Microbial infections remain the principal cause for high morbidity and mortality rates. While approximately 1400 human pathogens have been recognized, the majority of healthcare-associated infectious ...diseases are caused by only a few opportunistic pathogens (
e.g.
,
Pseudomonas aeruginosa
,
Staphylococcus aureus
,
Escherichia coli
), which are associated with increased antibiotic and antimicrobial resistance. Rapid detection, reliable identification and real-time monitoring of these pathogens remain not only a scientific problem but also a practical challenge of vast importance, especially in tailoring effective treatment strategies. Although the development of vaccinations and antibacterial drug treatments are the leading research, progress, and implementation of early warning, quantitative systems indicative of confirming pathogen presence are necessary. Over the years, various approaches, such as conventional culturing, straining, molecular methods (
e.g.
, polymerase chain reaction and immunological assays), microscopy-based and mass spectrometry techniques, have been employed to identify and quantify pathogenic agents. While being sensitive in some cases, these procedures are costly, time-consuming, mostly qualitative, and are indirect detection methods. A great challenge is therefore to develop rapid, highly sensitive, specific devices with adequate figures of merit to corroborate the presence of microbes and enable dynamic real-time measurements of metabolism. As an alternative, electrochemical sensor platforms have been developed as powerful quantitative tools for label-free detection of infection-related biomarkers with high sensitivity. This minireview is focused on the latest electrochemical-based approaches for pathogen sensing, putting them into the context of standard sensing methods, such as cell culturing, mass spectrometry, and fluorescent-based approaches. Description of the latest, impactful electrochemical sensors for pathogen detection will be presented. Recent breakthroughs will be highlighted, including the use of micro- and nano-electrode arrays for real-time detection of bacteria in polymicrobial infections and microfluidic devices for pathogen separation analysis. We will conclude with perspectives and outlooks to understand shortcomings in designing future sensing schemes. The need for high sensitivity and selectivity, low-cost implementation, fast detection, and screening increases provides an impetus for further development in electrochemical detectors for microorganisms and biologically relevant targets.
Electrochemical sensors designed for rapid diagnosis, detection and real-time monitoring of bacterial pathogens in hospital settings.
Perovskite oxides have attracted significant attention as energy conversion materials for metal-air battery and solid-oxide fuel-cell electrodes owing to their unique physical and electronic ...properties. Amongst these unique properties is the structural stability of the cation array in perovskites that can accommodate mobile oxygen ions under electrical polarization. Despite oxygen ion mobility and vacancies having been shown to play an important role in catalysis, their role in charge storage has yet to be explored. Herein we investigate the mechanism of oxygen-vacancy-mediated redox pseudocapacitance for a nanostructured lanthanum-based perovskite, LaMnO3. This is the first example of anion-based intercalation pseudocapacitance as well as the first time oxygen intercalation has been exploited for fast energy storage. Whereas previous pseudocapacitor and rechargeable battery charge storage studies have focused on cation intercalation, the anion-based mechanism presented here offers a new paradigm for electrochemical energy storage.
Electric vehicles and grid storage devices have potentialto become feasible alternatives to current technology, but only if scientists can develop energy storage materials that offer high capacity ...and high rate capabilities. Chemists have studied anatase, rutile, brookite and TiO2(B) (bronze) in both bulk and nanostructured forms as potential Li-ion battery anodes. In most cases, the specific capacity and rate of lithiation and delithiation increases as the materials are nanostructured. Scientists have explained these enhancements in terms of higher surface areas, shorter Li+ diffusion paths and different surface energies for nanostructured materials allowing for more facile lithiation and delithiation. Of the most studied polymorphs, nanostructured TiO2(B) has the highest capacity with promising high rate capabilities. TiO2(B) is able to accommodate 1 Li+ per Ti, giving a capacity of 335 mAh/g for nanotubular and nanoparticulate TiO2(B). The TiO2(B) polymorph, discovered in 1980 by Marchand and co-workers, has been the focus of many recent studies regarding high power and high capacity anode materials with potential applications for electric vehicles and grid storage. This is due to the material’s stability over multiple cycles, safer lithiation potential relative to graphite, reasonable capacity, high rate capability, nontoxicity, and low cost (Bruce, P. G.; Scrosati, B.; Tarascon, J.