Joshua R. Peterson

Highly efficient photochemical upconversion in a quasi-solid organogel

Despite the promise of photochemical upconversion as a means to extend the light-harvesting capabilities of a range of photovoltaic solar energy conversion devices, it remains a challenge to create efficient, solid-state upconverting materials. Until now, a material has yet to be found which is as efficient as a liquid composition. Here, a gelated photochemical upconversion material is reported with a performance indistinguishable from an otherwise identical liquid composition. The sensitizer phosphorescence lifetime, Stern–Volmer quenching constants and upconversion performance (6% under one-sun illumination) were all found to be unchanged in a quasi-solid gelated sample when compared to the liquid sample. The result paves the way to a new family of efficient photochemical upconversion materials comprised of macroscopically solid, but microscopically liquid gel, for application in photovoltaics and photocatalytic water-splitting.

Zwitterionic Phenyl Layers: Finally, Stable, Anti-Biofouling Coatings that Do Not Passivate Electrodes

Organic coatings on electrodes that limit biofouling by proteins but are of sufficiently low impedance to still allow Faradaic electrochemistry to proceed at the underlying electrode are described for the first time. These organic coatings formed using simple aryl diazonium salts present a zwitterionic surface and exhibit good electrochemical stability. The layers represent a low impedance alternative to the oligo (ethylene glycol) (OEG)-based anti-biofouling coatings and are expected to find applications in electrochemical biosensors and implantable electrodes. Two different zwitterionic layers grafted to glassy carbon surfaces are presented and compared to a number of better-known surfaces, including OEG-based phenyl-layer-grafted glassy carbon surfaces and OEG alkanethiol SAMs coated on gold, to allow the performance of these new layers to be compared to the body of work on other anti-biofouling surfaces. The results suggest that phenyl-based zwitterionic coatings are as effective as the OEG SAMs at resisting the nonspecific adsorption of bovine serum albumin and cytochrome c, as representative anionic and cationic proteins at physiological pH, whereas the impedance of the zwitterionic phenyl layers are two orders of magnitude lower than OEG SAMs.

Grafting of poly(ethylene glycol) on click chemistry modified Si(100) surfaces.

Poly(ethylene glycol) (PEG) is one of the most extensively studied antifouling coatings due to its ability to reduce protein adsorption and improve biocompatibility. Although the use of PEG for antifouling coatings is well established, the stability and density of PEG layers are often inadequate to provide optimum antifouling properties. To improve on these shortcomings, we employed the stepwise construction of PEG layers onto a silicon surface. Acetylene-terminated alkyl monolayers were attached to nonoxidized crystalline silicon surfaces via a one-step hydrosilylation procedure with 1,8-nonadiyne. The acetylene-terminated surfaces were functionalized via a copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction of the surface-bound alkynes with an azide to produce an amine terminated layer. The amine terminated layer was then further conjugated with PEG to produce an antifouling surface. The antifouling surface properties were investigated by testing adsorption of human serum albumin (HSA) and lysozyme (Lys) onto PEG layers from phosphate buffer solutions. Detailed characterization of protein fouling was carried out with X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) combined with principal component analysis (PCA). The results revealed no fouling of albumin onto PEG coatings whereas the smaller protein lysozyme adsorbed to a very low extent.

Photoinduced reduction of catalytically and biologically active Ru(II)bisterpyridine-cytochrome c bioconjugates.

Ruthenium(II)bisterpyridine chromophores were covalently linked to iso-1 cytochrome c from yeast to create light-activated donor-acceptor bioconjugates.

Self-assembled light-driven photosynthetic-respiratory electron transport chain hybrid proton pump

One of the fundamental biochemical reactions providing the foundation of life is photosynthesis occurring in plants and cyanobacteria. Photon energy is converted into stored chemical energy which flows through various metabolic processes that in the case of most aerobic organisms, terminates in the electron transport chain. In this study we demonstrate a synthetic hybrid photosynthetic-respiratory chain based on ruthenium(II)-terpyridine linked to cytochrome c and coupled with cytochrome c oxidase. Upon irradiation at an initial pH of 7.2, we observe proton pumping at a rate of ≈3.3 × 103 H+ per s across the polymer bilayer generating a gradient up to ΔpH ≈ 0.2. Remarkably, cytochrome c oxidase appears to have a greater than 50% native mitochondrial orientation in the polymersome membrane. Our photoactive hybrid electron-proton chain generates a proton gradient that can store chemical energy which is a step towards the development of a model artificial protocell.

The Bioconjugation of Redox Proteins to Novel Electrode Materials

The immobilization of redox proteins on electrode surfaces has been crucial for understanding the fundamentals of electron transfer in biological systems and has led to the development of biosensors and other bioelectronic devices. Novel materials, such as carbon nanotubes, gold and other metallic nanoparticles, carbon nanofibre and mesoporous materials have been widely used in the construction of these bioelectrodes, and have been shown to greatly improve the efficiency of electron transfer between the electrode and the redox centre of the protein. The use of these materials has spawned a diversity of covalent and non-covalent techniques for protein immobilization that offer different advantages and disadvantages to the performance of the bioelectrode. This review covers the important properties of these novel electrode materials relevant to the bioconjugation of proteins, and discusses the various methods of attachment from recent examples in the literature.

