Biological surface science

Biological surface science (BioSS), as defined here is the broad interdisciplinary area where properties and processes at interfaces between synthetic materials and biological environments are investigated and biofunctional surfaces are fabricated. Six examples are used to introduce and discuss the subject: Medical implants in the human body, biosensors and biochips for diagnostics, tissue engineering, bioelectronics, artificial photosynthesis, and biomimetic materials. They are areas of varying maturity, together constituting a strong driving force for the current rapid development of BioSS. The second driving force is the purely scientific challenges and opportunities to explore the mutual interaction between biological components and surfaces.

Model systems range from the unique water structures at solid surfaces and water shells around proteins and biomembranes, via amino and nucleic acids, proteins, DNA, phospholipid membranes, to cells and living tissue at surfaces. At one end of the spectrum the scientific challenge is to map out the structures, bonding, dynamics and kinetics of biomolecules at surfaces in a similar way as has been done for simple molecules during the past three decades in surface science. At the other end of the complexity spectrum one addresses how biofunctional surfaces participate in and can be designed to constructively participate in the total communication system of cells and tissue.

Biofunctional surfaces call for advanced design and preparation in order to match the sophisticated (bio) recognition ability of biological systems. Specifically this requires combined topographic, chemical and visco-elastic patterns on surfaces to match proteins at the nm scale and cells at the micrometer scale. Essentially all methods of surface science are useful. High-resolution (e.g. scanning probe) microscopies, spatially resolved and high sensitivity, non-invasive optical spectroscopies, self-organizing monolayers, and nano- and microfabrication are important for BioSS. However, there is also a need to adopt or develop new methods for studies of biointerfaces in the native, liquid state.

For the future it is likely that BioSS will have an even broader definition than above and include native interfaces, and that combinations of molecular (cell) biology and BioSS will contribute to the understanding of the “living state”.     

Computation with DNA on surfaces

DNA computation has the potential to tackle computationally difficult problems that have real-world implications. The parallel search capabilities of DNA make it a valuable tool to approach problems that have a large number of possible solutions, for which conventional computers have limited potential. Surface science can play a significant role in harnessing the parallel nature of DNA for computation. This article briefly reviews conventional computing architecture, discusses DNA computation, and describes the role of surface science in DNA computation.     

Molecular secondary ion emission from adenine overlayers in dependence on the primary ion species and substrate material

The influence of the primary ion species (He⁺, Ne⁺, Ar⁺, Kr⁺, Xe⁺ and SF₅⁺) and substrate material (graphite, Al, Cu, Ag and Pb) on the secondary ion emission from molecular overlayers of the purine base adenine was investigated in dependence on the layer thickness. The measurements showed an increasing yield with increasing mass of the primary ions and its number of constituents. The yield enhancement, defined as the ratio between the maximum yield obtained from approximately a monolayer coverage of adenine to the yield obtained from a multilayer coverage, was shown to depend on the substrate material. However, a clear dependence on the primary ion species was not found.     

RAIRS investigations on the orientation and intermolecular interactions of adenine on Cu(1 1 0)

The adsorption of the DNA base adenine (C₅N₅H₅) on Cu(1 1 0) has been investigated as a function of coverage and temperature using reflection absorption infrared spectroscopy. These data provide important information on the nature of the local adsorbed complex and the intermolecular lateral interactions that come into play at high coverages. The RAIR spectra are consistent with an adsorption geometry in which the molecular ring is substantially tilted from the surface plane and in which the two amino hydrogens are equidistant from the surface, thus rationalising the appearance of a very strong βNH₂ scissoring mode, along with the activity of in-plane vibrational modes and the observation of the symmetric ν_symNH₂ stretch, but not the asymmetric ν_asymNH₂ stretch. In addition, coordination to the metal surface is proposed to occur at the N(9) position with a possible additional interaction through the N(3) position, both of which are the favoured coordination points in the metal complexes of adenine. This is a strong interaction and leads to a highly stable adsorbed layer. Our data also provide the first direct evidence of hydrogen bonding in the adlayer as coverage is increased, attributed to interactions between the amino group of one molecule and the N(1) and N(7) positions of a neighbouring species. When adsorption is carried out at room temperature, a very heterogeneous adlayer is created in which a diversity of molecular aggregates co-exist. However, upon annealing, a more ordered hydrogen bonded adlayer is formed in which one type of hydrogen bonding assembly is preferred. Finally, we propose that the hydrogen bonded assemblies created at a surface probably involve bent hydrogen bonds which arise from a compromise between the strong molecule-metal interactions that orientate the molecule and weaker lateral hydrogen bonding interactions that dictate the two-dimensional architecture.     

