Chemosensors, Volume 8, Issue 4 (December 2020) – 47 articles

Nanocomposite thin films, sensitive to methane at the room temperature (25–30 °C), have been prepared, starting from SnSe₂ powder and Zn(II)-5,10,15,20-tetrakis-(4-aminophenyl)- -porphyrin (ZnTAPP) powder, that were fully characterized by XRD, UV-VIS, FT-IR, Nuclear Magnetic Resonance (¹H-NMR and ¹³C-NMR), Atomic Force Microscopy (AFM), SEM and Electron Paramagnetic Resonance (EPR) techniques. Film deposition was made by drop casting from a suitable solvent for the two starting materials, after mixing them in an ultrasonic bath. The thickness of these films were estimated from SEM images, and found to be around 1.3 μm. These thin films proved to be sensitive to a threshold methane (CH₄) concentration as low as 1000 ppm, at a room temperature of about 25 °C, without the need for heating the sensing element. The nanocomposite material has a prompt and reproducible response to methane in the case of air, with 50% relative humidity (RH) as well. A comparison of the methane sensing performances of our new nanocomposite film with that of other recently reported methane sensitive materials is provided. It is suitable for signaling gas presence before reaching the critical lower explosion limit concentration of methane at 50,000 ppm. Full article

The determination of paracetamol is a common need in pharmaceutical and environmental samples for which a low-cost, rapid, and accurate sensor would be highly desirable. We develop a novel pencil graphite lead electrode (PGE) modified with single-wall carbon nanotubes (SWCNTs) and polyvinylpyrrolidone (PVP) polymer (PVP/SWCNT/PGE) for the voltammetric quantification of paracetamol. The sensor shows remarkable analytical performance in the determination of paracetamol at neutral pH, with a limit of detection of 0.38 μM and a linear response from 1 to 500 μM using square-wave voltammetry (SWV), which are well suited to the analysis of pharmaceutical preparations. The introduction of the polymer PVP can cause dramatic changes in the sensing performance of the electrode, depending on its specific architecture. These effects were investigated using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM). The results indicate that the co-localization and dispersion of PVP throughout the carbon nanotubes on the electrode are key to its superior electrochemical performance, facilitating the electrical contact between the nanotubes and with the electrode surface. The application of this sensor to commercial syrup and tablet preparations is demonstrated with excellent results. Full article

Thermochromic urea (U) organogel immobilized with a thermochromic tricyanofuran hydrazone (TCFH) chromophore was developed. Thermochromic TCFH chromophore bearing two nitro functional groups on a hydrazone recognition unit was synthesized via an azo-coupling reaction of tricyanofuran (TCF) heterocyclic moiety containing an active methyl group with the diazonium chloride salt of 2,4-dinitroaniline comprising two strongly electron-withdrawing nitro groups. The molecular structure of both intermediates and TCFH dye were characterized by several analytical methods, including ¹H NMR, ¹³C NMR, IR, mass spectroscopy (MS), and elemental analysis. The thermochromic responsiveness could be attributed to the charge delocalization of TCFH as well as to the presence of an intramolecular charge transfer. The generated organogel displayed a thermoreversible sol–gel transition associated with color change. The origin of the monitored thermochromism is a conformational change of the tricyanofuran hydrazone backbone due to the temperature-driven deprotonation–protonation reversible process. The prepared urea–tricyanofuran hydrazone (UTCFH) thermometer acted as a diagnostic tool providing an instant color change between yellow, orange, red and purple upon changing the temperature of the UTCFH organogel in dimethyl sulfoxide (DMSO). This color change was proportionally correlated with increasing the temperature from 44 to 63 °C. The UTCFH organogel composed of urea and push-π-pull hydrazone type tricyanofuran chromophore immobilized physically in the urea organogel was found to function as a temperature-driven chromic thermometer. This chromogenic UTCFH organogel in DMSO displayed a phase transition at 41–48 °C. The morphological properties of the gel internal fibrous nanostructure (80–120 nm) were monitored by scanning electron microscopy (SEM). The colorimetric measurements were monitored by UV–Vis absorption spectroscopy. The chromogenic thermometer demonstrated a good reversibility without fatigue. The mechanism accounting for thermochromism of UTCFH organogel is proposed. Full article

