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Thiagarajan S, Price E, Connors L, Dettman A, Koh AS. Study of n-Alkanethiol Self-Assembly Behavior on Iron Particles: Effect of Alkyl Chain Length and Adsorption Solvent on Resulting Iron-Based Magnetorheological Fluids. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2022; 38:13506-13521. [PMID: 36279502 DOI: 10.1021/acs.langmuir.2c02014] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/16/2023]
Abstract
Self-assembled monolayers (SAMs) of organic molecules on metal surfaces are a type of inexpensive surface coating often used to improve metal substrate properties for sensors, electrochemistry, and nanofabrication applications. Iron, specifically, is one of the most commonly used metals, both as a pure metal and as an alloy due to its high conductivity, strong ferromagnetism, and low cost. However, magnetorheological fluids, which have shown impressive energy dampening in fields from civil infrastructure to biomedical devices utilizing iron dispersions, have suffered from low reliability and efficiency due to iron particle oxidation, corrosion, and settling. To understand the effect of self-assembled monolayers on iron and both the adsorbed particle's resistance against aggregation and performance impact, this work performs an in-depth study on alkanethiol-based self-assembled monolayers on iron particles. Adsorption of alkanethiols and the generation of SAMs on micron-sized iron particles were evaluated as a function of adsorption solvent polarity and alkanethiol chain length. Maximum alkanethiol loading, determined from appropriate isotherms, was found to strongly be a function of both parameters. Alkanethiol adsorption increased with increasing alkyl chain length and increasing solvent log P values in polar solvents. With respect to magnetorheologically relevant parameters, alkanethiol adsorption did not show any significant effect on both the magnetic properties of iron (as particles) and fluid on-state yield stress. The colloidal stability of n-alkanethiol adsorbed iron-based magnetorheological fluids (MRFs) was a function of both n-alkanethiol chain length and the iron particle adsorption solvent. MRFs composed of hexadecanethiol adsorbed iron prepared in polar solvents like methanol and ethanol showed excellent sedimentation stability compared to all other MRFs prepared in this study.
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Affiliation(s)
- Sandhiya Thiagarajan
- Department of Chemical and Biological Engineering, University of Alabama, Tuscaloosa, Alabama35487, United States
| | - Emma Price
- Department of Chemical and Biological Engineering, University of Alabama, Tuscaloosa, Alabama35487, United States
| | - Lela Connors
- Department of Chemical and Biological Engineering, University of Alabama, Tuscaloosa, Alabama35487, United States
| | - Aubrey Dettman
- Department of Mechanical Engineering, University of Alabama, Tuscaloosa, Alabama35487, United States
| | - Amanda S Koh
- Department of Chemical and Biological Engineering, University of Alabama, Tuscaloosa, Alabama35487, United States
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Bhadra P, Siu SWI. Effect of Concentration, Chain Length, Hydrophobicity, and an External Electric Field on the Growth of Mixed Alkanethiol Self-Assembled Monolayers: A Molecular Dynamics Study. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2021; 37:1913-1924. [PMID: 33503375 DOI: 10.1021/acs.langmuir.0c03414] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Growing functionalized self-assembled monolayers (SAMs) with fewer defects and lower cost is the focus of ongoing investigations. In the present study, molecular dynamics simulations were performed to investigate the process of SAM formation on a gold substrate from mixed alkanethiolates in ethanol solution. Using the mixed-SAM system of 11-mercaptoundecanoic acid (MUA) with either 1-decanethiol (C9CH3) or 6-mercaptohexanol (C6OH) in a 3:7 ratio as the standard SAM model, we systematically investigated the effects of the concentration, chain length, functional group, and an external electric field on SAM growth. The results showed that the initial growth rate and surface coverage of the SAM are dependent on the ligand concentration. At a certain high concentration (about 1.2-1.5 times the minimum concentration), the final surface coverage is optimal. Reducing the chain length and increasing the proportion of hydrophobic diluting molecules are effective ways to improve the surface coverage, but the compositional ligands have to be changed, which may not be desirable for the functional requirements of SAMs. Furthermore, by investigating the behavior of the alkanethiolates and ethanol solvent under an applied external field, we find that a strong electric field with a proper field direction can facilitate the generation of defect-free monolayers. These findings will contribute to the understanding of mixed-SAM formation and provide insight into experimental design for efficient and effective SAM formation.
