Isotope Dilution Analysis for Particle Mass Determination Using Single-Particle Inductively Coupled Plasma Time-of-Flight Mass Spectrometry: Application to Size Determination of Silver Nanoparticles.

This paper describes methodology based on the application of isotope dilution (ID) in single-particle inductively coupled plasma time-of-flight mass spectrometry (spICP-ToFMS) mode for the mass determination (and sizing) of silver nanoparticles (AgNPs). For this purpose, and considering that the analytical signal in spICP-MS shows a transient nature, an isotope dilution equation used for online work was adapted and used for the mass determination of individual NPs. The method proposed measures NP isotope ratios in a particle-to-particle approach, which allows for the characterization of NP mass (and size) distributions and not only the mean size of the distribution. For the best results to be obtained, our method development (undertaken through the analysis of the reference material NIST RM 8017) included the optimization of the working conditions for the best precision and accuracy in isotope ratios of individual NPs, which had been only reported to date with multicollector instruments. It is shown that the precision of the measurement of these ratios is limited by the magnitude of the signals obtained for each NP in the mass analyzer (counting statistics). However, the uncertainty obtained for the sizing of NPs in this approach can be improved by careful method optimization, where the most important parameters are shown to be the selection of the spike isotopic composition and concentration. Although only AgNPs were targeted in this study, the method presented, with the corresponding adaptations, could be applied to NPs of any other composition that include an element with different naturally available isotopes.

Synthesis, characterisation and multi-modal intracellular mapping of cisplatin nano-conjugates.

The synthesis of nanocarriers for the delivery of the antitumor drug cisplatin is reported. Multimodal-imaging consisting of surface enhanced Raman scattering and laser ablation inductively coupled plasma time of flight mass spectrometry was used to visualise the intracellular uptake of both the nanocarrier and drug.

New Model for Quantifying the Nanoparticle Concentration Using SERS Supported by Multimodal Mass Spectrometry.

Surface-enhanced Raman scattering (SERS) is widely explored for the elucidation of underlying mechanisms behind biological processes. However, the capability of absolute quantitation of the number of nanoparticles from the SERS response remains a challenge. Here, we show for the first time the development of a new 2D quantitation model to allow calibration of the SERS response against the absolute concentration of SERS nanotags, as characterized by single particle inductively coupled plasma mass spectrometry (spICP-MS). A novel printing approach was adopted to prepare gelatin-based calibration standards containing the SERS nanotags, which consisted of gold nanoparticles and the Raman reporter 1,2-bis(4-pyridyl)ethylene. spICP-MS was used to characterize the Au mass concentration and particle number concentration of the SERS nanotags. Results from laser ablation inductively coupled plasma time-of-flight mass spectrometry imaging at a spatial resolution of 5 µm demonstrated a homogeneous distribution of the nanotags (between-line relative standard deviation < 14%) and a linear response of 197Au with increasing nanotag concentration (R2 = 0.99634) in the printed gelatin standards. The calibration standards were analyzed by SERS mapping, and different data processing approaches were evaluated. The reported calibration model was based on an "active-area" approach, classifying the pixels mapped as "active" or "inactive" and calibrating the SERS response against the total Au concentration and the particle number concentration, as characterized by spICP-MS. This novel calibration model demonstrates the potential for quantitative SERS imaging, with the capability of correlating the nanoparticle concentration to biological responses to further understand the underlying mechanisms of disease models.

The potential of bioprinting for preparation of nanoparticle-based calibration standards for LA-ICP-ToF-MS quantitative imaging.

This paper discusses the feasibility of a novel strategy based on the combination of bioprinting nano-doping technology and laser ablation-inductively coupled plasma time-of-flight mass spectrometry analysis for the preparation and characterization of gelatin-based multi-element calibration standards suitable for quantitative imaging. To achieve this, lanthanide up-conversion nanoparticles were added to a gelatin matrix to produce the bioprinted calibration standards. The features of this bioprinting approach were compared with manual cryosectioning standard preparation, in terms of throughput, between batch repeatability and elemental signal homogeneity at 5 µm spatial resolution. By using bioprinting, the between batch variability for three independent standards of the same concentration of 89Y (range 0-600 mg/kg) was reduced to 5% compared to up to 27% for cryosectioning. On this basis, the relative standard deviation (RSD) obtained between three independent calibration slopes measured within 1 day also reduced from 16% (using cryosectioning) to 5% (using bioprinting), supporting the use of a single standard preparation replicate for each of the concentrations to achieve good calibration performance using bioprinting. This helped reduce the analysis time by approximately 3-fold. With cryosectioning each standard was prepared and sectioned individually, whereas using bio-printing it was possible to have up to six different standards printed simultaneously, reducing the preparation time from approximately 2 h to under 20 min (by approximately 6-fold). The bio-printed calibration standards were found stable for a period of 2 months when stored at ambient temperature and in the dark.