The surface science of enzymes

One of the largest challenges to science in the coming years is to find the relation between enzyme structure and function. Can we predict which reactions an enzyme catalyzes from knowledge of its structure—or from its amino acid sequence? Can we use that knowledge to modify enzyme function? To solve these problems we must understand in some detail how enzymes interact with reactants from its surroundings. These interactions take place at the surface of the enzyme and the question of enzyme function can be viewed as the surface science of enzymes. In this article we discuss how to describe catalysis by enzymes, and in particular the analogies between enzyme catalyzed reactions and surface catalyzed reactions. We do this by discussing two concrete examples of reactions catalyzed both in nature (by enzymes) and in industrial reactors (by inorganic materials), and show that although analogies exist and the two kinds of catalyst can be described by similar tools, nature and human effort have come up with different solutions. This on the other hand implies that new and improved catalysts may be made by learning from nature.     

Scanning probe microscopy characterization of gold-chemisorbed poplar plastocyanin mutants

Two poplar plastocyanin mutants adsorbed onto gold electrodes have been characterized at single molecule level by scanning probe microscopy. Immobilization of the two redox metalloprotein mutants on Au(1 1 1) surface was achieved by either a disulphide bridge (PCSS) or a single thiol (PCSH), both the anchoring groups having been introduced by site-directed mutagenesis. Scanning tunneling microscopy (STM) and atomic force microscopy (AFM) analysis gives evidence of a stable and robust binding of both mutants to gold. The lateral dimensions, as estimated by STM, and the height above the gold substrate, as evaluated by AFM, of the two mutants well agree with crystallographic sizes. A narrower height distribution is observed for PCSS compared to PCSH, corresponding to a more homogeneous orientation of the former mutant adsorbed onto gold. Major differences between the mutants are observed by electrochemical STM. In particular, the image contrast of adsorbed PCSS is affected by tuning the external electrochemical potential to the redox levels of the mutant, consistent with some involvement of copper active site in the tunneling process. On the contrary, no contrast variation is observed in electrochemical STM of adsorbed PCSH. Moreover, scanning tunneling spectroscopy experiments reveal asymmetric I–V characteristics for single PCSS proteins, reminiscent of a rectifying-like behaviour, whereas an almost symmetric I–V relation is observed for PCSH.     

Surface characteristics of self-assembled microporous Ti-6Al-4V compacts fabricated by electro-discharge-sintering in air

A single electro-discharge-sintering (EDS) pulse (1.0 kJ/0.7 g), from a 300 (F capacitor, was applied to atomized spherical Ti-6Al-4V powder in air to produce microporous compact. A solid core surrounded by a porous layer was self-assembled by a discharge in the middle of the compact. X-ray photoelectron spectroscopy was used to study the surface characteristics of the compact material. C, N, O and Ti were the main constituents, with smaller amounts of Al and V. The surface was lightly oxidized and was primarily in the form of TiO₂. A lightly etched EDS sample showed the surface form of metallic Ti, indicating that EDS breaks down the oxide film of the as-received Ti-6Al-4V powder during the discharge process. The EDS Ti-6Al-4V compact surface also contained small amounts of TiN in addition to TiO₂, resulting in the reaction between nitrogen in air and the Ti substrate in times as short as 125 μs.     

Domain state model for exchange bias: thickness dependence of diluted antiferromagnetic Co1−yO on exchange bias in Co/CoO

The thickness dependence of different diluted antiferromagnetic Co_1−yO layers on the exchange bias (EB) in ferro/antiferromagnetic Co/Co_1−yO bilayers is investigated. For undiluted samples the EB decreases above a layer thickness of 5 nm whereas it increases and saturates for AFM layers thicker than 20 nm for diluted samples. These findings support the domain state model for EB.     

