Determination of the Distance Between the Cytochrome and Dehydrogenase Domains of Immobilized Cellobiose Dehydrogenase by Using Surface Plasmon Resonance with a Center of Mass Based Model

Changes in the tertiary conformation of adsorbed biomolecules can induce detectable shifts (Δθr) in the surface plasmon resonance (SPR) angle. Here it is shown how to calculate the corresponding shifts in the adsorbate\u27s center of mass (Δzavg) along the sensing surface normal from the measured Δθr. The novel developed model was used for determining the mean distance between the cytochrome (CYT) and flavodehydrogenase (DH) domains of the enzyme cellobiose dehydrogenase (CDH) isolated from the fungi Neurospora crassa, Corynascus thermophilus, and Myriococcum thermophilum as a function of pH, [Ca2+], and substrate concentration. SPR confirmed the results from earlier electrochemical and SAXS studies stating that the closed conformation, where the two domains are in close vicinity, is stabilized by a lower pH and an increased [Ca2+]. Interestingly, an increasing substrate concentration in the absence of any electron acceptors stabilizes the open conformation as the electrostatic repulsion due to the reaped electrons pushes the DH and CYT domains apart. The accuracy of distance determination was limited mostly by the random fluctuations between replicate measurements, and it was possible to detect movements <1 nm of the domains with respect to each other. The results agreed with calculations using already established models treating conformational changes as contraction or expansion of the thickness of the adsorbate layer (tprotein). Although the models yielded equivalent results, in this case, the Δzavg-based method also works in situations, where the adsorbate\u27s mass is not evenly distributed within the layer

Size dependence of silver nanoparticle removal in a wastewater treatment plant mesocosm measured by FAST single particle ICP-MS

The quantities of engineered nanoparticles (NP) released to the environment are often influenced by their fate in waste water treatment plants (WWTP). Here, 40 nm silver NP (AgNP) were spiked into a mesocosm simulating the process used at a major municipal WWTP. The evolution of the mass distributions and number concentrations were followed by fast acquisition speed technique single particle inductively coupled mass spectrometry (FAST spICP-MS) using a high-resolution ICP-MS. It was thus possible to detect smaller Ag containing NP than hitherto possible in similar studies. These small particles (ca. 5-10 nm in corresponding metallic Ag equivalent spherical diameter) were possibly dissolved Ag+ precipitated as Ag2S particles. They were detected immediately upon spiking and were stable with respect to aggregation and thus much less removed by the WWTP process compared to the 40 nm AgNP. The results also suggested that any transformation of the latter AgNP occurred without dissolution. Most of these larger AgNP were probably removed by aggregation with large floc particles and subsequent sedimentation with the suspended particulate matter in the simulated WWTP process. The results have implications for differentiating the fate of nanoparticles as a function of size and demonstrate how spICP-MS can reveal such size-dependent fate dynamics

Versailles project on advanced materials and standards (VAMAS) interlaboratory study on measuring the number concentration of colloidal gold nanoparticles

We describe the outcome of a large international interlaboratory study of the measurement of particle number concentration of colloidal nanoparticles, project 10 of the technical working area 34, "Nanoparticle Populations" of the Versailles Project on Advanced Materials and Standards (VAMAS). A total of 50 laboratories delivered results for the number concentration of 30 nm gold colloidal nanoparticles measured using particle tracking analysis (PTA), single particle inductively coupled plasma mass spectrometry (spICP-MS), ultraviolet-visible (UV-Vis) light spectroscopy, centrifugal liquid sedimentation (CLS) and small angle X-ray scattering (SAXS). The study provides quantitative data to evaluate the repeatability of these methods and their reproducibility in the measurement of number concentration of model nanoparticle systems following a common measurement protocol. We find that the population-averaging methods of SAXS, CLS and UV-Vis have high measurement repeatability and reproducibility, with between-labs variability of 2.6%, 11% and 1.4% respectively. However, results may be significantly biased for reasons including inaccurate material properties whose values are used to compute the number concentration. Particle-counting method results are less reproducibile than population-averaging methods, with measured between-labs variability of 68% and 46% for PTA and spICP-MS respectively. This study provides the stakeholder community with important comparative data to underpin measurement reproducibility and method validation for number concentration of nanoparticles

Versailles project on advanced materials and standards (VAMAS) interlaboratory study on measuring the number concentration of colloidal gold nanoparticles

We describe the outcome of a large international interlaboratory study of the measurement of particle number concentration of colloidal nanoparticles, project 10 of the technical working area 34, "Nanoparticle Populations" of the Versailles Project on Advanced Materials and Standards (VAMAS). A total of 50 laboratories delivered results for the number concentration of 30 nm gold colloidal nanoparticles measured using particle tracking analysis (PTA), single particle inductively coupled plasma mass spectrometry (spICP-MS), ultraviolet-visible (UV-Vis) light spectroscopy, centrifugal liquid sedimentation (CLS) and small angle X-ray scattering (SAXS). The study provides quantitative data to evaluate the repeatability of these methods and their reproducibility in the measurement of number concentration of model nanoparticle systems following a common measurement protocol. We find that the population-averaging methods of SAXS, CLS and UV-Vis have high measurement repeatability and reproducibility, with between-labs variability of 2.6%, 11% and 1.4% respectively. However, results may be significantly biased for reasons including inaccurate material properties whose values are used to compute the number concentration. Particle-counting method results are less reproducibile than population-averaging methods, with measured between-labs variability of 68% and 46% for PTA and spICP-MS respectively. This study provides the stakeholder community with important comparative data to underpin measurement reproducibility and method validation for number concentration of nanoparticles

