Chemosensors, Volume 11, Issue 1 (January 2023) – 72 articles

Nanoparticles (NPs) represent emerging pollutants that still pose analytical challenges for their detection in environmentally relevant samples due to their extremely low concentrations, high colloidal background, and the need to perform speciation analysis. They are also one of the interfering matrices during the analysis of metal ions and contaminants in water samples. Currently, conventional analytical techniques such as Transmission Electron Microscopy (TEM) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) are used for the detection of NPs, but such techniques require bulky instrumentation and are difficult to be automated for online analysis. In this study, we aim to develop a nanoparticle-imprinted hydrogel (NPIH, NANOGEL) to detect and capture NPs in water samples. The principle of the Nanogel originates from the well-known concept of molecularly imprinted polymers (MIPs). Cadmium sulfide/Selenide/Zinc sulfide core/shell quantum dots (QDs) were used as the template NP, creating specific pore cavities in the Nanogel that can selectively bind to certain analytes. Quantification of NPs detected in water samples was then made possible by transducing this selective detection process into an analytical signal using a quartz crystal microbalance (QCM). The Nanogel was shown to demonstrate good repeatability, reproducibility, and stability in terms of its performance. The high selectivity of the Nanogel was determined to be attributed to the size of cavities and their surface characteristics. Ionic interference was present and, heavy metal cations showed an affinity for the NANOGEL synthesized; however, they were demonstrated to be minimized by the selection of porogenic solvents during the synthesis of NANOGEL. We believe that the Nanogel would provide a highly selective and sensitive approach for the detection of NPs in aqueous samples and the removal of NPs from contaminated water resources. It will serve useful in environmental applications. Full article

Mezcal is a traditional Mexican spirit produced by distilling fermented agave, with a unique taste directly related to its volatile compound composition. Thus, the present research proposed the surface plasmon resonance (SPR) technique as a potential method to differentiate mezcals, studying several parameters at angular interrogations and at a fixed angle. The study evaluated eight mezcals from different agave species using SPR and gas chromatography-mass spectrometry (GC-MS). Despite the similarities in mezcal spirits corresponding to the same ethanol content and the same artisanal method, it was possible to obtain well-differentiated characteristics by SPR parameters, such as the width of the curve, the resonant angle, and reflectance intensities. Therefore, it was possible to demonstrate the potential use of the SPR technique as a rapid first approach to a screening test to differentiate types of spirits. Full article

Fast protein and metabolite liquid chromatography (FPLMC) was introduced years ago to enable the easy separation of high-molecular compounds such as proteins from small molecules and the identification of the low-molecular substances. In this paper, the method is applied for the rapid evaluation of freshness and monitoring the aging of animal meat and fish. A novel chromatographic sensor was developed with a deep UV LED-based photometric detection unit (255–265 nm), an original flow cuvette and registration scheme; the processing of a chromatogram with the sensor takes approximately 15 min. Strict isochronism between the elution of ATP metabolites, mainly hypoxanthine (Hx) and inosine monophosphate (IMP), and the time of maturation of meat or fish, was discovered. A new freshness index H* = [Hx]/[IMP] was introduced, which is proportional to the instrumental delay time in the FPMLC chromatograms: the H* index < 0.5 indicates the presence of inosine monophosphate (IMP) and the high quality of the meat or fish. Reasonably strong correlations were revealed between data obtained by FPMLC and total volatile basic nitrogen TVB-N (for fish) or volatile fatty acids VFA (for meat) content. Moreover, putative nucleotide salvage and an increase in the concentration of IMP were observed in fish after heat treatment using the FPMLC sensor and NMR technique. Full article

Bacterial biofilms are a major cause of harm related to medical infections and biofouling. Thus, 80% of total infections are caused by biofilm-forming microorganisms. Consequently, knowledge of biofilm formation stages is crucial to develop effective treatments to prevent their formation in medical implants, tools, and devices. For this purpose, quartz crystal microbalance (QCM) sensors are becoming a good alternative to analytical methods for the real-time monitoring of bacterial growth in liquid media culture. In a previous paper, the authors described an affordable multi-channel measurement instrument based on QCM sensors. However, in order to validate its correct operation, complementary experimental measurements based on bacterial biofilm growth were performed. In this work, the experimental measurements that allow the identification of the different biofilm formation stages are described. The results obtained are discussed. Full article

