Ultraflexible Screen‐Printed Graphitic Electroanalytical Sensing Platforms

The pursuit of ultraflexible sensors has arisen from the recent implementation of electrochemical sensors into wearable clothing where extensive mechanical stress upon the sensing platform is likely to occur. Such scenarios have witnessed screen‐printed electrodes being incorporated into the waistband of undergarments for the determination of key analytes while others have reported incorporation into a neoprene wetsuit. In these conformations, the substrates which the sensors are printed upon need to be ultraflexible and capable of withstanding extensive individual mechanical stress. Therefore the composition, thickness and its combination of screen‐printed ink require extensive consideration. A common short‐coming within the field of screen‐printed derived sensors is the lack of consideration towards the substrate material employed, and is rather in favour of the development of new electrode geometries and screen‐printing inks. In this paper we explore the screen‐printing of graphite based electroanalytical sensing platforms onto graphic paper commonly used in house‐hold printers, and for the first time both tracing paper and ultraflexible polyester‐based substrates are used. These sensors are electrochemically benchmarked with the redox probes hexaammine‐ruthenium(III) chloride and potassium ferrocyanide(II). The effect of mechanical contortion upon two types of electrode substrates is also performed where it was found that these ultraflexible based polyester‐based electrodes are superior to the previously reported ultraflexible paper electrodes since they can withstand extensive mechanical contortion, yet they still give rise to useful electrochemical performances. Most importantly the ultraflexible polyester electrodes do not suffer from capillary action as observed in the case of paper‐based sensors causing the solution to wick‐up the electrode towards the electrical connections resulting in electrical shorting, therefore compromising the electrochemical measurement; as such this new substrate can be used as a replacement for paper‐based substrates and yet still be resilient to extreme mechanical contortion. A new configuration is also explored using these electrode substrate supports where the working carbon electrode contains the electrocatalyst, cobalt(II) phthalocyanine (CoPC), and is benchmarked towards the electroanalytical sensing of the model analytes citric acid and hydrazine which demonstrate excellent sensing capabilities in comparison to previously reported screen‐printed electrodes.     

Back‐to‐Back Screen‐Printed Electroanalytical Sensors: Extending the Potential Applications of the Simplistic Design

In our previous paper (Analyst, 2014 , 139, 5339) we introduced the concept of the back‐to‐back electrochemical design where the commonly overlooked back of screen‐printed electrodes are utilised to provide electroanalytical enhancements in screen‐printed electroanalytical sensors. In this configuration the overall sensor comprises of a flexible polyester substrate which has a total of two working, counter and reference electrodes present on the sensor, with a set of electrodes on each side of the substrate. The sensors are designed to allow for a commonly shared electrical connection to the potentiostat and do not require any specialised connections. In this paper we demonstrate proof‐of‐concept extending the electroanalytical utility of the back‐to‐back screen‐printed electrode sensors to bulk modified single‐walled carbon‐nanotubes and electrocatalytic cobalt phthalocyanine microband electrodes. The electroanalytical applications of these novel electrode configuration are exemplified towards the sensing of dopamine, capsaicin and hydrazine. This paper demonstrates the versatility of the back‐to‐back configuration where different surface modifications can be readily employed giving rise to enhancements in sensor performance.     

Textile‐based Electrochemical Sensing: Effect of Fabric Substrate and Detection of Nitroaromatic Explosives

This study examines the influence of textile substrates upon the behavior of wearable screen‐printed electrodes and demonstrates the attractive sensing properties of these sensors towards the detection of nitroaromatic explosives. Compared to electrodes printed on common cotton or polyester substrates, GORE‐TEX‐based electrochemical sensors display reproducible background cyclic voltammograms, reflecting the excellent water‐repellant properties of the GORE‐TEX fabric. The wetting properties of different printed textile electrodes are elucidated using contact angle measurements. The influence of laundry washing and mechanical stress is explored. The GORE‐TEX‐based printed electrodes exhibit favorable detection of 2,4‐dinitrotoluene (DNT) and 2,4,6‐trinitrotoluene (TNT) explosives, including rapid detection of DNT vapor.     

