Chemosensors

22 pages, 2707 KiB

Open AccessEditor’s ChoiceReview

Metal Nanoparticle and Quantum Dot Tags for Signal Amplification in Electrochemical Immunosensors for Biomarker Detection

by Anton Popov, Benediktas Brasiunas, Asta Kausaite-Minkstimiene and Almira Ramanaviciene

Chemosensors 2021, 9(4), 85; https://doi.org/10.3390/chemosensors9040085 - 18 Apr 2021

Cited by 28 | Viewed by 5184

Abstract

With the increasing importance of healthcare and clinical diagnosis, as well as the growing demand for highly sensitive analytical instruments, immunosensors have received considerable attention. In this review, electrochemical immunosensor signal amplification strategies using metal nanoparticles (MNPs) and quantum dots (Qdots) as tags [...] Read more.

With the increasing importance of healthcare and clinical diagnosis, as well as the growing demand for highly sensitive analytical instruments, immunosensors have received considerable attention. In this review, electrochemical immunosensor signal amplification strategies using metal nanoparticles (MNPs) and quantum dots (Qdots) as tags are overviewed, focusing on recent developments in the ultrasensitive detection of biomarkers. MNPs and Qdots can be used separately or in combination with other nanostructures, while performing the function of nanocarriers, electroactive labels, or catalysts. Thus, different functions of MNPs and Qdots as well as recent advances in electrochemical signal amplification are discussed. Additionally, the methods most often used for antibody immobilization on nanoparticles, immunoassay formats, and electrochemical methods for indirect biomarker detection are overviewed. Full article

(This article belongs to the Special Issue Electrochemical Immunosensor)

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13 pages, 4663 KiB

Open AccessArticle

Carboxylated Graphene Nanoribbons for Highly-Selective Ammonia Gas Sensors: Ab Initio Study

by Pavel V. Barkov and Olga E. Glukhova

Chemosensors 2021, 9(4), 84; https://doi.org/10.3390/chemosensors9040084 - 18 Apr 2021

Cited by 8 | Viewed by 3128

Abstract

The character and degree of influence of carboxylic acid groups (COOH) on the sensory properties (particularly on the chemoresistive response) of a gas sensor based on zigzag and armchair graphene nanoribbons are shown. Using density functional theory (DFT) calculations, it is found that [...] Read more.

The character and degree of influence of carboxylic acid groups (COOH) on the sensory properties (particularly on the chemoresistive response) of a gas sensor based on zigzag and armchair graphene nanoribbons are shown. Using density functional theory (DFT) calculations, it is found that it is more promising to use a carboxylated zigzag nanoribbon as a sensor element. The chemoresistive response of these nanoribbons is higher than uncarboxylated and carboxylated nanoribbons. It is also revealed that the wet nanoribbon reacts more noticeably to the adsorption of ammonia. In this case, carboxyl groups primarily attract water molecules, which are energetically favorable to land precisely on these regions and then on the nanoribbon’s basal surface. Moreover, the COOH groups with water are adsorption centers for ammonia molecules. That is, the carboxylated zigzag nanoribbon can be the most promising. Full article

(This article belongs to the Special Issue Gustatory and Olfactory Sensing Technologies and Applications)

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39 pages, 3803 KiB

Open AccessEditor’s ChoiceReview

Microneedle Arrays for Sampling and Sensing Skin Interstitial Fluid

by Navid Kashaninejad, Ahmed Munaz, Hajar Moghadas, Sharda Yadav, Muhammad Umer and Nam-Trung Nguyen

Chemosensors 2021, 9(4), 83; https://doi.org/10.3390/chemosensors9040083 - 16 Apr 2021

Cited by 69 | Viewed by 11675

Abstract

Dermal interstitial fluid (ISF) is a novel source of biomarkers that can be considered as an alternative to blood sampling for disease diagnosis and treatment. Nevertheless, in vivo extraction and analysis of ISF are challenging. On the other hand, microneedle (MN) technology can [...] Read more.

Dermal interstitial fluid (ISF) is a novel source of biomarkers that can be considered as an alternative to blood sampling for disease diagnosis and treatment. Nevertheless, in vivo extraction and analysis of ISF are challenging. On the other hand, microneedle (MN) technology can address most of the challenges associated with dermal ISF extraction and is well suited for long-term, continuous ISF monitoring as well as in situ detection. In this review, we first briefly summarise the different dermal ISF collection methods and compare them with MN methods. Next, we elaborate on the design considerations and biocompatibility of MNs. Subsequently, the fabrication technologies of various MNs used for dermal ISF extraction, including solid MNs, hollow MNs, porous MNs, and hydrogel MNs, are thoroughly explained. In addition, different sensing mechanisms of ISF detection are discussed in detail. Subsequently, we identify the challenges and propose the possible solutions associated with ISF extraction. A detailed investigation is provided for the transport and sampling mechanism of ISF in vivo. Also, the current in vitro skin model integrated with the MN arrays is discussed. Finally, future directions to develop a point-of-care (POC) device to sample ISF are proposed. Full article

(This article belongs to the Section Analytical Methods, Instrumentation and Miniaturization)

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15 pages, 2501 KiB

Open AccessArticle

Electrochemical Approach to Detection of Chlorophene in Water Catalyzed by a Laccase Modified Gold Electrode

by Gabriela Elizabeth Quintanilla-Villanueva, Donato Luna-Moreno, Araceli Sánchez-Álvarez, Juan Francisco Villarreal-Chiu, José Manuel Rodríguez-Delgado and Melissa Marlene Rodríguez-Delgado

Chemosensors 2021, 9(4), 82; https://doi.org/10.3390/chemosensors9040082 - 16 Apr 2021

Cited by 1 | Viewed by 2788

Abstract

Despite the increasing number of reports that relate antimicrobial chlorophene (CP) with health and environmental effects, few studies have addressed biosensing technologies to detect this threat. This work proposed an electrochemical approach for the detection of CP using laccase enzymes as an alternative [...] Read more.

