Colorimetric and fluorimetric pH sensing using polydiacetylene embedded within PVC-PCL nanofibers

The applicability of model polydiacetylenes (PDAs) in hydrogen ions sensitive optodes was tested. Nanofibers mats were electrospun using a mixture of polyvinyl chloride (PVC) and polycaprolactone (PCL) together with 10, 12-tricosadiynoic acid (TCDA) or 10,12-pentacosadiynoic acid (PCDA). After the polymerization the mats were applied in colorimetric and fluorimetric pH sensors. The PDAs were formed by photopolymerization with a UV lamp (254 nm), resulting in a change of mats color from white to dark blue. The morphology of both fiber mats is similar (SEM images), and the average diameters of fibers were estimated as equal to 228±73 and 248±61 nm for TCDA and PCDA, respectively. As the pH increases, the color of the fiber mat changes from blue to red and the process can be followed visually. The result obtained by computer image analysis showed a sigmoidal increase in the intensity of red and a decrease in the intensity of blue color with increasing pH. A similar sigmoidal response is observed for the dependence of the emission intensity on the pH. Changes in the recorded signal occur in the pH range from 7 to 8.5 or from 8 to 9.5 for mats with TCDA and PCDA, respectively. Both readout modes can be successfully used for pH sensing with proposed nanofibrous mats in the range of pH close to the physiological pH range.     

Preparation of Fe−Co−LDH/MXene modified electrode for sensitive determination of arsenic (III) in aquatic system

3-dimensional (3D) Fe−Co−LDH/MXene composite was synthesized by in-situ synthesis and assembly of Fe−Co−LDH rod around MXene under hydrothermal condition. Due to the unique 3D configuration and good conductivity, the obtained Fe−Co−LDH/MXene modified glassy carbon electrode (Fe−Co−LDH/MXene/GCE) showed excellent electrochemical activity for As(III) detection. Via square-wave anodic stripping voltammetry, the response current on Fe−Co−LDH/MXene/GCE had good linear relationship with As(III) concentrations (1∼1000 ppt) with superior sensitivity (0.22 μA ppt⁻¹ cm⁻²) and low detection limit (0.9 ppt). The mechanism of As(III) adsorption was demonstrated. The electrode showed excellent anti-interference ability. Real water sample analysis demonstrated the Fe−Co−LDH/MXene/GCE was deployable in aqua-system.     

An Electrochemical Sensor Fabricated by Sonochemical Approach for Determination of the Antipsychotic Drug Haloperidol

A nanocomposite (Ho₂O₃NPs/BNT) was synthesized by decorating holmium(III)oxide nanoparticles (H₂O₃NPs) on bentonite (BNT) through a realizable sonochemical approach for the electrochemical detection of haloperidol (Hlp). A glassy carbon electrode was modified with this nanocomposite. The Ho₂O₃NPs/BNT modified electrode outperformed bare and other modified electrodes in terms of electrochemical performance for Hlp detection in a pH 8.0 phosphate buffer. The proposed electrochemical platform showed a wide linear range (0.01 μM–24 μM), low detection limit (2.4 nM), and high sensitivity by square wave voltammetry. In addition, the proposed electrochemical sensor met the clinical criteria in terms of stability, selectivity, and repeatability.     

Electrochemical Sensor for Selective Detection of Meldonium in Urine by Voltammetry

A highly sensitive electrochemical sensor based on arenediazonium tosylates was designed to detect meldonium in urine. The effect of the concentration of ArN2⁺OTs⁻ arenediazonium tosylate modifier and various substituents was studied. Basic operating parameters for voltammetric meldonium detection were established and the procedure for urine sample preparation was developed. The following values were obtained: limit of detection (LOD) 0.005 mg ⋅ L⁻¹ (P=0.95) and limit of quantification (LOQ) 0.01 mg ⋅ L⁻¹. The relationship between the analytical signal and meldonium concentration in the solution ranging from 0.01 to 400 mg ⋅ L⁻¹ was described by a linear function. The meldonium concentration error did not exceed 18 %. The analysis time for a single urine sample was reduced to 15 minutes.     

State-of-the-art molecular imprinted colorimetric sensors and their on-site inspecting applications

Molecular imprinted colorimetric sensors can realize visual semi-quantitative analysis without the use of any equipment. With the advantages of low cost, fast response, ease of handling, and excellent recognition ability, the molecular imprinted colorimetric sensor shows great application potential in the field of sample rapid assay. Molecular imprinted colorimetric sensors can be prepared in various forms to meet the needs of different sample determination, such as film, hydrogel, strip, and adsorption coating. In this review, the preparation methods for various types of molecularly imprinted colorimetric sensors are systematically introduced. Their applications in the field of on-site biological sample detection, drug detection, disease treatment, chiral substance detection and separation, environmental analysis, and food safety detection are introduced. The limitations encountered in the practical application are presented, and the future development directions prospect.     