Versailles project on advanced materials and standards (VAMAS) interlaboratory study on measuring the number concentration of colloidal gold nanoparticles

We describe the outcome of a large international interlaboratory study of the measurement of particle number concentration of colloidal nanoparticles, project 10 of the technical working area 34, "Nanoparticle Populations" of the Versailles Project on Advanced Materials and Standards (VAMAS). A total of 50 laboratories delivered results for the number concentration of 30 nm gold colloidal nanoparticles measured using particle tracking analysis (PTA), single particle inductively coupled plasma mass spectrometry (spICP-MS), ultraviolet-visible (UV-Vis) light spectroscopy, centrifugal liquid sedimentation (CLS) and small angle X-ray scattering (SAXS). The study provides quantitative data to evaluate the repeatability of these methods and their reproducibility in the measurement of number concentration of model nanoparticle systems following a common measurement protocol. We find that the population-averaging methods of SAXS, CLS and UV-Vis have high measurement repeatability and reproducibility, with between-labs variability of 2.6%, 11% and 1.4% respectively. However, results may be significantly biased for reasons including inaccurate material properties whose values are used to compute the number concentration. Particle-counting method results are less reproducibile than population-averaging methods, with measured between-labs variability of 68% and 46% for PTA and spICP-MS respectively. This study provides the stakeholder community with important comparative data to underpin measurement reproducibility and method validation for number concentration of nanoparticles

New single particle methods for detection and characterization of nanoparticles in environmental samples

Nanoparticles (NP) are being used in rapidly increasing quantities which has resulted in concerns about possible harmful effects for health and environment. NP are already undergoing similar risk assessment programs as conventional chemicals, and due to their enhanced surface reactivities it has been proposed that the use of NP should be regulated by specific legislation based on particle size. Number based concentrations and size distributions are thought to be more relevant dose metrics for toxicology than the mass of NP. Because NP are prone to processes such as aggregation, dissolution, or adsorption on surfaces characterization is required during the whole test. To measure the emission of NP and exposure levels in the environment the methods have to be capable of quantifying and sizing particles of interest at parts per billion level concentrations or lower. Nanoparticle tracking analysis (NTA) was evaluated for measurement of number concentration and size distributions. The technique was considered suitable for monitoring and measuring exposure at relatively high (> 106 particles mL-1) concentrations; however, NTA is relatively unspecific in the sense that it is difficult to distinguish particles of different materials. To increase sensitivity and specificity single particle inductively coupled plasma mass spectrometry (spICP-MS) was developed for element specific characterization of particles in liquid samples. Validation of both the number concentration and sizing capabilities was carried out at concentrations as low as 102 particles mL-1.The capabilities of spICP-MS as a fast screening tool for NP was evaluated, and the method was used to quantify trace level contamination of WC particles emitted from wear of winter tire studs and hard coatings. Variable pressure or environmental scanning electron microscopes (ESEM) can be applied on a waist range of sample types with no or very little sample preparation. Therefore backscattered electron (BSE) imaging in such instrument was chosen as a base for developing a method for quantification of particles in solid samples. The technique was applied for quantifying particles in toxicity tests involving soil biota, and was concluded to be sensitive enough to cover the concentration range that is typically of interest in such tests. Finally it was concluded that due to the tremendous amount of information obtained on a single particle basis, electron microscopy is a suitable complementing technique for spICP-MS measurements, which otherwise give little information about the structure of the particles

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

Application of single particle ICP-MS (spICPMS) for measurement of the size and number concentration, c(p), of nanoparticles is currently hampered by insufficient accuracy. The relative contributions of different types of noise to the overall uncertainty during spICPMS measurements of Ag and Au nanoparticle dispersions were quantified showing that the accuracy of spICPMS is mainly limited by the uncertainty in nebulization efficiency (f(neb)). This uncertainty was improved by correcting f(neb) for analyte partitioning effects during nebulization, and the calculated Ag and Au nanoparticle sizes were in close agreement with sizes determined by scanning electron microscopy. The duration of the particle events was measured, which allowed correction for incomplete particle events and detector dead time, and determination of the effective dwell time for particle counting. The c(p) measured with spICPMS agreed with that measured by counting particles deposited on filters, and calculated from the mass concentration of the analyte

Determining Number Concentrations and Diameters of Polystyrene Particles by Measuring the Effective Refractive Index of Colloids Using Surface Plasmon Resonance

The capabilities of surface plasmon resonance (SPR) for characterization of colloidal particles were evaluated for 100, 300, and 460 nm nominal diameter polystyrene (PS) latexes. First the accuracy of measuring the effective refractive index (n(eff)) of turbid colloids using SPR was quantified. It was concluded that for submicrometer sized PS particles the accuracy is limited by the reproducibility between replicate injections of samples. An SPR method was developed for obtaining the particle mean diameter (d(part)) and the particle number concentration (c(p)) by fitting the measured n(eff) of polystyrene (PS) colloids diluted in series with theoretical values calculated using the coherent scattering theory (CST). The d(part) and c(p) determined using SPR agreed with reference values obtained from size distributions measured by scanning electron microscopy (SEM), and the mass concentrations stated by the manufacturer. The 100 nm particles adsorbed on the sensing surface, which hampered the analysis. Once the adsorption problem has been overcome, the developed SPR method has potential to become a versatile tool for characterization of colloidal particles. In particular, SPR could form the basis of rapid and accurate methods for measuring the c(p) of submicrometer particles in dispersion