Accumulation of molybdenum in major organs following repeated oral administration of bis-choline tetrathiomolybdate in the Sprague Dawley rat.

Molybdenum is an essential dietary trace element required for several critical enzyme systems. High intake is associated with toxicity in ruminants and animal studies. The proposed therapeutic use of molybdenum-based drugs poses a potential risk for accumulation through chronic administration of therapeutic doses of this element. The current experiment was designed to study the effect of daily dosing of a molybdenum compound, bis-choline tetrathiomolybdate (TTM), in Sprague Dawley rats using laser ablation inductively coupled plasma time-of-flight mass spectrometry (LA-ICP-ToF-MS) and two dosing levels of TTM for up to 3 months. To investigate if molybdenum accumulation was associated with tissue toxicity, histopathology, haematology and clinical biochemistry markers of toxicity were incorporated into the study design. There were no behavioural signs of toxicity to the rats, and no clinical or anatomic pathology was associated with treatment. The current data did show a progressive accumulation of molybdenum within the adrenal gland, kidneys, liver, spleen, brain and testes. Although this was not associated with tissue toxicity within the 3-month study design, greater exposure over a longer period of time has the potential for producing adverse pathophysiological cellular function. Tissue toxicity, as a result of local excessive accumulation of molybdenum over time, has clear implications for the therapeutic use of molybdenum in humans and demands sensitive monitoring of tissue molybdenum levels to avoid toxicity. The current study highlights the shortcomings of conventional biomonitoring approaches to detect molybdenum accumulation with the goal of avoiding molybdenum-associated toxicity.

Biogenic metallic elements in the human brain?

The chemistry of copper and iron plays a critical role in normal brain function. A variety of enzymes and proteins containing positively charged Cu+, Cu2+, Fe2+, and Fe3+ control key processes, catalyzing oxidative metabolism and neurotransmitter and neuropeptide production. Here, we report the discovery of elemental (zero-oxidation state) metallic Cu0 accompanying ferromagnetic elemental Fe0 in the human brain. These nanoscale biometal deposits were identified within amyloid plaque cores isolated from Alzheimer's disease subjects, using synchrotron x-ray spectromicroscopy. The surfaces of nanodeposits of metallic copper and iron are highly reactive, with distinctly different chemical and magnetic properties from their predominant oxide counterparts. The discovery of metals in their elemental form in the brain raises new questions regarding their generation and their role in neurochemistry, neurobiology, and the etiology of neurodegenerative disease.

Emerging Approaches to Investigate the Influence of Transition Metals in the Proteinopathies.

Transition metals have essential roles in brain structure and function, and are associated with pathological processes in neurodegenerative disorders classed as proteinopathies. Synchrotron X-ray techniques, coupled with ultrahigh-resolution mass spectrometry, have been applied to study iron and copper interactions with amyloid ß (1-42) or α-synuclein. Ex vivo tissue and in vitro systems were investigated, showing the capability to identify metal oxidation states, probe local chemical environments, and localize metal-peptide binding sites. Synchrotron experiments showed that the chemical reduction of ferric (Fe3+) iron and cupric (Cu2+) copper can occur in vitro after incubating each metal in the presence of Aß for one week, and to a lesser extent for ferric iron incubated with α-syn. Nanoscale chemical speciation mapping of Aß-Fe complexes revealed a spatial heterogeneity in chemical reduction of iron within individual aggregates. Mass spectrometry allowed the determination of the highest-affinity binding region in all four metal-biomolecule complexes. Iron and copper were coordinated by the same N-terminal region of Aß, likely through histidine residues. Fe3+ bound to a C-terminal region of α-syn, rich in aspartic and glutamic acid residues, and Cu2+ to the N-terminal region of α-syn. Elucidating the biochemistry of these metal-biomolecule complexes and identifying drivers of chemical reduction processes for which there is evidence ex-vivo, are critical to the advanced understanding of disease aetiology.