Surface property effects in the immobilization of L-lactate oxidase on gold electrodes by self-assembled monolayers.

Metal-reducing subsurface bacteria like Geobacter sulfurreducens can reductively precipitate water-soluble uranium salts. However, very little information is available about this bacteria's uranium reduction mechanism. Most of the metabolic investigations are based on genetic analysis, where specific proteins are either deleted or overexpressed to elucidate its role in the electron transfer process. However these approaches to identify the electron carriers are limited because mutation of one gene can cause multiple phenotypic changes resulting in alterations of the native uranium reductase machinery. Yet, these limitations can be bypassed through the use of nanoscale in vitro platforms that mimic the Geobacter cell envelope electron carrier machinery. Therefore, we constructed nanostructured biomimetic interfaces equipped with Geobacter’s most abundant and conserved electron carrying cytochromes (periplasmic cytochrome PpcA and outer membrane cytochrome OmcB) to mimic the cell membrane electron transfer mechanism and adapted it to the platform capable of spectroelectrochemical determination. Spectroelectrochemical techniques combines electrochemistry and spectroscopic measurements, and offers advantage offering capability to assess changes in specific molecules in the system as a function of electric potential. We built working electrode form a transparent slide coated with gold (~100 Ao thickness) and covered with self assembled monolayer (SAM) of thiolipids. Formation of SAM on the gold electrodes shielded the protein solution from degradation at the electrode surface, and furthermore provided us with the capability of controlling the access of species in solution towards working electrode. Redox activity of Geobacter cytochrome c PpcA was measured electrochemically by technique like cyclic voltammetry and chronoamperometry, where changes in current at the working electrode are monitored as a function of applied potential. High transparency of the working electrode allowed us to measure reduction of PpcA spectrophotometrically by presence of three characteristic absorption bands, called Soret or gamma peak which shift from ~408 in oxidized form to ~420 in reduced form, alpha (α) peak at ~ 552 nm and beta (β) at ~ 521 nm. The cytochrome was immobilized onto a mixed self assembled monolayer of alkanethiols on a gold electrode. The ratio of carboxy acid terminating alkane group to alcohol terminating alkane group was optimized for the immobilization of protein in active conformation. Immobilized PpcA was characterized electrochemically by cyclic voltammetry, chronoamperometry and square wave voltammetry. Immobilized PpcA showed stable electrochemical response and was capable of being redox active in the immobilized state. The midpoint redox potential of immobilized PpcA was -372 mV vs. Ag/AgCl, also within the orders obtained for PpcA in solution (-374 mV vs. Ag/AgCl). Thus the immobilized PpcA at the SAM electrode was capable of direct electron transfer without any need of mediator resulting precise control over electrochemical potential. Based on the hypothesis that PpcA may be transfer electrons produced in respiration to OmcB as part of Geobacter’s electron transport chain, we attempted to demonstrate electron transfer from PpcA to OmcB in optically transparent thin layer cell. Addition of OmcB-containing membrane vesicles to the PpcA, yielded a small increase in the CV peak of PpcA. Since OmcB membrane vesicles, are not capable of direct electron transfer to and from the electrode, the increase in the current can be attributed to the catalytic reduction of OmcB by reduced PpcA. Redox spectra of the cytochromes monitored in the multipotential step experiments showed additional evidence of reduction of OmcB from PpcA. Change were observed in the Soret Peak at 410 and 420 nm, and 552 peaks as a function of electrode potential. The biomimetic system assembled here was intended to simulate electron transfer within Geobacter’s cell envelope, in which electrons produced in respiration are transferred from the inner membrane (mimicked by the SAM coated gold electrode) through the periplasm (mimicked by the PpcA layer bound to the SAM) to outer membrane cytochromes (mimicked by the OmcB-containing microsomes. This study’s establishment of a biomimetic redox-active cell envelope (BRACE) provides a new research platform with which to study Geobacter electron transport to extracellular electron acceptors. This nanoplatform integrating the key components of Geobacter’s electron transfer machinery will allow us to study the activity of native redox components in a controllable system. The information obtained about the redox interaction between cytochrome provides interesting insights about the mechanism of electron transfer in Geobacter which may lead to more successful strategies for groundwater uranium fixation.

