Health initiatives worldwide demand affordable point-of-care devices to aid in the reduction of morbidity and mortality rates of high-incidence infectious and noncommunicable diseases. However, the production of robust and reliable easy-to-use diagnostic platforms showing the ability to quantitatively measure several biomarkers in physiological fluids and that could in turn be decentralized to reach any relevant environment remains a challenge. Here, we show the particular combination of paper-microfluidic technology, electrochemical transduction, and magnetic nanoparticle-based immunoassay approaches to produce a unique, compact, and easily deployable multiplex device to simultaneously measure interleukin-8, tumor necrosis factor-α, and myeloperoxidase biomarkers in sputum, developed with the aim of facilitating the timely detection of acute exacerbations of chronic obstructive pulmonary disease. The device incorporates an on-chip electrochemical cell array and a multichannel paper component, engineered to be easily aligned into a polymeric cartridge and exchanged if necessary. Calibration curves at clinically relevant biomarker concentration ranges are produced in buffer and artificial sputum. The analysis of sputum samples of healthy individuals and acutely exacerbated patients produces statistically significant biomarker concentration differences between the two studied groups. The device can be mass-produced at a low cost, being an easily adaptable platform for measuring other disease-related target biomarkers.
Microfluidics , Nanoparticles , Humans , Sputum , Point-of-Care Systems , Biomarkers/analysis
Sweat secreted by the human eccrine sweat glands can provide valuable biomarker information during exercise. Real-time non-invasive biomarker recordings are therefore useful for evaluating the physiological conditions of an athlete such as their hydration status during endurance exercise. This work describes a wearable sweat biomonitoring patch incorporating printed electrochemical sensors into a plastic microfluidic sweat collector and data analysis that shows the real-time recorded sweat biomarkers can be used to predict a physiological biomarker. The system was placed on subjects carrying out an hour-long exercise session and results were compared to a wearable system using potentiometric robust silicon-based sensors and to commercially available HORIBA-LAQUAtwin devices. Both prototypes were applied to the real-time monitoring of sweat during cycling sessions and showed stable readings for around an hour. Analysis of the sweat biomarkers collected from the printed patch prototype shows that their real-time measurements correlate well (correlation coefficient ≥ 0.65) with other physiological biomarkers such as heart rate and regional sweat rate collected in the same session. We show for the first time, that the real-time sweat sodium and potassium concentration biomarker measurements from the printed sensors can be used to predict the core body temperature with root mean square error (RMSE) of 0.02 °C which is 71% lower compared to the use of only the physiological biomarkers. These results show that these wearable patch technologies are promising for real-time portable sweat monitoring analytical platforms, especially for athletes performing endurance exercise.
Biosensing Techniques , Wearable Electronic Devices , Humans , Sweat/chemistry , Body Temperature , Electrolytes , Biomarkers/analysis
SARS-CoV-2, a positive-strand RNA virus has caused devastating effects. The standard method for COVID diagnosis is based on polymerase chain reaction (PCR). The method needs expensive reagents and equipment and well-trained personnel and takes a few hours to be completed. The search for faster solutions has led to the development of immunological assays based on antibodies that recognize the viral proteins that are faster and do not require any special equipment. Here, we explore an innovative analytical approach based on the sandwich oligonucleotide hybridization which can be adapted to several biosensing devices including thermal lateral flow and electrochemical devices, as well as fluorescent microarrays. Polypurine reverse-Hoogsteen hairpins (PPRHs) oligonucleotides that form high-affinity triplexes with the polypyrimidine target sequences are used for the efficient capture of the viral genome. Then, a second labeled oligonucleotide is used to detect the formation of a trimolecular complex in a similar way to antigen tests. The reached limit of detection is around 0.01 nM (a few femtomoles) without the use of any amplification steps. The triplex enhanced nucleic acid detection assay (TENADA) can be readily adapted for the detection of any pathogen requiring only the knowledge of the pathogen genome sequence.
