Chemosensors, Volume 10, Issue 10 (October 2022) – 61 articles

Semiconductor-based gas sensors are of great interest in both industrial and research settings, but poor selectivity has hindered their further development. Current efforts including doping, surface modifications and facet controlling have been proved effective. However, the “methods-selectivity” correlation is ambiguous because of uncontrollable defects and surface states during the experiments. Here, as a case study, using a DFT method, we studied the adsorption features of commonly tested gases—CH₂O, H₂, C₂H₅OH, CH₃COCH₃, and NH_3—on facets of $\mathrm{ZnO}\left(000\overline{1}\right)$, $\mathrm{ZnO}\left(10\overline{1}0\right)$ and $\mathrm{ZnO}\left(10\overline{1}1\right)$. The adsorption energies and charge transfers were calculated, and adsorption selectivity was analyzed. The results show $\mathrm{ZnO}\left(000\overline{1}\right)$ has obvious CH₂O adsorption selectivity; $\mathrm{ZnO}\left(10\overline{1}0\right)$ has a slight selectivity to C₂H₅OH and NH₃; and $\mathrm{ZnO}\left(10\overline{1}1\right)$ has a slight selectivity to H₂, which agrees with the experimental results. The mechanism of the selective adsorption features was studied in terms of polarity, geometric matching and electronic structure matching. The results show the adsorption selectivity is attributed to a joint effort of electronic structure matching and geometric matching: the former allows for specific gas/slab interactions, the latter decides the strength of the interactions. As the sensing mechanism is probably dominated by gas–lattice interactions, this work is envisioned to be helpful in designing new sensing material with high selectivity. Full article

Surfaces with antifouling properties are critical for optimizing biosensors to improve the selectivity and specificity of analyte detection in complex biological samples. This work describes the four-step synthesis of 3-dithiothreitol propanoic acid (DTT_COOH), a new antifouling thiol linker that (a) significantly reduces fouling of raw human serum samples and (b) binds amino receptors via its terminal carboxylic acid group. DTT_COOH was successfully functionalized on quartz crystal microbalance (QCM) discs and used to anchor penicillin-binding aptamers. Relative to bare and coated (11-mercaptoundecanoic acid (MUA) and 1-undecanethiol (UDT)) QCM crystals, DTT_COOH’s antifouling improved by approximately 75–86%. Following aptamer/ethanolamine extension, the modified DTT_COOH layer reduced serum fouling by approximately 95–97% compared to bare and coated (MUA, UDT) crystals. QCM with dissipation (QCM-D) monitoring, contact goniometry, and cyclic voltammetry techniques were used to compare the DTT_COOH surfaces with quartz crystals functionalized with hydrophobic and hydrophilic molecules. Full article

The formation of stable binary water-soluble sub-micellar aggregates of cetyltrimethylammonium bromide-copper-pyrocatechol violet complex (CTAB-Cu-PCV) diminishes the stability and absorbance of the Cu-PCV complex. A new flow injection spectrophotometric sensing strategy used for the determination of CTAB in commodity personal care antiseptics and water samples has been established relying on the above-mentioned concept. Based on the reduction of the absorption of the Cu-PCV solution by the injection of CTAB solution at pH 6.0 and 430 nm, a linear absorbance decrease was observed over the CTAB concentration range of 2.0 to 100.0 µg mL⁻¹ (r = 0.987). The analysis method showed limits of detection (3.3 ơ) and quantification (10 ơ) of 0.08 and 0.27 µg mL⁻¹, respectively. The precision (RSD) for five replicate determinations was 7.9 and 3.7% at 10 and 50 µg mL⁻¹, respectively. The developed method was applied successfully to the determination of CTAB in personal care products, namely skin lotion and vaginal wash, in addition to water samples. The corresponding RSD (n = 5) values were ≤8.2%. Full article