Myxoid liposarcoma and Ewing sarcoma are the two most common tumor types that are characterized by the FET (FUS, EWSR1 and TAF15) fusion oncogenes. These FET fusion oncogenes are considered to have the same pathological mechanism. However, the cellular similarities between cells from the different tumor entities remain unknown. Here, we profiled individual myxoid liposarcoma and Ewing sarcoma cells to determine common gene expression signatures. Five cell lines were analyzed, targeting 76 different genes. We employed unsupervised clustering, focusing on self-organizing maps, to identify biologically relevant subpopulations of tumor cells. In addition, we outlined the basic concepts of self-organizing maps. Principal component analysis and a t-distributed stochastic neighbor embedding plot showed gradual differences among all cells. However, we identified five distinct and robust subpopulations using self-organizing maps. Most cells were similar to other cells within the same tumor entity, but four out of five groups contained both myxoid liposarcoma and Ewing sarcoma cells. The major difference between the groups was the overall transcriptional activity, which could be linked to cell cycle regulation. We conclude that self-organizing maps are useful tools to define biologically relevant subpopulations and that myxoid liposarcoma and Ewing sarcoma exhibit cells with similar gene expression signatures. Full article

Impedimetric biosensors are used for detecting a wide range of analytes. The detection principle is a perspective for the development of new types of analytical devices for biomolecular diagnosis of diseases. Of particular interest are biosensors with very high sensitivities, capable of detecting trace amounts of biomarkers or drugs in biological fluids. Impedimetric biosensors possess a potential for increased sensitivity, since their electrodes can be modified with nanostructured materials, in particular zinc oxide. In this work, a miniature biosensor with an array of zinc oxide nanorods synthesized by the hydrothermal method has been created. Protein A was immobilized on the resulting structure, which was previously tested for binding to omalizumab by capillary electrophoresis. Using impedance spectroscopy, it was possible to detect the binding of omalizumab at concentrations down to 5 pg/mL. The resulting structures are suitable for creating reusable biosensor systems, since ZnO-coated electrodes are easily cleaned by photocatalytic decomposition of the bound molecules. The biosensor is promising for use in Point-of-Care systems designed for fast, multimodal detection of molecular markers of a wide range of diseases. Full article

In this work, graphene-oxide-decorated porous ZnO nanosheets were prepared using a hydrothermal method. The graphene oxide/porous ZnO nanosheet (GO/ZnO nanosheet) composites were characterized with SEM, HRTEM, XRD, Raman spectroscopy, XPS and BET. The results indicate that the ZnO nanosheets have a porous, single-crystal structure. Thin GO nanosheets closely cover the surface of porous ZnO nanosheets. The sensing performance of GO/ZnO nanosheet composites is investigated. At the optimized temperature of 300 °C, the GO/ZnO nanosheet composites exhibit a superior sensing performance in n-propanol detection. In a wide range of 5–200 ppm, the composites exhibit a linear response to n-propanol. Moreover, the sensing performance of the GO/ZnO nanosheet composites to n-propanol is largely higher than that to other VOC gases, indicating a high selectivity in n-propanol detection. This can be ascribed to the higher electron-separation efficiency and larger depletion layer brought by the modification of the GO on ZnO nanosheets. It is considered that the GO/ZnO nanosheet composites have a great application potential in n-propanol detection. Full article

