A new look at an old classic: implementation of a SERS-based water hardness titration.

The routine use of SERS as an analytical technique has been hindered by practical considerations among which the irreproducibility of its signals and the lack of robustness of its calibration. In the present work, we examine a strategy to perform quantitative SERS without the need for calibration. The method reinvests a colorimetric volumetric titration procedure to determine water hardness but involves monitoring the progression of the titration through the SERS signal of a complexometric indicator. Upon reaching the equivalence between the chelating titrant and the metal analytes, the SERS signal abruptly jumps, which conveniently serves as an end-point marker. Three mineral waters spanning divalent metal concentrations varying by a factor of 25 were successfully titrated in this way, with satisfactory accuracy. Remarkably, the developed procedure can be run in less than an hour, without laboratory-grade carrying capacity and would be relevant for field measurements.

Magnetite-Arginine Nanoparticles as a Multifunctional Biomedical Tool.

Iron oxide nanoparticles are a promising platform for biomedical applications, both in terms of diagnostics and therapeutics. In addition, arginine-rich polypeptides are known to penetrate across cell membranes. Here, we thus introduce a system based on magnetite nanoparticles and the polypeptide poly-l-arginine (polyR-Fe3O4). We show that the hybrid nanoparticles exhibit a low cytotoxicity that is comparable to Resovist®, a commercially available drug. PolyR-Fe3O4 particles perform very well in diagnostic applications, such as magnetic particle imaging (1.7 and 1.35 higher signal respectively for the 3rd and 11th harmonic when compared to Resovist®), or as contrast agents for magnetic resonance imaging (R2/R1 ratio of 17 as compared to 11 at 0.94 T for Resovist®). Moreover, these novel particles can also be used for therapeutic purposes such as hyperthermia, achieving a specific heating power ratio of 208 W/g as compared to 83 W/g for Feridex®, another commercially available product. Therefore, we envision such materials to play a role in the future theranostic applications, where the arginine ability to deliver cargo into the cell can be coupled to the magnetite imaging properties and cancer fighting activity.

A frugal implementation of Surface Enhanced Raman Scattering for sensing Zn2+ in freshwaters - In depth investigation of the analytical performances.

Surface Enhanced Raman Scattering (SERS) has been widely praised for its extreme sensitivity but has not so far been put to use in routine analytical applications, with the accessible scale of measurements a limiting factor. We report here on a frugal implementation of SERS dedicated to the quantitative detection of Zn2+ in water, Zn being an element that can serve as an indicator of contamination by heavy metals in aquatic bodies. The method consists in randomly aggregating simple silver colloids in the analyte solution in the presence of a complexometric indicator of Zn2+, recording the SERS spectrum with a portable Raman spectrometer and analysing the data using multivariate calibration models. The frugality of the sensing procedure enables us to acquire a dataset much larger than conventionally done in the field of SERS, which in turn allows for an in-depth statistical analysis of the analytical performances that matter to end-users. In pure water, the proposed sensor is sensitive and accurate in the 160-2230 nM range, with a trueness of 96% and a precision of 4%. Although its limit of detection is one order of magnitude higher than those of golden standard techniques for quantifying metals, its sensitivity range matches Zn levels that are relevant to the health of aquatic bodies. Moreover, its frugality positions it as an interesting alternative to monitor water quality. Critically, the combination of the simple procedure for sample preparation, abundant SERS material and affordable portable instrument paves the way for a realistic deployment to the water site, with each Zn reading three to five times cheaper than through conventional techniques. It could therefore complement current monitoring methods in a bid to solve the pressing needs for large scale water quality data.

Reducing Conditions Favor Magnetosome Production in Magnetospirillum magneticum AMB-1.

Magnetotactic bacteria (MTB) are a heterogeneous group of Gram-negative prokaryotes, which all produce special magnetic organelles called magnetosomes. The magnetosome consists of a magnetic nanoparticle, either magnetite (Fe3O4) or greigite (Fe3S4), embedded in a membrane, which renders the systems colloidaly stable, a desirable property for biotechnological applications. Although these bacteria are able to regulate the formation of magnetosomes through a biologically-controlled mechanism, the environment in general and the physico-chemical conditions surrounding the cells in particular also influence biomineralization. This work thus aims at understanding how such external conditions, in particular the extracellular oxidation reduction potential, influence magnetite formation in the strain Magnetospirillum magneticum AMB-1. Controlled cultivation of the microorganisms was performed at different redox potential in a bioreactor and the formation of magnetosomes was assessed by microscopic and spectroscopic techniques. Our results show that the formation of magnetosomes is inhibited at the highest potential tested (0 mV), whereas biomineralization is facilitated under reduced conditions (-500 mV). This result improves the understanding of the biomineralization process in MTB and provides useful information in sight of a large scale production of magnetosomes for different applications.