The spherical diffusion that occurs when using ultramicroelectrodes (i.e., electrodes with a characteristic size of 1–10 µm) contributes to a higher mass transfer rate. This leads to equalization of the depletion rates of the near-electrode layer due to the electrochemical reaction and to the supply of the product from the solution depth. This is the reason why, for ultramicroelectrodes, a limiting size of the spherical layer exists in which the concentration gradient is localized (diffusion layer). Thus, a stationary mass transfer mode is achieved, which is expressed in the sigmoidal CV curve’s shape. In ultramicroelectrode arrays, when the diffusion hemispheres are separated, a steady-state diffusion is realized. However, with a decrease in the interelectrode distance, which leads to the diffusion spheres intersection, a mixed regime arises, which is not fully time-independent. The resulting voltammogram’s shape change can serve as an analytical signal in the study of substances with differing diffusion coefficients, since the diffusion layer growth rate and, consequently, the area of intersection of neighboring spheres, depends on it. This work shows the applicability of voltammetry using ensembles of ultramicroelectrodes operating in the transient mode for the analysis of mixtures of electrochemically active compounds with close electrode reaction parameters, such as exchange currents and electrode potential. Ferrocenemethanol esters are used as an example. The applicability of cyclic voltammetry on the UME array for analysis of mixtures was illustrated by means of finite element modelling. The reliability of the modelling results was experimentally proved for ferrocenemethanol esters with glycine and triglycine. Full article

Flexible pressure sensors usually exhibit high sensitivity, excellent resolution, and can be mass-produced. Herein, a high-resolution, capacitive, paper-based, 3D-printed pressure sensor with a simple, low-cost preparation method is proposed. The sensor has a wide detection range (300–44,000 Pa), a short response time (<50 ms), and high mechanical stability during repeated loading/unloading (3750 Pa). It can measure the weight of an object precisely, from which the shape of the object can be predicted. The sensor can also perform gait detection. The advantages presented by low-cost, high sensitivity, wide detection range, and the ability to be mass-produced make these sensors potential candidates for applications in contact detection and wearable medical devices. Full article

Hollow nanocone arrays are fabricated by a low-cost and efficient colloidal lithography (CL) technique. The hollow nanocone arrays are then reversed to make only the tips contact the substrate. The optical properties of the obverse and inverse hollow nanocone arrays are determined by the surrounding environment, showing different reflection spectra and structure dependence. The inverse hollow nanocone arrays show a relative index sensitivity of 70% per RIU with strict linearity. The fluorescence of fluorophore or staining cells can be facilely enhanced by placing them on the tips of the hollow nanocone arrays, while having no quenching effect. The study of the obverse and inverse hollow nanocone arrays can benefit the understanding of the effect of the environment on the plasmonic resonances. The hollow nanocone arrays are promising to serve as high-performance plasmonic sensors and versatile substrates for surface-enhanced fluorescence imaging. Full article

Though 2,5-dihydroxyterephthalic acid (DHT) is composed of a single benzene molecule, it is blue-emissive in common organic solvents and in the solid state. Like most organic fluorophores, DHT is not soluble in water, which limits its versatile use in metal ion detection in an aqueous medium. To improve the water solubility of DHT and its use as a molecular sensor in aqueous solutions, its deprotonated form, DHT-K, was synthesized through the simple one-pot reaction of DHT with KOH. Compared with DHT, DHT-K was highly soluble in water and emitted yellow fluorescence in the solution and the solid. In addition, DHT-K showed high selectivity for Al ions, exhibiting fluorescence wavelength changes from 540 to 495 nm depending on the Al ion concentration. A linear relationship between the fluorescence intensity of DHT-K and Al ion concentration was established ranging from 18.96 to 247 μM with a detection limit of 1.84 µM. The binding stoichiometry between DHT-K and Al ions was determined by Job’s plot and found to be 1:2. Upon exposure to Al ions, DHT-K showed significant changes in fluorescence color and emission wavelength, whereas no fluorescence changes were observed by the addition of various metal ions such as Zn²⁺, Mg²⁺, Ca²⁺, Cu²⁺, Fe³⁺, and Co²⁺. Thus, DHT-K can be applied as a fluorescent sensor that can selectively detect Al ions in aqueous solutions. Full article