A mechanistic study of Pt particle electrodeposition and growth on a self-assembled monolayer as an active template

Introduction. The self-assembly technique is one of the best methods to arrange the molecule in order onto the solid substrate surface and the alkylthiol self-assembled monolayers (SAMs) on gold and alkyl SAMs on silicon have been widely studied because of their high stability, high packing density, and high orientation [1,2]. Thus, they are expected to apply to the modern nanotechnology such as sensors, wetting control, corrosion inhibition, and biomolecular and molecular electric devices [1,2]. Moreover, using the binding group terminated SAM as a substrate, multilayer with various functionalities can be constructed. In order to control the multilayer thickness and functionality, we have to construct highly oriented and well-packed SAMs with binding group as a terminal group [3]. In this study, we constructed four kinds of binding group terminated SAMs such as 4-mercaptobenzoic acid (4-MBA) and 3-mercaptopropionic acid (3-MPA) SAMs on Au(111) and 2-methoxy ethyl (2-ME) and 11-ethoxy undecyl (11-EU) SAMs on Si(111) by various preparation conditions and their characteristics were estimated by electrochemical measurements for the reductive desorption, angle-resolved X-ray photoelectron spectroscopy (ARXPS), attenuated total reflection - Fourier transformed infrared (ATR-FTIR) spectroscopy, and contact angle measurements. Experimentals. After Au(111) single crystal disks were annealed by a gas burner and quenched with ultrapure water, they were immersed in ethanol solution containing 1 mM 4-MBA or 1 mM 3-MPA for certain periods at room temperature. From the results of the electrochemical measurements for the reductive desorption and of ARXP specta, density, stability, and orientation of the constructed 4-MBA and 3-MPA SAMs were investigated in order to find the optimum preparation conditions of the densely-packed and well-oriented SAMs on Au(111). After etching of n-typed Si(111) prisms, 2-ME and 11-EU SAMs were prepared on Si(111) by dipping Si prism into liquid state of 2-ME or 11-EU under UV light irradiation and nitrogen atmosphere for several hours. From the results of the ATR-FTIR spectra and contact angle measurement, density, stability, and orientation of the constructed 2-ME and 11-EU SAMs were investigated in order to find the optimum preparation conditions of the densely-packed and well-oriented SAMs on Si(111). Results and Discussion. Linear sweep voltammograms (LSVs) measured in a deaerated 0.1 M KOH at Au(111) electrodes modified with the 4-MBA SAMs, which were prepared for several dipping periods, showed cathodic peaks due to the reductive desorption of 4-MBA, around -0.60 V. With increasing of the dipping period, the peak potential shifted to negative, namely stability increased, and the surface coverage of 4-MBA, namely density, increased. However, full width of half maximum (fwhm) of the cathodic peak, which shows homogeneity of SAM’s orientation, decreased until the dipping period of 1 h and then increased with increasing of the dipping period. This result indicated that repulsion interaction between carboxylate groups should increase with increasing of the dipping period, namely density. For 5 h dipping, the surface coverage was saturated to 0.52 nmol cm-2. From the XP spectrum of the 4-MBA SAM, we confirmed that the 4-MBA SAM prepared by the dipping period of 5 h is highly stable. As compared with 4-MBA SAM on Au(111) prepared for the same dipping period, 3-MPA SAM on Au(111) was less stable, less densely-packed, and less highly oriented, because van der Waals interaction between 4-MBA molecules, namely hydrophobic interaction between phenyl groups, should be stronger than that between 3-MPA, namely hydrophobic interaction between propyl chains. Modification of metal complex molecules such as metallo-porphyrin and metallo-phthalocyanine on the 4-MBA SAM modified Au(111) is now under investigation. On the other hand, 2-ME and 11-EU SAMs on Si(111) was relatively stable, because C-Si bonding energy is higher than S-Au bonding energy. As compared with 2-ME SAM on Si(111) for the same preparation period, 11-EU SAM was more stable, more densely-packed, and more highly oriented on Ai(111), because van der Waals interaction between 11-EU, namely hydrophobic interaction between longer chains, should be higher than those between shorter chains. Now we are trying to find preparation condition to construct more stable, densely-packed, and highly oriented 2-ME SAM on Si(111) because shorter chain SAM is easy to use as a substrate for multilayer formation. References. [1] A. Ulman, An Introduction to Ultrathin Organic Films from Langmuir-Blodgett to Self-Assembly, Academic Press, New York (1990).[2] T. Kondo, R. Yamada, and K. Uosaki, in Organized Organic Ultrathin Films – Fundamentals and Applications, Wiley-VCH, Chap 2 (2012).[3] T. Arisaka, B. Zhang, N. Aoki, and T. Kondo, 224th ECS Meeting, San Francisco, #44 (2013).

