Noninvasive Solution for Electrochemical Impedance Spectroscopy on Metallic Works of Art

Metallic works of art of cultural relevance are continuously subjected to corrosion as the environment becomes increasingly polluted. A fast and simple method to in situ assess the conservation conditions is therefore required. This paper describes the development and performance of dry and gel-based electrodes which can be used to assess the surface conservation state without the need to move the artifacts and which do not cause any damage to them. The electrodes can be used with a portable electrochemical impedance spectroscopy system, without employing electrochemical cells. The proposed solution does not provide all the information that one can obtain using an electrochemical cell, but it can discriminate between protective coatings. It can be used to assess the protective capability of corrosion product layers and natural patinas, and it can therefore enable a noninvasive routine surface assessment to be conducted that could be extremely useful for people working in the field of conservation of cultural heritag

Low-cost electrochemical impedance spectroscopy system for corrosion monitoring of metallic antiquities and works of art

Electrochemical impedance spectroscopy (EIS) is recognized to be a powerful and noninvasive technique to test the integrity of protective coatings on memorials, but commercial EIS systems are rather costly though versatile devices. This paper describes a low cost and portable EIS system that is based on a compact digital signal processor (DSP) board and embeds the potentiostatic function so that it can be used without requiring an external potentiostat. The software that runs on the DSP is designed to analyze the electrochemical impedance only in a reduced frequency range in order to produce a simple corrosion alert result. The device is equipped with a digital interface and can be connected to a personal computer to carry out a complete frequency analysis and perform a more complex data processing

Fabrication and Characterization of Electrochemical Glucose Sensors

Electrochemical sensors based on the nanostructure of the semiconductor materials are of tremendous interest to be utilized for glucose monitoring. The sensors, based on the nanostructure of the semiconductor materials, are the third generations of the glucose sensors that are fast, sensitive, and cost-effect for glucose monitoring. Glucose sensors based on pure zinc oxide nanorods (NRs) grown on different substrates, such ITO, FTO, and Si/SiO2/Au, were investigated in this research. Silicon nanowire (NW)- based glucose sensors were also studied. First, an enzyme-based glucose sensor was fabricated out of glass/ITO/ZnO NRs/BSA/GOx/nafion membrane. The sensor was tested amperometrically at different glucose concentrations. The device showed a high sensitivity and a lower limit of detection in the order of 10.911 mA/cm2 mM and 0.22 μM, respectively. In addition, the device exhibited a fast and a sharp amperometric time response of ~3 s with different glucose concentrations. The high surface-to-volume ratio provided by the ZnO NRs was investigated by characterizing the sensor with and without the ZnO NRs grown on Si/SiO2/Au substrates. The sensor showed almost a negligible amperometric response to the changes in the glucose concentrations without ZnO NRs. After applying the ZnO NRs, the sensor exhibited a linear response to the glucose concentrations from 1-8 mM. Furthermore, very clear oxidation peaks were observed at the scan rates of 100 and 200 mV/s in the presence of 2 mM of the glucose. The device showed no dependency on different scan rates without applying the ZnO NRs. An enzyme-free glucose sensor was fabricated based on ZnO NRs grown on FTO and modified with Fe2O3. The device showed a high sensitivity and a wide amperometric linear response on the order of 0.052 μA/cm2 and from 100-400 mg/dL, respectively. Reactive ion etching and nanosphere lithography methods were utilized to grow the Si NWs vertically on top of a silicon wafer. The sensor showed a high linearity from 1-9 mM for changes in glucose concentrations. In addition, the high surface-to-volume ratio provided by the Si NWs helped in adsorbing higher concentrations of the enzyme

Desarrollo de una celda electroquímica en gel para la evaluación in situ del patrimonio cultural metálico

