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BACKGROUND. Inadequate tuberculosis (TB) diagnostics are a major hurdle in the reduction of disease burden, and accurate point-of-care tests (POCTs) are urgently needed. We assessed the diagnostic accuracy of Fujifilm SILVAMP TB lipoarabinomannan (FujiLAM) POCT for TB diagnosis in HIV-negative outpatients and compared it with Alere Determine TB LAM Ag (AlereLAM) POCT and a laboratory-based ultrasensitive electrochemiluminescence LAM research assay (EclLAM). METHODS. In this multicenter diagnostic test accuracy study, we recruited HIV-negative adults with symptoms suggestive of pulmonary TB presenting to outpatient health care centers in Peru and South Africa. Urine samples were tested using FujiLAM, AlereLAM, and EclLAM, and the diagnostic accuracy was assessed against a microbiological reference standard (MRS) and a composite reference standard. RESULTS. Three hundred seventy-two HIV-negative participants were included and the prevalence of microbiologically confirmed TB was 30%. Compared with the MRS, the sensitivities of AlereLAM, FujiLAM, and EclLAM were 10.8% (95% confidence interval [CI] 6.3%–18.0%), 53.2% (95% CI 43.9%–62.1%), and 66.7% (95% CI 57.5%–74.7%), respectively. The specificities of AlereLAM, FujiLAM, and EclLAM were 92.3% (95% CI 88.5%–95.0%), 98.9% (95% CI 96.7%–99.6%), and 98.1% (95% CI 95.6%–99.2%), respectively. Positive likelihood ratios of AlereLAM, FujiLAM, and EclLAM were 1.4, 46.2, and 34.8, respectively, and positive predictive values were 37.5%, 95.2%, and 93.7%, respectively. CONCLUSION. Compared with AlereLAM, FujiLAM detected 5 times more patients with TB in HIV-negative participants, had a high positive predictive value, and has the potential to improve rapid diagnosis of TB at the point-of-care. EclLAM demonstrated that additional sensitivity gains are possible, which highlights LAM’s potential as a biomarker. Additional research is required to assess FujiLAM’s performance in prospective cohorts, its cost-effectiveness, and its impact in real-world clinical settings. FUNDING. Global Health Innovative Technology Fund, the UK Department for International Development, the Dutch Ministry of Foreign Affairs, the Bill and Melinda Gates Foundation, the Australian Department of Foreign Affairs and Trade, the German Federal Ministry of Education and Research through Kreditanstalt für Wiederaufbau, and the NIH and National Institute of Allergy and Infectious Diseases.

The use of the scanning electrochemical microscope (SECM) to probe the kinetics of charge-transfer processes at bilayer lipid membranes (BLM) is presented. Analysis of the SECM tip response demonstrates that an unmodified BLM behaves as an insulator, whereas a BLM doped with iodine shows some positive feedback. The SECM technique thus allows one to probe processes at a BLM and determine the kinetics of the charge-transfer process. The SECM can also be used to determine the shape of the BLM.

The electron transfer (ET) rate at the interface between two immiscible electrolyte solutions was probed as a function of the driving force and distance between redox centers by scanning electrochemical microscopy. The adsorption of phospholipids at the interface resulted in a decrease in the rate of interfacial ET between aqueous redox species and the oxidized form of zinc porphyrin in benzene. The fraction of the interfacial area covered with lipid (θ) was evaluated from the measured heterogeneous rate constants (kf). The dependence of θ vs lipid concentration in benzene fit a Langmuir isotherm. For complete monolayers of phospholipids, kf was a function of the number of methylene groups in a hydrocarbon chain. The driving force dependencies of interfacial ET rates (Tafel plots) were measured for several aqueous redox couples. They were linear, with a transfer coefficient of α ≅ 0.5 when the driving force for ET (ΔG°) was not too high, in agreement with Marcus theory, and leveled off to the diffusion-co...

Several classes of sol-gel derived, fuel-cell-type gas sensors are described. The electrochemical sensors are comprised of a hydrophobically modified silicate network and a dispersion of carbon powder and inert metal (palladium or platinum in the zero valent state) or organometallic (e.g., cobalt porphyrin) catalyst modifier. The carbon powder provides conductivity, the Ormosil network assures high porosity, which is pertinent for gas permeation through the back of the electrodes, and the hydrophobic functional group assures that only a thin layer at the outermost section of the electrode is wetted by the electrolyte, thus providing fast dynamic response.

