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Chemosensors, Volume 9, Issue 6 (June 2021) – 35 articles

Cover Story (view full-size image): Molecularly imprinted polymers (MIPs) are synthetic recognition materials obtained by the polymerisation of functional and cross-linking monomers in the presence of a template. They are attractive, not only for their recognition properties that are close to those of natural receptors and their availability for a wide range of targets, but also for their superior chemical and physical stability compared to biological receptors. Since the late 1990s, the continuous development of MIPs as sensing elements in bio-/chemo-sensors has been driven by the need for simple devices with optimum selectivity for the detection of various compounds in different fields. View this paper.
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Article
A High-Response Electrochemical As(III) Sensor Using Fe3O4–rGO Nanocomposite Materials
Chemosensors 2021, 9(6), 150; https://doi.org/10.3390/chemosensors9060150 - 18 Jun 2021
Cited by 5 | Viewed by 916
Abstract
Nowadays, heavy metal ion pollution in water is becoming more and more common, especially arsenic, which seriously threatens human health. In this work, we used Fe3O4–rGO nanocomposites to modify a glassy carbon electrode and selected square wave voltametric electrochemical [...] Read more.
Nowadays, heavy metal ion pollution in water is becoming more and more common, especially arsenic, which seriously threatens human health. In this work, we used Fe3O4–rGO nanocomposites to modify a glassy carbon electrode and selected square wave voltametric electrochemical detection methods to detect trace amounts of arsenic in water. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) showed that Fe3O4 nanoparticles were uniformly distributed on the rGO sheet, with a particle size of about 20 nm. Raman spectroscopy and electrochemical impedance spectroscopy (EIS) showed that rGO provides higher sensitivity and conductive substrates. Under optimized experimental conditions, Fe3O4–rGO-modified glassy carbon electrodes showed a higher sensitivity (2.15 µA/ppb) and lower limit of detection (1.19 ppb) for arsenic. They also showed good selectivity, stability, and repeatability. Full article
(This article belongs to the Special Issue Chemical Sensors Based on Organic-Inorganic Nanocomposites)
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Review
Nanocomposite Materials Based on Electrochemically Synthesized Graphene Polymers: Molecular Architecture Strategies for Sensor Applications
Chemosensors 2021, 9(6), 149; https://doi.org/10.3390/chemosensors9060149 - 18 Jun 2021
Cited by 4 | Viewed by 1487
Abstract
The use of graphene and its derivatives in the development of electrochemical sensors has been growing in recent decades. Part of this success is due to the excellent characteristics of such materials, such as good electrical and mechanical properties and a large specific [...] Read more.
The use of graphene and its derivatives in the development of electrochemical sensors has been growing in recent decades. Part of this success is due to the excellent characteristics of such materials, such as good electrical and mechanical properties and a large specific surface area. The formation of composites and nanocomposites with these two materials leads to better sensing performance compared to pure graphene and conductive polymers. The increased large specific surface area of the nanocomposites and the synergistic effect between graphene and conducting polymers is responsible for this interesting result. The most widely used methodologies for the synthesis of these materials are still based on chemical routes. However, electrochemical routes have emerged and are gaining space, affording advantages such as low cost and the promising possibility of modulation of the structural characteristics of composites. As a result, application in sensor devices can lead to increased sensitivity and decreased analysis cost. Thus, this review presents the main aspects for the construction of nanomaterials based on graphene oxide and conducting polymers, as well as the recent efforts made to apply this methodology in the development of sensors and biosensors. Full article
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Article
Sensing Atrazine Herbicide Degradation Products through Their Interactions with Humic Substances by Surface-Enhanced Raman Scattering
Chemosensors 2021, 9(6), 148; https://doi.org/10.3390/chemosensors9060148 - 16 Jun 2021
Cited by 1 | Viewed by 983
Abstract
In this work, we have developed a simple method to carry out the quantitative analysis of deethylhydroxyatrazine (DEHA), the most abundant metabolite of atrazine herbicide (ATZ), based on the surface-enhanced Raman scattering technique. Since this ATZ product can undergo pH-dependent tautomerization, a previous [...] Read more.
In this work, we have developed a simple method to carry out the quantitative analysis of deethylhydroxyatrazine (DEHA), the most abundant metabolite of atrazine herbicide (ATZ), based on the surface-enhanced Raman scattering technique. Since this ATZ product can undergo pH-dependent tautomerization, a previous characterization of the DEHA vibrational spectrum was accomplished. This study consisted of the Raman scattering study, both experimental and theoretical, of the enolic and ketonic tautomers of this molecule. SERS spectra were recorded at different pH in order to assess the effect of the metal surface in nanoparticles along with the pH on the structure of DEHA and to find the optimal experimental conditions of the quantitative detection of DEHA. Additionally, the interaction of DEHA with two types of humic acid reference standards, the Elliot humic and leonardite humic ones, was also performed by SERS. This interaction was conducted with two different objectives: to evaluate the interaction mechanism of the ATZ degradation product with humic substances and to check if this interaction can modify the sensitivity of the SERS detection of DEHA. The results presented in this study have clearly demonstrated that SERS spectroscopy is a very powerful technique for characterizing DEHA and other triazine sub-products at a very low concentration in water and also for analyzing the interaction of these important pollutants with humic substances. Full article
(This article belongs to the Section Optical Chemical Sensors)
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Article
Optimization of Classification Prediction Performances of an Instrumental Odour Monitoring System by Using Temperature Correction Approach
Chemosensors 2021, 9(6), 147; https://doi.org/10.3390/chemosensors9060147 - 16 Jun 2021
Cited by 4 | Viewed by 1021
Abstract
Odour emissions generated by industrial and environmental protection plants are often a cause of nuisances and consequent conflicts in exposed populations. Their control is a key action to avoid complaints. Among the odour measurement techniques, the sensory-instrumental method with the application of Instrumental [...] Read more.
