Redox-Active Monolayers on ITO Prepared by Post-Amidation and Direct Esterification and Their Spectroelectrochemical Characterization

Abstract

A redox-active monolayer on an optically transparent electrode constitutes a typical platform for spectroelectrochemical sensing. The necessity for its sophistication arises from the availability of multi-dimensional sensing signals. Simultaneous monitoring of the redox current and color change synchronized with the oxidation state change significantly enhances sensitivity and selectivity. This study aimed to elucidate the modification of an indium tin oxide (ITO) electrode with a viologen monolayer with an ordered orientation. Novel methods were developed to immobilize a viologen molecule bearing a carboxyl group to form assembled monolayers through a condensation reaction using 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide with N-hydroxy-succinimide (EDC/NHS). In the two methods of immobilization, one utilizes a two-step process to firstly form an aromatic siloxane base layer and subsequently attach the viologen derivative through an amide linkage by post-amidation. The other employs a direct ester linkage between the hydroxyl groups of the ITO surface and the carboxyl group of the viologen derivative. The latter method was also applied to immobilize a ferrocenyl group at a very short distance from the ITO surface. Potential-modulated UV-visible transmission absorption spectral measurement techniques with oblique incidence of plane-polarized light were employed to determine the orientation of the longitudinal axis of the reduced form of the viologen. The frequency dependence data of the potential-modulated transmission absorption signals were utilized to analyze the electron transfer kinetics. The performance of the two viologen-modified electrodes was compared to that of an ITO modified by post-amidation to the most commonly used base layer prepared with 3-aminopropyl triethoxysilane.

Keywords

Redox-active monolayer / ITO electrode / Absorption spectroscopy / Molecular orientation / EDC/NHS

Supporting Information

Additional information as noted in the text. This material is available free of charge via the internet at https://jelectrochem.xmu.edu.cn/journal/

Acknowledgements

We thank financial supports by the Grant-in-Aid of Scientific Research of Challenging Research (Exploratory) (JP23K17738) to TS from MEXT of Japan and by the 41st grant of research from Nippon Sheet Glass Foundation for Materials Science and Engineering to TS. We also thank Dr. Hong-Xiang Wang (Nagasaki University) for her help in translating the abstract from English to Chinese.

Conflicts of Interest statements

The authors declare that they have no conflict of interest.

Data Availability

The data generated during the current study are available from the corresponding author on reasonable request.

Author contributions

All authors have given approval to the manuscript. Takamasa Sagara: Conceptualization (Lead), Project administration (Lead), Supervision (Lead), Analysis (Supporting), Writing –original draft (Lead), Writing – review & editing (Lead), Funding acquisition (Lead); Sae Nakai: Investigation and Analysis (Lead), Methodology (Lead), Visualization (Lead), Writing –original draft (Supporting), Writing – review & editing (Supporting); Ryusuke Yofu: Investigation and Analysis (Lead), Methodology (Lead), Visualization (Lead), Writing – review & editing (Supporting); Shota Kojin: Investigation and Analysis (Lead), Methodology (Lead), Visualization (Lead), Writing – review & editing (Supporting).

References

[1] Markovich I, Mandler D. Preparation and characterization of octadecylsilane monolayers on indium-tin oxide (ITO) surfaces[J]. J. Electroanal. Chem., 2001, 500(1-2): 453-460.

[2] Sagiv J. Organized monolayers by adsorption. 1. Formation and structure of oleophobic mixed monolayers on solid surfaces[J]. J. Am. Chem. Soc., 1980, 102(1): 92-98.

[3] Untereker D F, Lennox J C, Wier L M, Moses P R, Murray R W. Chemically modified electrodes: Part IV. Evidence for formation of monolayers of bonded organosilane reagents[J]. J. Electroanal. Chem., 1977, 81(2): 309-318.

[4] Borges-Muñoz A C, Miller D P, Zurek E, Colón L A. Silanization of superficially porous silica particles with p-aminophenyltrimethoxysilane[J]. Microchem. J., 2019, 147: 263-268.