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Affiliation(s)
- Pratiti Bhadra
- Department of Computer and Information Science, University of Macau, Taipa, Macau
| | - Shirley W I Siu
- Department of Computer and Information Science, University of Macau, Taipa, Macau
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Kowalczyk A, Yu C. Ethanol vs. water: influence of the terminal functional group of the alkyl chain and environment of the self-assembly process on electron transport through the thiol layer. RSC Adv 2020; 10:21582-21592. [PMID: 35518744 PMCID: PMC9054384 DOI: 10.1039/d0ra04235h] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2020] [Accepted: 05/30/2020] [Indexed: 11/23/2022] Open
Abstract
Self-assembly of alkanethiol chains on metallic surfaces is a spontaneous process which leads to the formation of highly ordered layers. However, the organization of the thiol chains on the surface strongly depends on the intermolecular interactions between the terminal groups in the chain. The solution environment also plays an important role. In this paper we present the effect of solution solvent (water and ethanol) and the presence of various hydrophilic terminal groups (–OH, –NH2 and –COOH) on the quality and electrochemical properties of the formed alkanethiol layers. In the studies we applied voltammetry, atomic force microscopy and quartz crystal microbalance to characterize the morphology, packing density and ability to electron exchange through the thiol layer. The blocking properties of the formed SAMs expressed as the electron-transfer rate constant as well as their organization have been examined using a model electrochemical probe, Fe(CN)63−. With the increase in the polarity of the terminal functional group the regularity of the thiol layer decreased. The organization of the thiol chains on the surface strongly depends on the intermolecular interactions between the terminal groups in the chain and the solution environment.![]()
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Affiliation(s)
- Agata Kowalczyk
- Faculty of Chemistry
- University of Warsaw
- PL-02-093 Warsaw
- Poland
- State Key Laboratory of Electroanalytical Chemistry
| | - Cong Yu
- State Key Laboratory of Electroanalytical Chemistry
- Changchun Institute of Applied Chemistry
- Chinese Academy of Sciences
- Changchun 130022
- PR China
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Venkata Jagadeesh R, Lakshminarayanan V. Effect of solvents on the self-assembly of long chain alkylphosphonic acids on indium tin oxide surface - In situ studies on the adsorption kinetics and electron transfer process. J Electroanal Chem (Lausanne) 2019. [DOI: 10.1016/j.jelechem.2019.01.016] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
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Orságová Králová Z, Oriňak A, Oriňaková R, Petruš O, Macko J, Radoňak J, Sukovská Lakyová L, Jurašeková Z, Smith R, Strečková M, Koval K. Electrochemically deposited silver detection substrate for surface-enhanced Raman spectroscopy cancer diagnostics. JOURNAL OF BIOMEDICAL OPTICS 2018; 23:1-11. [PMID: 29981226 DOI: 10.1117/1.jbo.23.7.075002] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/27/2018] [Accepted: 06/18/2018] [Indexed: 05/20/2023]
Abstract
Surface-enhanced Raman spectroscopy (SERS) of blood plasma on an electrochemically prepared silver surface has been studied as a label-free, noninvasive diagnostic test for colorectal cancer. Indium tin oxide glass substrates were modified with 0.01 mol dm - 3 silver nitrate using the pulsed double-potentiostatic method. The prepared silver substrates were tested with Rhodamine 6G as a model analyte and the surface with the highest signal enhancement was selected. This silver dendritic surface was used as a diagnostic substrate for SERS measurements of human blood plasma. A group of oncological patients with declared colorectal carcinoma (n = 15) and the control group of healthy volunteers (n = 15) were compared. The biomolecular changes in chemical composition in the cancer samples were detected by statistical processing of the resulting SERS spectra. About 94% specificity and 100% sensitivity were achieved for the analysis by the ratio of the SERS peak intensity at 725 cm - 1 for adenine to the peak intensity at 638 cm - 1 for tyrosine and 100% specificity and sensitivity by using principal component analysis. This method of SERS diagnostics of colorectal cancer, which does not require the nanoparticle preparation, mixing, and incubation of plasma with a colloidal solution as in conventional tests, is a rapid, inexpensive method, which could be introduced as a primary diagnostic test.