A lo largo de toda la historia, la humanidad ha tratado de preservar ciertos objetos que por diversos motivos han adquirido un valor y un significado para la sociedad que los ha poseído, constituyendo su patrimonio cultural. En ese esfuerzo por preservar el pasado para las generaciones presentes y futuras, la investigación científica ha ido adquiriendo una relevancia progresiva. La ciencia de la conservación trata de comprender los problemas y aportar soluciones para la conservación del patrimonio, tanto desde el punto de vista tecnológico como estratégico o de sostenibilidad. El adecuado diseño y planificación de las estrategias de conservación de los objetos y colecciones del patrimonio cultural son fundamentales, y deben tener en cuenta las limitaciones tecnológicas y de recursos. El fin de esta tesis ha sido contribuir desde la Ciencia e Ingeniería de Materiales a este objetivo, concretamente en el ámbito del patrimonio cultural metálico, desarrollando una herramienta de diagnóstico del estado de conservación y de los sistemas de protección para este tipo de bienes culturales. El principal problema para la conservación del patrimonio metálico es la corrosión, que tiene lugar por interacción entre el objeto metálico y el medio que lo rodea. Para enfrentarse a este problema, los conservadores de patrimonio metálico cuentan con dos estrategias: el control de las condiciones ambientales –lo que no siempre es posible- o el empleo de recubrimientos protectores, que lo aíslen del medio, que es el método más habitual en la práctica de la conservación. Sin embargo, cualquier método presenta limitaciones, por lo que resulta de gran relevancia el poder evaluar la eficacia y la duración de los sistemas empleados, antes de que aparezcan efectos negativos en el objeto. Así, los recubrimientos habituales en conservación –principalmente ceras y barnices acrílicos- tienen una capacidad protectora bastante limitada y deben ser renovados cada cierto tiempo. Esto conlleva la necesidad de conocer y evaluar el comportamiento de los sistemas aplicados, con especial hincapié en su durabilidad. La espectroscopía de impedancia electroquímica (EIS) es una técnica electroquímica que permite estudiar los procesos de corrosión en los metales en diferentes medios y evaluar la capacidad protectora de los recubrimientos, por lo que a priori resulta una técnica idónea para este propósito. Sin embargo, la aplicación de la EIS a la conservación del patrimonio cultural metálico no es una práctica generalizada, por las dificultades particulares que presenta su aplicación en este campo. Las características propias de los bienes culturales, hacen que en muchos casos los estudios de laboratorio no sean suficientes, y que el objeto no se pueda trasladar, por lo que resulta imprescindible la realización de medidas in situ, directamente sobre la superficie del objeto a conservar. La aplicación de técnicas electroquímicas requiere montar una celda electroquímica, en la que poner en contacto la superficie del material que se va a estudiar con un electrólito líquido y los electrodos auxiliares (electrodo de referencia y contraelectrodo). Esta tarea resulta compleja en el caso de superficies irregulares y no horizontales como las de una escultura. Para dar una solución a este problema, el objetivo de esta tesis ha sido el desarrollo de una celda electroquímica con un electrólito en gel, específicamente diseñada para la realización de medidas in situ sobre patrimonio cultural. Para el diseño se han tenido en cuenta diversos factores relacionados con este tipo de medidas, tales como la forma y tamaño de la celda para facilitar su colocación en la superficie de la obra, la naturaleza, geometría y posición de los electrodos para obtener una señal de calidad, o el tipo de soporte adecuado para lograr una buena estabilidad mecánica. El trabajo se ha estructurado en varios apartados, si bien no recorrido su no ha sido lineal, ya que los avances y dificultades en cada uno de los aspectos o subapartados han contribuido al desarrollo de los demás. El primer paso ha sido comprobar la posibilidad de realizar medidas de impedancia utilizando un electrólito gelificado con agar, abordando cuestiones como la validez, reproducibilidad o repetividad de los resultados. Una vez verificada la obtención de medidas de calidad y comparables a las de un electrólito tradicional, se ha estudiado en mayor detalle la contribución del agar en las medidas, para establecer la concentración más adecuada tanto desde el punto de vista electroquímico como mecánico. En esta misma línea, se ha comparado el comportamiento del agar y de la agarosa, uno de los dos polisacáridos que componen este material, y que es el responsable de las propiedades gelificantes. El siguiente paso ha sido analizar en detalle el comportamiento del sistema completo, incluyendo los electrodos (de referencia y contraelectrodo) para optimizar el diseño. Así, se han estudiado diferentes configuraciones de celda con electrodos de distinta naturaleza y geometría, un factor que ha demostrado su relevancia para minimizar la aparición de artefactos en las medidas al emplearse electrólitos de baja conductividad. En paralelo al desarrollo y estudio de la celda, se han realizado medidas sobre diferentes sustratos para evaluar la aplicabilidad del sistema desarrollado a la resolución de problemas de conservación. Por un lado, se han realizado ensayos de laboratorio sobre probetas de bronce y acero patinable con diversas pátinas y recubrimientos, simulando cuestiones que se abordan habitualmente en la conservación del patrimonio metálico; por otro lado, se han realizado estudios in situ, sobre obra real (principalmente escultura moderna y contemporánea del Museo Arqueológico Nacional, Museo de Escultura de Leganés y colección de escultura del campus de la Universidad Politécnica de Valencia), para comprobar y validar el diseño de la celda en su modo de aplicación final, e ir introduciendo las modificaciones necesarias para solventar las dificultades prácticas que se iban encontrando en diferentes situaciones. Todo ello ha permitido concluir con éxito con el diseño de una celda electroquímica con electrólito en gel, adecuada para la realización de medidas electroquímicas in situ sobre el patrimonio cultural metálico, aportando una nueva