7 research outputs found
Distance Dependence of Electron Transfer Kinetics for Azurin Protein Adsorbed to Monolayer Protected Nanoparticle Film Assemblies
The distance dependence and kinetics of the heterogeneous electron transfer (ET) reaction for the redox protein azurin adsorbed to an electrode modified with a gold nanoparticle film are investigated using cyclic voltammetry. The nanoparticle films are comprised of nonaqueous nanoparticles, known as monolayer-protected clusters (MPCs), which are covalently networked with dithiol linkers. The MPC film assembly serves as an alternative adsorption platform to the traditional alkanethiolate self-assembled monolayer (SAM) modified electrodes that are commonly employed to study the ET kinetics of immobilized redox proteins, a strategy known as protein monolayer electrochemistry. Voltammetric analysis of the ET kinetics for azurin adsorbed to SAMs of increasing chain length results in quasi-reversible voltammetry with significant peak splitting. We observed rate constants (k°ET) of 12−20 s−1 for the protein at SAMs of shorter alkanethiolates that decays exponentially (β = 0.9/CH2 or 0.8/Å) at SAMs of longer alkanethiolates (9−11 methylene units) or an estimated distance of 1.23 nm and is representative of classical electronic tunneling behavior over increasing distance. Azurin adsorbed to the MPC film platforms of increasing thickness results in reversible voltammetry with very little voltammetric peaks splitting and nearly negligible decay of the ET rate over significant distances up to 20 nm. The apparent lack of distance dependence for heterogeneous ET reactions at MPC film assemblies is attributed to a two-step mechanism involving extremely fast electronic hopping through the MPC film architecture. These results suggest that MPC platforms may be used in protein monolayer electrochemistry to create adsorption platforms of higher architecture that can accommodate greater than monolayer protein coverage and increase the Faradaic signal, a finding with significant implications for amperometric biosensor design and development
A cultura escolar em conflito: ensino técnico e matemática moderna em Portugal
DisponÃvel em: http://www2.pucpr.br/reol/pb/index.php/dialogo?dd1=16276&dd99=view&dd98=pbO artigo estuda as transformações exigidas à s escolas do ensino profissional português durante a reforma da matemática moderna que ocorrem a partir de finais dos anos 1960. Em primeiro lugar, traça um quadro das normas associadas à s escolas técnicas portuguesas antes da reforma, recorrendo à legislação fundadora, aos manuais e a artigos de opinião de professores. Em segundo, detalha o debate que antecipou a introdução da reforma recorrendo a artigos e aopiniões expressas durante os cursos preparatórios, onde são notórias as pressões para mudanças na cultura escolar, especialmente nas suas representações, suscitadas pela nova matemática. Finalmente, observar-se como se materializou a reforma nos livros de texto da experiência
Spontaneous self-assembly and disassembly of colloidal gold nanoparticles induced by tetrakis(hydroxymethyl) phosphonium chloride
Detergent-Mediated Formation of β‑Hematin: Heme Crystallization Promoted by Detergents Implicates Nanostructure Formation for Use as a Biological Mimic
Hemozoin is a unique biomineral that
results from the sequestration
of toxic free heme liberated as a consequence of hemoglobin degradation
in the malaria parasite. Synthetic neutral lipid droplets (SNLDs)
and phospholipids were previously shown to support the rapid formation
of β-hematin, abiological hemozoin, under physiologically relevant
pH and temperature, though the mechanism by which heme crystallization
occurs remains unclear. Detergents are particularly interesting as
a template because they are amphiphilic molecules that spontaneously
organize into nanostructures and have been previously shown to mediate
β-hematin formation. Here, 11 detergents were investigated to
elucidate the physicochemical properties that best recapitulate crystal
formation in the parasite. A strong correlation between the detergent’s
molecular structure and the corresponding kinetics of β-hematin
formation was observed, where higher molecular weight polar chains
promoted faster reactions. The larger hydrophilic chains correlated
to the detergent’s ability to rapidly sequester heme into the
lipophilic core, allowing for crystal nucleation to occur. The data
presented here suggest that detergent nanostructures promote β-hematin
formation in a similar manner to SNLDs and phospholipids. Through
understanding mediator properties that promote optimal crystal formation,
we are able to establish an in vitro assay to probe this drug target
pathway
Coffee Rings as Low-Resource Diagnostics: Detection of the Malaria Biomarker <i>Plasmodium falciparum</i> Histidine-Rich Protein-II Using a Surface-Coupled Ring of Ni(II)NTA Gold-Plated Polystyrene Particles
We report a novel, low-resource malaria
diagnostic platform inspired
by the coffee ring phenomenon, selective for <i>Plasmodium falciparum</i> histidine-rich protein-II (<i>Pf</i>HRP-II), a biomarker
indicative of the <i>P. falciparum</i> parasite strain.
In this diagnostic design, a recombinant HRP-II (rcHRP-II) biomarker
is sandwiched between 1 μm NiÂ(II)Ânitrilotriacetic acid (NTA)
gold-plated polystyrene microspheres (AuPS) and NiÂ(II)ÂNTA-functionalized
glass. After rcHRP-II malaria biomarkers had reacted with NiÂ(II)ÂNTA-functionalized
particles, a 1 μL volume of the particle–protein conjugate
solution is deposited onto a functionalized glass slide. Drop evaporation
produces the radial flow characteristic of coffee ring formation,
and particle–protein conjugates are transported toward the
drop edge, where, in the presence of rcHRP-II, particles bind to the
NiÂ(II)ÂNTA-functionalized glass surface. After evaporation, a wash
with deionized water removes nonspecifically bound materials while
maintaining the integrity of the surface-coupled ring produced by
the presence of the protein biomarker. The dynamic range of this design
was found to span 3 orders of magnitude, and rings are visible with
the naked eye at protein concentrations as low as 10 pM, 1 order of
magnitude below the 100 pM <i>Pf</i>HRP-II threshold recommended
by the World Health Organization. Key enabling features of this design
are the inert and robust gold nanoshell to reduce nonspecific interactions
on the particle surface, inclusion of a water wash step after drop
evaporation to reduce nonspecific binding to the glass, a large diameter
particle to project a large two-dimensional viewable area after ring
formation, and a low particle density to favor radial flow toward
the drop edge and reduce vertical settling to the glass surface in
the center of the drop. This robust, antibody-free assay offers a
simple user interface and clinically relevant limits of biomarker
detection, two critical features required for low-resource malaria
detection