Passenger safety requires that in commercial airplanes hydraulic actuators be powered by fire-resistant hydraulic fluids. As a downside, such fluids are hygroscopic which means that these tend to accumulate humidity from the environment and that the dissolved humidity tends to produce acidity which can corrode all kinds of metallic components inside a hydraulic system. As such damage in safety-critical subsystems is hard to localize and expensive to repair, sensor technologies are required which allow the state of water contamination and fluid degradation to be routinely checked and necessary maintenance actions to be scheduled in a way that causes minimum flight interruptions. The paper reviews progress that has been made in developing such sensor systems and in commissioning these into practical flight operation. Sensor technologies that proved optimally adapted to this purpose are multi-channel non-dispersive (NDIR) systems working in the mid-infrared range. Additional options concern optical absorption sensors working in the near-infrared and visible ranges as well as fluorescence sensors. Full article

Fused filament fabrication (FFF) is a 3D printing method that is attracting increased interest in the development of miniaturized electrochemical sensor systems due to its versatility, low cost, reproducibility, and capability for rapid prototyping. A key component of miniaturized electrochemical systems is the reference electrode (RE). However, reports of the fabrication of a true 3D-printed RE that exhibits stability to variations in the sample matrix remain limited. In this work, we report the development and characterization of a 3D-printed Ag|AgCl|gel-KCl reference electrode (3D-RE). The RE was constructed using a Ag|AgCl wire and agar-KCl layer housed in a watertight 3D-printed acrylonitrile butadiene styrene (ABS) casing. The novel feature of our electrode is a 3D-printed porous junction that protects the gel electrolyte layer from chloride ion leakage and test sample contamination while maintaining electrical contact with the sample solution. By tuning the 3D printing filament extrusion ratio (k), the porosity of the junction was adjusted to balance the reference electrode potential stability and impedance. The resulting 3D-RE demonstrated a stable potential, with a potential drift of 4.55 ± 0.46 mV over a 12-h period of continuous immersion in 0.1 M KCl, and a low impedance of 0.50 ± 0.11 kΩ. The 3D-RE was also insensitive to variations in the sample matrix and maintained a stable potential for at least 30 days under proper storage in 3 M KCl. We demonstrate the application of this 3D-RE in cyclic voltammetry and in pH sensing coupled with electrodeposited iridium oxide on a gold electrode. Our method offers a viable strategy for 3D printing a customizable true reference electrode that can be readily fabricated on demand and integrated into 3D-printed miniaturized electrochemical sensor systems. Full article

The interaction of 4′-(N,N-dimethylamino)-6-hydroxyflavylium cation with double stranded (ds-) DNA/RNA was studied by UV/Vis spectrophotometry, circular dichroism (CD), and also steady-state and time-resolved emission spectroscopies at neutral and weakly acidic conditions. At pH 5, the studied molecule, in its flavylium cationic form, showed considerable binding affinities (5 < logK_s < 6) for all ds-DNA/RNA, contrary to chalcones forms (dominant at pH 7), which did not show binding to polynucleotides. Flavylium cation intercalated into ds-DNAs at variance to dominant groove aggregation within ds-RNA, which was reported by RNA-specific bisignate induced CD spectrum (ICD) bands. The intrinsically negligible fluorescence of flavylium was strongly increased upon the addition of DNA or RNA, whereby both the fluorescence intensity and emission lifetimes of complexes differed considerably: the strongest emission increase was observed for AU-RNA (detection limit estimated to 10 nM) followed by AT-DNAs and the much weaker effect of GC-DNAs. Both fluorescence sensitivity on the ds-DNA/RNA secondary structure and sequence-selective ICD bands make the flavylium–chalcones system an intriguing pH-switchable new probe for distinguishing between various polynucleotide sequences. Full article