Self-assembled monolayers (SAMs) have numerous applications, for example, engine wear inhibitors, surface profiling signal enhancement, nanostructure production, sensor production, and catalysis. The adsorbed SAM structure has a major impact on the properties of the outer monolayer surface which dictates the performance and viability of the SAM for individual applications. Substrate growth phases of SAMs have been extensively studied, and two structures have been identified. Initially, a lying down SAM structure is formed that evolves into a standing up structure. It is often critical to know how both structures form as a function of substrate immersion time to be able to design the properties of this structure. The formation of mercaptopropionic acid (MPA) SAMs on gold has been studied. Electrochemical impedance spectroscopy (EIS) was used to measure the adsorption isotherms at five temperatures in the range 4-40 degrees C. Infrared reflectance absorption spectroscopy (IRRAS) was also used, and the results show close agreement. A new monolayer adsorption isotherm is proposed which models SAM structure formation as a function of immersion time, representing all phases of SAM adsorption. This model represents a significant improvement on previous models based on Langmuir and Kisliuk adsorption isotherms that only model the fractional coverage of a surface with a SAM. The new model predicts the optimum immersion time taken for an MPA monolayer on gold to attain a surface saturated with MPA. It accounts for temperature effects on the rate of formation and the degree of monolayer disorder. It has potential for use in other SAM systems and may become the method of choice for modeling many instances of sequential substrate adsorption of two different structures, each of which exhibits different properties, as a function of immersion time.

