Chemosensors, Volume 12, Issue 1 (January 2024) – 16 articles

Cruciferous vegetables (Brassicaceae family) are a rich source of phytochemicals, in particular glucosinolates (GLS) and their hydrolysis products, isothiocyanates and nitriles. These phytochemicals may act as chemosensors, attracting insects, such as Pieris rapae, and stimulating oviposition. There is a lack of information on the concentrations of isothiocyanates and nitriles when an insect affects a Brassicaceae plant. In the current study, some GLS hydrolysis products were determined in healthy and Pieris rapae-infected organic cultivated broccoli plants, as well as the infesting insects’ larvae, using gas chromatography-mass spectrometry (GC-MS). This study investigated the following phytochemicals: phenethyl isothiocyanate (PEITC), erucin (ER), 3-(methylthio)propyl isothiocyanate (3MIC), and 1-cyano-4-(methylthio)butane (5MITN). All these components were quantified in the aerial and underground parts of the plants and were found in high concentrations in the roots. Among the phytochemicals studied, 5MITN presented the highest concentration in all the broccoli samples but was especially high in the stalks of the infected plants. Moreover, the analysis of a sample of Pieris rapae larvae, fed from the hosted broccoli, revealed the presence of PEITC and ER. These findings indicate that the infestation of broccoli with Pieris rapae may affect the distribution of PEITC, ER, 3MIC, and 5MITN throughout the plant. An extension of our study to conventional cultivated broccoli showed that the roots are indeed rich in GLS hydrolysis products. Full article

In this work, a ferrocene-containing gallic acid-derivative modified carbon-nanotube paste electrode (Gal-Fc-CNT), obtained through simple mechanical mixing, was studied for the fast simultaneous voltammetric determination of doxorubicin (DOX), capecitabine (CPB), and cyclophosphamide (CPP) as cytostatic indices based on their cumulative signals and the selective determination of DOX. The individual and simultaneous electrochemical behavior of DOX, CPB, and CPP, studied through cyclic voltammetry (CV) on the Gal-Fc-CNT paste electrode at various pHs and potential ranges, allowed for the development of a simple simultaneous determination method as a cytostatic index at a pH of 12 using square-wave voltammetry, which allowed for a better performance than reported electrodes for each individual cytostatic. A faster and selective detection of DOX, with a limit of detection of 75 ng·L⁻¹, was achieved using square-wave voltammetry at a pH of 3. The good results obtained for the real tap water assessment indicated the applicability of the Gal-Fc-CNT paste electrode for practical applications (water samples). Full article

Biofilms are ubiquitous at interfaces of natural and technical origin. Depending on type and application, biofilm formation is desired or has to be prevented. Therefore, reliable detection of initial biofilm growth is essential in many areas. One method of biofilm monitoring is the electrochemical impedance spectroscopy. Among other factors, this method is heavily dependent on the electrode geometry. In order to achieve a high measurement sensitivity, the electrode size must be chosen according to the biofilm that is to be measured. This paper presents an approach for simulating and modeling the optimal electrode geometry for a specific biofilm. First, a geometric model of a biofilm with up to 6000 individual bacteria is generated. The simulated impedances are used to calculate which electrode geometry maximizes sensitivity depending on the biofilm height. In the chosen example of an E. coli biofilm in a nutrient solution, the optimum size of an interdigital electrode (bar gap equals width) was 2.5 µm for a biofilm height of up to 2 µm. The used algorithms and models can be simply adapted for other biofilms. In this way, the most sensitive electrode geometry for a specific biofilm measurement can be determined with minimal effort. Full article

Ethylene, an important phytohormone, significantly influences plant growth and the ripeness of fruits and vegetables. During the transportation and storage of agricultural products, excessive ethylene can lead to economic losses due to rapid deterioration. Metal oxide semiconductor (MOS)-based chemo-resistive sensors are a promising technology for the detection of ethylene due to their low cost, high sensitivity, portability, etc. This review comprehensively summarizes the materials, fabrications, agricultural applications, and sensing mechanisms of these sensors. Moreover, the current challenges are highlighted and the potential solutions are proposed. Full article

