Chemosensors

Two inexpensive and simple methods for synthesis of carbon nanodots were applied and compared to each other, namely a hydrothermal and microwave-assisted method. The synthesized carbon nanodots were characterized using transmission electron microscopy (TEM), ultraviolet-visible (UV-Vis), photoluminescence (PL), Fourier transform-infrared spectroscopy (FTIR), and X-ray diffraction (XRD). The synthesized microwave carbon nanodots had smaller particle size and were thus chosen for better electrochemical performance. Therefore, they were used for our modification process. The proposed electrodes performance characteristics were evaluated according to the IUPAC guidelines, showing linear response in the concentration range 10⁻⁶–10⁻², 10⁻⁷–10⁻², and 10⁻⁸–10⁻² M of tobramycin with a Nernstian slope of 52.60, 58.34, and 57.32 mV/decade for the bare, silver nanoparticle and carbon nanodots modified carbon paste electrodes, respectively. This developed potentiometric method was used for quantification of tobramycin in its co-formulated dosage form and spiked human plasma with good recovery percentages and without interference of the co-formulated drug loteprednol etabonate and excipients. Full article

Metal oxide semiconductors have found widespread applications in chemical sensors based on electrical transduction principles, in particular for the detection of a large variety of gaseous analytes, including environmental pollutants and hazardous gases. This review recapitulates the progress in copper oxide nanomaterial-based devices, while discussing decisive factors influencing gas sensing properties and performance. Literature reports on the highly sensitive detection of several target molecules, including volatile organic compounds, hydrogen sulfide, carbon monoxide, carbon dioxide, hydrogen and nitrogen oxide from parts-per-million down to parts-per-billion concentrations are compared. Physico-chemical mechanisms for sensing and transduction are summarized and prospects for future developments are outlined. Full article

In recent years, mathematical modelling has known an overwhelming integration in different scientific fields. In general, modelling is used to obtain new insights and achieve more quantitative and qualitative information about systems by programming language, manipulating matrices, creating algorithms and tracing functions and data. Researchers have been inspired by these techniques to explore several methods to solve many problems with high precision. In this direction, simulation and modelling have been employed for the development of sensitive and selective detection tools in different fields including environmental control. Emerging pollutants such as pesticides, heavy metals and pharmaceuticals are contaminating water resources, thus threatening wildlife. As a consequence, various biosensors using modelling have been reported in the literature for efficient environmental monitoring. In this review paper, the recent biosensors inspired by modelling and applied for environmental monitoring will be overviewed. Moreover, the level of success and the analytical performances of each modelling-biosensor will be discussed. Finally, current challenges in this field will be highlighted. Full article

Bacterial infections have become a significant challenge in terms of public health, the food industry, and the environment. Therefore, it is necessary to address these challenges by developing a rapid, cost-effective, and easy-to-use biosensor for early diagnosis of bacterial pathogens. Herein, we developed a simple, label-free, and highly sensitive immunosensor based on electrochemical detection using the [email protected]₂–PANI nanocomposite. The conductivity of the glassy carbon electrode is greatly enhanced using the [email protected]₂–PANI nanocomposite and a self-assembled monolayer of mercaptopropionic acid on the gold nanoparticle surface was employed for the covalent immobilization of antibodies to minimize the nonspecific adsorption of bacterial pathogens on the electrode surface. The biosensor established a high selectivity and sensitivity with a low limit of detection of 10 CFU/mL, and detected Escherichia coli within 30 min. Moreover, the developed biosensor demonstrated a good linear detection range, practical utility in urine samples, and electrode regenerative studies. Full article

In this paper, a novel NL-Fe³⁺ ensemble was designed as a fluorescent chemosensor for highly selective detection of pyrophosphate (PPi) in DMSO/H₂O (2:8/v:v, pH = 7.2) solution and living cells. NL showed a strong affinity for Fe³⁺ and was accompanied by obvious fluorescence quenching. Upon the addition of PPi to the generated NL-Fe³⁺ ensemble, the fluorescence and absorption spectra were recovered completely. Spectroscopic investigation showed that the interference provoked by common anions such as adenosine-triphosphate (ATP), adenosine diphosphate (ADP), and phosphates (Pi) can be ignored. The detection limit of NL-Fe³⁺ to PPi was calculated to be 1.45 × 10⁻⁸ M. Intracellular imaging showed that NL-Fe³⁺ has good membrane permeability and could be used for the detection of PPi in living cells. A B3LYP/6-31G(d,p) basis set was used to optimize NL and NL-Fe³⁺ complex. Full article