COVID-19 , Nucleic Acids , Humans , SARS-CoV-2/genetics , COVID-19/diagnosis , Oligonucleotides/chemistry , Polymerase Chain Reaction , RNA, Viral/genetics , RNA, Viral/analysis , Nucleic Acid Amplification Techniques/methods
Current procedures for the assessment of chronic wound infection are time-consuming and require complex instruments and trained personnel. The incidence of chronic wounds worldwide, and the associated economic burden, urge for simple and cheap point-of-care testing (PoCT) devices for fast on-site diagnosis to enable appropriate early treatment. The enzyme myeloperoxidase (MPO), whose activity in infected wounds is about ten times higher than in non-infected wounds, appears to be a suitable biomarker for wound infection diagnosis. Herein, we develop a single-component foldable paper-based device for the detection of MPO in wound fluids. The analyte detection is achieved in two steps: (i) selective immunocapture of MPO, and (ii) reaction of a specific dye with the captured MPO, yielding a purple color with increasing intensity as a function of the MPO activity in infected wounds in the range of 20-85 U/mL. Ex vivo experiments with wound fluids validated the analytic efficiency of the paper-based device, and the results strongly correlate with a spectrophotometric assay.
Body Fluids , Wound Infection , Colorimetry , Coloring Agents , Humans , Paper , Point-of-Care Testing , Wound Infection/diagnosis
Bread waste is a major part of food wastage which could be upcycled to produce functional materials, following the principles of the circular bioeconomy. This work shows that bread waste can be recycled and valorized to produce a composite conductive material with excellent properties for chemical sensor applications. Here, dry bread is impregnated with an aqueous solution of a silver precursor and pyrolyzed to produce a porous carbon matrix containing Ag nanoparticles with diameters ranging from 20 to 40 nm. These particles perform as catalytic redox centers for the electrochemical detection of halide ions (Cl-, Br-, and I-) and organohalide target molecules such as sucralose and trichloroacetic acid. A thorough analytical characterization is carried out to show the potential application of the developed material for the manufacturing of electrochemical sensor approaches. The material preparation is sustainable, low-cost, simple, and upscalable. These are ideal features for the large-scale manufacturing by screen-printing technologies of single-use electrochemical sensors for the rapid analysis of halogenated organic pollutants in waters.
Lab-on-a-chip devices incorporating valves and pumps can perform complex assays involving multiple reagents. However, the instruments used to drive these chips are complex and bulky. In this article, a new wax valve design that uses light from a light emitting diode (LED) for both opening and closing is reported. The valves and a pumping chamber are integrated in lab-on-a-foil chips that can be fabricated at low cost using rapid prototyping techniques. A chip for the implementation of enzyme-linked immunosorbent assays (ELISA) is designed. A porous nitrocellulose material is used for the immobilization of capture antibodies in the microchannel. A compact generic instrument with an array of 64 LEDs, a linear actuator to drive the pumping chamber, and absorbance detection for a colorimetric readout of the assay is also presented. Characterization of all the components and functionalities of the platform and the designed chip demonstrate their potential for assay automation.
Lab-On-A-Chip Devices , Microfluidics , Automation , Colorimetry , Enzyme-Linked Immunosorbent Assay
Introducción: La evaluación anatómica músculo esquelética por imagen en la exploración clínica del pie diabético es la fotografía digital que evalúa la morfología superficial. Objetivos: Validar la obtención de las imágenes fotográficas del pie, calcular las mediciones longitudinales, angulares y el índice del arco plantar, de las imágenes fotográficas del pie por fotogrametría, y basados en estas, categorizar la normalidad de la forma en sujetos sanos. Métodos: Estudio exploratorio en 30 individuos sanos evaluados en la Unidad clínica de pie diabético en la ciudad de Trujillo, mediante un prototipo de cámaras alrededor de un podoscopio y un software de análisis de imágenes. La imagen fotográfica fue evaluada por mediciones longitudinales, angulares y el índice del arco plantar. Resultados: Los pacientes evaluados tenían una edad media de 25,06+/-11,95 años, y predominaron las mujeres. La longitud