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- Atomic Force Microscopy (2)
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Results of an interlaboratory comparison on size characterization of SiO2 airborne nanoparticles using on-line and off-line measurement techniques are discussed. This study was performed in the framework of Technical Working Area (TWA) 34—'Properties of Nanoparticle Populations' of the Versailles Project on Advanced Materials and Standards (VAMAS) in the project no. 3 'Techniques for characterizing size distribution of airborne nanoparticles'. Two types of nano-aerosols, consisting of (1) one population of nanoparticles with a mean diameter between 30.3 and 39.0 nm and (2) two populations of non-agglomerated nanoparticles with mean diameters between, respectively, 36.2–46.6 nm and 80.2–89.8 nm, were generated for characterization measurements. Scanning mobility particle size spectrometers (SMPS) were used for on-line measurements of size distributions of the produced nano-aerosols. Transmission electron microscopy, scanning electron microscopy, and atomic force microscopy were used as off-line measurement techniques for nanoparticles characterization. Samples were deposited on appropriate supports such as grids, filters, and mica plates by electrostatic precipitation and a filtration technique using SMPS controlled generation upstream. The results of the main size distribution parameters (mean and mode diameters), obtained from several laboratories, were compared based on metrological approaches including metrological traceability, calibration, and evaluation of the measurement uncertainty. Internationally harmonized measurement procedures for airborne SiO2 nanoparticles characterization are proposed.
The effects of long-term application of different organic amendments, as compared to mineral fertilizer, on Zn, Cu and Pb content and leachability in a luvisol derived from loess were assessed. The organic fertilizers, applied since 1962, were compost (COM) – from green organic household waste, sewage sludge (SLU) – from municipal water treatment facilities, farmyard manure (FYM) and the doses applied since 1997 were 90 t ha-1, 10 t ha-1 and 9 t ha-1, once in 3 years, respectively. The kinetics of metals extraction with 0.05 mol dm-3 EDTA at pH 6.0 has been studied. The two first-order reactions model was fitted to the kinetic data and allowed to distinguish two pools for each metal: a 'labile' fraction (Q1), quickly extracted with a rate constant k1, and a 'moderately labile' fraction (Q2), more slowly extracted, with a rate constant k2. Simultaneously, the pseudo-total metal contents in the soil samples were determined after digestion with aqua regia (3:1 HCl + HNO3). The obtained parameters Q1, k1, Q2, k2, for the kinetics of extraction of each metal in the three replicates of each fertilization mode, as well as the pseudo-total metal contents, were statistically analysed. COM and SLU application resulted in an increase of the total contents of Pb, Zn and Cu in soil. Further, the percentage of labile Zn and Pb also increased in consequence of the application of those amendments, particularly COM. The increase was more noticeable for Zn. FYM, despite not increasing the total content of Pb, Zn or Cu, did also have an effect on the leachability of Zn and Pb, increasing their labile fraction in soil. These results point to a potential risk of increasing metals mobility in soil, mainly Zn, associated to the use of organic amendments, particularly COM or SLU.
The analytical potential of a nanosecond laser ablation inductively coupled plasma mass spectrometer (ns-LA-ICP-SFMS) system, equipped with an ultra-fast wash-out ablation chamber, is critically investigated for fast and highly spatially resolved (∼μm) qualitative elemental distribution within single cells. Initially, a low surface roughness (< 10 nm) thin In–SnO2 layer (total coating thickness ∼200 nm) deposited on glass is employed to investigate the size, morphology and overlapping of laser-induced craters obtained at different laser repetition rates, making use of Atomic Force Microscopy (AFM). Conical craters with a surface diameter of about 2 µm and depths of about 100 nm were measured after a single laser shot. Furthermore, the influence of the sampling distance (i.e. distance between the sample surface and the inner sniffer of the ablation chamber) on the LA-ICP-MS ion signal wash-out time is evaluated. A significant decrease of the transient 120Sn+ ion signal is noticed after slight variations (±200 μm) around the optimum sampling position. Ultra-fast wash-outs (< 10 ms) are achieved reducing the aerosol mixing from consecutive laser shots even when operating the laser at high repetition rates (25 – 100 Hz). Fast and highly spatially resolved images of elemental distribution within mouse embryonic fibroblast cells (NIH/3T3 fibroblast cells) and human cervical carcinoma cells (HeLa cells), incubated with gold nanoparticles (Au NPs) and Cd-based quantum dots (QDs), respectively, are determined at the optimized operating conditions. Elemental distribution of Au and Cd in single cells is achieved using a high scanning speed (50 µm/s) and high repetition rate (100 Hz). The results obtained for the distribution of fluorescent Cd-based QDs within the HeLa cells are in good agreement with those obtained by confocal microscopy. The size, morphology and overlapping of laser-induced craters in the fixed cells are also investigated using AFM, observing conical craters with a surface diameter of about 2.5 µm and depths of about 800 nm after a single laser shot.
The analytical potential of a nanosecond laser ablation coupled plasma mass spectrometer (ns-LA-ICP-SFMS)system is investigated for fast and highly spatially resolved (~µm) elemental distribution within single cells. The size, morphology and overlapping of laser-induced craters has been investigated with Atomic Force Microscopy (AFM).
High spatially resolved quantitative bioimaging of CdSe/ZnS Quantum Dots uptake in two kinds of cells is investigated combining laser ablation inductively coupled plasma mass spectrometry and the spatially resolved analysis of dried pL-droplets from a solution with a known concentration of Quantum Dots. Single cells and dried pL-droplets are morphologically characterized by Atomic Force Microscopy. A number concentration of CdSe/ZnS QDs between 3.5 104 and 48 104 is estimated to be uptaken by several selected single cells, after being incubated in the presence of a QDs suspension added to a standard cell culture medium. Mono-elemental bioimaging at subcellular resolution seems to show a higher number concentration of the CdSe/ZnS QDs in the cytosol around the cell nucleus.