Odour emissions generated by industrial and environmental protection plants are often a cause of nuisances and consequent conflicts in exposed populations. Their control is a key action to avoid complaints. Among the odour measurement techniques, the sensory-instrumental method with the application of Instrumental Odour Monitoring Systems (IOMSs) currently represents an effective solution to allow a continuous classification and quantification of odours in real time, combining the advantages of conventional analytical and sensorial techniques. However, some aspects still need to be improved. The study presents and discusses the investigation and optimization of the operational phases of an advanced IOMS, applied for monitoring of environmental odours, with the aim of increasing their performances and reliability of the measures. Accuracy rates of over 98% were reached in terms of classification performances. The implementation of automatic correction systems for the resistance values of the measurement sensors, by considering the influence of the temperature, has been proven to be a solution to further improve the reliability of IOMS. The proposed approach was based on the application of corrective coefficients experimentally determined by analyzing the correlation between resistance values and operating conditions. The paper provides useful information for the implementation of real-time management activities by using a tailor-made software, able to increase and enlarge the IOMS fields of application. Full article
(This article belongs to the Special Issue Chemometric Tools for Monitoring Air Type Profiles)
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Article
Nitrogen and Sulfur Co-Doped Graphene as Efficient Electrode Material for L-Cysteine Detection
Chemosensors 2021, 9(6), 146; https://doi.org/10.3390/chemosensors9060146 - 16 Jun 2021
Cited by 3 | Viewed by 811
Abstract
Two graphene samples co-doped with nitrogen and sulfur were synthesized by the hydrothermal method using thiourea as doping and reducing agent for graphene oxide (GO). An appropriate amount of thiourea was added to the aqueous dispersion of GO, previously sonicated for 30 min. [...] Read more.
Two graphene samples co-doped with nitrogen and sulfur were synthesized by the hydrothermal method using thiourea as doping and reducing agent for graphene oxide (GO). An appropriate amount of thiourea was added to the aqueous dispersion of GO, previously sonicated for 30 min. The mixture was poured into an autoclave and placed in the oven for 3 h, at 120 and 200 °C. The samples were denoted NSGr-120 and NSGr-200, respectively, in agreement with the reaction temperatures. They were next morphologically and structurally characterized by advanced techniques, such as SEM/TEM, XPS, XRD, and FTIR. According to XPS analysis, the NSGr-120 sample has higher amounts of heteroatoms in comparison with NSGr-200, indicating that the reaction temperature is a crucial factor that affects the doping degree. In order to reveal the influence of the doping degree on the electrochemical performances of graphene-modified electrodes, they were tested in solutions containing L-cysteine molecules. The electrode with the best electrocatalytic performances, GC/NSGr-120, was tested to detect L-cysteine in a pharmaceutical drug, proving its applicability in real sample analysis. Full article
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Review
Recent Advances in Vertically Aligned Nanocomposites with Tunable Optical Anisotropy: Fundamentals and Beyond
Chemosensors 2021, 9(6), 145; https://doi.org/10.3390/chemosensors9060145 - 16 Jun 2021
Cited by 1 | Viewed by 981
Abstract
Developing reliable and tunable metamaterials is fundamental to next-generation optical-based nanodevices and computing schemes. In this review, an overview of recent progress made with a unique group of ceramic-based functional nanocomposites, i.e., vertically aligned nanocomposites (VANs), is presented, with the focus on the [...] Read more.
Developing reliable and tunable metamaterials is fundamental to next-generation optical-based nanodevices and computing schemes. In this review, an overview of recent progress made with a unique group of ceramic-based functional nanocomposites, i.e., vertically aligned nanocomposites (VANs), is presented, with the focus on the tunable anisotropic optical properties. Using a self-assembling bottom-up deposition method, the as-grown VANs present great promise in terms of structural flexibility and property tunability. Such broad tunability of functionalities is achieved through VAN designs, material selection, growth control, and strain coupling. The as-grown multi-phase VAN films also present enormous advantages, including wafer scale integration, epitaxial quality, sharp atomic interface, as well as designable materials and geometries. This review also covers the research directions with practical device potentials, such as multiplex sensing, high-temperature plasmonics, magneto-optical switching, as well as photonic circuits. Full article
(This article belongs to the Special Issue Anisotropic Nanomaterials for Sensing Applications)
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Communication
A Boost Converter Employing Quadratic Sawtooth Waveform Generator for SiPM-Based Radiation Sensors
Chemosensors 2021, 9(6), 144; https://doi.org/10.3390/chemosensors9060144 - 16 Jun 2021
Viewed by 861
Abstract
This paper proposes an optimized step-up power converter using a quadratic sawtooth waveform generator for a silicon photomultiplier (SiPM) used as a radiation sensor for mobile radiation dosimeters. Although our step-up converter uses the topology of a switched inductor boost converter in voltage [...] Read more.
This paper proposes an optimized step-up power converter using a quadratic sawtooth waveform generator for a silicon photomultiplier (SiPM) used as a radiation sensor for mobile radiation dosimeters. Although our step-up converter uses the topology of a switched inductor boost converter in voltage mode, it achieves a fast transient performance thanks to the proposed quadratic sawtooth waveform generator, which can increase the loop bandwidth. As a result, the proposed boost converter can stably regulate the bias voltage of an SiPM, even in a situation where the radiation particles are injected. In addition, since the proposed quadratic sawtooth waveform generator can be designed with low power, it was able to achieve 86% peak efficiency even under the light load conditions. Full article
(This article belongs to the Special Issue Radiation-Based Sensors and Nanosensors)
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Article
A Potentiometric Electronic Tongue as a Discrimination Tool of Water-Food Indicator/Contamination Bacteria
Chemosensors 2021, 9(6), 143; https://doi.org/10.3390/chemosensors9060143 - 16 Jun 2021
Cited by 3 | Viewed by 979
Abstract
Microorganism assessment plays a key role in food quality and safety control but conventional techniques are costly and/or time consuming. Alternatively, electronic tongues (E-tongues) can fulfill this critical task. Thus, a potentiometric lab-made E-tongue (40 lipid sensor membranes) was used to differentiate four [...] Read more.