In order to study the interfacial electron transfer, selfassembled monolayers (SAMs) on electrode surface have been attractive as a model system because they provide a stable and structurally well-defined monolayer with an adjustable thickness and desirable function. This characteristic of SAMs affords an opportunity to study fundamental issues such as the effects of distance and interfacial structure on the long-range electron transfer kinetics between a redox active species and an electrode. Weaver and Li obtained the first evidence of the distance-dependence of heterogeneous electron transfer rate constant for reduction of pentaaminecobalt(III) complexes anchored to gold and mercury surface. After Chidsey and co-workers reported heterogeneous electron transfer rate and electron tunneling constant (β) for the ferrocene-terminated alkanethiol monolayers with different alkyl chain length, a number of groups have reported β values for SAMs containing redox couples such as pentaamine (pyridine) Ru(II) complex, Os(II) bipyridyl complex, viologen, naphtoquinone, azobenzene, and hydroquinone. All of these reports demonstrated that the logarithmic heterogeneous apparent rate constant (kapp) linearly decreases as the distance between the electroactive center and the electrode surface increases as expected by Marcus theory. Those investigations on the distance dependence of electron transfer gave β values which are roughly ranging from 0.7 to 1.3 per methylene unit in the alkyl chain spacer. It is interesting to note that these β values are quite similar each other in their magnitude even though the electroactive SAMs contain different redox molecules and they follow significantly different electron transfer mechanism each other. For example, the electron transfer of ruthenium complex containing pentaamine and pyridine tether is highly reversible due to one-electron outer-sphere redox couple. However, redox center such as azobenzene undergoes substantially slow heterogeneous electron transfer because of its protonation reaction and structural change during its 2e−, 2H redox process. Among these redox centers studied, the electron transfer kinetics of a hydroquinone (H2Q) is also quite complicated due to its 2e −, 2H transfer reaction though Laviron presented a theoretical treatment of proton-coupled electron transfer reaction based on the nine-member square scheme. The electrochemical properties of hydroquinone/benzoquinone derivatives have been extensively studied in solutions because of their important biological activities. Especially, Hubbard and Soriaga have studied on the orientation of various quinones and mercaptohydroquinone derivatives adsorbed on metal surfaces using thin-layer electrochemistry. And Uosaki and coworkers have investigated the pH dependent redox behaviors of mercaptohydroquinone adsorbed on gold surface. We have reported the distance dependence of heterogeneous proton-coupled electron transfer rate constant of H2Q redox center in ω-mercaptoalkylhydroquinone SAMs on gold in 0.1 M HClO4 solution a few years ago. The β value reported for the H2Q-SAMs was 1.04 ± 0.06 and it was in good agreement with the values for the electroactive SAM systems reported up to now. However, the electron transfer kinetics of the H2Q-SAMs on gold shows remarkably different kinetic behavior in 0.1 M NaOH solution. In this note, we report an unusual observation for long range electron transfer in the ω-mercaptoalkylhydroquinone SAMs on gold electrode in a strong basic media. At this moment, the distance dependence of electron transfer of H2Q group is not observed in basic solution unlike that in acidic condition. Almost zero value of β determined from this phenomenon, to the best of our knowledge, is the first one in investigation of electron tunneling constant for long range electron transfer in the electroactive SAMs so far. The present work provides some understandings on the controlling factors related to proton-coupled electron transfer reaction nature.

A coordinatively unsaturated FeII complex bearing a pentadentate ligand (N,N',N'-tris(2-pyridyl-methyl)-1,2-diaminoethane) functionalized with a cyclic disulfide group has been prepared in order to graft reactive metal entities as self-assembled monolayers (SAMs) on gold electrodes. Prior to grafting, exogenous ligand exchange has been investigated by cyclic voltammetry (CV) in solution, showing that the nature of the first coordination sphere (N5)FeII-X (X = Cl-, OTf-, MeCN, acetone) can be tuned, thanks to the control of the chemical conditions. The FeII complex has been immobilized on gold electrodes by spontaneous (passive) adsorption as well as by an electro-assisted method. The resulting SAMs were characterised by XPS and AFM analyses. CV experiments implementing these SAMs as working electrodes showed that the first coordination sphere of the grafted FeII complex can be controlled by adjusting the chemical conditions, similarly to the studies in a homogeneous solution. Finally, the supported FeII complex proved to be reactive with superoxide generated at the electrode surface by reduction of dissolved dioxygen. Under the employed conditions, leaking of the metal complex was not observed.

Electrochemical performance of a [Ru(NH 3 ) 6 ] 3+/2+ redox couple at gold electrodes modified by alkanethiol self assembled monolayer (SAM) films of the type [-SH -(CH 2 ) n -CH 3 ] with different number of methylene units (n = 2 to 10) in the presence and absence of glucose additives has been studied using fast scan cyclic and steady-state voltammetry. Specific scatter of measured rate constants caused by enhanced sensitivity of this probe to minor defects of SAMs has been observed in a general agreement with the published data for thicker SAMs (n = 9 to 18). In addition, we have disclosed the anomalous viscosity-imposed drop of the heterogeneous rate constant for the case of Au electrodes modified by thinner n-alkanethiol SAMs (n = 2, 4). Taking into the account the fact of [Ru(NH 3 ) 6 ] 3+/2+ couple's capability to penetrate into the SAM interior, we ascribe the obtained results to the manifestation of the solvent-friction mechanism under the condition where the redox species presumably together with a few of solvating water molecules reside in a SAM's peripheral interior marked by much higher local viscosity (slower dielectric relaxation) compared to the electrolyte solution.

