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Chemosensors, Volume 8, Issue 1 (March 2020) – 21 articles

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Cover Story (view full-size image) A simple optical detection method for the real-time polar monitoring of chemiluminescence (CL) [...] Read more.
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Open AccessArticle
Polymer Nanoparticle Identification and Concentration Measurement Using Fiber-Enhanced Raman Spectroscopy
Chemosensors 2020, 8(1), 21; https://doi.org/10.3390/chemosensors8010021 - 14 Mar 2020
Viewed by 284
Abstract
We present a measurement technique for chemical identification and concentration measurement of polymer nanoparticles in aqueous solution, which is achieved using Raman spectroscopy. This work delivers an improvement in measurement sensitivity of 40 times over conventional Raman measurements in cuvettes by loading polymer [...] Read more.
We present a measurement technique for chemical identification and concentration measurement of polymer nanoparticles in aqueous solution, which is achieved using Raman spectroscopy. This work delivers an improvement in measurement sensitivity of 40 times over conventional Raman measurements in cuvettes by loading polymer nanoparticles into the hollow core of a microstructured optical fiber. We apply this “fiber-enhanced” system to measure the concentration of two separate samples of polystyrene particles (diameters of 60 nm and 120 nm respectively) with concentrations in the range from 0.07 to 0.5 mg/mL. The nanoliter volume formed by the fiber presents unique experimental conditions where nanoparticles are confined within the fiber core and prevented from diffusing outside the incident electromagnetic field, thereby enhancing their interaction. Our results suggest an upper limit on the size of particle that can be measured using the hollow-core photonic crystal fiber, as the increasing angular distribution of scattered light with particle size exceeds the acceptance angle of the liquid-filled fiber. We investigate parameters such as the fiber filling rate and optical properties of the filled fiber, with the aim to deliver repeatable and quantifiable measurements. This study thereby aids the on-going process to create compact systems that can be integrated into nanoparticle production settings for in-line measurements. Full article
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Open AccessArticle
A Biological-Based Photovoltaic Electrochemical Cell: Modelling the Impedance Spectra
Chemosensors 2020, 8(1), 20; https://doi.org/10.3390/chemosensors8010020 - 10 Mar 2020
Viewed by 286
Abstract
The impedance response of an electrochemical cell able to convert sunlight into electrical power is analyzed and discussed. Light conversion is due to a photosynthetic system known as reaction center, which is the core of photosynthesis in several living beings. Under illumination, an [...] Read more.
The impedance response of an electrochemical cell able to convert sunlight into electrical power is analyzed and discussed. Light conversion is due to a photosynthetic system known as reaction center, which is the core of photosynthesis in several living beings. Under illumination, an abrupt transformation drives the cell electrical response from insulator to conductor and a photocurrent is observed. The impedance spectrum shows a peculiar shape which significantly modifies after the protein activation. It has been analyzed by means of a graphical/analytical/numerical procedure. Some impedance graphical representations are indicated as the most appropriate to suggest the design of an equivalent electrical circuit. Then, the analytical expression of this circuit is formulated and used to set-up a custom Phyton code useful for fitting experimental data. Finally, an appropriate normalization procedure is proposed, which validates data in dark and light and can be useful as a fast screening of measurements. Full article
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Open AccessArticle
Vertically Coupling ZnO Nanorods onto MoS2 Flakes for Optical Gas Sensing
Chemosensors 2020, 8(1), 19; https://doi.org/10.3390/chemosensors8010019 - 02 Mar 2020
Cited by 1 | Viewed by 421
Abstract
Hybrid structures composed of layered one-dimensional (1D) and two-dimensional (2D) materials opened new perspectives and opportunities through the build-up of hetero-junctions with versatile layered structures and led to fascinating fundamental phenomena and advanced devices. We succeeded in depositing by magnetron sputtering vertically aligned [...] Read more.
