In this work we explore the possibility of using anti-crown ether (C₆HgF₄)₃ as a membrane-active component for potentiometric cross-sensitive sensors. Anti-crown ligands were already employed as ionophores in plasticized polymeric membranes, however the results of these studies are contradictory. In [1] mercury-carborundum-3 was employed to construct a chloride-selective sensor, while in [2] another anti-crown ligand was reported to be selective towards tetramethyl amine cations. At the same time some recent studies have explored the interaction between three-mercury anticrown ethers and anions and reported on formation of sandwich-type complexes [3].
In order to clarify the electrochemical sensitivity patterns of anti-crown based sensors we have studied plasticized polymeric membranes containing cation and anion-exchanging additives and various solvents-plasticizers. We explored the electrochemical sensitivity of these membranes in a wide variety of aqueous solutions of inorganic salts. Alkaline, alkaline-earth and d-elements salts with different anions were studied. It was found that the sensors based on anti-crown (C₆HgF₄)₃ exhibit cationic sensitivity and no considerable anionic responses were observed. The highest sensitivity values were obtained for Cs⁺ (51 mV/dec) among single-charged cations, and for Pb²⁺ (19 mV/dec) among double-charged cations. No sharp selectivity towards particular cations was found. These features can be successfully employed in construction of cross-sensitive polymeric sensors for developing novel multisensor arrays.

References

1. Ibrahim H.A.Badr, Martin Diaz, M. Frederick Hawthorne, Leonidas G. Bachas.//Anal. Chem., v.71, p.1371-1374 (1999).
2. Zhenning Yan, Zhixian Zhou, Yanglie Wu, Shur, V. B.,Tikhonova, I. A.,// Analytical Letters, v.38, p.377-383 (2005).
3. K.I. Tugashov, D.A. Gribanyov, F.M. Dolgushin, A.F. Smol’yakov, A.S. Peregudov, M.Kh. Minacheva, L.A. Tikhonova, V.B. Shur // Organometallics, v.35, p.2197 (2016).

This work presents a proof-of-concept assay for the quantification of small molecules based on aptamer recognition and electrochemiluminescence (ECL) readout. The testosterone-binding aptamer (TESS.1) was used to demonstrate the novel methodology. The analytical capability of the ECL array towards testosterone detection was studied using different incubation protocols. Concurrently, and to improve the analytical performance, the optimal concentration of the TESS.1 aptamer was investigated. Subsequently, the selectivity of the proposed array was assessed by performing negative control experiments with a randomized ssDNA sequence and two other steroids, i.e. deoxycholic acid (DCA) and hydrocortisone (HC). In parallel, complementary analytical techniques were employed to confirm the suggested mechanism: i) native nano-electrospray ionization mass spectrometry (native nESI-MS) was used to determine the stoichiometry of binding, and for the characterization of aptamer-target interactions; and, ii) isothermal titration calorimetry (ITC) was carried out to elucidate the dissociation constant (K_d) of TESS.1 for testosterone. The combination of these techniques provided a complete understanding of the aptamer performance, the binding mechanism, affinity and selectivity. This research will pave the way for the development of new aptamer-based biosensor assays coupled with ECL sensing for the detection of relevant small molecules.

Electronic tongues are devices used in the analysis of aqueous matrices for classification or quantification tasks. Sensor arrays in electronic tongues are composed of several sensors of different materials, a data acquisition unit and a pattern recognition system. These sensors can be of electrochemical type and one of the analytical methods carried out in the aqueous matrix corresponds to cyclic voltammetry. After performing the cyclic voltammetry, each sensor yields a voltammogram that relates the response in current to the change in voltage applied to the working electrode. A great amount of data is obtained in the experimental procedure. A conventional way to extract features of raw signals of the voltammograms obtained in an electronic tongue is by selecting specific features, related to the peaks recorded for the reduction and oxidation processes, such as potentials for the maximum current, maximum current values and widths of the observed peaks. In this work, a novel data processing methodology is developed for sensor arrays of a cyclic voltammetry electronic tongue. This methodology is composed of several stages such as data normalization through group scaling method and a nonlinear feature extraction step with locally linear embedding (LLE) technique. A reduced size feature vector is obtained that serves as input to a K-Nearest Neighbors (KNN) supervised classifier algorithm. A Leave-one-out cross validation procedure is performed to obtain the final classification accuracy. The methodology is validated with a data set of five different juices as liquid substances. Finally, 80% of classification accuracy was obtained.

We present newly developed electrochemical sensors based on screen-printed carbon electrodes functionalized with nanostructured bismuth species for paracetamol detection. We produced the nanostructures by thermal conversion of Bi(NO₃)₃ forming two subnitrates (BiONO₃ and Bi₅O₇NO₃) testing their performances through cyclic voltammetry experiments and compared in terms of the kinetic rate constant, the sensitivity, and the limit of detection.

