Nanoprobes used to extract photosynthetic electrons from algae cells

Photosynthesis is the very basic process in nature by which almost all plants convert solar energy into chemical energy. The process takes place in chloroplasts, the cellular powerhouses that are also responsible for the green color in leaves and algae. In the presence of visible light, carbon dioxide and water are transformed into glucose and oxygen during a complex series of chemical reactions. In nut shell, water is split into oxygen, protons and electrons. Sunlight penetrates the chloroplast and zaps the electrons to a high energy level, and a protein promptly grabs them. The electrons are passed down a series of proteins, which successively capture more and more of the electrons' energy to synthesize sugars until all the electrons' energy is spent.

Since ages, Human being have been extracting this energy for its own benefit through several means. The most common, simple, old but dirty way is by simply burning fossil fuels such as coal, natural gas and oil.

An intriguing novel approach has now been demonstrated by researchers at Stanford and Yonsei Universities. They have inserted ultrasharp gold nanoelectrodes (custom-made, AFM- compatible, nanoscale electrochemical probes that were shaped in the form of a flat, sharp needle with an aspect ratio of 10 and tip diameter of less than 30 nm) into living algae cells and extracted electrons, thereby harnessing an – albeit very tiny – electrical current. This is electricity production that doesn't release carbon into the atmosphere. The only byproducts of photosynthesis are protons and oxygen.

The ultrasharp nanoprobes associated with the system allowed for penetration of the cell or chloroplast membranes using relatively low force and without disrupting the integrity of the cell (the cell membrane seals around the hydrophobic insulating material of the electrode). The team, led by Fritz B. Prinz demonstrates the aerobic extraction of photosynthetic high-energy electrons, both with and without mediators, from the single-celled alga Chlamydomonas reinhardtii.This approach potentially reduces energy losses associated with the multistep transformation of solar energy into products used for the production of biodiesel and bioelectricity. In addition, the system allows direct monitoring of specific charge transfer reactions in live cells, leading to broad applications for investigating developmental processes and the responses of cells and organelles to light and chemical stimuli. Reference: Nano Lett., 2010, 10 (4), 1137–1143 Authors: WonHyoung Ryu, Seoung-Jai Bai, Joong Sun Park, Zubin Huang, Jeffrey Moseley, Tibor Fabian, Rainer J. Fasching, Arthur R. Grossman and Fritz B. Prinz.

Detection of ethanol by polymer-dye based chemiresistor sensor

The conductive blend of the poly (3,4-ethylene dioxythiophene) and polystyrene sulfonated acid (PEDOT-PSS) polymers doped with Methyl Red (MR) dye in the acid form were used as the basis for a chemiresistor sensor for detection of ethanol vapor.

This Au│Polymers-dye blend│Au device was manufactured by chemical vapor deposition and spin-coating, the first for deposition of the metal electrodes onto a glass substrate, and the second for preparation of the organic thin film forming ~1.0 mm² of active area. The electrical resistance dependence was found for ethanol vapor carried by nitrogen gas and in humidity,sensitivity at 1.15 for limit detection of 26.25 ppm analyte and an operating temperature of 25 °C. The sensing process is quickly reversible and shows very a low power consumption of 20 μW.

The thin film morphology of ~200 nm thickness was analyzed by Atomic Force Microscopy (AFM), where it was observed to have a peculiarly granulometric surface favorable to adsorption. This work indicates that PEDOT-PSS doped with MR dye to compose blend film shows good performance like resistive sensor.

Reference : Sensors 2010, 10(4), 2812-2820

Nanoparticle catalyst : two-phase catalysis and easy recovery

In the field of biofuel upgrade catalysis, it is highly desirable to have catalyst that can be easily recovered after the reaction is complete and which can stabilize emulsions.

Surfactant molecules have been widely used to increase the interfacial surface area and aid the transfer of molecules between the two phases. However, these surfactants can also be difficult to separate from the final product mixtures.Oxide nanoparticles have previously been used to stabilize oil-in-water emulsions because their hydrophilicity preferentially orients them toward the aqueous phase at the interface. Carbon nanotubes have also been shown to produce emulsions, but of the water-in-oil variety because they are hydrophobic. However, both the type of nanoparticles have application for only limited set of reactions.