Hybrid structures composed of layered one-dimensional (1D) and two-dimensional (2D) materials opened new perspectives and opportunities through the build-up of hetero-junctions with versatile layered structures and led to fascinating fundamental phenomena and advanced devices. We succeeded in depositing by magnetron sputtering vertically aligned 1D ZnO nanorods on 2D MoS2 flakes obtained by exfoliation, preserving the structure of the 2D materials. The photoluminescence (PL) optical properties of the hybrid structure were assessed towards developing a contactless optical chemical sensor. Full article
(This article belongs to the Special Issue Optical Chemosensors and Biosensors)
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Open AccessArticle
In-Parallel Polar Monitoring of Chemiluminescence Emission Anisotropy at the Solid–Liquid Interface by an Optical Fiber Radial Array
Chemosensors 2020, 8(1), 18; https://doi.org/10.3390/chemosensors8010018 - 29 Feb 2020
Viewed by 375
Abstract
Chemiluminescence (CL) detection is widely employed in biosensors and miniaturized analytical devices since it offers high detectability and flexible device design (there are no geometry requirements for the measurement cell, except the ability to collect the largest fraction of emitted photons). Although the [...] Read more.
Chemiluminescence (CL) detection is widely employed in biosensors and miniaturized analytical devices since it offers high detectability and flexible device design (there are no geometry requirements for the measurement cell, except the ability to collect the largest fraction of emitted photons). Although the emission anisotropy phenomenon for an emitting dipole bound to the interface between two media with different refractive index is well known for fluorescence, it is still poorly investigated for CL reactions, in which the excited-state reaction products can diffuse in solution before the photon emission event. In this paper, we propose a simple method for the real-time evaluation of the CL emission anisotropy based on a radial array of optical fibers, embedded in a poly(methyl methacrylate) semicylinder and coupled with a Charge-Coupled Device (CCD) camera through a suitable interface. The polar-time evolutions of the CL emission have been studied for catalyzing enzymes immobilized onto a solid surface (heterogeneous configuration) or free in solution (homogeneous configuration). Evidence of the anisotropy phenomenon is observed, indicating that the lifetime of the excited-state products of the enzyme-catalyzed reactions is shorter than the time required for their diffusion in solution at a distance at which the CL can be considered isotropic. These results open new perspectives in the development of CL-based miniaturized analytical devices. Full article
(This article belongs to the Special Issue Optical Chemosensors and Biosensors)
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Open AccessArticle
Immunomagnetic Separation of Microorganisms with Iron Oxide Nanoparticles
Chemosensors 2020, 8(1), 17; https://doi.org/10.3390/chemosensors8010017 - 27 Feb 2020
Viewed by 474
Abstract
The early detection of Legionella in water reservoirs, and the prevention of their often fatal diseases, requires the development of rapid and reliable detection processes. A method for the magnetic separation (MS) of Legionella pneumophila by superparamagnetic iron oxide nanoparticles is developed, which [...] Read more.
The early detection of Legionella in water reservoirs, and the prevention of their often fatal diseases, requires the development of rapid and reliable detection processes. A method for the magnetic separation (MS) of Legionella pneumophila by superparamagnetic iron oxide nanoparticles is developed, which represents the basis for future bacteria detection kits. The focus lies on the separation process and the simplicity of using magnetic nanomaterials. Iron oxide nanoparticles are functionalized with epoxy groups and Legionella-specific antibodies are immobilized. The resulting complexes are characterized with infrared spectroscopy and tested for the specific separation and enrichment of the selected microorganisms. The cell-particle complexes can be isolated in a magnetic field and detected with conventional methods such as fluorescence detection. A nonspecific enrichment of bacteria is also possible by using bare iron oxide nanoparticles (BIONs), which we used as a reference to the nanoparticles with immobilized antibodies. Furthermore, the immunomagnetic separation can be applied for the detection of multiple other microorganisms and thus might pave the way for simpler bacterial diagnosis. Full article
(This article belongs to the Special Issue Functionalized Nanomaterials for Sensing Application)
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Open AccessArticle
Synthesis and Antibacterial Activity of Rhodanine-Based Azo Dyes and Their Use as Spectrophotometric Chemosensor for Fe3+ Ions
Chemosensors 2020, 8(1), 16; https://doi.org/10.3390/chemosensors8010016 - 25 Feb 2020
Viewed by 362
Abstract
This research includes the design and synthesis of new derivatives for rhodanine azo compounds (4ac) containing a naphthalene ring. Physiochemical properties of the synthesized compounds were determined by their melting points, FTIR, 1H-NMR, 13C-NMR, and elemental analysis [...] Read more.
