Molecularly imprinted sol-gel electrochemical sensor for sildenafil based on a pencil graphite electrode modified by Preyssler heteropolyacid/gold nanoparticles/MWCNT nanocomposite

One-pot synthesis of a novel conductive molecularly imprinted gel as the recognition element and signal amplifier for the selective electrochemical detection of amaranth in foods

Herein, we prepared a self-crosslinked conductive molecularly imprinted gel (CMIG) using cationic guar gum (CGG), chitosan (CS), β-cyclodextrin (β-CD), amaranth (AM) and multi-walled carbon nanotubes (MWCNTs) by a simple one-pot low temperature magnetic stirring method. The imine bonds, hydrogen-bonding interactions and electrostatic attractions between CGG, CS and AM facilitated CMIG gelation, while β-CD and MWCNTs enhanced the adsorption capacity and conductivity of CMIG, respectively. Next, the CMIG was deposited onto the surface of a glassy carbon electrode (GCE). After selective removal of AM, a highly sensitive and selective CMIG-based electrochemical sensor was obtained for AM determination in foods. The CMIG allowed specific recognition of AM and could also be used for signal amplification, thus improving the sensitivity and selectivity of the sensor. Due to the high viscosity and self-healing properties of the CMIG, the developed sensor was very durable retaining a 92.1% of original current after 60 consecutive measurements. Under optimal conditions, the CMIG/GCE sensor showed a good linear response for AM detection (0.02-150 μM) with a limit of detection of 0.003 μM. AM recovery tests were performed in milk powder and white vinegar samples, yielding satisfactory recoveries (89.00%-111.00%). Furthermore, the levels of AM in two kinds of carbonated drinks were analyzed with the constructed sensor and an ultraviolet spectrophotometry method, with no significant difference found of the two methods. This work demonstrates that CMIG based electrochemical sensing platforms allow the cost-effective detection of AM, with the CMIG technology likely being widely applicable to the detection of other analytes.

A Comprehensive Review on Analytical Techniques for Determination of Sex Stimulants, PDE5 Inhibitors in Different Matrices with Special Focus on the Electroanalytical Methods

Erectile dysfunction (ED) is one of the most common chronic diseases affecting men and its incidence increases with aging. Due to its substantial influence on the quality of life, phosphodiesterase type-5 (PDE5) inhibitors have been implemented to treat ED by increasing the penile blood flow that results in improving erection. PDE5 inhibitors is a class of drugs that affects many pharmacological sectors, and it is essential to review the different analytical methods described for their determination. Few reviews were published concerning this group of drugs. For this reason, this review article gathers the different analytical methods used to determine PDE5 inhibitors in pharmaceutical and biological samples over the past 20 years. Different analytical techniques were used to analyze these compounds in different matrices such as separation methods (capillary electrophoresis, LC-MS, UPLC-MS/MS, and GC-MS), spectroscopic methods (UV-visible methods, FT-IR spectroscopy and spectrofluorometry) and electrochemical methods (polarography, voltammetry and potentiometry). This review focuses on the different electrochemical methods and their use in analytical determination of PDE5 inhibitors in pharmaceutical dosage forms and biological samples. Moreover, it discusses the different modified electrodes used for their electroanalytical determination and the behavior of the studied drugs at different modified electrodes. Additionally, this review discusses the pharmacokinetics of the studied compounds and their interactions with other co-administered drugs especially the metabolic interactions between the studied compounds and other co-administered drugs in different matrices. This literature survey would provide a beneficial guide for future analytical investigation of PDE5 inhibitors.

Polyoxometalate Functionalized Sensors: A Review

Polyoxometalates (POMs) are a class of metal oxide complexes with a large structural diversity. Effective control of the final chemical and physical properties of POMs could be provided by fine-tuning chemical modifications, such as the inclusion of other metals or non-metal ions. In addition, the nature and type of the counterion can also impact POM properties, like solubility. Besides, POMs may combine with carbon materials as graphene oxide, reduced graphene oxide or carbon nanotubes to enhance electronic conductivity, with noble metal nanoparticles to increase catalytic and functional sites, be introduced into metal-organic frameworks to increase surface area and expose more active sites, and embedded into conducting polymers. The possibility to design POMs to match properties adequate for specific sensing applications turns them into highly desirable chemicals for sensor sensitive layers. This review intends to provide an overview of POM structures used in sensors (electrochemical, optical, and piezoelectric), highlighting their main functional features. Furthermore, this review aims to summarize the reported applications of POMs in sensors for detecting and determining analytes in different matrices, many of them with biochemical and clinical relevance, along with analytical figures of merit and main virtues and problems of such devices. Special emphasis is given to the stability of POMs sensitive layers, detection limits, selectivity, the pH working range and throughput.

