Self-assembled MnO2 nanowires were hydrothermally synthesized and electrically characterized under different conditions. The nanowires were approximately 3–10 µm long and about 20–100 nm in diameter. Single nanowires were aligned perpendicularly across two parallel gold electrode transducers by means of the dielectrophoresis (DEP) technique. Resistivity changes in synthetic air, nitrogen, and NO2 were tested in a range from 100 °C up to 300 °C. The resistivity changes were observed to account for the oxygen reduction on the NWs’ surface as the electrons were moving from the NWs to the oxygen. The resistivity was explored through a constant current arrangement test. Based on the resistivity changes, electrical properties, such as activation energy and type of semiconductor, were estimated.
Food safety is one of the most contemporary subjects under the scope of the scientific community since it is a fundamental issue for the general population. The desire to use a simple, inexpensive, easy-to-read package freshness-indicator led to a multitude of proposals for package real-time sensors for food freshness indicators. The sensors’ design strategy is to target a physical or chemical modification that occurs by the spoiling process, such as changes in temperature, moisture, or the detection of foodborne pathogens. One of the most common approaches is evaluating changes in pH, since a significant amount of food spoilage occurs with significant alterations (e.g., acidity increases on dairy products). However, some safety concerns emerge from the use of complex artificial chemical molecules such as pH indicators in active labels/packages for food. Naturally occurring anthocyanins are a safe alternative to classic pH indicators and have been applied as sensitive molecules for pH changes aimed at the development of active labels and active packing for food. This proposal briefly reviews the latest scientific contributions on the application of anthocyanins in food spoilage sensors.
The voltammetric behavior of hydroxocobalamin (OH-CBL) was firstly studied by employing a bare boron-doped diamond electrode as a working electrode. It was found that OH-CBL provided four anodic signals on BDDE in acidic supporting electrolytes and one cathodic signal. The anodic peak situated at +412 mV (vs. Ag|AgCl|KCl (sat.) recorded in 0.1 mol/L H2SO4) was found to be suitable for analytical purposes due to its position and shape. A novel voltammetric approach based on differential pulse voltammetry was developed and it was found as a sensitive analytical tool, with low limit of detection (LD = 13.2 nmol/L), applicable in analysis of vitamin preparations.
The aim of this work was the synthesis of functional hydrogel materials obtained via photopolymerization. The resulting systems were characterized in terms of chemical structure using Fourier transform infrared spectroscopy. Subsequently, their sorption capacity and surface morphology were determined along with roughness analysis. The resulting materials have been modified with fluorescein dye and can be used in many branches of industry and medicine, for example, in innovative diagnostic systems.
Citrus, a genus of flowering plants in the Rutaceae family, holds substantial market importance as a crop worldwide. After prolonged periods of breeding and extensive hybridization, numerous species have emerged, each possessing a unique metabolism that produces a diverse array of secondary metabolites. It is important to note that phenolic compounds, in particular phenols and flavonoids, are among the most important secondary metabolites in Citrus flowers. These chemical compositions of Citrus flowers differ depending on various factors, such as variety, fruit maturity, environmental conditions, storage conditions, and extraction methods. Nevertheless, phenolic compounds extracted from Citrus flowers are well-recognized for their bioavailability characteristics and exhibit numerous health-promoting effects, including antioxidant, anti-inflammatory, anti-cancer, and antibacterial activities in humans. The information contained in this document provides a comprehensive summary of the latest investigations conducted on the subject matter. The aim is to thoroughly comprehend the biological functions of the bioactive compounds in the Citrus flowers and their potential impacts on various biological systems, shedding light on their potential therapeutic applications.
In this work, germanene and its derivatives (Ge-H, Ge-CH3, Ge-C3-CN) were explored as electrochemical impedimetric platforms to develop a competitive immunoassay for the direct detection of gut-derived metabolites, kynurenic acid (KA) and quinolinic acid (QA). The competition occurs between the free KA/QA standards and BSA-conjugated antigens for a fixed amount of primary antibody binding sites. This affects the electron transfer rate of the [Fe(CN)6]3−/4− redox couple and changes the charge transfer resistance (Rct) on the electrode surface. The impedimetric signal measured due to the change in Rct is then correlated to the KA and QA concentration.
