PEDOT: Dye-Based, Flexible Organic Electrochemical Transistor for Highly Sensitive pH Monitoring

Organic electrochemical transistors (OECTs) are bioelectronic devices able to bridge electronic and biological domains with especially high amplification and configurational versatility and thus stand out as promising platforms for healthcare applications and portable sensing technologies. Here, we have optimized the synthesis of two pH-sensitive composites of PEDOT (poly­(3,4-ethylenedioxythiophene)) doped with pH dyes (BTB and MO, i.e., Bromothymol Blue and Methyl Orange, respectively), showing their ability to successfully convert the pH into an electrical signal. The PEDOT:BTB composite, which exhibited the best performance, was used as the gate electrode to develop an OECT sensor for pH monitoring that can reliably operate in a two-fold transduction mode with super-Nernstian sensitivity. When the OECT transconductance is employed as analytical signal, a sensitivity of 93 ± 8 mV pH unit^–1 is achieved by successive sampling in aqueous electrolytes. When the detection is carried out by dynamically changing the pH of the same medium, the offset gate voltage of the OECT shifts by (1.1 ± 0.3) × 10² mV pH unit^–1. As a further step, the optimized configuration was realized on a PET substrate, and the performance of the resulting flexible OECT was assessed in artificial sweat within a medically relevant pH range

Physical and Electrochemical Properties of PEDOT:PSS as a Tool for Controlling Cell Growth

Conducting polymers are promising materials for tissue engineering applications, since they can both provide a biocompatible scaffold for physical support of living cells, and transmit electrical and mechanical stimuli thanks to their electrical conductivity and reversible doping. In this work, thin films of one of the most promising materials for bioelectronics applications, poly­(3,4-ethylenedioxythiophene) poly­(styrenesulfonate) (PEDOT:PSS), are prepared using two different techniques, spin coating and electrochemical polymerization, and their oxidation state is subsequently changed electrochemically with the application of an external bias. The electrochemical properties of these different types of PEDOT:PSS are studied through cyclic voltammetry and spectrophotometry to assess the effectiveness of the oxidation process and its stability over time. Their surface physical properties and their dependence on the redox state of PEDOT:PSS are investigated using atomic force microscopy (AFM), water contact angle goniometry and sheet resistance measurements. Finally, human glioblastoma multiforme cells (T98G) and primary human dermal fibroblasts (hDF) are cultured on PEDOT:PSS films with different oxidation states, finding that the effect of the substrate on the cell growth rate is strongly cell-dependent: T98G growth is enhanced by the reduced samples, while hDF growth is more effective only on the oxidized substrates that show a strong chemical interaction with the cell culture medium

Electrically Controlled “Sponge Effect” of PEDOT:PSS Governs Membrane Potential and Cellular Growth

PEDOT:PSS is a highly conductive material with good thermal and chemical stability and enhanced biocompatibility that make it suitable for bioengineering applications. The electrical control of the oxidation state of PEDOT:PSS films allows modulation of peculiar physical and chemical properties of the material, such as topography, wettability, and conductivity, and thus offers a possible route for controlling cellular behavior. Through the use of (i) the electrophysiological response of the plasma membrane as a biosensor of the ionic availability; (ii) relative abundance around the cells via X-ray spectroscopy; and (iii) atomic force microscopy to monitor PEDOT:PSS film thickness relative to its oxidation state, we demonstrate that redox processes confer to PEDOT:PSS the property to modify the ionic environment at the film–liquid interface through a “sponge-like” effect on ions. Finally, we show how this property offers the capability to electrically control central cellular properties such as viability, substrate adhesion, and growth, paving the way for novel bioelectronics and biotechnological applications

Iridium(III) Complexes with Phenyl-tetrazoles as Cyclometalating Ligands

Ir­(III) cationic complexes with cyclometalating tetrazolate ligands were prepared for the first time, following a two-step strategy based on (i) a silver-assisted cyclometalation reaction of a tetrazole derivative with IrCl₃ affording a bis-cyclometalated solvato-complex <b>P</b> ([Ir­(ptrz)₂­(CH₃CN)₂]⁺, Hptrz = 2-methyl-5-phenyl-2<i>H</i>-tetrazole); (ii) a substitution reaction with five neutral ancillary ligands to get [Ir­(ptrz)₂L]⁺, with L = 2,2′-bypiridine (<b>1</b>), 4,4′-di-<i>tert</i>-butyl-2,2′-bipyridine (<b>2</b>), 1,10-phenanthroline (<b>3</b>), and 2-(1-phenyl-1<i>H</i>-1,2,3-triazol-4-yl)­pyridine (<b>4</b>), and [Ir­(ptrz)₂L₂]⁺, with L = <i>tert</i>-butyl isocyanide (<b>5</b>). X-ray crystal structures of <b>P</b>, <b>2</b>, and <b>3</b> were solved. Electrochemical and photophysical studies, along with density functional theory calculations, allowed a comprehensive rationalization of the electronic properties of <b>1</b>–<b>5</b>. In acetonitrile at 298 K, complexes equipped with bipyridine or phenanthroline ancillary ligands (<b>1</b>–<b>3</b>) exhibit intense and structureless emission bands centered at around 540 nm, with metal-to-ligand and ligand-to-ligand charge transfer (MLCT/LLCT) character; their photoluminescence quantum yields (PLQYs) are in the range of 55–70%. By contrast, the luminescence band of <b>5</b> is weak, structured, and blue-shifted and is attributed to a ligand-centered (LC) triplet state of the tetrazolate cyclometalated ligand. The PLQY of <b>4</b> is extremely low (<0.1%) since its lowest level is a nonemissive triplet metal-centered (³MC) state. In rigid matrix at 77 K, all of the complexes exhibit intense luminescence. Ligands <b>1</b>–<b>3</b> are also strong emitters in solid matrices at room temperature (1% poly­(methyl methacrylate) matrix and neat films), with PLQYs in the range of 27–70%. Good quality films of <b>2</b> could be obtained to make light-emitting electrochemical cells that emit bright green light and exhibit a maximum luminance of 310 cd m^–2. Tetrazolate cyclometalated ligands push the emission of Ir­(III) complexes to the blue, when compared to pyrazolate or triazolate analogues. More generally, among the cationic Ir­(III) complexes without fluorine substituents on the cyclometalated ligands, <b>1</b>–<b>3</b> exhibit the highest-energy MLCT/LLCT emission bands ever reported