The synthesis of BiONO₃ was also modified by adding polyethylene glycol achieving a higher oxidation peak current, lower oxidation peak potential, and assured a faster paracetamol reaction due to a higher kinetic rate constant of 42.0 ± 9.8 ms⁻¹. Furthermore, we observed a lesser ΔEp of up to 243 ± 10 mV with a higher chance of reversible reaction doubling at the same time the sensitivity of a bare carbon electrode with a limit of detection of up to 2.24 ± 0.03 μM. Paracetamol-BiONO₃ system was further investigated through computational approach evaluating the geometry of transitional state and the electron transfer values reaching a very good agreement with the empirical data.

p-Coumaric acid is a hydroxy derivative of cinnamic acid, the hydroxyl group being in para position in the phenyl group. PCA has antioxidant [1], antibacterial [2], [3], and anti-inflammatory [4], [5] properties and it could be a precursor for the production of flavors and fragrances used in foods or chemicals. This compound has a large number of important applications in the nutraceutical, pharmaceutical, materials and chemical industry.

The present study aims to develop a novel electrochemical sensor based on carbon nanofibers and cobalt phthalocyanine deposited onto screen-printed electrode (CNF-CoPc/SPE) useful for the detection of p-coumaric acid in various fitoproducts.

The deposition of CNF and CoPc was carried out by casting technique in two stages. The sensor surface was initially analyzed by FTIR technique being observed the change of the functional group present on the surface after successive modification. The electrochemical behavior of CNF-CoPc/SPE was studied in aqueous solutions of p-coumaric acid using as electrolyte a phosphate buffer solution of pH 5.0. Cyclic voltammetry and square wave voltammetry were used as detection techniques. In the voltammograms are observed two peaks pairs related to the redox processes of p-coumaric acid from the solution and to CoPc immobilized into the carbonaceous matrix. In order to study the influence of the scan rate on the voltammetric response, the cyclic voltammograms of CNF-CoPc/SPE were recorded at different scan rates between 0.1 and 1.0 V·s^-1. It was obtained a linear dependence between I_a and v½, which demonstrates that the redox process of p-coumaric acid is controlled by the diffusion process. The CNF-CoPc/SPE was further used to perform a calibration curve using p-coumaric acid solutions in the concentration range 0.1-202.5 mM. Low value of LOD equal of 9.29´10^-7M was obtained. Furthermore, the sensor has been shown to have good sensitivity, selectivity and reproducibility for the detection of p-coumaric acid. The p-coumaric acid from three fitoproducts was qualitatively and quantitatively determined using CNF-CoPc/SPE sensor with good sensitivity. The results were validated by FTIR method and compared with the values provided by the producers obtaining good correlations. The sensor developed in this study could be used in the fitoproduct quality control.

References

[1] J. Peng et al., „Coumaric Acid Protects Human Lens Epithelial Cells against Oxidative Stress-Induced Apoptosis by MAPK Signaling”, Oxidative Medicine and Cellular Longevity, vol. 2018, pp. 1–7, 2018, doi: 10.1155/2018/8549052.

[2] Y. C. Boo, „p-Coumaric Acid as An Active Ingredient in Cosmetics: A Review Focusing on its Antimelanogenic Effects”, Antioxidants, vol. 8, nr. 8, p. 275, aug. 2019, doi: 10.3390/antiox8080275.

[3] M. Contardi et al., „Combining dietary phenolic antioxidants with polyvinylpyrrolidone: transparent biopolymer films based on p-coumaric acid for controlled release”, J. Mater. Chem. B, vol. 7, nr. 9, pp. 1384–1396, feb. 2019, doi: 10.1039/C8TB03017K.

[4] M. Kheiry, M. Dianat, M. Badavi, S. A. Mard, și V. Bayati, „p-Coumaric Acid Attenuates Lipopolysaccharide-Induced Lung Inflammation in Rats by Scavenging ROS Production: an In Vivo and In Vitro Study”, Inflammation, vol. 42, nr. 6, pp. 1939–1950, dec. 2019, doi: 10.1007/s10753-019-01054-6.

[5] W. Kim, D. Lim, și J. Kim, „p -Coumaric Acid, a Major Active Compound of Bambusae Caulis in Taeniam, Suppresses Cigarette Smoke-Induced Pulmonary Inflammation”, Am. J. Chin. Med., vol. 46, nr. 02, pp. 407–421, ian. 2018, doi: 10.1142/S0192415X18500209.

The electronic and optical properties of the newly synthesized Molybdenum dinitride (MoN₂) in the hypothetical 2H structure analogous to MoS₂ is investigated using the Density Functional Theory (DFT) full potential linearized augmented plane wave (FP-LAPW) method and the Modified Becke-Johnson (mBJ) approximation. The aim is to investigate the optoelectronic properties of this compound for potential optical sensing applications and compare with the capabilities of MoS₂ in this field.

