Chemosensors, Volume 7, Issue 4 (December 2019) – 20 articles

Electrochemical sensors and biosensors have been proposed as fast and cost effective analytical tools, meeting the robustness and performance requirements for industrial process monitoring. In wine production, electrochemical biosensors have proven useful for monitoring critical parameters related to alcoholic fermentation (AF), malolactic fermentation (MLF), determining the impact of the various technological steps and treatments on wine quality, or assessing the differences due to wine age, grape variety, vineyard or geographical region. This review summarizes the current information on the voltamperometric biosensors developed for monitoring wine production with a focus on sensing concepts tested in industry-like settings and on the main quality parameters such as glucose, alcohol, malic and lactic acids, phenolic compounds and allergens. Recent progress featuring nanomaterial-enabled enhancement of sensor performance and applications based on screen-printed electrodes is emphasized. A case study presents the monitoring of alcoholic fermentation based on commercial biosensors adapted with minimal method development for the detection of glucose and phenolic compounds in wine and included in an automated monitoring system. The current challenges and perspectives for the wider application of electrochemical sensors in monitoring industrial processes such as wine production are discussed. Full article

The increasing demand for sensitive electrochemical sensors in various medical and industrial applications promotes the fabrication of novel sensing materials with improved electrocatalytic and analytical performances. This work deals with the development of a composite material based on gold nanoparticles (AuNPs) embedded in poly(3,4-ethylenedioxythiophene) (PEDOT) layer for electrochemical determination of caffeic acid (CA). CA is a phenolic compound with excellent antioxidant properties that is present in vegetables, fruits, and alcoholic and non-alcoholic beverages. Its analytical quantification is of great interest in food production monitoring and healthcare applications. Therefore, the development of sensitive analytical devices for CA monitoring is required. The AuNPs have been prepared in situ onto PEDOT coated glassy carbon electrode (GC) by means of an innovative procedure consisting on the use of a sinusoidal voltage (SV) superimposed on a constant potential. The physico-chemical properties of the PEDOT-AuNPs composite material were investigated by a range of techniques including cyclic voltammetry, electrochemical quartz crystal microbalance, and scanning electron microscopy. The glassy carbon electrode/poly(3,4-ethylenedioxythiophene)-gold nanoparticles-sinusoidal voltage (GC/PEDOT-AuNPs-SV) sensor exhibited good analytical performance toward the CA quantification with a linear response over a wide concentration range from 10 µM to 1 mM. In addition, the proposed GC/PEDOT-AuNPs-SV sensor was successfully applied in the determination of total polyphenols content expressed as equivalents of CA in juice samples. Full article

Hydrogen peroxide (H₂O₂) is an important molecule within the human body, but many of its roles in physiology and pathophysiology are not well understood. To better understand the importance of H₂O₂ in biological systems, it is essential that researchers are able to quantify this reactive species in various settings, including in vitro, ex vivo and in vivo systems. This review covers a broad range of H₂O₂ sensors that have been used in biological systems, highlighting advancements that have taken place since 2015. Full article

Research into optical fiber refractometers yielded remarkable results over the past decade. Numerous sensing schemes were proposed and demonstrated, which possessed different advantages while facing unique limitations. On top of their obvious applications in measuring refractive index changes of the ambient environment, several studies reported advanced applications of such sensors in heavy metal ion detection by means of surface coating of the refractometers with heavy metal ion sensitive materials. This paper surveys the effort these optical fiber metal ion sensors based on surface coated optical fiber refractometer, discusses different technologies and methods involved, and highlights recent notable advancements. Full article

The massive production of nanostructures with controlled features and high surface area is a challenging and timely task in view of developing effective materials for sensing and catalysis. Herein, functional ZnO nanostructures, named microflowers (MFs) have been prepared by a facile and rapid chemical bath deposition. ZnO MFs show an intriguing sheets-composed spheroidal shape, with diameters in the range 0.2–2.5 µm, whose formation is achieved by a complexing action by F in an aqueous solution of zinc nitrate hexahydrate and hexamethylenetetramine. The evolution of the physical and structural properties of the material, following post-deposition thermal annealing, has been investigated by scanning electron microscopy (SEM), energy dispersive X-ray analyses (EDX), photoluminescence (PL) and X-ray diffraction (XRD) techniques. The effectiveness of ZnO MFs in UV detection has also been tested to account for the potentiality of these nanostructures. Full article