One-pot synthesis of high molecular weight synthetic heteroprotein dimers driven by charge complementarity electrostatic interactions.

Despite the importance of protein dimers and dimerization in biology, the formation of protein dimers through synthetic covalent chemistry has not found widespread use. In the case of maleimide-cysteine-based dimerization of proteins, we show here that when the proteins have the same charge, dimerization appears to be inherently difficult with yields around 1% or less, regardless of the nature of the spacer used or whether homo- or heteroprotein dimers are targeted. In contrast, if the proteins have opposing (complementary) charges, the formation of heteroprotein dimers proceeds much more readily, and in the case of one high molecular weight (>80 kDa) synthetic dimer between cytochrome c and bovine serum albumin, a 30% yield of the purified, isolated dimer was achieved. This represents at least a 30-fold increase in yield for protein dimers formed from proteins with complementary charges, compared to when the proteins have the same charge, under otherwise similar conditions. These results illustrate the role of ionic supramolecular interactions in controlling the reactivity of proteins toward bis-functionalized spacers. The strategy here for effective synthetic dimerization of proteins could be very useful for developing novel approaches to study the important role of protein-protein interactions in chemical biology.

Synthesis and Luminescence Properties of Iridium(III) Azide- and Triazole-Bisterpyridine Complexes

We describe here the synthesis of azide-functionalised iridium(III) bisterpyridines using the “chemistry on the complex” strategy. The resulting azide-complexes are then used in the copper(I)-catalysed azide-alkyne Huisgen 1,3-dipolar cycloaddition “click chemistry” reaction to from the corresponding triazole-functionalised iridium(III) bisterpyridines. The photophysical characteristics, including lifetimes, of these compounds were also investigated. Interestingly, oxygen appears to have very little effect on the lifetime of these complexes in aqueous solutions. Unexpectedly, sodium ascorbate acid appears to quench the luminescence of triazole-functionalised iridium(III) bisterpyridines, but this effect can be reversed by the addition of copper(II) sulfate, which is known to oxidize ascorbate under aerobic conditions. The results demonstrate that iridium(III) bisterpyridines can be functionalized for use in “click chemistry” facilitating the use of these photophysically interesting complexes in the modification of polymers or surfaces, to highlight just two possible applications.

Surface Epitope Coverage Affects Binding Characteristics of Bisphenol-A Functionalized Nanoparticles in a Competitive Inhibition Assay

The biomolecule interface is a key element in immunosensor fabrication, which can greatly influence the sensor performance. This paper explores the effects of surface epitope coverage of small molecule functionalized nanoparticle on the apparent affinity (avidity) of antibody in a competitive inhibition assay using bisphenol-A (BPA) as a model target. An unconventional two-antibody competitive inhibition ELISA (ci-ELISA) using thiolated BPA modified gold nanoparticles (cysBPAv-AuNP) as a competing reagent was devised for this study. It was shown that the antibody complexation with cysBPAv-AuNPs required a minimum number of surface epitopes on the nanoparticle to form a sufficiently strong interaction and reliable detection. The binding of cysBPAv-AuNP to anti-BPA antibodies, for limited antibody binding sites, was enhanced by a greater number of epitope-modified nanoparticles (cysBPAv-AuNP) as well as with higher epitope coverage. Increasing the molar concentration of epitope present in an assay enhanced the binding between anti-BPA antibodies and cysBPAv-AuNP. This implies that, to increase the limit of detection of a competitive inhibition assay, a reduced molar concentration of epitope should be applied. This could be achieved by either lowering the epitope coverage on each cysBPAv-AuNP or the assay molar concentration of cysBPAv-AuNP or both of these factors.

Demonstrating the Use of Bisphenol A-functionalised Gold Nanoparticles in Immunoassays

Spherical gold nanoparticles (5-nm diameter) were modified with a small-molecule thiolated bisphenol A (BPA) ligand to achieve an estimated coverage of ~3.3 × 10–10 mol cm–2, or 180 ligands per particle. The modified particles were tested in an enzyme-linked immunosorbent assay (ELISA) format to measure functionality and were shown to bind specifically to anti-BPA antibody while resisting the non-specific adsorption of an antibody with no affinity for BPA. It was found that the use of 10 % ethanol as a co-solvent was required in the ELISA as aqueous buffers alone resulted in poor binding between anti-BPA antibody and the functionalised nanoparticles. This is likely due to the hydrophobic nature of the BPA ligand limiting its solubility, and therefore its availability for antibody interactions, in purely aqueous environments. To our knowledge, this is the first example of a nanoparticle modified with a small organic molecule being used in an ELISA assay.