Two highly fluorescent calix[4]arene-containing phenylene-alt-ethynylene-carbazolylene polymers (Calix-PPE-CBZs) were used in the detection of explosives from the nitroaromatic compounds (NACs) family, in solution and in vapour phases. Both fluorophores exhibit high sensitivity and selectivity towards NACs detection. The quenching efficiencies in solution, assessed through static Stern-Volmer constants (K_SV), follow the order picric acid (PA) >> 2,4,6-trinitrotoluene (TNT) > 2,4-dinitrotoluene > (2,4-DNT) > nitrobenzene (NB). These correlate very well with the NACs electron affinities, as evaluated from their lowest unoccupied molecular orbitals (LUMOs) energies, indicating a photo-induced electron transfer as the dominant mechanism in fluorescence quenching. Moreover, and most interesting, detection of TNT, 2,4-DNT and NB vapours via thin-films of Calix-PPE-CBZs revealed a remarkably sensitive response to these analytes, comparable to state-of-the-art chemosensors. The study also analyses and compares the current results to previous disclosed data on the detection of NACs by several calix[4]arene-based conjugated polymers and non-polymeric calix[4]arenes-carbazole conjugates, overall highlighting the superior role of calixarene and carbazole structural motifs in NACs’ detection performance. Density functional theory (DFT) calculations performed on polymer models were used to support some of the experimental findings. Full article

This review presents the basic characteristics of MXene, a novel 2D nanomaterial with many outstanding properties applicable to electrochemical sensing and biosensing. The second part deals with electrochemical impedance spectroscopy (EIS) and its beneficial features applicable to ultrasensitive electrochemical sensing and label-free biosensing. The main part of the review presents recent advances in the integration of MXene to design electrochemical interfaces. EIS was used to evaluate the effect of anodic potential on MXene and the effect of the MXene preparation route and for characterization of MXene grafted with polymers. It also included the application of EIS as the main transducing tool for antibody- and aptamer-based biosensors or biosensors integrating molecularly imprinted polymers. Full article

As laccase (produced by Botrytis cinerea) can significantly alter the properties of wine, winemakers frequently use commercially available colorimetric kits and spectrophotometers to measure the activity of this enzyme in grapes, must and wine. Although the used kits are based on electrochemically active substrates (such as syringaldazine and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid), ABTS), the electrochemical determination of laccase activity as an alternative to the colorimetric determination was not thoroughly investigated up to now. Therefore, in the present work, we explored the electrochemical determination of laccase activity. Laccase activity measurements were carried out using either carbon fiber microelectrodes or screen-printed electrodes as working electrodes, either syringaldazine or ABTS as the electrochemically active laccase substrate, and either cyclic voltammetry or constant potential amperometry as the electrochemical method. The best performing approach, which combines ABTS, screen-printed gold electrodes, and constant potential amperometry, allowed identifying laccase positive must sample (i.e., must samples with › 3U/mL laccase) in about 5 min. Full article

Digitization of industrial processes using new technologies (IoT—Internet of Things, IoE—Internet of Everything), including the agriculture industry, are globally gaining growing interest. The precise management of production inputs is essential for many agricultural companies because limited or expensive sources of water and nutrients could make sustainable production difficult. For these reasons, precise data from fields, plants, and greenhouses have become more important for decision making and for the proper dosage of water and nutrients. On the market are a variety of sensors for monitoring environmental parameters within a precise agricultural area. However, the high price, data storage/transfer functionality are limiting so cost-effective products capable to transfer data directly to farmers via wireless IoT networks are required. Within a given scope, low-price sensor elements with an appropriate level of sensor response are required. In the presented paper, we have developed fully printed sensor elements and a dedicated measuring/communicating unit for IoT monitoring of soil moisture. Various fabrication printing techniques and a variety of materials were used. From the performed study, it is obvious that fully printed sensor elements based on cheap and environmentally friendly carbon layers printed on the wood substrate can compete with conventionally made sensors based on copper. Full article

