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This work describes the development and testing of a sensitive and selective potentiometric nitrate microsensor based on doped polypyrrole films. Utilizing 6–7 µm carbon fibers as a substrate for pyrrole electropolymerization allowed fabrication of flexible, miniature and inexpensive sensors for in situ monitoring of nitrate. The sensors have a rapid response (several seconds) and in their characteristics are competitive with expensive commercial nitrate ion selective electrodes (ISE), exhibiting Nernstian behavior (slopes 54 ± 1 mV per log cycle of nitrate concentration (n=8), at T=22°C), a linear response to nitrate concentrations spanning three orders of magnitude (0.1–10⁻⁴ M or 6200–6.2 ppm of NO₃⁻), and a detection limit of (3 ± 1) × 10⁻⁵ M (1.25–2.5 ppm). After a 2-month-period, the response was unchanged, and after 4.5 months, one version of the electrode continued to exhibit significant sensitivity to nitrate. Several polypyrrole nitrate microsensors were embedded sequentially downstream from a point source of nitrate solution in an intermediate scale physical groundwater model as a test of their performance under simulated environmental conditions. The microsensors responded appropriately to the approaching nitrate solution front, demonstrating dispersion and attenuation of the nitrate concentrations that increased with distance from the source.

Many studies over the last two decades have employed the pyrrole polymerization processes, including several utilizing polypyrrole (PPY) doping with various ions and the application of these doped polypyrrole films as ion selective electrodes (ISE). This work extends these studies in two directions: 1) miniaturization of an ise for nitrate anions, based on nitrate-doped PPY films on a substrate of 7 um carbon fibers, and 2) application of these PPY(no3-) electrodes to nitrate transport experiments in an intermediate scale physical aquifer model, which is a prototype of environmental (in situ) measurements of nitrate in soils. Successful completion of this project will lead to the deployment of distributed nitrate sensor networks in complex environments, including soils, ground and surface waters.

This work examines the potential role of embedded, networked sensing (ENS) protocols in monitoring the fate and transport of contaminants in the subsurface. The ultimate goal is to deploy a large dense array of chemical sensors for the purpose of identifying key transport parameters that are spatially distributed (e.g., porous media dispersivity) and, in some cases, temporally varying (e.g., nonaqueous phase liquid source zones). While there is clearly a need for further development in chemical sensor technology, the need to prepare to deploy new sensors in distributed networks is equally great. In this work, we first examine heat transfer phenomena as a surrogate for mass transfer in an intermediate scale physical aquifer model. Using a relatively standard data acquisition system (National Instruments A/D converter with Labview software), we continuously monitor water temperature over time and space throughout the model system. For well-defined heat sources, we developed closed-form solutions to the governing differential equations that are suitable for analyzing our data. Then, by embedding these closed solutions into our data acquisition routines, we were able to identify phenomenological parameters in real-time. Moving toward more relevant systems, we next demonstrate the use of a single nitrate sensor placed down-gradient of a finite pulse source of nitrate in a three-dimensional porous medium. Other potential applications and implications of ENS protocols in environmental monitoring networks will be discussed in terms of supporting ENS issues of self-adaptation, self- calibration, and coordinated actuation of responses.

While individual single‐wall carbon nanotubes (SWCNTs) have remarkable strength and electrical conductivity, SWCNT networks fabricated from dispersions have inferior properties due to nanotube bundling, limiting the potential applications of SWCNT materials. Herein, a common dye molecule (purpurin) is used to exfoliate SWCNTs via noncovalent functionalization and to fabricate SWCNT materials by a simple solution‐based process. The advantageous noncovalent interactions result in efficient exfoliation and metallic SWCNT enrichment, affording SWCNT materials with high mechanical robustness and electrical conductivity. This method is used to prepare mechanically robust SWCNT films and flexible transparent conductive electrodes. [ABSTRACT FROM AUTHOR]

