A uniform measurement expression for cross method comparison of nanoparticle aggregate size distributions.

Available measurement methods for nanomaterials are based on very different measurement principles and hence produce different values when used on aggregated nanoparticle dispersions. This paper provides a solution for relating measurements of nanomaterials comprised of nanoparticle aggregates determined by different techniques using a uniform expression of a mass equivalent diameter (MED). The obtained solution is used to transform into MED the size distributions of the same sample of synthetic amorphous silica (nanomaterial comprising aggregated nanoparticles) measured by six different techniques: scanning electron microscopy in both high vacuum (SEM) and liquid cell setup (Wet-SEM); gas-phase electrophoretic mobility molecular analyzer (GEMMA); centrifugal liquid sedimentation (CLS); nanoparticle tracking analysis (NTA); and asymmetric flow field flow fractionation with inductively coupled plasma mass spectrometry detection (AF4-ICP-MS). Transformed size distributions are then compared between the methods and conclusions drawn on methods' measurement accuracy, limits of detection and quantification related to the synthetic amorphous silca's size. Two out of the six tested methods (GEMMA and AF4-ICP-MS) cross validate the MED distributions between each other, providing a true measurement. The measurement accuracy of other four techniques is shown to be compromised either by the high limit of detection and quantification (CLS, NTA, Wet-SEM) or the sample preparation that is biased by increased retention of smaller nanomaterials (SEM). This study thereby presents a successful and conclusive cross-method comparison of size distribution measurements of aggregated nanomaterials. The authors recommend the uniform MED size expression for application in nanomaterial risk assessment studies and clarifications in current regulations and definitions concerning nanomaterials.

Production of reference materials for the detection and size determination of silica nanoparticles in tomato soup.

A set of four reference materials for the detection and quantification of silica nanoparticles (NPs) in food was produced as a proof of principle exercise. Neat silica suspensions were ampouled, tested for homogeneity and stability, and characterized for total silica content as well as particle diameter by dynamic light scattering (DLS), electron microscopy (EM), gas-phase electrophoretic molecular mobility analysis (GEMMA), and field-flow fractionation coupled with an inductively coupled mass spectrometer (FFF-ICPMS). Tomato soup was prepared from ingredients free of engineered nanoparticles and was spiked at two concentration levels with the silica NP suspension. Homogeneity of these materials was found sufficient to act as reference materials and the materials are sufficiently stable to allow long-term storage and distribution at ambient temperature, providing proof of principle of the feasibility of producing liquid food reference materials for the detection of nanoparticles. The spiked soups were characterized for particle diameter by EM and FFF-ICPMS (one material only), as well as for the total silica content. Although questions regarding the trueness of the results from EM and FFF-ICPMS procedures remain, the data obtained indicate that even assigning values should eventually be feasible. The materials can therefore be regarded as the first step towards certified reference materials for silica nanoparticles in a food matrix.

Chip electrophoresis of gelatin-based nanoparticles.

Recently, biodegradable nanoparticles received increasing attention for pharmaceutical applications as well as applications in the food industry. With the current investigation we demonstrate chip electrophoresis of fluorescently (FL) labeled gelatin nanoparticles (gelatin NPs) on a commercially available instrument. FL labeling included a step for the removal of low molecular mass material (especially excess dye molecules). Nevertheless, for the investigated gelatin NP preparation two analyte peaks, one very homogeneous with an electrophoretic net mobility of µ = -24.6 ± 0.3 × 10(-9) m(2) /Vs at the peak apex (n = 17) and another more heterogeneous peak with µ between approximately -27.2 ± 0.2 × 10(-9) m(2) /Vs and -36.6 ± 0.2 × 10(-9) m(2) /Vs at the peak beginning and end point (n = 11, respectively) were recorded. Filtration allowed enrichment of particles in the size range of approximately 35 nm (pore size employed for concentration of gelatin NPs) to 200 nm (pore size employed during FL labeling). This corresponded to the very homogeneous peak linking it to gelatin NPs, whereas the more heterogeneous peak probably corresponds to gelatin not cross-linked to such a high degree (NP building blocks). Several further gelatin NP preparations were analyzed according to the same protocol yielding peaks with electrophoretic net mobilities between -23.3 ± 0.3 × 10(-9) m(2) /Vs and -28.9 ± 0.2 × 10(-9) m(2) /Vs at peak apexes (n = 15 and 6). Chip electrophoresis allows analyte separation in less than two minutes (including electrophoretic sample injection). Together with the high sensitivity of the FL detection - the LOD as derived for the first main peak of the applied dye from the threefold standard deviation of the background noise values 80 pM for determined separation conditions - this leads to a very promising high throughput separation technique especially for the analysis of bionanoparticles. For gelatin NP preparations, chip electrophoresis allows for example the comparison of preparation batches concerning the amount of NPs and gelatin building blocks as well as the indirect assessment of the degree of gelatin cross-linking (from obtained FL signals).

