Bipolar Electrode Array Embedded in a Polymer Light-Emitting Electrochemical Cell

Label-Free Electrochemiluminescence Imaging of Single-Cell Adhesions by Using Bipolar Nanoelectrode Array

A label-free and fast approach for positive electrochemiluminescence (ECL) imaging of single cells by bipolar nanoelectrode array is proposed. The reduction of oxygen at a platinized gold nanoelectrode array in a closed bipolar electrochemical system is coupled with an oxidative ECL process at the anodic side. For elevating the ECL imaging contrast of single cells, a driving voltage of -2.0 V is applied to in situ generate oxygen confined beneath cells that is subsequently used for ECL imaging at 1.1 V. High oxygen concentration in the confined space resulting from steric hindrance generates prominent oxygen reduction current at the cathodic side and higher ECL intensity at the anodic side, allowing positive ECL imaging of the cells adhesion region with excellent contrast. Cell morphology and adhesion strength can be successfully imaged with high image acquisition rate. This approach opens a new avenue for label-free imaging of single cells.

Oxygen Generation Using Catalytic Nano/Micromotors

Gaseous oxygen plays a vital role in driving the metabolism of living organisms and has multiple agricultural, medical, and technological applications. Different methods have been discovered to produce oxygen, including plants, oxygen concentrators and catalytic reactions. However, many such approaches are relatively expensive, involve challenges, complexities in post-production processes or generate undesired reaction products. Catalytic oxygen generation using hydrogen peroxide is one of the simplest and cleanest methods to produce oxygen in the required quantities. Chemically powered micro/nanomotors, capable of self-propulsion in liquid media, offer convenient and economic platforms for on-the-fly generation of gaseous oxygen on demand. Micromotors have opened up opportunities for controlled oxygen generation and transport under complex conditions, critical medical diagnostics and therapy. Mobile oxygen micro-carriers help better understand the energy transduction efficiencies of micro/nanoscopic active matter by careful selection of catalytic materials, fuel compositions and concentrations, catalyst surface curvatures and catalytic particle size, which opens avenues for controllable oxygen release on the level of a single catalytic microreactor. This review discusses various micro/nanomotor systems capable of functioning as mobile oxygen generators while highlighting their features, efficiencies and application potentials in different fields.

Optical analysis of light-emitting electrochemical cells

The light-emitting electrochemical cell (LEC) is a contender for emerging applications of light, primarily because it offers low-cost solution fabrication of easily functionalized device architectures. The attractive properties originate in the in-situ formation of electrochemically doped transport regions that enclose an emissive intrinsic region, but the understanding of how this intricate doping structure affects the optical performance of the LEC is largely lacking. We combine angle- and doping-dependent measurements and simulations, and demonstrate that the emission zone in our high-performance LEC is centered at ~30% of the active-layer thickness (dal) from the anode. We further find that the emission intensity and efficiency are undulating with dal, and establish that the first emission maximum at dal ~ 100 nm is largely limited by the lossy coupling of excitons to the doping regions, whereas the most prominent loss channel at the second maximum at dal ~ 300 nm is wave-guided modes.

Enhanced Bipolar Electrochemistry at Solid-State Micropores: Demonstration by Wireless Electrochemiluminescence Imaging

Bipolar electrochemistry (BPE) is a powerful method based on the wireless polarization of a conductive object that induces the asymmetric electroactivity at its two extremities. A key physical limitation of BPE is the size of the conductive object because the shorter the object, the larger is the potential necessary for sufficient polarization. Micrometric and nanometric objects are thus extremely difficult to address by BPE due to the very high potentials required, in the order of tens of kV or more. Herein, the synergetic actions of BPE and of planar micropores integrated in a microfluidic device lead to the spatial confinement of the potential drop at the level of the solid-state micropore, and thus to a locally enhanced polarization of a bipolar electrode. Electrochemiluminescence (ECL) is emitted in half of the electroactive micropore and reveals the asymmetric polarization in this spatial restriction. Micrometric deoxidized silicon electrodes located in the micropore are polarized at a very low potential (7 V), which is more than 2 orders of magnitude lower compared to the classic bipolar configurations. This behavior is intrinsically associated with the unique properties of the micropores, where the sharp potential drop is focused. The presented approach offers exciting perspectives for BPE of micro/nano-objects, such as dynamic BPE with objects passing through the pores or wireless ECL-emitting micropores.

Wireless Coupling of Conducting Polymer Actuators with Light Emission

Combining the actuation of conducting polymers with additional functionalities is an interesting fundamental scientific challenge and increases their application potential. Herein we demonstrate the possibility of direct integration of a miniaturized light emitting diode (LED) in a polypyrrole (PPy) matrix in order to achieve simultaneous wireless actuation and light emission. A light emitting diode is used as a part of an electroactive surface on which electrochemical polymerization allows direct incorporation of the electronic device into the polymer. The resulting free-standing polymer/LED hybrid can be addressed by bipolar electrochemistry to trigger simultaneously oxidation and reduction reactions at its opposite extremities, leading to a controlled deformation and an electron flow through the integrated LED. Such a dual response in the form of actuation and light emission opens up interesting perspectives in the field of microrobotics.