We developed a simple hydrothermal technique for the fabrication of a flexible integrated composite containing cerium vanadate (CeVO₄) and multi-walled carbon nanotubes (MWCNTs). The CeVO₄/MWCNTs composite possessed good conductivity and interesting electrochemical catalytic performance when immobilized on a glassy carbon electrode (GCE). This CeVO₄/MWCNTs-GCE sensor provided excellent analytical performance for the detection of the sulfonamide antibacterial drug sulfamethazine (SMZ). Benefiting from the significantly enlarged surface area of the modified electrode and the catalytic effect of CeVO₄-MWCNTs, the sensor offered high sensitivity, good stability, fine selectivity, and a remarkable limit of detection (LOD) of 0.02 μM. Furthermore, the sensor also exhibited ideal performance with good recovery and precision when applied to SMZ residue detection in real aquaculture water samples. Full article

In this work, the development and characterization of a new ceramic material modified with polyaniline powder obtained by a high-power ultrasound sol-gel route is presented. A preliminary screening of the conducting polymer electroactivity was performed by means of cyclic voltammetry in free analyte solution. Remarkable figures of merit for 4-chloro-3-methylphenol (PCMC) determination, selected as the model organic analyte, was obtained with the developed material: the sensitivity and the limit of detection were 2.40 μA/μM·cm² and 0.69 μM, respectively. The developed device was also successfully applied in the electrochemical determination of PCMC in water samples collected from different sources, obtaining recovery values ranging from 92% to 105%. The electrochemical performance of the device for the detection of other chlorophenols of interest was better in comparison with the bare electrode in all cases, due to the presence of the bulk modifier in the material. Therefore, the electrode material can be promoted for electrochemical assays of different chlorophenols in buffer and real water media for environmental monitoring. Full article

Oxytetracycline (OTC) is an environmental pollutant caused by the abuse of antibiotics, and its content in water is closely related to human health. Therefore, the development of a simple, rapid, and accurate method to detect OTC has become desirable. In this work, a ratiometric fluorescence probe based on deep red emissive CdTe quantum dots (QDs) modified by mercaptopropionic acid and Eu³⁺ is developed to accurately and rapidly detect OTC in water. After the addition of OTC, the photoluminescence intensity of CdTe QDs at 698 nm remains almost unchanged, while the peak at 617 nm intensifies within 40 s due to the coordination of Eu³⁺ with OTC. An excellent linear relationship is present between the photoluminescence intensity ratio of I₆₁₇/I₆₉₈ and the concentration of OTC. The limit of detection of the probe towards OCT is 5.4 nM. In addition, the probe shows good selectivity and anti-interference ability for OTC in the presence of other antibiotics, including other antibiotics, ions, and amino acids. The probe has been successfully applied to detect OTC in actual samples, demonstrating its potential for environmental application. Full article

Recently, the scientific community has shown a great interest about the Organ-on-Chip (OoC) devices, a special kind of micro-fabricated platforms capable of recapitulating the human physiology implementing the traditional cell culture methods and the concept of in vivo studies. Copper ions represent a cellular micronutrient that must be monitored for its potential hazardous effects. The application of electrochemical analysis for heavy metal ions detection and quantification in commercial cell culture media presents several issues due to electrolyte complexity and interferents. In fact, to the best of our knowledge, there is a lack of applications and OoC devices that implement the Anodic Stripping Voltammetry as an ion dosing technique due to the reasons reported above. In fact, considering just the peak intensity value from the measurement, it turns out to be challenging to quantify ion concentration since other ions or molecules in the media may interfere with the measurement. With the aim to overcome these issues, the present work aims to develop an automated system based on machine learning algorithms and demonstrate the possibility to build a reliable forecasting model for copper ion concentration on three different commercial cell culture media (MEM, DMEM, F12). Effectively, combining electrochemical measurements with a multivariate machine learning algorithm leads to a higher classification accuracy. Two different pH media conditions, i.e., physiological (pH 7.4) and acidic (pH 4), were considered to establish how the electrolyte influences the measurement. The experimental datasets were obtained using square-wave anodic stripping voltammetry (SWASV) and were used to carry out a machine learning trained model. The proposed method led to a significant improvement in Cu²⁺ concentration detection accuracy (96.6% for the SVM model and 93.1% for the NB model in MEM) as well as being able to monitor the pH solution. Full article

