Electroactive Interface for Enabling Spectroelectrochemical Investigations in Evanescent-Wave Cavity-Ring-Down Spectroscopy

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.

Adsorption Properties and Electron-transfer Rates of a Redox Probe at Different Interfaces of an Immunoassay Assembled on an Electro-active Photonic Platform

“…Also, the lowest binding affinity of Cyt-C was observed when the EA-IOW was functionalized with APTES, presumably due to the electrostatic repulsion between Cyt-C and APTES, which both have overall positive charges at neutral pH 44,45 . When compared to ITO/APTES interface a clear increase in the equilibrium constant for the bare ITO is seen, this may be attributed to the favorable adsorption based on the electrostatic attraction between positively charged amino acid residues (lysine) and the −OH groups of ITO; these results are agree well with reported work of Cyt-C adsorption onto ITO surface 39,46 . In Table 1 it is also noticed that the Ab in combination with the ProG species show a higher equilibrium, which indicates that most likely the ProG indeed works to properly orient the capturing Ab for efficient binding of analyte 47,48 .…”

Construction of Janus-structured ZnO@ZIF-8(-NH2)/cellulose nanofiber foam for highly efficient adsorption and photocatalysis-assisted desorption of tetracycline

“…This indicated that bi-sources of Zn and the ligand aided in the construction of more defective interfaces in C-ZnO 0.5 /ZAA foam, which was shown to have a high redox ability when compared to pure ZnO and ZIF-8. 103,104 Based on the above photo-electric performance analysis, C-ZnO 0.5 /ZAA foam had enhanced photo-absorption, photo-induced electrons, conductivity, and redox ability, endowing C-ZnO 0.5 /ZAA foam with efficient photocatalysis-assisted regeneration.…”

Cavity Ring-Down Spectroscopy: Recent Technological Advancements, Techniques, and Applications

“…Copyright 2020 American Chemical Society. (b) Reproduced from Alnaanah, S. A.; Roussel, T. J., Jr.; Ghithan, J. H.; Qatamin, A. H.; Irziqat, M. A.; Telfah, H.; Liu, J.; Mendes, S. B. Analytical Chemistry 2020 , 92 (16), 11288–11296 (ref ). Copyright 2020 American Chemical Society.…”

“…They reported a minimum detection limit of 1.2 pM for the detection of a mutated gene associated with sickle-cell anemia. However, Alnaanah et al, 111 in a recent study, demonstrated a unique electrically active EW-CRDS platform to investigate the spectroelectrochemical redox events (Figure 9b). They coated the TIR surface of a rightangled NBK-7 prism with an electroactive and highly transparent indium tin oxide (ITO) film of thickness about 13 nm.…”