total del pie y anchura del metatarso en el lado derecho fue de 226,55 ± 36,49 mm y 98,99 ± 22,71 mm respectivamente; y en el lado izquierdo fue de 229,81 ± 42,25 mm y 104,49 ± 16,84 mm respectivamente. El ángulo intermetatarsal del 1-2 rayo, ángulo intermetatarsal del 4-5 rayo y ángulo del retropié para el lado derecho fueron 14 ± 4º, 11 ± 3º y 2 ± 2º respectivamente; para el lado izquierdo 14 ± 3º, 9 ± 3º y 2 ± 2º respectivamente, y el índice plantar del arco derecho e izquierdo fueron 0,23 ± 0,2 y 0,22 ± 0,1 respectivamente. La variabilidad solo se presentó en el antepie en el 20 percent de los casos. Conclusiones: La obtención de las imágenes fotográficas del pie fueron válidas, las mediciones fueron menores o similares a otros estudios. La variabilidad de la normalidad solo se presentó en el antepie(AU)
Introduction: The musculoskeletal anatomical evaluation by imaging in the clinical examination of the diabetic foot is digital photography that assesses the superficial morphology. Objectives: To validate the obtaining of photographic images of the foot, to calculate the longitudinal and angular measurements and the index of the plantar arch, from the photographic images of the foot by photogrammetry, and to categorize the normality of the shape in healthy subjects, based on these photographic images. Methods: This an exploratory study in 30 healthy individuals evaluated at the Diabetic Foot Clinical Unit in Trujillo city, using a prototype of cameras around a podoscope and image analysis software. The photographic image was evaluated by longitudinal and angular measurements and the plantar arch index. Results: The patients evaluated had a mean age of 25.06+/-11.95 years, and women predominated. Total foot length and metatarsal width on the right side were 226.55 ± 36.49 mm and 98.99 ± 22.71 mm, respectively; and on the left side it was 229.81 ± 42.25 mm and 104.49 ± 16.84 mm, respectively. The 1st-2nd ray intermetatarsal angle, 4th-5th ray intermetatarsal angle and hindfoot angle for the right side were 14 ± 4º, 11 ± 3º and 2 ± 2º respectively; for the left side 14 ± 3º, 9 ± 3º and 2 ± 2º respectively, and the plantar index of the right and left arch were 0.23 ± 0.2 and 0.22 ± 0.1 respectively. Variability only occurred in the forefoot in 20 percent of cases. Conclusions: Obtaining of the photographic images of the foot was valid, measurements were smaller or similar to other studies. The variability of normality only appeared in the forefoot(AU)
Humans , Male , Female , Adolescent , Adult , Photogrammetry/methods , Diagnostic Techniques and Procedures , Foot/anatomy & histology , Physical Examination/methods , Foot Deformities/etiology , Epidemiology, Descriptive , Diabetic Foot
This work reports on the fabrication and performance of a new on-chip array of gold thin-film electrodes arranged into five individually addressable miniaturized electrochemical cells. Each cell shows a two-electrode configuration comprising a single working electrode and a counter/pseudo-reference electrode that is compartmentalized to be shared among all the cells of the array. Using this configuration, just six contact pads are required, which significantly reduces the chip overall surface area. Electrochemical characterization studies are carried out in solutions containing the two species of reversible redox pairs. The concentration of one redox species can reliably be measured at the working electrode by applying potentiostatic techniques to record the current due to the corresponding electrochemical reaction. The redox counterpart in turn undergoes an electrochemical process at the counter/pseudo-reference electrode, which, under optimized experimental conditions, injects current and keeps the applied potential in the electrochemical cell without limiting the current being recorded at the working electrode. Under these conditions, the electrode array shows an excellent performance in electrochemical detection studies without any chemical or electrical cross-talk between cells. The enzymatic activity of horseradish peroxidase, alkaline phosphatase and myeloperoxidase enzymes is analyzed using different redox mediators. Quasi-simultaneous measurements with the five electrochemical cells of the array are carried out within 1 s time frame. This array layout can be suitable for multiplexed electrochemical immunoassays and immunosensor approaches and implementation in simplified electrochemical ELISA platforms that make use of enzyme labels. Moreover, the array reduced dimensions facilitate the integration into compact fluidic devices.
