Nano-Engineering of Molecular Films by Self-Assembly and Langmuir-Blodgett Techniques

The availability of sophisticated and ultra-sensitive analytical tools and the maturity of organic synthesis have opened new possibilities for fabrication of molecular materials designed at the nanometer scale. Presently, the most promising and widely investigated methodologies are the self-assembly and Langmuir-Blodgett procedures. The former relies on the strong, preferential affinity of specific functional groups to solid surfaces, whereas the latter involves transfer of pre-formed mono layers at the air-water interface onto solid substrates. These techniques and their recent applications are reviewed

Nano-chemistry

Nanotechnology is a highly interdisciplinary field, with contributions from all fields: physics, chemistry, biology, materials science, engineering, and others. The explosive number of publications in this field makes it nearly impossible to give an extensive review even in chemistry alone. Nonetheless, one may track its emergence and rapid advancement from the point of view of a chemist\u27s. This paper aims to provide a conceptual overview of chemistry for nanotechnology, a brief classification of different approaches and applications, together with some sample cases

a-Helical polypeptide monolayers

In efforts to utilize the a-helical structural motif as a basic building block in the formation of supramolecular assemblies, a study of the self-assembly of a-helical poly(glutamate)s from dilute solution onto a solid support was initiated. In particular, poly(y-benzyl-L-glutamate) [PBLG], which has an unusually robust a-helical conformation, was functionalized at the amino terminus with a disulfide-containing moiety (lipoic acid), which in turn has a specific and strong chemisorptive interaction with gold surfaces. The same end group functionalization was used with the /i-alkyl side chain analogs of PBLG. The resulting self-assembled monolayers were characterized by grazing angle reflection infrared (GIR-IR) spectroscopy, angle dependent X-ray photoelectron spectroscopy, ellipsometry, atomic force microscopy, and wettability measurements. The self-assembled films were also compared with control monolayers prepared by the Langmuir-Blodgett deposition technique. It was found that the chemisorptive end group effectively changes the manner of adsorption from dilute solutions of low molecular weight lipoic-acid labelled PBLG [PBLGSS] compared with the non-functionalized PBLG of the same MW. This difference was especially reflected in the average orientation of the helices in the monolayer formed on gold: for the self-assembled PBLGSS monolayer, the average orientation of the helix axis appears to be random; in physisorbed PBLG, the helices lie in the plane of the gold surface. For higher MW polypeptides, the effect of the chemisorptive end group is significanly diminished and the polypeptides lie in the plane of the gold surface regardless of the disulfide functionality. This was explained in terms of the enhancement in the aggregate strength of the side chain-gold interaction as the MW is increased. For the poly(alkylglutamate)s, PCnLG, the chemisorptive end group did not appear to influence the orientation of the helices on gold; rather, the length of the side chains had a marked effect on the self-assembly process. The low stability of the a-helical conformation in the low MW PClgLG, coupled with the propensity for the side chains to crystallize, resulted in denaturation of the polypeptide on adsorption to gold—the (3-form was observed in the adsorbed films on gold. The high MW PC18LG adsorbs on gold with the a-helix mainly intact (with occasional p-form component or fraction) and the polymers lie in the plane of the substrate surface due mainly to the length of the backbone. The physisorbed and self-assembled films of polypeptides with n = 6 and 12 also show a parallel orientation of the helices on gold; again attributed to the high MW of these polymers

Composition ot Glvceride Esters of Lauric Acid bV FTIR Band Shape Analysis

Synthesis of glyceride esters of a fatty acid produces a mixture of isomers that are difficult to separate and analyze, requiring high temperature GC in most cases particularly for long-chain esters. In this paper, we present a fast estimation of the composition of the glyceride esters of lauric acid and glycerol (monolaurin, dilaurin, and trilaurin) by FTIR band shape analysis. The method uses the fact that the carbonyl stretching regions of the pure glycerides have differentband shapes, which implies any composite band of a mixture of glycerides may be resolved into the component peaks due to each glyceride. The carbonyl band region was fitted with five component peaks using a commercial peak-fitting program. The peak at 1745 cm-1 is characteristic of trilaurin whereas the peaks at 1740 cm-1 and 1731 cm-1 provide a unique height ratio for mono- and dilaurin. Calibration curves were prepared and a system of two equations may be solved to obtain the composition of mono-, di-, and trilaurin. This method was tested with known mixtures of the glycerides yielding estimates within ± 10 % composition units