Microorganism assessment plays a key role in food quality and safety control but conventional techniques are costly and/or time consuming. Alternatively, electronic tongues (E-tongues) can fulfill this critical task. Thus, a potentiometric lab-made E-tongue (40 lipid sensor membranes) was used to differentiate four common food contamination bacteria, including two Gram positive (Enterococcus faecalis, Staphylococcus aureus) and two Gram negative (Escherichia coli, Pseudomonas aeruginosa). Principal component analysis and a linear discriminant analysis-simulated annealing algorithm (LDA-SA) showed that the potentiometric signal profiles acquired during the analysis of aqueous solutions containing known amounts of each studied bacteria allowed a satisfactory differentiation of the four bacterial strains. An E-tongue-LDA-SA model (12 non-redundant sensors) correctly classified 98 ± 5% of the samples (repeated K-fold-CV), the satisfactory performance of which can be attributed to the capability of the lipid membranes to establish electrostatic interactions/hydrogen bonds with hydroxyl, amine and/or carbonyl groups, which are comprised in the bacteria outer membranes. Furthermore, multiple linear regression models, based on selected subsets of E-tongue sensors (12–15 sensors), also allowed quantifying the bacteria contents in aqueous solutions (0.993 ± 0.011 ≤ R2 ≤ 0.998 ± 0.005, for repeated K-fold-CV). In conclusion, the E-tongue could be of great value as a preliminary food quality and safety diagnosis tool. Full article
(This article belongs to the Section Applied Chemical Sensors)
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Article
Classification and Identification of Essential Oils from Herbs and Fruits Based on a MOS Electronic-Nose Technology
Chemosensors 2021, 9(6), 142; https://doi.org/10.3390/chemosensors9060142 - 16 Jun 2021
Cited by 23 | Viewed by 1376
Abstract
The frequent occurrence of adulterated or counterfeit plant products sold in worldwide commercial markets has created the necessity to validate the authenticity of natural plant-derived palatable products, based on product-label composition, to certify pricing values and for regulatory quality control (QC). The necessity [...] Read more.
The frequent occurrence of adulterated or counterfeit plant products sold in worldwide commercial markets has created the necessity to validate the authenticity of natural plant-derived palatable products, based on product-label composition, to certify pricing values and for regulatory quality control (QC). The necessity to confirm product authenticity before marketing has required the need for rapid-sensing, electronic devices capable of quickly evaluating plant product quality by easily measurable volatile (aroma) emissions. An experimental MAU-9 electronic nose (e-nose) system, containing a sensor array with 9 metal oxide semiconductor (MOS) gas sensors, was developed with capabilities to quickly identify and classify volatile essential oils derived from fruit and herbal edible-plant sources. The e-nose instrument was tested for efficacy to discriminate between different volatile essential oils present in gaseous emissions from purified sources of these natural food products. Several chemometric data-analysis methods, including pattern recognition algorithms, principal component analysis (PCA), and support vector machine (SVM) were utilized and compared. The classification accuracy of essential oils using PCA, LDA and QDA, and SVM methods was at or near 100%. The MAU-9 e-nose effectively distinguished between different purified essential oil aromas from herbal and fruit plant sources, based on unique e-nose sensor array responses to distinct, essential-oil specific mixtures of volatile organic compounds (VOCs). Full article
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Article
Development of a Natural Preservative from Chestnut Flowers: Ultrasound-Assisted Extraction Optimization and Functionality Assessment
Chemosensors 2021, 9(6), 141; https://doi.org/10.3390/chemosensors9060141 - 15 Jun 2021
Cited by 1 | Viewed by 1124
Abstract
This study was carried out with the aim of optimizing the ultrasound-assisted extraction (UAE) of phenolic compounds from male chestnut flowers (C. sativa Mill) to develop a bioactive extract with potential to be used as a natural antioxidant preservative ingredient in the [...] Read more.
This study was carried out with the aim of optimizing the ultrasound-assisted extraction (UAE) of phenolic compounds from male chestnut flowers (C. sativa Mill) to develop a bioactive extract with potential to be used as a natural antioxidant preservative ingredient in the food industry. Time (t, 1–39 min), solvent concentration (S, 0–100%), and ultrasonic power (P, 5–500 W) were used as the independent variables for a 5-level experimental circumscribed central composite design (CCCD) coupled with response surface methodology (RSM) to optimize the extraction of phenolic compounds by UAE. Regarding the variables, the three showed a significant effect on the extraction of phenolic compounds. The content of phenolic compounds (including flavonoids and tannins) and the extraction yield (extract weight gravimetrically assessed) were the response criteria for the optimization. Based on the statistically validated predictive polynomial models, it was possible to reach a maximum content of phenolic compounds at the global optimal conditions of 24 ± 3 min, 259 ± 16 W, and 51 ± 7% ethanol. Additionally, pentagalloyl-glucoside and trigalloyl-hexahydroxydiphenoyl-glucoside were the major phenolic compounds identified. The optimized extract was then analyzed for their biological properties. The bioactive potential of the chestnut flower extract obtained under these optimized conditions was evaluated using in vitro assays for antioxidant, anti-inflammatory, and antimicrobial activity, as well as cytotoxicity and hepatotoxicity tests. The results revealed that the enriched extract has antioxidant, antitumoral, and anti-inflammatory activities without toxicity issues. Overall, this study allowed to define the optimal conditions for the extraction of phenolic compounds from chestnuts male flowers by UAE, to obtain an enriched extract with biological properties that could be further used as a natural antioxidant ingredient with applications on functional foods. Full article
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Article
Pt Nanoparticles Anchored on NH2-MIL-101 with Efficient Peroxidase-Like Activity for Colorimetric Detection of Dopamine
Chemosensors 2021, 9(6), 140; https://doi.org/10.3390/chemosensors9060140 - 14 Jun 2021
Cited by 3 | Viewed by 1459
Abstract
Dopamine (DA) is an important catecholamine neurotransmitter that plays a highly relevant role in regulating the central nervous system, and abnormal DA content can cause many immune-related diseases. Hence, it is of significance to sensitively and specifically identify DA for clinical medicine. In [...] Read more.
Dopamine (DA) is an important catecholamine neurotransmitter that plays a highly relevant role in regulating the central nervous system, and abnormal DA content can cause many immune-related diseases. Hence, it is of significance to sensitively and specifically identify DA for clinical medicine. In this work, Pt/NH2-MIL-101 hybrid nanozymes with bimetallic catalytic centers were fabricated by forming coordinate bonds between Pt nanoparticles (Pt NPs) and –NH2 on metal–organic frameworks (MOF). The catalytic activity of Pt/NH2-MIL-101 was increased by 1.5 times via enlarging the exposure of more active sites and improving the activity of the active sites through the strategy of forming bimetallic catalytic centers. In the presence of DA, competing with 3, 3′, 5, 5′-tetramethylbenzidine (TMB) for the generated hydroxyl radicals (•OH), the blue oxidation state TMB (Ox-TMB) is reduced to colorless TMB, showing dramatic color changes. The Pt/NH2-MIL-101-based colorimetric assay enables the sensitive and robust detection of DA molecules with a detection limit of only 0.42 μM and has an observable potential in clinical applications. Full article
(This article belongs to the Special Issue Novel Molecular Optoelectronic Sensing)
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Article
Cost-Effective Real-Time Metabolic Profiling of Cancer Cell Lines for Plate-Based Assays
Chemosensors 2021, 9(6), 139; https://doi.org/10.3390/chemosensors9060139 - 13 Jun 2021
Cited by 2 | Viewed by 1368
Abstract
A fundamental phenotype of cancer cells is their metabolic profile, which is routinely described in terms of glycolytic and respiratory rates. Various devices and protocols have been designed to quantify glycolysis and respiration from the rates of acid production and oxygen utilization, respectively, [...] Read more.