Biosensing Techniques , Electrochemical Techniques , Electrodes , Gold , Horseradish Peroxidase , Immunoassay
Introducción: La evaluación anatómica musculoesquelética por imagen en la exploración clínica del pie es la fotografía digital que evalúa la morfología superficial. Objetivos: Validar la obtención de las imágenes fotográficas del pie, calcular las mediciones longitudinales, angulares y el índice del arco plantar de las imágenes mencionadas usando un podoscopio y fotogrametría en sujetos sanos y categorizar la normalidad de las mediciones. Métodos: Este estudio fue exploratorio y se realizó utilizando un prototipo de cámaras alrededor de un podoscopio y un software de análisis de imágenes. La imagen fotográfica fue evaluada por mediciones longitudinales, angulares y el índice plantar. Resultados: Los 30 sujetos sanos evaluados tenían una edad media de 25,06 ± 11,95 años, predominaban las mujeres con un 53,3 por ciento. La longitud total del pie, anchura del metatarso y altura del empeine media para el lado derecho en 226,55 ± 36,49mm, 98,99 ± 22,71 mm, y 36,32 ± 4,07 mm respectivamente; y para el lado izquierdo en 229,81 ± 42,25 mm, 104,49 ± 16,84mm y 36,31 ± 3,32 mm, respectivamente. El ángulo intermetatarsal del 1-2 rayo, ángulo intermetatarsal del 4-5 rayo y ángulo del retropié para el lado derecho fueron 14 ± 4º, 11 ± 3º y 2 ± 2º respectivamente, para el lado Izquierdo 14 ± 3º, 9 ± 3º y 2 ± 2º respectivamente y el índice plantar del arco derecho e izquierdo fueron 0,23 ± 0,2 y 0,22 ± 0,1, respectivamente. La variabilidad solo se presentó en el antepié en 20 por ciento. Conclusiones: La obtención de las imágenes fotográficas del pie fueron válidas, las mediciones fueron menores o similares a otros estudios. La variabilidad de normalidad solo se presentó en antepié(AU)
Introduction: Musculoskeletal anatomical assessment by imaging in clinical examination of the foot is digital photography assessing surface morphology. Objectives: To validate the acquisition of photographic images of the foot, to calculate the longitudinal, angular and plantar arch index measurements of the above images using a podoscope and photogrammetry in healthy subjects and to categorize the normality of the measurements. Methods: This study was exploratory and was performed using a prototype camera around a podoscope and image analysis software. The photographic image was evaluated by longitudinal, angular and plantar index measurements. Results: The 30 healthy subjects evaluated had a mean age of 25.06 ± 11.95 years, females predominated with 53.3 percent. The mean total foot length, metatarsal width and instep height for the right side at 226 55 ± 36.49mm, 98.99 ± 22.71 mm, and 36.32 ± 4.07 mm respectively; and for the left side at 229.81 ± 42.25 mm, 104.49 ± 16.84mm and 36.31 ± 3.32mm respectively. The 1-2 ray intermetatarsal angle, 4-5 ray intermetatarsal angle and rearfoot angle for the right side were 14 ± 4º, 11 ± 3º and 2 ± 2º respectively; for the Left side 14 ± 3º, 9 ± 3º and 2 ± 2º respectively and the plantar index of the right and left arch were 0.23 ± 0.2 and 0.22 ± 0.1 respectively. Variability was only present in the forefoot at 20 percent. Conclusions: The photographic images of the foot were valid, the measurements were lower or similar to other studies. The variability of normality was only present in the forefoot(AU)
Humans , Male , Female , Adult , Forefoot, Human , Photogrammetry , Foot , Epidemiology, Descriptive
The development of diagnostic tools for measuring a wide spectrum of target analytes, from biomarkers to other biochemical parameters in biological fluids, has experienced a significant growth in the last decades, with a good number of such tools entering the market. Recently, a clear focus has been put on miniaturized wearable devices, which offer powerful capabilities for real-time and continuous analysis of biofluids, mainly sweat, and can be used in athletics, consumer wellness, military, and healthcare applications. Sweat is an attractive biofluid in which different biomarkers could be noninvasively measured to provide rapid information about the physical state of an individual. Wearable devices reported so far often provide discrete (single) measurements of the target analytes, most of them in the form of a yes/no qualitative response. However, quantitative biomarker analysis over certain periods of time is highly demanded for many applications such as the practice of sports or the precise control of the patient status in hospital settings. For this, a feasible combination of fluidic elements and sensor architectures has been sought. In this regard, this paper shows a concise overview of analytical tools based on the use of capillary-driven fluidics taking place on paper or fabric devices integrated with solid-state sensors fabricated by thick film technologies. The main advantages and limitations of the current technologies are pointed out together with the progress towards the development of functional devices. Those approaches reported in the last decade are examined in detail.