Despite the increasing number of reports that relate antimicrobial chlorophene (CP) with health and environmental effects, few studies have addressed biosensing technologies to detect this threat. This work proposed an electrochemical approach for the detection of CP using laccase enzymes as an alternative recognition element immobilized onto thin-film gold electrodes. The electrochemical parameters of the detection method, under controlled conditions, resulted in a limit of detection (0.14 ± 0.06 mg L⁻¹) and quantification (0.48 ± 0.04 mg L⁻¹) that agreed with concentrations of CP that already had been measured in natural water samples. Nevertheless, during the analysis of natural river water samples, the provided method suffered a drawback due to matrix effects reflected in the obtained recovery percentage, the value of which was 62.0 ± 2.4% compared to the 101.3 ± 3.5% obtained by the HPLC reference method. These detrimental effects were mainly attributed to organic matter, SO4-2, and Cl- present in river samples. Full article

(This article belongs to the Special Issue Colorimetric Sensors and Biosensors for Healthcare, Food Safety, Environmental Monitoring and Biosecurity Applications)

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19 pages, 5621 KiB

Open AccessArticle

Efficient Oxidase Biosensors Based on Bioelectrocatalytic Surfaces of Electrodeposited Ferrocenyl Polycyclosiloxanes—Pt Nanoparticles

by Alvaro Boluda, Carmen M. Casado, Beatriz Alonso and M. Pilar García Armada

Chemosensors 2021, 9(4), 81; https://doi.org/10.3390/chemosensors9040081 - 15 Apr 2021

Cited by 8 | Viewed by 2604

Abstract

The in-situ synthesis of catalytic surfaces with metallic nanoparticles must overcome the issues related to particle aggregation and polydispersity in the particle size. This work achieves it by using two electrodeposited ferrocenyl polycyclosiloxane polymers (MFPP and FPP) as templates for electro-synthesize Pt nanoparticles [...] Read more.

The in-situ synthesis of catalytic surfaces with metallic nanoparticles must overcome the issues related to particle aggregation and polydispersity in the particle size. This work achieves it by using two electrodeposited ferrocenyl polycyclosiloxane polymers (MFPP and FPP) as templates for electro-synthesize Pt nanoparticles (PtNPS). In addition, this new electrode surface combines two efficient electrocatalysts: Ferrocene and Pt nanoparticles, with synergistic biocatalytic properties that constitute an electrocatalytic framework for the covalent immobilization of xanthine oxidase. In this work, we present the results of the kinetic, electrochemical and analytical studies of the prepared electrodes. These results showed that the PtNPs/FPP system is the best bioelectrocatalytic surface and improves other more complex xanthine oxidase devices based on the hydrogen peroxide oxidation, allowing the use of lower measuring potential with good sensitivity, wider linear ranges and low detection limits. In addition, this electrode provides the novelty of allowing the measurement of xanthine through the enzymatic consumption of oxygen at potential −0.1 V with a sensitivity of 1.10 A M⁻¹ cm⁻², linear ranges of 0.01–0.1 and 0.1–1.4 mM, low detection limit (48 nM) and long-term stability. The new device has been successfully applied to the determination of xanthine in fish meat. Full article

(This article belongs to the Special Issue Detection of Analytes with Medical Relevance Using Porphyrins and/or Graphene-Based Materials)

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15 pages, 2898 KiB

Open AccessArticle

Quartz Crystal Microbalance (QCM) Based Biosensor Functionalized by HER2/neu Antibody for Breast Cancer Cell Detection

by Merve Yılmaz, Monireh Bakhshpour, Ilgım Göktürk, Ayşe Kevser Pişkin and Adil Denizli

Chemosensors 2021, 9(4), 80; https://doi.org/10.3390/chemosensors9040080 - 14 Apr 2021

Cited by 18 | Viewed by 4353

Abstract

The heterogeneity and metastatic features of cancer cells lead to a great number of casualties in the world. Additionally, its diagnosis as well as its treatment is highly expensive. Therefore, development of simple but effective diagnostic systems which detect the molecular markers of [...] Read more.

The heterogeneity and metastatic features of cancer cells lead to a great number of casualties in the world. Additionally, its diagnosis as well as its treatment is highly expensive. Therefore, development of simple but effective diagnostic systems which detect the molecular markers of cancer is of great importance. The molecular changes on cancer cell membranes serve as targets, such as HER2/neu receptor which is detected on the surface of highly metastatic breast cancer cells. We have aimed to develop a specific and simple quartz crystal microbalance (QCM)-based system to identify HER2/neu expressing breast cancer cells via a receptor-specific monoclonal antibody. First, the QCM chip was coated with polymeric nanoparticles composed of hydroxyethylmethacrylate (HEMA) and ethylene glycol dimethacrylate (EDMA). The nanoparticle coated QCM chip was then functionalized by binding of HER2/neu antibody. The breast cancer cells with/without HER2/neu receptor expression, namely, SKBR3, MDA-MB 231 and also mouse fibroblasts were passed over the chip at a rate of 10–500 cells/mL and the mass changes (Δm) on cell/cm² unit surface of sensor were detected in real-time. The detection limit of the system was 10 cells/mL. Thus, this QCM-based HER2/neu receptor antibody functionalized system might be used effectively in the detection of HER2/neu expressing SKBR3 breast cancer cells. Full article

(This article belongs to the Special Issue Recent Advances in Quartz Crystal Microbalance-Based Sensor Applications)

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26 pages, 5315 KiB

Open AccessEditor’s ChoiceReview

Application of PEDOT:PSS and Its Composites in Electrochemical and Electronic Chemosensors

by Nan Gao, Jiarui Yu, Qingyun Tian, Jiangfan Shi, Miao Zhang, Shuai Chen and Ling Zang

Chemosensors 2021, 9(4), 79; https://doi.org/10.3390/chemosensors9040079 - 13 Apr 2021

Cited by 84 | Viewed by 12150

Abstract

Poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) is a highly important and attractive conducting polymer as well as commercially available in organic electronics, including electrochemical and electronic chemosensors, due to its unique features such as excellent solution-fabrication capability and miscibility, high and controllable conductivity, excellent chemical and [...] Read more.

Poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) is a highly important and attractive conducting polymer as well as commercially available in organic electronics, including electrochemical and electronic chemosensors, due to its unique features such as excellent solution-fabrication capability and miscibility, high and controllable conductivity, excellent chemical and electrochemical stability, good optical transparency and biocompatibility. In this review, we present a comprehensive overview of the recent research progress of PEDOT:PSS and its composites, and the application in electrochemical and electronic sensors for detecting liquid-phase or gaseous chemical analytes, including inorganic or organic ions, pH, humidity, hydrogen peroxide (H₂O₂), ammonia (NH₃), CO, CO₂, NO₂, and organic solvent vapors like methanol, acetone, etc. We will discuss in detail the structural, architectural and morphological optimization of PEDOT:PSS and its composites with other additives, as well as the fabrication technology of diverse sensor systems in response to a wide range of analytes in varying environments. At the end of the review will be given a perspective summary covering both the key challenges and potential solutions in the future research of PEDOT:PSS-based chemosensors, especially those in a flexible or wearable format. Full article

(This article belongs to the Special Issue Chemical and Biosensors: A Theme Issue in Honor of Professor Otto S. Wolfbeis)

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15 pages, 4307 KiB

Open AccessArticle

Drift Compensation on Massive Online Electronic-Nose Responses

by Jianhua Cao, Tao Liu, Jianjun Chen, Tao Yang, Xiuxiu Zhu and Hongjin Wang

Chemosensors 2021, 9(4), 78; https://doi.org/10.3390/chemosensors9040078 - 11 Apr 2021

Cited by 14 | Viewed by 2978

Abstract

Gas sensor drift is an important issue of electronic nose (E-nose) systems. This study follows this concern under the condition that requires an instant drift compensation with massive online E-nose responses. Recently, an active learning paradigm has been introduced to such condition. However, [...] Read more.

Gas sensor drift is an important issue of electronic nose (E-nose) systems. This study follows this concern under the condition that requires an instant drift compensation with massive online E-nose responses. Recently, an active learning paradigm has been introduced to such condition. However, it does not consider the “noisy label” problem caused by the unreliability of its labeling process in real applications. Thus, we have proposed a class-label appraisal methodology and associated active learning framework to assess and correct the noisy labels. To evaluate the performance of the proposed methodologies, we used the datasets from two E-nose systems. The experimental results show that the proposed methodology helps the E-noses achieve higher accuracy with lower computation than the reference methods do. Finally, we can conclude that the proposed class-label appraisal mechanism is an effective means of enhancing the robustness of active learning-based E-nose drift compensation. Full article

(This article belongs to the Collection State-of-the-Art in Chemical Sensors Modelling and Theoretical Statements)

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14 pages, 4323 KiB

Open AccessArticle

Quantitative Determination of the Surface Distribution of Supported Metal Nanoparticles: A Laser Ablation–ICP–MS Based Approach

by Davide Spanu, Gilberto Binda, Marcello Marelli, Laura Rampazzi, Sandro Recchia and Damiano Monticelli

Chemosensors 2021, 9(4), 77; https://doi.org/10.3390/chemosensors9040077 - 10 Apr 2021

Cited by 3 | Viewed by 2803

Abstract

A laser ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS) based method is proposed for the quantitative determination of the spatial distribution of metal nanoparticles (NPs) supported on planar substrates. The surface is sampled using tailored ablation patterns and the data are used to define three-dimensional [...] Read more.

A laser ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS) based method is proposed for the quantitative determination of the spatial distribution of metal nanoparticles (NPs) supported on planar substrates. The surface is sampled using tailored ablation patterns and the data are used to define three-dimensional functions describing the spatial distribution of NPs. The volume integrals of such interpolated surfaces are calibrated to obtain the mass distribution of Ag NPs by correlation with the total mass of metal as determined by metal extraction and ICP–MS analysis. Once this mass calibration is carried out on a sacrificial sample, quantifications can be performed over multiple samples by a simple micro-destructive LA–ICP–MS analysis without requiring the extraction/dissolution of metal NPs. The proposed approach is here tested using a model sample consisting of a low-density polyethylene (LDPE) disk decorated with silver NPs, achieving high spatial resolution over cm²-sized samples and very high sensitivity. The developed method is accordingly a useful analytical tool for applications requiring both the total mass and the spatial distribution of metal NPs to be determined without damaging the sample surface (e.g., composite functional materials and NPs, decorated catalysts or electrodic materials). Full article

(This article belongs to the Section Materials for Chemical Sensing)

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14 pages, 1716 KiB

Open AccessArticle

Flexible Potentiometric Sensor System for Non-Invasive Determination of Antioxidant Activity of Human Skin: Application for Evaluating the Effectiveness of Phytocosmetic Products

by Aleksey V. Tarasov, Ekaterina I. Khamzina, Maria A. Bukharinova and Natalia Yu. Stozhko

Chemosensors 2021, 9(4), 76; https://doi.org/10.3390/chemosensors9040076 - 9 Apr 2021

Cited by 6 | Viewed by 3151

Abstract

In contemporary bioanalysis, monitoring the antioxidant activity (AOA) of the human skin is used to assess stresses, nutrition, cosmetics, and certain skin diseases. Non-invasive methods for skin AOA monitoring have certain advantages over invasive methods, namely cost-effectiveness, lower labor intensity, reduced risk of [...] Read more.

In contemporary bioanalysis, monitoring the antioxidant activity (AOA) of the human skin is used to assess stresses, nutrition, cosmetics, and certain skin diseases. Non-invasive methods for skin AOA monitoring have certain advantages over invasive methods, namely cost-effectiveness, lower labor intensity, reduced risk of infection, and obtaining results in the real-time mode. This study presents a new flexible potentiometric sensor system (FPSS) for non-invasive determination of the human skin AOA, which is based on flexible film electrodes (FFEs) and membrane containing a mediator ([Fe(CN)₆]^3–/4–). Low-cost available materials and scalable technologies were used for FFEs manufacturing. The indicator FFE was fabricated based on polyethylene terephthalate (PET) film and carbon veil (CV) by single-sided hot lamination. The reference FFE was fabricated based on PET film and silver paint by using screen printing, which was followed by the electrodeposition of precipitate containing a mixture of silver chloride and silver ferricyanide (SCSF). The three-electrode configuration of the FPSS, including two indicator FFEs (CV/PET) and one reference FFE (SCSF/Ag/PET), has been successfully used for measuring the skin AOA and evaluating the impact of phytocosmetic products. FPSS provides reproducible (RSD ≤ 7%) and accurate (recovery of antioxidants is almost 100%) results, which allows forecasting its broad applicability in human skin AOA monitoring as well as for evaluating the effectiveness of topically and orally applied antioxidants. Full article

(This article belongs to the Special Issue Electrochemical Sensors for Antioxidant/Oxidant Activity Monitoring)

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16 pages, 7988 KiB

Open AccessArticle

Visible and Near-Infrared Image Acquisition and Fusion for Night Surveillance

by Hyuk-Ju Kwon and Sung-Hak Lee

Chemosensors 2021, 9(4), 75; https://doi.org/10.3390/chemosensors9040075 - 8 Apr 2021

Cited by 13 | Viewed by 3741

Abstract

Image fusion combines images with different information to create a single, information-rich image. The process may either involve synthesizing images using multiple exposures of the same scene, such as exposure fusion, or synthesizing images of different wavelength bands, such as visible and near-infrared [...] Read more.