herramienta para avanzar en la conservación de este tipo de patrimonio.Along history, mankind has sought to preserve certain objects which, for multiple reasons, have acquired a special value and a meaning for the society that owned them, constituting their cultural heritage. In this effort to preserve the past for the present and future generations, scientific research has gained an increasing relevance. Conservation science aims at understanding problems and provide solutions for the conservation of heritage, both from the technological and sustainable point of view. The proper design and planning of strategies for the conservation of cultural heritage objects and collections is essential, and should take into account both technological and resources limitations. The purpose of this thesis is to contribute through Materials Science and Engineering to this objective, in particular in the field of metallic cultural heritage, developing a tool of diagnosis of the state of conservation and evaluation of protection systems for this type of heritage. The main challenge for the conservation of the heritage metal is corrosion, which takes place because of the interaction between the metal object and its environment. To deal with this problem, metal conservators have two strategies: control of environmental conditions - which is not always possible - or the use of protective coatings to isolate the metal object from the environment, which is the most frequent solution in conservation practice. Nonetheless, any method has certain limitations. For this reason, it is of great importance being able to evaluate the effectiveness and lifespan of protective systems before damage occurs. Common coatings in heritage conservation –mainly waxes and acrylic varnishes- have a quite limited protective ability, and have to be renewed periodically. This entails the need of knowing and evaluating the behavior of applied protective coatings, with particular focus on durability. Electrochemical impedance spectroscopy (EIS) is an electrochemical technique that allows to investigate corrosion mechanisms of metals in different environments and to evaluate the protective properties of coatings. This makes EIS the ideal technique for this purpose. Unfortunately, the use of EIS in metal cultural heritage is not a widespread practice, due to the particular difficulties in applying this technique in heritage objects. The special characteristics of cultural heritage assets make it necessary to carry out on site measurements, directly on the surface of the object to preserve. The use of electrochemical techniques requires mounting an electrochemical cell, in which the surface of the material under study is placed in contact with a liquid electrolyte and the auxiliary electrodes (reference and counter electrode). This is not an easy task for irregular and non-horizontal surfaces as in a sculpture. To overcome this challenge, the objective of this thesis is to develop an electrochemical cell with a gelled electrolyte, specifically designed for conducting in situ electrochemical measurements on cultural heritage. The design has taken into account various factors related to this type of measures, such as the shape and size of the cell to be placed on the surface of the object, the nature, geometry and position of the electrodes to obtain a quality signal, or the fixing system to ensure a good mechanical stability. This work has been structured into several sections, although its progress has not been linear in time, since the advances and difficulties in each of the aspects or subsections have contributed to improve and develop the others. The first step has been checking the possibility of performing impedance measures using an agar gelled electrolyte, addressing issues such as validity, reproducibility, or repeatability of the results. Once verified the quality of measurements, comparable to a traditional electrolyte, detail the contribution of the agar been studied in greater detail, to establish the most appropriate concentration both from the electrochemical and mechanical point of view. With the same purpose the behavior of agar and agarose has been compared. The next step was to analyze in detail the behavior of the entire system, including electrodes (reference and counter electrode) to optimize the design. Thus, we have studied different configurations of cell with electrodes of different nature and geometry, a factor that has shown its relevance to minimize the appearance of artifacts in the measurements when using low-conductivity electrolytes. In parallel to the development and study of the cell, measurements on different substrates have been performed to assess the applicability of the developed system to solve conservation problems. On the one hand, laboratory tests on bronze and weathering steel coupons, with different patinas and coatings were performed, simulating issues usually addressed in metallic heritage conservation; on the other hand, studies have been conducted in situ on real work (mainly modern and contemporary sculpture of the National Archaeological Museum, Museum of Sculpture in Leganes and the sculpture collection at the Polytechnic University of Valencia campus), to check and validate the design of the cell in its final application mode, and to introduce the modifications necessary to solve the practical difficulties that were found in different situations. This has allowed concluding successfully with the design of an electrochemical cell with a gel electrolyte, suitable for carrying out on-site electrochemical measures on metallic cultural heritage, providing a new tool for a better conservation of this kind of heritage.El trabajo que aquí se presenta ha sido financiado por la beca FPI BES-2012-052716 y el proyecto HAR2011-22402 del Plan Nacional de I+D+i 2008-2011 del Ministerio de Ciencia e Innovación, el proyecto HAR2014-54893-R, HAR2014-54893-R, la Comunidad de Madrid y el fondo Social Europeo en el marco del Programa Geomateriales 2 (S2013/MIT 2914), y el proyecto IPERION-CH (European Union H2020, G.A. 654028).Programa de Doctorado en Ciencia e Ingeniería de Materiales por la Universidad Carlos III de MadridPresidente: Juan Carlos Galván Sierra.- Secretario: Antonia Jiménez Morales.- Vocal: Kepa Castro Ortiz de Pined