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Affiliation(s)
| | | | | | | | - Ján Macko
- Pavol Jozef Šafárik Univ. in Košice, Slovakia
| | | | | | | | | | | | - Karol Koval
- Institute of Materials Research SAS, Slovakia
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Hu J, He S, Zhang Y, Ma H, Zhang X, Chen Z. Theoretical Insights into the Solvent Polarity Effect on the Quality of Self-Assembled N-Octadecanethiol Monolayers on Cu (111) Surfaces. Molecules 2018; 23:molecules23040733. [PMID: 29565816 PMCID: PMC6017570 DOI: 10.3390/molecules23040733] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2018] [Revised: 03/14/2018] [Accepted: 03/21/2018] [Indexed: 11/16/2022] Open
Abstract
The effect of solvent polarity on the quality of self-assembled n-octadecanethiol (C18SH) on Cu surfaces was systematically analyzed using first-principles calculations. The results indicate that the adsorption energy for C18SH on a Cu surface is −3.37 eV, which is higher than the adsorption energies of the solvent molecules. The higher adsorption energy of dissociated C18SH makes the monolayer self-assembly easier on a Cu (111) surface through competitive adsorption. Furthermore, the adsorption energy per unit area for C18SH decreases from −3.24 eV·Å−2 to −3.37 eV·Å−2 in solvents with an increased dielectric constant of 1 to 78.54. Detailed energy analysis reveals that the electrostatic energy gradually increases, while the kinetic energy decreases with increasing dielectric constant. The increased electrostatic energies are mainly attributable to the disappearance of electrostatic interactions on the sulfur end of C18SH. The decreased kinetic energy is mainly due to the generated push force in the polar solvent, which limits the mobility of C18SH. A molecular dynamics simulation also confirms that the -CH3 site has a great interaction with CH3(CH2)4CH3 molecules and a weak interaction with CH3CH2OH molecules. The different types of interactions help to explain why the surface coverage of C18SH on Cu in a high-polarity ethanol solution is significantly larger than that in a low-polarity n-hexane solution at the stabilized stage.
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Affiliation(s)
- Jun Hu
- School of Chemical Engineering, Northwest University, Xi'an 710069, Shaanxi, China.
| | - Shijun He
- School of Chemical Engineering, Northwest University, Xi'an 710069, Shaanxi, China.
| | - Yaozhong Zhang
- State Key Laboratory of Eco-Hydraulics in Northwest Arid Region of China, Xi'an University of Technology, Xi'an 710048, Shaanxi, China.
| | - Haixia Ma
- School of Chemical Engineering, Northwest University, Xi'an 710069, Shaanxi, China.
| | - Xiaoli Zhang
- School of Chemical Engineering, Northwest University, Xi'an 710069, Shaanxi, China.
| | - Zhong Chen
- School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore.