Image fusion combines images with different information to create a single, information-rich image. The process may either involve synthesizing images using multiple exposures of the same scene, such as exposure fusion, or synthesizing images of different wavelength bands, such as visible and near-infrared (NIR) image fusion. NIR images are frequently used in surveillance systems because they are beyond the narrow perceptual range of human vision. In this paper, we propose an infrared image fusion method that combines high and low intensities for use in surveillance systems under low-light conditions. The proposed method utilizes a depth-weighted radiance map based on intensities and details to enhance local contrast and reduce noise and color distortion. The proposed method involves luminance blending, local tone mapping, and color scaling and correction. Each of these stages is processed in the LAB color space to preserve the color attributes of a visible image. The results confirm that the proposed method outperforms conventional methods. Full article

(This article belongs to the Special Issue Colorimetric Sensors and Biosensors for Healthcare, Food Safety, Environmental Monitoring and Biosecurity Applications)

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12 pages, 12970 KiB

Open AccessArticle

Amperometric L-Lactate Biosensor Based upon a Gold Nanoparticles/Reduced Graphene Oxide/Polyallylamine Hydrochloride Modified Screen-Printed Graphite Electrode

by Oana-Maria Istrate, Lucian Rotariu and Camelia Bala

Chemosensors 2021, 9(4), 74; https://doi.org/10.3390/chemosensors9040074 - 8 Apr 2021

Cited by 26 | Viewed by 4152

Abstract

This work describes a novel L-lactate biosensor based on the immobilization of L-lactate dehydrogenase enzyme on the screen-printed electrode modified with a ternary composite based on gold nanoparticles, electrochemically-reduced graphene oxide, and poly (allylamine hydrochloride). The enzyme was stabilized by crosslinking with glutaraldehyde. [...] Read more.

This work describes a novel L-lactate biosensor based on the immobilization of L-lactate dehydrogenase enzyme on the screen-printed electrode modified with a ternary composite based on gold nanoparticles, electrochemically-reduced graphene oxide, and poly (allylamine hydrochloride). The enzyme was stabilized by crosslinking with glutaraldehyde. Applied working potential, pH and NAD⁺ concentration were optimized. The biosensor reports a specific sensitivity of 1.08 µA/mM·cm² in a range up to 3 mM L-lactic acid with a detection limit of 1 µM. The operational and long-term stability as well as good selectivity allowed the L-lactic acid measurement in dairy products and wine samples. Full article

(This article belongs to the Section (Bio)chemical Sensing)

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11 pages, 2654 KiB

Open AccessArticle

Determination of Uric Acid in Artificial Saliva with Compact AMP3291 Reader and Au Nanoparticles Modified Electrode

by Jessica Piedras, Rocio B. Dominguez and Juan Manuel Gutiérrez

Chemosensors 2021, 9(4), 73; https://doi.org/10.3390/chemosensors9040073 - 7 Apr 2021

Cited by 18 | Viewed by 3866

Abstract

Uric acid (UA) is a residual product of purines in the body and has been proposed as a valuable biomarker for Diabetes Mellitus, renal disorder, hypertension and preeclampsia. This work presents a sensing platform for nonenzymatic UA detection using a screen-printed electrode [...] Read more.

Uric acid (UA) is a residual product of purines in the body and has been proposed as a valuable biomarker for Diabetes Mellitus, renal disorder, hypertension and preeclampsia. This work presents a sensing platform for nonenzymatic UA detection using a screen-printed electrode modified with gold nanoparticles (SPE-AuNps) operated with the compact and low-cost amperometric reader AMP3291. This laboratory-made instrument was designed using the analog front end LMP91000 and the microcontroller ESP32; the operational parameters like working potential, acquisition time and dynamic measuring range were configured for UA detection. The whole sensing system (AMP3291+ SPE-AuNps) was evaluated for nonenzymatic sensing of UA, showing a fast response time of 3.5 s, a sensitivity of 0.022 μA·μM⁻¹, a linear range from 20 to 200 μM (R² = 0.993) and a limit of detection of 11.91 μM. Throughout, a piece of commercial equipment was used for validation and noticeably the measurements with the AMP3291-based platform showed improved performance, indicating the feasibility of the developed instrument for UA monitoring and potentially for in situ decentralized applications. Finally, artificial saliva was used as model medium exhibiting interesting analytical parameters, encouraging to consider the reported system as a potentially valuable tool for monitoring UA for clinical applications in resource-limited settings. Full article

(This article belongs to the Section Analytical Methods, Instrumentation and Miniaturization)

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46 pages, 1425 KiB

Open AccessReview

Antioxidant Determination with the Use of Carbon-Based Electrodes

by Aurelia Magdalena Pisoschi, Aneta Pop, Florin Iordache, Loredana Stanca, Liviu Bilteanu and Andreea Iren Serban

Chemosensors 2021, 9(4), 72; https://doi.org/10.3390/chemosensors9040072 - 1 Apr 2021

Cited by 13 | Viewed by 4520

Abstract

Antioxidants are compounds that prevent or delay the oxidation process, acting at a much smaller concentration, in comparison to that of the preserved substrate. Primary antioxidants act as scavenging or chain breaking antioxidants, delaying initiation or interrupting propagation step. Secondary antioxidants quench singlet [...] Read more.