The Actinidia genus comprises 54 species and 21 varieties of which A. chinensis var. chinensis and A. chinensis var. deliciosa are the most commercialized ones. The nutritional properties of kiwifruit have prompted their global production to nearly reach the value of 4.5 million tons per year, with Asia being one of the top producers. This increment in their production has raised a parallel augment of associated organic wastes, especially when kiwifruits are used for processed products. The most abundant by-products obtained include skins, seeds and discarded fruits. This biomass has a huge potential for its high content of bioactive compounds, such as dietary fiber or polyphenols. Therefore, it has been targeted by the food industry as a sustainable and cost-effective source of natural ingredients, highly demanded by consumers. Indeed, kiwi skins and seeds have been pointed out as a relevant source of pectin followed by the kiwi pulp. Pectin is a recognized ingredient due to the organoleptic properties it may confer but also for its prebiotic capacities. The recovery of pectin has been mainly performed via the application of extraction techniques that implied the use of chemical reagents such as acids. Nowadays, the use of chemicals is negatively regarded for their associated side effects. Indeed, customers' claims for chemical-free food ingredients have triggered the development and application of green extraction techniques: ultrasonic, microwave, enzyme, supercritical fluid or electrical pulse. Pectin has been successfully extracted with these green techniques both in terms of yield and quality, improving results obtained with traditional extraction techniques. Therefore, the main objective of this work is to review the wide variability of green techniques applied to extract pectin along with the comparison of the optimal parameters as a basis for the future development of an optimized extraction method. In addition, this work also aims to disclose the potential of kiwifruit by-products as a source of pectin and their industrial applications for the development of functional foods, nutraceuticals, food additives or cosmetics.
The spread of invasive pests is accelerated by globalization and changes in climate conditions, posing a significant threat to agricultural and forest ecosystems. Advances in electronic nose sensors (e-noses) have opened new avenues for monitoring and detecting plant diseases and pests through the analysis of emitted volatile organic compounds (VOCs). The current work reviews the most recent developments in e-nose sensors and their application in plant disease and pest detection over the past five years. It also explores the challenges associated with VOC detection in agricultural settings where field sampling has a focal role in monitoring and management.
The air quality in modern cities and urban areas is strongly affected by chemical pollutants such as toxic gases, volatile organic compounds, and particulate matter. They are monitored by governmental agencies using regulatory monitoring stations, which are highly accurate, but also very expensive, bulky, and maintenance demanding. There is a compulsory need to monitor air quality at high spatial–temporal resolution in smart cities for public health protection and environmental sustainability. Properly calibrated low-cost and low-accuracy sensors are usually deployed in stationary and mobile nodes for urban air quality monitoring. A simple indicator of the current status of urban air pollution is the Air Quality Index (AQI) used to communicate the pollution level under the time-changing trend of a specific pollutant. In this study, continuous measurements have been performed in the city of Bari (southern Italy) by electrochemical gas sensors (NO2, O3, CO), optical particle counters (OPC) for particulate matter (PM10), and NDIR infrared sensors (CO2), including microsensors for temperature and relative humidity. The sensors have been installed in stationary nodes located in urban sites and in a mobile node mounted on a public bus moving on urban routes. AQI data gathered by the low-cost sensors have been compared with reference instrumentations as a case study of citizen science.
