Electrochemical Capacitance DNA Sensing at Hairpin-Modified Au Electrodes

An interfacial capacitance measurement electrochemical technique has been used for the sensing of self-assembled DNA hairpin probes (M. tuberculosis and B. anthracis) attached to Au electrodes. The double-layer capacitance (Cdl) was determined with electrochemical perturbations from 0.2 V to 0.5 V versus Ag/AgCl at a Au/M. tuberculosis DNA hairpin probe at surface coverage Au electrodes. The capacitance study was done at pH 7, which was necessary to maintain the M. tuberculosis and B. anthracis DNA probes closed during the electrochemical perturbation. Detailed experimental analysis carried out by repetitively switching the electrochemical potential between 0.2 and 0.5 V (versus Ag/AgCl) strongly supports the use of capacitance measurements as a tool to detect the hybridization of DNA targets. A large change in the capacitance deference between 0.2 and 0.5 V was observed in the DNA hybridization process. Therefore, no fluorophores or secondary transducers were necessary to sense a DNA target for both DNA hairpins

Chronoamperometric Study of Ammonia Oxidation in a Direct Ammonia Alkaline Fuel Cell under the Influence of Microgravity

This is a study of the chronoamperometric performance of the electrochemical oxidation of ammonia in an alkaline fuel cell for space applications. Under microgravity the performance of a fuel cell is diminished by the absence of buoyancy since nitrogen gas is produced. The following catalysts were studied: platinum nanocubes of ca. 10nm, platinum nanocubes on carbon Vulcan ™ and platinum on carbon nanoonion support of ca. 10nm. These nanomaterials were studied in order to search for catalysts that may reduce or counter the loss of ammonia oxidation current densities performance under microgravity conditions. Chronoamperometries at potential values ranging from 0.2 V to 1.2V vs. cathode potential (breathing Air/300ml/min/82737 Pa) in 1.0 M NH4OH (30ml/min in anode) were done during over 30 parabolas in NASA’s C9 airplane The Weightless Wonder in January 2016 from Ellington Field Houston. The current densities at 15s in the chronoamperometry experiments showed diminishing values under microgravity and in some cases improvements of up to 92%, for Pt-carbon nanoonions, and over 70% for the three catalysts versus ground at potentials ranging from 0.2 to 0.4V after 5 minutes of chronoamperometric conditions. At higher potentials, 1.0V or higher, Pt nanocubes and Pt-carbon nanoonions showed enhancements of up to 32% and 24%, respectively. At these higher potentials we will have a contribution of oxygen evolution. The changes in current behavior are attributed to the sizes of the catalyst materials and the time needed for the N2 bubbles detachment from the Pt surface under microgravity conditions.This work was financially supported by the NASA-MIRO Center for Advanced Nanoscale Materials at the University of Puerto Rico-Río Piedras Campus Grant number NNX10AQ17A and NASA-EPSCoR grant number NNX14AN18A, Puerto Rico NASA Space Grant Consortium: NASA cooperative agreement NNX10AM80H, NASA Flight Opportunities Program Announcement of Flight Opportunities (AFO) NOCT110 call #5 and Ministerio de Economía y Competitividad (projects CTQ2013-44083-P and CTQ2013-48280-C3-3-R)

Examining the Use of Nanocellulose Composites for the Sorption of Contaminants of Emerging Concern: An Experimental and Computational Study

The occurrence of contaminants of emerging concern (CECs) in water is an environmental issue that must be addressed to avoid damage to ecosystems and human health. Inspired by this current issue, in this work, we fabricated nanocellulose (NC) particles grafted with the block copolymer Jeffamine ED 600 (NC–Jeffamine) capable of adsorbing acetaminophen, sulfamethoxazole, and <i>N</i>,<i>N</i>-diethyl-<i>meta</i>-toluamide (DEET) from aqueous solution by electrostatic interactions. NC–Jeffamine composites were prepared by carboxylation of the NC surface via 2,2,6,6-tetramethyl-1-piperidinyloxy oxidation followed by the covalent attachment of Jeffamine using the <i>N</i>-(3-dimethylaminopropyl)-<i>N</i>′-ethylcarbodiimide/<i>N</i>-hydroxysulfosuccinimide sodium salt reaction. The reaction was followed and confirmed by Fourier transform infrared and conductometric titration. The physical characterization was performed by thermogravimetric analysis, Brunauer–Emmett–Teller analysis, scanning electron microscopy, dynamic light scattering, and Z-potential analysis. This material was used to study the adsorption profile of three CECs in deionized water, namely, acetaminophen, sulfamethoxazole, and DEET. The adsorption isotherms were obtained at pH 3, 7, and 9, where the best adsorption results corresponded to pH 9 because of the uniform dispersion of the adsorbate in solution. A computational study based on the density functional theory determined that the possible interactions of the CECs with the adsorbent material were related to hydrogen bonds and/or van der Waals forces. The calculated binding energies were used as a descriptor to characterize the optimum adsorption site of CECs onto NC–Jeffamine