Condensed tannins are short polymers of flavan-3-ols found in grapes (also known as proanthocyanidins). An investigation on the electrochemical oxidation of grapevine proanthocyanidins (PAs) on glassy carbon electrodes under various conditions was conducted for the first time. To study how the proanthocyanidins were oxidized, square-wave and cyclic voltammetry were used. There is a predominant oxidation peak associated with the extract of proanthocyanidins, and this can be attributed to the oxidation of catechol 3′,4′-dihydroxyl groups, which can form their oxidation peak. There are two electrons and two protons involved in the oxidation of the catechol group, which must be kept in mind when considering the oxidation of the catechol group. On the glassy carbon electrode (GCE), the PAs extracted from grapevine are oxidized by an adsorption-dependent mechanism as they interact with the GCE surface. As a result, it was found that the anodic peak current varied linearly with PAs’ concentrations in the range of 4 to 50 ppm, with a detection limit of 3.07 ppm (S/N = 3). There was a development in the surface concentration of the oxidation products at the GC electrode; as the scans progressed, the surface concentration of oxidation products at the electrode remained at 4.83 × 10⁻¹¹ mol cm⁻², indicating that they were immobilized on the GCE as oxidation products adsorbed on the electrode. Full article

Using the first-principles theory, the geometric and electronic properties of the Ru-doped PtTe₂ (Ru-PtTe₂) monolayer, and its sensing performance for three VOCs biomarkers, namely, 2-propenal (C₃H₄O), acetone (C₃H₆O) and isoprene (C₅H₈), were analyzed, to expound its potential for exhaled breath analysis and diagnosis of lung cancer. It was found that the Ru-substitution on the surface of the pristine PtTe₂ surface with a Te atom is energy-favorable, with the formation energy of −1.22 eV. Upon adsorption of the three VOC gas species, chemisorption was identified with the adsorption energies of −1.72, −1.12 and −1.80 eV for C₃H₄O, C₃H₆O and C₅H₈, respectively. The Ru-doping results in a strong magnetic property for the PtTe₂ monolayer, whereas the gas adsorption eliminates this magnetic behavior. The electronic properties reveal the sensing mechanism of the Ru-PtTe₂ monolayer for gas detection, and the bandgap change indicates its admirable positive sensing response for the three gas species. Therefore, we conclude that the Ru-PtTe₂ monolayer is a promising sensing material to realize the diagnosis of lung cancer through exhaled gas detection, with a remarkable decrease in its electrical conductivity. This work paves the way for further exploration of the PtTe₂-based gas sensor for early diagnosis of lung cancer, and we hope that more sensing materials can be investigated using the PtTe₂ monolayer. Full article

Hydrogen sulfide (H₂S) plays a crucial role in a variety of physiological and pathological processes, similar to other gaseous signaling molecules. The significant pathophysiological functions of H₂S have sparked a great deal of interest in the creation of fluorescent probes for H₂S monitoring and imaging. Using 3-cyanoumbelliferone as the push–pull fluorophore and a dinitrophenyl substituent as the response site, herein we developed a umbelliferone-based fluorescent probe 1 for H₂S, which exhibited a remarkable turn-on fluorescence response with a low detection limit (79.8 nM), high sensitivity and selectivity. The H₂S-sensing mechanism could be attributed to the cleavage of the ether bond between the dinitrophenyl group and the umbelliferone, leading to the recovery of an intermolecular charge transfer (ICT) process. Moreover, the probe had negligible cytotoxicity and good cell membrane permeability, which was successfully applied to image H₂S in MCF-7 cells and zebrafish. Full article

SnO₂ thin films were prepared by conventional and Glancing Angle Deposition reactive sputtering, and their gas sensing properties were investigated. The porosity of the as-prepared films was widely assessed using optical methods, and the sensing performances of these active layers were correlated with the evolution of surface and film porosity as a function of deposition conditions and annealing treatment. The sensor made of inclined columns grown at high sputtering pressure (6 × 10⁻³ mbar) and annealed at 500 °C in air exhibited the best response to benzene, with a limit of detection of 30 ppb. In addition, successful BTEX (i.e., benzene, toluene, ethylbenzene, and xylenes) discrimination was achieved by combining the sensing signals of four nanostructured tin-oxide-based gas sensors. Full article

In this article, we developed specific sensing of chloramphenicol (CAP) using strontium selenium nanoflower-adorned phosphorus-doped graphitic carbon nitride (Sr@Se/PGCN) nanocomposite. The synthesized Sr@Se/PGCN nanocomposite was characterized using spectrophotometric techniques. Electrochemical Impedance Spectroscopy (EIS), Cyclic Voltammetry (CV), and Differential Pulse Voltammetry (DPV) were used to examine the electrochemical performance of Sr@Se/PGCN nanocomposite. The Sr@Se/PGCN composite shows excellent performance with a linear range of 5–450 µM and an LOD of 2.7 nM. Furthermore, the present electrochemical CAP sensor exhibited high sensitivity, good stability, exceptional reproducibility, and an excellent recovery rate in real food samples. Full article

