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Alnaanah SA, Roussel TJ, Ghithan JH, Qatamin AH, Irziqat MA, Telfah H, Liu J, Mendes SB. Electroactive Interface for Enabling Spectroelectrochemical Investigations in Evanescent-Wave Cavity-Ring-Down Spectroscopy. Anal Chem 2020; 92:11288-11296. [PMID: 32689790 DOI: 10.1021/acs.analchem.0c01956] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
In this study, we report the development of an electrically active solid-liquid interface for the evanescent-wave cavity-ring-down spectroscopic (EW-CRDS) technique to enable spectroelectrochemical investigations of redox events. Because of a high-quality transparent conductive electrode film of indium tin oxide (ITO) coated on the interface of total internal reflection of the EW-CRDS platform, a cavity ring-down time of about 900 ns was obtained allowing spectroelectrochemical studies at solid-liquid interfaces. As a proof-of-concept on the capabilities of the developed platform, measurements were performed to address the effects of an applied electric potential to the adsorption behavior of the redox protein cytochrome c (Cyt-C) onto different interfaces, namely, bare-ITO, 3-aminopropyl triethoxysilane (APTES), and Cyt-C antibody. For each interface, the adsorption and desorption constants, the surface equilibrium constant, the Gibbs free energy of adsorption, and the surface coverage were optically measured by our electrically active EW-CRDS tool. Optical measurements at a set of constant discrete values of the applied electric potential were acquired for kinetic adsorption analysis. Cyclic voltammetry (CV) scans under synchronous optical readout were performed to study the effects of each molecular interface on the redox process of surface-adsorbed protein species. Overall, the experimental results demonstrate the ability of the electro-active EW-CRDS platform to unambiguously measure electrode-driven redox events of surface-confined molecular species at low submonolayer coverages and at a single diffraction-limited spot. Such capability is expected to open several opportunities for the EW-CRDS technique to investigate a variety of electrochemical phenomena at solid-liquid interfaces.
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Affiliation(s)
- Shadi A Alnaanah
- Department of Physics and Astronomy, University of Louisville, Louisville, Kentucky 40208, United States
| | - Thomas J Roussel
- Department of Bioengineering, University of Louisville, Louisville, Kentucky 40208, United States
| | - Jafar H Ghithan
- Department of Physics and Astronomy, University of Louisville, Louisville, Kentucky 40208, United States
| | - Aymen H Qatamin
- Department of Physics and Astronomy, University of Louisville, Louisville, Kentucky 40208, United States
| | - Mohammed A Irziqat
- Department of Physics and Astronomy, University of Louisville, Louisville, Kentucky 40208, United States
| | - Hamzeh Telfah
- Department of Chemistry, University of Louisville, Louisville, Kentucky 40292, United States
| | - Jinjun Liu
- Department of Chemistry, University of Louisville, Louisville, Kentucky 40292, United States
| | - Sergio B Mendes
- Department of Physics and Astronomy, University of Louisville, Louisville, Kentucky 40208, United States
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Akkilic N, Kamran M, Stan R, Sanghamitra NJM. Voltage-controlled fluorescence switching of a single redox protein. Biosens Bioelectron 2014; 67:747-51. [PMID: 25103339 DOI: 10.1016/j.bios.2014.07.051] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2014] [Revised: 07/14/2014] [Accepted: 07/22/2014] [Indexed: 02/07/2023]
Abstract
Heterogeneous electron transfer (ET) of the redox protein, wild-type azurin (wt-Az) from Pseudomonas aeruginosa, was monitored at the single-molecule (SM) level by fluorescence resonance energy transfer (FRET), one electron at a time. Azurin molecules were labeled with an organic fluorophore (Cy5), and the FRET-coupling between Cy5 and the redox center (copper) was used to study ET to a semi-transparent, 10nm thin gold electrode in an optical configuration. By using a confocal microscope and a bipotentiostat for control of the electrode potential, the oxidation and reduction processes of individual Az-Cy5 molecules were monitored. In the oxidized state of the redox center of the azurin molecule, the fluorescence emission of the covalently attached Cy5 was largely quenched by FRET ('off'-state), whereas the emission was recovered upon reduction ('on'-state). The work presented here, shows directly controlled single redox switching events of an individual redox protein and its thermodynamic dispersion. We show that the distribution of midpoint potentials (E0) of individual azurin molecules peaks at 45.7±0.5 mV with a full width at half maximum of 15 mV vs saturated calomel electrode (SCE).
