Mickaël Tharaud

Magnetic hyperthermia efficiency in the cellular environment for different nanoparticle designs.

Magnetic hyperthermia mediated by magnetic nanomaterials is one promising antitumoral nanotherapy, particularly for its ability to remotely destroy deep tumors. More and more new nanomaterials are being developed for this purpose, with improved heat-generating properties in solution. However, although the ultimate target of these treatments is the tumor cell, the heating efficiency, and the underlying mechanisms, are rarely studied in the cellular environment. Here we attempt to fill this gap by making systematic measurements of both hyperthermia and magnetism in controlled cell environments, using a wide range of nanomaterials. In particular, we report a systematic fall in the heating efficiency for nanomaterials associated with tumour cells. Real-time measurements showed that this loss of heat-generating power occurred very rapidly, within a matter of minutes. The fall in heating correlated with the magnetic characterization of the samples, demonstrating a complete inhibition of the Brownian relaxation in cellular conditions.

Chemical signature of magnetotactic bacteria

Significance Magnetite precipitates through either abiotic or biotic processes. Magnetotactic bacteria synthesize nanosized magnetite intracellularly and may represent one of the most ancient biomineralizing organisms. Thus, identifying bacterial magnetofossils in ancient sediments remains a key point to constrain life evolution over geological times. Although electron microscopy and magnetic characterizations allow identification of recent bacterial magnetofossils, sediment aging leads to variable dissolution or alteration of magnetite, potentially yielding crystals that barely preserve their structural integrity. Thus, reliable biosignatures surviving such modifications are still needed for distinguishing biogenic from abiotic magnetite. Here, we performed magnetotactic bacteria cultures and laboratory syntheses of abiotic magnetites. We quantified trace element incorporation into both types of magnetite, which allowed us to establish criteria for biomagnetite identification. There are longstanding and ongoing controversies about the abiotic or biological origin of nanocrystals of magnetite. On Earth, magnetotactic bacteria perform biomineralization of intracellular magnetite nanoparticles under a controlled pathway. These bacteria are ubiquitous in modern natural environments. However, their identification in ancient geological material remains challenging. Together with physical and mineralogical properties, the chemical composition of magnetite was proposed as a promising tracer for bacterial magnetofossil identification, but this had never been explored quantitatively and systematically for many trace elements. Here, we determine the incorporation of 34 trace elements in magnetite in both cases of abiotic aqueous precipitation and of production by the magnetotactic bacterium Magnetospirillum magneticum strain AMB-1. We show that, in biomagnetite, most elements are at least 100 times less concentrated than in abiotic magnetite and we provide a quantitative pattern of this depletion. Furthermore, we propose a previously unidentified method based on strontium and calcium incorporation to identify magnetite produced by magnetotactic bacteria in the geological record.

TiO2 nanomaterial detection in calcium rich matrices by spICPMS. A matter of resolution and treatment

High Ca concentrations in complex matrices such as river waters often hamper the detection of titanium nanomaterials (TiO2 NPs) by single particle inductively coupled plasma mass spectrometry (spICPMS), because of isobaric interference of 48Ca on the most abundant Ti isotope (48Ti). Several approaches were used to reduce this interference while measuring TiO2 in solutions with different Ca concentrations up to 100 mg L−1. ICP-MS/MS was used with ammonia as the reaction cell gas and high resolution (HR) ICP-MS was used under different resolution settings. These approaches were compared by measuring different Ti isotopes (47Ti and 49Ti). spICPMS data were then treated with a deconvolution method to filter out dissolved signals and identify the best approach to detect the lowest possible corresponding spherical size of TiO2 NPs (Dmin). ICP-MS/MS allowed for an important decrease of the theoretical Dmin compared to standard quadrupole ICP-MS, down to 64 nm in ultrapure water; however the sensitivity was reduced by the reaction gas and increasing Ca concentrations also increased the Dmin. The comparably higher sensitivity of HR-ICP-MS allowed for theoretically measuring a Dmin of 10 nm in ultrapure water. Combined with the deconvolution analysis, the highest resolution mode in HR-ICP-MS leads to the lowest Dmin at high Ca concentrations, even though significant broadening of the measured mass distributions occurred for TiO2 NPs at Ca concentrations up to 100 mg L−1.

Pd(0)‐Nanoparticles Embedded in Core‐Shell Nanogels as Recoverable Catalysts for the Mizoroki‐Heck Reaction

Core–shell nanogels are attractive stabilizers and supports for catalytically active metallic nanoparticles. Herein, we present the synthesis and the characterization of a nanostructured well‐defined core–shell nanogel with the ability to stabilize Pd0 nanoparticles in its core. This hybrid nanogel displays a remarkable stability in both the solid state and in solution. This feature allowed its successful application as a catalyst for the Mizoroki–Heck reaction between n‐butyl acrylate and a series of bromo‐ and iodoarenes. The yields spanned from good to excellent, and catalyst recycling could be achieved up to three times without a significant activity loss. Three‐phase tests indicated that the hybrid nanogel acts as a Pd0 nanoreservoir. The catalysis proceeds in a quasihomogeneous fashion as part of the catalytic activity occurs outside the nanogel, which explains the observed limited recyclability.

Study of the Optical Properties of Dissolved Organic Matter in the Seine River Catchment (France)

In this study, the optical properties of dissolved organic matter (DOM) were investigated using UV/visible photometry and excitation emission matrix (EEM) fluorescence spectroscopy. Differences in quality and quantity of organic carbon were observed and highlighted discrimination of organic matter typologies between the four studied areas in the catchment of the Seine river.