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Newcomb LB, Tevis ID, Atkinson MBJ, Gathiaka SM, Luna RE, Thuo M. Odd-even effect in the hydrophobicity of n-alkanethiolate self-assembled monolayers depends upon the roughness of the substrate and the orientation of the terminal moiety. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2014; 30:11985-11992. [PMID: 25233063 DOI: 10.1021/la5032569] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
The origin of the odd-even effect in properties of self-assembled monolayers (SAMs) and/or technologies derived from them is poorly understood. We report that hydrophobicity and, hence, surface wetting of SAMs are dominated by the nature of the substrate (surface roughness and identity) and SAM tilt angle, which influences surface dipoles/orientation of the terminal moiety. We measured static contact angles (θs) made by water droplets on n-alkanethiolate SAMs with an odd (SAM(O)) or even (SAM(E)) number of carbons (average θs range of 105.8-112.1°). When SAMs were fabricated on smooth "template-stripped" metal (M(TS)) surfaces [root-mean-square (rms) roughness = 0.36 ± 0.01 nm for Au(TS) and 0.60 ± 0.04 nm for Ag(TS)], the odd-even effect, characterized by a zigzag oscillation in values of θs, was observed. We, however, did not observe the same effect with rougher "as-deposited" (M(AD)) surfaces (rms roughness = 2.27 ± 0.16 nm for Au(AD) and 5.13 ± 0.22 nm for Ag(AD)). The odd-even effect in hydrophobicity inverts when the substrate changes from Au(TS) (higher θs for SAM(E) than SAM(O), with average Δθs |n - (n + 1)| ≈ 3°) to Ag(TS) (higher θs for SAM(O) than SAM(E), with average Δθs |n - (n + 1)| ≈ 2°). A comparison of hydrophobicity across Ag(TS) and Au(TS) showed a statistically significant difference (Student's t test) between SAM(E) (Δθs |Ag evens - Au evens| ≈ 5°; p < 0.01) but failed to show statistically significant differences on SAM(O) (Δθs |Ag odds - Au odds| ≈ 1°; p > 0.1). From these results, we deduce that the roughness of the metal substrate (from comparison of M(AD) versus M(TS)) and orientation of the terminal -CH2CH3 (by comparing SAM(E) and SAM(O) on Au(TS) versus Ag(TS)) play major roles in the hydrophobicity and, by extension, general wetting properties of n-alkanethiolate SAMs.
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Affiliation(s)
- Lucas B Newcomb
- Department of Chemistry, University of Massachusetts Boston , 100 Morrissey Boulevard, Boston, Massachusetts 02125, United States
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Nováková Z, Oriňáková R, Fedorková AS, Oriňák A. Electrochemical study of self-assembled monolayer adsorption. J Solid State Electrochem 2014. [DOI: 10.1007/s10008-014-2455-6] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Shen CH, Lin JC. Solvent and concentration effects on the surface characteristics and platelet compatibility of zwitterionic sulfobetaine-terminated self-assembled monolayers. Colloids Surf B Biointerfaces 2013; 101:376-83. [DOI: 10.1016/j.colsurfb.2012.07.035] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2012] [Revised: 07/23/2012] [Accepted: 07/26/2012] [Indexed: 10/28/2022]
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Bozzini B, Busson B, Gayral A, Humbert C, Mele C, Six C, Tadjeddine A. In situ electrochemical SFG/DFG study of CN- and nitrile adsorption at Au from 1-butyl-1-methyl-pyrrolidinium bis(trifluoromethylsulfonyl) amide ionic liquid([BMP][TFSA]) containing 4-{2-[1-(2-cyanoethyl)-1,2,3,4-tetrahydroquinolin-6-yl]diazenyl} benzonitrile (CTDB) and K[Au(CN)₂]. Molecules 2012; 17:7722-36. [PMID: 22732885 PMCID: PMC6268479 DOI: 10.3390/molecules17077722] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2012] [Revised: 05/22/2012] [Accepted: 05/23/2012] [Indexed: 11/29/2022] Open
Abstract
In this paper we report an in situ electrochemical Sum-/Difference Frequency Generation (SFG/DFG) spectroscopy investigation of the adsorption of nitrile and CN− from the ionic liquid 1-butyl-1-methyl-pyrrolidinium bis(trifluoromethylsulfonyl) amide ([BMP][TFSA]) containing 4-{2-[1-(2-cyanoethyl)-1,2,3,4-tetrahydroquinolin-6-yl]- diazenyl}benzonitrile (CTDB) at Au electrodes in the absence and in the presence of the Au-electrodeposition process from K[Au(CN)2]. The adsorption of nitrile and its coadsorption with CN− resulting either from the cathodic decomposition of the dye or from ligand release from the Au(I) cyanocomplex yield potential-dependent single or double SFG bands in the range 2,125–2,140 cm−1, exhibiting Stark tuning values of ca. 3 and 1 cm−1 V−1 in the absence and presence of electrodeposition, respectively. The low Stark tuning found during electrodeposition correlates with the cathodic inhibiting effect of CTDB, giving rise to its levelling properties. The essential insensitivity of the other DFG parameters to the electrodeposition process is due to the growth of smooth Au.