Vaping electronic cigarettes (e-cigarettes) has become a popular alternative to smoking tobacco. When an e-cigarette is activated, a liquid is vaporized by heating, producing an aerosol that users inhale. While e-cigarettes are marketed as less harmful than traditional cigarettes, there are ongoing concerns about their long-term health effects, including potential lung damage. Therefore, it is essential to closely monitor and study the composition of e-liquids. E-liquids typically consist of propylene glycol, glycerin, flavorings and nicotine, though there have been reports of non-compliant nicotine concentrations and the presence of illegal additives. This study explored spectroscopic techniques to examine the conformity of nicotine labeling and detect the presence of the not-allowed additives: the caffeine, taurine, vitamin E and cannabidiol (CBD) in e-liquids. A total of 236 e-liquid samples were carefully selected for analysis. Chemometric analysis was applied to the collected data, which included mid-infrared (MIR) and near-infrared (NIR) spectra. Supervised modeling approaches such as partial least squares-discriminant analysis (PLS-DA) and soft independent modeling of class analogy (SIMCA) were employed to classify the samples, based on the presence of nicotine and the targeted additives. This study demonstrates the efficacy of MIR and NIR spectroscopic techniques in conjunction with chemometric methods (SIMCA and PLS-DA) for detecting specific molecules in e-liquids. MIR with autoscaling data preprocessing and PLS-DA achieved 100% classification rates for CBD and vitamin E, while NIR with the same approach achieved 100% for CBD and taurine. Overall, MIR combined with PLS-DA yielded the best classification across all targeted molecules, suggesting its preference as a singular technique. Full article

This work consists of a study to detect prostate cancer using E-senses devices based on electronic tongue and electronic nose systems. Therefore, two groups of confirmed prostate cancer and control patients were invited to participate through urine and exhaled breath samples, where the control patients group was categorized as Benign Prostatic Hyperplasia, Prostatitis, and Healthy patients. Afterward, the samples were subsequently classified using Pattern Recognition and machine learning methods, where the results were compared through clinical history, obtaining a 92.9% success rate in the PCa and control samples’ classification accuracy by using eTongue and a 100% success rate of classification using eNose. Full article

Nowadays, mycotoxin contamination in cereals and wastewater exposes a safety hazard to consumer health. This work describes the design of a simple, low-cost, and sensitive origami microfluidic paper-based device using electrochemical detection for zearalenone determination. The microfluidic immunosensor was designed on a paper platform by a wax printing process. The graphitized carbon working electrode modified with carbon nanohorns-decorated nanoporous gold showed a higher surface area, sensitivity, and adequate analytical performance. Electrodes were characterized by scanning electron microscopy, energy-dispersive spectroscopy, and cyclic voltammetry. The determination of zearalenone was carried out through a competitive immunoassay using specific antibodies immobilized by a covalent bond on the electrode surface. In the presence of HRP-labeled enzyme conjugate, substrate, and catechol, zearalenone was detected employing the developed immunosensor by applying −0.1 V to the working electrode vs silver as a pseudo-reference electrode. A calibration curve with a linear range between 10 and 1000 µg Kg⁻¹ (R² = 0.998) was obtained, and the limit of detection and quantification for the electrochemical immunosensor were 4.40 and 14.90 µg Kg⁻¹, respectively. The coefficient of variation for intra- and inter-day assays was less than 5%. The selectivity and specificity of the sensor were evaluated, comparing the response against zearalenone metabolites and other mycotoxins that could affect the corn samples. Therefore, origami is a promising approach for paper-based electrochemical microfluidic sensors coupled to smartphones as a rapid and portable tool for in situ mycotoxins detection in real samples. Full article

The bismuth sulfide nanostructure has become a promising gas sensing material thanks to its exceptional intrinsic properties. However, pristine Bi₂S₃ as a room-temperature sensing material cannot achieve the highly sensitive detection of ppb-level NO₂ gas. Herein, 1D nanorods with self-assembled hierarchical Bi₂S₃ nanostructures were obtained via a simple hydrothermal process. The as-prepared hierarchical Bi₂S₃ nanostructures exhibited outstanding NO₂ sensing behaviors, such as a high response value (R_g/R_a = 5.8) and a short response/recovery time (τ₉₀ = 28/116 s) upon exposure to 1 ppm NO₂. The limit of detection of hierarchical Bi₂S₃ was down to 50 ppb. Meanwhile, the sensor exhibited excellent selectivity and humidity tolerance. The improved NO₂ sensing properties were associated with the self-assembled hierarchical nanostructures, which provided a rich sensing active surface and accelerated the diffusion and adsorption/desorption processes between NO₂ molecules and Bi₂S₃ materials. Additionally, the sensing response of hierarchical Bi₂S₃ nanostructures is much higher at 100% N₂ atmosphere, which is different from the chemisorption oxygen model. Full article

