Polymerization-based signal amplification for paper-based immunoassays

Diagnostic tests in resource-limited settings require technologies that are affordable and easy to use with minimal infrastructure. Colorimetric detection methods that produce results that are readable by eye, without reliance on specialized and expensive equipment, have great utility in these settings. We report a colorimetric method that integrates a paper-based immunoassay with a rapid, visible-light-induced polymerization to provide high visual contrast between a positive and a negative result. Using Plasmodium falciparum histidine-rich protein 2 as an example, we demonstrate that this method allows visual detection of proteins in complex matrices such as human serum and provides quantitative information regarding analyte levels when combined with cellphone-based imaging. It also allows the user to decouple the capture of analyte from signal amplification and visualization steps.Bill & Melinda Gates Foundation (Award 51308)United States. Defense Advanced Research Projects Agency (HR0011-12-2-0010)National Science Foundation (U.S.). Graduate Research FellowshipBurroughs Wellcome Fund (Career Award at the Scientific Interface

Fabrication of Paper-Templated Structures of Noble Metals

This manuscript describes a simple and rapid method for fabricating freestanding structures composed primarily (>94% w/w, and 55–80 at%) of noble metals (e.g., gold, silver, platinum, etc.) and having physical morphologies that resemble paper, thread, or fabric. In this method, templates (i.e., pieces of paper, or cotton fabric) are loaded with aqueous solutions of salts of noble metals, and then the cellulosic component is burned off in a furnace held at high temperatures (i.e., from 550 °C to 800 °C, depending on the procedure, in air). Even though the environment in a furnace is ostensibly oxidizing (e.g., hot air), the metal ions are reduced to elemental metal and form paper-template or fabric-templated structures that have morphologies similar to that of the material from which they were derived (i.e., paper or fabric). Paper template structures are fibrous, permeable to gases and liquids, electrically conductive, and in some cases (e.g., paper templated gold and paper template platinum structures), their surfaces are electroactive. The surface areas of paper-templated structures are more than 20 times higher than their projected areas. Paper-templated structures thus have properties that make them potentially useful in catalysis, sensing, and electroanalysis.Chemistry and Chemical Biolog

Folding Analytical Devices for Electrochemical ELISA in Hydrophobic R H Paper

This work describes a device for electrochemical enzyme-linked immunosorbent assay (ELISA) designed for low-resource settings and diagnostics at the point of care. The device is fabricated entirely in hydrophobic paper, produced by silanization of paper with decyl trichlorosilane, and comprises two zones separated by a central crease: an embossed microwell, on the surface of which the antigen or antibody immobilization and recognition events occur, and a detection zone where the electrodes are printed. The two zones are brought in contact by folding the device along this central crease; the analytical signal is recorded from the folded configuration. Two proof-of-concept applications, an electrochemical direct ELISA for the detection of rabbit IgG as a model antigen in buffer and an electrochemical sandwich ELISA for the detection of malarial histidine-rich protein from Plasmodium falciparum (Pf HRP2) in spiked human serum, show the versatility of this device. The limit of detection of the electrochemical sandwich ELISA for the quantification of Pf HRP2 in spiked human serum was 4 ng mL–1 (102 pmol L–1), a value within the range of clinically relevant concentrations.Chemistry and Chemical Biolog

The Metabolic and Antioxidant Activity Profiles of Aged Greek Grape Marc Spirits

In the last decade, “expressions” of grape marc spirits aged in wooden barrels of characteristic amber color and complex sensory attributes have been introduced. Yet studies on constituents migrating from the barrel to the beverage are scarce, and their metabolic profile remains unexplored. Furthermore, the literature on the assessment of their antioxidant activity is limited. NMR metabolomics and spectrophotometry have been implemented in 38 samples to elucidate the impact of the aging procedure on the metabolites’ composition and establish whether these beverages exhibit antioxidant activity. Provenance was related to fusel alcohols, esters, acetaldehyde, methanol, saccharides, and 2-phenylethanol, while ethyl acetate and ethyl lactate contributed to discriminating samples of the same winery. Identified metabolites such as vanillin, syringaldehyde, and sinapaldehyde were related to the aging procedure. The maturation in the barrel was also associated with an increase in xylose, glucose, fructose, and arabinose. The antioxidant potential of the aged Greek grape marc spirits resulting from their maturation in oak barrels was highlighted. The metabolic profiling and antioxidant potential of aged Greek grape marc spirits were assessed for the first time. Finally, the enrichment of the aromatic region was noted with the presence of metabolites with a furanic and phenolic ring derived, respectively, from the polysaccharides’ degradation or the thermal decomposition of lignin