Micro- and nano-devices for electrochemical sensing

Electrode miniaturization has profoundly revolutionized the field of electrochemical sensing, opening up unprecedented opportunities for probing biological events with a high spatial and temporal resolution, integrating electrochemical systems with microfluidics, and designing arrays for multiplexed sensing. Several technological issues posed by the desire for downsizing have been addressed so far, leading to micrometric and nanometric sensing systems with different degrees of maturity. However, there is still an endless margin for researchers to improve current strategies and cope with demanding sensing fields, such as lab-on-a-chip devices and multi-array sensors, brain chemistry, and cell monitoring. In this review, we present current trends in the design of micro-/nano-electrochemical sensors and cutting-edge applications reported in the last 10 years. Micro- and nanosensors are divided into four categories depending on the transduction mechanism, e.g., amperometric, impedimetric, potentiometric, and transistor-based, to best guide the reader through the different detection strategies and highlight major advancements as well as still unaddressed demands in electrochemical sensing

Selective detection of dopamine with an all PEDOT:PSS Organic Electrochemical Transistor

open6noAn all PEDOT:PSS Organic Electrochemical Transistor (OECT) has been developed and used for the selective detection of dopamine (DA) in the presence of interfering compounds (ascorbic acid, AA and uric acid, UA). The selective response has been implemented using a potentiodynamic approach, by varying the operating gate bias voltage and the scan rate. The trans-conductance curves allow to obtain a linear calibration plot for AA, UA and DA and to separate the redox waves associated to each compound; for this purpose, the scan rate is an important parameter to achieve a good resolution. The sensitivities and limits of detection obtained with the OECT have been compared with those obtained by potential step amperometric techniques (cyclic voltammetry and differential pulse voltammetry), employing a PEDOT:PSS working electrode: our results prove that the all-PEDOT:PSS OECT sensitivities and limits of detection are comparable or even better than those obtained by DPV, a technique that employs a sophisticate potential wave and read-out system in order to maximize the performance of electrochemical sensors and that can hardly be considered a viable readout method in practical applications.openGualandi, Isacco; Tonelli, Domenica; Mariani, Federica; Scavetta, Erika; Marzocchi, Marco; Fraboni, BeatriceGualandi, Isacco; Tonelli, Domenica; Mariani, Federica; Scavetta, Erika; Marzocchi, Marco; Fraboni, Beatric

Design of an electrochemically gated organic semiconductor for pH sensing

Since the development of potentiometric ion-selective electrodes, remarkable steps have been taken towards progressive simplification and improved robustness of pH sensing probes. In particular, the design of compact sensing architectures using solid-state components holds great potential for portable and wearable applications. Here we report the development of an electrochemically gated device for pH detection, combining the robustness of potentiometric-like transduction with an extremely simple and integrated geometry requiring no reference. The sensor is a two-point probe device comprising two thin polymeric films, i.e. a charge transport layer and a pH-sensitive layer, and exhibits a sensitivity of (8.3 ± 0.2) × 10−3 pH unit−1 in the pH range from 2 to 7. Thanks to the versatility and robustness of the optimised design, a textile pH sensor was fabricated whose performance is comparable with that of glass sensors

Heterobimetallic conducting polymers based on salophen complexes via electrosynthesis

In this work, we report the first electrochemical synthesis of two copolymeric bimetallic conducting polymers by a simple anodic electropolymerization method. The adopted precursors are electroactive transition metal (M = Ni, Cu and Fe) salophen complexes, which can be easily obtained by direct chemical synthesis. The resulting films, labeled poly-NiCu and poly-CuFe, were characterized by cyclic voltammetry in both organic and aqueous media, attenuated total reflectance Fourier transform infrared spectroscopy, UV-vis spectroscopy, scanning electron microscopy, and coupled energy dispersive X-ray spectroscopy. The films are conductive and exhibit great electrochemical stability in both organic and aqueous media (resistant over 100 cycles without significant loss in current response or changes in electrochemical behavior), which makes them good candidates for an array of potential applications. Electrochemical detection of ascorbic acid was performed using both materials