3D-Printed Bionic Ear for Sound Identification and Localization Based on In Situ Polling of PVDF-TrFE Film

Bionic acoustic sensors are an indispensable part to realize interactions between humans and robotics. In this work, a PVDF-TrFE sensor array with multiple active pixels combined with a 3D-printed bionic ear model is prepared, which can accurately detect sounds with different frequencies and locate the sound source from different directions. The PVDF-TrFE sensor array can clearly identify the sound within 25 cm, and the error between the accepted sound frequency and the original input frequency is less than 0.001%. Through the algorithm analysis of the input signal, the location of the sound source can be immediately analyzed. Compared with other acoustic sensors, this sensor has the advantages of being self-powered, small size, and high flexibility, which holds great potential for bionic applications.     

Rosa Damascena mediated ZnO-Red Ochre nanocomposite for the electrochemical determination of 5-Fluorouracil

In this study, ZnO-Red Ochre nanocomposite was green synthesized by Rosa Damascena (RD) extract (RDZRONCs). Proton Induced X-ray Emission microanalysis (Micro-PIXE) and X-ray diffraction (XRD) pattern confirmed the presence of hematite (Fe₂O₃), and quartz (SiO₂) mineral phases in the Red Ochre (RO) nanoclay. In addition, the XRD pattern shows the ZnO, ZnFe₂O₄, SiO₂, Fe₂O₃, and Si phases in the RDZRONCs that were green synthesized with natural RD extract and RO. The RDZRONCs were used to modify the carbon paste electrode (CPE) for the electrochemical determination of the anticancer drug 5-fluorouracil (5-FU). Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques were employed to investigate the surface behavior of modified CPE (RDZRONCs/CPE). The electrochemical behavior of 5-FU at the RDZRONCs/CPE was exanimated by CV, differential pulse voltammetry (DPV), chronoamperometry (CA), and chronocoulometry (CC). Based on the DPV technique, a linear relationship between peak current and concentration of 5-FU was obtained in the dynamic range of 0.05–140.0 μM and with a detection limit equal to 0.0016 μM. The selectivity of RDZRONCs/CPE for 5-FU was studied in the presence of different inorganic and organic species. Also, the content of 5-FU was measured in real samples by RDZRONCs/CPE.     

Fabrication of a novel electrochemical sensor based on tin disulfide/multi-walled carbon nanotunbes-modified electrode for rutin determination in natural vegetation

A tin disulfide and multi-walled carbon nanotube (SnS₂/CNTs) electrochemical sensor was constructed for the sensitive and selective determination of rutin in plants. Tin disulfide nanoflowers with various particle sizes were prepared by controlling the reaction time and composited with multi-walled CNTs. The morphology, crystal structure, and chemical composition of these SnS₂/CNTs composites were characterized using XRD, XPS, and SEM-EDS. Results illustrated that the SnS₂/CNTs had a large specific surface area, good conductivity, and remarkable electrocatalytic performance. The pH of the buffer solution, the scanning rate, and the amount of modified material were also optimized for the rapid detection of rutin. A 2-electron-2-proton mechanism, involving a few rapid and consecutive stages, was speculated to occur during rutin oxidation, based on the observed slope of -53 mV/pH. There was an appreciable linear relationship between the reductive peak current from DPV and the rutin concentration, ranging from 0.005-0.05 µmol/L and 0.1-6 µmol/L, with a detection limit of 0.22 nmol/L (S/N = 3). The sensor also demonstrated good selectivity, excellent sensitivity, and reproducibility when analyzing rutin in real plant samples, with satisfactory recovery, and was also highly consistent with results of HPLC, and thus could be used to evaluate the medicinal value of natural vegetation.     

Silver/graphene–polypyrrole composite for levosimendan detection

This study used a facile method to develop a novel silver/Graphene–polypyrrole (Ag/G–PPy)-modified electrode that can be used as an electrochemical sensor for levosimendan detection. The properties of the synthesized Ag/G–PPy-modified electrode were examined through field-emission scanning electron microscopy, x-ray diffraction, and transmission electron microscopy. The Ag/G–PPy-modified electrode exhibited satisfactory current signals toward levosimendan concentrations ranging from 0.21 to 6.88 μM and exhibited a low detection limit (0.12 μM). Accordingly, the proposed electrode can serve as a simple and inexpensive electrochemical sensor for levosimendan detection.     

Comparison of a single-use pH test strip and a glass electrode for potentiometric titration

The potentiometric titration of a carbonate mixture or an acetate solution is a common experiment in analytical laboratories. Typically, a glass electrode combined with a calomel or Ag/AgCl reference electrode is used to locate the equivalence points in neutralization titrations. The dissociation constants of weak acids and bases can be calculated from the pH at the half-neutralization point. Recently, a new commercial product for measuring pH has been developed. This novel acid–base detection strip is a single-use sensor that requires neither storage in a preservation liquid nor calibration prior to use. This study examined its suitability for the continuous monitoring of pH changes in potentiometric titrations of carbonate mixtures, acetate solutions, or ammonia solutions. There were no significant differences in the concentrations of solutions tested using a glass electrode and a pH test strip. The pK_a, pK_b, and pH values determined using the two systems differed by less than 5%. The results confirmed that the pH strips are suitable for continuously monitoring pH changes during neutralization titrations. However, the strips can only be used once.