Mitochondria are the source of internal heat which influences all cellular processes. Hence, monitoring mitochondrial temperature provides a unique insight into cell physiology. Using a thermosensitive fluorescent probe MitoThermo Yellow (MTY), we have shown recently that mitochondria within human cells are maintained at close to 50 °C when active, increasing their temperature locally by about 10 °C. Initially reported in the HEK293 cell line, we confirmed this finding in the HeLa cell line. Delving deeper, using MTY and MTX (MitoThermo X), a modified version of MTY, we unraveled some caveats related to the nature of these charged fluorophores. While enabling the assessment of mitochondrial temperature in HEK and HeLa cell lines, the reactivity of MTY to membrane potential variations in human primary skin fibroblasts precluded local temperature monitoring in these cells. Chemical modification of MTY into MTX did not result in a temperature probe unresponsive to membrane potential variations that could be universally used in any cell type to determine mitochondrial temperature. Thus, the cell-type dependence of MTY in measuring mitochondrial temperature, which is likely due to the variable binding of this dye to specific internal mitochondrial components, should imply cautiousness while using these nanothermometers for mitochondrial temperature analysis. Full article

Hypochlorite anion (ClO⁻) is a widely-used disinfectant and a microbicidal agent in the immune system. Accurate detection of ClO⁻ in environmental and biological samples by simply prepared chemosensors/chemodosimeters is important. Herein, we report that a naphthalimide–sulfonylhydrazine conjugate with an imine (C=N) linker, prepared via simple condensation, acts as an effective fluorescent chemodosimeter for ClO⁻. The molecule exhibits a weak emission, but ClO⁻-selective cleavage of its C=N bond creates a strong green emission. Ab initio calculation showed that the emission enhancement by ClO⁻ originates from the suppression of intramolecular electron transfer from the photoexcited naphthalimide through the C=N linker. This response enables selective and sensitive detection of ClO⁻ at physiological pH range (7–9) and allows fluorometric ClO⁻ imaging in the presence of cells. Full article

A new chemosensor UiO-66-N-Py (Py = 2-methinepyridine, N = imine nitrogen) based on isoreticular UiO-66 (University of Oslo) Metal–Organic Framework (MOF) containing 2-methinepyridine functionalized organic linker was solvothermally synthesized and characterized. This UiO-66-N-Py was very selective and sensitive for detecting the Fe³⁺ ion and sequential detection of the pyrophosphate (PPi) anion. The limits of detection for the Fe³⁺ ion and PPi were calculated to be 10 ppb (0.19 μM) and 50 ppb (0.3 μM), respectively. The quenching constant K_sv for Fe³⁺ and the binding constant for PPi were 1.4 × 10⁵ M⁻¹ and 1.7 × 10⁵ M⁻¹, respectively. The functionalization of UiO-66-NH₂ with 2-methinepyridine enhanced its fluorescence emission properties and introduced more binding sites for the analytes. We additionally studied the interaction of the sensor and the analytes with Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and Inductively Coupled Plasma Mass Spectrometry (ICP-MS). This chemosensor also demonstrated a regenerative emission property without loss in the detection ability for six consecutive cycles. Full article

Aflatoxins are highly toxic fungal secondary metabolites that often contaminate food and feed commodities. An electrochemical immunosensor for the determination of aflatoxin B₁ (AFB₁) was fabricated by immobilizing monoclonal AFB₁ antibodies onto a screen-printed gold electrode that was modified with carbo-methyldextran by N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride/N-hydroxysuccinimide cross-linking. An electrochemical interfacial modelling of biomolecular recognition was suggested and reasonably interpreted. Impedance technology was employed for the quantitative determination of AFB₁. The limit of detection concentration of AFB₁ for standard solutions and spiked pistachio samples was 0.5 ng/mL and 1 ng/mL, respectively. The immunosensor was able to successfully determine AFB₁ concentrations in the range of 4.56–50.86 ng/mL in unknown pistachio samples. Comparative chromatographic analysis revealed that AFB₁ concentrations that were higher than 345 ng/mL were not within the immunosensor’s upper limits of detection. Selectivity studies against Ochratoxin A and Aflatoxin M₁ demonstrated that the proposed AFB₁ immunosensor was able to differentiate between these other fungal mycotoxins. The novel electrochemical immunosensor approach has the potential for rapid sample screening in a portable, disposable format, thus contributing to the requirement for effective prevention and the control of aflatoxin B₁ in pistachios. Full article