Antioxidants are compounds that prevent or delay the oxidation process, acting at a much smaller concentration, in comparison to that of the preserved substrate. Primary antioxidants act as scavenging or chain breaking antioxidants, delaying initiation or interrupting propagation step. Secondary antioxidants quench singlet oxygen, decompose peroxides in non-radical species, chelate prooxidative metal ions, inhibit oxidative enzymes. Based on antioxidants’ reactivity, four lines of defense have been described: Preventative antioxidants, radical scavengers, repair antioxidants, and antioxidants relying on adaptation mechanisms. Carbon-based electrodes are largely employed in electroanalysis given their special features, that encompass large surface area, high electroconductivity, chemical stability, nanostructuring possibilities, facility of manufacturing at low cost, and easiness of surface modification. Largely employed methods encompass voltammetry, amperometry, biamperometry and potentiometry. Determination of key endogenous and exogenous individual antioxidants, as well as of antioxidant activity and its main contributors relied on unmodified or modified carbon electrodes, whose analytical parameters are detailed. Recent advances based on modifications with carbon-nanotubes or the use of hybrid nanocomposite materials are described. Large effective surface area, increased mass transport, electrocatalytical effects, improved sensitivity, and low detection limits in the nanomolar range were reported, with applications validated in complex media such as foodstuffs and biological samples. Full article

(This article belongs to the Special Issue Electrochemical Sensors for Antioxidant/Oxidant Activity Monitoring)

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21 pages, 3292 KiB

Open AccessArticle

Hyperspectral Imaging to Characterize Table Grapes

by Mario Gabrielli, Vanessa Lançon-Verdier, Pierre Picouet and Chantal Maury

Chemosensors 2021, 9(4), 71; https://doi.org/10.3390/chemosensors9040071 - 1 Apr 2021

Cited by 25 | Viewed by 3968

Abstract

Table grape quality is of importance for consumers and thus for producers. Its objective quality is usually determined by destructive methods mainly based on sugar content. This study proposed to evaluate the possibility of hyperspectral imaging to characterize table grapes quality through its [...] Read more.

Table grape quality is of importance for consumers and thus for producers. Its objective quality is usually determined by destructive methods mainly based on sugar content. This study proposed to evaluate the possibility of hyperspectral imaging to characterize table grapes quality through its sugar (TSS), total flavonoid (TF), and total anthocyanin (TA) contents. Different data pre-treatments (WD, SNV, and 1st and 2nd derivative) and different methods were tested to get the best prediction models: PLS with full spectra and then Multiple Linear Regression (MLR) were realized after selecting the optimal wavelengths thanks to the regression coefficients (β-coefficients) and the Variable Importance in Projection (VIP) scores. All models were good at showing that hyperspectral imaging is a relevant method to predict sugar, total flavonoid, and total anthocyanin contents. The best predictions were obtained from optimal wavelength selection based on β-coefficients for TSS and from VIPs optimal wavelength windows using SNV pre-treatment for total flavonoid and total anthocyanin content. Thus, good prediction models were proposed in order to characterize grapes while reducing the data sets and limit the data storage to enable an industrial use. Full article

(This article belongs to the Section Analytical Methods, Instrumentation and Miniaturization)

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19 pages, 2693 KiB

Open AccessArticle

Electrospun Fibres of Chitosan/PVP for the Effective Chemotherapeutic Drug Delivery of 5-Fluorouracil

by Jamie J. Grant, Suresh C. Pillai, Tatiana S. Perova, Sarah Hehir, Steven J. Hinder, Marion McAfee and Ailish Breen

Chemosensors 2021, 9(4), 70; https://doi.org/10.3390/chemosensors9040070 - 31 Mar 2021

Cited by 48 | Viewed by 5386

Abstract

Electrospun nanofibrous mats consisting of chitosan (CS) and polyvinylpyrrolidone (PVP) were constructed. Tuning of solution and process parameters was performed and resulted in an electrospun system containing a 6:4 ratio of PVP:CS. This is a significant increase in the proportion of spun CS [...] Read more.

Electrospun nanofibrous mats consisting of chitosan (CS) and polyvinylpyrrolidone (PVP) were constructed. Tuning of solution and process parameters was performed and resulted in an electrospun system containing a 6:4 ratio of PVP:CS. This is a significant increase in the proportion of spun CS on the previously reported highest ratio PVP:CS blend. SEM analysis showed that the nanofibrous mats with 4 wt% CS/6 wt% PVP (sample E) comprised homogenous, uniform fibres with an average diameter of 0.569 μm. XPS analysis showed that the surface of the samples consisted of PVP. Raman and FTIR analysis revealed intermolecular interactions (via H-bonding) between PVP and CS. In FTIR spectra, the contribution of chitosan to CS/PVP complexes was shown by the downshift of the C=O band and by the linear increase in intensity of C-O stretching in CS. XPS analysis showed a smaller shift at the binding energy 531 eV, which relates to the amide of the acetylated functional groups. The obtained results demonstrate a sensitivity of Raman and FTIR tests to the presence of chitosan in PVP:CS blend. The chemotherapy drug 5-Fu was incorporated into the constructs and cell viability studies were performed. WST-8 viability assay showed that exposure of A549 human alveolar basal epithelial cells to 10 mg/mL 5-Fu loaded fibres was most effective at killing cells over 24 h. On the other hand, the constructs with loading of 1 mg/mL of drug were not efficient at killing A549 human alveolar basal epithelial cells. This study showed that CS/PVP/5-Fu constructs have potential in chemotherapeutic drug delivery systems. Full article

(This article belongs to the Special Issue Innovative Materials, Technologies, and Sensors)

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37 pages, 9766 KiB

Open AccessReview

Contribution of Nanomaterials to the Development of Electrochemical Aptasensors for the Detection of Antimicrobial Residues in Food Products

by Valérie Gaudin

Chemosensors 2021, 9(4), 69; https://doi.org/10.3390/chemosensors9040069 - 30 Mar 2021

Cited by 8 | Viewed by 3826

Abstract

The detection of antimicrobial residues in food products of animal origin is of utmost importance. Indeed antimicrobial residues could be present in animal derived food products because of animal treatments for curative purposes or from illegal use. The usual screening methods to detect [...] Read more.

