated for tasks in three work areas (fab, subfab, wastewater treatment) at a facility using engineered nanoparticles for CMP. Real-time measurements were collected using a condensation particle counter (CPC), optical particle counter, and scanning mobility particle spectrometer (SMPS). Filter-based samples were analyzed for total mass or the respirable fraction, and for specific metals of interest. Additional air sample filters were analyzed by transmission electron microscopy with energy dispersive x-ray spectroscopy (TEM/EDX) for elemental identification and to provide data on particle size, morphology, and concentration. Peak concentrations measured on the CPC ranged from 1 to 16 particles per cubic centimeter (P cm(-3)) for background and from 4 to 74 P cm(-3) during tasks sampled in the fab; from 1 to 60 P cm(-3) for background and from 3 to 84 P cm(-3) for tasks sampled in the subfab; and from 1160 to 45 894 P cm(-3) for background and from 1710 to 45 519 P cm(-3) during wastewater treatment system filter change tasks. Significant variability was seen among the repeated task measurements and among background comparisons in each area. Several data analysis methods were used to compare each set of task and background measurements. Increased concentrations of respirable particles were identified for some tasks sampled in each work area, although of relatively low magnitude and inconsistently among repeated measurements for specific tasks. Measurements with a portable SMPS indicated that nanoparticle number concentrations (channels 11.5-115.5nm) increased above background levels by 3.2 P cm(-3) during CMP tool set-up in the fab area but were not elevated when changing filters for the CMP wastewater treatment system. All results from mass concentration analysis were below the limits of detection. Characterization by TEM/EDX identified structures containing the elements of interest (Al, Si), primarily as agglomerates or aggregates in the 100-1000nm size range. Although health-based occupational exposure limits have not been established for nanoscale alumina, silica, or ceria, the measured concentrations by number and mass were below currently proposed benchmarks or reference values for poorly soluble low-toxicity nanoparticles.

Formation of certified reference materials and standard measurement guides for development of traceable measurements of mass fractions and sizes of nanoparticles in different media and biological matrixes on the basis of gamma-ray and optical spectroscopy

Metrological assurance has been developed and formed for a promising technique for measuring the mass fraction and number concentration of nanoparticles containing silver or zinc in different media, including those of a biological nature, i.e., the gamma-ray spectroscopy of neutron-activated samples along with dynamic light scattering. The advantage of this complex measurement technique over other approaches to analytically controlling nanomaterials is discussed. The certified reference materials and standard guides developed in order to ensure the uniformity and traceability of measurements are described. The technique is tested in experiments on the kinetics of accumulation and removal of silver nanoparticles in different organs and excrement of laboratory rats.

Measuring absolute nanoparticle number concentrations from particle count time series

Single-particle microscopy is important for characterization of nanoparticulate matter for which accurate concentration measurements are crucial. We introduce a method for estimating absolute number concentrations in nanoparticle dispersions based on a fluctuating time series of particle counts, known as a Smoluchowski process. Thus, unambiguous tracking of particles is not required and identification of single particles is sufficient. However, the diffusion coefficient of the particles must be estimated separately. The proposed method does not require precalibration of the detection region volume, as this can be estimated directly from the observations. We evaluate the method in a simulation study and on experimental data from a series of dilutions of 0.2- and 0.5-μm polymer nanospheres in water, obtaining very good agreement with reference values.