Robert A. Brizzolara

Sonication of bacteria, phytoplankton and zooplankton: Application to treatment of ballast water

We investigated the effect of high power ultrasound, at a frequency of 19 kHz, on the survival of bacteria, phytoplankton and zooplankton, in order to obtain estimates of effective exposure times and energy densities that could be applied to design of ultrasonic treatment systems for ballast water. Efficacy of ultrasonic treatment varied with the size of the test organism. Zooplankton required only 3-9s of exposure time and 6-19 J/mL of ultrasonic energy to realize a 90% reduction in survival. In contrast, decimal reduction times for bacteria and phytoplankton ranged from 1 to 22 min, and decimal reduction energy densities from 31 to 1240 J/mL. Our results suggest that stand-alone ultrasonic treatment systems for ballast water, operating at 19-20 kHz, may be effective for planktonic organisms >100 microm in size, but smaller planktonic organisms such as phytoplankton and bacteria will require treatment by an additional or alternative system.

Evidence for covalent attachment of purple membrane to a gold surface via genetic modification of bacteriorhodopsin

The objective of this work is to covalently attach bacteriorhodopsin (BR) to a gold surface via genetic substitution of cysteine for serine (S35C) at the 35th amino acid position. Samples of BR-containing purple membrane (PM) on gold were evaluated using atomic force microscopy (AFM) and x-ray photoelectron spectroscopy (XPS). AFM images reveal a surface coverage of S35C-containing PM fragments of approximately 25%. XPS measurements reveal a small excess of sulfur for S35C-containing PM on gold, and a much larger excess of sulfur on wildtype-containing PM on gold. In both cases, the excess sulfur is covalently bound to the gold surface and appears to originate from dissociated methyl mercaptan groups from methionine residues on the external surfaces of BR. We conclude that the quantity of excess sulfur is smaller for S35C than for wildtype because the S35C’s sulfhydryl binds some PM fragments to the surface, reducing the quantity of methyl mercaptan that can bind to the surface. It then follows that the r...

A method for patterning purple membrane using self-assembled monolayers

A method for patterning purple membrane on a substrate is described. This method involves the use of patterned self-assembled monolayers. The quantity of purple membrane adsorbed to glass terminated by various self-assembled monolayers was measured using angle resolved X-ray photoelectron spectroscopy. It was determined that purple membrane adsorbs to unmodified glass and amine-terminated glass surfaces. Hydrocarbon- and fluorocarbon-terminated glass inhibit the adsorption of purple membrane. To demonstrate a potential patterning methodology, an amine-terminated self-assembled monolayer (SAM) was photochemically substituted for a hydrocarbon-terminated SAM using UV radiation. Future work will involve the use of UV radiation in conjunction with a lithographic mask so that specific PM adsorption sites can be defined on a substrate.

Patterning multiple antibodies on polystyrene.

A method for patterning different antibodies on polystyrene is described. The polystyrene surface is coated with a material resistant to antibody adsorption and the coating material is selectively removed from the region where antibody adsorption is desired, exposing clean polystyrene. Upon immersion of the substrate in antibody solution, antibodies adsorb to the clean polystyrene, but not to the coated areas of the surface. Two methods have been used to remove the coating: ion beam sputtering and mechanical etching. The pattern was verified using gold-labeled antigen in conjunction with X-ray photoelectron spectroscopy and with FITC-labeled antigen and fluorescence microscopy. Substrates patterned in this way could be used in conjunction with a charge-coupled detector for a multi-analyte biosensor. This patterning technique is suitable for applications in which a fast, inexpensive fabrication process is necessary, for example, in single-use sensors.

Characterization of the Surface of α-FeOOH Powder by XPS

We report x-ray photoemission spectra of the surface of iron (III) oxyhydroxide (α-FeOOH) particles. Research grade purity (99.0%) α-FeOOH sample was commercially obtained from Alfa/AESAR. The XPS spectra were measured with the Physical Electronics Model 5400 X-ray Photoelectron Spectrometer using unmonochromated Mg Kα x-rays at two pass energy settings corresponding to analyzer energy resolutions of 1.34 and 0.54 eV. We present the survey spectrum (binding energy range of 0–1100 eV) measured at an analyzer energy resolution of 1.34 eV. Multiplexes of the C 1s, O 1s and 2s, Fe 2p and 3p photoemission lines, valence band region as well as the Fe L3VV Auger line were measured at an analyzer energy resolution of 0.54 eV. The XPS spectra indicate that the surface of α-FeOOH powdered material consists mainly of its bulk chemistry with small quantities of oxidized carbon and hydrocarbon as contaminants.

Assessment of overlayer thickness determination model by controlled monolayers

The thickness of carbon overlayers that spontaneously form on the surface of real‐world samples needs to be accurately determined to enhance the accuracy of quantitative surface compositional analysis. One method for this determination proposed by Ebel et al. [J. Electron. Spectrosc. 34, 313 (1984)] for use in x‐ray photoelectron spectroscopy determines the film thickness based on the area ratio of the C(1s) photoelectron and carbon (KVV) Auger peaks. The Ebel model has been evaluated in this work through the use of self‐assembled monolayers (SAMs). The SAM approach permits the comparison of film thicknesses determined by the model with the known thickness of the controlled monolayers. Data from the SAMs consistently fell below the curve predicted by the model. Discussions of potential sources for error are presented with respect to photoelectron attenuation models. Examination of these potential sources, however, could not identify a source of sufficient magnitude to account for the difference between pr...