Mexican Tequila is one of the most demanded import spirits in Europe. Its fast-raising worldwide request makes counterfeiting a profitable activity affecting both consumers and legal distillers. In this paper, a sensor-based methodology based on a combination of infrared measurements (IR) and multivariate data analysis (MVA) is presented. The case study is about differentiating two categories of white Tequila: pure Tequila (or ‘100% agave’) and mixed Tequila (or simply, Tequila). The IR spectra were treated and fused with a low-level approach. Exploratory data analysis was performed using PCA and partial least squares (PLS), whilst the authentication analyses were carried out with PLS-discriminant analysis (DA) and soft independent modeling for class analogy (SIMCA) models. Results demonstrated that data fusion of IR spectra enhanced the outcomes of the authentication models capable of differentiating pure from mixed Tequilas. In fact, PLS-DA presented the best results which correctly classified all fifteen commercial validation samples. The methodology thus presented is fast, cheap, and of simple application in the Tequila industry. Full article

This manuscript reports the use of nanoparticle-modified voltammetric sensors for the rapid and green determination of chemical oxygen demand in river waters and waters from agricultural waste. Four different variants of modified electrodes have been prepared: CuO nanoparticles electrogenerated over Cu and covered with Nafion film (CuO/Cu-Nf), and graphite–epoxy composites modified with Cu, CuO, and Cu–Ni alloy nanoparticles. The response features of these electrodes were assessed by calibrating them vs. glucose, glycine, ethyleneglycol, and hydrogenphtalate in alkaline media, as samples providing different difficulty in their (bio)degradation characteristics. The most sensitive electrode was demonstrated to be the (CuO/Cu-Nf) electrode, with an LOD of 12.3 mg O₂·L⁻¹. The joint information provided by the sensor array showed the ability of estimating both the organic load and the type of sample in terms of difficulty of degradation, in what can be named an intelligent sensor assembly. Full article

The processes of scattering slow positrons with the possible formation of positronium play an important role in the diagnosis of both composite materials, including semiconductor materials, and for the analysis of images obtained by positron tomography of living tissues. In this paper, we consider the processes of scattering positrons with the capture of an electron and the formation of positronium. When calculating the cross-section for the capture reaction, exchange effects caused by the rearrangement of electrons between colliding particles are taken into account. Comparison of the results of calculating the cross-section with a similar problem of electron capture by a proton showed that the mass effect is important in such a collision process. The loss of an electron by a lithium atom is more effective when it collides with a positron than with a proton or alpha particles. The dynamic equilibrium of the formation of positronium in the presence of a strong magnetic field is considered. It is shown that a strong magnetic field during tomography investigation shifts the dynamic equilibrium to the positronium concentration followed by positron annihilation with radiation of three gamma-quants. Full article

Biological applications of fluorescent probes are rapidly increasing in the supramolecular chemistry research field. Several organic dyes are being utilized currently in developing and advancing this attractive research area, of which diketopyrrolopyrrole (DPP) organic dyes show an exceptional photophysical features (high-fluorescence quantum yield (FQY), good photochemical and thermal stability) that are essential properties for biological applications. Great efforts have been made in recent years towards developing novel fluorescent DPPs by different chemists for such applications, and some positive results have been reported. As a result, this review article gives an account of the progress that has so far been made very recently, mainly within the last decade, in that we selectively focus on and discuss more from 2015 to present on some recent scholarly achievements of fluorescent DPPs: quantum yield, aggregation-induced emission (AIE), solid-state emission, bio-imaging, cancer/tumor therapy, mitochondria staining and some polymeric fluorescent DPPs. Finally, this review article highlights researchers working on luminescent DPPs and the future prospects in some key areas towards designing DPP-based fluorescent probes in order to boost their photophysical and biological applications more effectively. Full article

