Mixed-valent iron [Fe(II)-Fe(III)] minerals such as magnetite and green rust have received a significant amount of attention over recent decades, especially in the environmental sciences. These mineral phases are intrinsic and essential parts of biogeochemical cycling of metals and organic carbon and play an important role regarding the mobility, toxicity, and redox transformation of organic and inorganic pollutants. The formation pathways, mineral properties, and applications of magnetite and green rust are currently active areas of research in geochemistry, environmental mineralogy, geomicrobiology, material sciences, environmental engineering, and environmental remediation. These aspects ultimately dictate the reactivity of magnetite and green rust in the environment, which has important consequences for the application of these mineral phases, for example in remediation strategies. In this review we discuss the properties, occurrence, formation by biotic as well as abiotic pathways, characterization techniques, and environmental applications of magnetite and green rust in the environment. The aim is to present a detailed overview of the key aspects related to these mineral phases which can be used as an important resource for researchers working in a diverse range of fields dealing with mixed-valent iron minerals.

The feasibility of dissolved-core alginate-templated fluorescent microspheres as "smart tattoo" glucose biosensors was investigated in simulated interstitial fluid (SIF). The sensor works on the principle of competitive binding and fluorescence resonance energy transfer. The sensor consists of multilayer thin film coated alginate microspheres incorporating dye-labeled glucose receptor and competing ligand within the partially dissolved alginate core. In this study, different approaches for the sensing and detection chemistry were studied, and the response of encapsulated reagents was compared with the solution-phase counterparts. The glucose sensitivity of the encapsulated TRITC-Con A/FITC-dextran (500 kDa) assay in DI water was estimated to be 0.26%/mM glucose while that in SIF was observed to be 0.3%/mM glucose. The glucose sensitivity of TRITC-apo-GOx/FITC-dextran (500 kDa) assay was estimated to be 0.33%/mM glucose in DI water and 0.5%/mM glucose in SIF and both demonstrated a response in the range of 0-50 mM glucose. Therefore, it is hypothesized that the calcium ion concentration outside the microsphere (in the SIF) does not interfere with the response sensitivity. The sensor response was observed to exhibit a maximum response time of 120 s. The system further exhibited a sensitivity of 0.94%/mM glucose with a response in range of 0-50 mM glucose, using near-infrared dyes (Alexa Fluor-647-labeled dextran as donor and QSY-21-conjugated apo-GOx as acceptor), thereby making the sensor more amenable to in vivo use, when implanted in scattering tissue.

This is the premier study designed to evaluate the impact of thermal pre-treatment on the availability of polycyclic aromatic hydrocarbons (PAHs) for successive removal by chemical oxidation. Experiments were conducted in two soils having different PAH distribution originating from former coking plant sites (Homécourt, H, and Neuves Maisons, NM) located in northeast of France. Soil samples were pre-heated at 60, 100, and 150 °C for 1 week under inert atmosphere (N2). Pre-heating resulted in slight removal of PAHs (<10%) and loss of extractable organic matter (EOM). Then, these pre-heated soil samples were subjected to Fenton-like oxidation (H2O2 and magnetite) at room temperature. Chemical oxidation in soil without any pre-treatment showed almost no PAH degradation underscoring the unavailability of PAHs. However, chemical oxidation in pre-heated soils showed significant PAH degradation (19, 29, and 43% in NM soil and 31, 36, and 47% in H soil pre-treated at 60, 100, and 150 °C, respectively). No preferential removal of PAHs was observed after chemical oxidation in both soils. These results indicated the significant impact of pre-heating temperature on the availability of PAHs in contaminated soils and therefore may have strong implications in the remediation of contaminated soils especially where pollutant availability is a limiting factor.

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Microparticle optical sensors hold potential as implantable smart materials for in vivo analysis. In this work, the reversible response of dissolved-core alginate microspheres containing a homogeneous fluorescence resonance energy transfer (FRET)-based competitive binding assay for glucose was evaluated. The layer-by-layer self assembly technique was used to deposit multilayered nanofilm coatings on the alginate microspheres containing the assay, thereby stabilizing the sensor system when the alginate was de-crosslinked. The response to glucose was then determined in DI water and simulated interstitial fluid (SIF) using a flow cell to establish controlled, dynamic flow conditions for demonstrating reversibility. The glucose sensitivity under dynamic conditions was estimated to be 0.52%/mM glucose in DI water and 0.6%/mM glucose in simulated interstitial fluid; in both cases, the analytical response range was 0-30 mM glucose, covering both physiological (normoglycemia) and pathophysiological range (hyperglycemia and hypoglycemia). The sensor demonstrated a repeatable and reproducible response when tested over a period of one month, under dynamic flow conditions. Finally, in vitro cytotoxicity assays performed with L929 mouse fibroblast cell lines suggested that the dissolved-core alginate microsphere sensor system with nanofilm coating has sufficient biocompatibility for use as implantable glucose biosensors.

The incorporation of anti-inflammatory drug with glucose biosensors shows promise in improving sensor biocompatibility, thereby suggesting potential application of alginate microspheres as "smart tattoo" glucose sensors with increased functional longevity.

The incorporation of near-infrared dyes shows promise in improving sensor response because of their high sensitivity and improved tissue penetration of infrared light. The sensitivity for the sensors was approximately 1.5 times greater than that observed for visible dye sensors, and the new dye chemistry did not significantly alter the biocompatibility of the materials. These findings provide additional support for the potential application of alginate microspheres and similar systems such as "smart-tattoo" glucose sensors.

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