Dynamic Bipolar Electrode Array for Visualized Screening of Electrode Materials in Light-Emitting Electrochemical Cells

Charge injection at a metal/semiconductor interface is of paramount importance for many chemical and physical processes. The dual injection of electrons and holes, for example, is necessary for electroluminescence in organic light-emitting devices. In an electrochemical cell, charge transfer across the electrode interface is responsible for redox reactions and Faradic current flow. In this work, we use polymer light-emitting electrochemical cells (PLECs) to visually assess the ability of metals to inject electronic charges into a luminescent polymer. Silver, aluminum, and gold microdisks are deposited between the two driving electrodes of the PLEC in the form of a horizontal array. When the PLEC is polarized, the individual disks functioned as bipolar electrodes (BPEs) to induce redox p- and n-doping reactions at their extremities, which are visualized as strongly photoluminescence-quenched growth in the luminescent polymer. The three metals initially generate highly distinct doping patterns that are consistent with differences in their work function. Over time, the doped regions continue to grow in size. Quantitative analysis of the n/p area ratio reveals an amazing convergence to a single value for all 39 BPEs, regardless of their metal type and large variation in the size of individual doped areas. We introduce the concept of a dynamic BPE, which transforms from an initial metal disk of a fixed size to one that is a composite of p- and n-doped polymer joined by the initial metallic BPE. The internal structure of the dynamic BPE, as measured by the n/p area ratio, reflects the properties of only the mixed conductor of the PLEC active layer itself when the area ratio converges.

Laser-Induced Bipolar Electrochemistry-On-Demand Formation of Bipolar Electrodes in a Solid Polymer Light-Emitting Electrochemical Cell

Bipolar electrochemistry (BPEC) is a versatile and powerful technique that has found applications in sensing, chemical synthesis, catalysis, fuel cells, and batteries, among others. In BPEC, the reactions of interest occur at a wireless, bipolar electrode (BPE). BPEC is most commonly carried out in an electrochemical cell that contains an electrolyte solution, in which a metallic BPE is immersed and polarized when the wired driving electrodes are biased. In this article, we demonstrate BPEC in a solid light-emitting electrochemical cell (LEC) that does not initially contain a BPE. Shining a focused laser beam onto the mixed conductor LEC film causes the illuminated spot to function as a BPE from which redox reactions are induced and visualized. Separate experiments using a photosensitizer (widely used in polymer solar cells) confirm that a BPE is formed on-demand via photoabsorption that causes the illuminated spot to have elevated photoconductivity. The simplicity of laser-induced BPEC offers exciting opportunities to explore sciences and applications of BPEC in the new realm of solid-state organic photonic devices.

The Weak Microcavity as an Enabler for Bright and Fault-tolerant Light-emitting Electrochemical Cells

The light-emitting electrochemical cell (LEC) is functional at substantial active-layer thickness, and is as such heralded for being fit for low-cost and fault-tolerant solution-based fabrication. We report here that this statement should be moderated, and that in order to obtain a strong luminous output, it is fundamentally important to fabricate LEC devices with a designed thickness of the active layer. By systematic experimentation and simulation, we demonstrate that weak optical microcavity effects are prominent in a common LEC system, and that the luminance and efficiency, as well as the emission color and the angular intensity, vary in a periodic manner with the active-layer thickness. Importantly, we demonstrate that high-performance light-emission can be attained from LEC devices with a significant active-layer thickness of 300 nm, which implies that low-cost solution-processed LECs are indeed a realistic option, provided that the device structure has been appropriately designed from an optical perspective.

Enhancing the Overall Performances of Blue Light-Emitting Electrochemical Cells by Using an Electron-Injecting/Transporting Ionic Additive

Light-emitting electrochemical cells (LECs) have emerged as a promising emissive thin-film technology for next-generation solid-state lighting. However, blue LECs show low performances, which has remained a bottleneck for the fabrication of white LECs for lighting applications. Here, we demonstrate a remarkable enhancement of overall device performance for blue LECs by using an electron-injecting/transporting ionic additive, that is, [Zn(bpy)₃](PF₆)₂ (bpy is 2.2'-bipyridine, PF₆^- is hexafluorophosphate). It is revealed that adding [Zn(bpy)₃](PF₆)₂ into the active layers of blue LECs accelerates the device response, simultaneously enhances the brightness and efficiency, reduces the efficiency roll-offs, significantly improves the blue color stability upon the continuous electrical operation, and enhances the device operational stability at optimized conditions. The remarkable enhancement of the overall device performance upon adding [Zn(bpy)₃](PF₆)₂ results from facilitated electron injection/transport and thus more balanced electron-hole recombination and more centered recombination zone, as well as the reduction of phosphorescence concentration quenching in the LECs. The work demonstrates for the first time that the use of electron-injecting/transporting ionic additives such as [Zn(bpy)₃](PF₆)₂ is a facile yet effective strategy to remarkably boost the overall performances of blue LECs.