Characterization of cross-linked gelatin nanoparticles by electrophoretic techniques in the liquid and the gas phase.

Biodegradable nanoparticles (NPs) and hence e.g. NPs prepared from glutaraldehyde crosslinked gelatin (gelatin NPs) are lately receiving increased attention in various fields like pharmaceutical technology and nutraceutics as biocompatible carriers for hardly water soluble drugs, molecules intended for sustained release or targeted transport. However, in vivo application of such materials requires a thoroughly characterization of corresponding particles. In a previous manuscript we demonstrated the applicability of chip electrophoresis for the separation of gelatin NPs from NP building blocks. Following our previous results we intensified our efforts in the characterization of gelatin NPs by electrophoresis in the liquid (capillary and chip format) and the gas phase (gas phase electrophoretic mobility molecular analysis, GEMMA). In doing so, we demonstrated differences between nominally comparable (from the concentration of initially employed material for crosslinking) gelatin NP preparation batches concerning (i) the amount of obtained NPs, (ii) the degree of NP crosslinking, (iii) the amount of NP building blocks present within samples and (iv) the electrophoretic mobility diameter of NPs. Differences were even more pronounced when NP preparations from batches with different content of initially employed gelatin were compared. Additionally, we compared three setups for the removal of low molecular weight components from samples after fluorescence labeling of NPs. In overall, the combination of the three employed analytical methods for gelatin NP characterization - CE in the capillary and the chip format as well as GEMMA - allows a more thoroughly characterization of NP containing samples.

Comparative method evaluation for size and size-distribution analysis of gold nanoparticles.

Gold nanoparticles (GNPs) are popular colloidal substrates in various sensor, imaging, and nanomedicine applications. In separation science, they have raised some interest as a support for sample preparation. Reasons for their popularity are their low cost, ability for size-controlled synthesis with well-defined narrow nanoparticle size distributions, as well as straightforward surface functionalization by self-assembling (thiol-containing) molecules on the surface, which allows flexible introduction of functionalities for the selective capture of analytes. Most commonly, the method of first choice for size determination is dynamic light scattering (DLS). However, DLS has some serious shortcomings, and results from DLS may be misleading. For this reason, in this contribution several distinct complementary nanoparticle sizing methodologies were utilized and compared to characterize citrate-capped GNPs of different diameters in the range of 13-26 nm. Weaknesses and strengths of DLS, transmission electron microscopy, asymmetrical-flow field-flow fractionation and nanoelectrospray gas-phase electrophoretic mobility molecular analysis are discussed and the results comparatively assessed. Furthermore, the distinct GNPs were characterized by measuring their zeta-potential and surface plasmon resonance spectra. Overall, the combination of methods for GNP characterization gives a more realistic and comprehensive picture of their real physicochemical properties, (hydrodynamic) diameter, and size distribution.

Fast wheat variety classification by capillary gel electrophoresis-on-a-chip after single-step one-grain high molecular weight glutenin extraction.

Wheat variety identification based on one-step single-grain wheat extraction and fast capillary gel electrophoresis-on-a-chip (CGE-on-a-chip) analyses was evaluated for 15 different wheat varieties grown in Austria. The results of the capillary-based separation system were compared to the internationally accepted method from the International Union for the Protection of New Varieties of Plants which is based on time-consuming sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) analysis. Comparable protein patterns were observed making the CGE-on-a-chip system a promising tool for high-throughput analysis in food control. For the development of a robust method protein extraction, shelf life of wheat extracts and the instrument's variability were evaluated. It turned out that a one-step single-grain wheat extraction allowed the sample to be stored at 4 °C for up to 4 weeks without losing any valuable protein information. Furthermore, the technical variation of the whole method is very low making the biological variation of the selected wheat grains the only uncertain factor. Additionally, two unsupervised statistical methods (hierarchical cluster analysis and principal component analysis) were used for variety identification. Identification was successful for a reduced data set of 14 samples from five different wheat varieties making the combination of CGE-on-a-chip analysis of one-step single-grain extraction in combination with automatic data evaluation a promising tool for fast wheat differentiation (within a day).