Oxygen Gas Sensing Using a Hydrogel-Based Organic Electrochemical Transistor for Work Safety Applications

open8noOxygen depletion in confined spaces represents one of the most serious and underestimated dangers for workers. Despite the existence of several commercially available and widely used gas oxygen sensors, injuries and deaths from reduced oxygen levels are still more common than for other hazardous gases. Here, we present hydrogel-based organic electrochemical transistors (OECTs) made with the conducting polymer poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT:PSS) as wearable and real-time oxygen gas sensors. After comparing OECT performances using liquid and hydrogel electrolytes, we identified the best PEDOT:PSS active layer and hydrogel coating (30 µm) combination for sensing oxygen in the concentration range of 13–21% (v/v), critical for work safety applications. The fast O2 solubilization in the hydrogel allowed for gaseous oxygen transduction in an electrical signal thanks to the electrocatalytic activity of PEDOT:PSS, while OECT architecture amplified the response (gain ̴ 104). OECTs proved to have comparable sensitivities if fabricated on glass and thin plastic substrates, (−12.2 ± 0.6) and (−15.4 ± 0.4) µA/dec, respectively, with low power consumption (<40 µW). Sample bending does not influence the device response, demonstrating that our real-time conformable and lightweight sensor could be implemented as a wearable, noninvasive safety tool for operators working in potentially hazardous confined spaces.The work was supported by the European Union FESR FSE, PON Research and Innovation 2014-2020 and FSC, project number ARS01-00996 "TEXT-STYLENuovi tessuti intelligenti e sostenibilimultisettoriali per il design creative e stileMade-in-Italy" and by the Italian Ministry of Economic Development 2020-Project "AlmaMater patents-Monitoraggio in continuo di pH e idratazione-MIRAGE".openFrancesco Decataldo, Filippo Bonafè, Federica Mariani, Martina Serafini, Marta Tessarolo, Isacco Gualandi, Erika Scavetta, Beatrice FraboniFrancesco Decataldo, Filippo Bonafè, Federica Mariani, Martina Serafini, Marta Tessarolo, Isacco Gualandi, Erika Scavetta, Beatrice Frabon

Smart Bandaid Integrated with Fully Textile OECT for Uric Acid Real-Time Monitoring in Wound Exudate

: Hard-to-heal wounds (i.e., severe and/or chronic) are typically associated with particular pathologies or afflictions such as diabetes, immunodeficiencies, compression traumas in bedridden people, skin grafts, or third-degree burns. In this situation, it is critical to constantly monitor the healing stages and the overall wound conditions to allow for better-targeted therapies and faster patient recovery. At the moment, this operation is performed by removing the bandages and visually inspecting the wound, putting the patient at risk of infection and disturbing the healing stages. Recently, new devices have been developed to address these issues by monitoring important biomarkers related to the wound health status, such as pH, moisture, etc. In this contribution, we present a novel textile chemical sensor exploiting an organic electrochemical transistor (OECT) configuration based on poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) for uric acid (UA)-selective monitoring in wound exudate. The combination of special medical-grade textile materials provides a passive sampling system that enables the real-time and non-invasive analysis of wound fluid: UA was detected as a benchmark analyte to monitor the health status of wounds since it represents a relevant biomarker associated with infections or necrotization processes in human tissues. The sensors proved to reliably and reversibly detect UA concentration in synthetic wound exudate in the biologically relevant range of 220-750 μM, operating in flow conditions for better mimicking the real wound bed. This forerunner device paves the way for smart bandages integrated with real-time monitoring OECT-based sensors for wound-healing evaluation

OH radical Determination: synthesis of materials used for the modification of Pt and Glassy Carbon electrodes