In recent years, new strategies for bacteria determination have been developed in order to achieve rapid detection and adequate limits of detection for quantification of microorganisms. This review classifies voltammetric sensors according to whether the bacteria are directly or indirectly detected. Direct methods are based on the recognition of the bacteria themselves, either in labeled or label-free mode. In contrast, indirect methods detect a metabolite produced by the bacteria. New trends in bacteria sensors involve DNA analysis, which makes it possible to improve the sensitivity and specificity of measurements. Voltammetric sensors provide good linear ranges and low limits of detection and are useful for analysis of food and clinical and environmental samples. Full article

Due to the increasing importance of food quality/safety control, there is an imminent need to develop efficient methods for the rapid detection of pesticide residues in agricultural products. Herein, we proposed a simple and rapid detection approach to the in situ detection of residual pesticides on fruit/vegetable using surface-enhanced Raman spectroscopy (SERS). Flexible and transparent SERS substrates were fabricated by transferring Au@Ag core-shell nanorods (Au@Ag NRs) arrays to silicone membranes, with the single-layer Au@Ag NRs arrays prepared by the liquid–liquid interface self-assembly method. The as-prepared SERS sensor showed excellent SERS activity and repeatability, and it could be readily pasted onto the surface of fruit and vegetables for residual pesticide detection. For the inspection of thiram in contaminated strawberries, apples, and mushrooms, the limit of detection (LOD) could reach 2 ng/cm² with high measurement recovery and reproducibility. In general, this work provides an effective way for the preparation and application of flexible and transparent SERS substrates in food-safety control. Full article

The detection of toxic metals is indispensable for water safety. In this paper, a small molecule of aggregation-induced emission (AIE) with barbiturate group was synthesized. It combined with mercury ions to form a stable metal complex so as to enhance the color of the solution to achieve the visualization of ion detection. The fluorescent molecule showed good selectivity and anti-interference ability and had a low detection limit (DL = 22.27 nM) for mercury ion. Full article

This paper assesses a custom single-type electronic nose (eNose) applied to differentiate the complex aromas generated by the caffeinated and decaffeinated versions of one encapsulated espresso coffee mixture type. The eNose used is composed of 16 single-type (identical) metal–oxide semiconductor (MOX) gas sensors based on microelectromechanical system (MEMS). This eNose proposal takes advantage of the small but inherent sensing variability of MOX gas sensors in order to provide a multisensorial description of volatiles or aromas. Results have shown that the information provided with this eNose processed using LDA is able to successfully discriminate the complex aromas of one caffeinated and decaffeinated encapsulated espresso coffee type. Full article

In this study a variety of novel symmetrically and asymmetrically functionalized pillar[5]arenes were synthesized, structurally characterized and applied as ionophores in PVC-plasticized membrane potentiometric sensors. During the sensitivity studies it was found that these novel sensors demonstrate pronounced cationic response towards different metal ions in aqueous solutions. A selectivity evaluation revealed that the developed sensors do not possess sharp preferences to particular ions, but offer a broad cross-sensitivity and can be employed in potentiometric multisensor systems. Full article

Nitrite is harmful to people and animals when it is excessive in an environment. Traditional detection methods are time-consuming and are generally restricted by sensitivity. In this study, a simple and efficient electrochemical sensor made of a glassy carbon electrode (GCE), modified with MoS₂ nanosheets/carboxylic multiwall carbon nanotubes (MoS₂/MWCNT-COOH), was used to detect nitrite. Cyclic voltammetry (CV) was used for drawing the standard curve of nitrite. The properties of the modified materials were analyzed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electrochemical impedance spectroscopy (EIS). The modified electrode presents a great response to nitrite, shows a wide sensing range (10–10,000 μM) and shows a low detection limit (3.6 μM). The characterization of nanomaterials indicates that MoS₂/MWCNT-COOH has a big surface area (150.3 m² g⁻¹) and abundant pores (pore volume is 0.7085 cm³ g⁻¹). In addition, the sensor shows high sensitivity (0.35 μA μM⁻¹ cm⁻²), good reproducibility (RSD is 2.2%), and good stability (the responding current only decreased about 4% after 2 weeks). Therefore, the MoS₂/MWCNT-COOH-modified electrode is a potential analytical method in nitrite determination. Full article