Surface imprinting used for template recognition in nanocavities can be controlled and improved by surface morphological changes. Generally, the lithographic technique is used for surface patterning concerning sensing signal amplification in molecularly imprinted polymer (MIP) thin films. In this paper, we describe the effects of silanized silica molds on sensing the properties of MIP films. Porous imprinted poly(MAA–co–EGDMA) films were lithographically fabricated using silanized or non-treated normal silica replica molds to detect 2,4-dichlorophenoxyacetic acid (2,4-D) herbicide as the standard template. The silanized mold MIP film (st-MIP) (Δf = −1021 Hz) exhibited a better sensing response than the non-treated normal MIP (n-MIP) (Δf = −978 Hz) because the imprinting effects, which occurred via functional groups on the silica surface, could be reduced through silane modification. Particularly, two non-imprinted (NIP) films (st-NIP and n-NIP) exhibited significantly different sensing responses. The st-NIP (Δf_st-NIP = −332 Hz) films exhibited lower Δf values than the n-NIP film (Δf_n-NIP = −610 Hz) owing to the remarkably reduced functionality against nonspecific adsorption. This phenomenon led to different imprinting factor (IF) values for the two MIP films (IF_st-MIP = 3.38 and IF_n-MIP = 1.86), which was calculated from the adsorbed 2,4-D mass per poly(MAA–co–EGDMA) unit weight (i.e., Q_MIP/Q_NIP). Moreover, it was found that the st-MIP film had better selectivity than the n-MIP film based on the sensing response of analogous herbicide solutions. As a result, it was revealed that the patterned molds’ chemical surface modification, which controls the surface functionality of imprinted films during photopolymerization, plays a role in fabricating enhanced sensing properties in patterned MIP films. Full article

The sensitivity of conventional ion-sensitive field-effect transistors is limited to the Nernst limit (59.14 mV/pH). In this study, we developed a pH sensor platform based on a coplanar gate AlGaN/GaN metal-oxide-semiconductor (MOS) high electron mobility transistor (HEMT) using the resistive coupling effect to overcome the Nernst limit. For resistive coupling, a coplanar gate comprising a control gate (CG) and a sensing gate (SG) was designed. We investigated the amplification of the pH sensitivity with the change in the magnitude of a resistance connected in series to each CG and SG via Silvaco TCAD simulations. In addition, a disposable extended gate was applied as a cost-effective sensor platform that helped prevent damages due to direct exposure of the AlGaN/GaN MOS HEMT to chemical solutions. The pH sensor based on the coplanar gate AlGaN/GaN MOS HEMT exhibited a pH sensitivity considerably higher than the Nernst limit, dependent on the ratio of the series resistance connected to the CG and SG, as well as excellent reliability and stability with non-ideal behavior. The pH sensor developed in this study is expected to be readily integrated with wide transmission bandwidth, high temperature, and high-power electronics as a highly sensitive biosensor platform. Full article

During the past two decades, one–dimensional (1D) metal–oxide nanowire (NW)-based molecular sensors have been witnessed as promising candidates to electrically detect volatile organic compounds (VOCs) due to their high surface to volume ratio, single crystallinity, and well-defined crystal orientations. Furthermore, these unique physical/chemical features allow the integrated sensor electronics to work with a long-term stability, ultra-low power consumption, and miniature device size, which promote the fast development of “trillion sensor electronics” for Internet of things (IoT) applications. This review gives a comprehensive overview of the recent studies and achievements in 1D metal–oxide nanowire synthesis, sensor device fabrication, sensing material functionalization, and sensing mechanisms. In addition, some critical issues that impede the practical application of the 1D metal–oxide nanowire-based sensor electronics, including selectivity, long-term stability, and low power consumption, will be highlighted. Finally, we give a prospective account of the remaining issues toward the laboratory-to-market transformation of the 1D nanostructure-based sensor electronics. Full article

A selective and inexpensive chemical paper-based sensor for the detection of gaseous H₂S is presented. The triggering of the sensing mechanism is based on an arene-derivative dye which undergoes specific reactions in the presence of H₂S, allowing for colorimetric analysis. The dye is embedded into a porous cellulose matrix. We passively exposed the paper strips to H₂S generated in situ, while the absorbance was monitored via an optic fiber connected to a spectrophotometer. The kinetics of the emerging absorbance at 534 nm constitute the sensor response and maintain a very stable calibration signal in both concentration and time dimensions for quantitative applications. The time and concentration dependence of the calibration function allows the extraction of unusual analytical information that expands the potential comparability with other sensors in the literature, as the limit of detection admissible within a given exposure time. The use of this specific reaction ensures a very high selectivity against saturated vapors of primary interferents and typical volatile compounds, including alkanethiols. The specific performance of the proposed sensor was explicitly compared with other colorimetric alternatives, including standard lead acetate strips. Additionally, the use of a smartphone camera to follow the color change in the sensing reaction was also tested. With this straightforward method, also affordable for miniature photodiode devices, a limit of detection below the ppm scale was reached in both colorimetric approaches. Full article