Electrochemical Biosensors for Monitoring Complex Diseases and Comorbidities

abstract: Monitoring complex diseases and their comorbidities requires accurate and convenient measurements of multiple biomarkers. However, many state-of-the-art bioassays not only require complicated and time-consuming procedures, but also measure only one biomarker at a time. This noncomprehensive single-biomarker monitoring, as well as the cost and complexity of these bioassays advocate for a simple, rapid multi-marker sensing platform suitable for point-of-care or self-monitoring settings. To address this need, diabetes mellitus was selected as the example complex disease, with dry eye disease and cardiovascular disease as the example comorbidities. Seven vital biomarkers from these diseases were selected to investigate the platform technology: lactoferrin (Lfn), immunoglobulin E (IgE), insulin, glucose, lactate, low density lipoprotein (LDL), and high density lipoprotein (HDL). Using electrochemical techniques such as amperometry and electrochemical impedance spectroscopy (EIS), various single- and dual-marker sensing prototypes were studied. First, by focusing on the imaginary impedance of EIS, an analytical algorithm for the determination of optimal frequency and signal deconvolution was first developed. This algorithm helped overcome the challenge of signal overlapping in EIS multi-marker sensors, while providing a means to study the optimal frequency of a biomarker. The algorithm was then applied to develop various single- and dual-marker prototypes by exploring different kinds of molecular recognition elements (MRE) while studying the optimal frequencies of various biomarkers with respect to their biological properties. Throughout the exploration, 5 single-marker biosensors (glucose, lactate, insulin, IgE, and Lfn) and one dual-marker (LDL and HDL) biosensor were successfully developed. With the aid of nanoparticles and the engineering design of experiments, the zeta potential, conductivity, and molecular weight of a biomarker were found to be three example factors that contribute to a biomarker’s optimal frequency. The study platforms used in the study did not achieve dual-enzymatic marker biosensors (glucose and lactate) due to signal contamination from localized accumulation of reduced electron mediators on self-assembled monolayer. However, amperometric biosensors for glucose and lactate with disposable test strips and integrated samplers were successfully developed as a back-up solution to the multi-marker sensing platform. This work has resulted in twelve publications, five patents, and one submitted manuscripts at the time of submission.Dissertation/ThesisDoctoral Dissertation Biomedical Engineering 201

