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Phosphorus is one of the essential nutrients for plant growth, but it may be relatively unavailable to plants because of its chemistry. In soil, the majority of phosphorus is present in the form of a phosphate, usually as metal complexes making it bound to minerals or organic matter. Therefore, inorganic phosphate solubilization is an important process of plant growth promotion by plant associated bacteria and fungi. Non-nodulating plant species have been shown to thrive in low-nutrient environments, in some instances by relying on plant associated microorganisms called endophytes. These microorganisms live within the plant and help supply nutrients for the plant. Despite their potential enormous environmental importance, there are a limited number of studies looking at the direct molecular impact of phosphate solubilizing endophytic bacteria on the host plant. In this work, we studied the impact of two endophyte strains of wild poplar (Populus trichocarpa) that solubilize phosphate. Using a combination of x-ray imaging, spectroscopy methods, and proteomics, we report direct evidence of endophyte-promoted phosphorus uptake in poplar. We found that the solubilized phosphate may react and become insoluble once inside plant tissue, suggesting that endophytes may aid in the re-release of phosphate. Using synchrotron x-ray fluorescence spectromicroscopy, we visualized the nutrient phosphorus inside poplar roots inoculated by the selected endophytes and found the phosphorus in both forms of organic and inorganic phosphates inside the root. Tomography-based root imaging revealed a markedly different root biomass and root architecture for poplar samples inoculated with the phosphate solubilizing bacteria strains. Proteomics characterization on poplar roots coupled with protein network analysis revealed novel proteins and metabolic pathways with possible involvement in endophyte enriched phosphorus uptake. These findings suggest an important role of endophytes for phosphorus acquisition and provide a deeper understanding of the critical symbiotic associations between poplar and the endophytic bacteria.

Experimental electrochemistry offers unique opportunities for interactive instruction at all levels of education; however, widespread adoption in curricula is hindered by high costs associated with electrochemical instrumentation. Thus, the development of affordable instruments represents an essential step toward making electrochemistry accessible to everyone. While numerous commercially available three-electrode potentiostats exist, two-electrode potentiostats provide a simple and inexpensive alternative. Herein, we present the two-electrode SweepStat as a low-cost option capable of performing voltammetry and amperometry with comparable data acquisition to commercially available potentiostats valued from $4,000-40,000 USD. Additionally, the SweepStat's design facilitates current measurements in the nanoampere regime, permitting experiments with ultramicroelectrodes (UMEs; r[subscript electrode] < 25 [mu]). The fabrication, programming, and testing of this device constitute a valuable experimental exercise at the intersection of circuit design and construction, computer programing, and electrochemical analysis. A set of simple electrochemical experiments are presented for both macroelectrodes and UMEs, highlighting key electrochemical techniques, equations, and concepts. Furthermore, finite element modeling and commercial potentiostat comparisons are used to verify the efficacy of the SweepStat platform. The open-source nature of the SweepStat coupled with the wealth of electrochemical techniques and experiments that can be implemented with a simple two-electrode circuit offers an unparalleled opportunity for electrochemical instruction with extensive method development driven by student research.

Xerogel-based first-generationamperometric glucose biosensors,constructed through specific layer-by-layer assembly of films featuringglucose oxidase doped xerogel, a diffusion-limiting xerogel layer,and capped with both electropolymerized polyphenol and blended polyurethanesemipermeable membranes, are presented. The specific combination ofxerogels formed from specific silane precursors, including propyl-trimethoxysilane,isobutyl-trimethoxysilane, octyl-trimethoxysilane, and hydroxymethyl-triethoxysilane,exhibit impressive dynamic and linear ranges of detection (e.g., ≥24–28mM glucose) and low response times, as well as significant discriminationagainst common interferent species such as acetaminophen, ascorbicacid, sodium nitrite, oxalic acid, and uric acid as determined byselectivity coefficients. Additionally, systematic electrochemicaland contact angle studies of different xerogel silane precursors,varying in structure, chain length, and/or functional group, revealthat sensor performance is more dependent on the tunable porosity/permeabilityof the layered interfaces rather than the hydrophobic character orfunctional groups within the films. While the sensing performancelargely exceeds that of existing electrochemical glucose sensing schemesin the literature, the presented layered approach establishes thespecific functionality of each layer working in concert with eachother and suggests that the strategy may be readily adaptable to otherclinically relevant targets and is amenable to miniaturization foreventual in situ or in vivo sensing. [ABSTRACT FROM AUTHOR]

A planar electrode system was developed to permit the real-time, selective detection of hydrogen sulfide (H 2 S) from stimulated cells. Planar carbon electrodes were produced via stencil printing carbon ink through a laser cut vinyl mask. Electrodes were preconditioned using a constant potential amperometry methodology to prevent sensor drift resulting from elemental sulfur adsorption. Modification with a bilaminar coating (electropolymerized ortho -phenylenediamine and a fluorinated xerogel) facilitated high selectivity to H 2 S. To demonstrate the biological application of this planar sensor system, H 2 S released from 17β-estradiol-stimulated human umbilical vein endothelial cells (HUVECs) was quantified in situ in real-time. Stimulated HUVECs released sustained H 2 S levels for hours before returning to baseline. Cellular viability assays demonstrated negligible cell cytotoxicity at the electrochemical potentials required for analysis., Competing Interests: None., (This journal is © The Royal Society of Chemistry.)