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Affiliation(s)
- Benedetto Bozzini
- Department of Innovation Engineering, University of Salento, Via Monteroni, 73100 Lecce, Italy.
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Bozzini B, Busson B, Humbert C, Mele C, Raffa P, Tadjeddine A. Investigation of Au electrodeposition from [BMP][TFSA] room-temperature ionic liquid containing K[Au(CN)2] by in situ two-dimensional sum frequency generation spectroscopy. J Electroanal Chem (Lausanne) 2011. [DOI: 10.1016/j.jelechem.2011.07.004] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Bozzini B, Tondo E, Bund A, Ispas A, Mele C. Electrodeposition of Au from [EMIm][TFSA] room-temperature ionic liquid: An electrochemical and Surface-Enhanced Raman Spectroscopy study. J Electroanal Chem (Lausanne) 2011. [DOI: 10.1016/j.jelechem.2010.11.015] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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Feng G, Niu T, You X, Wan Z, Kong Q, Bi S. Studies on the effect of electrode pretreatment on the coverage of self-assembled monolayers of dodecanethiol on gold by electrochemical reductive desorption determination. Analyst 2011; 136:5058-63. [DOI: 10.1039/c1an15642j] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Dyne J, Lin YS, Lai LMH, Ginges JZ, Luais E, Peterson JR, Goon IY, Amal R, Gooding JJ. Some More Observations on the Unique Electrochemical Properties of Electrode-Monolayer-Nanoparticle Constructs. Chemphyschem 2010; 11:2807-13. [DOI: 10.1002/cphc.201000250] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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Abraham John S, Sagara T. Short-time preparation and electrochemical properties of a single layer of tetraoctylammonium bromide capped Au nanoparticles on dithiol self-assembled monolayer-modified Au electrode. J Electroanal Chem (Lausanne) 2009. [DOI: 10.1016/j.jelechem.2009.05.009] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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Dai J, Li Z, Jin J, Cheng J, Kong J, Bi S. Study of the solvent effect on the quality of dodecanethiol self-assembled monolayers on polycrystalline gold. J Electroanal Chem (Lausanne) 2008. [DOI: 10.1016/j.jelechem.2008.07.001] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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Clair S, Variola F, Kondratenko M, Jedrzejowski P, Nanci A, Rosei F, Perepichka DF. Self-assembled monolayer of alkanephosphoric acid on nanotextured Ti. J Chem Phys 2008; 128:144705. [DOI: 10.1063/1.2876421] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Potential dependence of the structure of water at the hydrophobic liquid interface. J Electroanal Chem (Lausanne) 2007. [DOI: 10.1016/j.jelechem.2007.06.016] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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Subramanian S, Sampath S. Enhanced stability of short- and long-chain diselenide self-assembled monolayers on gold probed by electrochemistry, spectroscopy, and microscopy. J Colloid Interface Sci 2007; 312:413-24. [PMID: 17451727 DOI: 10.1016/j.jcis.2007.03.021] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2007] [Revised: 03/10/2007] [Accepted: 03/12/2007] [Indexed: 11/16/2022]
Abstract
Well-ordered, compact, self-assembled monolayers (SAMs) of hexyl and dodecyl diselenides have been formed on oriented (111) gold surfaces. Monolayer formation has been effected by adsorption from neat diselenides as well as millimolar solutions of diselenides in alcohol. The monolayer formation is confirmed using electrochemical quartz crystal microbalance studies. The stability and permeability of the monolayers at various temperatures have been probed using reflection absorption infrared spectroscopy (RAIRS) and electrochemistry. The RAIRS studies in the dry state show the formation of highly ordered, compact structures when adsorbed from neat compounds compared to the monolayers adsorbed in the presence of alcohol. The monolayers adsorbed from neat diselenide are quite stable as a function of temperature irrespective of the chain length. The electrochemical studies based on the blocking behavior of the monolayers toward electron transfer between a diffusing species and the electrode surface reflect the stability and the compactness of the structure. The results point out that the presence of solvent molecules during the SAM formation hinders the organization of the monolayer structure, especially in the case of short-chain diselenide monolayers.