Opacity of P(MMA-MAA)-PMMA Composite Latex System with Varying MAA Concentration

Polymer composites of core-shell morphology are commonly used in the paint industry as opacity enhancer. These are usually made of block copolymer systems wherein the core is formed from a polymer that swells in the presence of a solvent and surrounded by a high glass transition polymeric shell. Thus, upon drying, the swollen regions turn into voids while leaving a hard shell. Here, composites based on poly(methyl methacrylate-butyl acrylate) [P(MMA-BuA)] (seed stage), poly(methyl methacrylate-methacrylic acid) [P(MMA-MAA)] (second stage), and poly(methyl methacrylate) [PMMA] (third stage) were synthesized through a multistage sequential emulsion polymerization and their opacity was investigated. The second stage formulation of P(MMA-MAA) system was varied by changing the methyl methacrylate (MMA): methacrylic acid (MAA) mole composition, and the dried films of these composite latexes were characterized by infrared spectroscopy (IR), differential scanning calorimetry (DSC), and atomic force microscopy (AFM). The AFM images and ammonium hydroxide (NH4 OH) swelling studies confirmed the successful incorporation of the seed (first) stage with the second and third stage polymerization with PMMA. The differences in PMAA concentrations among the second stage polymer compositions were determined from the IR spectra and glass transition temperature (Tg ) data. Investigations on the opacity and hiding power of these polymer composites were done using optical densitometry. The results show increasing absorbance, indicating increasing opacity, with increasing polymethacrylic acid (PMAA) concentration in the second stage composition

Fabrication of a 3D Printed Porous Junction for Ag|AgCl|gel-KCl Reference Electrode

Fused filament fabrication (FFF) is a 3D printing method that is attracting increased interest in the development of miniaturized electrochemical sensor systems due to its versatility, low cost, reproducibility, and capability for rapid prototyping. A key component of miniaturized electrochemical systems is the reference electrode (RE). However, reports of the fabrication of a true 3D-printed RE that exhibits stability to variations in the sample matrix remain limited. In this work, we report the development and characterization of a 3D-printed Ag|AgCl|gel-KCl reference electrode (3D-RE). The RE was constructed using a Ag|AgCl wire and agar-KCl layer housed in a watertight 3D-printed acrylonitrile butadiene styrene (ABS) casing. The novel feature of our electrode is a 3D-printed porous junction that protects the gel electrolyte layer from chloride ion leakage and test sample contamination while maintaining electrical contact with the sample solution. By tuning the 3D printing filament extrusion ratio (k), the porosity of the junction was adjusted to balance the reference electrode potential stability and impedance. The resulting 3D-RE demonstrated a stable potential, with a potential drift of 4.55 ± 0.46 mV over a 12-h period of continuous immersion in 0.1 M KCl, and a low impedance of 0.50 ± 0.11 kΩ. The 3D-RE was also insensitive to variations in the sample matrix and maintained a stable potential for at least 30 days under proper storage in 3 M KCl. We demonstrate the application of this 3D-RE in cyclic voltammetry and in pH sensing coupled with electrodeposited iridium oxide on a gold electrode. Our method offers a viable strategy for 3D printing a customizable true reference electrode that can be readily fabricated on demand and integrated into 3D-printed miniaturized electrochemical sensor systems