A fundamental phenotype of cancer cells is their metabolic profile, which is routinely described in terms of glycolytic and respiratory rates. Various devices and protocols have been designed to quantify glycolysis and respiration from the rates of acid production and oxygen utilization, respectively, but many of these approaches have limitations, including concerns about their cost-ineffectiveness, inadequate normalization procedures, or short probing time-frames. As a result, many methods for measuring metabolism are incompatible with cell culture conditions, particularly in the context of high-throughput applications. Here, we present a simple plate-based approach for real-time measurements of acid production and oxygen depletion under typical culture conditions that enable metabolic monitoring for extended periods of time. Using this approach, it is possible to calculate metabolic fluxes and, uniquely, describe the system at steady-state. By controlling the conditions with respect to pH buffering, O2 diffusion, medium volume, and cell numbers, our workflow can accurately describe the metabolic phenotype of cells in terms of molar fluxes. This direct measure of glycolysis and respiration is conducive for between-runs and even between-laboratory comparisons. To illustrate the utility of this approach, we characterize the phenotype of pancreatic ductal adenocarcinoma cell lines and measure their response to a switch of metabolic substrate and the presence of metabolic inhibitors. In summary, the method can deliver a robust appraisal of metabolism in cell lines, with applications in drug screening and in quantitative studies of metabolic regulation. Full article
(This article belongs to the Collection pH Sensors, Biosensors and Systems)
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Review
An Overview of the Recent Developments in Carbon Quantum Dots—Promising Nanomaterials for Metal Ion Detection and (Bio)Molecule Sensing
Chemosensors 2021, 9(6), 138; https://doi.org/10.3390/chemosensors9060138 - 11 Jun 2021
Cited by 4 | Viewed by 1544
Abstract
The fluorescent carbon quantum dots (CQDs) represent an emerging subset of carbonaceous nanomaterials, recently becoming a powerful tool for biosensing, bioimaging, and drug and gene delivery. In general, carbon dots are defined as zero-dimensional (0D), spherical-like nanoparticles with <10 nm in size. Their [...] Read more.
The fluorescent carbon quantum dots (CQDs) represent an emerging subset of carbonaceous nanomaterials, recently becoming a powerful tool for biosensing, bioimaging, and drug and gene delivery. In general, carbon dots are defined as zero-dimensional (0D), spherical-like nanoparticles with <10 nm in size. Their unique chemical, optical, and electronic properties make CQDs versatile materials for a wide spectrum of applications, mainly for the sensing and biomedical purposes. Due to their good biocompatibility, water solubility, and relatively facile modification, these novel materials have attracted tremendous interest in recent years, which is especially important for nanotechnology and nanoscience expertise. The preparation of the biomass-derived CQDs has attracted growing interest recently due to their low-cost, renewable, and green biomass resources, presenting also the variability of possible modification for the enhancement of CQDs’ properties. This review is primarily focused on the recent developments in carbon dots and their application in the sensing of different chemical species within the last five years. Furthermore, special emphasis has been made regarding the green approaches for obtaining CQDs and nanomaterial characterization toward better understanding the mechanisms of photoluminescent behavior and sensing performance. In addition, some of the challenges and future outlooks in CQDs research have been briefly outlined. Full article
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Article
Fluorination vs. Chlorination: Effect on the Sensor Response of Tetrasubstituted Zinc Phthalocyanine Films to Ammonia
Chemosensors 2021, 9(6), 137; https://doi.org/10.3390/chemosensors9060137 - 11 Jun 2021
Cited by 1 | Viewed by 1297
Abstract
In this work, the effect of fluorine and chlorine substituents in tetrasubstituted zinc phthalocyanines, introduced into the non-peripheral (ZnPcR4-np, R = F, Cl) and peripheral (ZnPcR4-p, R = F, Cl) positions of macrocycle, on their structure and chemiresistive sensor [...] Read more.
In this work, the effect of fluorine and chlorine substituents in tetrasubstituted zinc phthalocyanines, introduced into the non-peripheral (ZnPcR4-np, R = F, Cl) and peripheral (ZnPcR4-p, R = F, Cl) positions of macrocycle, on their structure and chemiresistive sensor response to low concentration of ammonia is studied. The structure and morphology of the zinc phthalocyanines films (ZnPcR4) were investigated by X-ray diffraction and atomic force microscopy methods. To understand different effects of chlorine and fluorine substituents, the strength and nature of the bonding of ammonia and ZnPcHal4 molecules were studied by quantum chemical simulation. It was shown on the basis of comparative analysis that the sensor response to ammonia was found to increase in the order ZnPcCl4-np < ZnPcF4-np < ZnPcF4-p < ZnPcCl4-p, which is in good agreement with the values of bonding energy between hydrogen atoms of NH3 and halogen substituents in the phthalocyanine rings. ZnPcCl4-p films demonstrate the maximal sensor response to ammonia with the calculated detection limit of 0.01 ppm; however, they are more sensitive to humidity than ZnPcF4-p films. It was shown that both ZnPcF4-p and ZnPcCl4-p and can be used for the selective detection of NH3 in the presence of carbon dioxide, dichloromethane, acetone, toluene, and ethanol. Full article
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Article
Thermal and Structural Properties of High Density Polyethylene/Carbon Nanotube Nanocomposites: A Comparison Study
Chemosensors 2021, 9(6), 136; https://doi.org/10.3390/chemosensors9060136 - 11 Jun 2021
Cited by 5 | Viewed by 1274
Abstract
The effects of functionalization of carbon nanotubes on the properties of nanocomposite sheets prepared from high-density polyethylene (HDPE) and carbon nanotubes (CNTs) were investigated. Carbon nanotubes were first oxidized, followed by amine group functionalization. The Fourier transform-infrared (FTIR) spectroscopy results confirm the presence [...] Read more.