Discontinuous, island-type gold films (typically [less than or equal to] 10 nm nominal thickness) prepared by evaporation of the metal on transparent substrates show a localized surface plasmon resonance (LSPR) extinction in the visible-to-NIR range and can be used as optical transducers for monitoring local refractive index change. Such transducers, operated in the transmission configuration, provide an effective scheme for label-free biological sensing using basic spectrophotometric equipment. Optimization of the sensitivity of LPSR transducers requires consideration of the distance between the metal island surface and the bound analyte, strongly affecting the optical response due to the fast decay of the evanescent field of localized plasmons. In the present work Au island based LSPR transducers were used to monitor antibody--antigen interactions, demonstrating the effect of the biorecognition interface thickness. Evaporated Au island films derivatized with IgG or hCG antigens were used as biological recognition elements for selective sensing of antibody binding, distinguishing between specific and nonspecific interactions. The LSPR results are supported by XPS and ellipsometry data as well as by AFM and HRSEM imaging, the latter providing actual visualization of the two protein binding steps. Increase of the recognition interface thickness leads to a concomitant decrease in the extinction and wavelength sensitivity, generally conforming to a model of an exponentially decaying surface plasmon (SP) evanescent field.

Lamellar structures of transition metal phosphorus trisulfides possess strong intralayer bonding, albeit adjacent layers are held by weak van der Waals interactions. Those compounds received enormous interest due to their unique combination of optical and long‐range magnetic properties. Among them, iron phosphorus trisulfide (FePS3) gathered special attention for being a semiconductor with an absorption edge in the near‐infrared, as well as showing an Ising‐like anti‐ferromagnetism. A successful growth of centimeter size bulk FePS3 crystals with a chemical yield above 70% is reported, whose crystallographic structure and composition are carefully identified by advanced electron microscopy methodologies, including atomic resolution elemental mapping, along with photoelectron spectroscopy. The knowledge on the optical activity of FePS3 is extended utilizing temperature‐dependent absorption and photoacoustic spectroscopies, while measurements are corroborated with density‐functional theory calculations. Temperature‐dependent experiments show a small and monotonic band‐edge energy shift down to 115 K and expose the interconnected importance of electron‐phonon coupling. Most of all, the correlation between the optical behavior and the magnetic phase transition is revealed, which shows the practical utilization of temperature‐dependent optical absorption to investigate magnetic interactions. [ABSTRACT FROM AUTHOR]

Herein, two different functionalities of one metallo‐organic film assembled on the surface of a transparent metal‐oxide electrode are described. Two redox‐active elements, electrochromic iron–polypyridyl complexes and catalytically active palladium centers, operate by applying different potentials in aqueous solutions. The color of the material can be cycled 1500 times from dark purple to colorless by electrochemically addressing the Fe2+/3+ centers at 0.0–1.0 V (vs Ag/Ag+). The differences between the transmittance of these two states is high: ΔT = 52%. Catalytic water oxidation can occur by palladium oxide particles that form in situ by applying a higher potential (1.22–2.0 V vs Ag/Ag+), resulting in the formation of hydrogen and oxygen. The catalyst is active for at least 7 h in an aqueous electrolyte at pH = 6.9, with a Faradaic efficiency of ≈70%. [ABSTRACT FROM AUTHOR]

Proteins are attractive as functional components in molecular junctions. However, controlling the electronic charge transport via proteins, held between two electrodes, requires information on their frontier orbital energy level alignment relative to the electrodes’ Fermi level (EF), which normally requires studies of UV Photoemission Spectroscopy (UPS) with HeI excitation. Such excitation is problematic for proteins, which can denature under standard measuring conditions. Here high‐sensitivity soft UV photoemission spectroscopy (HS‐UPS) combined with Constant Final State Yield Spectroscopy (CFS‐YS) is used to get this information for electrode/protein contacts. Monolayers of the redox protein Azurin, (Az) and its Apo‐form on Au substrates, have HOMO onset energies, obtained from CFS‐YS, differ by ≈0.2 eV, showing the crucial role of the Cu redox centre in the electron transport process. It is found that combined HS‐UPS/CFS‐YS measurements agree with the Photoelectron Yield Spectroscopy (PYS), showing potential of the HS‐UPS + CFS‐YS as a powerful tool to characterize and map the energetics of a protein‐electrode interfaces, which will aid optimizing design of devices with targeted electronic properties, as well as for novel applications. [ABSTRACT FROM AUTHOR]