Herein, we report the photocatalytic and fluorescence sensing applications of manganese-doped zinc oxide nanostructures synthesized by a solution combustion technique, using zinc nitrate as an oxidizer and urea as a fuel. The synthesized Mn-doped ZnO nanostructures have been analyzed in terms of their surface morphology, phase composition, elemental analysis, and optical properties with the help of scanning electron microscopy (SEM), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), and UV-Visible (UV-Vis) spectroscopy. A careful observation of the SEM micrograph reveals that the synthesized material was porous and grown in very high density. Due to a well-defined porous structure, the Mn-doped ZnO nanostructures can be used for the detection of ciprofloxacin, which was found to exhibit a significantly low limit of detection (LOD) value i.e., 10.05 µM. The synthesized Mn-doped ZnO nanostructures have been further analyzed for interfering studies, which reveals that the synthesized sensor material possesses very good selectivity toward ciprofloxacin, as it detects selectively even in the presence of other molecules. The synthesized Mn-doped ZnO nanostructures have been further analyzed for the photodegradation of methyl orange (MO) dye. The experimental results reveal that Mn-doped ZnO behaves as an efficient photocatalyst. The 85% degradation of MO has been achieved in 75 min using 0.15 g of Mn-doped ZnO nanostructures. The observed results clearly confirmed that the synthesized Mn-dopedZnO nanostructures are a potential scaffold for the fabrication of sensitive and robust chemical sensors as well as an efficient photocatalyst. Full article

Polymeric nanofiber matrices are promising structures to develop biosensing devices due to their easy and affordable large-scale fabrication and their high surface-to-volume ratio. In this work, the suitability of a polyamide 6 nanofiber matrix for the development of a label-free and real-time Fabry–Pérot cavity-based optical biosensor was studied. For such aim, in-flow biofunctionalization of nanofibers with antibodies, bound through a protein A/G layer, and specific biodetection of 10 µg/mL bovine serum albumin (BSA) were carried out. Both processes were successfully monitored via reflectivity measurements in real-time without labels and their reproducibility was demonstrated when different polymeric nanofiber matrices from the same electrospinning batch were employed as transducers. These results demonstrate not only the suitability of correctly biofunctionalized polyamide 6 nanofiber matrices to be employed for real-time and label-free specific biodetection purposes, but also the potential of electrospinning technique to create affordable and easy-to-fabricate at large scale optical transducers with a reproducible performance. Full article

An overview of noteworthy new methods of biomarker determination based on surface-enhanced Raman scattering (SERS) is presented. Biomarkers can be used to identify the occurrence and development of diseases, which furthers the understanding of biological processes in the body. Accurate detection of a disease-specific biomarker is helpful for the identification, early diagnosis and prevention of a disease and for monitoring during treatment. The search for and discovery of valuable biomarkers have become important research hotspots. Different diseases have different biomarkers, some of which are involved in metabolic processes. Therefore, the fingerprint characteristics and band intensities in SERS spectra have been used to identify metabolites and analyze markers. As a promising technique, SERS has been widely used for the quantitative and qualitative determination of different types of biomarkers for different diseases. SERS techniques provide new technologies for the diagnosis of disease-related markers and determining the basis for clinical treatment. Herein, several SERS-based methods with excellent sensitivity and selectivity for the determination of biomarkers for tumors, viruses, Alzheimer’s disease, cardiac muscle tissue injury, and cell activity are highlighted. Full article

Brain tumors, especially glioblastoma, remain the most aggressive form of all the cancers because of inefficient diagnosis and profiling. Nanostructures, such as metallic nanostructures, silica nano-vehicles, quantum dots, lipid nanoparticles (NPs) and polymeric NPs, with high specificity have made it possible to permeate the blood–brain barrier (BBB). NPs possess optical, magnetic and photodynamic properties that can be exploited by surface modification, bio composition, contrast agents’ encapsulation and coating by tumor-derived cells. Hence, nanotechnology has brought on a revolution in the field of diagnosis and imaging of brain tumors and cancers. Recently, nanomaterials with biomimetic functions have been introduced to efficiently cross the BBB to be engulfed by deep skin tumors and cancer malignancies for imaging. The review focuses on nanotechnology-based diagnostic and imaging approaches for exploration in brain tumors and cancers. Moreover, the review also summarizes a few strategies to image glioblastoma and cancers by multimodal functional nanocomposites for more precise and accurate clinical diagnosis. Their unique physicochemical attributes, including nanoscale sizes, larger surface area, explicit structural features and ability to encapsulate diverse molecules on their surface, render nanostructured materials as excellent nano-vehicles to cross the blood–brain barrier and convey drug molecules to their target region. This review sheds light on the current progress of various kinds of nanomaterials, such as liposomes, nano-micelles, dendrimers, carbon nanotubes, carbon dots and NPs (gold, silver and zinc oxide NPs), for efficient drug delivery in the treatment and diagnosis of brain cancer. Full article