Electronic Tongues Employing Electrochemical Sensors

This review presents recent advances concerning work with electronic tongues employing electroanalytical sensors. This new concept in the electroanalysis sensor field entails the use of chemical sensor arrays coupled with chemometric processing tools, as a mean to improve sensors performance. The revision is organized according to the electroanalytical technique used for transduction, namely: potentiometry, voltammetry/amperometry or electrochemical impedance. The significant use of biosensors, mainly enzyme‐based is also presented. Salient applications in real problem solving using electrochemical electronic tongues are commented.     

Electrochemical sensors and biosensors based on redox polymer/carbon nanotube modified electrodes: A review

The aim of this review is to present the contributions to the development of electrochemical sensors and biosensors based on polyphenazine or polytriphenylmethane redox polymers together with carbon nanotubes (CNT) during recent years. Phenazine polymers have been widely used in analytical applications due to their inherent charge transport properties and electrocatalytic effects. At the same time, since the first report on a CNT-based sensor, their application in the electroanalytical chemistry field has demonstrated that the unique structure and properties of CNT are ideal for the design of electrochemical (bio)sensors. We describe here that the specific combination of phenazine/triphenylmethane polymers with CNT leads to an improved performance of the resulting sensing devices, because of their complementary electrical, electrochemical and mechanical properties, and also due to synergistic effects. The preparation of polymer/CNT modified electrodes will be presented together with their electrochemical and surface characterization, with emphasis on the contribution of each component on the overall properties of the modified electrodes. Their importance in analytical chemistry is demonstrated by the numerous applications based on polymer/CNT-driven electrocatalytic effects, and their analytical performance as (bio) sensors is discussed.     

Disposable Graphite Foil Based Electrodes and Their Application in Pharmaceutical Analysis

This paper explores a new source of graphite for working electrodes, which presents advantages such as low electrical resistance, good flexibility, favorable mechanical performance, versatility to design electrodes in almost any size and very low cost. The new electrodes were investigated in batch electrochemical cells as associated with flow injection analysis systems. Cyclic voltammetry, stripping voltammetry, and amperometry associated with flow injection analysis techniques were applied for the determination of ascorbic acid, zinc and paracetamol in pharmaceutical formulations, respectively. Well‐established analytical methods were applied for comparison purposes. The results herein demonstrate the potential of graphite foils as working electrodes in different electroanalytical methods, offering the possibility of producing disposable sensors for routine applications.     

Nanoporous Carbon Materials for Electrochemical Sensing

Nanoporous carbon materials are highly important materials for a wide array of applications. Here we show that nanoporous carbon can act as highly active materials for electrochemical sensing. We observed that nanoporous carbon material exhibits a faster heterogeneous electron transfer than graphite and pure carbon nanotubes. Nanoporous carbon exhibits a superior electrochemical performance for sensing of important biomarkers such as dopamine, ascorbic acid, uric acid, NADH, DNA bases, and forensic‐related compounds such as nitroaromatic explosives.     

Thin Films and Composites Based on Graphene for Electrochemical Detection of Biologically‐relevant Molecules

Graphene is one of the most studied materials ever, owing to its exceptional electronic, mechanical and thermal properties, which allow for many different types of application. In this review, we shall concentrate on the use of graphene and derivatives for electrochemical sensors and biosensors, where emphasis is placed on the importance of surface functionalization as this permits synergistic combinations with other nanomaterials and biomolecules. In addition to describing recent advances in graphene‐based electroanalytical applications, we discuss a few examples of their use in detecting small biomolecules and in immunosensing for a few diseases using films and composites. Also discussed are the possible methods for mass production of graphene, which is key to low‐cost biosensors for implantable devices and portable systems in point‐of‐care diagnosis.     