The effects of functionalization of carbon nanotubes on the properties of nanocomposite sheets prepared from high-density polyethylene (HDPE) and carbon nanotubes (CNTs) were investigated. Carbon nanotubes were first oxidized, followed by amine group functionalization. The Fourier transform-infrared (FTIR) spectroscopy results confirm the presence of oxygenated and amide groups at the surface of the CNTs after each treatment. The HDPE/CNT nanocomposites sheets were prepared using a melt compounding method. Six types of CNTs were used; pristine Single-walled Carbon nanotubes (SWCNT) and pristine Multi-walled Carbon nanotubes (MWCNT), oxidized (O-SWCNT and O-MWCNT) and amide (Amide-SWCNT and Amide-MWCNT). All prepared nanocomposite sheets were characterized using Thermal gravimetric analysis (TGA), Differential scanning calorimetry (DSC), X-ray diffraction (XRD) and scanning electronic microscope (SEM). TGA results measured increased thermal stability of the polymer with the addition of CNTs, O-MWCNT showed the best enhancement. XRD measurements confirmed that the addition of CNTs did not change the crystal structure of the polymer, although the crystallinity was decreased. The maximum crystallinity decrease resulted from O-SWNTs addition to the polymer matrix. SEM imaging showed that oxidized and functionalized CNTs have more even dispersion in the polymer matrix compared with pristine CNTs. Full article
(This article belongs to the Special Issue Nanomaterials Based on Bio/Chemical Sensors)
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Article
Quantum Chemical Studies and Electrochemical Investigations of Polymerized Brilliant Blue-Modified Carbon Paste Electrode for In Vitro Sensing of Pharmaceutical Samples
Chemosensors 2021, 9(6), 135; https://doi.org/10.3390/chemosensors9060135 - 10 Jun 2021
Cited by 5 | Viewed by 1080
Abstract
To develop an electrochemical sensor for electroactive molecules, the choice and prediction of redox reactive sites of the modifier play a critical role in establishing the sensing mediating mechanism. Therefore, to understand the mediating mechanism of the modifier, we used advanced density functional [...] Read more.
To develop an electrochemical sensor for electroactive molecules, the choice and prediction of redox reactive sites of the modifier play a critical role in establishing the sensing mediating mechanism. Therefore, to understand the mediating mechanism of the modifier, we used advanced density functional theory (DFT)-based quantum chemical modeling. A carbon paste electrode (CPE) was modified with electropolymerization of brilliant blue, later employed for the detection of paracetamol (PA) and folic acid (FA). PA is an analgesic, anti-inflammatory and antipyretic prescription commonly used in medical fields, and overdose or prolonged use may harm the liver and kidney. The deficiency of FA associated with neural tube defects (NTDs) and therefore the quantification of FA are very essential to prevent the problems associated with congenital deformities of the spinal column, skull and brain of the fetus in pregnant women. Hence, an electrochemical sensor based on a polymerized brilliant blue-modified carbon paste working electrode (BRB/CPE) was fabricated for the quantification of PA and FA in physiological pH. The real analytical applicability of the proposed sensor was judged by employing it in analysis of a pharmaceutical sample, and good recovery results were obtained. The potential excipients do not have a significant contribution to the electro-oxidation of PA at BRB/CPE, which makes it a promising electrochemical sensing platform. The real analytical applicability of the proposed method is valid for pharmaceutical analysis in the presence of possible excipients. The prediction of redox reactive sites of the modifier by advanced quantum chemical modeling-based DFT may lay a new foundation for researchers to establish the modifier–analyte interaction mechanisms. Full article
(This article belongs to the Section Analytical Methods, Instrumentation and Miniaturization)
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Communication
Terbium(III) as a Fluorescent Probe for Molecular Detection of Ascorbic Acid
Chemosensors 2021, 9(6), 134; https://doi.org/10.3390/chemosensors9060134 - 09 Jun 2021
Cited by 1 | Viewed by 1019
Abstract
Fluorescence analysis is a simple and a highly sensitive method for detection of small amounts of biologically active substances. In this study, a complexation of terbium(III) chelates with 1,10-phenanthroline and ascorbic acid (AA) and luminescent properties of complexes were investigated. The influence of [...] Read more.
Fluorescence analysis is a simple and a highly sensitive method for detection of small amounts of biologically active substances. In this study, a complexation of terbium(III) chelates with 1,10-phenanthroline and ascorbic acid (AA) and luminescent properties of complexes were investigated. The influence of pH and solubilization of complexes by micellar solutions of nonionic, cationic, and anionic surfactants on fluorescence was studied. The quenching effect of terbium ion fluorescence was detected upon an introduction of ascorbic acid. The quenching effect of the complex with mixed ligands Tb(1,10-phenanthroline)-AA allows for the detection of ascorbic acid with the limit of 7.4 × 10−5 mol·L−1. Full article
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Review
Fluoro-Substituted Metal Phthalocyanines for Active Layers of Chemical Sensors
Chemosensors 2021, 9(6), 133; https://doi.org/10.3390/chemosensors9060133 - 08 Jun 2021
Cited by 6 | Viewed by 1435
Abstract
Metal phthalocyanines bearing electron-withdrawing fluorine substituents were synthesized a long time ago, but interest in the study of their films has emerged in recent decades. This is due to the fact that, unlike unsubstituted phthalocyanines, films of some fluorinated phthalocyanines exhibit the properties [...] Read more.
Metal phthalocyanines bearing electron-withdrawing fluorine substituents were synthesized a long time ago, but interest in the study of their films has emerged in recent decades. This is due to the fact that, unlike unsubstituted phthalocyanines, films of some fluorinated phthalocyanines exhibit the properties of n-type semiconductors, which makes them promising candidates for application in ambipolar transistors. Apart from this, it was shown that the introduction of fluorine substituents led to an increase in the sensitivity of phthalocyanine films to reducing gases. This review analyzes the state of research over the last fifteen years in the field of applications of fluoro-substituted metal phthalocyanines as active layers of gas sensors, with a primary focus on chemiresistive ones. The active layers on the basis of phthalocyanines with fluorine and fluorine-containing substituents of optical and quartz crystal microbalance sensors are also considered. Attention is paid to the analysis of the effect of molecular structure (central metal, number and type of fluorine substituent etc.) on sensor properties of fluorinated phthalocyanine films. Full article
(This article belongs to the Special Issue Nanomaterials Based on Bio/Chemical Sensors)
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Article
Red Seaweeds as a Source of Nutrients and Bioactive Compounds: Optimization of the Extraction
Chemosensors 2021, 9(6), 132; https://doi.org/10.3390/chemosensors9060132 - 08 Jun 2021
Cited by 8 | Viewed by 1702
Abstract
The present work aimed to determine the nutritional composition (ash, protein, fat, carbohydrate content and energy value), phenolic compounds, pigments and organic acids content of three typical red algae from the Northwest of Spain: Chondrus crispus, Mastocarpus stellatus, and Gigartina pistillata [...] Read more.