The halide anions are essential for supporting life. Therefore, halide anion analyses are of paramount importance. For this reason, we have performed both qualitative and quantitative ana- lyses of halides (chloride, bromide, iodide) using the Tl(III) complex of azodye, 4-(2-pyridylazo)re- sorcinol (PAR), a potential new chemical reagent/sensor that utilizes the substitution reaction whereas the Tl(III)PAR complex reacts with a halide to yield a more stable thallium(III)-halide while releasing the PAR ligand in a process accompanied by color change of the solution. The experimental conditions (e.g., pH, ratio metal ion-to-ligand ratio, etc.) for the substitution reaction between the metal complex and a halide were optimized to achieve increased sensitivity and a lower limit of detection (chloride 7 mM, bromide 0.15 mM, iodide 0.05 mM). It is demonstrated that this single chemosensor can, due to release of colored PAR ligand and the associated analyte-specific changes in the UV/VIS spectra, be employed for a multicomponent analysis of mixtures of anions (chloride + bromide, chloride + iodide, bromide + iodide). The spectrophotometric data evaluated by artificial neural networks (ANNs) enable distinguishing among the halides and to determine halide species concentrations in a mixture. The Tl(III)-PAR complex was also used to construct sensor arrays utilizing a standard 96-well plate format where the output was recorded at several wavelengths (up to 7) using a conventional plate reader. It is shown that the data obtained using a digital scanner employing only three different input channels may also be successfully used for a subsequent ANN analysis. The results of all approaches utilized for data evaluation were similar. To increase the practical utility of the chemosensor, we have developed a test paper strip indicator useful for routine naked-eye visual determination of halides. This test can also be used for halide anion determination in solutions using densitometer. The methodology described in this paper can be used for a simple, inexpensive, and fast routine analysis both in a laboratory as well as in a field setting. Full article

This work presents the development and validation of an electroanalytical method for Pb(II) determination in a single drop. The electrochemical sensors used were an unmodified screen-printed electrode (SPE) and a Bi-film SPE (BiFSPE). Anodic square wave stripping voltammetry (SWASV) was performed at an accumulation potential of −1.5 V vs. Ag/AgCl and an accumulation time of 60 s. Electroanalysis with an unmodified SPE did not yield satisfactory results, whereas the BiFSPE was a much better analysis method. The linear concentration using the BiFSPE was in the range of 138.8–162.5 µg/L. The accuracy and precision were evaluated for different spiked concentrations, but the method using the unmodified SPE was neither accurate nor precise. Using the BiFSPE, the method was found to be both accurate and precise for Pb(II) determination at a concentration of 140.0 μg/L, with recovery and relative standard deviation (RSD) of 106.6% and 12.1%, respectively. In addition, using the BiFSPE, LOD and LOQ values of 1.2 μg/L and 3.3 μg/L were obtained, respectively. The possible interference effect on Pb(II) stripping signal was checked in the presence of Cd(II), Zn(II), Cu(II), Sn(IV), Sb(III), Hg(II), Fe(III), As(V), K(I), I⁻, Ca(II), and NO_3⁻. Electrochemical impedance spectroscopy measurements were also performed for the unmodified SPE and BiFSPE. The application of single drop Pb(II) analysis was tested by real water sample analysis. Full article

The nanostructuring of a sensing membrane is performed through colloidal nanosphere lithography (NSL) techniques with a tiny polystyrene nanobead template 100 nm in size. The solvent ratio adjustment has been proven to be effective in assisting the monolayer deposition of small templating particles with minimal defects. Two distinct structures, namely, a billowy gold nanostructure (BGN) where the nanobead template is left unetched and a gold nanoframe array (GNA) with a regular ring-like structure after template removal, are used for the extended-gate field-effect transistor (EGFET) electrodes. The GNA structure generates an electroactive surface area significantly (~20%) larger than its geometrical area as well as a greater surface roughness than the BGN. When integrated with the portable constant voltage–constant current (CVCC) FET circuitry for pH screening to determine the optimized measurement conditions for H₂O₂ sensing, the GNA sensing membrane also shows more improved Nernstian sensitivity at ~50 mV/pH than the BGN electrode. The more optimized sensitivity is then proven using the GNA in the detection of H₂O₂, the most common representative reactive oxygen species (ROS) involved in the environment, food, and neurodegenerative diseases, such as Parkinson´s and Alzheimer´s diseases. The GNA electrode has a sensitivity of 70.42 mV/log µM [H₂O₂] and a limit of detection (LoD) of 1.183 µM H₂O₂. The integrated ion sensing system employing unique, highly ordered gold array gate electrodes and a portable CVCC circuit system has shown a stable real-time output voltage signal, representing an alternative to bulky conventional FET devices for potential on-site H₂O₂ detection. Full article