This study presents a method for printing flexible chemiresistors comprising thin film transducers based on cross-linked gold nanoparticles (GNPs). First, interdigitated silver paste electrodes are printed onto polyimide (PI) foil via dispenser printing. Second, coatings of GNPs and dithiol/monothiol blends are inkjet-printed onto these electrode structures. 1,9-Nonanedithiol (9DT) is used as cross-linking agent and a variety of monothiols are added to tune the sensors’ chemical selectivity. When dosing these sensors with different analyte vapors (n-octane, toluene, 4-methyl-2-pentanone, 1-butanol, 1-propanol, ethanol, water; concentration range: 25–2000 ppm) they show fully reversible responses with short response and recovery times. The response isotherms follow a first-order Langmuir model, and their initial slopes reveal sensitivities of up to 4.5 $\times {10}^{-5}$ppm⁻¹. Finally, it is demonstrated that arrays of printed sensors can be used to clearly discern analytes of different polarity. Full article

A sensitive electrochemical detection method for Salmonella spp. was described, based on the use of Hechtia argentea lectin immobilised on a screen-printed gold electrode. The lectin was extracted from Hechtia argentea, a plant belonging to the Bromeliaceae family. The lectin with molecular weight near 27.4 kDa showed selectivity towards D-mannose, contained on the lipopolysaccharide cell wall of Salmonella spp. Carbohydrate selectivity of the lectin was measured as a change in impedance with respect to concentration. The binding of the bacteria to the biosensor surface increased impedance with increasing concentrations of Salmonella spp., achieving a linear range of detection of 15–2.57 × 10⁷ CFU mL⁻¹, with a limit of detection of 5 CFU mL⁻¹. Increases in impedance were measured using electrochemical impedance spectroscopy and analysed using Nyquist plots. The biosensor was applied in analysis of hen egg samples, and the results were consistent with those obtained using the official analysis methodology. Full article

This work demonstrates a method to optimize materials and dimensions of piezoelectric cantilevers for electronic nose applications via finite element analysis simulations. Here we studied the optimum piezoelectric cantilever configuration for detection of cadaverine, a biomarker for meat ageing, to develop a potential electronic nose for the meat industry. The optimized cantilevers were fabricated, characterized, interfaced using custom-made electronics, and tested by approaching meat pieces. The results show successful measurements of cadaverine levels for meat pieces with different ages, hence, have a great potential for applications within the meat industry shelf-life prediction. Full article

This paper describes the sensitive properties of screen-printed carbon electrodes (SPCE) modified by using three different electroactive chemical compounds: Meldola’s Blue, Cobalt Phthalocyanine and Prussian Blue, respectively. It was demonstrated that the Prussian Blue (PB) modified SPCE presented electrochemical signals with the highest performances in terms of electrochemical process kinetics and sensitivity in all the solutions analyzed. PB-SPCE was demonstrated to detect Phe through the influence it exerts on the redox processes of PB. The PB-SPCE calibration have shown a linearity range of 0.33–14.5 µM, a detection limit (LOD) of 1.23 × 10⁻⁸ M and the standard deviation relative to 3%. The PB-SPCE sensor was used to determine Phe by means of calibration and standard addition techniques on pure samples, on simple pharmaceutical samples or on multicomponent pharmaceutical samples. Direct determination of the concentration of 4 × 10⁻⁶–5 × 10⁻⁵ M Phe in KCl solution showed that the analytical recovery falls in the range of 99.75–100.28%, and relative standard deviations in the range of 2.28–3.02%. The sensors were successfully applied to determine the Phe in pharmaceuticals. The validation of the method was performed by using the FTIR, and by comparing the results obtained by PB-SPCE in the analysis of three pharmaceutical products of different concentrations with those indicated by the producer. Full article

