This review describes recent advances in electrochemical impedance spectroscopy (EIS) with an emphasis on its novel applications to various electrochemistry-related problems. Section 1 discusses the development of new EIS techniques to reduce measurement time. For this purpose, various forms of multisine EIS techniques were first developed via a noise signal synthesized by mixing ac waves of various frequencies, followed by fast Fourier transform of the signal and the resulting current. Subsequently, an entirely new concept was introduced in which true white noise was used as an excitation source, followed by Fourier transform of both excitation and response signals. Section 2 describes novel applications of the newly developed techniques to time-resolved impedance measurements as well as to impedance imaging. Section 3 is devoted to recent applications of EIS techniques, specifically traditional measurements in various fields with a special emphasis on biosensor detections.

Electrochemical Impedance Spectroscopy

The gas sensors fabricated by using conducting polymers such as polyaniline (PAni), polypyrrole (PPy) and poly (3,4-ethylenedioxythiophene) (PEDOT) as the active layers have been reviewed. This review discusses the sensing mechanism and configurations of the sensors. The factors that affect the performances of the gas sensors are also addressed. The disadvantages of the sensors and a brief prospect in this research field are discussed at the end of the review.

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Gas Sensors Based on Conducting Polymers

The design of advanced, nanostructured materials at the molecular level is of tremendous interest for the scientific and engineering communities because of the broad application of these materials in the biomedical field. Among the available techniques, the layer-by-layer assembly method introduced by Decher and co-workers in 1992 has attracted extensive attention because it possesses extraordinary advantages for biomedical applications: ease of preparation, versatility, capability of incorporating high loadings of different types of biomolecules in the films, fine control over the materials’ structure, and robustness of the products under ambient and physiological conditions. In this context, a systematic review of current research on biomedical applications of layer-by-layer assembly is presented. The structure and bioactivity of biomolecules in thin films fabricated by layer-by-layer assembly are introduced. The applications of layer-bylayer assembly in biomimetics, biosensors, drug delivery, protein and cell adhesion, mediation of cellular functions, and implantable materials are addressed. Future developments in the field of biomedical applications of layer-by-layer assembly are also discussed.

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Biomedical Applications of Layer‐by‐Layer Assembly: From Biomimetics to Tissue Engineering

This article gives an overview of the application of nanomaterials in environmental remediation. In the area of environmental remediation, nanomaterials offer the potential for the efficient removal of pollutants and biological contaminants. Nanomaterials in various shapes/morphologies, such as nanoparticles, tubes, wires, fibres etc., function as adsorbents and catalysts and their composites with polymers are used for the detection and removal of gases (SO2, CO, NOx, etc.), contaminated chemicals (arsenic, iron, manganese, nitrate, heavy metals, etc.), organic pollutants (aliphatic and aromatic hydrocarbons) and biological substances, such as viruses, bacteria, parasites and antibiotics. Nanomaterials show a better performance in environmental remediation than other conventional techniques because of their high surface area (surface-to-volume ratio) and their associated high reactivity. Recent advances in the fabrication of novel nanoscale materials and processes for the treatment of drinking water and industrial waste water contaminated by toxic metal ions, radionuclides, organic and inorganic solutes, bacteria and viruses and the treatment of air are highlighted. In addition, recent advances in the application of polymer nanocomposite materials for the treatment of contaminants and the monitoring of pollutants are also discussed. Furthermore, the research trends and future prospects are briefly discussed.

A review on nanomaterials for environmental remediation

Conducting polymers in chemical sensors and arrays

Electrochemical impedance spectroscopy (EIS) measurement, performed in the presence of a redox agent, is a convenient method to measure molecular interactions of electrochemically inactive compounds taking place on the electrode surface. High sensitivity of the method, being highly advantageous, can be also associated with nonspecific impedance changes that could be easily mistaken for specific interactions. Therefore, it is necessary to be aware of all possible causes and perform parallel control experiments to rule them out. We present the results obtained during the early stages of aptamer-based sensor development, utilizing a model system of human alpha thrombin interacting with a thiolated DNA aptamer, immobilized on gold electrodes. EIS measurements took place in the presence of iron ferrocyanides. In addition to known method limitations, that is, inability to discriminate between specific and nonspecific binding (both causing impedance increase), we have found other factors leading to nonspecific impedance changes, such as: (i) initial electrode contamination; (ii) repetitive measurements; (iii) additional cyclic voltammetry (CV) or differential pulse voltammetry (DPV) measurements; and (iv) additional incubations in the buffer between measurements, which have never been discussed before. We suggest ways to overcome the method limitations.

Challenges of electrochemical impedance spectroscopy in protein biosensing.

New approaches are needed to solve environmental measurement problems associated with mobile sources for the measurements of CO, NOx, aromatic hydrocarbons HC and particulates. There is a need to develop fast, rapid, cost effective, low power, and non-intrusive rugged sensors that can be easily installed. In order to be useful as a sensor, the device and technique should be able to detect the emissions from at relevant low concentrations. Our effort has focused on the use of highly organized ultrathin conducting polymer/metal oxide (SnO2 and/or TiO2) films for sensing of CO gas for the first time. The supramolecular approach has been utilized to fabricate films of conducting materials via in situ layer-by-layer (LBL) self-assembly technique. We have used UV–vis spectroscopy, atomic force microscopy (AFM), conductivity and AC impedance measurements to quantify the different characteristics of the ultrathin nanocomposite polymer films to ensure reproducibility, stability and reliability in CO sensing.

CO gas sensing from ultrathin nano-composite conducting polymer film

NO2 gas sensing based on ordered ultrathin films of conducting polymer and its nanocomposite

We present a novel approach to synthesize MnZnferrite (MZF)–NiMnZnferrite(NiMZF)–Polyaniline (PANI) particles, where MnZnferrite is the magnetic core, and PANI is the conducting layer. The commercial ferrite and Ni–ferrite particles are primarily used, and the PANI–ferrite particles with a hybrid structure are synthesized via an oxidative electrochemical polymerization of aniline in an aqueous solution, which contains well-dispersed ferrite particles. The influence of ferrite content with respect to the electrical and ferromagnetic properties of the composite has been investigated by Electrochemical Impedance Spectroscopy (EIS) and DC field-cooled, zero-field cooled susceptibilities and M–H loop measurements. The origin of their electrical and ferromagnetic properties is also discussed based on structural characterizations including Fourier Transform Infrared (FT-IR) spectroscopy and X-Ray Diffraction (XRD).

Matt Aldissi

Papers

Challenges of electrochemical impedance spectroscopy in protein biosensing.

CO gas sensing from ultrathin nano-composite conducting polymer film

NO2 gas sensing based on ordered ultrathin films of conducting polymer and its nanocomposite

Synthesis and the physical properties of MnZn ferrite and NiMnZn ferrite–polyaniline nanocomposite particles

Polypyrrole composites for shielding applications