Marjorie Montero-Jiménez

We present a methodology that enhances the analytical performance of organic electrochemical transistors (OECTs) by continuously cycling the devices through gate potential sweeps during sensing experiments. This continuous cycling methodology (CCM) enables real-time acquisition of full transfer curves, allowing simultaneous monitoring of multiple characteristic parameters. We show that the simultaneous temporal evolution of several OECT response parameters (threshold voltage (V_TH), maximum transconductance (g_max), and maximum transconductance potential (V_G,gmax)) provides highly sensitive descriptors for detecting pH changes and macromolecule adsorption on OECTs based on polyaniline (PANI) and poly(3,4-ethylenedioxythiophene) (PEDOT) channels. Moreover, the method allows reconstruction of I_DS–t (drain–source current vs. time) profiles at any selected gate potential, enabling the identification of optimal gate voltage (V_G) values for maximizing sensitivity. This represents a substantial improvement over traditional measurements at fixed V_G, which may suffer from reduced sensitivity and parasitic reactions associated with gate polarization. Moreover, the expanded set of parameters obtained with the CCM provides deeper insight into the physicochemical processes occurring at both gate and channel electrodes. We demonstrate its applicability in monitoring polyelectrolyte and enzyme adsorption, and detecting urea and glucose through enzyme-mediated reactions. Owing to its versatility and the richness of the information it provides, the CCM constitutes a significant advance for the development and optimization of OECT-based sensing platforms.

We present a methodology that enhances the analytical performance of organic electrochemical transistors (OECTs) by continuously cycling the devices through gate-potential sweeps during sensing experiments. This continuous cycling method (CCM) enables real-time acquisition of full transfer curves, allowing simultaneous monitoring of multiple characteristic parameters. We show that the simultaneous temporal evolution of several OECT response parameters (VTH, VG,gmax, and gmax) provides highly sensitive descriptors for detecting pH changes and macromolecule adsorption on OECTs based on PANI and PEDOT channels. Moreover, the method allows reconstruction of IDS–time profiles at any selected gate potential, enabling the identification of optimal VG values for maximizing sensitivity. This represents a substantial improvement over traditional measurements at fixed VG, which may suffer from reduced sensitivity and parasitic reactions associated with gate polarization. Moreover, the expanded set of parameters obtained with the CCM provides deeper insight into the physicochemical processes occurring at both gate and channel electrodes. We demonstrate its applicability to monitoring polyelectrolyte and enzyme adsorption as well as detecting urea and glucose through enzyme-mediated reactions. Owing to its versatility and the richness of the information it provides, the CCM constitutes a significant advance for the development and optimization of OECT-based sensing platforms.

We present the construction of an organic electrochemical transistor (OECT) based on poly(3,4-ethylendioxythiophene, PEDOT) and polyallylamine (PAH) and its evaluation as a bioelectronic platform for urease integration and urea sensing. The OECT channel was fabricated in a one-step procedure using chemical polymerization. Then, urease was immobilized on the surface by electrostatic interaction of the negatively charged enzyme at neutral pH with the positively charged surface of PEDOH-PAH channels. The real-time monitoring of the urease adsorption process was achieved by registering the changes on the drain–source current of the OECT upon continuous scan of the gate potential during enzyme deposition with high sensitivity. On the other hand, integrating urease enabled urea sensing through the transistor response changes resulting from local pH variation as a consequence of enzymatic catalysis. The response of direct enzyme adsorption is compared with layer-by-layer integration using polyethylenimine. Integrating a polyelectrolyte over the adsorbed enzyme resulted in a more stable response, allowing for the sensing of urine even from diluted urine samples. These results demonstrate the potential of integrating enzymes into the active channels of OECTs for the development of biosensors based on local pH changes.

The fabrication of efficient organic electrochemical transistors (OECTs)-based biosensors requires the design of biocompatible interfaces for the immobilization of biorecognition elements, as well as the development of robust channel materials to enable the transduction of the biochemical event into a reliable electrical signal. In this work, PEDOT-polyamine blends are shown as versatile organic films that can act as both highly conducting channels of the transistors and non-denaturing platforms for the construction of the biomolecular architectures that operate as sensing surfaces. To achieve this goal, we synthesized and characterized films of PEDOT and polyallylamine hydrochloride (PAH) and employed them as conducting channels in the construction of OECTs. Next, we studied the response of the obtained devices to protein adsorption, using glucose oxidase (GOx) as a model system, through two different strategies: The direct electrostatic adsorption of GOx on the PEDOT-PAH film and the specific recognition of the protein by a lectin attached to the surface. Firstly, we used surface plasmon resonance to monitor the adsorption of the proteins and the stability of the assemblies on PEDOT-PAH films. Then, we monitored the same processes with the OECT showing the capability of the device to perform the detection of the protein binding process in real time. In addition, the sensing mechanisms enabling the monitoring of the adsorption process with the OECTs for the two strategies are discussed.

