Useful oriented immobilization of antibodies on chimeric magnetic particles: direct correlation of biomacromolecule orientation with biological activity by AFM studies.

The preparation and performance of a suitable chimeric biosensor based on antibodies (Abs) immobilized on lipase-coated magnetic particles by means of a standing orienting strategy are presented. This novel system is based on hydrophobic magnetic particles coated with modified lipase molecules able to orient and further immobilize different Abs in a covalent way without any previous site-selective chemical modification of biomacromolecules. Different key parameters attending the process were studied and optimized. The optimal preparation was performed using a controlled loading (1 nmol Ab g(-1) chimeric support) at pH 9 and a short reaction time to recover a biological activity of about 80%. AFM microscopy was used to study and confirm the Abs-oriented immobilization on lipase-coated magnetic particles and the final achievement of a highly active and recyclable chimeric immune sensor. This direct technique was demonstrated to be a powerful alternative to the indirect immunoactivity assay methods for the study of biomacromolecule-oriented immobilizations.

Reconstitution of respiratory complex I on a biomimetic membrane supported on gold electrodes.

For the first time, respiratory complex I has been reconstituted on an electrode preserving its structure and activity. Respiratory complex I is a membrane-bound enzyme that has an essential function in cellular energy production. It couples NADH:quinone oxidoreduction to translocation of ions across the cellular (in prokaryotes) or mitochondrial membranes. Therefore, complex I contributes to the establishment and maintenance of the transmembrane difference of electrochemical potential required for adenosine triphosphate synthesis, transport, and motility. Our new strategy has been applied for reconstituting the bacterial complex I from Rhodothermus marinus onto a biomimetic membrane supported on gold electrodes modified with a thiol self-assembled monolayer (SAM). Atomic force microscopy and faradaic impedance measurements give evidence of the biomimetic construction, whereas electrochemical measurements show its functionality. Both electron transfer and proton translocation by respiratory complex I were monitored, simulating in vivo conditions.

Dextran-lipase conjugates as tools for low molecular weight ligand immobilization in microarray development.

The development of effective array biosensors relies heavily on careful control of the density of surface-immobilized ligands on the transducing platform. In this paper we describe the synthesis of new dextran-lipase conjugates for use in immobilizing low molecular weight haptens onto glass planar waveguides for immunosensor development. The conjugates were synthesized by immobilizing bacterial thermoalkalophilic lipases (Geobacillus thermocatenulatus lipase 2, BTL2) on agarose macroporous beads, followed by covalent coupling to dextran networks of variable molecular weight (1500-40000). The chimeras were immobilized via nonspecific hydrophobic interactions onto glass planar waveguides modified with 1,1,1,3,3,3-hexamethyldisilazane to obtain highly ordered and homogeneous molecular architectures as confirmed by atomic force microscopy. Microcystin LR (MCLR) was covalently bound to the dextran-BTL2 conjugates. The usefulness of this approach in immunosensor development was demonstrated by determining amounts of MCLR down to a few picograms per liter with an automated array biosensor and evanescent wave excitation for fluorescence measurements of attached DyLight649-labeled secondary antibody. Modifying BTL2 with dextrans of an increased molecular weight (>6000) provided surfaces with an increased loading capacity that was ascribed to the production of three-dimensional surfaces by the effect of analyte binding deep in the volume, leading to expanded dynamic ranges (0.09-136.56 ng L(-1)), lower limits of detection (0.007 ± 0.001 ng L(-1)), and lower IC50 values (4.4 ± 0.7 ng L(-1)). These results confirm the effectiveness of our approach for the development of high-performance biosensing platforms.

Physicochemical characterization of Acidiphilium sp. biofilms.

The biofilm formation of a strain of the extremophile bacterium Acidiphilium sp., capable of donating electrons directly to electrodes, was studied by different surface characterization techniques. We develop a method that allows the simultaneous study of bacterial biofilms by means of fluorescence microscopy and atomic force microscopy (AFM), in which transparent graphitic flakes deposited on a glass substrate are used as a support for the biofilm. The majority of the cells present on the surface were viable, and the growth of the biofilms over time showed a critical increase of the extracellular polymeric substances (EPS) as well as the formation of nanosized particles inside the biofilm. Also, the presence of Fe in Acidiphilium biofilms was determined by X-ray photoelectron spectroscopy (XPS), whereas surface-enhanced infrared absorption spectroscopy indicated the presence of redox-active proteins.

Oriented immobilization of a membrane-bound hydrogenase onto an electrode for direct electron transfer.