Organic Nanoflowers from a Wide Variety of Molecules Templated by a Hierarchical Supramolecular Scaffold

Nanoflowers (NFs) are flowered-shaped particles with overall sizes or features in the nanoscale. Beyond their pleasing aesthetics, NFs have found a number of applications ranging from catalysis, to sensing, to drug delivery. Compared to inorganic based NFs, their organic and hybrid counterparts are relatively underdeveloped mostly because of the lack of a reliable and versatile method for their construction. We report here a method for constructing NFs from a wide variety of biologically relevant molecules (guests), ranging from small molecules, like doxorubicin, to biomacromolecules, like various proteins and plasmid DNA. The method relies on the encapsulation of the guests within a hierarchically structured particle made from supramolecular G-quadruplexes. The size and overall flexibility of the guests dictate the broad morphological features of the resulting NFs, specifically, small and rigid guests favor the formation of NFs with spiky petals, while large and/or flexible guests promote NFs with wide petals. The results from experiments using confocal fluorescence microscopy, and scanning electron microscopy provides the basis for the proposed mechanism for the NF formation

Photoelectrochemical Solar Cells Prepared From Nanoscale Zerovalent Iron Used for Aqueous Cd²⁺ Removal

Nanoscale zerovalent iron (nZVI) particles have been widely studied in the environmental sciences for wastewater treatment. These types of nanoparticles react in aqueous media producing metal oxides, which can be photoactive in the ultraviolet energy region. This prompted us to examine alternatives for the preparation of nanomaterials using nZVI in the presence of 6 and 30 ppm of Cd²⁺ in aqueous solutions. These Cd²⁺ concentrations are representative of contaminated regions of Puerto Rico such as the Las Cucharillas Marsh in Cataño. Comprehensive chemical and physical characterization of the resulting nZVI products after their exposure to Cd²⁺ was done. Further studies of the resulting nanostructures were completed using a photoelectrochemical solar cell (PSC) as the photoanode material. Incident photon-to-current efficiency (IPCE) and electrochemical impedance spectroscopy (EIS) analysis of these PSCs showed active photochemical properties in the ultraviolet range for the sample exposed to 30 ppm of Cd²⁺. Changes in the structure and chemical oxidation states of the species were observed in transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy analysis was attributed to these photochemical properties. These results show an alternative synthetic method for producing iron oxides for photocatalytic applications, and a possible strategy for reuse of nZVI after water remediation treatments

Assessing the Suitability of Cellulose-Nanodiamond Composite As a Multifunctional Biointerface Material for Bone Tissue Regeneration

Interfacial surface properties, both physical and chemical, are known to play a critical role in achieving long-term stability of cell–biomaterial interactions. Novel bone tissue engineering technologies, which provide a suitable interface between cells and biomaterials and mitigate aseptic osteolysis, are sought and can be developed via the incorporation of nanostructured materials. In this sense, engineered nanobased constructs provide an effective interface and suitable topography for direct interaction with cells, promoting faster osseointegration and anchoring. Therefore, herein we have investigated the surface functionalization, biocompatibility, and effect of cellulose-nanodiamond conjugates on osteoblast proliferation and differentiation. Cellulose nanocrystals (CNC) were aminated through a 3-aminopropyltriethyoxysilane (APTES) silylation, while nanodiamonds (ND) were treated with a strong acid oxidation reflux, as to produce carboxyl groups on the surface. Thereafter, the two products were covalently joined through an amide linkage, using a common bioconjugation reaction. Human fetal osteoblastic cells (hFOB) were seeded for 7 days to investigate the in vitro performance of the cellulose-nanodiamond conjugates. By employing immunocytochemistry, the bone matrix expression of osteocalcin (OC) and bone sialoprotein (BSP) was analyzed, demonstrating the viability and capacity of osteoblasts to proliferate and differentiate on the developed composite. These results suggest that cellulose-nanodiamond composites, which we call oxidized biocompatible interfacial nanocomposites (oBINC), have the potential to serve as a biointerface material for cell adhesion, proliferationand differentiation because of their osteoconductive properties and biocompatibility; furthermore, they show promising applications for bone tissue regeneration