Air transports several pollutants, including particulate matter (PM), which can produce cardiovascular and respiratory diseases. Thus, it is a challenge to control pollutant emissions before releasing them to the environment. Until now, filtration has been the most efficient processes for removing PM. Therefore, the electrospinning procedure has been applied to obtain membranes with a high filtration efficiency and low pressure drop. This review addressed the synthesis of polymers that are used for fabricating high-performance membranes by electrospinning to remove air pollutants. Then, the most influential parameters to produce electrospun membranes are indicated. The main results show that electrospun membranes are an excellent alternative to having air filters due to the versatility of the process, the capacity for controlling the fiber diameter, porosity, high filtration efficiency and low-pressure drop.

El mercurio es considerado un contaminante altamente peligroso debido a su elevada toxicidad y a su carácter acumulativo. Presenta varios efectos en la salud humana tales como: trastornos del sistema nervioso, deterioro intelectual, problemas gastrointestinales y cáncer. El uso de técnicas electroquímicas es una alternativa para la cuantificación de mercurio a niveles traza, debido a su bajo costo y buena sensibilidad. En este trabajo de investigación se evaluó un microelectrodo de fibra de carbono modificado con nanopartículas de oro para la determinación de mercurio (II) en medio acuoso. Se realizó la modificación superficial de la fibra de carbono electrodepositando nanopartículas de oro, a un potencial de -0,1 V durante 100 s, y se utilizó microscopía electrónica de barrido y voltamperometría cíclica para confirmar la presencia de nanopartículas de oro. Se cuantificó el mercurio (II) mediante voltamperometría de redisolución anódica de pulso diferencial. Se obtuvo un rango lineal, en la curva de calibración, entre 50 - 100 µg L^-1 de mercurio (II). Los límites de detección y de cuantificación obtenidos fueron de 38 y 46 µg L^-1, respectivamente. La validación de la metodología se realizó mediante porcentaje de recuperación, obteniendo valores entre 94 y 104 % y desviación estándar relativa (RSD, por sus siglas en inglés) entre 3,6 y 4,7 %. El método propuesto muestra características útiles para su implementación en el monitoreo de contaminación por mercurio.

In this work, a new hydrogen peroxide (H₂O₂) electrochemical sensor was fabricated. Prussian blue (PB) was electrodeposited on a glassy carbon (GC) electrode modified with zirconia doped functionalized carbon nanotubes (ZrO₂-fCNTs), (PB/ZrO₂-fCNTs/GC). The morphology and structure of the nanostructured system were characterized by scanning and transmission electron microscopy (TEM), atomic force microscopy (AFM), specific surface area, X-ray diffraction (XRD), thermogravimetric analysis (TGA), Raman and Fourier transform infrared (FTIR) spectroscopy. The electrochemical properties were studied by cyclic voltammetry (CV) and chronoamperometry (CA). Zirconia nanocrystallites (6.6 ± 1.8 nm) with cubic crystal structure were directly synthesized on the fCNTs walls, obtaining a well dispersed distribution with a high surface area. The experimental results indicate that the ZrO₂-fCNTs nanostructured system exhibits good electrochemical properties and could be tunable by enhancing the modification conditions and method of synthesis. The fabricated sensor could be used to efficiently detect H₂O₂, presenting a good linear relationship between the H₂O₂ concentration and the peak current, with quantification limit (LQ) of the 10.91 μmol·L⁻¹ and detection limit (LD) of 3.5913 μmol·L⁻¹.