Fluorescent amikacin modified nitrogen, sulfur co-doped carbon dots (amikacin modified N,S-CDs) were synthesized by a facile and low-cost one-step microwave-assisted specifically for selective detection of Gram-negative bacteria Escherichia coli (E. coli). Amikacin is a semi-synthetic amino glycoside antibiotic and it was employed in this study to increase the fluorescence response of N,S-CDs by providing binding ligand towards E. coli. The effect of thiourea content as the source of nitrogen and sulfur dopants was investigated prior to the preparation of amikacin modified N,S-CDs. The formation of amikacin modified N,S-CDs were characterized by using Fourier transform infrared (FTIR), X-ray diffraction (XRD), Transmission electron microscope (TEM), UV-Vis spectrophotometer, and spectrofluorometer. Amikacin modified N,S-CDs was identified to be successfully synthesized from the wavenumber shift of the C=O stretching mode. Amikacin modified N,S-CDs were amorphous with an average size of 7 nm. Fluorescence spectra showed that the highest intensity was obtained at thiourea content of 50% and amikacin mass of 25 mg. By comparing fluorescence responses of all the investigated amikacin modified N,S-CDs, the limit of detection (LOD) was attained by 25 mg amikacin modified N,S-CDs at 1.526 cfu mL⁻¹. Full article

We developed a new label-free biosensor technique for the detection of messenger ribonucleic acid (mRNA) that can be used in the prognosis and diagnosis of certain diseases. We observed a dependence of the negative dielectrophoresis (DEP) force applied to polystyrene microspheres (PMs) in conjugation with different types of mRNA and the frequency of the electric field produced by interdigitated microelectrodes. Since the frequency dependence of the negative DEP force is an effective transduction mechanism for the detection of mRNA, this sensing technology has the potential to be used in the diagnosis and identification of gene expression that is associated with various human disease. Full article

The paper presents the results of the study of the possibilities of using color metal complexes to detect the presence of chemical warfare agents (CWA) in liquid or aerosol form. Aluminon/Fe³⁺ and Eriochrome Cyanine R/Cu²⁺ coordination complexes and their ability to detect CWA in liquid phase are discussed. Detection systems have been demonstrated on instances of simple detection papers exposed to drops of real CWAs. Detection papers showed a positive response to G-series nerve agents and vesicant lewisite. Other liquid CWA do not interfere and the systems are also resistant to common organic solvents and a wide range of industrial chemicals. Full article

This study presents a bioelectric cell-based biosensor for the monitoring of the pyrethroid pesticide cypermethrin, a voltage-gated sodium channel blocker, in tobacco samples. For this purpose, neuroblastoma cells were used as biorecognition elements. The potential interference by the tobacco major alkaloid nicotine on the detection of cypermethrin was also studied. In addition, fluorescence microscopy revealed a specific pattern of neuroblastoma cell calcium efflux (Ca²⁺) after treatment with nicotine or cypermethrin. Finally, actual field-derived tobacco extracts were used for assessing matrix effects on the biosensor’s performance. The biosensor could detect cypermethrin in concentrations up to 1.5 μg mL⁻¹ without being influenced by the presence of nicotine and possibly other tobacco alkaloids. Though not selective for cypermethrin, the neuroblastoma-based biosensor system appears to be a promising alternative to laborious analysis methodologies for rapid, high throughput and cost-efficient screening of this pyrethroid in tobacco samples in the near future. Full article