The importance of the helical structure of a MamC-derived magnetite-interacting peptide for its function in magnetite formation.

Biomineralization is the process of mineral formation by organisms and involves the uptake of ions from the environment in order to produce minerals, with the process generally being mediated by proteins. Most proteins that are involved in mineral interactions are predicted to contain disordered regions containing large numbers of negatively charged amino acids. Magnetotactic bacteria, which are used as a model system for iron biomineralization, are Gram-negative bacteria that can navigate through geomagnetic fields using a specific organelle, the magnetosome. Each organelle comprises a membrane-enveloped magnetic nanoparticle, magnetite, the formation of which is controlled by a specific set of proteins. One of the most abundant of these proteins is MamC, a small magnetosome-associated integral membrane protein that contains two transmembrane α-helices connected by an ∼21-amino-acid peptide. In vitro studies of this MamC peptide showed that it forms a helical structure that can interact with the magnetite surface and affect the size and shape of the growing crystal. Our results show that a disordered structure of the MamC magnetite-interacting component (MamC-MIC) abolishes its interaction with magnetite particles. Moreover, the size and shape of magnetite crystals grown in in vitro magnetite-precipitation experiments in the presence of this disordered peptide were different from the traits of crystals grown in the presence of other peptides or in the presence of the helical MIC. It is suggested that the helical structure of the MamC-MIC is important for its function during magnetite formation.

Combined Experimental and Theoretical Approach to the Kinetics of Magnetite Crystal Growth from Primary Particles.

It is now recognized that nucleation and growth of crystals can occur not only by the addition of solvated ions but also by accretion of nanoparticles, in a process called nonclassical crystallization. The theoretical framework of such processes has only started to be described, partly due to the lack of kinetic or thermodynamic data. Here, we study the growth of magnetite nanoparticles from primary particles-nanometer-sized amorphous iron-rich precursors-in aqueous solution at different temperatures. We propose a theoretical framework to describe the growth of the nanoparticles and model both a diffusion-limited and a reaction-limited pathway to determine which of these best describes the rate-limiting step of the process. We show that, based on the measured iron concentration and the related calculated concentration of primary particles at the steady state, magnetite growth is likely a reaction-limited process, and within the framework of our model, we propose a phase diagram to summarize the observations.

Single crystalline superstructured stable single domain magnetite nanoparticles.

Magnetite nanoparticles exhibit magnetic properties that are size and organization dependent and, for applications that rely on their magnetic state, they usually have to be monodisperse. Forming such particles, however, has remained a challenge. Here, we synthesize 40 nm particles of magnetite in the presence of polyarginine and show that they are composed of 10 nm building blocks, yet diffract like single crystals. We use both bulk magnetic measurements and magnetic induction maps recorded from individual particles using off-axis electron holography to show that each 40 nm particle typically contains a single magnetic domain. The magnetic state is therefore determined primarily by the size of the superstructure and not by the sizes of the constituent sub-units. Our results fundamentally demonstrate the structure - property relationship in a magnetic mesoparticle.

Design of simultaneous antimicrobial and anticoagulant surfaces based on nanoparticles and polysaccharides.

The rational design of silver nanoparticles encapsulated in an anticoagulant, hemocompatible polysaccharide, 6-O-chitosan sulfate, is presented. Three different approaches are described for the immobilization of these core shell particles on cellulosic surfaces. The mass of the immobilized particles is quantified using a quartz crystal microbalance with dissipation (QCM-D). The antimicrobial activity of the surfaces towards E. coli MG 1655 [R1-16] is investigated by live/dead assays using fluorescence staining. All surfaces treated with the designed nanoparticles exhibit excellent antimicrobial activity towards E. coli MG 1655 [R1-16]. Anticoagulant properties of blood plasma on the nanoparticle treated surfaces have been determined using QCM-D. In comparison with the unmodified substrates, the total coagulation time as well as the thrombin formation time and fibrin clotting time of surfaces modified with nanoparticles are significantly increased.

Chitosan-silane sol-gel hybrid thin films with controllable layer thickness and morphology.

The preparation of thin films of chitosan-silane hybrid materials by combining sol-gel processing and spin coating is reported. A variety of silanes can be used as starting materials for the preparation of such thin films, namely tetraethoxysilane, tri-tert-butoxysilanol, trimethylethoxysilane, p-trifluoromethyltetra-fluorophenyltriethoxysilane, trivinylmethoxysilane, (methoxymethyl)trimethyl-silane, and hexamethoxydisilane. These silanes are subjected to a sol-gel process before they are added to acidic chitosan solutions. The chitosan:silane ratio is kept constant at 6:1 (w/w) and dilutions with ethanol are prepared and spin coated. Depending on the degree of dilution, film thickness can be controlled in a range between 5 and 70 nm. For the determination of additional surface properties, static water contact angle measurements and atomic force microscopy have been employed.