A hydrogen peroxide (H₂O₂) sensor and biosensor based on modified multi-walled carbon nanotubes (CNTs) with titanium dioxide (TiO₂) nanostructures was designed and evaluated. The construction of the sensor was performed using a glassy carbon (GC) modified electrode with a TiO₂–CNT film and Prussian blue (PB) as an electrocalatyzer. The same sensor was also employed as the basis for H₂O₂ biosensor construction through further modification with horseradish peroxidase (HRP) immobilized at the TiO₂–fCNT film. Functionalized CNTs (fCNTs) and modified TiO₂–fCNTs were characterized by Transmission Electron Microscopy (TEM), Fourier Transform Infrared Spectroscopy (FTIR), and X-Ray DifFraction (XRD), confirming the presence of anatase over the fCNTs. Depending on the surface charge, a solvent which optimizes the CNT dispersion was selected: dimethyl formamide (DMF) for fCNTs and sodium dodecylsulfate (SDS) for TiO₂–fCNTs. Calculated values for the electron transfer rate constant (ks) were 0.027 s⁻¹ at the PB–fCNT/GC modified electrode and 4.7 × 10⁻⁴ s⁻¹ at the PB–TiO₂/fCNT/GC electrode, suggesting that, at the PB–TiO₂/fCNT/GC modified electrode, the electronic transfer was improved. According to these results, the PB–fCNT/GC electrode exhibited better Detection Limit (LD) and Quantification Limit (LQ) than the PB–TiO₂/fCNT/GC electrode for H₂O₂. However, the PB film was very unstable at the potentials used. Therefore, the PB–TiO₂/fCNT/GC modified electrode was considered the best for H₂O₂ detection in terms of operability. Cyclic Voltammetry (CV) behaviors of the HRP–TiO₂/fCNT/GC modified electrodes before and after the chronoamperometric test for H₂O₂, suggest the high stability of the enzymatic electrode. In comparison with other HRP/fCNT-based electrochemical biosensors previously described in the literature, the HRP–fCNTs/GC modified electrode did not show an electroanalytical response toward H₂O₂.

We report on two new electrochemical sensors which, coupled to differential pulse voltammetry, constitutes a useful tool for diagnosis of heavy metal pollution. The electrochemical sensors AgHgNf/Cu and the AgBiNf/Cu were obtained by deposition of bimetallic particles of AgHg or AgBi on copper electrodes covered with a Nafion (Nf) film, respectively. Micrographs of the electrode’s surface showed evenly scattered bimetallic particles, with an approximate diameter of 150 nm, embedded in the Nafion (Nf) film. In order to test the electrodes, the hydrogen evolution signal according to the Brdička reaction was measured for the determination of cysteine-rich peptides (CRp) produced by plants. To check the accuracy of the electrodes, real samples of Nicotiana tabacum cells exposed to cytotoxic levels of cadmium were tested. The AgHgNf/Cu electrode produced detection limits (DLs) of 0.088 µmol L⁻¹ for Cysteine and 0.139µmol L⁻¹ for Glutathione, while for the AgBiNf/Cu electrode DLs were 0.41 µmol L⁻¹ for cysteine and 0.244 µmol L⁻¹ for glutathione. Thus, the new electrodes could be a useful analytical electrochemical system very convenient for fieldwork. The electrodes were capable of direct, accurate, and sensitive detection of synthesized peptides, despite the complex matrix where the Nicotiana tabacum cells were grown.

Long-term cadmium intake can be very dangerous to human health due to its toxic effects. Although people can be contaminated with this element from different sources, contaminated food is probably the most important one. Foods such as vegetables and fruits can become contaminated with cadmium existing in soils, irrigation water, or chemical fertilizers. Some plants produce an excess of cysteine-rich peptides (CRp) when affected by high concentrations of heavy metals such as cadmium, thus indicating the presence of this type of contamination. Among these plants is tamarillo (Solanum betaceum), which is locally known as “tree tomato”. This is a native plant widely consumed in the Ecuadorian Andes because of its abundance, low cost, and high content of vitamin C and fiber. The fact that Solanum betaceum produces CRp upon contamination with heavy metals means that this plant may be able to accumulate heavy metals. If this is the case, the plant can possibly be used as an indicator of metal pollution. The main goals of the present work were to evaluate the possibility of using Solanum betaceum as an indicator of metal contamination in plants and to examine its capability to accumulate metals. Both goals were met by determination of the amounts of CRp produced by Solanum betaceum cells cultivated in vitro in the laboratory under controlled conditions in the presence of different concentrations of cadmium. The CRp determination was carried out by means of electrogeneration of iodine in an iodide solution containing reduced glutathione as a biological thiol model. Solanum betaceum cells were grown in a Murashige and Skoog solution enriched with a 30 g L⁻¹ sugar aqueous solution and 1 mg L⁻¹ 2,4-dichlorophenoxyacetic acid. The results of these experiments confirmed the following: (1) CRp production is a function of the amount of cadmium present as a contaminant up to a limiting value after which cell apoptosis occurs; (2) Solanum betaceum accumulates cadmium; (3) the analytical method used is appropriate for CRp determination; and (4) CRp determination is a valid alternative to detect contamination by heavy metals in plants.