The genus Thymus encompasses a wide array of taxa, many of which remain underexplored in terms of their phytochemical profile. In this study, we investigated the phytochemical composition of volatile compounds of five Thymus species native to Greece using gas chromatography combined with mass spectrometry. Two samples of T. parnassicus collected from Mts Parnitha and Parnassos were studied. The predominant compounds in the Parnitha sample were α-cadinol (13.53%), E-caryophyllene (11.83%) and selin-11-en-4α-ol (7.29%). The sample from Mt. Parnassos exhibited a high concentration of E-caryophyllene (35.20%) followed by β-bisabolene (10.41%). Additionally, two species, namely T. leucotrichus subsp. leucotrichus and T. atticus, were collected on Mt. Chelmos (Peloponnese). The essential oil of T. leucotrichus was rich in elemol (35.56%), α-eudesmol (11.15%) and β-eudesmol (6.11%). Thymus atticus exhibited a high concentration in linalool (63.04%) and p-cymene (25.63%). In addition, two samples of T. holosericeus collected from Kefalonia Ιsland were both rich in geraniol (89.9% and 87.7%, respectively). We also examined the volatile profile of T. laconicus, a local endemic species of SE Peloponnese (Lakonia area), which remains unexplored. Carvacrol (32.7%) and p-cymene (29.7%) were identified as the dominant compounds. Our study contributes valuable insights into the chemical profile of Thymus spp. and sheds further light on the well-known chemical polymorphism within this genus. Full article

The decolorization process plays a pivotal role in refining Ginkgo ketone ester by primarily eliminating ginkgolic acids, a toxic component. Presently, the conventional testing method involves sending samples for analysis, causing delays that impact formulation production. Hence, the development of a rapid process control method becomes imperative. This study introduces a swift detection approach for three ginkgolic acids during Ginkgo ketone ester’s decolorization. Initially, an ultra-high-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method assessed ginkgolic acid C13:0, ginkgolic acid C15:1, and ginkgolic acid C17:1 concentrations in 91 decolorized solution samples, establishing reference values. Subsequently, using a portable Raman spectrometer, Raman spectra of the decolorized liquid within the 3200–200 cm⁻¹ wavelength range were collected. Ultimately, employing partial least squares regression (PLSR) and ResNeXt50 deep learning algorithms, two quantitative calibration models correlated the ginkgolic acid content to Raman spectral data. Both models exhibited high predictive accuracy, with the ResNeXt50 model demonstrating superior performance. The prediction set correlation coefficients ($R_p^2$) for ginkgolic acid C13:0, ginkgolic acid C15:1, and ginkgolic acid C17:1 were 0.9962, 0.9971, and 0.9974, respectively, with root mean square error of prediction (RMSEP) values of 0.0144, 0.0130, and 0.0122 μg/mL. In contrast, the PLSR model yielded $R_p^2$ values of 0.9862, 0.9839, and 0.9480, with RMSEP values of 0.0273, 0.0305, and 0.0545 μg/mL for the three ginkgolic acids. The ResNeXt50 model not only showcased higher precision but also enhanced interpretability, as analyzed through gradient-weighted class activation mapping (Grad-CAM). The integration of Raman spectroscopy and the ResNeXt50 quantitative calibration model furnishes a real-time and precise approach to monitor ginkgolic acid content in the decolorized solution during Ginkgo ketone ester preparation. This significant advancement establishes a robust framework for implementing quality control measures in the decolorization process. Full article

The detection and monitoring of toxic and harmful gases play a vital role in environmental protection, human health, and industrial and agricultural production. However, it is still challenging to develop gas sensors for the detection of toxic and harmful gases with high sensitivity, good recovery and excellent selectivity. In this study, WO₃/Al₂O₃/graphite composite materials were used for an MEMS 2-CEES gas sensor (dichlorodiethyl sulfide simulation), and the corresponding sensing properties were explored. The experimental results show that when the working temperature is 340 °C, the response of the sensor to 2-CEES gas with a concentration of 5.70 ppm is 69%, the response time is 5 s and the recovery time is 42 s. The sensor also has the advantages of long-term stability and high selectivity. Furthermore, the MEMS gas sensor array based on WO₃/Al₂O₃/graphite composite materials has been achieved and also exhibits excellent sensing performance. Overall, this study provides a strategy for realizing high-performance dichlorodiethyl sulfide gas sensors. Full article