[5] Ebner A, Hinterdorfer P, Gruber H J. Comparison of different aminofunctionalization strategies for attachment of single antibodies to AFM cantilevers[J]. Ultramicroscopy, 2007, 107(10-11): 922-927.

[6] Pour F A, Zandi H. DFT electron transport study of quantum dot sensitized solar cells linkers[J]. Optik, 2017, 143: 199-204.

[7] Clegg R S, Hutchison J E. Hydrogen-bonding, self-sssembling monolayers: Ordered molecular films for study of through-peptide electron transfer[J]. Langmuir, 1996, 12(22): 5239-5243.

[8] Clegg R S, Hutchison J E. Control of monolayer assembly atructure by hydrogen bonding rather than by adsorbate-substrate templating[J]. J. Am. Chem. Soc., 1999, 121(22): 5319-5327.

[9] Valiokas R, Östblom M, Svedhem S, Svensson S C T, Liedberg B J. Thermal stability of self-assembled monolayers:  Influence of lateral hydrogen bonding[J]. Phys. Chem. B, 2002, 106(40): 10401-10409.

[10] Sek S, Misicka A, Bilewicz R. Effect of interchain hydrogen bonding on electron transfer through alkanethiol monolayers containing amide bonds[J]. J. Phys. Chem., 2000, 104(22): 5399-5402.

[11] Ikeda T, Tahara K, Kadoya T, Tajima H, Toyoda N, Yasuno S, Ozawa Y, Abe M. Ferrocene on insulator: Silane coupling to a SiO₂ surface and influence on electrical transport at a buried interface with an organic semiconductor layer[J]. Langmuir, 2020, 36(21): 5809-5819.

[12] Wang B, Tahara H, Sagara T. Driving quick and large amplitude contraction of viologen-incorporated poly-L-lysine-based hydrogel by reduction[J]. ACS Appl. Mater. Interfaces, 2018, 10(42), 36415-36424.

[13] Katz E, Itzhak N, Willner I. Electron transfer in self-assembled monolayers of N-methyl-N’-carboxyalkyl-4,4’-bipyridinium linked to gold electrode[J]. Langmuir, 1993, 9(5): 1392-1396.

[14] Kurniawan C, Noguchi H, Masuda T, Uosaki K. Spectroelectrochemical evidence of the role of viologen moiety as an electron transfer mediator from ITO substrate to a Pt complex acting as a confined molecular catalyst for hydrogen evolution reaction[J]. Electrochem. Commun., 2016, 62: 56-59.

[15] Gardner T J, Daniel Frisbie C, Wrighton M S. Systems for orthogonal self-assembly of electroactive monolayers on Au and ITO: An approach to molecular Electronics[J]. J. Am. Chem. Soc., 1995, 117(26): 6927-6933.

[16] Chen X, Luais E, Darwish N, Ciampi S, Thordarson P, Gooding J J. Studies on the effect of solvents on self-assembled monolayers formed from organophosphonic acids on indium tin oxide[J]. Langmuir, 2012, 28(25): 9487-9495.

[17] Kemal Havarea A, Can M, Demic S, Okur S, Kus M, Aydın H, Yagmurcukardes N, Tari S. Modification of ITO surface using aromatic small molecules with carboxylic acid groups for OLED applications[J]. Synth. Met., 2011, 161(21-22): 2397-2404.

[18] Aydın E B, Aydın M, Sezgintürk M K. A highly sensitive immunosensor based on ITO thin films covered by a new semi-conductive conjugated polymer for the determination of TNFα in human saliva and serum samples[J]. Biosens. Bioelectron, 2017, 97:169-176.

[19] Wang W L, Zhai J, Jiang L, Bai F L, Ren Y J, Zhang B, Cai S M. Novel photoactive self-assembled rigid monolayer of a perylene derivative: fabrication and characterization[J]. Colloids Surf., A, 2005, 257-258: 489-495.

[20] Guo Y, Zhao J W, Zhu J J. Study on the intermolecular interactions between the functional moieties in ferrocene-terminated alkanethiol self-assembled monolayer on gold[J]. Thin Solid Films, 2008, 516(10): 3051-3057.