In situ observations by magnetic resonance imaging for formation and dissociation of tetrahydrofuran hydrate in porous media

Tetrahydrofuran (THF) hydrate has long been used as a substitute for methane hydrate in laboratory studies. This article investigated the formation and dissociation characteristics of THF hydrate in porous media simulated by various-sized quartz glass beads. The formation and dissociation processes of THF hydrate are observed using magnetic resonance imaging (MRI) technology. The hydrate saturation during the formation is obtained based on the MRI data. The experimental result suggests that the third surface has an effect on hydrate formation. THF hydrate crystals lean to form on the glass beads and in their adjacent area as well as from the wall of the sample container firstly. Furthermore, as the pore size diminishes, or as the formation temperature decreases, the nucleation gets easier and the formation processes faster. However, the dissociation rate is mostly dependent on the dissociation temperature rather than on the pore size.     

Facile synthesis of low-dimensional SnO2 nanostructures: An investigation of their performance and mechanism of action as anode materials for lithium-ion batteries

Owing to high-energy density of rechargeable lithium-ion batteries (LIBs), they have been investigated as an efficient electrochemical power sources for various energy applications. High theoretical capacities of tin oxide (SnO₂) anodes have led us a path to meet the ever-growing demands in the development of high-performance electrode materials for LIBs. In this paper, a facile approach is described for the synthesis of porous low-dimensional nanoparticles and nanorods of SnO₂ for application in LIBs with the help of Tween-80 as a surfactant. The SnO₂ samples synthesized at different reaction temperatures produced porous nanoparticles and nanorods with average diameters of ~7–10 nm and ~70–110 nm, respectively. The SnO₂ nanoparticle electrodes exhibit a high reversible charge capacity of 641.1 mAh/g at 200 mA/g after 50 cycles, and a capacity of 340 mAh/g even at a high current density of 1000 mA/g during the rate tests, whereas the porous nanorod electrodes delivers only 526.3 mAh/g at 200 mA/g after 50 cycles and 309.4 mAh/g at 1000 mA/g. It is believed that finer sized SnO₂ nanoparticles are much more favorable to trap more Li⁺ ion during electrochemical cycling, resulting in a large irreversible capacity. In contrast, rapid capacity fading was observed for the porous nanorods, which is the result of their pulverization resulting from repeated cycling.     

Sonochemical synthesis and structural characterization of a new nanostructured Co(II) supramolecular coordination polymer with Lewis base sites as a new catalyst for Knoevenagel condensation

A new Co(II) mixed-ligand coordination supramolecular polymer with composition [Co₂(ppda)(4-bpdh)₂(NO₃)₂]_n (1) (where, ppda = p-phenylenediacrylic acid, 4-bpdh = 2,5-bis(4-pyridyl)-3,4-diaza-2,4-hexadiene) was synthesized using solvothermal, mechanochemical and sonochemical methods. Compound 1 and the new nanostructure have been characterized by single-crystal X-ray, infrared spectroscopy (IR), powder X-ray diffraction (PXRD) analysis and scanning electron microscopy (SEM). The thermal stability of compound 1 was also studied by thermal gravimetric analysis (TGA). The surface area of these compounds was determined by BET. The single-crystal X-ray data shows a new interesting two-dimensional coordination polymer (CP). In addition, the effect of various sonication concentrations of initial reagents, power of ultrasound irradiation and also the time on the size and morphology of nano-structured coordination polymer 1 were evaluated. Moreover, it has been demonstrated that the nanostructure of the CP1 can be used as a catalyst in Knoevenagel condensation reaction.     

New planar substrates for the in situ synthesis of peptide arrays

The performance of new cellulose membranes, aminofunctionalized via a PEG spacer, as a solid support in the synthesis of peptide arrays is described. The new membranes are stable to trifluoroacetic acid (TFA) and strong aqueous base for days. These properties extend the scope of synthesis considerably, e.g., more efficient side chain cleavage protocols can be applied which yielded peptides of improved purity. For the first time, cellulose membranes with a loading as high as 5 micromol/cm2 were accessible. Additionally, newly developed polypropylene membranes with hydroxy- or amino functionalities were successfully employed for the SPOT synthesis of peptides and phosphopeptides. The membranes are compatible with antibody binding as well as enzymatic phosphorylation assays.     