The electrochemical oxidation of CA19-9 tagged with L-Histidine (CA199-His) was investigated for the first time with screen-printed electrodes (DS) modified with graphene oxide (DS/GO) or thermally reduced graphene oxide (DS/TRGO). Successive cyclic voltammograms (CV) measurements performed with bare and DS/TRGO electrodes proved that the intensity of the oxidation peak (I _peak) is time-dependent. In fact, the oxidation signal increased over time, reached a maximum and then decreased due to the saturation of the surface with CA199-His molecules. The interaction of CA199-His with GO, TRGO, or graphite was additionally studied by isothermal calorimetry, a useful tool for accessing information regarding the biomolecule adsorption on graphene surface. The adsorption of CA199-His on TRGO was generating a higher heat, suggesting quantitative and efficient interactions. At the same time, in the case of TRGO, the saturation was not reached, indicating the existence of more free binding sites than in the case of GO and graphite. As such, the carbohydrate marker CA199-His showed a higher affinity for the TRGO surface than for the graphite or GO surfaces. The lack of saturation in the case of TRGO may indicate a continuous structural modification of the antigen when interacting with the graphene surface. Full article

The paper presents the synthesis and preliminary characterization of two novel solid-phase sorbents for iron(III), resulting from the functionalization of ethylene-vinyl alcohol copolymer (EVOH) with deferoxamine, DFO (DFO@EVOH), and a novel tripodal 3-hydroxy-4-pyridinone, named 3,4-HP (3,4-HP@EVOH). DFO and 3,4-HP have been covalently bonded to EVOH, using carbonyldiimidazole as a coupling agent. Before their use as Fe(III) sorbents, they were warm-pressed to obtain a thin film. Polymers have been characterized by conventional physico-chemical techniques; furthermore, the sorption properties towards Fe(III) were investigated. The physico-chemical characterization of the new solid-state devices demonstrates the effective linkage of the two receptors on the polymeric support. Despite a relatively low sorption capacity for both materials, the stoichiometry and the complexation constants of Fe(III)/DFO@EVOH and Fe(III)/3,4-HP@EVOH are in pretty good agreement with those obtained for the same ligands in aqueous solutions. Full article

Ginkgo biloba is one of the most important sources of active compounds, mainly flavonoids and phenolic compounds. Due to its importance related to pharmaceutical practice, the making of a qualitative and quantitative method for the detection and quantification of active compounds from Ginkgo biloba pharmaceutical products is desirable. In this study, the content of biological active compounds from Ginkgo biloba products was estimated using cyclic voltammetry. The electrochemical determination of active compounds was carried out by using a screen-printed carbon electrode modified with carbon nanotubes. The studies regarding parameter optimization were made using solutions containing potassium ferrocyanide and catechol, respectively. In both cases, the redox processes of studied compounds was observed, which were controlled by the diffusion phenomenon. We analyzed two pharmaceutical products containing Ginkgo biloba, a RX product (recipe medicine requires a medical prescription to be dispensed) and an OTC (Over-The-Counter, which can be obtained without a prescription) product. The cyclic voltammograms of the two products showed two redox processes due to the antioxidant properties of the products. It was found that the RX product had a greater content of active compounds compared to the OTC product. Therefore, the voltammetric method has great utility for the determination of compounds with redox properties from pharmaceutical products containing Ginkgo biloba. Full article

The conventional CO electrochemical gas sensor uses aqueous H₂SO₄ solution as electrolyte, with inevitable problems, such as the drying and leakage of electrolyte. Thus, research on new alternative electrolytes is an attractive field in electrochemical gas sensors. In this paper, the application of a new fumed SiO₂ gel electrolyte was studied in electrochemical gas sensors. The effects of fumed SiO₂ and H₂SO₄ contents on the performance of the CO gas sensor were investigated. The results showed that the optimized composition of the SiO₂ gel electrolyte was 4.8% SiO₂, 38% H₂SO₄, and 0.005% polyvinyl alcohol (PVA). Compared with aqueous H₂SO₄, the gel electrolyte had better water retention ability. The signal current of the sensor was proportional to the CO concentration. The sensitivity to CO was 78.6 nA/ppm, and the response and recovery times were 31 and 38 s, respectively. The detection limit was 2 ppm. The linear range was from 2 to 500 ppm. The gel electrolyte CO sensor possesses equivalent performance to that with aqueous electrolyte. Full article