Effects of Humidity,Temperature and Bismuth Electrodeposition on Electroanalytical Performances of Nafion‐coated Printed Electrodes for Cd2+ and Pb2+ Detection

The synergistic use of Nafion polymeric membrane and in situ electrodeposited bismuth film is a worthwhile strategy to develop electrochemical sensors for the detection of Cd²⁺ and Pb²⁺. However, Nafion thin films morphological and conductivity properties have a strong dependence on the environmental conditions, such as relative humidity and temperature, while the bismuth in situ electroplating can affect the repeatability of measurements. With the aim to overcome these drawbacks, the effects of the storage environmental conditions were investigated to improve the morphological stability and electroanalytical performances of Nafion film‐based sensor for the detection of Cd²⁺ and Pb²⁺. Nafion‐coated graphite‐based screen‐printed electrodes were stored at different humidity and temperature conditions and characterised by using square wave anodic stripping voltammetry, cyclic voltammetry, electrochemical impedance spectroscopy, and scanning electron microscopy. Significant differences were observed at the varying of humidity conditions, with an enhancement of sensor electrochemical performances at lower humidity. Furthermore, different approaches for bismuth in situ electrodeposition on Nafion‐coated screen‐printed electrodes were compared by using overlap or removal approach. This study disclosed considerable differences in the electrochemical performances and morphology of the resulting bismuth‐sensor, obtaining an enhancement of the working stability for the removal approach.     

Electrochemical Impedance Spectroscopy in the Characterisation and Application of Modified Electrodes for Electrochemical Sensors and Biosensors

Electrochemical impedance spectroscopy is finding increasing use in electrochemical sensors and biosensors, both in their characterisation, including during successive phases of sensor construction, and in application as a quantitative determination technique. Much of the published work continues to make little use of all the information that can be furnished by full physical modelling and analysis of the impedance spectra, and thus does not throw more than a superficial light on the processes occurring. Analysis is often restricted to estimating values of charge transfer resistances without interpretation and ignoring other electrical equivalent circuit components. In this article, the important basics of electrochemical impedance for electrochemical sensors and biosensors are presented, focussing on the necessary electrical circuit elements. This is followed by examples of its use in characterisation and in electroanalytical applications, at the same time demonstrating how fuller use can be made of the information obtained from complete modelling and analysis of the data in the spectra, the values of the circuit components and their physical meaning. The future outlook for electrochemical impedance in the sensing field is discussed.     

Nanomaterials in Electrochemical Sensing Area: Applications and Challenges in Food Analysis

Recently, nanomaterials have received increasing attention due to their unique physical and chemical properties, which make them of considerable interest for applications in many fields, such as biotechnology, optics, electronics, and catalysis. The development of nanomaterials has proven fundamental for the development of smart electrochemical sensors to be used in different application fields such, as biomedical, environmental, and food analysis. In fact, they showed high performances in terms of sensitivity and selectivity. In this report, we present a survey of the application of different nanomaterials and nanocomposites with tailored morphological properties as sensing platforms for food analysis. Particular attention has been devoted to the sensors developed with nanomaterials such as carbon-based nanomaterials, metallic nanomaterials, and related nanocomposites. Finally, several examples of sensors for the detection of some analytes present in food and beverages, such as some hydroxycinnamic acids (caffeic acid, chlorogenic acid, and rosmarinic acid), caffeine (CAF), ascorbic acid (AA), and nitrite are reported and evidenced.     

Customized Bio‐functionalization of Nanocomposite Carbon Paste Electrodes for Electrochemical Sensing: A Mini Review

Over the past few decades, the (bio)functionalization of carbon nanomaterials (CNMs), such as nanohorns, carbon nanotubes, graphene, graphite and related with a wide range of (bio)modifiers have been extensively studied for their incorporation on different pure metal or carbon electrode surfaces via drop‐casting. However, CNMs are also shown to be important functional additives for polymers, having great potential to produce rigid nanocomposite materials with a range of enhanced properties, including mechanical, optical, electrical, thermal and electrochemical. The high malleability derived from the host polymer allows alternative strategies that can be carried out in order to incorporate different types of (bio)modifiers in/on/into a polymeric nanocomposite electrode. Accordingly, this mini review overviews the main methodologies used for the bio‐functionalization of electrochemical transducers based on nanocomposite carbon paste electrodes (NC‐CPEs). Additionally, the most extensively (bio)modifiers used in electrochemical (bio)sensing, together with their various electrocatalytical performance are also discussed, fact that might serve as a general outlook for planning further research.     