Perovskite-type mixed-metal oxides are of particular interest as semiconductor gas sensors due to the variability in the material composition and the stability of sensing parameters. LaFeO₃ is a p-type semiconductor with relatively high conductivity and gas sensitivity. However, less is known about the sensitivity and sensing mechanisms of LaFeO₃ modified by catalytic noble metals. In this work, we used a microwave-assisted sol–gel method to synthesize perovskite LaFeO₃ nanoparticles with an average size of 20–30 nm and a specific surface area of 6–8 m²/g. LaFeO₃ was modified by 2–5 wt.% Ag and Pd nanoparticles via the impregnation route. Using X-ray photoelectron spectroscopy, the additives were observed in the partially oxidized states Ag₂O/Ag and PdO/Pd, respectively. Electric conduction and sensitivity to noxious gases were characterized by electrophysical measurements. It was shown that LaFeO₃ modified by Ag and Pd had improved sensitivity and selectivity to CO, and the sensing behavior persisted in a wide range of relative humidity. Pristine and Ag-modified LaFeO₃ had the maximum sensitivity to CO at a temperature of 200 °C, while modification with Pd resulted in a decreased optimal operating temperature of 150 °C. In situ infrared spectroscopy revealed that supported Pd nanoparticles specifically catalyzed CO oxidation at the surface of LaFeO₃ at room temperature, which was the likely reason for the improved sensitivity and decreased optimal operating temperature of LaFeO₃/Pd sensors. On the other hand, Ag nanoparticles were deduced to activate CO oxidation by lattice oxygen at the surface of LaFeO₃, providing enhanced CO sensitivity at a higher temperature. Full article

Porous (pr-)SnO₂-based powders were synthesized by ultrasonic spray pyrolysis employing home-made polymethylmethacrylate (PMMA) microspheres (typical particle size: 70 nm in diameter), and effects of the Cu_xO addition to the pr-SnO₂ powder on the acetone and toluene sensing properties were investigated. Well-developed spherical pores reflecting the morphology of the PMMA microsphere templates were formed in the SnO₂-based powders, which were quite effective in enhancing the acetone and toluene responses. The 0.8 wt% Cu-added pr-SnO₂ sensor showed the largest acetone response at 350 °C among all the sensors. Furthermore, we clarified that the addition of Cu_xO onto the pr-SnO₂ decreased the concentration of carrier electrons and the acetone-oxidation activity, leading to the improvement of the acetone-sensing properties of the pr-SnO₂ sensor. Full article

Hydrogen sulfide (H₂S) and sulfur dioxide (SO₂) are two typical decomposition byproducts of sulfur hexafluoride (SF₆), commonly used as an insulating medium in electrical equipment; for instance, in gas circuit breakers and gas insulated switchgears. In our work, fiber-like p-CuO/n-ZnO heterojunction gas sensing materials were successfully prepared via the electrospinning method to detect the SF₆ decomposition byproducts, H₂S and SO₂ gases. The sensing results demonstrated that p-CuO/n-ZnO nanofiber sensors have good sensing performance with respect to H₂S and SO₂. It is noteworthy that this fiber-like p-CuO/n-ZnO heterojunction sensor exhibits higher and faster response–recovery time to H₂S and SO₂. The enhanced sensor performances can probably be attributed to the sulfuration–desulfuration reaction between H₂S and the sensing materials. Moreover, the gas sensor exhibited a high response to the low exposure of H₂S and SO₂ gas (below 5 ppm). Towards the end of the paper, the gas sensing mechanism of the prepared p-CuO/n-ZnO heterojunction sensors to SO₂ and H₂S is discussed carefully. Calculations based on first principles were carried out for Cu/ZnO to construct adsorption models for the adsorption of SO₂ and H₂S gas molecules. Information on adsorption energy, density of states, energy gap values and charge density were calculated and compared to explain the gas-sensitive mechanism of ZnO on SO₂ and H₂S gases. Full article

