Effect of Exposure Concentration and Growth Conditions on the Association of Cerium Oxide Nanoparticles with Green Algae.

The increasing release of engineered nanoparticles (NPs) into aquatic ecosystems makes it crucial to understand the interactions of NPs with aquatic organisms, such as algae. In this study, the association of CeO2 NPs with unicellular algae (Raphidocelis subcapitata) and changes to the cellular elemental profile were investigated using three exposure concentrations (1, 50, and 1000 µg CeO2/L) at two different algal growth conditions-exponential and inhibited growth (1% glutaraldehyde). After a 24 h-exposure, algal suspensions were settled by gravity and CeO2-NP/algae association was analyzed by single-cell inductively coupled plasma quadrupole mass spectrometry (sc-ICP-QMS) and ICP time-of-flight MS (sc-ICP-TOFMS). Concurrent detection of the cellular fingerprint with cerium indicated NP association with algae (adsorption/uptake) and changes in the cellular elemental profiles. Less than 5% of cells were associated with NPs when exposed to 1 µg/L. For 50 µg/L exposures in growing and inhibited cell treatments, 4% and 16% of cells were associated with CeO2 NPs, respectively. ICP-TOFMS analysis made it possible to exclude cellular exudates associated with CeO2 NPs due to the cellular fingerprint. Growing and inhibited cells had different elemental profile changes following exposure to CeO2 NPs-e.g., growing cells had higher Mg and lower P contents independent of CeO2 concentration compared to inhibited cells.

High-Throughput Sizing, Counting, and Elemental Analysis of Anisotropic Multimetallic Nanoparticles with Single-Particle Inductively Coupled Plasma Mass Spectrometry.

Nanoparticles (NPs) have wide applications in physical and chemical processes, and their individual properties (e.g., shape, size, and composition) and ensemble properties (e.g., distribution and homogeneity) can significantly affect the performance. However, the extrapolation of information from a single particle to the ensemble remains a challenge due to the lack of suitable techniques. Herein, we report a high-throughput single-particle inductively coupled plasma mass spectrometry (SP-ICP-MS)-based protocol to simultaneously determine the size, count, and elemental makeup of several thousands of (an)isotropic NPs independent of composition, size, shape, and dispersing medium with atomistic precision in a matter of minutes. By introducing highly diluted nebulized aqueous dispersions of NPs directly into the plasma torch of an ICP-MS instrument, individual NPs are atomized and ionized, resulting in ion plumes that can be registered by the mass analyzer. Our proposed protocol includes a phase transfer step for NPs synthesized in organic media, which are otherwise incompatible with ICP-MS instruments, and a modeling tool that extends the measurement of particle morphologies beyond spherical to include cubes, truncated octahedra, and tetrahedra, exemplified by anisotropic Cu NPs. Finally, we demonstrate the versatility of our method by studying the doping of bulk-dilute (<1 at. %) CuAg nanosurface alloys as well as the ease with which ensemble composition distributions of multimetallic NPs (i.e., CuPd and CuPdAg) can be obtained providing different insights in the chemistry of nanomaterials. We believe our combined protocol could deepen the understanding of macroscopic phenomena involving nanoscale structures by bringing about a statistics renaissance in research areas including, among others, materials science, materials chemistry, (nano)physics, (nano)photonics, catalysis, and electrochemistry.

Analysis of complex particle mixtures by asymmetrical flow field-flow fractionation coupled to inductively coupled plasma time-of-flight mass spectrometry.

Asymmetrical flow field-flow fractionation (AF4) hyphenated with inductively coupled plasma-mass spectrometry (ICP-MS) has been widely used to characterize metal containing particles. This study demonstrates the advantages of coupling AF4 with ICP-time-of-flight mass spectrometry (ICP-TOFMS) in standard and single particle modes to determine size distribution, elemental composition, and number concentration of composite particles. The coupled system was used to characterize two complex particle mixtures. The first mixture consisted of particles extracted from micro-alloyed steels with two size populations of different elemental composition. The second mixture consisted of particles extracted from soil spiked with various engineered nanoparticles (ENPs). The equivalent hydrodynamic sizes of individual micro-alloyed steel particles were up to 6 times larger than the sizes determined by single particle (sp)-ICP-TOFMS. The larger AF4 sizes were attributed to the presence of a surface coating, which is not reflected in the core size determined by sp-ICP-TOFMS. Two particle populations could not be separated by AF4 due to their broad size distributions but were resolved by sp-ICP-TOFMS using their unique elemental signatures. Multi-angle light scattering and ICP-TOFMS signals of soil suspensions increased with the spiked ENP concentrations. However, only after conducting full element screening and single particle fingerprinting by ICP-TOFMS could this increase be attributed to enhanced extraction efficiency of natural particles and the risk for false conclusions be eliminated. In this study, we describe how AF4 coupled to ICP-TOFMS can be applied to study complex samples of inorganic particles which contain organic compounds.