The interaction of redox enzymes with electrodes is of great interest for studying the catalytic mechanisms of redox enzymes and for bioelectronic applications. Efficient electron transport between the biocatalysts and the electrodes has achieved more success with soluble enzymes than with membrane enzymes because of the higher structural complexity and instability of the latter proteins. In this work, we report a strategy for immobilizing a membrane-bound enzyme onto gold electrodes with a controlled orientation in its fully active conformation. The immobilized redox enzyme is the Ni-Fe-Se hydrogenase from Desulfovibrio vulgaris Hildenborough, which catalyzes H(2)-oxidation reversibly and is associated with the cytoplasmic membrane by a lipidic tail. Gold surfaces modified with this enzyme and phospholipids have been studied by atomic force microscopy (AFM) and electrochemical methods. The combined study indicates that by a two-step immobilization procedure the hydrogenase can be inserted via its lipidic tail onto a phospholipidic bilayer formed over the gold surface, allowing only mediated electron transfer between the enzyme and electrode. However, a one-step immobilization procedure favors the formation of a hydrogenase monolayer over the gold surface with its lipidic tail inserted into a phospholipid bilayer formed on top of the hydrogenase molecules. This latter method has allowed for the first time efficient electron transfer between a membrane-bound enzyme in its native conformation and an electrode.

Ordering phthalocyanine-C60 fullerene conjugates on individual carbon nanotubes.

We report on the remarkable organization properties of a covalently-linked phthalocyanine-C(60) fullerene conjugate which is able to self-organize by means of non-covalent interactions on the outer wall of single-walled carbon nanotubes (SWCNTs).

Polypyrrole-glucose oxidase biosensor. Effect of enzyme encapsulation in multilamellar vesicles on analytical properties.

In this paper, we present the analytical properties of a new type of polypyrrole-based, enzymatic amperometric biosensor. It is produced by encapsulating the enzyme, glucose oxidase (GOx), into onion-type multilamellar vesicles (MLV). We compare its properties to those of a classical GOx-polypyrrole biosensor. When MLV are used to embed GOx in polypyrrole (PPy), GOx behaves as a Michaelis-Menten enzyme. Without MLV, a deviation to the Michaelis-Menten behaviour is observed for high glucose concentrations. Kinetics parameters of both types of biosensors are studied as a function of the surface charge synthesis: GOx encapsulation induces a 200-fold increase of the apparent maximal current (I(m)(app)) and a 10-fold increase of the apparent Michaelis constant (K(m)(app)). Sensitivity is improved by a factor of 5. GOx is also shown to be less sensitive to inhibiting ions (Cl(-)) when MLV are used. A residual amperometric response of 43% instead of 3% is measured. Finally, the long-term stability of biosensors is improved by the GOx encapsulation. All these results are partially explained by our previous study on the morphology of PPy films fabricated with GOx encapsulated into onion-type MLV (Olea et al., 2007).

Time-dependence structures of coordination network wires in solution.

We present a mechanochemistry-based procedure to isolate individual chains on surfaces of a ruthenium MMX polymer. After sonication of solutions containing the two building blocks of the mentioned MMX polymer, time-depending structures are formed in the solution. The architecture of the different structures obtained in this process, as a function of the time, is monitored using atomic force microscopy. The resulting structures exhibit uniform subnanometer diameters over microns length, in agreement with the expected diameter for an individual polymer chain. From the atomic force microscope images, we infer a long persistence length for the linear structures. Finally, the effect of the temperature solution in the formation of the different structures is also addressed.

Design and non-covalent DNA binding of platinum(II) metallacalix[4]arenes.

A set of cyclic tetranuclear complexes of the metallacalix[4]arene type with formula [{Pt(en)(L)}(4)](4+) (en=ethylenediamine; 2: LH=5-chloro-2-hydroxypyrimidine (5-Cl-Hpymo); 3: LH=5-bromo-2-hydroxypyrimidine (5-Br-Hpymo); 4: LH=5-iodo-2-hydroxypyrimidine (5-I-Hpymo)) have been obtained from the reaction between cis-protected square-planar [Pt(en)(H(2)O)(2)](2+) metal entities and LH in aqueous media. Additionally, the binding properties of 2, 3, 4 and their congener [{Pt(en)(L)}(4)](4+) (1: LH=2-hydroxypyrimidine (Hpymo)) with calf thymus-DNA (ct-DNA) have been studied by using different techniques including circular and linear dichroism (CD and LD, respectively) and UV-visible absorbance spectroscopies, gel electrophoresis, fluorescence competitive-binding studies and atomic force microscopy (AFM). The results are consistent with significant non-covalent interactions taking place between the polynuclear cyclic species and ct-DNA. Moreover, gel electrophoresis, linear dichroism titrations and AFM images of ct-DNA with metallacalixarenes show ct-DNA coiling at low metallacalixarene concentrations and upon subsequent increments in metallacalixarene concentration ct-DNA can be seen to uncoil with concomitant formation of long and inflexible ct-DNA structures.