Surface coating is used for materials to achieve a desired surface property without changing the whole material. Polyelectrolyte multilayer (PEM) deposition may be one of the most versatile techniques to create conformal surface coating in large area with a great control over the film thickness in nano-meter scale. These multilayer films are assembled through, so called, the layer-by-layer (LbL) deposition process which is the repetitive, sequential dipping of the substrate into the oppositely charged polyelectrolytes solutions. PEM films can be used for various substrates (glass slides, silicon wafer, plastics, etc.) without any difficult treatment. Moreover, the functional groups which remained reactive after the film deposition allow further chemical reactions such as the polymer micro-contact printing and the selective crosslinking. Due to these advantages, many studies using the LbL technique have conducted intensively to create functional coatings for electro-optical and biomedical applications. Other frequently used method of surface coating is self-assembled monolayer (SAM) formation. SAM can form organic interfaces with the properties largely controlled by the end groups of the molecules comprising of the film. Certainly, these two methods are the most competitive fabrication techniques of surface coating. While the surface properties of most SAMs are presented by the nature of the end groups of SAM molecules, PEM films exhibit their surface properties that are orchestrated by the chemical compositions of the polyelectrolyte film and physical factors such as surface morphology, thickness, etc.. If these two very different materials meet, what phenomena will occur at the interface? How would they compensate their discrepancy? In this paper, we present a study of the coating system that was fabricated as a mixture of PEM and SAM. The hybrid films were prepared by polyelectrolyte multilayers comprised of hydrophilic polyelectrolytes assembled atop of hydrophobic SAM films. We have observed a unique phase separation of the SAM/PEM hybrid film, which lead the formation of nano-pores of the film surface. Surface properties including wetting and biological interaction behaviors of the hybrid films are also discussed in this paper.

Self-assembled monolayer(SAM)로 변형된 금 전극 위로 폴리피롤의 전기화학적 석출 과정을 수용액 상태에서 in-situ EQCM (Electrochemical Quartz Crystal Microbalance)과 ex-situ AFM (Atomic Force Microscopy)을 이용하여 조사하였다. 금 전극에서 cyclic voltammetry로 살펴본 폴리머의 석출은 산화 제한 전위 (anodic limiting potential) 값에 매우 의존적이었으며 주사 횟수에는 의존하지 않았다. 제한 산화 전위가 0.8V (vs Ag | ArCl) 이상일 때 폴리머의 석출은 크게 증가하였다. 그리고 주사 횟수가 증가하면서 질량의 비이상적 변화가 관찰되었는데 이것은 폴리피롤 필름의 rearrangement가 원인이라고 생각된다. 1-dodecanethiol SAM 전극과 thiophene SAM전극에서는 폴리머가 3차원적으로 성장하며 필름의 rearrangement를 수반하였지만 BPUS <TEX>$(Bis(\omega(N-pyrrolyl)-n-undecyl)disulfide)$</TEX> SAM 전극에서는 2차원적인 layer-by-layer 성장을 하고 필름의 rearrangement는 관찰되지 않았다. 폴리머가 급격하게 전극 면으로 석출되면 사슬 모양과 도너츠 모양의 폴리머를 만들며, 정류 상태에 이르면서 주름잡힌 폴리머 필름이 생성되는 것이 원자 힘 현미경 (Atomic Force Microscopy) 이미지로 관찰되었다. The growth of Polypyrrole film has been investigated during electropolymerization in an aqueous solution on bare and SAM modified gold electrodes by in-situ EQCM and ex-situ AFM. According to the result of cyclic voltammetry measurements, in the case of a bare gold electrode, the electrochemical deposition of polypyrrole were dependent on the limiting oxidative potential, but not on scan numbers. When the limiting potential higher than 0.8 V was applied on the electrode, the amount of polypyrrole deposited on a gold electrode was rapidly increased and the abnormal mass change attributed to the rearrangement of polypyrrole films was observed as the scan number increased. The polypyrrole film Prepared on electrodes modified with 1-dodecanethiol SAM or thiophene SAM grew 3-dimensionally with the rearrangement of film. However, in the case of BPUS SAM, 2-dimensional layer-by-layer growth of film was observed without the rearrangement of film. AFM images showed films with chain-shaped and/ or donut-shaped polymers when grown rapidly and a wrinkled film at the steady state condition.