The present work aimed to determine the nutritional composition (ash, protein, fat, carbohydrate content and energy value), phenolic compounds, pigments and organic acids content of three typical red algae from the Northwest of Spain: Chondrus crispus, Mastocarpus stellatus, and Gigartina pistillata; as well as their antioxidant and antimicrobial activities. Furthermore, the present work compared two extraction techniques: conventional heat assisted extraction (HAE) and high pressure assisted extraction (HPAE) to maximize the yield and the concentration of target compounds. Different independent variables were considered for the response study. Time (t) and percentage of ethanol of the solvent (S) were chosen for both techniques and temperature (T) and pressure (P) were used for HAE and HPAE, respectively. The experiments were designed following a response surface methodology (RSM) approach. The obtained results showed a similar nutritional composition between algae samples: low-fat content and high content of proteins, carbohydrates and energy. All tested algae showed good antioxidant and antimicrobial properties. Finally, HEA demonstrated to be the most efficient extraction technique. This study confirms the potential of red algae to be part of the human diet as a source of non-animal protein, due to its nutritional content, phenolic profile, pigments concentration and bioactive properties, which proves that HAE is the optimum technique for the extraction maximization. Full article
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Article
Growth of Defect-Induced Carbon Nanotubes for Low-Temperature Fruit Monitoring Sensor
Chemosensors 2021, 9(6), 131; https://doi.org/10.3390/chemosensors9060131 - 07 Jun 2021
Cited by 3 | Viewed by 1325
Abstract
Herein, a carbon nanotubes-based sensor has been grown for the purpose of ethylene detection. The prepared CNTs had a crystalline structure with a smooth surface of 11.0 nm in diameter and 10.0 µm in length. The low-intensity graphite peak (G-band) as compared to [...] Read more.
Herein, a carbon nanotubes-based sensor has been grown for the purpose of ethylene detection. The prepared CNTs had a crystalline structure with a smooth surface of 11.0 nm in diameter and 10.0 µm in length. The low-intensity graphite peak (G-band) as compared to the peak of the defect (D-band) characterizes the defects in the CNTs. An MWNTs-gas sensor was fabricated for monitoring the ethylene gas. The highest response was recorded at a low operating temperature of 30 °C. The sensor was also examined at 300 ppb up to 10 ppm and it showed a response of 2% up to 28%. The sensor response and recovery time constants were varied from 60 to 300 s, depending on the gas concentration. The results that were obtained for the synthetic ethylene gas were also compared with the real measurements for banana ripening. The results confirmed that the sensor is appropriate for the monitoring of fruit ripening. Full article
(This article belongs to the Special Issue Advanced Sensors Based on Carbon Nanotubes)
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Article
Pomological Descriptors, Phenolic Compounds, and Chemical Monitoring in Olive Fruits Irrigated with Dairy Treated Wastewater
Chemosensors 2021, 9(6), 130; https://doi.org/10.3390/chemosensors9060130 - 04 Jun 2021
Viewed by 951
Abstract
In this work, the pomological characteristics, phenolic composition, and chemical contents modification in response to treated wastewater (TWW) irrigation was studied on olive fruits. The experiment was carried out during two successive years (2016/2017) on olive trees (cv. Chemlali). Three irrigation treatments were [...] Read more.
In this work, the pomological characteristics, phenolic composition, and chemical contents modification in response to treated wastewater (TWW) irrigation was studied on olive fruits. The experiment was carried out during two successive years (2016/2017) on olive trees (cv. Chemlali). Three irrigation treatments were adopted and two TWW irrigation levels were applied (T1: 20% ETc; T2: 40% ETc; CT: Control Treatment (rainfed condition)). Results show that TWW irrigation leads to increased fruit fresh weight and water content, whatever the level applied. In addition, fruit oil content remained unaffected by TWW irrigation. Moreover, this agronomic practice preserves some phenolic compound contents like verbascoside, therefore fruits nutritional value. A positive feature was then observed following TWW irrigation. In fact, oleuropein, tyrosol, luteolin-7-glucoside, and pinoresinol amounts were enhanced in treated olive fruits. On the other hand, TWW irrigated trees with a level of 40% ETc (T2) produced olive fruits richer in Mg and K than those cultivated in rainfed conditions (CT). Fruits Zn, Mn, and Pb contents decreased as a result of olive trees TWW irrigation. Full article
(This article belongs to the Section Analytical Methods, Instrumentation and Miniaturization)
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Article
A Study on the Combination of Enzyme Stabilizers and Low Temperatures in the Long-Term Storage of Glutamate Biosensor
Chemosensors 2021, 9(6), 129; https://doi.org/10.3390/chemosensors9060129 - 03 Jun 2021
Viewed by 1115
Abstract
The importance of physiological glutamate has been widely demonstrated in cognitive and memory processes, as well as in neurotransmission. The involvement of physiological glutamate in several pathologies has also been established. Therefore, analytical devices for studying variations in physiological glutamate are of fundamental [...] Read more.