MMX polymer chains on surfaces.

Fibres of [Ru(2)Br(micro-O(2)CEt)4]n polymer have been isolated on different surfaces under specific conditions, and morphologically characterised by AFM and STM, showing an unexpected helical internal structure.

Modeling leakage kinetics from multilamellar vesicles for membrane permeability determination: application to glucose.

The glucose permeability of bilayers formed from phosphatidylcholine, Brij30, and sodium octadecyl sulfate has been determined via an enzymatic reaction. Glucose is encapsulated in either uni- or multilamellar vesicles (MLV) and its concentration in the dispersion medium is monitored by spectrophotometry analysis through the rate of glucose oxidase-catalyzed reaction of glucose oxidation. A kinetic model of leakage, taking explicitly into account one, two, or n(w)-walls (n(w) >> 1) for the vesicles and assuming an enzymatic Michaelis-Menten behavior, is proposed and used to fit the experimental data. The two-wall model was chosen to fit experimental data obtained on MLV since an average value of 1.7 bilayers was estimated for MLV by cryo-TEM imaging. A permeability value of 5.8 +/- 4.4 10(-9) cm/s was found. The proposed model is validated by the measurement of the bilayer permeability deduced from the modeling of glucose leakage from unilamellar vesicles with the same composition. In this latter case, a value of 8.3 +/- 0.7 10(-9) cm/s is found for the permeability, which is within the error bar of the value found with MLV.

Assembling of dimeric entities of Cd(II) with 6-mercaptopurine to afford one-dimensional coordination polymers: synthesis and scanning probe microscopy characterization.

The direct reaction between 6-mercaptopurine (6-MP) and Cd(II) under different conditions yields either [Cd2(6-MP)4(NO3)2](NO3)2 (1) or [Cd(6-MP-)2.2H2O]n (4). Compound 1 behaves as the building block of the polymer [Cd(6-MP2-)2]n[Ca(H2O)6]n (3), by deprotonation of 6-MP ligand. In the reaction of 1 to give 3, the dinuclear compound [Cd2(6-MP)4(H2O)2](NO3)4.2H2O (2) can be isolated as an intermediate. Polymers 3 and 4 convert into each other in water via deprotonation-protonation reactions. The structures of compounds 1-3 have been determined by X-ray diffraction. Given the small differences in the arrangement shown in the crystal structures of the polymer 4 and the polyanion of 3, the stabilities and energetics of the two arrangements have been examined by DFT calculations to determine the possibility of identifying new conformations of both polymers. In addition, the two polymers have been characterized on surfaces by means of AFM. The direct reaction between 6-MP and Cd(II) and the deprotonation of the polymer 4 have proven to be useful routes for the isolation of one-dimensional systems on surfaces. The development of new strategies to characterize these types of polymers on surfaces opens the possibility to perform nanoscale studies on their properties and their potential use as nanomaterials.

Scanning probe microscopy characterization of single chains based on a one-dimensional oxalato-bridged manganese(II) complex with 4-aminotriazole.

The compound [Mn(mu-ox)(4atr)2]n (1) (ox = oxalato and 4atr = 4-amine-1,2,4-triazole) has been synthesized and characterized by FT-IR spectroscopy, thermal analysis, variable-temperature magnetic measurements, and X-ray single-crystal diffraction methods. The crystal structure of compound 1 consists of one-dimensional linear chains in which trans-[Mn(4atr)2]2+ units are sequentially bridged by centrosymmetric bis-bidentate oxalato ligands. Cryomagnetic measurements show an overall antiferromagnetic behavior of the compound. Isolated chains of this polymer have been obtained by sonication of 1 in ethanol or treatment of the polymer with NaOH and morphologically characterized on highly oriented pyrolitic graphite and mica surfaces by atomic force microscopy and scanning tunneling microscopy. The procedures employed to obtain single chains of this coordination polymer open a route for future nanotechnological applications of these types of materials.