Time-Resolved Luminescence Spectroelectrochemistry at Screen-Printed Electrodes: Following the Redox-Dependent Fluorescence of [Ru(bpy)3]2

Anion Sensing through Redox-Modulated Fluorescent Halogen Bonding and Hydrogen Bonding Hosts

Anion sensing via either optical or electrochemical readouts has separately received enormous attention, however, a judicious combination of the advantages of both modalities remains unexplored. Toward this goal, we herein disclose a series of novel, redox-active, fluorescent, halogen bonding (XB) and hydrogen bonding (HB) BODIPY-based anion sensors, wherein the introduction of a ferrocene motif induces remarkable changes in the fluorescence response. Extensive fluorescence anion titration, lifetime and electrochemical studies reveal anion binding-induced emission modulation through intramolecular photoinduced electron transfer (PET), the magnitude of which is dependent on the nature of both the XB/HB donor and anion. Impressively, the XB sensor outperformed its HB congener in terms of anion binding strength and fluorescence switching magnitude, displaying significant fluorescence turn-OFF upon anion binding. In contrast, redox-inactive control receptors display a turn-ON response, highlighting the pronounced impact of the introduction of the redox-active ferrocene on the optical sensing performance. Additionally, the redox-active ferrocene motif also serves as an electrochemical reporter group, enabling voltammetric anion sensing in competitive solvents. The combined advantages of both sensing modalities were further exploited in a novel, proof-of-principle, fluorescence spectroelectrochemical anion sensing approach, enabling simultaneous and sensitive read out of optical and electrochemical responses in multiple oxidation states and at very low receptor concentration.

Enhanced spectroelectrochemistry with lossy-mode resonance optical fiber sensor

Spectroelectrochemical (SEC) measurements play a crucial role in analytical chemistry, utilizing transparent or semitransparent electrodes for optical analysis of electrochemical (EC) processes. The EC readout provides information about the electrode's state, while changes in the transmitted optical spectrum help identify the products of EC reactions. To enhance SEC measurements, this study proposes the addition of optical monitoring of the electrode. The setup involves using a polymer-clad silica multimode fiber core coated with indium tin oxide (ITO), which serves as both the electrode and an optical fiber sensor. The ITO film is specifically tailored to exhibit the lossy-mode resonance (LMR) phenomenon, allowing for simultaneous optical monitoring alongside EC readouts. The LMR response depends on the properties of the ITO and the surrounding medium's optical properties. As a result, the setup offers three types of interrogation readouts: EC measurements, optical spectrum analysis corresponding to the volume of the analyte (similar to standard SEC), and LMR spectrum analysis reflecting the state of the sensor/electrode surface. In each interrogation path, cyclic voltammetry (CV) experiments were conducted individually with two oxidation-reduction reaction (redox) probes: potassium ferricyanide and methylene blue. Subsequently, simultaneous measurements were performed during chronoamperometry (CA) with the sensor, and the cross-correlation between the readouts was examined. Overall, this study presents a novel and enhanced SEC measurement approach that incorporates optical monitoring of the electrode. It provides a comprehensive understanding of EC processes and enables greater insights into the characteristics of the analyte.

Survey of Recent Advances in Molecular Fluorophores, Unconjugated Polymers, and Emerging Functional Materials Designed for Electrofluorochromic Use

In this review, recent advances that exploit the intrinsic emission of organic materials for reversibly modulating their intensity with applied potential are surveyed. Key design strategies that have been adopted during the past five years for developing such electrofluorochromic materials are presented, focusing on molecular fluorophores that are coupled with redox-active moieties, intrinsically electroactive molecular fluorophores, and unconjugated emissive organic polymers. The structural effects, main challenges, and strides toward addressing the limitations of emerging fluorescent materials that are electrochemically responsive are surveyed, along with how these can be adapted for their use in electrofluorochromic devices.

Operando Imaging of Chemical Activity on Gold Plates with Single-Molecule Electrochemiluminescence Microscopy

Classical electrochemical characterization tools cannot avoid averaging between the active reaction sites and their support, thus obscuring their intrinsic roles. Single-molecule electrochemical techniques are thus in high demand. Here, we demonstrate super-resolution imaging of Ru(bpy)₃ ²⁺ based reactions on Au plates using single-molecule electrochemiluminescence microscopy. By converting electrochemical signals into optical signals, we manage to achieve the ultimate sensitivity of single-entity chemistry, that is directly resolving the single photons from individual electrochemical reactions. High spatial resolution, up to 37 nm, further enables mapping Au chemical activity and the reaction kinetics. The spatiotemporally resolved dynamic structure-activity relationship on Au plates shows that the restructuring of catalysts plays an important role in determining the reactivity. Our approach may lead to gaining new insights towards evaluating and designing electrocatalytic systems.

Electrochemical Detection and Characterization of Nanoparticles with Printed Devices

Innovative methods to achieve the user-friendly, quick, and highly sensitive detection of nanomaterials are urgently needed. Nanomaterials have increased importance in commercial products, and there are concerns about the potential risk that they entail for the environment. In addition, detection of nanomaterials can be a highly valuable tool in many applications, such as biosensing. Electrochemical methods using disposable, low-cost, printed electrodes provide excellent analytical performance for the detection of a wide set of nanomaterials. In this review, the foundations and latest advances of several electrochemical strategies for the detection of nanoparticles using cost-effective printed devices are introduced. These strategies will equip the experimentalist with an extensive toolbox for the detection of nanoparticles of different chemical nature and possible applications ranging from quality control to environmental analysis and biosensing.

Ruthenium and manganese metalloporphyrins modified screen-printed electrodes for bio-relevant electroactive targets

Ruthenium(II) 5-(4[Formula: see text]-sulfanylmethylphenyl)-10,15,20-triphenylporphyrin (Ru-TPP-SH) and manganese(III) 5-(4[Formula: see text]-sulfanylmethylphenyl)-10,15,20-triphenylporphyrin (Mn-TPP-SH) were synthesized, spectroscopically characterized and drop casted to modify screen-printed electrodes (SPEs). The modified SPEs were then tested against the redox target [Fe(CN)6][Formula: see text] in comparison with the bare SPE and SPE modified with the free porphyrin. The best performing one, [Formula: see text]. Mn-TPP-SH was used for the electrochemical detection of 1,4–benzoquinone, serotonin, caffeic and ascorbic acids, the latter also in association with uric acid, showing good electrocatalytic properties. The tunability of the metal-TPP-SH through the choice of the coordinating metal, the drop casting conditions and possible further functionalization make this type of porphyrin a good candidate for further developments of porphyrin-modified SPEs.

Recent advances in spectroelectrochemistry

The integration of two quite different techniques, conventional electrochemistry and spectroscopy, into spectroelectrochemistry (SEC) provides a complete description of chemically driven electron transfer processes and redox events for different kinds of molecules and nanoparticles. SEC possesses interdisciplinary advantages and can further expand the scopes in the fields of analysis and other applications, emphasizing the hot issues of analytical chemistry, materials science, biophysics, chemical biology, and so on. Considering the past and future development of SEC, a review on the recent progress of SEC is presented and selected examples involving surface-enhanced Raman scattering (SERS), ultraviolet-visible (UV-Vis), near-infrared (NIR), Fourier transform infrared (FTIR), fluorescence, as well as other SEC are summarized to fully demonstrate these techniques. In addition, the optically transparent electrodes and SEC cell design, and the typical applications of SEC in mechanism study, electrochromic device fabrication, sensing and protein study are fully introduced. Finally, the key issues, future perspectives and trends in the development of SEC are also discussed.