In recent years, reagentless aptamer biosensors, named aptasensors, have shown significant advancements. Particularly, electrochemical aptasensors could change the field of biosensors in this era, where digitalization seems to be a common goal of many fields. Biomedical devices are integrating electronic technologies for detecting pathogens, biomolecules, small molecules, and ions, and the physical-chemical properties of nucleic acid aptamers makes them very interesting for these devices. Aptamers can be easily synthesized and functionalized with functional groups for immobilization and with redox chemical groups that allow for the conversion of molecular interactions into electrical signals. Furthermore, non-labeled aptamers have also been utilized. This review presents the current challenges involved in aptasensor architectures based on gold electrodes as transducers. Full article

Volatile organic compounds (VOCs) are among the most abundant air pollutants. Their high concentrations can adversely affect the human body, and therefore, early detection of VOCs is of outmost importance. Among the different VOCs, in this review paper we have focused our attention to the monitoring of acetaldehyde by chemiresistive gas sensors fabricated from nanostructured semiconducting metal oxides. These sensors can not only provide a high sensing signal for detection of acetaldehyde but also high thermal and mechanical stability along with a low price. This review paper is divided into three major sections. First, we will introduce acetaldehyde as an important VOC and the importance of its detection. Then, the fundamentals of chemiresistive gas sensors will be briefly presented, and in the last section, a survey of the literature on acetaldehyde gas sensors will be presented. The working mechanism of acetaldehyde sensors, their structures, and configurations are reviewed. Finally, the future development outlook and potential applications are discussed, giving a complete panoramic view for researchers working and interested in acetaldehyde detection for different purposes in many fundamental and applicative fields. Full article

While nucleic acid and protein analysis approaches continue to see significant breakthroughs, analytical strategies for glycan determination have by comparison seen slower technological advances. Here we provide a strategy for glycan probe development using an engineered lectin fusion that can be incorporated into various common pathology lab assay formats including Western blot and agglutination assays. In this proof of concept, we use the natural lectin, Pseudomonas fluorescens agglutinin (PFA), capable of binding core Man alpha(1-3)-Man alpha(1-6)-Man units, where this lectin has previously been shown to bind to the glycans presented by the gp120 coat protein of (HIV) Human Immunodeficiency Virus. In our strategy, we engineered the lectin to possess a fusion of the biotin mimetic tag equence of amino acids V-S-H-P-Q-A-P-F. With the glycan receptive PFA directly linked to the biotin mimic, we could facilitate a probe for various standard clinical assay formats by virtue of coupling to streptavidin-HRP (horseradish peroxidase) or streptavidin beads for Western blot and agglutination assays respectively. We found the PFA fusion retained low nanomolar affinity for gp120 by ELISA (Enzyme Linked Immunosorbent Assay) and microscale thermophoresis. This probe engineering strategy proved effective in the relevant assay formats that may now allow detection for the presence of glycans containing the core Man alpha(1-3)-Man alpha(1-6)-Man units recognized by PFA. Full article

The Wigner–Eckart theorem is used for considering the collective effects related to ordering spins in systems of identical particles in ferro- and antiferromagnetic electronic systems, as well as magnetic effects that occur in high spin systems. The Hamiltonian, written in the spin representation in the form obtained by Heisenberg, Dirac, and van Vleck used to describe spin ordering in systems of particles with spin ½, is not appropriate for a description of particle systems with a spin different from ½. “High” spin particles in the spin representation need other forms of the Hamiltonian of the exchange interaction in the spin representation. The Hamiltonian for high-spin particles has been developed from the first principles, and the effects of magnetic ordering in systems of identical particles with arbitrary spin are considered in this review. An effect of giant negative magnetoresistance in the Indium antimonide has been interpreted from the exchange contribution of a high spin heavy holes point of view. Full article