飞秒激光直写生物凝胶模板原位合成纳米粒子

为了制备具有可控复杂形状和特定化学性质的聚合物微结构,提出了一种飞秒激光直写生物凝胶模板原位合成纳米粒子的方法。首先,采用飞秒激光直写技术加工带有COOH基团的复杂三维结构的生物凝胶模板,用氢氧化钠处理使COOH基团离子化为COO^-基团;然后,用金属盐溶液处理,使金属离子与COO^-基团螯合,形成纳米粒子结晶核。通过多次循环盐溶液处理步骤,控制模板中纳米粒子的粒径与含量。实验结果表明：所制备的生物凝胶模板具有亚100 nm分辨率和10 μm量级尺寸,纳米粒子含量高达9%。该法简单高效,具有很好的应用前景。     

Facile in situ hydrothermal synthesis of BiVO4/MWCNT nanocomposites as high performance visible-light driven photocatalysts

Visible-light responsive monoclinic BiVO₄/MWCNT nanocomposites were facilely prepared via an in situ hydrothermal method by using sodium dodecyl sulfonate (SDS) as a guiding surfactant. The as-prepared BiVO₄/MWCNT nanocomposites were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman spectroscopy, field emission scanning electron microscopy (FE-SEM), the Fourier transform infrared spectroscopy (FTIR) and UV–vis diffuse reflectance spectroscopy. The results showed that the hydrothermal temperature and adding SDS had significant influence on the morphology and size of BiVO₄. The photocatalytic activities of BiVO₄/MWCNT nanocomposites were investigated by degrading methylene blue (MB) under visible-light irradiation. Remarkable enhancement in photodecomposition of MB was observed with BiVO₄/MWCNT composite compared with bare BiVO₄ particles. This improvement of photocatalytic was attributed to the effective charge transfer from BiVO₄ nanocrystals to MWCNT, which promoted the migration efficiency of photogenerated electron–hole. Furthermore, a possible mechanism for the photocatalytic oxidative degradation was also discussed.     

Porous silicon with β-cyclodextrin modified surface for photoluminescence sensing of organic molecules in gas and liquid phase

Porous silicon surface was modified by photochemically activated hydrosilylation reaction with permethyl-6^I-alkenoylamino-6^I-deoxy-β-cyclodextrins terminated with linear alkenoyl spacers of various lengths. As compared to unmodified surface, derivatized surfaces revealed modified photoluminescence response in the presence of controlled amounts of various organic molecules in gas and liquid phase. For the selected set of analytes we observed most significant modification of photoluminescence response for aromatic compounds what corresponds to optimum molecular size for strong host–guest interaction with β-cyclodextrin cavity. Aliphatic compounds quenched photoluminescence from both unmodified and surface modified porous silicon. For low gas phase concentrations of aromatic analytes β-cyclodextrin modified porous silicon revealed photoluminescence enhancement, at higher concentrations common photoluminescence quenching was observed. The size-dependent host–guest interaction between β-cyclodextrin cavity and detected molecule was observed in photoluminescence quenching in the presence of aliphatic molecules in liquid phase. The role of the strength of host–guest interactions between detected analytes and β-cyclodextrin cavity on photoluminescence sensor response is discussed.     

A sonochemical synthesis of SrTiO3 supported N-doped graphene oxide as a highly efficient electrocatalyst for electrochemical reduction of a chemotherapeutic drug

A sonochemical based green synthesis method playa powerful role in nanomaterials and composite development. In this work, we developed a perovskite type of strontium titanate via sonochemical process. SrTiO₃ particles were incorporated with nitrogen doped graphene oxide through simple ultrasonic irradiation method. The SrTiO₃/NGO was characterized by various analytical methods. The nanocomposite of SrTiO₃/NGO was modified with laser-induced graphene electrode (LIGE). The SrTiO₃/NGO/LIGE was applied for electrochemical sensor towards chemotherapeutic drug detection (nilutamide). Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques have been used to examine the electrochemical performance of nilutamide (anti-cancer drug). DPV was found to be more sensitive and found to exhibit a sensitivity 8.627 µA µM⁻¹ cm⁻² for SrTiO₃/NGO/LIGE with a wide linear range (0.02–892 µM) and low Limit of detection (LOD: 1.16 µM). SrTiO₃/NGO/LIGE has been examined for the detection of nilutamide in blood serum and urine samples and obtained a good recovery in the range of 97.2–99.72 %. The enhanced stability and selectivity and practical application results indicates the suitability of SrTiO₃/NGO/LIGE towards the detection of nilutamide drug in pharmaceutical industries.     

