We have developed a method to deposit Cu metal onto surface-attached DNA, forming nanowirelike structures that are ∼3 nm tall. DNA is first aligned on a silicon surface and then treated with aqueous Cu(NO 3 ) 2 . After the copper(II) has electrostatically associated with the DNA, it is reduced by ascorbic acid to form a metallic copper sheath around the DNA. The resulting nanostructures have been observed and characterized by atomic force microscopy. A more complete coating can be obtained by repeating the Cu(II) and ascorbic acid treatment. Control experiments involving treatments with aqueous solutions containing either NO 3or the divalent cation Mg 2+ show no change in DNA height upon ascorbic acid exposure. These experiments indicate that copper nanowires, which may be valuable as interconnects in nanoscale integrated circuitry, can be readily generated from DNA molecules on surfaces.

Supported lipid bilayers (SLBs) have contributed invaluable information about the physiochemical properties of cell membranes, but their compositional simplicity often limits the level of knowledge that can be gained about the structure and function of transmembrane proteins in their native environment. Herein, we demonstrate a generic protocol for producing polymer-supported lipid bilayers on glass surfaces that contain essentially all naturally occurring cell-membrane components of a cell line while still retaining transmembrane protein mobility and activity. This was achieved by merging vesicles made from synthetic lipids (PEGylated lipids and POPC lipids) with native cell-membrane vesicles to generate hybrid vesicles which readily rupture into a continuous polymer-supported lipid bilayer. To investigate the properties of these complex hybrid SLBs and particularly the behavior of their integral membrane-proteins, we used total internal reflection fluorescence imaging to study a transmembrane protease, β-secretase 1 (BACE1), whose ectoplasmic and cytoplasmic domains could both be specifically targeted with fluorescent reporters. By selectively probing the two different orientations of BACE1 in the resulting hybrid SLBs, the role of the PEG-cushion on transmembrane protein lateral mobility was investigated. The results reveal the necessity of having the PEGylated lipids present during vesicle adsorption to prevent immobilization of transmembrane proteins with protruding domains. The proteolytic activity of BACE1 was unadulterated by the sonication process used to merge the synthetic and native membrane vesicles; importantly it was also conserved in the SLB. The presented strategy could thus serve both fundamental studies of membrane biophysics and the production of surface-based bioanalytical sensor platforms.

Phosphatidylserine (PS) embedded within supported lipid bilayers (SLBs) was found to bind Cu2+ from solution with extraordinarily high affinity. In fact, the equilibrium dissociation constant was in the femtomolar range. The resulting complex formed in a 1:2 Cu2+ to PS ratio and quenches a broad spectrum of lipid-bound fluorophores in a reversible and pH-dependent fashion. At acidic pH values, the fluorophores were almost completely unquenched, while at basic pH values significant quenching (85–90%) was observed. The pH at which the transition occurred was dependent on the PS concentration and ranged from approximately pH 5 to 8. The quenching kinetics was slow at low Cu2+ concentrations and basic values pH (up to several hours), while the unquenching reaction was orders of magnitude more rapid upon lowering the pH. This was consistent with diffusion limited complex formation at basic pH, but rapid dissociation under acidic conditions. The tight binding of Cu2+ to PS may have physiological consequences under certain circumstances.

An electrophoretic-electroosmotic focusing (EEF) method was developed and used to separate membrane-bound proteins and charged lipids based on their charge-to-size ratio from an initially homogeneous mixture. EEF uses opposing electrophoretic and electroosmotic forces to focus and separate proteins and lipids into narrow bands on supported lipid bilayers (SLBs). Membrane-associated species were focused into specific positions within the SLB in a highly repeatable fashion. The steady-state focusing positions of the proteins could be predicted and controlled by tuning experimental conditions, such as buffer pH, ionic strength, electric field and temperature. Careful tuning of the variables should enable one to separate mixtures of membrane proteins with only subtle differences. The EEF technique was found to be an effective way to separate protein mixtures with low initial concentrations, and it overcame diffusive peak broadening to allow four bands to be separated simultaneously within a 380 μm wide isolated supported membrane patch.

The properties of iridium oxide pH sensors produced by electrochemically induced deposition on gold electrodes were examined as a function of the composition of the deposition solution, as well as the electrochemical deposition protocol. The composition of the Ir͑IV͒ deposition solutions, which included oxalate or ethylene diamine tetraacetic acid complexing agent or no complexing agent, had no effect on the slope of the calibration curves. The slope of the calibration curves was shown to increase from ca. 49 to 76 mV/pH unit with the fractional coverage of gold substrates with iridium oxide. Increasing the film thickness beyond the full coverage did not further increase the slope of the calibration curves but resulted in a progressive increase of their intercept values. The method of deposition, which involved a constant current, single potential pulse, alternating potential pulse, or cyclic potential protocol, affected the maximum rate of pH response as well as the capacitance of the iridium oxide sensors. The latter two properties of the sensors were investigated using a microelectrochemical time-of-flight method with galvanostatic proton generation and potentiometric sensing. The alternating potential pulse and cyclic potential methods produced films of smaller rate of pH response and of smaller capacitance relative to the iridium oxide films of the same thickness produced by the other two methods. This is likely due to a smaller microscopic porosity of the films prepared by the potential pulse and cyclic potential methods. The maximum rate of pH response obtained with 50 nm thick iridium oxide sensors varied from ca. 7 to 23 V/s. The specific capacitance of the iridium oxide films varied from ca. 900 to 9000 F/cm 3 .