Voltammetric picomolar determination of mercury, copper and cadmium using modified pencil graphite electrode with poly-L-cysteine and Fe3O4 nanoparticles

Cost-effective simultaneous determination of mercury, copper and cadmium ions was performed by differential pulse anodic stripping voltammetry (DPASV) using a pencil graphite electrode (PGE) modified with poly-L-cysteine (P-L-Cys) and Fe₃O₄ nanoparticles. Electropolymerization of L-cysteine was performed by cyclic voltammetry (CV) through applying different cycles. Also, Fe₃O₄ was deposited in a single step by applying a constant potential on the electrode surface in the presence of ferric nitrate. To enhance the sensitivity of measurement, several parameters such as monomer concentration, scan rate, number of cycles in electropolymerization, ferric nitrate concentration, Fe₃O₄ electrodeposition potential and time, and pH of the sample solution were optimized. The surface morphology of the modified electrode was examined by SEM and FTIR. Electrochemical impedance spectroscopy was conducted to investigate the impedance of the electrode surface. The linear ranges for cadmium, copper and mercury were 0.001‒2500, 0.0002‒3600 and 0.0001‒2500 nM with detection limits of 6.4 × 10^-13, 1.0 × 10^-13 and 9.0 × 10^-14 M, respectively. The stability and reproducibility of the electrode were investigated. Finally, the modified electrode was applied to determine mercury, copper and cadmium in real samples such as the groundwater, Caspian Sea and Tajan River water.

Covalent organic framework DQTP modified pencil graphite electrode for simultaneous determination of bisphenol A and bisphenol S

The sensitivity and selectivity of electrochemical analysis are challenging due to the materials used for electrode modification as well as electrical conductivity, catalytic activity and recognition ability of the working electrode. In this work, a portable 3D-printed electrochemical electrode clamp was designed and applied in combination with the developed covalent organic framework (COF DQTP)-modified pencil graphite electrode (DQTP/PGE). The β-ketoenamine-linked COF DQTP synthesized by 1,3,5-triformylphloroglucinol (TP) and 2,6-diaminoanthraquinone (DQ) through solvothermal method is a porous crystalline with excellent conductivity and large periodic π-arrays, coupled with commercial available pencil graphite electrode to fabricate a disposable sensor for simultaneous determination of environmental endocrine disruptors bisphenol A and bisphenol S. The DQTP/PGE sensor exhibited high electrical conductivity and catalytic activity, and a good linearity was obtained in a range of 0.5-30 μM for two bisphenols with a detection limit of 0.15 μM (S/N = 3). Moreover, the sensor showed a reproducible and stable response over one month with negligible interference, and an accepted recovery with real food packaging samples.

Molecularly imprinted polymer grafted on paper and flat sheet for selective sensing and diagnosis: a review

Molecularly imprinted polymers are efficient and selective adsorbents which act as artificial receptors for desired compounds with the ability to recognize the size, shape, and functional groups of the compounds simultaneously. A molecularly imprinted polymer is prepared by the polymerization of functional monomers around a template (analyte) molecule. Afterward, the removal of the template from the polymer matrix leaves a selective cavity behind. The fabrication and development of molecularly imprinted polymers grew rapidly, due to their low cost, simple preparation, selectivity, sensitivity, and stable physicochemical properties. Traditionally, molecularly imprinted polymers can be synthesized using two main methods, namely bulk and surface imprinting. For more efficient use of the latter method, researchers have developed molecularly imprinted polymers grafted on the solid-phase matrix (substrate). This grafting technique would be particularly useful for surface imprinting of macromolecules, such as proteins. Cellulose fibers of papers with unique properties such as being abundant, retaining a porous structure, having good adsorption properties, and possessing hydroxyl groups naturally have gained much attention as substrate. The goal of this review is to introduce molecularly imprinted polymer-grafted or molecularly imprinted polymer-coated paper, as an interesting, simple, and efficient method in the detection and separation of small and large molecules. Therefore, in the present paper, several recent preparation techniques and applications of molecularly imprinted polymer-grafted paper are reviewed and discussed in detail. Green, cost-effective, selective, and sensitive paper-based sensor prepared via grafting molecularly imprinted polymer on paper surface with the potential use for online detection trace of analytes in the point-of-care testing.

A Molecularly Imprinted Sol-Gel Electrochemical Sensor for Naloxone Determination

A molecularly imprinted sol-gel is reported for selective and sensitive electrochemical determination of the drug naloxone (NLX). The sensor was developed by combining molecular imprinting and sol-gel techniques and electrochemically grafting the sol solution onto a functionalized multiwall carbon nanotube modified indium-tin oxide (ITO) electrode. The sol-gel layer was obtained from acid catalyzed hydrolysis and condensation of a solution composed of triethoxyphenylsilane (TEPS) and tetraethoxysilane (TES). The fabrication, structure and properties of the sensing material were characterized via scanning electron microscopy, spectroscopy and electrochemical techniques. Parameters affecting the sensor's performance were evaluated and optimized. A sensor fabricated under the optimized conditions responded linearly between 0.0 µM and 12 µM NLX, with a detection limit of 0.02 µM. The sensor also showed good run-to-run repeatability and batch-to-batch performance reproducibility with relative standard deviations (RSD) of 2.5-7.8% (n = 3) and 9.2% (n = 4), respectively. The developed sensor displayed excellent selectivity towards NLX compared to structurally similar compounds (codeine, fentanyl, naltrexone and noroxymorphone), and was successfully used to measure NLX in synthetic urine samples yielding recoveries greater than 88%.