This research includes the design and synthesis of new derivatives for rhodanine azo compounds (4ac) containing a naphthalene ring. Physiochemical properties of the synthesized compounds were determined by their melting points, FTIR, 1H-NMR, 13C-NMR, and elemental analysis spectroscopic techniques. The biological activities of the newly prepared azo rhodanine compounds were evaluated against some pathogenic bacteria using three different bacterial species including (Escherichia coli., Pseudomonas aeruginosa, Staphylococcus aureus) and compared with amoxicillin as a reference drug. The results showed that our compounds have moderate-to-good vital activity against the mentioned pathogenic bacteria. The selectivity and sensitivity of the newly prepared rhodanine azo compounds with transition metals Co2+, Cu2+, Zn2+, Ni2+, and Fe3+ were studied using UV–vis and fluorescence spectroscopy techniques. Among the synthesized azos, azo 4c showed affinity toward Fe3+ ions with an association constant of 4.63 × 108 M−1. Furthermore, this azo showed high sensitivity toward Fe3+ ions with detection limits of 5.14 µM. The molar ratio and Benesi–Hildebrand methods confirmed the formation of complexes between azo 4c and Fe3+ with 1:2 binding stoichiometry. Therefore, azo 4c showed excellent potential for developing efficient Fe3+ chemosensors. Full article
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Open AccessArticle
Silver Chloride/Ferricyanide-Based Quasi-Reference Electrode for Potentiometric Sensing Applications
Chemosensors 2020, 8(1), 15; https://doi.org/10.3390/chemosensors8010015 - 23 Feb 2020
Viewed by 483
Abstract
Processes’ occurring at the Ag/AgCl/Cl, ([Fe(CN)6]3–/4–) ions interface study results are presented. Conditions are selected for the mixed salts’ precipitate formation on the silver surface. It has been shown that the potential of a silver screen-printed electrode [...] Read more.
Processes’ occurring at the Ag/AgCl/Cl, ([Fe(CN)6]3–/4–) ions interface study results are presented. Conditions are selected for the mixed salts’ precipitate formation on the silver surface. It has been shown that the potential of a silver screen-printed electrode (AgSPE) coated with a mixed precipitate containing silver chloride/ferricyanide is stable in the presence of [Fe(CN)6]3–/4–. The electrode can serve as a quasi-reference electrode (QRE) in electrochemical measurements in media containing ions [Fe(CN)6]3−/4−. The electrode is formed during polarization of AgSPE (0.325 V vs. Ag/AgCl/KCl, 3.5 M) in a solution containing chloride- and ferri/ferrocyanides ions. The results of the obtained QRE study by potentiometry, scanning electron microscopy and cyclic voltammetry are presented. The proposed QRE was used in a sensor system to evaluate the antioxidant activity (AOA) of solutions by hybrid potentiometric method (HPM). The results of AOA assessment of fruit juices and biofluids obtained using new QRE and commercial Ag/AgCl RE with separated spaces do not differ. Full article
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Open AccessEditorial
Chemical Sensors for Heavy Metals/Toxin Detection
Chemosensors 2020, 8(1), 14; https://doi.org/10.3390/chemosensors8010014 - 22 Feb 2020
Viewed by 392
Abstract
Nowadays, the huge release of pollutants into the environment has become a significant problem in many countries and entire regions [...] Full article
(This article belongs to the Special Issue Chemical Sensors for Heavy Metals/Toxin Detection)
Open AccessArticle
Microfluidic Mixer with Automated Electrode Switching for Sensing Applications
Chemosensors 2020, 8(1), 13; https://doi.org/10.3390/chemosensors8010013 - 21 Feb 2020
Cited by 1 | Viewed by 355
Abstract
An electronic tongue (e-tongue) is a multisensory system usually applied to complex liquid media that uses computational/statistical tools to group information generated by sensing units into recognition patterns, which allow the identification/distinction of samples. Different types of e-tongues have been previously reported, including [...] Read more.