Recently, a team of scientists at University of Oklahoma have develop a family of of solid catalysts that can stabilize water-oil emulsions and catalyze reactions at the liquid/liquid interface. By depositing palladium onto carbon nanotube–inorganic oxide hybrid nanoparticles, biphasic hydrodeoxygenation and condensation catalysis in three substrate classes of interest in biomass refining has been demonstrated. Microscopic characterization of the emulsions supports localization of the hybrid particles at the interface.

Ref: Science, Vol. 327, 5961, 68 - 72

Authors: Steven Crossley, Jimmy Faria, Min Shen, Daniel E. Resasco

Effective catalysis using supported Au25 cluster

It's been almost a decade since first report on successful catalysis by supported gold cluster came out. Since then, it has been a hot area of research and scientist are working hard to explore new strategies for catalysis using similar systems.

Recently, an interesting report published in Chem Commun. by Tsukuda and his coworkers wh talks about efficient and highly selective epoxidation of styrene by HAP (hydroxyapatite: Ca₁₀(PO₄)₆(OH)₂ ) supported Au25 cluster using TBHP as oxidant. Synthesis of supported Au25 on HAP involves deposition of Au₂₅ clusters protected by 18 glutathionate (GS) ligands, Au₂₅(SG)₁₈, on an HAP support and then calcine the composite to remove the GS ligands.

It is expected that Au₂₅(SG)₁₈ get adsorbed on HAP by electrostatic interaction between Ca²⁺/PO₄³⁻ moieties and the GS ligands, and that HAP could stabilize bare Au₂₅ clusters against sintering due to strong interaction with the PO₄^3– moiety.

High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) is used to confirm the size and distribution of resulting Au clusters. Further, TG analysis is used to confirm the loss of thiol group from the surface after calcination at 300 degree C in vaccum.
Oxidation of styrene in toluene at 80 °C using anhydrous TBHP as an oxidant yielded styrene oxide as a major product in every case ( slectivity almost 100%) when Au25 support on HAP system is used as catalyst. Catayst also show excellent reusability without any significant loss in either the catalytic activity or the selectivity.

Reference : Chem. Commun., 2010, 46, 550 - 552

A Novel approach for phase-tranfer of metal ions and its applications in nanoparticle synthesis

One of the crucial step preceding the synthesis of nanoparticles is the phase transfer of metal salts from water to an organic medium. Metal ions could not be transferred to the organic phase by direct mixing of an aqueous metal salt solution with an organic solvent. The most well-known approach is the use of long chain ammonium salt like tetraoctylammonium bromide (TOAB) to tranfer metal ions from aqueous phase to organic phase. The phase tranfer approach suggested in a recent research article in Nature Materials, involves mixing the aqueous solution of metal ions with an ethanolic solution of dodecylamine (DDA), and extracting the coordinating compounds formed between the metal ions and DDA into toluene. It has several advantages:

(a) good ion uptake by the complexing agent, enabling fast binding with the metal ion, (b) high stability against hydrolysis, (c) selective ion complexation of heavy metals, along with no affinity for alkali or alkaline earth ions that are usually present in high concentrations in water and soil, (d) sufficiently high binding strength for the metal ions to be extracted and (e) preference of the metal complex derived for the organic phase over the aqueous phase, which would be of interest for applications in environmental remediation, such as the extraction of heavy metals from water and soil.

