Designs, formats and applications of lateral flow assay: A literature review

This manuscript provides a brief overview of latest research involving the use of lateral flow assay for qualitative and quantitative analysis in different areas. The excellent features and versatility of detection formats make these strips an ideal choice for point of care applications. We outline and critically discuss detection formats, molecular recognition probes, labels, and detection systems used in lateral flow assay. Applications in different fields along with selected examples from the literature have been included to show analytical performance of these devices. At the end, we summarize accomplishments, weaknesses and future challenges in the area of lateral flow strips

COVID-19 chloroquine drug detection using novel, highly sensitive SnO2-based electrochemical sensor

A highly sensitive, selective, stable, and cost-effective SnO2-based electrochemical sensor is reported for the detection of chloroquine phosphate (CQP). Hydrothermal synthesis is used to synthesize SnO2 nanoparticles, which are mixed with graphite and form a highly electrochemically active composite. The SnO2 nanoparticles and SnO2/graphite composite are fully characterized physico- and electrochemically. Using the optimal SnO2/graphite composite, an excellent analytical performance is demonstrated with an electrode sensitivity of 35.7 µA/µM.cm2, a linear range of 0.1–23.3 µM, and limits of detection and quantification of 0.01 µM and 0.04 µM, respectively. High CQP selectivity with minimal interference at 100 × concentration of interferents is shown. The sensor is also highly repeatable and reproducible with RSD of 2.46 % and 1.86 %, respectively, and can retain > 85 % of its activity upon storage. The validity of the new sensor for real sample analysis is shown by applying it to CQP tablets using the standard addition method, obtaining an excellent percentage recovery of ∼ 102 %. The low cost, facile processing, and superior performance of the SnO2/graphite electrode make it an up-and-coming candidate for the commercial electrochemical detection of CQP and other small molecules

Copper enhanced guanine electrochemical signal for nucleic acids detection in municipal tertiary wastewater

An electroanalytical method is developed for guanine detection based on its electrochemical oxidation on a clay-modified carbon paste electrode (clay-CPE). The electrochemical guanine signal is found to be significantly enhanced upon its complexation with Cu2+ ions. Cu2+-guanine complex formation is studied using UV–Vis spectroscopy and electrochemical pulse voltammetry at different ratios, with 1:2 Cu2+:guanine found to be the optimal stoichiometry. The clay modifier and the electrode are fully characterized using electron microscopy, Fourier-transform infrared, X-ray photoelectron and X-ray fluorescence spectroscopies, and X-ray diffractometry. The analytical method is fully optimized regarding the electrolyte, technique, and electrochemical parameters. A calibration curve is built obtaining a linear range of 0.1–45 µM, a limit of detection of 0.16 µM, a limit of quantification of 0.54 µM, and a sensitivity of 1.1 µA/µM, which are among the best reported so far and achieved with an environmentally friendly and low-cost method. Our system is very selective with minimal interference in the presence of interferents with concentrations as high as 100× that of guanine. The Cu2+-mediated clay-CPE-based analytical method is applied for the detection of nucleic acid in real-life wastewater, which is critical to achieving efficient wastewater treatment. This demonstrates the applicability of our method for environmental purposes and opens the door for other applications as well, such as diagnostics

Development and characterization of a clay-HDTMABr composite for the removal of Cr(VI) from aqueous solutions with special emphasis on the electrochemical interface

This research aims to study the removal of chromium in its toxic form, Cr (VI), from wastewater, using clay and modified clay with Hexadecyltrimethyl ammonium bromide (HDTMABr)as adsorbents. The modified clay is obtained by impregnating a known quantity of HDTMABr into the clay. The two materials were characterized by different techniques, such as X-ray diffraction, which is used to determine the inorganic composition and the phyllite structures it contains. Thermal analysis TGA isused to understand the thermal behavior as function of the sintering temperature. Nitrogen adsorption/desorption is used to get the pores' size and surface area, using the Brunauer-Emmett-Teller (BET) theory. Scanning electron microscopy (SEM) coupled with Energy Dispersive X-ray Spectroscopy (SEM/EDAX) is used to study the surface morphology of the bare clay and the HDTMABr/clay. The operating conditions, such as contact times, pH, and adsorption temperatures, were studied, and optimized to improve the efficiency of the adsorption process. The adsorption is favored in acidic medium and room temperature, giving adsorption capacities for Cr(VI) of 12 mg/g and 250 mg/g for the clay and clay/HDTMABr, respectively. The reaction kinetics were studied and found to fit a pseudo-second-order model. The standard entropy (ΔS°), enthalpy (ΔH°), and Gibbs free energy (ΔG°) changes indicate that the chromium (VI) adsorption process is a physical, spontaneous, endothermic process. Cyclic voltammetry (CV) and the electrochemical impedance spectroscopy (EIS) are used for the electrochemical characterization of the raw clay and clay/HDTMABr in [Fe(CN)6]3-/4-/ 0.1 M KCl solution. The linear scan anodic stripping voltammetry (LSASV) is used for the reduction the Cr(VI) to Cr(III), indicating that Cr(VI) accumulates better at the surface of clay/HDTMABr compared to the bare graphite and the raw clay