Measurements of surface concentration and charge number per adsorbed molecule for a thiolipid monolayer tethered to the Au(111) surface by a long hydrophilic chain

The electrochemical behaviour of nanoporous gold modified with self-assembled monolayers is investigated with regard to its point of zero charge (pzc) and proton transfer reaction. Due to their high surface-to-volume ratio and conductivity, nanoporous electrodes represent promising materials for numerous applications, including the immobilization of biomolecules in biotechnology and biosensing. Therefore, the fundamental understanding and controllability of the surface state of the electrode is essential. To achieve a precise surface charge control, nanoporous gold (npAu) is modified with self-assembled monolayers (SAMs) of different lengths (3-mercaptopropionic acid (MPA) and 16-mercaptohexadecanoic acid (MHDA)). Cyclic voltammetry and impedance spectroscopy are used to determine the pzc. The most distinct pzc, and thus the most precise charge control, is found for the long-chain MHDA. Subsequently, the proton transfer reaction was investigated as a function of pH and scan rate. The observed protonation/deprotonation reaction was qualitatively well in line with the literature for planar gold electrodes, albeit the fraction of electrochemical controllable SAMs increased by a factor of 10 compared to planar electrodes indicating attractive application potential.

Hydrophobic, methyl-terminated self-assembled monolayer (SAM) surfaces can be used to reduce friction. Among methyl-terminated SAMs, the frictional properties of alkanethiol SAMs and silane SAMs have been well-studied. In this research, we investigated friction of methyl-terminated n-hexatriacontane (C36) SAM and compared its friction properties with the alkanethiol and silane SAMs. Alkane SAM does not have an anchoring group. The alkane molecules stand on the surface by physical adsorption, which leads to a higher surface mobility of alkane molecules. We found that C36 SAM has a higher coefficient of friction than that of octadecyltrichlorosilane (OTS) silane. When an atomic force microscope (AFM) tip was swiped across the alkane SAM with a loading force, we found that the alkane SAM can withstand the tip loading pressure up to 0.48 GPa. Between 0.48 and 0.49Ga, the AFM tip partially penetrated the SAM. When the tip moved away, the deformed SAM healed and maintained the structural integrity. When the loading pressure was higher than 0.49 GPa, the alkane SAM was shaved into small pieces by the tip. In addition, we found that the molecular tilting of C36 molecules interacted with the tribological properties of the alkane SAM surface. On one hand, a higher loading force can push the rod-like alkane molecules to a higher tilting angle; on the other hand, a higher molecular tilting leads to a lower friction surface.

Oxidation states and CO ligand exchange kinetics in a self-assembled monolayer (SAM) of an oxo-centered triruthenium cluster [Ru(3)(mu3-O)(mu-CH3COO)6(CO)(L1)(L2)] (L1 = [(NC5H4)CH2NHC(O)(CH2)10S-]2, L2 = 4-methylpyridine) have been extensively investigated on the surface of a gold electrode in aqueous and nonaqueous solutions. The SAM exhibits three consecutive one-electron transfers and four oxidation states, which have been characterized by electrochemistry, in situ infrared spectroscopy, and in situ sum frequency generation (SFG) vibrational spectroscopy measurements. The original electron-localized state of the Ru cluster center was changed to electron delocalization states by oxidation or reduction of the central Ru ions. These changes are revealed by the IR absorptions of the CO ligand and the bridging acetate ligands of the triruthenium cluster in the SAM. The IR absorptions of the two kinds of ligands are strongly dependent on the oxidation state of the Ru cluster center. One-electron oxidation of the central Ru ion in the SAM triggers a CO ligand liberation process. Solvent molecules may then occupy the CO site to result in a CO-free SAM. One-electron reduction of this CO-free SAM in a CO-saturated solution leads to re-coordination of the CO ligand into the SAM. Both processes can be precisely controlled by tuning the electrode potential. The kinetics of the CO exchange cycle in the SAM, including liberation and coordination, has been investigated by in situ IR and SFG measurements for the first time. The CO exchange cycle is significantly dependent on the temperature. The reaction rate greatly decreases with decreasing solution temperature, which is an important factor in the CO ligand exchange process. The activation energies of both CO liberation and coordination have been evaluated from the reaction rate constants obtained at various temperatures.