An electronic tongue (e-tongue) is a multisensory system usually applied to complex liquid media that uses computational/statistical tools to group information generated by sensing units into recognition patterns, which allow the identification/distinction of samples. Different types of e-tongues have been previously reported, including microfluidic devices. In this context, the integration of passive mixers inside microchannels is of great interest for the study of suppression/enhancement of sensorial/chemical effects in the pharmaceutical, food, and beverage industries. In this study, we present developments using a stereolithography technique to fabricate microfluidic devices using 3D-printed molds for elastomers exploring the staggered herringbone passive mixer geometry. The fabricated devices (microchannels plus mixer) are then integrated into an e-tongue system composed of four sensing units assembled on a single printed circuit board (PCB). Gold-plated electrodes are designed as an integral part of the PCB electronic circuitry for a highly automated platform by enabling faster analysis and increasing the potential for future use in commercial applications. Following previous work, the e-tongue sensing units are built functionalizing gold electrodes with layer-by-layer (LbL) films. Our results show that the system is capable of (i) covering basic tastes below the human gustative perception and (ii) distinguishing different suppression effects coming from the mixture of both strong and weak electrolytes. This setup allows for triplicate measurements in 12 electrodes, which represents four complete sensing units, by automatically switching all electrodes without any physical interaction with the sensor. The result is a fast and reliable data acquisition system, which comprises a suitable solution for monitoring, sequential measurements, and database formation, being less susceptible to human errors. Full article
(This article belongs to the Special Issue Printed Chemical Sensors)
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Open AccessArticle
Towards an Integrated System as Point-of-Care Device for the Optical Detection of Sepsis Biomarkers
Chemosensors 2020, 8(1), 12; https://doi.org/10.3390/chemosensors8010012 - 11 Feb 2020
Viewed by 405
Abstract
Severe infection and sepsis are a common, expensive, and frequently fatal conditions in critically ill patients. The sepsis diagnosis is not trivial, since it is an extremely complex chain of events involving inflammatory and anti-inflammatory processes, cellular reactions, and circulatory disorders. For these [...] Read more.
Severe infection and sepsis are a common, expensive, and frequently fatal conditions in critically ill patients. The sepsis diagnosis is not trivial, since it is an extremely complex chain of events involving inflammatory and anti-inflammatory processes, cellular reactions, and circulatory disorders. For these reasons, delay in diagnosis and initiation of drug treatments have shown to be crucial for this pathology. Moreover, a multitude of biomarkers has been proposed, many more than for other pathologies. In order to select optimal treatments for the highly heterogeneous group of sepsis patients and to reduce costs, novel multiplexed tools that better characterize the patient and his or her specific immune response are highly desired. In order to achieve the fundament of drastically improved multi-analyte detection and to attain low limits of detection in diagnostics, the area of point-of-care testing (POCT) technology is developing quickly, leading to the production of instruments, the reliability of which is continuously increasing. For this purpose, a selection of two biomarkers—C-reactive protein (CRP) and neopterin (NP)—was studied in this paper and a fluorescence-based integrated optical system, suitable for future POCT applications, was implemented that is capable of performing the simultaneous measurement of the two different biomarkers in replicate. A limit of detection of 10 and 2.1 µg L−1 was achieved for CRP and NP spiked in commercially available human serum, respectively. Moreover, measurements on both biomarkers were also performed on serum samples collected from septic patients. Full article
(This article belongs to the Special Issue Optical Chemosensors and Biosensors)
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Open AccessArticle
Electrochemical Behavior and Detection of Diclofenac at a Microporous Si3N4 Membrane Modified Water–1,6-dichlorohexane Interface System
Chemosensors 2020, 8(1), 11; https://doi.org/10.3390/chemosensors8010011 - 05 Feb 2020
Viewed by 419
Abstract
The electrochemical behavior when the liquid–liquid interface was modified by commercially available, microporous silicon nitride membrane, was achieved using cyclic voltammetry with tetramethyl ammonium. The transfer characteristics of the ionizable drug diclofenac (DCF), as an anti-inflammatory, anti-rheumatic, antipyretic, and analgesic [...] Read more.