Questa tesi descrive lo sviluppo di un elettrodo modificato con un polimero isolante per la determinazione indiretta del radicale OH. I polimeri testati sono stati polifenolo, polipirrolo e polipirrolo sovraoossidato ed il primo è risultato quello con le migliori prestazioni. Il film di modificante è stato depositato per elettropolimerizzazione del fenolo in ambiente acido, su un elettrodo di carbone vetroso (GC) ed è risultato isolante e perfettamente adeso al GC, impedendo il trasferimento di carica alle più comuni sonde redox. L’attacco dei radicali OH, generati dalla reazione di Fenton o dalla fotolisi di H2O2, rimuove parzialmente il polimero dal GC, ripristinando parzialmente il comportamento conduttore dell’elettrodo. L’entità della degradazione del film polifenolico è stata valutata sfruttando la corrente relativa alla sonda redox Ru(NH3)63+, che rappresenta il segnale analitico per la determinazione del radicale OH. L’elettrodo è stato impiegato per stimare le prestazioni di foto catalizzatori a base di nanoparticelle di TiO2, ottenendo risultati correlati a quelli ricavati da un metodo HPLC. Inoltre esso è stato usato per sviluppare una nuova procedura per la determinazione della capacità di scavenging verso i radicali OH, che è stata applicata all’analisi di composti puri e campioni reali. I risultati erano confrontabili con quelli determinati con metodiche standardizzate, comunemente impiegate per la determinazione della capacità antiossidante. Inoltre è stato condotto uno studio riguardante la modifica di un elettrodo di platino con un idrossido misto a strati a base di cobalto e alluminio (LDH). In particolare si sono valutati gli effetti di diversi pretrattamenti del Pt sulle caratteristiche e prestazioni elettrocatalitiche del film di LDH nei confronti dell’ossidazione di anilina, fenolo e acido salicilico. Questi composti possono essere impiegati come molecole sonda per la determinazione del radicale OH e rivestono interesse da un punto di vista elettroanalitico perché portano facilmente alla passivazione della superficie di Pt.The development of a cheap modified electrode for the indirect detection of OH radical is described. The method is based on the attack of OH radicals on the modifier and the quantification of its degradation is evaluated by electroanalytical approaches. Polyphenol, polypyrrole and overoxidized polypyrrole were tested as modifiers for the determination and, from our experiments, polyphenol resulted the best one. The modified electrode was prepared by electropolymerization of phenol in acid environment on glassy carbon (GC). The film perfectly covered the GC surface and inhibited the charge transfer of many redox species. The attack of OH radicals generated by Fenton reaction or H2O2 photolysis partly removed the polymer from GC and the conductor behavior of the electrode was partially restored. The degree of degradation of the polyphenol is the analytical signal and was quantified by cyclic voltammetry and chronoamperometry, using the redox probe Ru(NH3)63+. The electrode was used to evaluate the performances of different photocatalysts based on TiO2 nanoparticles and the results were successfully compared with those obtained from a more traditional HPLC method. A new procedure for the determination of the scavenging activity towards OH radicals was developed using the polyphenol modified GC. The results obtained for pure compounds and real samples were comparable to those from standardized methods which are widely employed to estimate the antioxidant capacity. Furthermore, the modification of a Pt electrode with a double layered hydroxide, based on Co and Al, (LDH) was deeply investigated. In particular, we studied the effects of different pretreatments of Pt surface on the characteristics and performances of the LDH film towards the electrocatalytic oxidation of aniline, phenol and salicylic acid. These compounds can be used as probe molecules for hydroxyl radical detection and are very interesting from an electroanalytical point of view since they lead to Pt passivation

A new electrochemical sensor for OH radicals detection

A new, cheap modified electrode for indirect detection of OH radical is described. A glassy carbon (GC) electrode was modified with a polyphenol film prepared by oxidative potentiostatic ectropolymerization of 0.05 M phenol in 1 M H2SO4. The film having a thickness of ~10 nm perfectly covered the GC surface and inhibited the charge transfer of many redox species. The degradation of the polyphenol film, that was induced by OH radicals generated by Fenton reaction or by H2O2 photolysis, is the analytical signal and it was evaluated by cyclic voltammetry and chronoamperometry using the redox probe Ru(NH3)63+. Some simulations of the kinetics of the reactions occurring in the solution bulk and near the electrode surface were carried out to fully understand the processes that lead to the analytical signal. The modified electrode was used to evaluate the performances of different TiO2-based photocatalysts and the results were successfully compared with those obtained from a traditional HPLC method that is based on the determination of the hydroxylation products of salicylic acid

Reduced Graphene Oxide and Carbon Nanotubes for the development of polyphenols amperometric biosensors

Biosensors for sensitive, rapid and precise determination of phenolic compounds are attracting growing interest in environmental control and protection as well as in food industry. Laccase (Lac) and tyrosinase (Tyr) are multicopper oxidase enzymes that catalyze the oxidation of phenol derivatives to the relevant quinones with the concomitant reduction of oxygen directly to water without the formation of reactive oxygen intermediates. Here we present the development of amperometric biosensors based on Lac or Tyr physically adsorbed on glassy carbon electrodes modified with carbon-based nanomaterials. Carbon-based nanomaterials are often employed in electrochemistry for their beneficial properties and in the last few years they have been frequently used in the development of biosensors to enhance the electron transfer between the electrode and the enzyme. Graphene represents an excellent material for sensing applications due to properties like fast heterogeneous electron transfer, large surface area, high mechanical strength, ease of functionalization, high conductivity and good biocompatibility. The electron transfer rates on graphene sheets obtained by electrochemical reduction of graphene oxide (GO) are similar to those observed for carbon nanotubes and higher than those of glassy carbon electrodes since the reduction of oxygen functional groups at edge and basal planes produces defect sites. The electrochemical reduction of GO is a versatile method to obtain a graphene layer (rGO) on the electrode surface which still displays some controllable oxygen-containing functionalities, usable for covalent or physical immobilization of enzymes. The enzyme immobilization represents a rather critical issue because the methods used for this procedure significantly influence the biosensor properties, operability and long-term stability. Among the methods available in the case of tyrosinase and laccase, the most commonly employed is the physical entrapment, obtained by a cross-linking with bovine serum albumin (BSA) and glutaraldehyde (GA)