The detection of antimicrobial residues in food products of animal origin is of utmost importance. Indeed antimicrobial residues could be present in animal derived food products because of animal treatments for curative purposes or from illegal use. The usual screening methods to detect antimicrobial residues in food are microbiological, immunological or physico-chemical methods. The development of biosensors to propose sensitive, cheap and quick alternatives to classical methods is constantly increasing. Aptasensors are one of the major trends proposed in the literature, in parallel with the development of immunosensors based on antibodies. The characteristics of electrochemical sensors (i.e., low cost, miniaturization, and portable instrumentation) make them very good candidates to develop screening methods for antimicrobial residues in food products. This review will focus on the recent advances in the development of electrochemical aptasensors for the detection of antimicrobial residues in food products. The contribution of nanomaterials to improve the performance characteristics of electrochemical aptasensors (e.g., Sensitivity, easiness, stability) in the last ten years, as well as signal amplification techniques will be highlighted. Full article

(This article belongs to the Special Issue Aptasensors: Applications in Life Science and Environmental Technology)

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15 pages, 16377 KiB

Open AccessArticle

A Deferasirox Derivative That Acts as a Multifaceted Platform for the Detection and Quantification of Fe³⁺

by Axel Steinbrueck, Adam C. Sedgwick, Suh-Mi Hwang, Sajal Sen, Michael Y. Zhao, Dan-Ying Huang, Daniel M. Knoll, Yu-Ying Wang and Jonathan L. Sessler

Chemosensors 2021, 9(4), 68; https://doi.org/10.3390/chemosensors9040068 - 30 Mar 2021

Cited by 1 | Viewed by 3597

Abstract

Here, we report that ExSO₃H, a synthetically accessible, water-soluble, non-toxic derivative of the clinical iron chelator deferasirox, acts as a colorimetric chemosensor that permits the detection and quantification of Fe³⁺ in aqueous samples at pH 2–5. In addition, we observed [...] Read more.

Here, we report that ExSO₃H, a synthetically accessible, water-soluble, non-toxic derivative of the clinical iron chelator deferasirox, acts as a colorimetric chemosensor that permits the detection and quantification of Fe³⁺ in aqueous samples at pH 2–5. In addition, we observed that a fluorescent turn-on response was produced when this chelator was allowed to interact with human serum albumin (HSA). This fluorescence was quenched in the presence of Fe³⁺, thus allowing us to monitor the presence of this biologically important metal cation via two independent methods. Full article

(This article belongs to the Special Issue Applications of Chemosensors in Real-World Sample Analysis)

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26 pages, 9119 KiB

Open AccessReview

Nanodiagnosis and Nanotreatment of Cardiovascular Diseases: An Overview

by Fakhara Sabir, Mahmood Barani, Mahwash Mukhtar, Abbas Rahdar, Magali Cucchiarini, Muhammad Nadeem Zafar, Tapan Behl and Simona Bungau

Chemosensors 2021, 9(4), 67; https://doi.org/10.3390/chemosensors9040067 - 30 Mar 2021

Cited by 34 | Viewed by 8427

Abstract

Cardiovascular diseases (CVDs) are the world’s leading cause of mortality and represent a large contributor to the costs of medical care. Although tremendous progress has been made for the diagnosis of CVDs, there is an important need for more effective early diagnosis and [...] Read more.

Cardiovascular diseases (CVDs) are the world’s leading cause of mortality and represent a large contributor to the costs of medical care. Although tremendous progress has been made for the diagnosis of CVDs, there is an important need for more effective early diagnosis and the design of novel diagnostic methods. The diagnosis of CVDs generally relies on signs and symptoms depending on molecular imaging (MI) or on CVD-associated biomarkers. For early-stage CVDs, however, the reliability, specificity, and accuracy of the analysis is still problematic. Because of their unique chemical and physical properties, nanomaterial systems have been recognized as potential candidates to enhance the functional use of diagnostic instruments. Nanomaterials such as gold nanoparticles, carbon nanotubes, quantum dots, lipids, and polymeric nanoparticles represent novel sources to target CVDs. The special properties of nanomaterials including surface energy and topographies actively enhance the cellular response within CVDs. The availability of newly advanced techniques in nanomaterial science opens new avenues for the targeting of CVDs. The successful application of nanomaterials for CVDs needs a detailed understanding of both the disease and targeting moieties. Full article

(This article belongs to the Special Issue Nanostructured Devices for Biochemical Sensing)

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15 pages, 3275 KiB

Open AccessArticle

Boosting Selectivity and Sensitivity to Biomarkers of Quantum Resistive Vapour Sensors Used for Volatolomics with Nanoarchitectured Carbon Nanotubes or Graphene Platelets Connected by Fullerene Junctions

by Sananda Nag, Mickaël Castro, Veena Choudhary and Jean-Francois Feller

Chemosensors 2021, 9(4), 66; https://doi.org/10.3390/chemosensors9040066 - 28 Mar 2021

Cited by 4 | Viewed by 3442

Abstract

Nanocarbon-based vapour sensors are increasingly used to make anticipated diagnosis of diseases by the analysis of volatile organic compound (VOC) biomarkers from the breath, i.e., volatolomics. However, given the tiny number of molecules to detect, usually only tens of parts per billion (ppb), [...] Read more.

Nanocarbon-based vapour sensors are increasingly used to make anticipated diagnosis of diseases by the analysis of volatile organic compound (VOC) biomarkers from the breath, i.e., volatolomics. However, given the tiny number of molecules to detect, usually only tens of parts per billion (ppb), increasing the sensitivity of polymer nanocomposite chemoresistive transducers is still a challenge. As the ability of these nanosensors to convert the interactions with chemical compounds into changes of resistance, depends on the variations of electronic transport through the percolated network of the conducting nanofillers, it is a key parameter to control. Actually, in this conducting architecture, the bottlenecks for electrons’ circulation are the interparticular junctions giving either ohmic conduction in the case of close contacts or quantum tunnelling when jumps though gaps are necessary. This in turn depends on a number of nanometric parameters such as the size and geometry of the nanofillers (spherical, cylindrical, lamellar), the method of structuring of the conductive architecture in the sensory system, etc. The present study focuses on the control of the interparticular junctions in quantum-resistive vapour sensors (vQRS) by nanoassembling pristine CNT or graphene covalently or noncovalently functionalized with spherical Buckminster fullerene (C₆₀) into a percolated network with a hybrid structure. It is found that this strategy allows us to significantly boost, both selectivity and sensitivity of pristine CNT or graphene-based transducers exposed to a set of seven biomarkers, ethanol, methanol, acetone, chloroform, benzene, toluene, cyclohexane and water. This is assumed to result from the spherical fullerene acting on the electronic transport properties at the nanojunctions between the CNT or graphene nanofillers. Full article

(This article belongs to the Special Issue Nanocomposites Chemical Sensors)

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11 pages, 3631 KiB

Open AccessCommunication

A Novel Thiosemicarbazide-Based Fluorescent Chemosensor for Hypochlorite in Near-Perfect Aqueous Solution and Zebrafish

by Minji Lee, Donghwan Choe, Soyoung Park, Hyeongjin Kim, Soomin Jeong, Ki-Tae Kim and Cheal Kim

Chemosensors 2021, 9(4), 65; https://doi.org/10.3390/chemosensors9040065 - 28 Mar 2021

Cited by 6 | Viewed by 3406

Abstract

A novel thiosemicarbazide-based fluorescent sensor (AFC) was developed. It was successfully applied to detect hypochlorite (ClO⁻) with fluorescence quenching in bis-tris buffer. The limit of detection of AFC for ClO⁻ was analyzed to be 58.7 μM. Importantly, AFC [...] Read more.