The electrochemical behavior when the liquid–liquid interface was modified by commercially available, microporous silicon nitride membrane, was achieved using cyclic voltammetry with tetramethyl ammonium. The transfer characteristics of the ionizable drug diclofenac ( DCF ), as an anti-inflammatory, anti-rheumatic, antipyretic, and analgesic treatment in common use in biomedical applications, were also investigated across microporous silicon nitride-modified liquid interface. Thus, some thermodynamic variables for DCF , such as the standard Gibbs energy of transfer, the standard transfer potential and lipophilicity were estimated. Furthermore, the influence of possible interfering substances (ascorbic acid, sugar, amino acid, urea, and metal ions) on the detection of DCF was investigated. An electrochemical DCF sensor is investigated using differential pulse voltammetry (DPV) as the quantification technique, a linear range of 8–56 µM and a limit of detection of 1.5 µM was possible due to the miniaturized interfaces formed within silicon nitride. Full article
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Open AccessArticle
Label-Free Colorimetric Detection of Urine Glucose Based on Color Fading Using Smartphone Ambient-Light Sensor
Chemosensors 2020, 8(1), 10; https://doi.org/10.3390/chemosensors8010010 - 27 Jan 2020
Viewed by 644
Abstract
In this work, a label-free colorimetric assay was developed for the determination of urine glucose using smartphone ambient-light sensor (ALS). Using horseradish peroxidase—hydrogen peroxide—3,3′,5,5′-tetramethylbenzidine (HRP-H2O2-TMB) colored system, quantitative H2O2 was added to samples to-be-determined for deepest [...] Read more.
In this work, a label-free colorimetric assay was developed for the determination of urine glucose using smartphone ambient-light sensor (ALS). Using horseradish peroxidase—hydrogen peroxide—3,3′,5,5′-tetramethylbenzidine (HRP-H2O2-TMB) colored system, quantitative H2O2 was added to samples to-be-determined for deepest color. The presence of glucose oxidase in urine led to the formation of H2O2 and the reduction of TMBred. As a result of this, the color of the urine faded and the solution changed from deep blue to light blue. We measured the illuminance of the transmitted light by a smartphone ambient light sensor, and thereby color changes were used to calculate the content of urine glucose. After method validation, this colorimetric assay was practically applied for the determination of urine samples from diabetic patients. Good linearity was obtained in the range of 0.039–10.000 mg/mL (R2 = 0.998), and a limit of detection was 0.005 mg/mL. Our method was had high accuracy, sensitivity, simplicity, rapidity, and visualization, providing a new sensor to be potentially applicable for point-of-care detection of urine glucose. Full article
(This article belongs to the Special Issue Optical Chemosensors and Biosensors)
Open AccessEditorial
Acknowledgement to Reviewers of Chemosensors in 2019
Chemosensors 2020, 8(1), 9; https://doi.org/10.3390/chemosensors8010009 - 21 Jan 2020
Viewed by 348
Abstract
The editorial team greatly appreciates the reviewers who have dedicated their considerable time and expertise to the journal’s rigorous editorial process over the past 12 months, regardless of whether the papers are finally published or not [...] Full article
Open AccessArticle
Formaldehyde and Total VOC (TVOC) Commercial Low-Cost Monitoring Devices: From an Evaluation in Controlled Conditions to a Use Case Application in a Real Building
Chemosensors 2020, 8(1), 8; https://doi.org/10.3390/chemosensors8010008 - 14 Jan 2020
Viewed by 1032
Abstract
Formaldehyde and volatile organic compounds (VOCs) are major indoor pollutants with multiple origins. Standard methods exist to measure them that require analytical expertise and provide, at best, an average value of their concentrations. There is a need to monitor them continuously during periods [...] Read more.
Formaldehyde and volatile organic compounds (VOCs) are major indoor pollutants with multiple origins. Standard methods exist to measure them that require analytical expertise and provide, at best, an average value of their concentrations. There is a need to monitor them continuously during periods of several days, weeks, or even months. Recently, portable devices have become available. Two categories of portable devices are considered in this research paper: connected objects for the general public (price <500 €) and monitoring portable devices for professional users (price in the range >500 to 5000 €). The ISO method (ISO 16000-29) describes the standard for VOC detector qualification. It is quite complex and is not well adapted for a first qualitative evaluation of these low-cost devices. In this paper, we present an experimental methodology used to evaluate commercial devices that monitor formaldehyde and/or total volatile organic compounds (TVOC) under controlled conditions (23 °C, 50–65% relative humidity (RH)). We conclude that none of the connected objects dedicated to the general public can provide reliable data in the conditions tested, not even for a qualitative evaluation. For formaldehyde monitoring, we obtained some promising results with a portable device dedicated to professional users. In this paper, we illustrate, with a real test case in an office building, how this device was used for a comparative analysis. Full article
(This article belongs to the Special Issue Chemical Sensors for Air Quality Monitoring)
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Open AccessReview
Methods for Early Detection of Microbiological Infestation of Buildings Based on Gas Sensor Technologies
Chemosensors 2020, 8(1), 7; https://doi.org/10.3390/chemosensors8010007 - 06 Jan 2020
Viewed by 580
Abstract
In this review, the problem of microbiological infestation of buildings was discussed. The techniques of detection were described as well, with special attention drawn to the rapid-early detection methods based on gas sensor arrays. The physical and chemical conditions of the building environment [...] Read more.