Biosensing Techniques , Wearable Electronic Devices , Biomarkers , Humans , Sweat , Textiles
During the malolactic fermentation of red wines, L-malic acid is mainly converted to L-lactic acid. Both acids should be precisely measured during the entire process to guarantee the quality of the final wine, thus making real-time monitoring approaches of great importance in the winemaking industry. Traditional analytical methods based on laboratory procedures are currently applied and cannot be deployed on-site. In this work, we report on the design and development of a bi-parametric compact analytical flow system integrating two electrochemical biosensors that could be potentially applied in this scenario. The developed flow-system will allow for the first time the simultaneous measurement of both acids in real scenarios at the real-time and in remote way. Miniaturized thin-film platinum four-electrode chips are fabricated on silicon substrates by standard photolithographic techniques and further implemented in a polymeric fluidic structure. This includes a 15 µL flow cell together with the required fluidic channels for sample and reagent fluid management. The four-electrode chip includes counter and pseudo-reference electrodes together with two working electrodes. These are sequentially modified with electropolymerized polypyrrole membranes that entrap the specific receptors for selectively detecting both target analytes. The analytical performance of both biosensors is studied by chronoamperometry, showing a linear range from 5 × 10-6 to 1 × 10-4 M (LOD of 3.2 ± 0.3 × 10-6 M) and from 1 × 10-7 to 1 × 10-6 M (LOD of 6.7 ± 0.2 × 10-8 M) for the L-lactate and the L-malate, respectively. Both biosensors show long-term stability, retaining more than the 90% of their initial sensitivity after more than 30 days, this being a prerequisite for monitoring the whole process of the malolactic fermentation of the red wines (time between 20 and 40 days). The flow system performance is assessed with several wine samples collected during the malolactic fermentation process of three red wines, showing an excellent agreement with the results obtained with the standard method.
Ascorbate oxidases are an enzyme group that has not been explored to a large extent. So far, mainly ascorbate oxidases from plants and only a few from fungi have been described. Although ascorbate oxidases belong to the well-studied enzyme family of multi-copper oxidases, their function is still unclear. In this study, Af_AO1, an enzyme from the fungus Aspergillus flavus, was characterized. Sequence analyses and copper content determination demonstrated Af_AO1 to belong to the multi-copper oxidase family. Biochemical characterization and 3D-modeling revealed a similarity to ascorbate oxidases, but also to laccases. Af_AO1 had a 10-fold higher affinity to ascorbic acid (KM = 0.16 ± 0.03 mM) than to ABTS (KM = 1.89 ± 0.12 mM). Furthermore, the best fitting 3D-model was based on the ascorbate oxidase from Cucurbita pepo var. melopepo. The laccase-like activity of Af_AO1 on ABTS (Vmax = 11.56 ± 0.15 µM/min/mg) was, however, not negligible. On the other hand, other typical laccase substrates, such as syringaldezine and guaiacol, were not oxidized by Af_AO1. According to the biochemical and structural characterization, Af_AO1 was classified as ascorbate oxidase with unusual, laccase-like activity.
Ascorbate Oxidase/metabolism , Aspergillus flavus/enzymology , Laccase/metabolism , Amino Acid Sequence , Ascorbate Oxidase/chemistry , Copper/metabolism , Kinetics , Laccase/chemistry , Models, Molecular , Oxidation-Reduction , Substrate Specificity
In healthcare, new diagnostic tools that help in the diagnosis, prognosis, and monitoring of diseases rapidly and accurately are in high demand. For in-situ measurement of disease or infection biomarkers, point-of-care devices provide a dramatic speed advantage over conventional techniques, thus aiding clinicians in decision-making. During the last decade, paper-based analytical devices, combining paper substrates and electrochemical detection components, have emerged as important point-of-need diagnostic tools. This review highlights significant works on this topic over the last five years, from 2015 to 2019. The most relevant articles published in 2018 and 2019 are examined in detail, focusing on device fabrication techniques and materials applied to the production of paper fluidic and electrochemical cell architectures as well as on the final device assembly. Two main approaches were identified, that are, on one hand, those ones where the fabrication of the electrochemical cell is done on the paper substrate, where the fluidic structures are also defined, and, on the other hand, the fabrication of those ones where the electrochemical cell and liquid-driving paper component are defined on different substrates and then heterogeneously assembled. The main limitations of the current technologies are outlined and an outlook on the current technology status and future prospects is given.