Preparation of Sodalite and Faujasite Clay Composite Membranes and Their Utilization in the Decontamination of Dye Effluents

The present work describes the deposition of two zeolite films, sodalite and faujasite, by the hydrothermal method to tune the mesopores of clay support, which are prepared from a widely available clay depot from the central region of Morocco (Midelt). The clay supports were prepared by a powder metallurgy method from different granulometries with activated carbon as a porosity agent, using uniaxial compression followed by a sintering process. The 160 µm ≤ Φ ≤ 250 µm support showed the highest water flux compared to the supports made from smaller granulometries with a minimum water flux of 1405 L.m−2·h−1 after a working time of 2 h and 90 min. This support was chosen for the deposition of sodalite (SOM) and faujasite (FAM) zeolite membranes. The X-ray diffraction of sodalite and faujasite showed that they were well crystallized, and the obtained spectra corresponded well with the sought phases. Such findings were confirmed by the SEM analysis, which showed that SOM was crystalized as fine particles while the FAM micrographs showed the existence of crystals with an average size ranging from 0.53 µm to 1.8 µm with a bipyramidal shape and a square or Cubo octahedral base. Nitrogen adsorption analysis showed that the pore sizes of the supports got narrowed to 2.28 nm after deposition of sodalite and faujasite. The efficiencies of SOM and FAM membranes were evaluated by filtration tests of solutions containing methyl orange (MO) using a flow loop, which were developed for dead-end filtration. The retention of methylene orange (MO) followed the order: SOM > FAM > 160 µm ≤ Φ ≤ 250 µm clay support with 55%, 48% and 35%, respectively. Size exclusion was the predominant mechanism of filtration of MO through SOM, FAM, and the support. However, the charge repulsion between the surface of the membrane and the negatively charged MO have not been ruled out. The point of zero charge (pzc) of the clay support, SOM and FAM membrane were pHpzc = 9.4, pHpzc = 10.6, and pHpzc = 11.4, respectively. Filtrations of MO were carried out between pH = 5.5 and pH = 6.5, which indicated that the surface of the membranes was positively charged while MO was negatively charged. The interaction of MO with the membranes might have happened through its vertical geometry

NMR and kinetic studies of the interactions of [Au(<i>cis</i>-DACH)Cl₂]Cl and [Au(<i>cis</i>-DACH)₂]Cl₃ with potassium cyanide in aqueous solution

<div><p>The interactions of [Au(<i>cis</i>-DACH)Cl₂]Cl and [Au(<i>cis</i>-DACH)₂]Cl₃ [where <i>cis</i>-DACH is <i>cis</i>-1,2-diaminocyclohexane] with enriched KCN were carried out in CD₃OD and D₂O, respectively. The reaction pathways of these complexes were studied by ¹H, ¹³C, ¹⁵N NMR, UV spectrophotometry, and electrochemistry. The kinetic data for the reaction of cyanide with [Au(<i>cis</i>-DACH)₂]Cl₃ are <i>k</i> = 18 M⁻¹s⁻¹, ∆<i>H</i>^≠ = 11 kJ M⁻¹, ∆<i>S</i>^≠ = −185 JK⁻¹ M⁻¹, and <i>E</i>_a = 13 kJ M⁻¹ with square wave voltammetric (SWV) peak +1.35 V, whereas the kinetic data for the reaction of cyanide ion with [Au(<i>cis</i>-DACH)Cl₂]Cl are <i>k</i> = 148 M⁻¹s⁻¹, ∆<i>H</i>^≠ = 39 kJM⁻¹, ∆<i>S</i>^≠ = −80 JK^-1 M⁻¹, and <i>E</i>_a = 42 kJM⁻¹ along with SWV peak +0.82 V, indicating much higher reactivity of [Au(<i>cis</i>-DACH)Cl₂]Cl toward cyanide than [Au(<i>cis</i>-DACH)₂]Cl₃. The interaction of these complexes with potassium cyanide resulted in an unstable [Au(¹³CN)₄]⁻ species which readily underwent reductive elimination reaction to generate [Au(¹³CN)₂]⁻ and cyanogen.</p></div