In this article, silver nanowires (AgNWs) were prepared and introduced into the double-layer photoanode of dye-sensitized solar cells (DSSCs). Silver nanowires with a diameter of about 50–60 nm and a length of 1–2 mm were prepared by the polyol method. The power conversion efficiency of the double-layer photoanode DSSC made of [email protected]₂ and [email protected]₂ composite materials is 6.38%. Compared with the unmodified DSSC, the composite double-layer photoanode combined with AgNWs and AgNPs increased the efficiency of DSSC by 58.7%. This increased efficiency was mainly due to the localized surface plasmon resonance effect caused by AgNPs and AgNWs. The increased light collection was caused by the plasma effect of AgNPs, and it increased the short-circuit photocurrent density (J_SC). The conductive properties of AgNWs improved interface charge transfer and delay charge recombination. The effect of a low light environment on DSSC efficiency was also investigated, and the best photovoltaic conversion efficiency under an irradiance of 10 mW/cm² was found to be 8.78%. Full article

Herein, a feasible chemical reduction method followed by intensive mixing was applied for the preparation of an attractive material based on graphite studded with cuprous oxide nanoparticle-based cubes (Cu₂ONPs–[email protected]). Transmission electron microscope (TEM), scanning electron microscope (SEM), X-ray diffraction (XRD) and cyclic voltammetry (CV) were utilized for characterization. Cuprous oxide nanoparticles (Cu₂ONPs), with a diameter range mainly distributed from 4 to 20 nm, aggregate to form microcubes (Cu₂ONPs–C) with an average diameter of about 367 nm. Paste electrode was prepared using Cu₂ONPs–[email protected] (Cu₂ONPs–[email protected]/PE) for voltametric quantification of the musculotropic antispasmodic drug: mebeverine hydrochloride (MEB). The electrochemical behavior of MEB was studied using CV, and the optimum analytical parameters were investigated using square wave adsorptive anodic stripping voltammetry (SWAdASV). Moreover, density functional theory (DFT) was used to emphasize the ability of MEB to form a complex with Cu²⁺, confirming the suggested electrochemical behavior of MEB at Cu₂ONPs–[email protected]/PE. With good stability and high reproducibility, SWAdASV of Cu₂ONPs–[email protected]/PE shows successful quantification of MEB over the concentration range of 5.00 × 10⁻¹¹–1.10 × 10⁻⁹ M with lower limit of detection (LOD) and lower limit of quantification (LOQ) values of 2.41 × 10⁻¹¹ M and 8.05 × 10⁻¹¹ M, respectively. Finally, accurate quantification of MEB in dosage forms (tablets) and biological fluids (spiked human urine and plasma samples) was achieved using Cu₂[email protected]/PE. Full article

In this work, p-type oxide semiconductors, Co₃O₄ and complex oxides Ni_xCo_3−xO₄ (x = 0.04, 0.07, 0.1), were studied as materials for sub-ppm H₂S sensing in the temperature range of 90–300 °C in dry and humid air. Nanocrystalline Co₃O₄ and Ni_xCo_3−xO₄ (x = 0.04, 0.07, 0.1) were prepared by coprecipitation of cobalt and nickel oxalates from nitrate solutions and further annealing at 300 °C. The surface reactivity of the obtained materials toward H₂S both in dry and humid atmosphere (relative humidity at 25 °C R.H. = 60%) was investigated using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Sensor measurements showed a decrease in sensor signal toward 1 ppm H₂S with an increase in Ni content because of a decrease in chemisorbed surface oxygen species. On the other hand, sensor signal increases for all samples with increasing the relative humidity that depends on reactivity of the surface hydroxyl groups, which stimulate the decomposition of surface sulfites and provide better surface regeneration at higher temperature. This assumption was additionally confirmed by the faster saturation of the conductivity curve and a decrease in the sensor response time in humid air. Full article