Biomarkers/analysis , Biosensing Techniques/methods , Paper , Biomarkers, Tumor/genetics , Biomarkers, Tumor/metabolism , Electrochemical Techniques , Humans , Point-of-Care Systems
Performance of electroanalytical lab-on-a-chip devices is often limited by the mass transfer of electroactive species toward the electrode surface, due to the difficulty in applying external convection. This article describes the powerful signal enhancement attained with a 2.54 GHz miniature acoustic resonator integrated with an electrochemical device in a miniaturized cell. Acoustic resonator and an on-chip gold thin-film three-electrode electrochemical cell were arranged facing each other inside a structured poly(methyl methacrylate) chamber. Cyclic voltammetric and chronoamperometric responses of 1 mM ferrocene-methanol were recorded under resonator's actuation at powers ranging from 0 to 1 W. Finite element analysis was carried out to study the sono-electroanalytical process. Acoustic resonator's actuation greatly enhances the mass transport of electroactive species toward the electrode surface. The diffusion limited cyclic voltammetric and chronoamperometric currents increase around 10 and 20 times, respectively, with an input power of 1 W compared to those recorded under stagnant conditions. The improvement in electroanalytical process is mainly associated with acoustic resonator's vibration induced fluid streaming. The advantages of a miniaturized acoustic resonator, including the submillimeter small size, amenability for mass fabrication, cost effectiveness, low energy consumption, as well as outstanding enhancement of coupled electrochemical processes, will enable the production of highly sensitive compact electroanalytical devices.
The presence of high levels of arsenic in waters poses a threat to the human health in many countries all over the world. Effective surveillance programs of water quality require the implementation of in-field tests to assess early the presence of this metal ion and other contaminants. To date, there exist few market-available analytical approaches that suffer from important limitations related to cost, in addition to complex reactions, very long analysis times, and/or high limits of detection. This work describes a robust electrochemical sensor integrated into a modular microfluidic system that shows a clear potential to be deployed for the on-site monitoring of inorganic As(III) species. Flexible and transparent microfluidic modules are fabricated by rapid prototyping techniques and include different microfluidic components among them, flow cells where electrochemical sensors can be easily and reversibly inserted. The electrochemical sensor comprises a gold nanoparticle (AuNP)-modified gold thin-film electrode that is readily applied to the sensitive detection of As(III) by anodic stripping linear sweep voltammetry. The microfluidic system enables the automatic sensor calibration, sample uptake, and preconditioning as well as As(III) detection. The system response to As(III) is linear in a concentration range of 1-150 µg L-1, with a detection limit of 0.42 µg L-1, which is well below the threshold value of 10 µg L-1 set by the World Health Organization. Analysis of tap water and two water samples from two Argentinean aquifers, spiked with different As(III) concentrations, demonstrates the excellent performance of the system.
Arsenic/analysis , Water Pollutants, Chemical/analysis , Drinking Water/analysis , Electrochemical Techniques/instrumentation , Electrochemical Techniques/methods , Electrodes , Gold/chemistry , Lab-On-A-Chip Devices , Limit of Detection , Metal Nanoparticles/chemistry , Microfluidic Analytical Techniques/instrumentation , Microfluidic Analytical Techniques/methods , Reproducibility of Results
The synthesis of organic-inorganic nanocomposites that can interact with different environmental pollutants and can be mass-produced are very promising materials for the fabrication of chemical sensor devices. Among them, metal (or metal oxide) nanoparticles doped conductive porous carbon composites can be readily applied to the production of electrochemical sensors and show enhanced sensitivity for the measurement of water pollutants, thanks to the abundant accessible and functional sites provided by the interconnected porosity and the metallic nanoparticles, respectively. In this personal account, an overview of several synthesis routes of porous carbon composites containing metallic nanoparticles is given, paying special attention to those based on sol-gel techniques. These are very powerful to synthesize hybrid porous materials that can be easily processed into powders and thin films, so that they can be implemented in electrode fabrication processes based on screen-printing and lithography techniques, respectively. We emphasize the sol-gel routes developed in our group for the synthesis of bismuth or gold nanoparticle doped porous carbon composites applied to fabricate electrochemical sensors that can be scaled down to produce miniaturized on-chip sensing devices for the sensitive detection of heavy metal pollutants in water. The trend towards the miniaturization of electrochemical sensors to be readily employed as analytical tools in environmental monitoring follow the market requirements of rapid and accurate on-site analysis, small sample consumption and waste production, as well as potential for continuous or semi-continuous in-situ determination of a wide variety of target analytes.