Advanced sensors technology survey

This project assesses the state-of-the-art in advanced or 'smart' sensors technology for NASA Life Sciences research applications with an emphasis on those sensors with potential applications on the space station freedom (SSF). The objectives are: (1) to conduct literature reviews on relevant advanced sensor technology; (2) to interview various scientists and engineers in industry, academia, and government who are knowledgeable on this topic; (3) to provide viewpoints and opinions regarding the potential applications of this technology on the SSF; and (4) to provide summary charts of relevant technologies and centers where these technologies are being developed

Molecular Microfluidic Bioanalysis: Recent Progress in Preconcentration, Separation, and Detection

This chapter reviews the state-of-art of microfluidic devices for molecular bioanalysis with a focus on the key functionalities that have to be successfully integrated, such as preconcentration, separation, signal amplification, and detection. The first part focuses on both passive and electrophoretic separation/sorting methods, whereas the second part is devoted to miniaturized biosensors that are integrated in the last stage of the fluidic device

Two-dimensional material-based nanosensors for detection of low-molecular-weight molecules

Low-molecular-mass small molecules play important roles in biological processes and often serve as disease-related biomarkers for diagnosis. Accurate detection of small molecules remains challenging for conventional sensors due to their limited sensitivities. Two-dimensional (2D) materials, thanks to their atomic level thickness, can be extraordinarily sensitive to external perturbations and therefore well-suited for sensing applications. This dissertation explores the use of 2D materials, including primarily graphene and transition metal dichalcogenides, in the detection of low-molecular-weight and low-charge molecules. This work starts with the study of methods that allow for efficient and clean transfer of graphene grown on Cu using chemical vapor deposition (CVD), which is a critical step for achievement of large-area and high-quality graphene for device fabrication. In addition to the conventional wet-etching transfer method, we have studied on the method of electrochemical delamination, which is more time-efficient and allows for recycling of the Cu foil. Generation of bubbles during the electrochemical reaction is minimized by tuning the experimental parameters, thereby minimizing transfer-induced damages to graphene. We then fabricate the graphene-based field effect transistor (FET) and use the graphene FET as biosensors. First, the sensor is configured as an electrolyte-gated FET. With appropriate biochemical functionalization of the graphene, the FET sensors have been used to detect multiple small-molecule biomarkers including glucose and insulin via their affinity binding with receptors. Then, on a flexible substrate, we demonstrate real-time measurement of tumor necrosis factor alpha, a signal protein that regulates immune cells. We then simplified the sensor structure using a bottom local-gate to replace the external electrode as required in the previous electrolyte gated FET. Using the bottom local-gated FET sensor we have carried out real-time monitoring of the variation of pH in solutions. In addition to the electrical sensors, highly sensitive and multifunctional plasmonic sensors have also been developed by combining the unique optical properties of graphene with engineered metallic metasurfaces. The plasmonic sensors operating in mid-infrared region are configured as either metallic metasurface or hybrid graphene-metallic metasurface. Using a metallic metasurface, we demonstrate simultaneous quantification and fingerprinting of protein molecules. Using a hybrid graphene-metallic metasurface, we demonstrate optical conductivity-based ultrasensitive biosensing. In contrast to refractive-index-based sensors, the sensitivity of the hybrid metasurface sensor is not limited by the molecular masses of analytes. A monolayer of the sub-nanometer chemicals can be readily detected and differentiated on the hybrid metasurface. Reversible detection of glucose is carried out via the affinity binding of glucose with boronic acid immobilized on the graphene of the hybrid metasurface. The lowest detection limit achieved in our work is 36 pg/mL, which is considerably lower than that for the existing optical sensors. Despite the high sensitivity of graphene, the zero band-gap of graphene fundamentally impedes its use in digital electronic devices. In contrast, two-dimensional semiconductors, such as transition metal dichalcogenide (TMDC) with non-zero band gaps, holds great potential for developing practical electronic devices and sensors. Monolayers of TMDC materials are particularly attractive for development of deeply scaled devices, although the contact resistance between metal and the monolayer TMDC has been so large to significantly limit the performance of the devices. We present a high-performance monolayer MoS2 FET with a monolayer graphene as bottom local gate. The graphene gate is found to significantly improve the dielectric strength of the oxide layer compared to the lithographically patterned metal gate. This in turn allows for the use of very thin gate dielectric layer (~5 nm) and application of a strong displacement field to lower the contact resistance. Benefiting from the low contact resistance, the monolayer MoS2 FET offers a high on/off ratio (108) and low subthreshold slope (64 mV/decade). Additionally, thanks to the highly efficient electrostatic coupling through the ultrathin gate dielectric layer, short-channel (50 nm and 14 nm) devices are realized that exhibit excellent switching characteristics. In summary, this dissertation presents significant contributions to 2D material-based electronic and optoelectronic nanosensors, especially for detection of small molecules. Perspectives are made in the end of the thesis, on future studies needed to realize practical applications of these sensors and other 2D material-based products