In this review, the problem of microbiological infestation of buildings was discussed. The techniques of detection were described as well, with special attention drawn to the rapid-early detection methods based on gas sensor arrays. The physical and chemical conditions of the building environment conducive to the development of microorganisms and the technical conditions influencing the problem of microbiological infestation were investigated. Additionally, the harmful effects on human health caused by the microbiological contamination were discussed, with a short review of particular groups of microorganisms causing sick building syndrome. Among the detection techniques, the traditional microbiological techniques as well as the molecular and chemical methods were presented. Different designs of the gas sensor arrays together with the various techniques of analyzing the received multidimensional signal were described, analyzed, and compared in detail. Full article
(This article belongs to the Special Issue Advanced Electronic Noses and Chemical Detection Systems)
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Open AccessArticle
k-NN and k-NN-ANN Combined Classifier to Assess MOX Gas Sensors Performances Affected by Drift Caused by Early Life Aging
Chemosensors 2020, 8(1), 6; https://doi.org/10.3390/chemosensors8010006 - 03 Jan 2020
Viewed by 511
Abstract
The drift of metal oxide semiconductor (MOX) chemical sensors is one of the most important topics in this field. The work aims to test the performance of MOX gas sensors over the aging process. Firstly, sensors were tested with ethanol to understand their [...] Read more.
The drift of metal oxide semiconductor (MOX) chemical sensors is one of the most important topics in this field. The work aims to test the performance of MOX gas sensors over the aging process. Firstly, sensors were tested with ethanol to understand their behavior and response changes. In parallel, beers with different alcoholic content were analyzed to assess what happened in a real application scenario. With ethanol analysis, it was possible to quantify drift of the baseline of the sensors and changes that could affect their responses over time (from day 1 to day 51). Conversely, the beer dataset has been exploited to evaluate how two different classifiers perform the classification task based on the alcohol content of the samples. A hybrid k-nearest neighbors artificial neural network (k-NN-ANN) approach and “standard” k-NN were used to evaluate to distinguish among the samples when the measures were affected by drift. To achieve this goal, data acquired from day one to day six were used as training to predict data collected up to day 51. Overall, performances of the two methods were similar, even if the best result in terms of accuracy is reached by k-NN-ANN (96.51%). Full article
(This article belongs to the Special Issue Advanced Electronic Noses and Chemical Detection Systems)
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Open AccessArticle
Screen Printed Electrode Based Detection Systems for the Antibiotic Amoxicillin in Aqueous Samples Utilising Molecularly Imprinted Polymers as Synthetic Receptors
Chemosensors 2020, 8(1), 5; https://doi.org/10.3390/chemosensors8010005 - 29 Dec 2019
Cited by 2 | Viewed by 752
Abstract
Molecularly Imprinted Polymers (MIPs) were synthesised for the selective detection of amoxicillin in aqueous samples. Different functional monomers were tested to determine the optimal composition via batch rebinding experiments. Two different sensor platforms were tested using the same MIP solution; one being bulk [...] Read more.