Control of purple membrane adsorption to a glass surface using self‐assembled monolayers

There is a considerable interest in the use of biological materials in electronic device applications. For example the purple membrane, a photoactive biological material, may have an application in artificial retinas. To fabricate devices such as artificial retinas from the purple membrane, a means of patterning the biological material on the substrate surface is needed. We have explored the use of self‐assembled monolayers to achieve the control of the adsorption of the purple membrane to a glass surface. By changing the terminal group of the self‐assembled monolayer, the affinity of the surface for the purple membrane is controlled. The adsorbed purple membrane films have been examined with x‐ray photoelectron spectroscopy and fluorescence microscopy. The x‐ray photoelectron spectroscopy data reveal that the purple membrane adsorbs to a clean glass surface in the amount 0.84 μg/cm2. Modifying the glass surface with a fluorocarbon‐based self‐assembled monolayer reduces the amount of purple membrane adsorbed by a factor of 9.3, to 0.09 μg/cm2. In the future, these results combined with one of the existing methods for patterning self‐assembled monolayers, will provide a means of spatially controlling the adsorption of the purple membrane on a substrate. Thus, this work represents an important first step in the patterning of purple membrane structures and devices on a surface.

Cysteine by X-Ray Photoelectron Spectroscopy

Cysteine is one of the 20 amino acids, and one of the two sulfur-containing amino acids. The highly reactive sulfhydryl group is often used for conjugating proteins to other entities. Furthermore, in a thin film, measurement of chemical shifts of the constituent atoms of cysteine are important in determining its interaction with a surface. Also, cysteine plays an important role in determining the conformation of proteins by forming disulfide bonds. As such, spectra of bulk films of cysteine serve as an important baseline for studies of these phenomena. In this work, an aqueous solution prepared from cysteine powder was poured into a recessed sample holder and allowed to dry. This formed a block of dried cysteine approximately 1/4 in. thick. The spectra were acquired at liquid nitrogen temperature. The atomic concentrations measured with XPS agree well with those expected for cycteine, assuming the small amount of excess carbon is due to adventitious material. Predominantly zwitterionic character is observed in the O 1s and N 1s spectra. A small amount of either neutral species or condensed polypeptide is also observed. The S 2p binding energy indicates that the sulfur is predominantly disulfide, with a small amount of free sulfhydryl.

The effect of solid surface tension and exposure to elevated hydrodynamic shear on Pseudomonas fluorescens biofilms grown on modified titanium surfaces

Abstract The solid surface tension of titanium was varied by using organosilane monolayers of various terminations, minimising differences in other material properties. Both the quantity of Pseudomonas fluorescens biofilms grown on the modified surfaces, and the percentage of biofilm remaining after exposure to hydrodynamic shear stress, varied significantly as a function of solid surface tension. The quantity of biofilm was less on chloropropyl-terminated surfaces than on an alkyl-terminated surfaces. However, the percentage of biofilm remaining after exposure to hydrodynamic shear stress (which depends on the adhesion and cohesion strengths of the biofilm) was less for the alkyl-terminated surface than for the chloropropyl-terminated surface, for one of the two sample sets analysed. These results demonstrate the importance of differentiating between the quantity of biofilm on a surface and the adhesion and cohesion strength of the biofilm, and may help explain discrepancies in the existing literature regarding the effect of solid surface tension on the propensity of a surface for microfouling.

Substrate photoelectron enhancement of carbonaceous overlayer Auger emission: effect of the substrate on carbon overlayer thickness determination in XPS

The Ebel Model, which characterizes a sample consisting of a thin carbonaceous overlayer on a substrate of a different material, provides a relationship between the carbon 1s and Auger peak intensities and the overlayer thickness. In this paper, Ebel model predictions for six substrate materials (silicon, aluminum, titanium, copper, silver and gold) are compared with experimental data from samples prepared using self-assembled monolayer and Langmuir-Blodgett techniques. Although the agreement between the experimentally measured carbon 1s/carbon Auger ratio and the Ebel Model was very good for silicon and aluminum and good for titanium, copper and silver, the experimentally determined ratio was consistently lower than that predicted by the Ebel Model for the gold substrate. For a 1.3 nm thick carbon layer on gold, the discrepancy between the measurement and the Ebel Model was 26%. We therefore modified the Ebel Model to include the effects of photoionization of carbon atoms in the overlayer by substrate photoelectrons. We refer to this as the Substrate Effect Model. Agreement between the Substrate Effect Model and the experimental data is very good for all six substrates examined. Because the Substrate Effect Model gives an accurate relationship between the carbon peak intensities and overlayer thickness, it can be used to determine an unknown overlayer thickness and to improve the accuracy of XPS quantitative analysis by accounting for the presence of the ubiquitous adventitious carbon layer. To this end, Substrate Effect Model results are presented for 40 substrate elements of technological interest and for overlayer thicknesses of 1,2 and 5 nm.