Through the selection of N-type organic semiconductor molecules and the method of supramolecular self-assembly at the solvent phase interface, a perylene tetracarboxylic diimide (PTCDIs) nanofiber film with loose and porous morphology was constructed via in situ deposition on the surface of ITO conductive glass. Then, the P-type organic semiconducting polymer poly(3,4−ethylenedioxythiophene) (PEDOT) was grown in the fiber interweaving network of this film via quantitative electrochemical polymerization, thus preparing a PTCDIs@PEDOT composite film with N−P heterojunction architecture. The composite film has a nanometer-sized N−P heterojunction interpenetrating network structure, which is beneficial for full exposure to and contact of hydrogen peroxide vapor (HPV). The response time is 5.76 min, the recovery time is 5.53 min, and the response to 1.0 ppm concentration of HPV is 1.76. The PTCDIs@PEDOT film has good moisture resistance and improved sensitivity and signal response for gas-phase H2O2 detection.
In this work, a “green” electrochemical paper-based device (ePAD) for the voltammetric determination of Tl(I) is described. A mini voltammetric cell was patterned on chromatographic paper by using screen printing to deposit three carbon electrodes and plotting with hydrophobic ink to form a circular assay zone. The sample was added to the assay zone (which was pre-loaded with Bi(III)) and Tl(I) was quantified using anodic stripping voltammetry (ASV). The experimental conditions and potential interferences were studied. The limit of detection was at the low μg L−1 level, indicating that these devices can serve successfully as fit-for-purpose disposable voltammetric sensors for Tl(I).
Air pollution is a current problem for the environment and public health. Its impact needs to be monitored in urban agglomerates and critical hot spots such as airports. Green aviation with low air emissions is a sustainable goal for the future. The air pollutants are monitored by governmental agencies that employ regulatory monitoring stations, which are very accurate but also very expensive, bulky, and maintenance demands. On the contrary, low-cost sensor systems can offer a proper solution to cover large areas at high spatial-temporal resolution. However, the low-cost air quality sensors are less accurate than reference analyzers operating in the regulatory stations. To enhance the sensor accuracy, field calibration, and data correction with reference instrumentation is a valid strategy to improve sensor data quality. In this study, a sensor system with a selected set of air quality gas sensors (NO2, O3) and particulate matter (PM10, PM2.5) has been developed and deployed in a near-city space-airport at Grottaglie (Southern Italy) to perform measurements in a period of 4 months, from October 2021 to February 2022. The sensor units installed in the Airbox system used for this measurements campaign are the GS+4NO2 (DD Scientific) for NO2 measurements, the O3-3E1F (City Technology, Sensoric) for O3 measurements, and the NextPM (Tera Sensor) for PM10 and PM2.5 measurements. Data gathered by the low-cost air quality sensors have been compared to reference instrumentations both co-located (ca. 1 m distance) together with low-cost sensors (PM10, R2 > 0.87; PM2.5, R2 > 0.50) and a distributed regulatory network of 14 environmental stations operating in the local area around space-airport at a distance ranging from 3 to 26 km.
As a future energy source, hydrogen is used in many industrial applications, such as chemicals, semiconductors, transportation, etc. Hydrogen gas, which has many unusual properties compared to other gases, has the risk of being flammable and explosive when it is present in the atmosphere at concentrations of 4% and higher. We need hydrogen sensors both to determine the risks in advance and because we do not want hydrogen gas, which is a source of energy, to be lost due to leakage. Hydrogen sensors are used in hydrogen production plants to determine hydrogen purity, for leakage and safety in all areas where hydrogen gas is used, and also in the medical field, as hydrogen gas is a marker in disease diagnosis. In the context of classifying hydrogen sensors according to their physicochemical sensing mechanisms, resistive metallic hydrogen sensors stand out as a prevalent choice, with Pd, Pt, and their alloy counterparts being commonly employed as designated sensing materials. In this study, nanostructured platinum (Pt) and Pt alloy-based resistive hydrogen sensors are reviewed and discussed in detail. The sensing mechanism of Pt-based resistive hydrogen sensors has been explained by the scattering of charge carriers at the surface, coupled with its defects and grain boundaries, and by the formation of hydride (PtHx) phenomena, depending on the increase or decrease in resistance in the hydrogen environment.