Iota-carrageenan hydrolysis by Pseudoalteromonas carrageenovora IFO12985

We report iota-carrageenan hydrolysis by Pseudoalteromonas carrageenovora IFO 12985. Kappa-carrageenase and lambda-carrageenase were previously isolated from this organism, but iota-carrageenase activity had not been reported in the literature. P. carrageenovora was grown in iota-carrageenan-based liquid medium. Using the zone of depression assay, transfer of aliquots of the culture to solid medium with 2% iota- and kappa-carrageenan showed extensive hydrolysis of iota-carrageenan. Analysis of the hydrolysates by C-13 Nuclear Magnetic Resonance spectroscopy confirmed degradation of the iota-carrageenan. Hydrolytic activity of P. carrageenovora grown in iota-carrageenan was compared with that of the same organism grown in kappa-carrageenan. Cell-free supernatants from each yielded subtle differences in hydrolytic profiles, but showed degradation patterns consistent with hydrolysis to fragments smaller than 1.4 kDa, corresponding to six or fewer monosaccharide units. Different protein expression bands on SDS-PAGE were also observed for the cell-free supernatants of P. carrageenovora grown in iota- versus kappa-carrageenan, with lower kappa-carrageenase expression observed in the organism grown in iota-carrageenan

Nucleic-Acid Based Lateral Flow Strip Biosensor via Competitive Binding for Possible Dengue Detection

A low-cost, simple, rapid and selective nucleic-acid based lateral flow strip biosensor (LFSB) for possible dengue viral RNA detection is described in this study. The detection is based on competitive binding, where gold nanoparticles (AuNPs), with average size of ~10 nm confirmed using UV-Vis, TEM and AFM images, are used as visualizing agents. These are bioconjugated with DNA which competitively binds with its complementary strand either in the sample or in the test line of the LFSB. The detection scheme reduces the number of probes which effectively lowers the cost for the design of the test strip. The whole test took less than five minutes to complete and a red line signifies a negative result, while the absence of the line signifies a positive result. Quantification of the intensity of the red band reveals proportionality of the color to the amount of DNA present in the sample. The visual limit of detection of the LFSB is 10-7 M. It demonstrates selectivity in a blood matrix and selectivity over a synthetic Influenza. This study brings us closer to an amplification-free, point-of-care method for dengue detection

Polyaniline In Situ Grafted to Graphene Sheets

Graphene is one of the most promising allotropes of carbon with wide applications in nanotechnology. Modification of graphene by chemical means can further expand its uses. Here, liquid-exfoliated graphene is functionalized with p-aminophenyl moiety using p-nitrophenyl diazonium salts which were diazotized in situ then reduced by tin(II) chloride. The aminophenyl-graphene thus produced is further modified to form polyaniline-graphene (PANI-GNH) by in situ oxidative graft polymerization of aniline using ammonium peroxydisulfate as oxidizing agent. The properties of the PANI-GNH were compared with polyaniline/graphene blends by Raman, infrared and UV-Visible spectroscopy, and cyclic voltammetry. Indeed, PANI-GNH registered different spectrochemical and electrochemical properties compared with the physically blended PANI and GNH, a manifestation of the effect of chemical grafting on the overall property of the modified graphene

Assessment of Quantity and Quality of Microplastics in the Sediments, Waters, Oysters, and Selected Fish Species in Key Sites Along the Bombong Estuary and the Coastal Waters of Ticalan in San Juan, Batangas

Microplastics (or MPs; \u3c 5 mm in size) pollution is largely unstudied in the Philippines. From an environmental sustainability standpoint, it is important to understand the characteristics, abundance, and environmental fate of plastic debris of various sizes, and these include microplastics that are not more easily and readily detected. In this study, we assessed the extent of microplastics contamination in the sediments, waters, oysters, and selected fishes found in the rivers and coastal areas of Ticalan, Batangas, which were identified from water quality parameters as Class C and CS, respectively. The microplastics were extracted from these samples by chemical digestion of the matrix, series of filtration, and separation by flotation through a density gradient to finally isolate the microplastics which were not dissolved by chemical digestion. The isolated samples were imaged by optical microscopy and characterized based on their descriptive attributes. The results showed the presence of microplastics in all the samples tested, which were found mostly in the form of filaments, fragments, films, and pellets – with most showing weathered, degraded, or angular and irregular surfaces. Identification was done through spectral matching of the Fourier transform infrared spectra of isolated fragments with that of known plastics, although identification in some cases is made uncertain by possibility of degradation of the plastics in the environment. The majority of the isolates showed signature absorption bands of the C-H stretching vibrations of polyethylene-based plastics