-M. Nanomaterials for Rechargeable Lithium Batteries. Angew. Chem., Int. Ed. 2008, 47, 2930–2946). One of the most interesting properties of TiO2(B) is that both bulk and nanostructured forms lithiate and delithiate through a surface redox or pseudocapacitive charging mechanism, giving rise to stable high rate charge/discharge capabilities in the case of nanostructured TiO2(B). When other polymorphs of TiO2 are nanostructured, they still mainly intercalate lithium through a bulk diffusion-controlled mechanism. TiO2(B) has a unique open crystal structure and low energy Li+ pathways from surface to subsurface sites, which many chemists believe to contribute to the pseudocapacitive charging. Several disadvantages exist as well. TiO2(B), and titania in general, suffers from poor electronic and ionic conductivity. Nanostructured TiO2(B) also exhibits significant irreversible capacity loss (ICL) upon first discharge (lithiation). Nanostructuring TiO2(B) can help alleviate problems with poor ionic conductivity by shortening lithium diffusion pathways. Unfortunately, this also increases the likelihood of severe first discharge ICL due to reactive Ti–OH and Ti–O surface sites that can cause unwanted electrolyte degradation and irreversible trapping of Li+. Nanostructuring also results in lowered volumetric energy density, which could be a considerable problem for mobile applications. We will also discuss these problems and proposed solutions. Scientists have synthesized TiO2(B) in a variety of nanostructures including nanowires, nanotubes, nanoparticles, mesoporous-ordered nanostructures, and nanosheets. Many of these structures exhibit enhanced Li+ diffusion kinetics and increased specific capacities compared to bulk material, and thus warrant investigation on how nanostructuring influences lithiation behavior. This Account will focus on these influences from both experimental and theoretical perspectives. We will discuss the surface charging mechanism that gives rise to the increased lithiation and delithiation kinetics for TiO2(B), along with the influence of dimensional confinement of the nanoarchitectures, and how nanostructuring can change the lithiation mechanism considerably.
Urea electrooxidation has attracted considerable interest as an alternative anodic reaction in the electrochemical generation of hydrogen due to both the lower electrochemical potential required to ...drive the reaction and also the possibility of eliminating a potentially harmful substance from wastewater during hydrogen fuel production. Nickel and nickel-containing oxides have shown activities comparable to those of precious-metal catalysts for the electrooxidation of urea in alkaline conditions. Herein, we investigate the use of nanostructured LaNiO3 perovskite supported on Vulcan carbon XC-72 as an electrocatalyst. This catalyst exhibits an exceptionally high mass activity of ca. 371 mA mgox –1 and specific activity of 2.25 A mg–1 cmox –2 for the electrooxidation of urea in 1 M KOH, demonstrating the potential applications of Ni-based perovskites for direct urea fuel cells and low-energy hydrogen production. While LaNiO3 is shown to be stable at low overpotentials, through in-depth mechanistic studies the catalyst surface was observed to restructure and there was apparent CO2 poisoning of the LaNiO3 upon extended cycling, a result that may be extended to other Ni-based systems.
The ability to design and characterize uniform, bimetallic alloy nanoparticles, where the less active metal enhances the activity of the more active metal, would be of broad interest in catalysis. ...Herein, we demonstrate that simultaneous reduction of Ag and Pd precursors provides uniform, Ag-rich AgPd alloy nanoparticles (∼5 nm) with high activities for the oxygen reduction reaction (ORR) in alkaline media. The particles are crystalline and uniformly alloyed, as shown by X-ray diffraction and probe corrected scanning transmission electron microscopy. The ORR mass activity per total metal was 60% higher for the AgPd2 alloy relative to pure Pd. The mass activities were 2.7 and 3.2 times higher for Ag9Pd (340 mA/mgmetal) and Ag4Pd (598 mA/mgmetal), respectively, than those expected for a linear combination of mass activities of Ag (60 mA/mgAg) and Pd (799 mA/mgPd) particles, based on rotating disk voltammetry. Moreover, these synergy factors reached 5-fold on a Pd mass basis. For silver-rich alloys (Ag≥4Pd), the particle surface is shown to contain single Pd atoms surrounded by Ag from cyclic voltammetry and CO stripping measurements. This morphology is favorable for the high activity through a combination of modified electronic structure, as shown by XPS, and ensemble effects, which facilitate the steps of oxygen bond breaking and desorption for the ORR. This concept of tuning the heteroatomic interactions on the surface of small nanoparticles with low concentrations of precious metals for high synergy in catalytic activity may be expected to be applicable to a wide variety of nanoalloys.