The potential drop across the interface between two immiscible electrolyte solutions (ITIES), φ, can be quantitatively controlled and varied by changing the ratio of concentrations of the potential-determining ion in the two liquid phases. This approach was used to study the potential dependence of the rate constant for electron transfer (ET) at the ITIES (kf) by scanning electrochemical microscopy (SECM) with no external potential bias applied. The Tafel plot obtained for ET between aqueous Ru(CN)64- and the oxidized form of zinc porphyrin in benzene was linear with a transfer coefficient, α = 0.5, determined from the slope of a plot of ln kf vs φ, in agreement with conventional ET theory. The observed change in the ET rate with the interfacial potential drop cannot be attributed to concentration effects and represents the potential dependence of the apparent rate constant. This result is discussed in relation to the interface thickness and structure. The SECM was also used to study solid phase formation...

Palladium-modified carbon ceramic composite gas electrodes (Pd/CCE) are presented and characterized. The electrodes are comprised of graphite powder percolating through hydrophobically modified silica xerogels. The electrodes were prepared by mixing Pd salt and carbon powder with the sol-gel precursors and reduction of palladium ions after xerogel formation. The morphology and surface characteristics of the composite materials were examined by electron microscopy, X-ray microanalysis, nitrogen adsorption and water wetting angle measurements. Oxygen reduction was used as a model reaction to probe the characteristics of the wetted section of the Pd/CCEs. Voltammetric studies and polarization curves were employed to elucidate the size and structure of the active layer as a function of palladium content.

A new class of sol-gel-derived electrochemical gas sensors, comprised of a homogeneous dispersion of catalyst-modified carbon powder in porous, organically modified silica, is introduced. The porous structure of the electrode material permits high gas permeability. Their hydrophobic surface rejects water, leaving only a very thin layer at the outermost surface in contact with the electrolyte and thus minimizing effects of liquid side mass transfer. The carbon powder provides electric conductivity, and the catalyst guarantees selectivity and sensitivity. Heat-treated Co tetramethoxymesoporphyrin modified composite ceramic-carbon electrodes exemplify this new class of gas sensors. Detection of several gases by anodic (sulfur dioxide) or cathodic (carbon dioxide and oxygen) reactions is demonstrated. Metrological characteristics of a prototype oxygen sensor are presented.

The electrochemical mechanism of pyrolyzed carbon supported Co-tetramethoxymeso-porphyrin (Co-TMMP) catalysis of oxygen reduction is studied by a fuel-cell-type hydrophobic ceramic-carbon composite electrode (CCE), made of sol-gel-derived graphite-silica material. Only a thin layer at the outermost surface of the hydrophobic porous CCE is in contact with the electrolyte, thus minimizing effects of electrode structure on the current density. This property makes CCEs most useful for elucidation of kinetic mechanisms of gas electrodes. At low cathodic overpotentials, oxygen reduction in acidic solution on heat-treated Co-TMMP supported graphite powder exhibits first-order kinetics with respect to adsorbed di-oxygen, which obeys Langmuir adsorption isotherm. The activation energy of oxygen reduction equals 7.5 {+-} 0.4 kcal/mol. Half-order oxygen dependence is observed at high overpotentials, and the reaction is limited by the rate of hydrogen peroxide conversion.

Sol-gel derived indicator ceramic carbon electrodes (CCEs) made of graphite powder entrapped in hydrophobically modified silica gel are presented. Voltammetric characteristics of the electrodes are compared with other classes of graphite electrodes. Background current, double layer capacitance and metrological characteristics, including renewal repeatability, interelectrode reproducibility and operational stability for various solvents are presented. The indicator CCEs exhibit better stability than carbon paste electrodes and their renewal is easier and more reproducible than that of glassy carbon electrodes.

A new class of composite electrodes made of sol-gel derived carbon-silica materials is introduced. Modifed porous composite carbon-silica electrodes can exhibit hydrophobic or hydrophilic surface characteristics and can serve as an indicator (inert) electrode, as a potentiometric (selective or reference) electrode, and in amperometric sensing and biosensing. The composite (carbon) ceramic electrodes (CCP) are rigid, porous, easily modified chemically and have a renewable external surface. The electrodes otter higher stability than carbon paste electrodes, and they are moreamenable to chemical modification than monolithic and (organic) composite carbon electrodes

A procedure for the preparation of macroporous silica films suitable for planar chromatography is described. The films are produced by a low pH catalyses of alkyltrialkoxysilanes in oversaturated solution of pore forming organic compounds. A segregated three phase system yields thick films (10–60 µm) that have good adhesion to silica glass supports, uniform, mirror like surface and intercalated micron-dimension pores that permit capillarity driven elution of solvents through the film. A phase diagram demonstrating optimal operating conditions for macroporous and microporous film formation is introduced and analyzed.

Spherical ultramicroelectrodes with diameters of 1-30 μm have been prepared by seff-assembly of Au nanoparticles and 1,9-nonanedithiol molecules at the tip end of glass micropipets. The electrodes were characterized by optical and scanning electron microscopy, cyclic voltammetry in aqueous and acetonitrile solution, and scanning electrochemical microscopy approach curves. A modified theory for hemispherical electrodes was used to compute the approach curves, which agreed with the Experimental results. The construction strategy represents a bottom-up approach to the fabrication of microspherical electrodes.