A novel thiosemicarbazide-based fluorescent sensor (AFC) was developed. It was successfully applied to detect hypochlorite (ClO⁻) with fluorescence quenching in bis-tris buffer. The limit of detection of AFC for ClO⁻ was analyzed to be 58.7 μM. Importantly, AFC could be employed as an efficient and practical fluorescent sensor for ClO⁻ in water sample and zebrafish. Moreover, AFC showed a marked selectivity to ClO⁻ over varied competitive analytes with reactive oxygen species. The detection process of AFC to ClO⁻ was illustrated by UV–visible and fluorescent spectroscopy and electrospray ionization–mass spectrometry (ESI–MS). Full article

(This article belongs to the Section Optical Chemical Sensors)

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38 pages, 12187 KiB

Open AccessReview

Trends in the Implementation of Advanced Plasmonic Materials in Optical Fiber Sensors (2010–2020)

by María Elena Martínez-Hernández, Pedro J. Rivero, Javier Goicoechea and Francisco J. Arregui

Chemosensors 2021, 9(4), 64; https://doi.org/10.3390/chemosensors9040064 - 27 Mar 2021

Cited by 16 | Viewed by 4557

Abstract

In recent years, the interaction between light and metallic films have been proven to be a highly powerful tool for optical sensing applications. We have witnessed the development of highly sensitive commercial devices based on Surface Plasmon Resonances. There has been continuous effort [...] Read more.

In recent years, the interaction between light and metallic films have been proven to be a highly powerful tool for optical sensing applications. We have witnessed the development of highly sensitive commercial devices based on Surface Plasmon Resonances. There has been continuous effort to integrate this plasmonic sensing technology using micro and nanofabrication techniques with the optical fiber sensor world, trying to get better, smaller and cost-effective high performance sensing solutions. In this work, we present a review of the latest and more relevant scientific contributions to the optical fiber sensors field using plasmonic materials over the last decade. The combination of optical fiber technology with metallic micro and nanostructures that allow plasmonic interactions have opened a complete new and promising field of study. We review the main advances in the integration of such metallic micro/nanostructures onto the optical fibers, discuss the most promising fabrication techniques and show the new trends in physical, chemical and biological sensing applications. Full article

(This article belongs to the Section Optical Chemical Sensors)

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14 pages, 4160 KiB

Open AccessArticle

A Sensitive and Portable Deep-UV Absorbance Detector with a Microliter Gas Cell Compatible with Micro GC

by Sulaiman Khan, David Newport and Stéphane Le Calvé

Chemosensors 2021, 9(4), 63; https://doi.org/10.3390/chemosensors9040063 - 27 Mar 2021

Cited by 5 | Viewed by 3141

Abstract

Deep-UV absorption spectrometry for detection of toxic airborne gases, for instance, Benzene, Toluene, Ethylbenzene, and Xylenes (BTEX) has drawn considerable attention owing to its high sensitivity and reliability. However, the development of a deep-UV absorbance detector having good sensitivity, portability, and a low-volume [...] Read more.

Deep-UV absorption spectrometry for detection of toxic airborne gases, for instance, Benzene, Toluene, Ethylbenzene, and Xylenes (BTEX) has drawn considerable attention owing to its high sensitivity and reliability. However, the development of a deep-UV absorbance detector having good sensitivity, portability, and a low-volume gas cell with applicability for a micro Gas Chromatography (μGC) is challenging. Herein we present a novel, self-referenced, and portable deep-UV absorbance detector with a microliter (275 μL) gas cell having minimal dead volume. It has excellent compatibility with μGC for detection of individual BTEX components in a mixed sample at a sub-ppm level. The design consists of the latest, portable, and cost-effective optical and electronic components, i.e., deep-UV LED, hollow-core waveguide, and photodiodes. The detector directly measures the absorbance values in volts using an integrated circuit with a log-ratio amplifier. The prototype was tested with direct injection of toluene-N₂ (1.5 ppm to 50 ppm) and good linearity (R² = 0.99) with a limit of detection of 196 ppb was obtained. The absorbance detector with μGC setup was tested with a BTEX mixture in N₂ at different GC column temperatures. All the BTEX species were sequentially separated and detected with an individual peak for a concentration range of 2.5 ppm to 10 ppm. Full article

(This article belongs to the Special Issue Advances in Analytical Systems for Gaseous Mixture)

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12 pages, 1213 KiB

Open AccessArticle

Bioanalytical Detection of Steroid Abuse in Sports Based on the Androgenic Activity Measurement

by Pilar Martín-Escudero, Jesus A. Muñoz-Guerra, Soledad Vargas García-Tenorio, Ester Serrano-Garde, Ana Belén Soldevilla-Navarro, Nuria Cortes-Carrillo, Mercedes Galindo-Canales, Nayade del Prado, Manuel Fuentes-Ferrer, Cristina Fernández-Pérez, Peter Alexander Behnisch and Abraham Brouwer

Chemosensors 2021, 9(4), 62; https://doi.org/10.3390/chemosensors9040062 - 26 Mar 2021

Cited by 1 | Viewed by 3584

Abstract

The anabolic androgenic steroids (AAS) are the most frequently consumed performance enhancing drugs (PED) in sports. In the anti-doping field, the detection of AAS is carried out by the analysis of the athlete’s urine using methodologies based on liquid/gas chromatography-mass spectrometry. Unfortunately, the [...] Read more.