Cells can sense, signal, and organize via mechanical forces. The ability of cells to mechanically sense and respond to the presence of other cells over relatively long distances (e.g., ∼100 μm, or ...∼10 cell-diameters) across extracellular matrix (ECM) has been attributed to the strain-hardening behavior of the ECM. In this study, we explore an alternative hypothesis: the fibrous nature of the ECM makes long-range stress transmission possible and provides an important mechanism for long-range cell-cell mechanical signaling. To test this hypothesis, confocal reflectance microscopy was used to develop image-based finite-element models of stress transmission within fibroblast-seeded collagen gels. Models that account for the gel’s fibrous nature were compared with homogenous linear-elastic and strain-hardening models to investigate the mechanisms of stress propagation. Experimentally, cells were observed to compact the collagen gel and align collagen fibers between neighboring cells within 24 h. Finite-element analysis revealed that stresses generated by a centripetally contracting cell boundary are concentrated in the relatively stiff ECM fibers and are propagated farther in a fibrous matrix as compared to homogeneous linear elastic or strain-hardening materials. These results support the hypothesis that ECM fibers, especially aligned ones, play an important role in long-range stress transmission.
Fluoroethylene carbonate (FEC) has become a standard electrolyte additive for use with silicon negative electrodes, but how FEC affects solid electrolyte interphase (SEI) formation on the silicon ...anode’s surface is still not well understood. Herein, SEI formed from LiPF6-based carbonate electrolytes, with and without FEC, were investigated on 50 nm thick amorphous silicon thin film electrodes to understand the role of FEC on silicon electrode surface reactions. In contrast to previous work, anhydrous and anoxic techniques were used to prevent air and moisture contamination of prepared SEI films. This allowed for accurate characterization of the SEI structure and composition by X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry depth profiling. These results show that FEC reduction leads to fluoride ion and LiF formation, consistent with previous computational and experimental results. Surprisingly, we also find that these species decrease lithium-ion solubility and increase the reactivity of the silicon surface. We conclude that the effectiveness of FEC at improving the Coulombic efficiency and capacity retention is due to fluoride ion formation from reduction of the electrolyte, which leads to the chemical attack of any silicon-oxide surface passivation layers and the formation of a kinetically stable SEI comprising predominately lithium fluoride and lithium oxide.
Perovskites are of great interest as replacements for precious metals and oxides used in bifunctional air electrodes involving the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). ...Herein, we report the synthesis and activity of a phase-pure nanocrystal perovskite catalyst that is highly active for the OER and ORR. The OER mass activity of LaNiO3, synthesized by the calcination of a rapidly dried nanoparticle dispersion and supported on nitrogen-doped carbon, is demonstrated to be nearly 3-fold that of 6 nm IrO2 and exhibits no hysteresis during oxygen evolution. Moreover, strong OER/ORR bifunctionality is shown by the low total overpotential (1.02 V) between the reactions, on par or better than that of noble metal catalysts such as Pt (1.16 V) and Ir (0.92 V). These results are examined in the context of surface hydroxylation, and a new OER cycle is proposed that unifies theory and the unique surface properties of LaNiO3.
We present a series of perovskite electrocatalysts that are highly active for both the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) in an aqueous alkaline electrolyte. ...Lanthanum-based perovskites containing different transition metal active sites (LaBO3, B = Ni, Ni0.75Fe0.25, Co, Mn) are synthesized by a general colloidal method, yielding phase pure catalysts of homogeneous morphology and surface area (8–14 m2/g). Each perovskite’s ability to catalyze the OER and ORR is examined using thin film rotating disk electrochemistry (RDE). LaCoO3 supported on nitrogen-doped carbon is shown to be ∼3 times more active for the OER than high-surface-area IrO2. Furthermore, LaCoO3 is demonstrated to be highly bifunctional by having a lower total overpotential between the OER and ORR (ΔE = 1.00 V) than Pt (ΔE = 1.16) and Ru (ΔE = 1.01). The OER and ORR pathways are perturbed by the introduction of peroxide disproportionation functionality via support interactions and selective doping of the catalyst. LaNi0.75Fe0.25O3’s ability to disproportionate peroxide is hypothesized to be responsible for the ∼50% improvement over LaNiO3 in catalytic activity toward the ORR, despite similar electronic structure. These results allow us to examine the pathways for OER and ORR in context of support interactions, transition metal redox processes, and catalytic bifunctionality.
We report here all inorganic CsPbI3 planar junction perovskite solar cells fabricated by thermal coevaporation of CsI and PbI2 precursors. The best devices delivered power conversion efficiency (PCE) ...of 9.3 to 10.5%, thus coming close to the reference MAPbI3-based devices (PCE ≈ 12%). These results emphasize that all inorganic lead halide perovskites can successfully compete in terms of photovoltaic performance with the most widely used hybrid materials such as MAPbI3.
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