Figure on the right :TEM images of metal nanoparticles. (1) Ag derived with HDD, (2) Au, (3) worm-like Pd and (4) Pt from Pt(IV), derived with TBAB. Alloy nanoparticles of (5) Ag–Au, (6) Pd–Pt, (7) Pt–Rh and (8) Pt–Ru, synthesized by co-reduction of the metal precursors with TBAB. Core–shell nanoparticles of (9) 7.4nm Au@Ag, (10) 12.7nm Au@Ag, (11) 3.9nm Pt@Ag and (12) 9.2nm Pt@Ag, synthesized by seed-mediated growth. Core–shell nanoparticles of (13) Ag@Au and (14) Ag@Pt, synthesized by the replacement reaction. (15) Pt hollow spheres synthesized by BSPP treatment of Ag@Pt nanoparticles. (16) Ag–Pd alloy synthesized by the replacement reaction. Semiconductor nanocrystals of (17) Ag2S, (18) CdS, (19) HgS and (20) PbS. Hybrid nanoparticles of (21) Ag2S–Au, (22) CdS–Au, (23) CuS–Au, (24) PbS–Au, (25) Ag2S–Ag, (26) CdS–Ag, (27) CuS–Ag and (28) PbS–Ag. Core–shell nanoparticles of Au@Ag2S synthesized with Au/Ag2S precursor molar ratios of (29) 1:1 and (30) 1:3.

Ref: Nature Materials 8, 683 - 689 (2009)

Authors: Jun Yang, Edward Sargent, Shana Kelley& Jackie Y. Ying

Improved sensing and catalytic properties of Tungsten oxide nanorods using Gold nanoparticles

In present world, with industrial and scientific developments, the effective detection of toxic and hazardous gases, as well as the degradation of organic pollutants has become imperative. Among other materials, tungsten oxide has attracted greater attentions for its distinctive photocatalytic and electrochromic properties. Many attempts have been made to enhance the gas sensitivity of semiconductor gas sensors, one of which involved the doping of dopants in the films.Also, the photocatalytic properties are usually known to improve by functionalizing the material with catalytical active metals (Pt, Pd and Au). Present protocols for synthesizing such materials often require high temperature and induce impurities in the final products when catalysts and templates are introduced into the reaction system, further limiting their application field.

In a current study carried out in China, a self-assembly approach for building nanoarchitectures with WO₃ nanorods (WO₃ NRs) and Au nanoparticles (Au NPs) as building blocks and further fabricating chemical sensors with highly enhanced performances has been reported. It is generally considered that monodispersed Au NPs act as a catalyst not only in the gas response but also in the photocatalytic activity.

Compared with pure WO₃NRs, Au NP@WO₃ NRs exhibit not only highly improved response and selectivity for H₂ gas detection but also high photocatalytic activity for the degradation of rhodamine B(RhB) under irradiation of simulated sunlight.

For further details, please read : J. Phys. Chem. C, Article ASAP

Authors: Q. Xiang, G. F. Meng, H. B. Zhao, Y. Zhang, H. Li, W. J. Ma and J. Q. Xu

Multifunctional thin film assemblies of molecularly-linked metal nanoparticles

Ability to tune the size, shape, and composition at the nano-particles has led to the growth of extensive research in the area of novel multifunctional materials. The ability to engineer the interparticle properties for fabricating nanoparticle assemblies in macroscopic scales is also very important from the perspective of exploiting the collective properties of the nanopoarticle assemblies as multifunctional materials for practical applications that involve surface or interfacial processes.

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The exploration of nanoparticle-structured molecular recognition is an important front in many emerging chemical and biological sensor technologies. The viability of introducing noncovalent character (e.g., hydrogen bonding) through shell molecules provides tunable molecular interactions for enhancing selectivity, which parallels synthetic or biological receptors.Through investigation of these nano-particle assemblies implies that both non-covalent and covalent interactions are important for manipulating the interparticle properties in the multifunctional nanostructures. The noncovalent interparticle interactions are useful for regulating molecular recognition and sensing properties, whereas the covalent interactions facilitate the assembly of stable interfacial nanostructures.

The viability of the one-step molecularly mediated assemblies also open technological prospects to combine the nanostructure-tuning capabilities with the electrical, optical, magnetic, and spectroscopic properties for designing chemical sensors, biosensors, and medical probes. Implications of insights to expanding the exploration of nanoparticle thin film assemblies for a wide range of technological applications has been discussed in details in a recent article in Langmuir.

Ref: Langmuir, 2010, 26 (2), pp 618–632

Authors: Lingyan Wang, Jin Luo, Mark J. Schadt and Chuan-Jian Zhong