Self-assembled monolayer (SAM) films have attracted immense attention for both fundamental and applied research. A SAM is composed of a large number of molecules with a head group that chemisorbs onto a substrate, a tail group that interacts with the outer surface of the film, and a spacer (backbone) chain group that connects the head and tail groups resulting in a coating. Interactions between spacer groups of different molecules, such as van der Waals forces and/or hydrogen bonding, hasten SAM film formation and contribute to its stability. In this dissertation, SAM and thin films have been formed onto copper and aluminum oxide surfaces by reaction with 1H,1H,2H,2H-perfluorodecyldimethylchlorosilane (PFMS), 1H,1H,2H,2H-perfluorodecyltrichlorosilane (PFTS), 1H,1H,2H,2H-perfluorodecylphosphonic acid (PFDP), octylphosphonic acid (OP), decylphosphonic acid (DP), and octadecylphosphonic acid (ODP). The properties and stability of the films were investigated employing complementary surface analysis techniques: X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), friction force microscopy (FFM), a derivative of AFM, contact angle measurements (CAMs), and Fourier transform infrared reflection/absorption spectroscopy (FT-IRRAS). The perfluoroalkylsilane SAM on Cu is found to be extremely hydrophobic typically having sessile drop static contact angles of more than 130° for pure water and a surface energy of 14 mJ/m2 (mN/m). FFM showed a significant reduction in the adhesive force and friction coefficient of PFMS modified Cu (PFMS/Cu) compared to unmodified Cu. Treatment by exposure to harsh conditions showed that PFMS/Cu SAM can withstand boiling nitric acid (pH=1.8), boiling water, and warm sodium hydroxide (pH=12, 60 °C) solutions for at least 30 minutes. Furthermore, no SAM degradation was observed when PFMS/Cu was exposed to warm nitric acid solution for up to 70 min at 60 °C or 50 min at 80 °C. XPS and FT-IRRAS data reveal a coordination of the PFMS silicon (Si) atom with a cuprate (CuO) molecule present on the oxidized copper substrate. The data give good evidence that the stability of the SAM film on the PFMS modified oxidized Cu surface is largely due to the formation of a siloxy-copper (-Si-O-Cu-) bond via a condensation reaction between silanol (-Si-OH) and copper hydroxide (CuOH). For a PFTS modified Cu surface (PFTS/Cu), the sessile drop static contact angle of pure water has been measured to be more than 125° and the surface energy to be typically less than 16 mJ/m2. Stability tests show that the PFTS/Cu film can survive in boiling pure water for one hour, boiling nitric acid (pH 1.5 or 1.8) for 30 minutes, sodium hydroxide solution (pH 12, 70 °C) for 30 minutes, and autoclave conditions (steam at 134 °C and 3 atmospheres) for 15 minutes. The more commonly used self-assembled monolayer (SAM) modifications of Cu surfaces, e.g. thiol compounds, are significantly less stable than PFTS/Cu. Extremely hydrophobic (low surface energy) and stable PFMS/Cu SAMs and PFTS/Cu films could be useful as corrosion inhibitors in micro/nanoelectronic devices and/or as promoters for anti-wetting, low adhesion surfaces or drop-wise condensation on heat exchange surfaces. XPS analysis confirmed the presence of perfluorinated and non-perfluorinated alkylphosphonate molecules on the PFDP, DP, and ODP SAMs deposited at the aluminum oxide coated silicon (Al/Si) surfaces. The sessile drop static contact angle of pure water on PFDP SAMs was typically more than 130° and on DP and ODP typically more than 125° indicating that the phosphonic acid SAMs reacted with Al samples were very hydrophobic. The surface roughness for PFDP/Al, DP/Al, ODP/Al, and bare Al was approximately 35 nm, as determined by AFM. The surface energy for PFDP/Al was determined to be approximately 11 mJ/m2 by the Zisman plot method compared to 21 mJ/m2 and 20 mJ/m2 for DP/Al and ODP/Al, respectively. PFDP/Al gave the lowest adhesion and friction force while bare Al gave the highest. The adhesion and friction forces for ODP/Al and DP/Al SAMs were in between. ODP, DP, and OP SAMs have been studied in detail on relatively flat aluminum oxide surfaces. The rms surface roughness for ODP/Al, DP/Al, OP/Al, and bare Al was less than 15 nm, as determined by AFM. The sessile drop static contact angle of pure water on ODP/Al and DP/Al was typically more than 115° and on OP/Al typically less than 105°. The surface energy for ODP/Al and DP/Al was determined to be approximately 21 mJ/m2 and 22 mJ/m2, respectively, compared to 26 mJ/m2 for OP/Al. ODP/Al and OP/Al were studied by FFM to better understand their micro-/nano-tribological properties. ODP/Al gave the lowest coefficient of friction values while bare Al gave the highest. The adhesion forces for ODP/Al and OP/Al were comparable. The chemical stability of ODP/Al, PFDP/Al, DP/Al, OP/Al, and PFMS/Al SAMs has been inspected by exposure to warm nitric acid (pH 1.8, 30 min, 60-95 °C). The XPS data and stability against harsh chemical conditions indicate that a type of bond forms between a phosphonic acid (PA) or silane molecule and the oxidized Al surface. Stability tests using warm nitric acid (pH 1.8, 30 min, 60-95 °C) show ODP/Al SAMs to be most stable followed by PFDP/Al, DP/Al, PFMS/Al, and OP/Al SAMs. For PFTS/Al, stability tests demonstrate that modified aluminum is able to survive exposure to warm nitric acid (pH = 1.8, 60 °C, 30 min) indicating some degree of robustness. Hydrophobic, low adhesion, and robust aluminum surfaces have useful applications for micro/nano-electromechanical systems (MEMS/NEMS), such as digital micro-mirror devices (DMDs). These studies are expected to aid in the design and selection of proper lubricants for MEMS/NEMS.