As compared to MoS₂, which is a semiconductor, MoN₂ is found to be a semi metal from the band structure and the density of states (DOS) plots. The dielectric function, optical conductivity and the optical constants, namely, the refractive index, the reflectivity, the extinction and absorption coefficients are evaluated and compared with those of MoS₂ and discussed with reference to the sensing performance.

It is one of the great challenges to improve the sensitivity for early detection of biomarker in Alzheimer's disease (AD). In this work, an electrochemical aptasensor was prepared based on thionine (Th) - functionalized three - dimensional carbon nanomaterials (reduced graphene oxide (rGO) and multi-walled carbon nanotubes (MWCNTs) immobilized aptamer for the analysis of Aβ oligomers (AβO), one of the AD biomarkers. Th, the positively charged planar aromatic molecule, could form a large number of π - conjugated structures with rGO and MWCNTs, thereby bringing extra stability to the conjugated macromolecules and improve the structural stability and capacitive properties of Th-rGO-MWCNTs nanocomposites. Under the optimal conditions, DPV response decreased with the increase of AβO concentration. The aptasensor has a good linear range of 0.0443 pM to 443.00 pM with a LOD of 0.01 pM. It also has excellent stability and selectivity for AβO detection. This aptasensor thus has a great potential for early diagnosis of AD.

Micro gas sensors detect the presence of substances, but can hardly identify them. We developed a novel approach of probing referenceable ionization energies. It extends the photoionization principle towards tunable energies via replacement of photons by accelerated photo electrons.

The device comprises UV-LED illumination, an atmospherically stable photoelectron emission layer with a nano-vacuum electronics accelerator realized in thin film technology and charged particle measurement. A voltage variation at the accelerator provides electrons of tunable energies. The resulting system works at high pressures and reaches ambient laboratory air operability. We were able to prove that variable electron energies can be used for VOC detection using ethyl and butyl acetates, methyl mercaptan, alcoholes, DMSO and trichloro ethylene. The signals observed are resulting from ion scattering which overlays the original electron beam current and can be described borrowing from the old models of thyratron electron tubes and ion mobility spectrometers. The energy resolution which has been reached so far is 0,2 eV and is discussed with respect to the achievable performance data that have been estimated on the basis of theoretical considerations.

Extreme fire is not fully understood, and its data has not yet been accounted into the current wildfires’ prediction models. Recent research on flammable gases (i.e., volatile organic compounds, VOC) released by the heated vegetation has shown that, under specific conditions (e.g., extreme heat, humidity, wind, and topography), VOC might foster fire ignition sources and explain sudden changes in fire behaviour, particularly in the most susceptible and flammable forests (eucalypt forests).

The so-called electronic noses are instruments, “capable of recognising complex gases, which comprise an array of electronic sensors with partial specificity and an appropriate pattern-recognition system”, are suited to most monitoring applications as they provide high sensitivity, as well as accurate and swift responses for VOC concentrations. However, forest environments consist of a complex mixture of gases; the most suitable sensor must classify and quantify the target VOC. To improve the sensor’s sensitivity, different nanomaterials can be used as coatings. The ability to tune nanostructured thin films' composition enhances the sensor's intrinsic (chemical or physical) properties.

This work aims to develop a sensor array to monitor eucalyptol (from eucalyptus tree) levels (100 to 1000 ppm). The development of different nanostructures for sensor coating to find the best combination to the target compound will be evaluate through layer-by-layer films and simple or functionalized (e.g., COOH functional group) Multiwalled carbon nanotube based films produced by RF-magnetron sputtering. The detection of the target compound was achieved by measuring the impedance spectra of thin-films when in contact with the gas inside a custom made vacuum chamber system. The impedance spectra will be accessed with a Solartron 1260 Impedance Analyzer in the frequency range of 1 Hz to 1 MHz, by applying 25 mV. The sensor devices array forming the e-nose concept, consist of ceramic or BK7 solid support with deposited gold interdigitate electrodes, coated with the films aforementioned.

Tuberculosis (TB) is one of those diseases that can affect a huge number of people on a global scale. In many regions, the lack of speedy TB diagnosis is responsible for its propagation. Analyzing, testing, and early diagnosis can contain TB-causative bacterium, Mycobacterium tuberculosis (Mtb). Biosensing is the deck that allows rapid, sensitive, and selective detection which in turn can serve the purpose for rapid and precise detection of TB. In our work, based on miniaturized sensing strategies, focuses on detecting the virus by using affordable cost-high efficiency processes with the help of loop-mediated isothermal amplification (LAMP) analysis and screen printed electrodes (SPE) implemented on a commercial potentiostat. The device measures the current response generated from the interaction between the target molecules and the SPE using cyclic voltammetry (CV). The system (LAMP-EC) proposes a promising electrochemical sensor for the detection of TB that can be clinically adopted by dint to its feasibility and high sensitivity. Our purpose is to make it an integrated lab-on-chip quantitative rapid point-of-care in both high- and low-resource settings across the TB endemic regions.