Nobel metal can be used to form a category of nanoparticles, termed noble metal nanoparticles (NMNPs), which are inert (resistant to oxidation/corrosion) and have unique physical and optical properties. NMNPs, particularly gold and silver nanoparticles (AuNPs and AgNPs), are highly accurate and sensitive visual biosensors for the analytical detection of a wide range of inorganic and organic compounds. The interaction between noble metal nanoparticles (NMNPs) and inorganic/organic molecules produces colorimetric shifts that enable the accurate and sensitive detection of toxins, heavy metal ions, nucleic acids, lipids, proteins, antibodies, and other molecules. Hydrogen bonding, electrostatic interactions, and steric effects of inorganic/organic molecules with NMNPs surface can react or displacing capping agents, inducing crosslinking and non-crosslinking, broadening, or shifting local surface plasmon resonance absorption. NMNPs-based biosensors have been widely applied to a series of simple, rapid, and low-cost diagnostic products using colorimetric readout or simple visual assessment. In this mini review, we introduce the concepts and properties of NMNPs with chemical reduction synthesis, tunable optical property, and surface modification technique that benefit the development of NMNPs-based colorimetric biosensors, especially for the visual quantification. The “aggregation strategy” based detection principle of NMNPs colorimetric biosensors with the mechanism of crosslinking and non-crosslinking have been discussed, particularly, the critical coagulation concentration-based salt titration methodology have been exhibited by derived equations to explain non-crosslinking strategy be applied to NMNPs based visual quantification. Among the broad categories of NMNPs based biosensor detection analyses, we typically focused on four types of molecules (melamine, single/double strand DNA, mercury ions, and proteins) with discussion from the standpoint of the interaction between NMNPs surface with molecules, and DNA engineered NMNPs-based biosensor applications. Taken together, NMNPs-based colorimetric biosensors have the potential to serve as a simple yet reliable technique to enable visual quantification. Full article

In this study, we designed two types of gas-sensor chips with silicon–carbon film, doped with CuO, as the sensitive layer. The first type of gas-sensor chip consists of an Al₂O₃ substrate with a conductive chromium sublayer of ~10 nm thickness and 200 Ω/□ surface resistance, deposited by magnetron sputtering. The second type was fabricated via the electrochemical deposition of a silicon–carbon film onto a dielectric substrate with copper electrodes formed by photoelectrochemical etching. The gas sensors are sensitive to the presence of CO and CH₄ impurities in the air at operating temperatures above 150 °C, and demonstrated p- (type-1) and n-type (type-2) conductivity. The type-1 gas sensor showed fast response and recovery time but low sensitivity, while the type-2 sensor was characterized by high sensitivity but longer response and recovery time. The silicon–carbon films were characterized by the presence of the hexagonal 6H SiC polytype with the impurities of the rhombohedral 15 R SiC phase. XRD analysis revealed the presence of a CuO phase. Full article

The feasibility of a compact, modular sensing system able to quantify the presence of nitrogen, phosphorus and potassium (NPK) in nutrient-containing fertilizer water was investigated. Direct UV-Vis spectroscopy combined with optical fibers were employed to design modular compact sensing systems able to record absorption spectra of nutrient solutions resulting from local producer samples. N, P, and K spectral interference was studied by mixtures of commercial fertilizer solutions to simulate real conditions in hydroponic productions. This study demonstrates that the use of bands for the quantification of nitrogen with linear or logarithmic regression models does not produce analytical grade calibrations. Furthermore, multivariate regression models, i.e., Partial Least Squares (PLS), which consider specimens interference, perform poorly for low absorbance nutrients. The high interference present in the spectra has proven to be solved by an innovative self-learning artificial intelligence algorithm that is able to find interference modes among a spectral database to produce consistent predictions. By correctly modeling the existing interferences, analytical grade quantification of N, P, and K has proven feasible. The results of this work open the possibility of real-time NPK monitoring in Micro-Irrigation Systems. Full article