Disposable highly ordered pyrolytic graphite-like electrodes: Tailoring the electrochemical reactivity of screen printed electrodes

We demonstrate that the electron transfer properties of disposable screen printed electrodes can be readily tailored via the introduction of a polymeric formulation into the ink used to fabricate these electrochemical platforms. This approach allows the role of the binder on the underpinning electrochemical properties to be explored and allows the electrochemical reactivity of the screen printed electrodes to be tailored from that of edge plane to basal plane of highly ordered pyrolytic graphite.     

Controlled‐Potential‐Based Electrochemical Sulfide Sensors: A Review

Due to their potential applications in industry and potent toxicity to the environment, sulfides and their detection have attracted the attention of researchers. To date, a large number of controlled‐potential techniques for electrochemical sulfide sensors have been developed, thanks to their simplicity, reasonable limit of detection (LOD), and good selectivity. Different researchers have applied different strategies for developing selective and sensitive sulfide sensors. However, there has been no systematic review on controlled‐potential techniques for sulfide sensing. In light of this absence, the main aim of this review article is to summarize various strategies for detecting sulfide in different media. The efficiencies of the developed sulfide sensors for detecting sulfide in its various forms are determined, and the essential parameters, including sensing strategies, working electrodes, detection media, pH, LOD, sensitivity, and linear detection range, are emphasized in particular. Future research in this area is also recommended. It is expected that this review will act as a basis for further research on the fabrication of sulfide sensors for practical applications.     

用于抗生素检测的纳米材料基电化学传感器研究进展

近年来,抗生素作为基本的治疗药物在医学、畜牧业、水产养殖业等方面被广泛应用,但其过量使用造成的抗生素残留问题也给生态环境、食品安全和人类健康造成严重的威胁.鉴于此,纳米电化学传感器在抗生素快速检测方面的研究成为热点,也取得了可观的进展.本文首先对抗生素进行了简单介绍,通过分析抗生素的电化学性质,综述了不同结构和类型的纳...     

A novel strategy for fabrication,activation and cleaning of fully 3D printed flexible planar electrochemical platforms

In recent years, 3D printing of carbon-based conductive filaments has received growing attention for assembling electrodes to be used in a wide variety of electroanalytical devices and applications. Despite the large amount of work present in literature concerning the development of three-dimensional (3D) conductive structures, its potential as dry deposition method for assembling two-dimensional (2D) electrodes to be used in planar configuration is still largely unexplored. In fact, the possibility to rapidly change the geometry of the electrochemical circuits, associated with the reduction of waste and the absence of solvents, which are instead important components of ink and paste formulations, makes this strategy a valid green and efficient alternative to other deposition approaches such as screen-printing technology. We report here a rapid and solvent-free method for assembling fully 3D printed flexible planar electroanalytical platforms (3DEPs) to be used with microliters of liquid. At the same time, a novel protocol for the surface pre-treatment of 3D printed electrodes based on ultrasonication in aqueous NaOH solution followed by electrochemical activation using the same medium, is presented. In addition, the same procedure has proved to be efficient for cleaning the electrode surface after electrochemical passivation, thus confirming the validity of both time-efficient and environmentally-friendly assembling and activation/cleaning procedures developed which allow efficient and reusable electrodes to be produced. Finally, 3DEPs were tested by a proof-of-concept quantification of a commonly used food dye (Brilliant Blue, E-133) in commercial solutions used for homemade food coloring.     