A sensitive and flexible detection method for organophosphorus pesticides (OPs) detection is a crucial request to avoid their further expanded pollution. Herein, an acetylcholinesterase (AChE) electrochemical sensor, based on the co-modification of ZIF-8 and graphene (GR), was constructed for the detection of OPs. ZIF-8/GR composite can provide a stable and biocompatible environment for the loading of AChE and can accelerate the chemical reaction on the electrode surface. After optimization, the linear detection range of the constructed AChE-CS/GR/ZIF-8/GCE sensor for ICP was 0.5–100 ng/mL (1.73–345.7 nM), and the limit of detection was 0.18 ng/mL (0.62 nM). Moreover, high sensitivity and high specificity of the sensor were also achieved in actual cabbage and tap water samples. Therefore, it has great potential for the application of organophosphorus pesticide residue analysis. Full article

Fluorescence and colorimetric solid sensors for caustic media and biogenic amine vapors have been prepared. For this purpose, several hydrazone derivatives of naphthalimides were synthesized and anchored to a photo-crosslinked membrane functionalized with acid chloride groups. The membranes were characterized using different techniques, and their thermal properties and swelling degree were determined. The new naphthalimides and the membranes were evaluated as sensors by determining the change in their spectroscopic properties of absorption and fluorescence with pH. The polymeric sensors exhibit improved stability and can be reused, as a consequence of their solid character and the reversibility of the process. Furthermore, membranes were evaluated as a sensor of trimethylamine vapors through their absorption and fluorescence bands, and the color change in the membrane showed that it could be used to detect basic media with the naked eye. Finally, membranes were packaged in Petri dishes at a controlled temperature with fresh fish bought in the local market. Then, the real chance of using the sensory materials was determined by analyzing the color change in samples. Full article

A 3D cobalt metal–organic framework (Co–MOF), [Co₃(BDC)₃(DMU)₂], was utilized to prepare Cu@Co–MOF composite in a deposition–reduction process. Cu@Co–MOF/GCE (GCE = glassy carbon electrode) electrode was prepared by “drop–coating” method. Cu@Co–MOF/GCE shows excellent electrocatalytic activity for Glu detection. The chronoamperometric response of Cu@Co–MOF/GCE to Glu concentration (C_Glu) displays linear relationships in two C_Glu sections with calculated sensitivities of 282.89 μA mM⁻¹ cm⁻² within 0.005–0.4 mM Glu and 113.15 μA mM⁻¹ cm⁻² within 0.4–1.8 mM Glu. The detection limit is calculated as 1.6 μM at S/N = 3. Cu@Co–MOF/GCE also exhibits a rapid current response, high anti–interference, stability, and repeatability to Glu detection. Cu@Co–MOF/GCE was applied to detect Glu in human serum and orange juice. All found C_Glu are very close to those added C_Glu with low RSDs and high recoveries. Cu@Co–MOF/GCE as a non–enzymatic electrochemical sensor of Glu has high sensitivity, selectivity, accuracy, and reliability. Full article

Hydrogels, as a type of three-dimensional porous material, have attracted a lot of attention in the fields of drug delivery, artificial tissue engineering, and sensing. Due to their excellent biocompatibility and high sensitivity to external stimuli, they are widely used in the development of various sensors. Among them, the sensors constructed based on the sol–gel transition of target-responsive hydrogels are particularly welcome. Herein, the status of the sensors on the basis of sol–gel transition has been presented. The types of hydrogel sensors and the analytical methods in various application scenarios are illustrated. In addition, the future trends of the sensing systems based on sol–gel transition are briefly discussed. Full article

With the continuous emission of greenhouse gases, the greenhouse effect is becoming more and more serious. CO₂, CH₄, and N₂O are three typical greenhouse gases, and in order to limit their emissions, it is imperative that they are accurately monitored. In this paper, the doping behavior of Ti on the surface of HfSe₂ is investigated, based on the first-nature principle. Additionally, the parameters of adsorption energy and the transfer charges of Ti−HfSe₂ for CO₂, CH₄, and N₂O are calculated and compared, while the sensing characteristics of Ti−HfSe₂ are analyzed. The results show that the structure is most stable when Ti is located above the lower-layer Se atom. The CO₂ and N₂O adsorption systems with large adsorption energies and transfer charges are a chemical adsorption, while the CH₄ system is a physical adsorption with small adsorption energies and transfer charges. In addition, Ti−HfSe₂ has a good sensitivity and recovery time for CO₂ at 298 K, which is feasible for industrial application. All the contents of this paper provide theoretical guidance for the implementation of Ti−HfSe₂ as a gas-sensitive material for the detection of greenhouse gas components. Full article