The increasing world population leads to the growing demand for food production without expanding cultivation areas. In this sense, precision agriculture optimizes the production and input usage by employing sensors to locally monitor plant nutrient within agricultural fields. Here, we have used an electronic tongue sensing device based on impedance spectroscopy to recognize distinct soil samples (sandy and clayey) enriched with macronutrients. The e-tongue setup consisted of an array of four sensing units formed by layer-by-layer (LbL) films deposited onto 3D-printed graphene-based interdigitated electrodes (IDEs). The IDEs were fabricated in 20 min using the fused deposition modeling process and commercial polylactic acid-based graphene filaments. The e-tongue comprised one bare and three IDEs functionalized with poly(diallyldimethylammonium chloride) solution/copper phthalocyanine-3,4′,4″,4‴-tetrasulfonic acid tetrasodium salt (PDDA/CuTsPc), PDDA/montmorillonite clay (MMt-K), and PDDA/poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) LbL films. Control samples of sandy and clayey soils were enriched with different concentrations of nitrogen (N), phosphorus (P), and potassium (K) macronutrients. Sixteen soil samples were simply diluted in water and measured using electrical impedance spectroscopy, with data analyzed by principal component analysis. All soil samples were easily distinguished without pre-treatment, indicating the suitability of 3D-printed electrodes in e-tongue analysis to distinguish the chemical fertility of soil samples. Our results encourage further investigations into the development of new tools to support precision agriculture. Full article

The new molecularly imprinted polymer (MIP) membrane based on cassava starch—Fe₃O₄—was developed to detect acetaminophen and caffeine simultaneously with the differential pulse voltammetry (DPV) method. Cassava starch was reacted with sodium tripolyphosphate (STPP) as a crosslinking agent, while acetaminophen and caffeine were added as templates. The Fe₃O₄ nanoparticles in the composite were added to increase the sensor’s sensitivity. The experimental results show that the ratio between cassava starch:STPP:acetaminophen/caffeine in the mixture for MIP membranes influences the sensitivity of the sensor obtained. MIP membranes with the best sensitivity is produced at a mixture ratio of 2:2:1. The sensor performance is also affected by the pH of the solution and the type of buffer solution used. The sensor works very well at pH 2 in PB solution. Sensors produced from GCE modified with MIP membrane from cassava starch—Fe₃O₄ with acetaminophen and caffeine as templates have linear range concentrations, respectively, at 50–2000 µM and 50–900 µM. Sensor sensitivity was 0.5306 A/M against acetaminophen and 0.4314 A/M against caffeine with Limit of Detection (LoD), respectively, 16 and 23 µM. Sensor selectivity and sensitivity are better than those without MIP and can be applied for the determination of the content of acetaminophen in headache medicine, with an accuracy of 96–99% and with Relative Standard Deviation (RSD) 0.9–2.56%. Full article

A unique chemical analytical approach is proposed based on the integration of chemical radiophysics with electrochemistry at the catalytically-active surface. This approach includes integration of: radiofrequency modulation polarography with platinum electrodes, applied as film enthrakometers for microwave measurements; microwave thermal analysis performed on enthrakometers as bolometric sensors; catalytic measurements, including registration of chemical self-oscillations on the surface of a platinum enthrakometer as the chemosensor; measurements on the Pt chemosensor implemented as an electrochemical chip with the enthrakometer walls acting as the chip walls; chemotron measurements and data processing in real time on the surface of the enthrakometric chip; microwave electron paramagnetic resonance (EPR) measurements using an enthrakometer both as a substrate and a microwave power meter; microwave acceleration of chemical reactions and microwave catalysis оn the Pt surface; chemical generation of radio- and microwaves, and microwave spin catalysis; and magnetic isotope measurements on the enthrakometric chip. The above approach allows one to perform multiparametric physical and electrochemical sensing on a single active enthrakometric surface, combining the properties of the selective electrochemical sensor and an additive physical detector. Full article

Cadmium selenide (CdSe) quantum dots (QDs) were synthesized by water phase synthesis method using 3-mercaptopropionic acid (3-MPA) as a stabilizer, and they were applied to the detection of copper ions (Cu²⁺). The results showed that CdSe QDs have excellent selectivity and sensitivity toward Cu²⁺. The fluorescence intensity of CdSe QDs decreased with the increase of Cu²⁺ concentration. The linear range was from 30 nM to 3 μM, and the detection limit was 30 nM. Furthermore, CdSe QDs were used for detecting the concentration of Cu²⁺ in oysters. The content of Cu²⁺ was 40.91 mg/kg, which was close to the one measured via flame atomic absorption spectrometry (FAAS), and the relative error was 1.81%. Therefore, CdSe QDs have a wide application prospect in the rapid detection of copper ions in food. Full article