The anabolic androgenic steroids (AAS) are the most frequently consumed performance enhancing drugs (PED) in sports. In the anti-doping field, the detection of AAS is carried out by the analysis of the athlete’s urine using methodologies based on liquid/gas chromatography-mass spectrometry. Unfortunately, the detection of unknown compounds is not possible. BDS’s AR CALUX^® bio detection technology was studied as an indirect method to detect the administration of a single dose of testosterone (T). Twelve T and placebo single dose administered men volunteers underwent a triple-blind crossover clinical trial. The UGT2B17 deletion was present among the volunteers and evenly distributed in heterozygous (ins/del), wild-type homozygous (ins/ins), and mutated homozygous (del/del) groups. A significant statistical difference in terms of bioluminescence was observed after the testosterone (T) administration for the three types of polymorphic groups. The ratio of means between the pre- and post-T administration periods, depending on the type of polymorphism, was in group ins/ins 3.31 (CI. 95%: 2.07–5.29), group ins/del 4.15 (CI 95%: 3.05–5.67), and group del/del 2.89 (CI 95%: 2.42–3.46). The results of the study are very promising, as they may offer us the possibility of designing a detection approach that, based on intra-individual monitoring of androgenic values, in the UGT2B17 deletion type. Full article

(This article belongs to the Section Analytical Methods, Instrumentation and Miniaturization)

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13 pages, 3494 KiB

Open AccessArticle

Silver Inkjet-Printed Electrode on Paper for Electrochemical Sensing of Paraquat

by Patricia Batista Deroco, Dagwin Wachholz Junior and Lauro Tatsuo Kubota

Chemosensors 2021, 9(4), 61; https://doi.org/10.3390/chemosensors9040061 - 25 Mar 2021

Cited by 28 | Viewed by 5380

Abstract

The use of fully printed electrochemical devices has gained more attention for the monitoring of clinical, food, and environmental analytes due to their low cost, great reproducibility, and versatility characteristics, serving as an important technology for commercial application. Therefore, a paper-based inkjet-printed electrochemical [...] Read more.

The use of fully printed electrochemical devices has gained more attention for the monitoring of clinical, food, and environmental analytes due to their low cost, great reproducibility, and versatility characteristics, serving as an important technology for commercial application. Therefore, a paper-based inkjet-printed electrochemical system is proposed as a cost-effective analytical detection tool for paraquat. Chromatographic paper was used as the printing substrate due its sustainable and disposable characteristics, and an inkjet-printing system deposited the conductive silver ink with no further modification on the paper surface, providing a three-electrode system. The printed electrodes were characterized with scanning electron microscopy, cyclic voltammetry, and chronopotentiometry. The proposed sensor exhibited a large surface area, providing a powerful tool for paraquat detection due to its higher analytical signal. For the detection of paraquat, square-wave voltammetry was used, and the results showed a linear response range of 3.0–100 μM and a detection limit of 0.80 µM, along with the high repeatability and disposability of the sensor. The prepared sensors were also sufficiently selective against interference, and high accuracy (recovery range = 96.7–113%) was obtained when applied to samples (water, human serum, and orange juice), showing the promising applicability of fully printed electrodes for electrochemical monitoring. Full article

(This article belongs to the Special Issue Paper-Based Sensors and Microfluidic Devices)

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26 pages, 1908 KiB

Open AccessEditor’s ChoiceReview

A Review of Microfluidic Detection Strategies for Heavy Metals in Water

by Annija Lace and John Cleary

Chemosensors 2021, 9(4), 60; https://doi.org/10.3390/chemosensors9040060 - 24 Mar 2021

Cited by 40 | Viewed by 8717

Abstract

Heavy metal pollution of water has become a global issue and is especially problematic in some developing countries. Heavy metals are toxic to living organisms, even at very low concentrations. Therefore, effective and reliable heavy metal detection in environmental water is very important. [...] Read more.

Heavy metal pollution of water has become a global issue and is especially problematic in some developing countries. Heavy metals are toxic to living organisms, even at very low concentrations. Therefore, effective and reliable heavy metal detection in environmental water is very important. Current laboratory-based methods used for analysis of heavy metals in water require sophisticated instrumentation and highly trained technicians, making them unsuitable for routine heavy metal monitoring in the environment. Consequently, there is a growing demand for autonomous detection systems that could perform in situ or point-of-use measurements. Microfluidic detection systems, which are defined by their small size, have many characteristics that make them suitable for environmental analysis. Some of these advantages include portability, high sample throughput, reduced reagent consumption and waste generation, and reduced production cost. This review focusses on developments in the application of microfluidic detection systems to heavy metal detection in water. Microfluidic detection strategies based on optical techniques, electrochemical techniques, and quartz crystal microbalance are discussed. Full article

(This article belongs to the Special Issue Colorimetric Sensors and Biosensors for Healthcare, Food Safety, Environmental Monitoring and Biosecurity Applications)

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11 pages, 2129 KiB

Open AccessEditor’s ChoiceArticle

Electrochemical Detection of Prostate Cancer Biomarker PCA3 Using Specific RNA-Based Aptamer Labelled with Ferrocene

by Alexei Nabok, Hisham Abu-Ali, Sarra Takita and David P. Smith

Chemosensors 2021, 9(4), 59; https://doi.org/10.3390/chemosensors9040059 - 24 Mar 2021

Cited by 26 | Viewed by 5219

Abstract

This paper reports on a feasibility study of electrochemical in-vitro detection of prostate cancer biomarker PCA3 (prostate cancer antigen 3) in direct assay with specific RNA aptamer labelled with a redox group (ferrocene) and immobilized on a screen-printed gold electrode surface. The cyclic [...] Read more.

This paper reports on a feasibility study of electrochemical in-vitro detection of prostate cancer biomarker PCA3 (prostate cancer antigen 3) in direct assay with specific RNA aptamer labelled with a redox group (ferrocene) and immobilized on a screen-printed gold electrode surface. The cyclic voltammograms and electrochemical impedance spectroscopy methods yield encouraging results on the detection of PCA3 in a range of concentrations from 1 μg/mL down to 0.1 ng/mL in buffer solutions. Both anodic and cathodic current values in cyclic voltammograms measurements and charge transfer resistance values in electrochemical impedance spectroscopy experiments correlate with the PCA3 concentration in the sample. Kinetics studies of the binding of the PCA3 to our aptamer demonstrated high specificity of the reaction with a characteristic affinity constant of approximately

4 \cdot 10^{- 10}

molar. The results of this work provide a background for the future development of novel, highly sensitive and cost-effective diagnostic methodologies for prostate cancer detection. Full article

(This article belongs to the Special Issue Electrochemical Immunosensor)

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Chemosensors, Volume 9, Issue 4 (April 2021) – 27 articles

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