Mercury pollution is a global environmental problem, especially in low-resource areas where artisanal iron mining is taking place and industrialization is on the rise. Therefore, there is a demand for simple methods for the determination of toxic metals at low. In this study, an on-field membrane lateral flow test system for sensitive and specific detection of Hg²⁺ in natural waters matrix is proposed. For this purpose, mercaptosuccinic acid (MSA) conjugated with protein-carrier (bovine serum albumin) was pre-impregnated in the test zone of the strip and used as a capping agent for mercury complexation. Quantitative evaluation of the analyte was provided by the use of gold nanoparticles stabilized with Tween-20 as a detecting agent. The sensing principle relies on the formation of Au–Hg nanoalloy during the migration of a solution containing Hg²⁺ along the strip, followed by capture in the test zone with the formation of a colored complex. Under optimum conditions, the proposed lateral flow test exhibited the linear correlation between color intensity in the test zone from the concentration of Hg²⁺ in the range of 0.04–25 ng/mL. The total analysis time was 11 min, without the need for the usage of additional instrumentation. The detection limit was estimated to be 0.13 ng/mL, which is 45 times lower than the WHO guidelines. The applicability of the proposed lateral flow test was confirmed by the analysis of natural waters, with the recoveries ranging from 70 to 120%. Due to the high affinity of Au to Hg and the use of a capping agent for mercury complexing, the developed system demonstrates high selectivity toward Hg²⁺. Compared to existing analytical methods, the proposed approach can be easily implemented and is characterized by economy and high analytical performance. Full article

Metal-organic frameworks (MOFs) are emerging class of ordered porous materials consisting of metal clusters and organic ligands. High porosity, adjustable topology, composition and structural diversity have earned MOFs extensive popularity in various fields, including biosensing. This review focuses on understanding the role of MOFs in biosensing, mainly as efficient signal probes, nanozymes and nanocarriers. It also provides the recent advances of MOFs in sensing biomacromolecules such as protein, peptide, DNA, RNA and polysaccharide. In addition, the challenge, and perspectives, of MOFs in biosensing are presented, based on our opinion. Full article

Twisting intramolecular charge transfer (TICT) is a common nonradiative relaxation pathway for a molecule with a flexible substituent, effectively reducing the fluorescence quantum yield (FQY) by swift twisting motions. In this work, we investigate coumarin 481 (C481) that contains a diethylamino group in solution by femtosecond transient absorption (fs-TA), femtosecond stimulated Raman spectroscopy (FSRS), and theoretical calculations, aided by coumarin 153 with conformational locking of the alkyl arms as a control sample. In different solvents with decreasing polarity, the transition energy barrier between the fluorescent state and TICT state increases, leading to an increase of the FQY. Correlating the fluorescence decay time constant with solvent polarity and viscosity parameters, the multivariable linear regression analysis indicates that the chromophore’s nonradiative relaxation pathway is affected by both hydrogen (H)-bond donating and accepting capabilities as well as dipolarity of the solvent. Results from the ground- and excited-state FSRS shed important light on structural dynamics of C481 undergoing prompt light-induced intramolecular charge transfer from the diethylamino group toward –C=O and –CF₃ groups, while the excited-state C=O stretch marker band tracks initial solvation and vibrational cooling dynamics in aprotic and protic solvents (regardless of polarity) as well as H-bonding dynamics in the fluorescent state for C481 in high-polarity protic solvents like methanol. The uncovered mechanistic insights into the molecular origin for the fluorogenicity of C481 as an environment-polarity sensor substantiate the generality of ultrafast TICT state formation of flexible molecules in solution, and the site-dependent substituent(s) as an effective route to modulate the fluorescence properties for such compact, engineerable, and versatile chemosensors. Full article