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Affiliation(s)
- S Subramanian
- Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560 012, India
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Ganesh V, Pal SK, Kumar S, Lakshminarayanan V. Self-assembled monolayers (SAMs) of alkoxycyanobiphenyl thiols on gold surface using a lyotropic liquid crystalline medium. Electrochim Acta 2007. [DOI: 10.1016/j.electacta.2006.09.037] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Cohen-Atiya M, Nelson A, Mandler D. Characterization of n-alkanethiol self-assembled monolayers on mercury by impedance spectroscopy and potentiometric measurements. J Electroanal Chem (Lausanne) 2006. [DOI: 10.1016/j.jelechem.2006.04.018] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Hleli S, Martelet C, Abdelghani A, Bessueille F, Errachid A, Samitier J, Hays H, Millner P, Burais N, Jaffrezic-Renault N. An immunosensor for haemoglobin based on impedimetric properties of a new mixed self-assembled monolayer. MATERIALS SCIENCE & ENGINEERING. C, MATERIALS FOR BIOLOGICAL APPLICATIONS 2006. [DOI: 10.1016/j.msec.2005.10.054] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Ganesh V, Lakshminarayanan V. Self-assembled monolayers of alkanethiols on gold prepared in a hexagonal lyotropic liquid crystalline phase of Triton X-100/water system. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2006; 22:1561-70. [PMID: 16460075 DOI: 10.1021/la0519296] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
In this paper, we have reported a new method of preparing self-assembled monolayers (SAMs) of decanethiol and hexadecanethiol on gold surface by using a lyotropic liquid crystalline phase as an adsorbing medium. The stability and blocking ability of these SAMs were characterized using grazing angle Fourier transform infrared (FTIR) spectroscopy and electrochemical techniques such as cyclic voltammetry and electrochemical impedance spectroscopy. The lyotropic liquid crystalline medium possesses a hexagonal structure consisting of a nonionic surfactant Triton X-100, water, and the corresponding thiol, which provides a highly hydrophobic environment to solubilize the alkanethiols and later to facilitate their delivery to the gold surface. We find that the SAMs formed from the hexagonal liquid crystalline phase are highly compact and have excellent electrochemical blocking ability towards the redox probes compared to conventional SAMs prepared from commonly used organic solvents such as ethanol. From the impedance studies, we have determined the capacitance of the monolayer-coated electrodes and the surface coverage of the SAM, which has been found to be >99.98% on gold surface. We have also estimated the extent of ionic permeability through the film and measured the rate constants for the redox reactions on the SAM-modified electrodes. Our results show that the rate constants of [Fe(CN)6](3-/4-) and [Ru(NH3)6](2+/3+) redox couples are very much lower in the case of monolayers prepared in liquid crystalline phase compared to the SAM formed in 1 mM thiol in ethanol solution, suggesting a better blocking ability of the SAMs in the former case. From the grazing angle FTIR spectroscopic studies and capacitance measurements, we have ruled out any coadsorption of surfactant molecules on the Au surface. These results suggest that SAMs of very low defect density and extremely low ionic permeability can be obtained when a hexagonal lyotropic liquid crystalline phase is used as an adsorbing medium.