The importance of physiological glutamate has been widely demonstrated in cognitive and memory processes, as well as in neurotransmission. The involvement of physiological glutamate in several pathologies has also been established. Therefore, analytical devices for studying variations in physiological glutamate are of fundamental importance, particularly in preclinical studies. The necessary knowledge to develop and characterize biosensors for glutamate detection is often restricted to only a few research groups. However, many more groups have sought to implant such analytical devices to study the glutamatergic system in vivo. On this basis, a series of studies was undertaken to explore the medium-term storage of biosensors, thereby allowing their usage results to be differentiated from their construction and characterization processes to facilitate the wider diffusion and use of such sensors. Therefore, it has become vital to determine the best storage conditions to extend the life and functionality of these biosensors, especially due to the diachronic instability of the enzyme present on the surface. In the present study, we analyzed the impact of glycols, such as glycerol and triethylene glycol, as enzyme stabilizers coupled with long-term storage at low temperatures (−20 and −80 °C) on biosensor performance. The biosensors were observed for 5 months and evaluated for their enzymatic activity by measuring the VMAX(app) and KM(app). The analytical features were also evaluated in terms of the Linear Region Slope, which is one the most important parameters for indicating the efficiency and the sensitivity of biosensors. Interestingly, both glycols proved to be capable of increasing enzymatic activity and maintaining good biosensor efficiency over time. Moreover, the combination with low-temperature storage highlighted the different behaviors of the two glycols. In particular, glycerol was more effective in stabilizing the enzyme and maintaining analytical performance when the biosensors were stored at −20 °C. Instead, triethylene glycol performed the same function as glycerol but when the biosensors were stored at −80 °C. Full article
(This article belongs to the Section (Bio)chemical Sensing)
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Article
“Out of Pocket” Protein Binding—A Dilemma of Epitope Imprinted Polymers Revealed for Human Hemoglobin
Chemosensors 2021, 9(6), 128; https://doi.org/10.3390/chemosensors9060128 - 03 Jun 2021
Cited by 8 | Viewed by 1222
Abstract
The epitope imprinting approach applies exposed peptides as templates to synthesize Molecularly Imprinted Polymers (MIPs) for the recognition of the parent protein. While generally the template protein binding to such MIPs is considered to occur via the epitope-shaped cavities, unspecific interactions of the [...] Read more.
The epitope imprinting approach applies exposed peptides as templates to synthesize Molecularly Imprinted Polymers (MIPs) for the recognition of the parent protein. While generally the template protein binding to such MIPs is considered to occur via the epitope-shaped cavities, unspecific interactions of the analyte with non-imprinted polymer as well as the detection method used may add to the complexity and interpretation of the target rebinding. To get new insights on the effects governing the rebinding of analytes, we electrosynthesized two epitope-imprinted polymers using the N-terminal pentapeptide VHLTP-amide of human hemoglobin (HbA) as the template. MIPs were prepared either by single-step electrosynthesis of scopoletin/pentapeptide mixtures or electropolymerization was performed after chemisorption of the cysteine extended VHLTP peptide. Rebinding of the target peptide and the parent HbA protein to the MIP nanofilms was quantified by square wave voltammetry using a redox probe gating, surface enhanced infrared absorption spectroscopy, and atomic force microscopy. While binding of the pentapeptide shows large influence of the amino acid sequence, all three methods revealed strong non-specific binding of HbA to both polyscopoletin-based MIPs with even higher affinities than the target peptides. Full article
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Review
CuxO Nanostructure-Based Gas Sensors for H2S Detection: An Overview
Chemosensors 2021, 9(6), 127; https://doi.org/10.3390/chemosensors9060127 - 02 Jun 2021
Cited by 7 | Viewed by 1537
Abstract
H2S gas is a toxic and hazardous byproduct of the oil and gas industries. It paralyzes the olfactory nerves, with concentrations above 100 ppm, resulting in loss of smell; prolonged inhalation may even cause death. One of the most important semiconducting [...] Read more.
H2S gas is a toxic and hazardous byproduct of the oil and gas industries. It paralyzes the olfactory nerves, with concentrations above 100 ppm, resulting in loss of smell; prolonged inhalation may even cause death. One of the most important semiconducting metal oxides for the detection of H2S is CuxO (x = 1, 2), which is converted to CuxS upon exposure to H2S, leading to a remarkable modulation in the resistance and appearance of an electrical sensing signal. In this review, various morphologies of CuxO in the pristine form, composites of CuxO with other materials, and decoration/doping of noble metals on CuxO nanostructures for the reliable detection of H2S gas are thoroughly discussed. With an emphasis to the detection mechanism of CuxO-based gas sensors, this review presents findings that are of considerable value as a reference. Full article
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Review
Recent Microfluidic Innovations for Sperm Sorting
Chemosensors 2021, 9(6), 126; https://doi.org/10.3390/chemosensors9060126 - 01 Jun 2021
Cited by 6 | Viewed by 1785
Abstract
Sperm selection is a clinical need for guided fertilization in men with low-quality semen. In this regard, microfluidics can provide an enabling platform for the precise manipulation and separation of high-quality sperm cells through applying various stimuli, including chemical agents, mechanical forces, and [...] Read more.
Sperm selection is a clinical need for guided fertilization in men with low-quality semen. In this regard, microfluidics can provide an enabling platform for the precise manipulation and separation of high-quality sperm cells through applying various stimuli, including chemical agents, mechanical forces, and thermal gradients. In addition, microfluidic platforms can help to guide sperms and oocytes for controlled in vitro fertilization or sperm sorting using both passive and active methods. Herein, we present a detailed review of the use of various microfluidic methods for sorting and categorizing sperms for different applications. The advantages and disadvantages of each method are further discussed and future perspectives in the field are given. Full article
(This article belongs to the Special Issue Microfluidic Biosensing Platform)
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Article
Sensing Properties of NiO Loaded SnO2 Nanoparticles—Specific Selectivity to H2S
Chemosensors 2021, 9(6), 125; https://doi.org/10.3390/chemosensors9060125 - 01 Jun 2021
Cited by 2 | Viewed by 1266
Abstract
NiO-loaded SnO2 powders were prepared involving two chemical procedures. The mesoporous SnO2 support was synthesized by a hydrothermal route using Brij 35 non-ionic surfactant as a template. The nickel loadings of 1 and 10 wt.%. NiO were deposited by the wet [...] Read more.
NiO-loaded SnO2 powders were prepared involving two chemical procedures. The mesoporous SnO2 support was synthesized by a hydrothermal route using Brij 35 non-ionic surfactant as a template. The nickel loadings of 1 and 10 wt.%. NiO were deposited by the wet impregnation method. The H2S sensing properties of xNiO-(1-x)SnO2 (x = 0, 1, 10%) thick layers deposited onto commercial substrates have been investigated with respect to different potential interfering gases (NO2, CO, CO2, CH4, NH3 and SO2) over a wide range of operating temperatures and relative humidity specific for in-field conditions. Following the correlation of the sensing results with the morphological ones, 1wt.% NiO/SnO2 was selected for simultaneous electrical resistance and work function investigations. The purpose was to depict the sensing mechanism by splitting between specific changes over the electron affinity induced by the surface coverage with hydroxyl dipoles and over the band bending induced by the variable surface charge under H2S exposure. Thus, it was found that different gas-interaction partners are dependent upon the amount of H2S, mirrored through the threshold value of 5 ppm H2S, which from an applicative point of view, represents the lower limit of health effects, an eight-hour TWA. Full article
(This article belongs to the Collection Sustainable Metal Oxide Materials for Sensing Applications)
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Article
Synthesis, Characterization and Gas Sensing Study of ZnO-SnO2 Nanocomposite Thin Films
Chemosensors 2021, 9(6), 124; https://doi.org/10.3390/chemosensors9060124 - 30 May 2021
Cited by 8 | Viewed by 1522
Abstract
Thin nanocomposite films composed of ZnO and SnO2 at 0.5–5 mol.% concentrations were synthesized by a new solid-phase low-temperature pyrolysis under the developed protocols. This hetero-oxide material was thoroughly studied by X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy [...] Read more.