Excessive use of animal manure as fertilizers can lead to pollution through the introduction of nitrogen, phosphorus, and other mineral compounds to the environment. Wet chemical analytical methods are traditionally used to determine the precise chemical composition of manure to manage the application of animal waste to the soil. However, such methods require significant resources to carry out the processes. Affordable, rapid, and accurate methods of analyses of various chemical components present in animal manure, therefore, are valuable in managing soil and mitigating water pollution. In this study, a stacked regression ensemble approach using near-infrared spectroscopy was developed to simultaneously determine the amount of dry matter, total ammonium nitrogen, total nitrogen, phosphorus pentoxide, calcium oxide, magnesium oxide, and potassium oxide contents in both cattle and poultry manure collected from livestock production areas in France and Reunion Island. The performance of the stacked regression, an ensemble learning algorithm that is formed by collating the well-performing models for prediction was then compared with that of various other machine learning techniques, including support vector regression (linear, polynomial, and radial), least absolute shrinkage and selection operator, ridge regression, elastic net, partial least squares, random forests, recursive partitioning and regression trees, and boosted trees. Results show that stack regression performed optimally well in predicting the seven abovementioned chemical constituents in the testing set and may provide an alternative to the traditional partial least squares method for a more accurate and simultaneous method in determining the chemical properties of animal manure. Full article

Dumped waste is not only a problem from an aesthetic point of view, but also has an environmental polluting effect, or can even pose a direct danger if the waste is dumped in illegal landfills in an uncontrolled manner with unknown composition. In the case of soil pollution, the assessment of the changing microbial state can be used as an indicator of initial changes, since waste as a pollutant impacts the diversity of the landfill’s microbial community. The degree of change depends on the qualitative and quantitative composition of the pollutants, which can be measured through the microbial phospholipid fatty acid (PLFA) pattern. The aim was a comprehensive assessment of the soil microbiological and toxicological hazards of various illegal landfill. Cluster-analysis of the average principal component revealed significant differences between the experimental sites. In comparison with the control site, the percentage of fatty acid biomarkers of Gram-positive bacteria was significantly higher in the contaminated areas, as well as the ratio of trans/cis isomerization in the case of 16:1ω7 and 18:1ω7 fatty acids. The inverse tendency was observed in the relative quantities of fatty acid biomarkers of Gram-negative bacteria compared to Actinomycetes, and in the fungal-bacterial ratio. Full article

We leveraged chemical-induced changes to microwave signal propagation characteristics (i.e., S-parameters) to characterize the detection of aliphatic alcohol (methanol, ethanol, and 2-propanol) vapors using TCNQ-doped HKUST-1 metal-organic-framework films as the sensing material, at temperatures under 100 °C. We show that the sensitivity of aliphatic alcohol detection depends on the oxidation potential of the analyte, and the impedance of the detection setup depends on the analyte-loading of the sensing medium. The microwaves-based detection technique can also afford new mechanistic insights into VOC detection, with surface-anchored metal-organic frameworks (SURMOFs), which is inaccessible with the traditional coulometric (i.e., resistance-based) measurements. Full article

An electrochemical sensor based on a molecularly imprinted polymer membrane (MIP) was developed. The electrochemical sensor was prepared by electropolymerization of o-phenylenediamine (O-PD) on the surface of glassy carbon electrode (GCE), modified by AuNPs@covalent organic framework (COF) microspheres with ascorbic acid (AA) as template molecule. First, ultrasmall polyvinylpyrrolidone (PVP)-coated AuNPs were prepared by a chemical reduction method. Then, 1,3,5-tri(p-formylphenyl)benzene (TFPB) and N-boc-1,4-phenylene diamine (NBPDA) underwent an ammonaldehyde condensation reaction on PVP-coated AuNPs to form AuNPs@COF_TFPB-NBPDA microspheres. The porous spherical structure of AuNPs@ COF_TFPB-NBPDA could accelerate the mass transfer, enlarge the specific surface area, and enhance the catalytic activity of PVP-coated AuNPs. The electrochemical sensors, based on AuNPs@ COF_TFPB-NBPDA/GCE and nMIPs/AuNPs@COF_TFPB-NBPDA/GCE, were applied for the detection of AA, with a detection limit of 1.69 and 2.57 μM, as well as linear ranges of 5.07 to 60 mM and 7.81 to 60 mM. The nMIPs/AuNPs@COF_TFPB-NBPDA sensor had satisfactory stability, selectivity, and reproducibility for AA detection. Full article