Palladium-modified carbon ceramic composite gas electrodes (Pd/CCE) are presented and characterized. The electrodes are comprised of graphite powder percolating through hydrophobically modified silica xerogels. The electrodes were prepared by mixing Pd salt and carbon powder with the sol-gel precursors and reduction of palladium ions after xerogel formation. The morphology and surface characteristics of the composite materials were examined by electron microscopy, X-ray microanalysis, nitrogen adsorption and water wetting angle measurements. Oxygen reduction was used as a model reaction to probe the characteristics of the wetted section of the Pd/CCEs. Voltammetric studies and polarization curves were employed to elucidate the size and structure of the active layer as a function of palladium content.

Scanning electrochemical microscopy (SECM) is a powerful new tool for studying chemical and biological processes. It records changes in faradaic current as a microelectrode ([less than equal]7 [mu]m in diameter) is moved across the surface of a sample. The current varies as a function of both distance from the surface and the surface's chemical and electrical properties. We used SECM to examine in vivo topography and photosynthetic electron transport of individual guard cells in Tradescantia fluminensis, to our knowledge the first such analysis for an intact plant. We measured surface topography at the micrometer level and concentration profiles of O2 evolved in photosynthetic electron transport. Comparison of topography and oxygen profiles above single stomatal complexes clearly showed photosynthetic electron transport in guard cells, as indicated by induction of O2 evolution by photosynthetically active radiation. SECM is unique in its ability to measure topography and chemical fluxes, combining some of the attributes of patch clamping with scanning tunneling microscopy. In this paper we suggest several questions in plant physiology that it might address.

Sol-gel derived composite silica-carbon electrodes exhibit favorable electrochemical characteristics. The electrodes benefit from the conductivity and electrochemical advantages of the carbon powder, from the favorable properties of the ceramic network and from the versatility of the sol-gel process. Hydrophobie composite electrodes reject water, only their outermost surface is wetted and they exhibit good signal to background currents. A comparison of several types of carbon powders reveals that higher carbon loading and larger surface area electrodes can be attained by incorporation of dense graphite powder. When high surface area, small size carbon-black powder is used, a homogeneous distribution of microelectrodes, separated by insulating modified silica is formed. This ensemble of microelectrodes increases the sensitivity of the CCEs by more than two orders of magnitude as compared to glassy carbon electrode and graphite CCEs.

A novel approach to the development of acidity and alkalinity field tests, based on length of stain detectors, is discussed. The detectors consist of glass capillaries filled with sol–gel silica powder doped with pH indicators. When water is sampled through the tube detectors the alkaline or acidic species titrate the silanol groups on the glass surface, in the presence of the immobilized indicator, and colour a section of the capillary. The length of the coloured section depends on the alkalinity (or acidity) of the sampled solution. The effects of glass parameters, such as concentration of the silanol groups and the type and concentration of the immobilized pH indicators, are discussed.

The electrochemical doping and undoping processes of poly-(3,3‘‘-didodecyl-2,2‘:5‘,2‘‘-terthiophene) (poly(33‘‘DDTT)) were studied by scanning electrochemical microscopy (SECM) to characterize the electron transfer of the polymer with a redox mediator in solution when the polymer was at different oxidation levels. SECM showed that electron exchange processes of oxidized poly(33‘‘DDTT) were localized at the polymer/solution interface rather than inside the film. Poly(33‘‘DDTT) in the neutral state did not allow the permeation of redox species to the underlying metal and behaved like a completely passivating film. A modified expression for the effective electron-transfer rate constant, keff, was obtained by grouping the terms concerned with charge transport across the polymeric film, and the values of keff were calculated from SECM approach curves. The values of keff for the electron transfer between poly(33‘‘DDTT) film and methyl viologen (MV+/2+) as the redox couple ranged between 10-5 and 10-1 cm s-1, de...

The rates of electron transfer (ET) between two redox species through a monolayer of saturated dipalmytoyl phosphocholine and polyconjugated 2(3-(diphenylhexatrienyl)propanoyl)-1-hexadecanoyl-sn-glycero-3-phosphocholine phospholipids adsorbed at the interface of two immiscible electrolyte solutions (ITIES) were measured by scanning electrochemical microscopy. Comparison of the ET rates shows that addition of phospholipids with conjugated hydrocarbon chains increases the ET rate by at least a factor of 2 compared to films with only saturated hydrocarbon chains. This difference was sufficiently high to obtain information about distribution of lipid molecules in monolayers formed by mixing two lipids. Lateral scanning of an ultramicroelectrode tip across the lipid monolayer comprised of two different phospholipids showed that each lipid forms microsize domains. The rate of ET across a monolayer of lipid adsorbed at the ITIES was also probed as a function of temperature. A sharp decrease in ET rate with tempe...