Nanoparticles containing magnetic materials, such as magnetite (Fe3O4), are particularly useful for imaging and separation techniques. As these nanoparticles are generally considered to be biologically and chemically inert, they are typically coated with metal catalysts, antibodies or enzymes to increase their functionality as separation agents. Here, we report that magnetite nanoparticles in fact possess an intrinsic enzyme mimetic activity similar to that found in natural peroxidases, which are widely used to oxidize organic substrates in the treatment of wastewater or as detection tools. Based on this finding, we have developed a novel immunoassay in which antibody-modified magnetite nanoparticles provide three functions: capture, separation and detection. The stability, ease of production and versatility of these nanoparticles makes them a powerful tool for a wide range of potential applications in medicine, biotechnology and environmental chemistry.

[1] We studied in situ colloid mobilization under transient flow conditions using columns repacked with Hanford sediments. Rainfall infiltration was experimentally simulated using different flow rates and initial moisture conditions. Five series of column experiments were performed with initial infiltration rates of 0.018, 0.036, 0.072, 0.144, and 0.288 cm/min, and the columns reached water saturations in the range of 53 to 81%. The infiltration of water into the columns provided unfavorable conditions for colloid attachment to the sediments. Colloids were eluted by the infiltrating water with the peak colloid concentrations in the outflow coinciding with the arrival of the infiltration front. A larger flow rate led to a greater amount of colloids released from the column. The cumulative amount of colloids released was proportional to the column water content established after steady state flow rates were achieved. We used the advection-dispersion equation with a first-order colloid release reaction to analyze the experimental data. The colloid release rate coefficient increased with the increase of water content. We calculated forces exerted on colloids, and found that electrostatic and van der Waals interactions, calculated based on the DLVO (Derjaguin-Landau-Verwey-Overbeek) theory, and hydrodynamic forces, were all less important than capillary forces in controlling colloid release. In one experiment, the ionic strength of the infiltration solution was increased, such that colloid attachment was favorable. Nonetheless, colloids were mobilized and eluted with the infiltration front, implying that non-DLVO forces, such as capillary forces, played a prominent role in colloid mobilization.Citation: Shang, J., M. Flury, G. Chen, and J. Zhuang (2008), Impact of flow rate, water content, and capillary forces on in situ colloid mobilization during infiltration in unsaturated sediments, Water Resour. Res., 44, W06411,

Extracellular vesicles (EVs) released by mesenchymal stem cells (MSCs) have exhibited regenerative capability in animal models of ischemia–reperfusion (I/R) acute kidney injury (AKI) and are considered as potential alternatives to direct MSC therapy. However, real-time in vivo imaging of MSC-EVs in renal I/R injury has yet to be established. Renal intracellular targets of MSC-EVs responsible for their regenerative effects also remain elusive. Here, we report that we real-time observed MSC-EVs specifically accumulated in the injured kidney and were taken up by renal proximal tubular epithelia cells (TECs) via DPA-SCP with aggregation-induced emission (AIE) characteristics. DPA-SCP precisely tracked the fate of MSC-EVs in a renal I/R injury mouse model for 72 h and exhibited superior spatiotemporal resolution and tracking ability to popular commercially available EV tracker PKH26. Further analysis revealed that the accumulated MSC-EVs stimulated mitochondrial antioxidant defense and ATP production via activating the Keap1-Nrf2 signaling pathway, which protected TECs against oxidative insult by reducing mitochondrial fragmentation, normalizing mitochondrial membrane potential, and increasing mitochondrial DNA copy number. Increased microRNA-200a-3p expression in renal TECs induced by MSC-EVs was identified as a regulatory mechanism contributing to the protective actions on mitochondria as well as stimulating the renal signal transduction pathways. In conclusion, MSC-EVs accumulated in the renal tubules during renal I/R injury and promoted the recovery of kidney function via activating the Keap1-Nrf2 signaling pathway and enhancing mitochondrial function of TECs. DPA-SCP with AIE characteristics allows noninvasive and precise in vivo visualization of MSC-EVs in kidney repair.

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