Two-dimensional material (2DM)-based Field-Effect Transistors (FETs) have been postulated as a solid alternative for biosensing applications thanks to: (i) the possibility to enable chemical sensitivity by functionalization, (ii) an atomically thin active area which guarantees optimal electrostatic coupling between the sensing layer and the electronic active region, and (iii) their compatibility with large scale fabrication techniques. Although 2DM-based BioFETs have demonstrated notable sensing capabilities, other relevant aspects, such as the yield or device-to-device variability, will demand further evaluation in order to move them from lab-to-fab applications. Here, we focus on the latter aspect by analyzing the performance of MoS${}_2$-based BioFETs for the detection of DNA molecules. In particular, we explore the impact of the randomized location and activation of the receptor molecules at the sensing interface on the device response. Several sensing interface configurations are implemented, so as to evaluate the sensitivity dependence on device-to-device variability. Full article

We demonstrated that the hybrid core–shell nanostructure of Fe₃O₄ (core) and gold (shell) could be a good substrate candidate both for metal-enhanced fluorescence (MEF) and surface-enhanced Raman spectroscopy (SERS). The magnetic properties of the core material could provide functionalities such as the magnetically induced aggregation/distribution of nanostructures to increase the hot-spot density, while the nano-thickness gold shell allows for the plasmonic enhancement of both fluorescence and SERS. The gold-capped magnetic (Fe₃O₄) nanoparticles (GMPs) were facilely synthesized using a newly developed chemical method. The relative molar ratio of the constituent materials of the core–shell composite was optimized for tuning the plasmonic resonance wavelengths for MEF and SERS. We employed GMP-based MEF to detect alpha-fetoprotein (AFP), with concentrations ranging from 0.05 to 1000 ng/mL, and obtained a limit of detection (LOD) as low as 3.8 × 10⁻⁴ ng/mL. The signal enhancement factor (EF) in the GMP-based MEF was 1.5 at maximum. In addition, the GMPs were used in SERS to detect rhodamine B (RhB). Its LOD was 3.5 × 10⁻¹² M, and the EF was estimated to be about 2 × 10⁸. The hybrid core–shell nanoparticles could find potential applications in diagnostic assays based on MEF and SERS in various fields such as food verification, environmental testing/monitoring, and disease diagnosis. Full article

Titanium dioxide (TiO₂) nanoparticles (NPs) are widely used in industry and commercial products. Thus, their potential risks to the environment and human health must be evaluated. Doping NPs with certain ions makes it possible to mix properties or generate new ones. Thus, in order to track TiO₂ NPs in biological assays, doping with europium (Eu³⁺) ions was performed, which luminesce in red. Here, we synthesized TiO₂ and Eu³⁺-doped TiO₂ nanocrystals (NCs) in anatase phase to verify the toxicity at different concentrations in Drosophila melanogaster and track the distribution of these NCs in vivo. We verified that the incorporation of europium improved the biocompatibility in relation to the pure samples. The presence of Eu³⁺-doped TiO₂ NCs in the gut, brain, and fat body of larvae and intestinal cells of adult animals was detected. Eu³⁺-doped TiO₂ NCs caused significant larval and pupal mortality rates, in addition to leading to the formation of reactive species, especially at high concentrations. Therefore, our data demonstrated it was possible to trace the Eu³⁺-doped TiO₂ NCs, but TiO₂ and Eu³⁺-doped TiO₂ NCs in anatase phase were toxic to fruit flies at the tested concentrations, and should be used with caution to minimize health risks. Full article