Thin nanocomposite films composed of ZnO and SnO2 at 0.5–5 mol.% concentrations were synthesized by a new solid-phase low-temperature pyrolysis under the developed protocols. This hetero-oxide material was thoroughly studied by X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) techniques to be compared with electrical and gas-sensing properties. We have found that the films have a poly-nanocrystal structure of ZnO and SnO2 crystals with characteristic grain sizes at 10–15 nm range. When comparing the chemiresistive response of the films with varied tin dioxide content, the sample of Sn:Zn optimum ratio taken as 1:99 yields 1.5-fold improvement upon to 5–50 ppm NO2 exposure at 200 °C. We argue that these remarkable changes have matured from both a reducing the intergrain potential barrier down to 0.58 eV and increasing the concentration of anionic vacancies at this rational composite. The results demonstrate that solid-phase low-temperature pyrolysis is a powerful technique for adjusting the functional gas-sensing properties of hetero-oxide film via modifying the ratio of the oxide components. Full article
(This article belongs to the Collection Sustainable Metal Oxide Materials for Sensing Applications)
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Review
Molecularly Imprinted Polymers for Chemical Sensing: A Tutorial Review
Chemosensors 2021, 9(6), 123; https://doi.org/10.3390/chemosensors9060123 - 26 May 2021
Cited by 32 | Viewed by 2201
Abstract
The field of molecularly imprinted polymer (MIP)-based chemosensors has been experiencing constant growth for several decades. Since the beginning, their continuous development has been driven by the need for simple devices with optimum selectivity for the detection of various compounds in fields such [...] Read more.
The field of molecularly imprinted polymer (MIP)-based chemosensors has been experiencing constant growth for several decades. Since the beginning, their continuous development has been driven by the need for simple devices with optimum selectivity for the detection of various compounds in fields such as medical diagnosis, environmental and industrial monitoring, food and toxicological analysis, and, more recently, the detection of traces of explosives or their precursors. This review presents an overview of the main research efforts made so far for the development of MIP-based chemosensors, critically discusses the pros and cons, and gives perspectives for further developments in this field. Full article
(This article belongs to the Section Materials for Chemical Sensing)
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Article
Compact Miniaturized Bioluminescence Sensor Based on Continuous Air-Segmented Flow for Real-Time Monitoring: Application to Bile Salt Hydrolase (BSH) Activity and ATP Detection in Biological Fluids
Chemosensors 2021, 9(6), 122; https://doi.org/10.3390/chemosensors9060122 - 25 May 2021
Viewed by 1042
Abstract
A simple and versatile continuous air-segmented flow sensor using immobilized luciferase was designed as a general miniaturized platform based on sensitive biochemiluminescence detection. The device uses miniaturized microperistaltic pumps to deliver flows and compact sensitive light imaging detectors based on BI-CMOS (smartphone camera) [...] Read more.
A simple and versatile continuous air-segmented flow sensor using immobilized luciferase was designed as a general miniaturized platform based on sensitive biochemiluminescence detection. The device uses miniaturized microperistaltic pumps to deliver flows and compact sensitive light imaging detectors based on BI-CMOS (smartphone camera) or CCD technology. The low-cost components and power supply make it suitable as out-lab device at point of need to monitor kinetic-related processes or ex vivo dynamic events. A nylon6 flat spiral carrying immobilized luciferase was placed in front of the detector in lensless mode using a fiber optic tapered faceplate. ATP was measured in samples collected by microdialysis from rat brain with detecting levels as low as 0.4 fmoles. The same immobilized luciferase was also used for the evaluation of bile salt hydrolase (BSH) activity in intestinal microbiota. An aminoluciferin was conjugatated with chenodeoxycholic acid forming the amide derivative aLuc-CDCA. The hydrolysis of the aLuc-CDCA probe by BSH releases free uncaged aminoluciferin which is the active substrate for luciferase leading to light emission. This method can detect as low as 0.5 mM of aLuc-CDCA, so it can be used on real faecal human samples to study BSH activity and its modulation by diseases and drugs. Full article
(This article belongs to the Special Issue Microfluidic Biosensing Platform)
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Article
Colorimetric Aptasensor for Detecting Bacillus carboniphilus Using Aptamer Isolated with a Non-SELEX-Based Method
Chemosensors 2021, 9(6), 121; https://doi.org/10.3390/chemosensors9060121 - 24 May 2021
Viewed by 1033
Abstract
B. carboniphilus is a naphtha-degradative strain (NDS) that uses hydrocarbons for its growth and causes microbiologically influenced corrosion (MIC) in naphtha pipelines. To date, there have been no studies on receptors or sensors for the detection of B. carboniphilus. We isolate B. [...] Read more.
B. carboniphilus is a naphtha-degradative strain (NDS) that uses hydrocarbons for its growth and causes microbiologically influenced corrosion (MIC) in naphtha pipelines. To date, there have been no studies on receptors or sensors for the detection of B. carboniphilus. We isolate B. carboniphilus-specific aptamers with a non-SELEX-based method, which employs repetitive cycles of centrifugation-based partitioning. The binding affinities of three aptamers are evaluated by obtaining their dissociation constants (Kd), which range from 13.2 to 26.3 nM. The BCA-05 aptamer with the lowest Kd value is employed for a two-stage label-free aptasensing platform to verify the aptamer selectivity using colorimetric detection of B. carboniphilus. This platform starts with the aptamer-bacteria binding step, and the concentration of residual aptamer after binding depends on the amount of the target bacteria. Then, the amount of separated residual aptamer determines the degree of salt-induced aggregation of gold nanoparticles (AuNPs), which results in a color change from red to blue. The AuNP color change is expressed as the ratio of absorbances at 630 and 520 nm (A630/A520). Under optimized conditions, this aptasensor shows reliable performance with a linear correlation in the range 104–107 CFU mL−1 and a limit of detection of 5 × 103 CFU mL−1. Full article
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