Electrochemical analysis of gildings in Valencia altarpieces: a cross-age study since fifteenth until twentieth century, Journal of Solid State Electrochemistry

[EN] The application of the voltammetry of microparticles methodology to the study of gildings in paintings and architectural ornaments is described. Nanosamples from pieces from different churches of the Comunitat Valenciana (Spain) covering since the fifteenth century until nowadays were studied upon attachment to graphite electrodes in contact with aqueous HCl and H2SO4 electrolytes. Electrochemical measurements, combined with field emission scanning electron microscopy X-ray microanalysis (FESEM-EDX) and atomic force microscopy (AFM) data, denoted that a common manufacturing technique was used with minimal variations along time. The relationship between specific voltammetric features associated to bulk gold and active surface sites, however, changed monotonically with time, thus suggesting the possibility of age monitoring.Financial support from the MINECO Projects CTQ2014-53736-C3-1-P, CTQ2014-53736-C3-2-P and MAT2015-65445-C2-2-R, which are supported with ERDF funds is gratefully acknowledged. Likewise financial support of the Comunidad de Madrid and structural funds of the EU through Programa Geomateriales 2 ref. S2013/MIT-2914 is acknowledged. The authors thank the Seccion de Investigacion Arqueologica Municipal de Valencia for kindly authorizing sampling to carry out this research. The authors also thank Dr. Jose Luis Moya Lopez and Mr. Manuel Planes Insausti (Microscopy Service of the Universitat Politecnica de Valencia) for their technical support.Ferragud Adam, JV.; Piquero-Cilla, J.; Domenech Carbo, MT.; Guerola Blay, V.; Company Climent, J.; Domenech Carbo, A. (2016). 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Degenerative diseases early stages biomarker detection using a silicon carbide (SiC) based biosensor

Alzheimer’s disease (AD) is a neurodegenerative disease with only late stage detection; thus, diagnosis is made when it is no longer possible to treat the disease, only its symptoms. Consequently, this often leads to caregivers who are the patient’s relatives, which adversely impacts the workforce along with severely diminishing the quality of life for all involved. It is, therefore, highly desirable to develop a fast, effective and reliable sensor to enable early-stage detection in an attempt to reverse disease progression. This research validates the detection of amyloid-beta 42 (Aβ42) using a Silicon Carbide (SiC) electrode, a fact that is unprecedented in the literature. Aβ42 is considered a reliable biomarker for AD detection, as reported in previous studies. To validate the detection with a SiC based electrochemical sensor, a gold (Au) electrode-based electrochemical sensor was used as a control. The same cleaning, functionalization and Aβ1–28 antibody immobilization steps were used on both electrodes. Sensor validation was carried out by means of Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS) aiming to detect an 0.5 µg·mL−1 Aβ42 concentration in 0.1 M buffer solution as a proof of concept. A repeatable peak directly related to the presence of Aβ42 was observed, indicating that a fast SiC-based electrochemical sensor was constructed and may prove to be a useful approach for the early detection of AD.MaestríaMagister en Ingeniería Electrónic