Molecularly Imprinted Polymers (MIPs) were synthesised for the selective detection of amoxicillin in aqueous samples. Different functional monomers were tested to determine the optimal composition via batch rebinding experiments. Two different sensor platforms were tested using the same MIP solution; one being bulk synthesized and surface modified Screen Printed Electrodes (SPEs) via drop casting the microparticles onto the electrode surface and the other being UV polymerized directly onto the SPE surface in the form of a thin film. The sensors were used to measure amoxicillin in conjunction with the Heat-Transfer Method (HTM), a low-cost and simple thermal detection method that is based on differences in the thermal resistance at the solid–liquid interface. It was demonstrated that both sensor platforms could detect amoxicillin in the relevant concentration range with Limits of Detection (LOD) of 1.89 ± 1.03 nM and 0.54 ± 0.10 nM for the drop cast and direct polymerisation methods respectively. The sensor platform utilising direct UV polymerisation exhibited an enhanced response for amoxicillin detection, a reduced sensor preparation time and the selectivity of the platform was proven through the addition of nafcillin, a pharmacophore of similar shape and size. The use of MIP-modified SPEs combined with thermal detection provides sensors that can be used for fast and low-cost detection of analytes on-site, which holds great potential for contaminants in environmental aqueous samples. The platform and synthesis methods are generic and by adapting the MIP layer it is possible to expand this sensor platform to a variety of relevant targets. Full article
(This article belongs to the Special Issue Novel 2D Material-Based Electrochemical Sensors)
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Open AccessArticle
Sequential Detection of Palladium and Chromium Oxyanion by a Fluorescein Based Chemosensor in Mixed Aqueous Media
Chemosensors 2020, 8(1), 4; https://doi.org/10.3390/chemosensors8010004 - 26 Dec 2019
Viewed by 520
Abstract
A new highly selective chemosensor, based on fluorescein-allyloxy benzene conjugate 1, was developed for the sequential detection of palladium and chromium oxyanions in a mixed aqueous media, and was studied by UV-visible and fluorescence spectroscopy. The sensing of palladium ions produces a [...] Read more.
A new highly selective chemosensor, based on fluorescein-allyloxy benzene conjugate 1, was developed for the sequential detection of palladium and chromium oxyanions in a mixed aqueous media, and was studied by UV-visible and fluorescence spectroscopy. The sensing of palladium ions produces a chemodosimetric and ratiometric change in the emission band of 1 from 450 to 525 nm, followed by the sensing of chromate ions by 2 that quenches the emission band at 525 nm in a buffered H2O: DMF solution (9:1, pH = 7.4). The rate constants of palladium and chromate ions were found to be 8.6 × 105 M−1, 2.1 × 105 M−1, and 5.4 × 104 M−1 respectively. The chemosensor 1 has a palladium detection limit of 49 ppb while the sequential detection limit of chromate ions (CrO42− and Cr2O72−) were 127 and 259 ppb. The ratiometric change in the emission is produced due to the deallylation of 1 by palladium to produce 2 that restores the ESIPT (excited state intramolecular proton transfer) of the phenolic ring and enhances the electron transfer (ET) phenomenon from the phenolic group to fluorescein. The sequential binding of chromate ions to 2 inhibits the ESIPT and causes chelation enhanced quenching (CHEQ) of the fluorescence. Full article
(This article belongs to the Special Issue Optical Chemosensors and Biosensors)
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Open AccessArticle
Application of Ba0.5Sr0.5TiO3 (Bst) Film Doped with 0%, 2%, 4% and 6% Concentrations of RuO2 as an Arduino Nano-Based Bad Breath Sensor
Chemosensors 2020, 8(1), 3; https://doi.org/10.3390/chemosensors8010003 - 25 Dec 2019
Viewed by 565
Abstract
Ba0.5Sr0.5TiO3 (BST) film doped with variations in RuO2 concentration (0%, 2%, 4%, and 6%) has been successfully grown on a type-p silicon substrate (100) using the chemical solution deposition (CSD) method and spin-coating at a speed of [...] Read more.