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Affiliation(s)
- V Ganesh
- Raman Research Institute, C.V. Raman Avenue, Sadashivanagar, Bangalore-560080, India
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Canaria CA, So J, Maloney JR, Yu CJ, Smith JO, Roukes ML, Fraser SE, Lansford R. Formation and removal of alkylthiolate self-assembled monolayers on gold in aqueous solutions. LAB ON A CHIP 2006; 6:289-95. [PMID: 16450040 DOI: 10.1039/b510661c] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
We report the development of novel reagents and approaches for generating recyclable biosensors. The use of aqueous media for the formation of protein binding alkylthiolate monolayers on Au surfaces results in accelerated alkylthiolate monolayer formation and improvement in monolayer integrity as visualized by fluorescence microscopy and CV techniques. We have also developed an electrocleaning protocol that is compatible with microfluidics devices, and this technique serves as an on-chip method for cleaning Au substrates both before and after monolayer formation. The techniques for the formation and dissociation of biotinylated SAMs from aqueous solvents reported here may be applied towards the development of Au-based sensor devices and microfluidics chips in the future. A potential use of these devices includes the specific capture and triggered release of target cells, proteins, or small molecules from liquid samples.
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Affiliation(s)
- Christie A Canaria
- Department of Chemistry, California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125, USA
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Zhao J, Bradbury CR, Huclova S, Potapova I, Carrara M, Fermín DJ. Nanoparticle-Mediated Electron Transfer Across Ultrathin Self-Assembled Films. J Phys Chem B 2005; 109:22985-94. [PMID: 16853995 DOI: 10.1021/jp054127s] [Citation(s) in RCA: 99] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The electrochemical behavior of arrays of Au nanoparticles assembled on Au electrodes modified by 11-mercaptoundecanoic acid (MUA) and poly-L-lysine (PLYS) was investigated as a function of the particle number density. The self-assembled MUA and PLYS layers formed compact ultrathin films with a low density of defects as examined by scanning tunneling microscopy. The electrostatic adsorption of Au particles of 19 +/- 3 nm on the PLYS layer resulted in randomly distributed arrays in which the particle number density is controlled by the adsorption time. In the absence of the nanoparticles, the dynamics of electron transfer involving the hexacynoferrate redox couple is strongly hindered by the self-assembled film. This effect is primarily associated with a decrease in the electron tunneling probability as the redox couple cannot permeate through the MUA monolayer at the electrode surface. Adsorption of the Au nanoparticles dramatically affects the electron-transfer dynamics even at low particle number density. Cyclic voltammetry and impedance spectroscopy were interpreted in terms of classical models developed for partially blocked surfaces. The analysis shows that the electron transfer across a single particle exhibits the same phenomenological rate constant of electron transfer as for a clean Au surface. The apparent unhindered electron exchange between the nanoparticles and the electrode surface is discussed in terms of established models for electron tunneling across metal-insulator-metal junctions.
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Affiliation(s)
- Jianjun Zhao
- Departement für Chemie und Biochemie, Universität Bern, Freiestrasse 3, CH-3012 Bern, Switzerland
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Helmy R, Kazakevich Y, Ni C, Fadeev AY. Wetting in Hydrophobic Nanochannels: A Challenge of Classical Capillarity. J Am Chem Soc 2005; 127:12446-7. [PMID: 16144365 DOI: 10.1021/ja053267c] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We report an investigation of the water-hydrophobic interface in well-defined nanochannels (R approximately 2-4 nm). Wetting in these systems cannot be described by classical (macroscopic) capillary theory: (1) water occupies only a fraction ( approximately 60%) of the pore volume, and (2) the capillary pressures are approximately 60-90% greater than predicted by the Laplace equation. The results suggest the presence of approximately 0.6 nm layer of low-density fluid (vapor) separating water from the hydrophobic solid.
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Affiliation(s)
- Roy Helmy
- Department of Chemistry and Biochemistry, Seton Hall University, South Orange, New Jersey 07079, USA
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