In this paper, silver-doped zinc oxide nanoparticles were synthesized by using a solution combustion technique, in which zinc nitrate is used as an oxidizer and tartaric acid as a fuel. The phase composition, morphology and structural properties of the as-synthesized zinc oxide and silver-doped zinc oxide were established by using powdered X-ray diffraction, field emission scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy studies. Due to well-defined morphologies and crystallinity, the pure zinc oxide and silver-doped zinc oxide nanostructures can be used as efficient chemical sensors for the detection of p-nitrophenol (PNP). ZnO was found to show a low value of the limit of detection (LOD), i.e., 2.175 µM/L, for p-nitrophenol sensing; moreover, a sharp decrease in the limit of detection was observed with an increase in the concentration of silver ions, and the LOD value decreased to 0.669 µM/L for 10 mol % silver-doped zinc oxide. It is therefore concluded that Ag-doped ZnO shows a lower limit of detection as compared to pure ZnO for p-nitrophenol sensing. Full article

We have developed a second-generation detection tube for colorimetric and fluorescence detection of phosgene and diphosgene in air. The tube is packed with pellets made of a mixture of microcrystalline cellulose and magnesium aluminum metasilicate treated with a suitable monoterpene (camphor, menthol) to increase porosity and specific surface area. We impregnated the pellets with a specific o-phenylenediamine-pyronin (PY-OPD) based reagent. The detector with this novel indication charge enables phosgene or diphosgene to be selectively and sensitively detected at concentrations lower than as would those posing acute health risk. Owing to the analytical colorimetric and, at the same time, fluorescence signal, the detector is very robust while featuring good sensitivity and variability. The colorimetric limits of detection were 0.3 mg/m³ (tristimulus colorimeter), resp. 5 mg/m³ (with the naked eye), fluorescence detection limits of 0.3 mg/m³ (with the naked eye), all at an air sample volume of 1 dm³. The response was practically immediate, acid vapors and gases, or diethyl chlorophosphate as a simulant of nerve warfare chemical agents, were disruptive. Full article

The detection and monitoring systems of low energy beta particles are of important concern in nuclear facilities and decommissioning sites. Generally, low-energy beta-rays have been measured in systems such as liquid scintillation counters and gas proportional counters but time is required for pretreatment and sampling, and ultimately it is difficult to obtain a representation of the observables. The risk of external exposure for low energy beta-ray emitting radioisotopes has not been significantly considered due to the low transmittance of the isotopes, whereas radiation protection against internal exposure is necessary because it can cause radiation hazard to into the body through ingestion and inhalation. In this review, research to produce various types of detectors and to measure low-energy beta-rays by using or manufacturing plastic scintillators such as commercial plastic and optic fiber is discussed. Furthermore, the state-of-the-art beta particle detectors using plastic scintillators and other types of beta-ray counters were elucidated with regard to characteristics of low energy beta-ray emitting radioisotopes. Recent rapid advances in organic matter and nanotechnology have brought attention to scintillators combining plastics and nanomaterials for all types of radiation detection. Herein, we provide an in-depth review on low energy beta emitter measurement. Full article

Vanadium pentoxide (V₂O₅) is a transition metal oxide with features such as high availability, good catalytic activity, unique electrical properties and high conductivity which are appropriate for gas sensing applications. In this review, we discuss different gas sensing aspects of V₂O₅ in pristine, doped, decorated and composite forms. Depending on its synthesis procedure, morphology, sensing temperature and surface conditions, the V₂O₅-based gas sensors show different responses to target gases. Herein, we have discussed the behavior of V₂O₅-based gas sensors to different gases and associated sensing mechanisms. This review paper can be a useful reference for the researchers who works in the field of gas sensors. Full article