[21] Nerngchamnong N, Thompson D, Cao L, Yuan L, Jiang L, Roemer M, Nijhuis C A. Nonideal Electrochemical behavior of ferrocenyl-alkanethiolate SAMs maps the microenvironment of the redox unit[J]. J. Phys. Chem. C, 2015, 119(38): 21978-21991.

[22] Huffman B L, Bredar A R C, Dempsey J L. Origins of non-ideal behaviour in voltammetric analysis of redox-active monolayers[J]. Nat. Rev. Chem. 2024, 8, 628-643.

[23] Zotti G, Schiavon S, Zecchin S, Berlin A, Pagani G. Adsorption of ferrocene compounds on Indium-Tin-Oxide electrodes. Enhancement of adsorption by decomposition of ferrocenium molecules by oxygen[J]. Langmuir, 1998, 14(7):1728-1733.

[24] Sagara T, Kato N, Toyota A, Nakashima N. Anomalous electroreflectance and absorption spectra of viologen radical cation in close proximity of gold nanoparticles at electrified interfaces[J]. Langmuir, 2002, 18(18): 6995-7001.

[25] Toyota A, Nakashima N, Sagara T. UV-visible transmission-absorption spectral study of Au nanoparticles on a modified ITO electrode at constant potentials and under potential modulation[J]. J. Electroanal. Chem., 2004, 565(2): 335-342.

[26] Komino T, Tajima H, Matsuda M. A relationship between molecular orientation and current-voltage characteristics in poly(3-hexylthiophene) thin film[J]. Chem. Lett., 2008, 37(7): 690-691.

[27] Sagara T. UV-visible reflectance spectroscopy of thin organic films at electrode surfaces[M]// Advances in Electrochemical Science and Engineering Vol. 9 (Alkire, C, Kolb, D M, Lipkowski, J, Ross, P. N. Eds), Weinheim: Wiley-VCH Verlag, 2006: 47-95.

[28] Sagara T, Kubo Y, Hiraishi K. Estimation of the orientation of heme in cytochrome c immobilized on a carboxylate-terminated alkanethiol monolayer on a Au electrode by the use of electroreflectance spectroscopy with polarized light incidence[J]. J. Phys. Chem. B, 2006, 110(33): 16550-16558.

[29] Sagara T, Hagi Y, Toyohara M. Binding of sulfate-terminated surfactants with different alkyl chain lengths to viologen sites covalently embedded in the interior of a self-assembled monolayer on a Au electrode[J]. Langmuir, 2022, 38(3): 979-986.

[30] Monk P M S. The viologens[M]. Chichester: John-Wiley & Sons, 1998.

[31] Sagara T, Eguchi H. Revisiting aqueous redox process of alkyl-linked bis-viologen: Evaluation of redox potential inversion[J]. Electrochim. Acta 2019, 295: 215-223.

[32] Patterson B C, Hurst J K. Pathways of viologen-mediated oxidation-reduction reactions across dihexadecyl phosphate bilayer membranes[J]. J. Phys. Chem., 1993, 97(2): 454-465.

[33] Sagara T, Maeda H, Yuan Y, Nakashima N. Voltammetric and electroreflectance study of thiol-functionalized viologen monolayers on polycrystalline gold: Effect of anion binding to a viologen moiety[J]. Langmuir, 1999, 15(11): 3823-3830.

[34] Sagara T, Kaba N, Komatsu M, Uchida M, Nakashima N. Estimation of average orientation of surface-confined chromophores on electrode surfaces using electroreflectance spectroscopy[J]. Electrochim. Acta, 1998, 43: 2183-2193.

[35] Laviron E. General expression of the linear potential sweep voltammogram in the case of diffusionless electrochemical systems[J]. J. Electroanal. Chem. Interfacial Electrochem., 1979, 101(1): 19-28.

[36] Wang H, Chen S F, Li L G, Jiang S Y. Improved method for the preparation of carboxylic acid and amine terminated self-assembled monolayers of alkanethiolates[J]. Langmuir, 2005, 20(7): 2633-2636.