Ba0.5Sr0.5TiO3 (BST) film doped with variations in RuO2 concentration (0%, 2%, 4%, and 6%) has been successfully grown on a type-p silicon substrate (100) using the chemical solution deposition (CSD) method and spin-coating at a speed of 3000 rpm for 30 s. The film on the substrate was then heated at 850 °C for 15 h. The sensitivity of BST film + RuO2 variations as a gas sensor were characterized. The sensitivity characterization was assisted by various electronic circuitry with the purpose of producing a sensor that is very sensitive to gas. The responses from the BST film + RuO2 variation were varied, depending on the concentration of the RuO2 dope. BST film doped with 6% RuO2 had a very good response to halitosis gases; therefore, this film was applied as the Arduino-Nano-based bad-breath detecting sensor. Before it was integrated with the microcontroller, the voltage output of the BST film was amplified using an op-amp circuit to make the voltage output from the BST film readable to the microcontroller. The changes in the voltage response were then shown on the prototype display. If the voltage output was ≤12.9 mV, the display would read “bad breath”. If the voltage output >42.1 mV, the display would read “fragrant”. If 12.9 mV < voltage output ≤ 42.1 mV, the display would read “normal”. Full article
(This article belongs to the Special Issue Thin Film Based Sensors Part II)
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Open AccessArticle
Synthesis of ZnO Flakes on Flexible Substrate and Its Application on Ethylene Sensing at Room Temperature
Chemosensors 2020, 8(1), 2; https://doi.org/10.3390/chemosensors8010002 - 19 Dec 2019
Viewed by 599
Abstract
As a hormone that determinates the level of fruit ripeness, ethylene concentration monitoring plays an important role in the agricultural field. One of the techniques that can be used to detect ethylene concentration is the sensing method. Zinc oxide (ZnO) is a multipurpose [...] Read more.
As a hormone that determinates the level of fruit ripeness, ethylene concentration monitoring plays an important role in the agricultural field. One of the techniques that can be used to detect ethylene concentration is the sensing method. Zinc oxide (ZnO) is a multipurpose metal oxide semiconductor with a wide application in sensing area. Here, we use a ZnO-based flexible sensor to identify the presence of ethylene gas at certain concentrations. The as-synthesized ZnO layers were deposited on a polyethylene terephthalate-indium doped tin oxide (PET-ITO) flexible substrate using a simple electrochemical deposition method. To enhance the performance of the ethylene sensor, a small amount of silver (Ag) was added to the seeding solution. From the study, it was revealed that the ZnO-Ag layers were able to identify the presence of ethylene gas at the lowest concentration of 29 ppm. The most optimal result was obtained using 1 mM Ag. This layer demonstrated a response of 17.2% and 19.6% of ethylene gas at concentrations of 29 and 50 ppm, with recovery times of four and eight minutes, respectively. Full article
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Open AccessArticle
Colorimetric Detection of Multiple Metal Ions Using Schiff Base 1-(2-Thiophenylimino)-4-(N-dimethyl)benzene
Chemosensors 2020, 8(1), 1; https://doi.org/10.3390/chemosensors8010001 - 18 Dec 2019
Viewed by 606
Abstract
In this paper, a Schiff base ligand 1-(2-thiophenylimino)-4-(N-dimethyl)benzene (SL1) bearing azomethine (>C=N-) and thiol (-SH) moieties capable of coordinating to metals and forming colored metal complexes was synthesized and examined as a colorimetric chemosensor. The sensing ability toward the metal ions [...] Read more.
In this paper, a Schiff base ligand 1-(2-thiophenylimino)-4-(N-dimethyl)benzene (SL1) bearing azomethine (>C=N-) and thiol (-SH) moieties capable of coordinating to metals and forming colored metal complexes was synthesized and examined as a colorimetric chemosensor. The sensing ability toward the metal ions of Cu2+, Cr3+, Fe2+ Ni2+, Co2+, Mg2+, Zn2+, Fe2+, Fe3+, NH4VO3 (V5+), Mn2+, Hg2+, Pb2+, and Al3+ was investigated in a mixture of H2O and dimethylformamide (DMF) solvent using the UV–Visible spectra monitoring method. The synthesized Schiff base ligand showed colorimetric properties with Cr3+, Fe2+, Fe3+, and Hg2+ ions, resulting in a different color change for each metal that could be identified easily with the naked eye. The UV–Vis spectra indicated a significant red shift (~69–288 nm) from the origin after the addition of the ligand to these metal ions, which may be due to ligand-to-metal charge-transfer (LMCT). On applying Job’s plot, it was indicated that the ligand binds to the metal ions in a 2:1 ligand-to-metal molar ratio. SL1 behaves as a bidentate ligand and binds through the N atom of the imine group and the S atom of the thiol group. The results indicate that the SL1 ligand is an appropriate coordination entity and can be developed for use as a chemosensor for the detection of Cr3+, Fe2+, Fe3+, and Hg2+ ions. Full article
(This article belongs to the Special Issue Optical Chemosensors and Biosensors)
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