The detection of heavy metal ions is becoming increasingly important for environmental monitoring and personal safety protection. Owing to their large surface area and suitable conductivity, metal oxide semiconductor nanocrystals have been utilized in chemically modified electrodes for the rapid and low-cost detection of heavy metal ions. However, their sensitivity and selectivity for cadmium ion (Cd²⁺) detection still remains a challenge. Here, a method of ultra-sensitive and selective Cd²⁺ detection based on WO₃-nanocrystal-modified electrodes is proposed and demonstrated. Colloidal WO₃ nanocrystals were synthesized via a solvothermal route and then deposited onto a carbon electrode using a spin-coating method, forming the modification layer at room temperature. The WO₃-nanocrystal-modified electrodes exhibit a remarkable signal transduction capability that converts Cd²⁺ adsorption into current output signals. The peak current was linear to the logarithm of the Cd²⁺ concentration from 1 nM to 10,000 nM when measured using the anodic stripping voltammetry method. The selectivity mechanism was studied and attributed to the high adsorption energy of cadmium on WO₃ compared to other heavy metal ions. Employment of WO₃ for a high-performance Cd²⁺-selective electrode opens many opportunities in portable ion-detection applications. Full article

Human activity today produces a large number of pollutants that end up in the environment, such as soil, water, and airborne particles. The first objective of this work is to introduce a new third-order multivariate calibration approach called self-weighted alternating quadrilinear decomposition (SWAQLD) for the analysis of organic pollutant of fluorene (FLU) in different water systems. One simulated and two real four-way data sets are used to study the potential of the proposed approach in comparison with two classical algorithms, namely alternating quadrilinear decomposition (AQLD) and parallel factor analysis (PARAFAC). The results of simulated data show that SWAQLD inherits the advantages of PARAFAC in terms of not only tolerance to experimental noise but also a fast convergence and a certain robustness to overestimation of the rank of the models from AQLD. The second objective of this work is to propose a new way of generating third-order data using excitation–emission matrix phosphorescence (EEMP) at room temperature for the study of the kinetic process of oxidation of FLU in complex chemical systems. The obtained rate constant and half-life of the FLU oxidation, on average, are 0.015 min⁻¹ and 45.5 min for free-interference water and 0.017 min⁻¹ and 40.0 min for wastewater, respectively. Research results show that SWAQLD coupled with EEMP allows the quantification and kinetic monitoring of FLU in analytical conditions of different complexities with excellent robustness to the choice of the number of model components. Full article

A new metal–organic framework based on cadmium(II) cations, di(p-carboxyphenyl)sulphone and 4,7-di(imidazol-1-yl)-2,1,3-benzothiadiazole was prepared, and its crystal structure was determined using single-crystal XRD analysis. MOF demonstrated bright luminescence with a maximum near 500 nm and quantum yield reaching 20%. In addition, this MOF demonstrated sensing properties towards antibiotics and a toxic natural polyphenol gossypol through effective luminescence quenching in an ethanol suspension. The determined detection limit for gossypol was among the lowest reported so far (0.65 µM), and did not significantly change in the interference experiments with cottonseed oil as background, indicating the possibility of using this MOF as a sensor for the detection and determination of gossypol in real-life samples. Full article

Self-powered sensors are gaining a lot of attention in recent years due to their possible application in the Internet of Things, medical implants and wireless and wearable devices. Human breath detection has applications in diagnostics, medical therapy and metabolism monitoring. One possible approach for breath monitoring is detecting the humidity in exhaled air. Here, we present an extremely sensitive, self-powered sensor for breath humidity monitoring. As a power source, the sensor uses electromagnetic energy harvested from the environment. Even electromagnetic energy harvested from the human body is enough for the operation of this sensor. The signal obtained using the human body as a source was up to 100 mV with an estimated power of 1 nW. The relatively low amount of energy that could be harvested in this way was producing a signal that was modulated by an interdigitated capacitor made out of electrochemically activated aluminum. The signal obtained in this way was rectified by a set of Schottky diodes and measured by a voltmeter. The sensor was capable of following a variety of different respiration patterns during normal breathing, exercise and rest, at the same time powered only by electromagnetic energy harvested from the human body. Everything happened in the normal environment used for everyday work and life, without any additional sources, and at a safe level of electromagnetic radiation. Full article