Monitoring the malolactic fermentation process is strictly required to guarantee the sensorial quality and freshness of red wines. This could be achieved by in-field and real-time continuous measurements of l-malate concentration in the fermentation tanks. The potential of a miniaturized amperometric bienzymatic biosensor as an analytical tool to be applied in such scenario is described in this paper. The biosensor comprises a thin-film gold electrode as transducer, malate dehydrogenase (MDH) and diaphorase (DP) enzymes together with nicotinamide adenine dinucleotide (NAD+) cofactor as the selective receptor and an adequate redox mediator to record the corresponding amperometric signal. Three different biosensor architectures are studied, whose main differences lie in the immobilization of the different chemical components onto the electrode surface. In all cases a fast-electrosynthethized polypyrrole (PPy) membrane is generated for this purpose. The experimental conditions are optimized and the best architecture shows a sensitivity of 1365 ± 110 mA M-1 cm-2 and a detection limit of 6.3 × 10-8 M in a concentration range of 1 × 10-7 M - 1 × 10-6 M. The biosensor presents an excellent working stability as it retains above 90% of its sensitivity after 37 days, thus enabling the monitoring of the malolactic fermentation of three red wines. The obtained results show excellent agreement with the standard colorimetric method.
Biosensing Techniques , Fermentation , Malates/analysis , Wine/analysis , Electrodes , Enzymes, Immobilized
The exfoliation and colloidal stabilization of layered transition metal dichalcogenides (TMDs) in an aqueous medium using functional biomolecules as dispersing agents have a number of potential benefits toward the production and practical use of the corresponding two-dimensional materials, but such a strategy has so far remained underexplored. Here, we report that DNA and RNA nucleotides are highly efficient dispersants in the preparation of stable aqueous suspensions of MoS2 and other TMD nanosheets at significant concentrations (up to 5-10 mg mL-1). Unlike the case of common surfactants, for which adsorption on 2D materials is generally based on weak dispersive forces, the exceptional colloidal stability of the TMD flakes was shown to rely on the presence of relatively strong, specific interactions of Lewis acid-base type between the DNA/RNA nucleotide molecules and the flakes. Moreover, the nucleotide-stabilized MoS2 nanosheets were shown to be efficient catalysts in the reduction of nitroarenes (4-nitrophenol and 4-nitroaniline), thus constituting an attractive alternative to the use of expensive heterogeneous catalysts based on noble metals, and exhibited an electrocatalytic activity toward the hydrogen evolution reaction that was not impaired by the possible presence of nucleotide molecules adsorbed on their active sites. The biocompatibility of these materials was also demonstrated on the basis of cell proliferation and viability assays. Overall, the present work opens new vistas on the colloidal stabilization of 2D materials based on specific interactions that could be useful toward different practical applications.
Transition Elements/chemistry , DNA , Nucleotides , RNA , Water
Thin carbon films deposited on technologically relevant substrates, such as silicon wafers, can be easily implemented in miniaturized electrochemical devices and used for sensing applications. However, a major issue in most carbon films is the weak film/substrate adhesion that shortens the working device lifetime. This paper describes the facile preparation of robust thin carbon films on silicon substrates by one-pot sol-gel synthesis. The improved adherence of these carbon films is based on the incorporation of silica through the controlled synthesis of a resorcinol/formaldehyde gel modified with aminopropyltriethoxysilane. The films demonstrate excellent adhesion to the silicon substrate, good homogeneity, excellent electrical conductivity and superior electrochemical performance. Moreover, this approach opens the door to the fabrication of carbon thin-film electrodes by photolithographic techniques.