This work reports new analytical applications of glassy carbon electrodes (GCE) modified with a nanohybrid obtained by non-covalent functionalization of multi-walled carbon nanotubes (MWCNTs) with human immunoglobulin G (IgG) (GCE/MWCNT-IgG). We report the label-free and non-amplified breast cancer 1 gen (BRCA1) biosensing based on the facilitated adsorption of the DNA probe at the nanohybrid modified GCE and the impedimetric detection of the hybridization event in the presence of the redox marker benzoquinone/hydroquinone. The resulting genosensor made the fast, highly selective, and sensitive quantification of BRCA1 gene possible, with a linear range between 1.0 fM and 10.0 nM, a sensitivity of (3.0 ± 0.1) × 10² Ω M⁻¹ (R² = 0.9990), a detection limit of 0.3 fM, and excellent discrimination of fully non-complementary and mismatch DNA sequences. The detection of BRCA1 in enriched samples of diluted human blood serum showed a recovery percentage of 94.6%. Another interesting analytical application of MWCNT-IgG-modified GCE based on the catalytic activity of the exfoliated MWCNTs is also reported for the simultaneous quantification of dopamine and uric acid in the presence of ascorbic acid, with detection limits at submicromolar levels for both compounds. Full article

Nanostructured color filters, particularly those generated by the extraordinary optical transmission (EOT) resonance of metal–dielectric nanostructures, have been intensively studied over the past few decades. In this work, we propose a hybrid array composed of a hole array and a disk array with the same working period within the 3–14 μm mid-infrared band. Through numerical simulations, near-perfect transmission (more than 99%) and a narrower linewidth at some resonance wavelengths were achieved, which is vital for highly sensitive sensing applications. This superior performance is attributed to the surface plasmon coupling resonance between the hole and disk arrays. A high tunability of the near-perfect transmission peak with varying structural parameters, characteristics of sensitivity to the background refractive index, and angle independence were observed. We expect that this metallic hole and disk coupling array is promising for use in various applications, such as in plasmon biosensors for the high-sensitivity detection of biochemical substances. Full article

In this research, we demonstrate a wavelength-stable continuous wave (CW) distributed feedback (DFB) quantum cascade laser (QCL) emitting at 7.2 μm using a surface metal grating approach without epitaxial regrowth. The deep metal grating provides an appropriate DFB coupling coefficient and enhanced thermal extraction, resulting in improved lasing performance and the realization of impressive wavelength stability. Quantitatively, the temperature tuning coefficient of the single-mode emission is only 0.54 nm/°C from 20 °C to 70 °C, and the current tuning coefficient of the single-mode emission is 3.2 nm/A from 1.0 A to 1.6 A. A DFB-QCL with a 2 mm cavity length exhibits a low threshold current of 0.6 A and a power of 1.1 W with a slope efficiency of 1 W/A in the CW mode at 300 K. A single-mode operation with a side mode suppression ratio of 33 dB and a single-lobed far-field without beam steering is obtained in the working temperature range of 20–70 °C The improved wavelength stability using a deep surface metal grating approach promises simplified fabrication, which is meaningful for the commercial applications of QCLs. Full article

This work tested near-infrared (NIR) and UV-visible (UV-Vis) spectroscopy coupled with chemometrics to characterize flours from different starch origins. In particular, eighteen starch-containing flours (e.g., type 00 flour, rye, barley, soybean, chestnut, potato, spelt, buckwheat, oat, millet, rice, durum wheat, amaranth, chickpea, sesame, corn, hemp and sunflower flours) were analyzed with a twofold objective: chemically characterizing the investigated flours and laying the groundwork for the development of a fast and suitable method that can identify the botanical source of starch in food. This could ensure ingredient traceability and aid in preventing/detecting food fraud. Untargeted approaches were used for this study, involving the simultaneous acquisition of a large amount of chemical information (UV-Vis on extracted starch and NIR signals on raw flours) coupled with chemometric techniques. UV-VIS spectra were acquired between 225 and 800 nm after sample pretreatment to extract starch. NIR spectra were acquired between 900 and 1700 nm using a poliSPEC NIRe portable instrument on the flours without any kind of pretreatments. An initial exploratory investigation was conducted using principal component analysis and cluster analysis, obtaining interesting preliminary information on patterns among the investigated flours. In particular, the UV-Vis model successfully discerned samples such as potato, chestnut, sunflower, durum wheat, sesame, buckwheat, rice, corn, spelt and 00-type flours. PCA model results obtained from the analysis of NIR spectra also provided comparable results with the UV-Vis model, particularly highlighting the differences observed between hemp and potato flours with soybean flour. Some similarities were identified between other flours, such as barley and millet, rye and oats, and chickpea and amaranth. Therefore, some flour samples underwent surface analysis via scanning electron microscope (SEM) using the Nova NanoSEM 450 to detect distinctive morphology. Full article