Herein, we have reported on a simple, environmentally friendly, and ultra-sensitive electrode material, SnO₂@p-rGO, used in a clean sustainable manner for rapid electrochemical determination of an anti-diabetic agent, repaglinide (RPG). Three-dimensional porous reduced graphene oxide nanostructure (p-rGO) was prepared via a low-temperature solution combustion method employing glycine. The aqueous extract of agricultural waste “cotton boll peel” served as stabilizing and reducing agents for the synthesis of SnO₂ nanoparticles. The structural and morphological characterization was carried out by XRD, Raman, SEM, EDX, FTIR, absorption, and TGA. The oxidation process of RPG was realized under adsorption controlled with the involvement of two protons and electrons. The sensor displayed a wider linearity between the concentration of RPG and oxidation peak current in the ranges of 1.99 × 10⁻⁸–1.45 × 10⁻⁵ M and 4.99 × 10⁻⁸–1.83 × 10⁻⁵ M for square-wave voltammetric and differential pulse voltammetric methods, respectively. The lower limit of detection value of 0.85 × 10⁻⁹ M was realized with the SWV method. The proposed sensor was applied for the quantification of RPG in fortified urine samples and pharmaceutical formulations. Furthermore, the sensor demonstrated reproducibility, long-term stability, and selectivity in the presence of metformin and other interferents, which made the proposed sensor promising and superior for monitoring RPG. Full article

Natural free amino acids present in plant extracts or tea infusions provide a unique flavor and potential effect on anxiety and blood pressure reduction. Accordingly, quantifying free amino acids in foods has been of interest to food science and analytical research fields. The ninhydrin solution-based assay is a colorimetric method based on the formation and detection of Ruhemann’s purple complex. Media-based colorimetric detection requires specialized facilities and personnel; moreover, it can suffer from the interference of the analyte color. In this study, we developed ninhydrin-loaded microcapsules and a simple free amino acids detection procedure, by simply dipping the microcapsules into the analyte solution for 3 min. Among the five tested natural free amino acids, theanine exhibited the highest colorimetric response to microcapsule-based detection, with a limit of detection of 0.826 mM. Full article

We built an integrated solid-contact ion-selective electrode (SCISE) system with the functionality of self-calibration. A multiplexed SCISE sensor (K⁺ and NO₃⁻ vs. Ag/AgCl) was fabricated on printed-circuit board (PCB) substrates and was subsequently embedded into a microfluidic flow cell for self-calibration and flow-through analysis. A PCB circuit that includes modules for both sensor readout and fluid control was developed. The sensors showed a fast and near-Nernstian response (56.6 for the K⁺ electrode and −57.4 mV/dec for the NO₃⁻ electrode) and maintained their performance for at least three weeks. The sensors also showed a highly reproducible response in an automated two-point calibration, demonstrating the potential for in situ monitoring. Lastly, the sensor system was successfully applied to measure mineral nutrients in plant sap samples. Full article

Heptamethine cyanine dyes were synthesized in good yields by the reaction between quaternary indoles and a pentamethinic salt, under mild reaction conditions minimizing photooxidation. These compounds were used as precursors to prepare meso-substituted derivatives. The cyanine dye precursors presented UV-Vis absorption, related to fully allowed electronic transitions and fluorescence emission in the NIR region, without any evidence of aggregation in both ground and excited states. The substitution at the meso position showed a fundamental role in their photophysics, with the main absorption in the green-orange region related to the monomeric species. Moreover, the excited state photophysics presented emission profiles dependent on the excitation wavelengths, complicating the correlation of spectroscopy and structure. Density Functional Theory and OO-SCS-MP2 calculations under different solvation conditions revealed the heavy impact of conjugation effects on ground and excited states’ geometries and electronic configurations of these compounds. Finally, the observed photophysical features of the meso-substituted heptamethine cyanine dyes were successfully used to explore their application as fluorescent probes in biological media, allowing stable staining in live and fixed cells. Full article