Ultrasound irradiation promoted enzymatic alcoholysis for synthesis of monoglyceryl phenolic acids in a solvent-free system

Monoglyceryl phenolic acids (MPAs) were known as the natural hydrophilic antioxidants which could be used in different fields such as food, pharmaceutical, cosmetic etc. A novel enzymatic route of MPAs synthesis by the alcoholysis of phenolic acid ethyl esters with glycerol under ultrasound irradiation in solvent free system was developed. Optimization of reaction parameters shows that a high conversion of above 97.4% can be obtained under the following conditions: phenolic acid ethyl esters to glycerol molar ratio of 1:10, with 6% catalyst (Novozym 435), at 60 °C and 200 rpm, with ultrasound input of 250 W, at 20 kHz frequency. Compared to the conventional stirring method, the activation energy for phenolic acid ethyl esters conversion was decreased from 65.0 kJ/mol to 32.1 kJ/mol under ultrasound promotion; the apparent kinetic constant (V_m/K_m) increased above 1.2-folds; the lipase amount decreased to 50%; the time required for the maximum conversion reduced up to 3-folds without damaging the lipase activity, which is the fastest report for enzymatic synthesis of MPAs.     

Confocal Raman microscopy for simultaneous monitoring of partitioning and disordering of tricyclic antidepressants in phospholipid vesicle membranes

Characterization of drug–membrane interactions is important in order to understand the mechanisms of action of drugs and to design more effective drugs and delivery vehicles. Raman spectra provide compositional and conformational information of drugs and lipid membranes, respectively, allowing membrane disordering effects and drug partitioning to be assessed. Traditional Raman spectroscopy and other widely used bioanalytical techniques such as differential scanning calorimetry (DSC) and nuclear magnetic resonance (NMR) typically require high sample concentrations. Here, we describe how temperature‐controlled, optical‐trapping confocal Raman microscopy facilitates the analysis of drug–membrane interactions using micromolar concentrations of drug, while avoiding drug depletion from solution by working at even lower lipid concentrations. The potential for confocal Raman microscopy as an effective bioanalytical tool is illustrated using tricyclic antidepressants (TCAs), which are cationic amphiphilic molecules that bind to phospholipid membranes and influence lipid phase transitions. The interaction of these drugs with vesicle membranes of differing head‐group charge is investigated while varying the ring and side‐chain structure of the drug. Changes in membrane structure are observed in Raman bands that report intra‐ and intermolecular order versus temperature. The partitioning of drugs into the membrane can also be determined from the Raman scattering intensities. These results demonstrate the usefulness of confocal Raman microscopy for the analysis of drug–membrane systems at biologically relevant drug concentrations. Effective tools for monitoring drug–membrane interactions are crucial for rational design of new drugs. Copyright © 2009 John Wiley & Sons, Ltd.     

Ultrasound promoted aminolysis of epoxides in aqueous media: a rapid procedure with no pH adjustment for additive-free synthesis of beta-aminoalcohols

An efficient and environmentally friendly procedure promoted by ultrasound irradiation is developed for stereoselective ring opening of various epoxides with aromatic and aliphatic amines under aqueous conditions in the presence of no catalyst or additive. Chemoselectivity of the protocol is shown by competition of piperidine and aniline to react with different epoxides resulting in exclusive formation of the respective products of piperidine.     

Effects of substitution of Ti for Fe in BiFeO3 films prepared by sol–gel process

Ti substituted BiFe_1−xTi_xO_3+δ films have been prepared on indium–tin oxide (ITO)/glass substrates by the sol–gel process. The films with x=0.00–0.20 were prepared at an annealing temperature of 600 °C. X-ray diffraction patterns indicate that all films adopt R3m structure and the films with x=0 and 0.10 show pure perovskite phase. Cross-section scanning shows the thickness of the films is about 300 nm. Through 0.05 Ti substitution, the 2P_r increases to 8.30 μC/cm² from 2.12 μC/cm² of the un-substituted BiFeO₃ film and show enhanced ferroelectricity at room temperature. The 2P_r values are 2.63 and 0.44 μC/cm² for the films with x=0.01 and 0.2, respectively. Moreover, the films with x=0.05 and 0.10 show enhanced dielectric property since the permittivity increases near 150 at the same measuring frequency. Through the substitution of Ti, the leakage conduction is reduced for the films with x=0.05–0.20.