Developing Graphene‐Based Nanohybrids for Electrochemical Sensing

Graphene‐based nanohybrid is considered to be the most promising nanomaterial for electrochemical sensing applications due to the defects created on the graphene oxide layers. These defects provide graphene oxide unique properties, such as excellent conductivity, large specific surface area, and electrocatalytic activity. These unique properties encourage scientists to develop novel graphene‐based nanohybrids and improve the sensing efficiency. This review, therefore, addresses this topic by comprehensively discussing the strategies to fabricate novel graphene based nanohybrids with high sensitivity. The combinations of graphene with various nanomaterials, such as metal nanoclusters, metal compound nanoparticles, carbon materials, polymers and peptides, in the direction of electrochemical sensing, were systematically analyzed. Meanwhile, the challenges in the functional design and application of graphene‐based nanohybrids were described and the reasonable solutions were proposed.     

Versatile Electrochemical Platform for the Determination of Phenol‐like Compounds Based on Laccases from Different Origins

Simple and fast methods for the monitoring of phenol‐like compounds are relevant in diverse fields ranging from waste management to neurosciences. Laccases are copper‐containing enzymes, which, depending on their origin, are able to oxidize different phenol compounds at different pH conditions. Through adequate laccase immobilization, disposable screen printed electrodes can be used as interphase to build amperometric phenol sensors. In this work three different laccases were studied for the determination of phenol‐like compounds, two of them are isoenzymes from Trametes trogii and the third one from Rhus vernicifera . Their immobilization on screen printed electrodes is presented for the construction of amperometric sensors. The electrode substrate is composed by graphite screen printed electrodes modified with carbon nanotubes and silica microspheres where, depending on the application, one of the three laccases is adsorbed. As each laccase shows an optimum working pH, they were conveniently selected to determine dopamine at physiological pH and catechol at acid pH. Determinations in the micromolar range were possible in both cases. Chronoamperometry shows to be an effective technique for their determinations, simpler than other electrochemical methods already presented in the literature.     

Molecularly Imprinted Polymers Combined with Electrochemical Sensors for Food Contaminants Analysis

Detection of relevant contaminants using screening approaches is a key issue to ensure food safety and respect for the regulatory limits established. Electrochemical sensors present several advantages such as rapidity; ease of use; possibility of on-site analysis and low cost. The lack of selectivity for electrochemical sensors working in complex samples as food may be overcome by coupling them with molecularly imprinted polymers (MIPs). MIPs are synthetic materials that mimic biological receptors and are produced by the polymerization of functional monomers in presence of a target analyte. This paper critically reviews and discusses the recent progress in MIP-based electrochemical sensors for food safety. A brief introduction on MIPs and electrochemical sensors is given; followed by a discussion of the recent achievements for various MIPs-based electrochemical sensors for food contaminants analysis. Both electropolymerization and chemical synthesis of MIP-based electrochemical sensing are discussed as well as the relevant applications of MIPs used in sample preparation and then coupled to electrochemical analysis. Future perspectives and challenges have been eventually given.     

Characterization and fabrication of disposable screen printed microelectrodes

We report the fabrication of disposable and flexible screen printed microelectrodes which are characterised with microscopy and cyclic voltammetry. These new type of screen printed electrochemical platforms consist of micro-sized graphite typically with radii of 60 to 100 microns are defined by an inert dielectric. The advantage of this type of electrochemical sensing platform is that each microelectrode is disposable and cost effective and thus does not require extensive cleaning or electrode pre-treatment between measurements. Prior to measurements the screen printed microelectrode needs only to be calibrated with a suitable redox probe, as is typically the case with microelectrodes. We show proof of concept that the screen printed microelectrodes are advantageous for electro-analytical measurements with the example of determination of lead via cathodic stripping voltammetry. The use of graphite screen printed microelectrodes allows comparable detection limits to that obtained in the literature at insonated boron doped diamond electrodes, without the need for power ultrasound – which otherwise limits the widespread applicability and ease of measurement.