In this paper, we propose a fully transparent and flexible high-performance pH sensor based on an amorphous indium gallium zinc oxide (a-IGZO) thin-film transistor (TFT) transducer with a coplanar dual-gate structure on polyimide substrates. The proposed pH sensor system features a transducer unit consisting of a floating gate (FG), sensing gate (SG), and control gate (CG) on a polyimide (PI), and an extended gate (EG) sensing unit on a separate glass substrate. We designed a capacitive coupling between (SG) and (CG) through the FG of an a-IGZO TFT transducer to contribute to sensitivity amplification. The capacitance ratio (C_SG/C_CG) increases linearly with the area ratio; therefore, the amplification ratio of the pH sensitivity was easily controlled using the area ratio of SG/CG. The proposed sensor system improved the pH sensitivity by up to 359.28 mV/pH (C_SG/C_CG = 6.16) at room temperature (300 K), which is significantly larger than the Nernstian limit of 59.14 mV/pH. In addition, the non-ideal behavior, including hysteresis and drift effects, was evaluated to ensure stability and reliability. The amplification of sensitivity based on capacitive coupling was much higher than the increase in the hysteresis voltage and drift rate. Furthermore, we verified the flexibility of the a-IGZO coplanar dual-gate TFT transducer through a bending test, and the electrical properties were maintained without mechanical damage, even after repeated bending. Therefore, the proposed fully transparent and highly sensitive a-IGZO coplanar dual-gate TFT-based pH sensor could be a promising wearable and portable high-performance chemical sensor platform. Full article

Instrument automation, technological advancements and improved computational power made separation science an extremely data-rich approach, requiring the use of statistical and data analysis tools that are able to optimize processes and combine multiple outputs. The use of chemometrics is growing, greatly improving the ability to extract meaningful information. Separation–multidetection generates multidimensional data, whose elaboration should not be left to the discretion of the operator. However, some applications or techniques still suffer from the lack of method optimization through DoE and downstream multivariate analysis, limiting their potential. This review aims at summarizing how chemometrics can assist analytical chemists in terms of data elaboration and method design, focusing on what can be achieved by applying chemometric approaches to separation science. Recent applications of chemometrics in separation analyses, in particular in gas, liquid and size-exclusion chromatography, together with field flow fractionation, will be detailed to visualize the state of the art of separation chemometrics, encompassing volatile, soluble and solid (colloidal) analytes. The samples considered will range from food chemistry and environmental chemistry to bio/pharmaceutical science. Full article

Macrolides are widely used in medicine and veterinary medicine, and are the leading antibiotics in terms of consumption. The release of macrolides and their metabolites into the environment through municipal wastewater can have an adverse effect on aquatic ecosystems and human health. In the present study, a method for the non-targeted screening and semi-quantitative determination of macrolide antibiotics and their derivatives in wastewater based on a combination of chromatographic separation and tandem mass spectrometric detection in precursor ion scan (PrecIS) mode has been proposed. Product ions with m/z 158 and 174 related to specific desosamine fragments were used as diagnostic ions for the PrecIS detection of the macrolide structures without (14- and 15-membered macrocycles) and with a (16-membered macrocycle) glycosylated desosamine moiety, respectively. The combination of the optimized solid phase extraction procedure and HPLC-MS/MS analysis in PrecIS mode allowed for the suspect screening of macrolides in municipal wastewater with limits of detection in the range of 4–150 ng L⁻¹. The developed approach made it possible to detect and tentatively identify in municipal wastewater 17 compounds belonging to the macrolide class, including azithromycin, clarithromycin, josamycin and 14 metabolites with a total concentration of 1450 ng L⁻¹. Full article

Detection of nitroaromatic compounds (NAC) is an important task since these substances are hazardous to both the biosphere and the society. Fluorescent sensors developed for NAC detection usually demonstrate a ‘turn-off’ response to the analyte, while ‘turn-on’ sensors are rarely reported. Here, we present a showcase report on new pyrene-imidazoporphyrin dyads that demonstrate an unusual analytic response to NAC with clear ‘turn-on’ behavior followed by an unexpected appearance of a new band, which can be ascribed to exciplex emission. The porphyrin backbone of the dyad also allows registration of its own fluorescence, providing an internal reference signal for ratiometric detection. The association constants in the order of 10⁴ M⁻¹ are reported. Full article