e14004 Background: CD20 antigen is an established target for antibody therapy like R. Understanding interactions of CD20 antigens is important for developing better agents and overcoming resistance. We have developed a new innovative biosensor based quantitative technique to study real time interaction of CD20 antigens with R using QCM Piezo-immunosensor, which can be used to characterize cell surface antigen, study interactions and understand mechanisms of resistance. Methods: Binding of R with SAM of peptide mimotopes of CD20 antigen was systematically characterized. Four peptide mimotopes of CD 20 antigen were selected from literature and redesigned to allow their SAM immobilizations on gold electrodes through a peptide linker with cysteine. The bindings of these peptides with R and control antibodies (Trastuzumab, Bevacizumab) were characterized by Quartz Crystal Microbalance (QCM). Among the four peptide mimotopes initially selected, the peptide designated as CN-14 was the most selective and sensitive for R binding, which was further characterized by ellipsometry, atomic force microscopy and QCM. Results: We have shown a systematic approach for using QCM technique to quantify the apparent binding of CD20 and R. As the GLU residue pKa of CN-14 increased, the affinity of the SAM to Rituximab increased while the selectivity decreased. This was attributed to the weakening of the salt bridge between the CN-14 ARG-10 and GLU-13 at higher pKa values for GLU-13. Conclusions: Interaction of CD20 antigens with antibodies will help physicians to determine the clinical efficacy and resistance mechanisms to antibodies like R. QCM is low cost, highly sensitive, fast, synthetic, assay which could be used as a basis for developing a new generation of affinity-based Immunosensor assays. Our study shows that peptide mimotopes have potential benefit in sensor applications as the peptide-peptide interactions in the SAM could be manipulated by the addition of functional groups to the peptide to influence binding of the target protein as well as for surface immobilization via SAM.