Hepatitis viral infections are the most common cause of hepatitis liver disease, which eventually leads to cancer and fibrosis if not detected early. Therefore, early detection would allow for preventive and therapeutic actions. Here, a surface-enhanced Raman spectroscopy (SERS)-based biosensor was developed using plasmonic molybdenum trioxide quantum dots (MoO3-QDs) as the SERS substrates. The nanostructured substrate of MoO3-QDs was functionalized with a proteoglycan (syndecan-1) as a novel bioreceptor for the target hepatitis E virus (HEV). The innovative biodetection system achieved a detection limit of 1.05 fg/mL for the tested HEV target (ORF2), indicating superb clinically relevant sensitivity and performance. The designed biosensing system incorporating a glycan motif as a bioreceptor instead of the conventional antibodies or aptamers presents new insights for the ultrasensitive detection of HEV and other infectious viruses.
The BDNF gene is associated with high degrees of variability in antidepressant treatments. The Val66Met polymorphism is widely known as a source of this variability, warranting growing interest in genotyping patients that undergo antidepressant treatment to better suit their needs. This paper reports on an electrochemical genosensing platform, based on gold electrodes, capable of detecting this polymorphism, through the use of synthetic enzymatically labeled DNA probes for two different BDNF alleles. The sensor showed promising results, and its applicability to real samples is currently being tested.
This overview concerns recent patents and patented technologies in relation to the development of hydrogel-based biosensors, published until 2022. As a result, 257 patent documents and 145 simple patent families have been searched through different specialized patent databases. Furthermore, the patent classification confirmed that the most claimed inventions concern chemical analysis of biological material and biospecific binding assay materials with an insoluble carrier for immobilizing immunochemicals. Overall, the research, development, and innovation concerning hydrogel-based biosensors are based on improvements in the synthesis of hydrogels, biomolecule immobilization and detection, as well as microelectronic device integration and microfabrication techniques. A collection of recent patented technologies is proposed at the end. In this respect, it aimed to demonstrate the potential trends and challenges in relation to the development of hydrogel-based biosensors.
In this work, an amperometric biosensor for lactate determination based on a sonogel–carbon transducer has been developed and evaluated using the lactate oxidase enzyme coated with a multipolymer layer as a bioreceptor. The biosensor obtained had adequate sensitivity (4.16 × 10−8 A mM−1) and a wide linear working range (0.2–20 mM) that allowed for the determination of lactate at high concentrations without showing enzyme saturation phenomena. The selectivity of the biosensor was also verified using interferents commonly observed in physiological samples. Moreover, a microfluidic cell was designed and fabricated to allow the determination of lactate with the proposed biosensor in a continuous regime. In the end, the viability of the biosensor was tested with the proposed flow system using synthetic samples, obtaining excellent results.
In this study, a portable desktop analyzer for the determination of fat content in milk is introduced. The prototype of the sensor consists of three light-emitting diodes (red, green, and blue) as a light source. The transmitted light is detected by a photoresistor and continuous voltage measurements provided by the microcontroller, and is recorded by a computer. The resulting univariate and multivariate models show that the developed analytical device is capable of determining fat content in raw and homogenized milk with sufficient accuracy.
The human cochlea is undeniably one of the most amazing organs in the body. One of its most intriguing features is its unique capability to convert sound waves into electrical nerve impulses. Humans can generally perceive frequencies between 20 Hz and 20 kHz with their auditory systems. Several studies have been conducted on building an artificial basilar membrane for the human cochlea (cochlear biomodel). It is possible to mimic the active behavior of the basilar membrane using micro-electromechanical systems (MEMSs). This paper proposes an array of MEMS bridge beams that are mechanically sensitive to the perceived audible frequency. They were designed to operate within the audible frequency range of bridge beams with 450 µm thickness and varying lengths between 200 µm and 2000 µm. As for the materials for the bridge beam structures, molybdenum (Mo), platinum (Pt), chromium (Cr) and gold (Au) have been considered. For the cochlear biomodel, gold has proven to be the best material, closely mimicking the basilar membrane, based on finite-element (FE) and lumped-element (LE) models.
