Why PEDOT:PSS Should Not Be Used for Raman Sensing of Redox States (and How It Could Be)

Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) has been recently proposed for Raman sensing of redox-active species in solution. Here, we investigated the rationale of this approach through systematic experiments, in which the Raman spectrum of PEDOT:PSS was analyzed in the presence of either nonoxidizing or oxidizing electrolytes. The results demonstrated that Raman spectra precisely reflect the conformation of PEDOT units and their interactions with PSS. Two different responses were observed. In the case of oxidizing electrolytes, the effect of charge transfer is accurately transduced in Raman spectrum changes. On the other hand, reduction induces a progressive separation between the PEDOT and PSS chains, which decreases their mutual interaction. This stimulus determines characteristic variations in the intensity, shape, and position of the Raman spectra. However, we demonstrated that the same effects can be obtained either by increasing the concentration of nonoxidizing electrolytes or by deprotonating PSS chains. This poses severe limitations to the use of PEDOT:PSS for this type of Raman sensing. This study allows us to revise most of the Raman results reported in the literature with a clear model, setting a new basis for investigating the dynamics of mixed electronic/ionic charge transfer in conductive polymers

Current-Driven Organic Electrochemical Transistors for Monitoring Cell Layer Integrity with Enhanced Sensitivity

AbstractIn this progress report an overview is given on the use of the organic electrochemical transistor (OECT) as a biosensor for impedance sensing of cell layers. The transient OECT current can be used to detect changes in the impedance of the cell layer, as shown by Jimison et al. To circumvent the application of a high gate bias and preventing electrolysis of the electrolyte, in case of small impedance variations, an alternative measuring technique based on an OECT in a current‐driven configuration is developed. The ion‐sensitivity is larger than 1200 mV V‐1dec‐1 at low operating voltage. It can be even further enhanced using an OECT based complementary amplifier, which consists of a p‐type and an n‐type OECT connected in series, as known from digital electronics. The monitoring of cell layer integrity and irreversible disruption of barrier function with the current‐driven OECT is demonstrated for an epithelial Caco‐2 cell layer, showing the enhanced ion‐sensitivity as compared to the standard OECT configuration. As a state‐of‐the‐art application of the current‐driven OECT, the in situ monitoring of reversible tight junction modulation under the effect of drug additives, like poly‐l‐lysine, is discussed. This shows its potential for in vitro and even in vivo toxicological and drug delivery studies

Digital Hermeneutics: From Interpreting with Machines to Interpretational Machines

International audienceToday, there is an emerging interest for the potential role of hermeneutics in reflecting on the practices related to digital technologies and their consequences. Nonetheless, such an interest has not yet given rise to a unitary approach nor to a shared debate. The primary goal of this paper is to map and synthetize the different existing perspectives in order to pave the way for an open discussion on the topic. The article is developed in two steps. In the first section, the authors analyze digital hermeneutics “in theory” by confronting and systematizing the existing literature. In particular, they stress three main distinctions among the approaches: 1) between “methodological” and “ontological” digital hermeneutics; 2) between data- and text-oriented digital hermeneutics and 3) between “quantitative” and “qualitative” credos in digital hermeneutics. In the second section, they consider digital hermeneutics “in action”, by critically analyzing the uses of digital data (notably tweets) for studying a classical object such as the political opinion. In the conclusion, we will pave the way to an ontological turn in digital hermeneutics. Most of this article is devoted to the methodological issue of interpreting with digital machines. The main task of an ontological digital hermeneutics would consist instead in wondering if it is legitimate, and eventually to which extent, to speak of digital technologies, or at least of some of them, as interpretational machines

Why PEDOT:PSS Should Not Be Used for Raman Sensing of Redox States (and How It Could Be)

Here we investigated the rationale of this approach through systematic experiments, in which the Raman spectrum of PEDOT:PSS was analyzed in the presence of either non-oxidizing and oxidizing electrolytes. The results demonstrated that Raman spectra precisely reflect the conformation of PEDOT units and their interactions with PSS. Two different responses were observed. In the case of oxidizing electrolytes, the effect of charge transfer is accurately transduced in Raman spectrum changes. On the other hand, reduction induces a progressive separation between the PEDOT and PSS chains, which decreases their mutual interaction. This stimulus determines characteristic variations in intensity, shape and position of the Raman spectra. However, we demonstrated that the same effects can be obtained either by increasing the concentration of non-oxidizing electrolytes or by deprotonating PSS chains. This poses severe limitations to the use of PEDOT:PSS for this type of Raman sensing. This study allows to revise most of the Raman results reported in literature with a clear model, setting a new basis for investigating the dynamics of mixed electronic/ionic charge transfer in conductive polymers

Compensated analog computation for an in-memory computation system

An in-memory computation (IMC) circuit includes a memory array formed by memory cells arranged in row-by-column matrix. Computational weights for an IMC operation are stored in the memory cells. Each column includes a bit line connected to the memory cells. A biasing circuit is connected between each bit line and a corresponding column output. A column combining circuit combines and integrates analog signals at the column outputs of the biasing circuits. Each biasing circuit operates to apply a fixed reference voltage level to its bit line. Each biasing circuit further includes a switching circuit that is controlled to turn on for a time duration controlled by asps comparison of a coefficient data signal to a ramp signal to generate the analog signal dependent on the computational weight. The ramp signal is generated using a reference current derived from a reference memory cell

Characterization and Programming Algorithm of Phase Change Memory Cells for Analog In-Memory Computing

In this paper, a thorough characterization of phase-change memory (PCM) cells was carried out, aimed at evaluating and optimizing their performance as enabling devices for analog in-memory computing (AIMC) applications. Exploiting the features of programming pulses, we discuss strategies to reduce undesired phenomena that afflict PCM cells and are particularly harmful in analog computations, such as low-frequency noise, time drift, and cell-to-cell variability of the conductance. The test vehicle is an embedded PCM (ePCM) provided by STMicroelectronics and designed in 90-nm smart power BCD technology with a Ge-rich Ge-Sb-Te (GST) alloy for automotive applications. On the basis of the results of the characterization of a large number of cells, we propose an iterative algorithm to allow multi-level cell conductance programming, and its performances for AIMC applications are discussed. Results for a group of 512 cells programmed with four different conductance levels are presented, showing an initial conductance spread under 6%, relative current noise less than 9% in most cases, and a relative conductance drift of 15% in the worst case after 14 h from the application of the programming sequence