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Affiliation(s)
- Namik Akkilic
- Leiden Institute of Physics, Huygens Laboratory, Leiden University, Leiden, The Netherlands.
| | - Muhammad Kamran
- Leiden Institute of Physics, Huygens Laboratory, Leiden University, Leiden, The Netherlands
| | - Razvan Stan
- Leiden Institute of Physics, Huygens Laboratory, Leiden University, Leiden, The Netherlands
| | - Nusrat J M Sanghamitra
- Leiden Institute of Physics, Huygens Laboratory, Leiden University, Leiden, The Netherlands
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O'Connell MA, de Cuendias A, Gayet F, Shirley IM, Mackenzie SR, Haddleton DM, Unwin PR. Evanescent wave cavity ring-down spectroscopy (EW-CRDS) as a probe of macromolecule adsorption kinetics at functionalized interfaces. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2012; 28:6902-6910. [PMID: 22489550 DOI: 10.1021/la3006053] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Evanescent wave cavity ring-down spectroscopy (EW-CRDS) has been employed to study the interfacial adsorption kinetics of coumarin-tagged macromolecules onto a range of functionalized planar surfaces. Such studies are valuable in designing polymers for complex systems where the degree of interaction between the polymer and surface needs to be tailored. Three tagged synthetic polymers with different functionalities are examined: poly(acrylic acid) (PAA), poly(3-sulfopropyl methacrylate, potassium salt) (PSPMA), and a mannose-modified glycopolymer. Adsorption transients at the silica/water interface are found to be characteristic for each polymer, and kinetics are deduced from the initial rates. The chemistry of the adsorption interfaces has been varied by, first, manipulation of silica surface chemistry via the bulk pH, followed by surfaces modified by poly(L-glutamic acid) (PGA) and cellulose, giving five chemically different surfaces. Complementary atomic force microscopy (AFM) imaging has been used for additional surface characterization of adsorbed layers and functionalized interfaces to allow adsorption rates to be interpreted more fully. Adsorption rates for PSPMA and the glycopolymer are seen to be highly surface sensitive, with significantly higher rates on cellulose-modified surfaces, whereas PAA shows a much smaller rate dependence on the nature of the adsorption surface.
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Ash PA, Vincent KA. Spectroscopic analysis of immobilised redox enzymes under direct electrochemical control. Chem Commun (Camb) 2011; 48:1400-9. [PMID: 22057715 DOI: 10.1039/c1cc15871f] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
This article reviews recent developments in spectroscopic analysis of electrode-immobilised enzymes under direct, unmediated electrochemical control. These methods unite the suite of spectroscopic methods available for characterisation of structural, electronic and coordination changes in proteins with the exquisite control over complex redox enzymes that can be achieved in protein film electrochemistry in which immobilised protein molecules exchange electrons directly with an electrode. This combination is particularly powerful in studies of highly active enzymes where redox states can be controlled even under fast electrocatalytic turnover. We examine examples in which UV-visible, IR, Raman and MCD spectroscopy have been combined with direct electrochemistry to probe redox-dependent chemistry, and consider future opportunities for 'direct' spectroelectrochemistry of immobilised enzymes.
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Affiliation(s)
- Philip A Ash
- Inorganic Chemistry Laboratory, Department of Chemistry, University of Oxford, South Parks Road, Oxford, OX1 3QR, UK
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Schnippering M, Neil SRT, Mackenzie SR, Unwin PR. Evanescent wave cavity-based spectroscopic techniques as probes of interfacial processes. Chem Soc Rev 2011; 40:207-20. [DOI: 10.1039/c0cs00017e] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
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