Novel Potentiometric Sensors for Determination of Melatonin and Oxomemazine in Biological Samples and in Pharmaceutical Formulations

Ruthenium-Anchored Carbon Sphere-Customized Sensor for the Selective Amperometric Detection of Melatonin

Melatonin (MT), a pineal gland hormone, regulates the sleep/wake cycle and is a potential biomarker for neurodegenerative disorders, depression, hypertension, and several cancers, including prostate cancer and hepatocarcinoma. The amperometric detection of MT was achieved using a sensor customized with ruthenium-incorporated carbon spheres (Ru-CS), possessing C- and O-rich catalytically active Ru surfaces. The non-covalent interactions and ion-molecule adducts between Ru and CS favor the formation of heterojunctions at the sensor-analyte interface, thus accelerating the reactions towards MT. The Ru-CS/Screen-printed carbon electrode (SPCE) sensor demonstrated the outstanding electrocatalytic oxidation of MT owing to its high surface area and heterogeneous rate constants and afforded a lower detection limit (0.27 μM), high sensitivity (0.85 μA μM -1 cm-2), and excellent selectivity for MT with the co-existence of crucial neurotransmitters, including norepinephrine, epinephrine, dopamine, and serotonin. High concentrations of active biomolecules, such as ascorbic acid and tyrosine, did not interfere with MT detection. The practical feasibility of the sensor for MT detection in pharmaceutical samples was demonstrated, comparable to the data provided on the product labels. The developed amperometric sensor is highly suitable for the quality control of medicines because of its low cost, simplicity, small sample size, speed of analysis, and potential for automation.

Highly Sensitive and Selective Detection of Melatonin in Biofluids by Antipyrine Based Fluorophore

A simple fluorescent based organic fluorophore was synthesized and it shows significant fluorescent intensity with melatonin (MLN). Hence, it was applicable to the detection of MLN by colorimetric and fluorimetric techniques at neutral pH. Under optimized experimental condition, the synthesized organic fluorophore detects MLN selectively in the presence of other interfering biomolecules through ICT mechanism. The melatonin sensing mechanism is supported by DFT and ¹H-NMR titration. Based on the findings, this method can be applied to design a simple clinical diagnostic tool for MLN.

Rapid, sensitive, and selective copper (II) determination using sensitive chromogenic azo dye based on sulfonamide

A simple methods have been developed for determination of Cu(II) ions in aqueous solutions. The spectrophotometric method relied mainly on the reaction between Cu(II) ions and the azo dye ligand named N-diaminomethylene-4-(2,4-dihydroxy-phenylazo)-benzenesulfonamide (H₂L) at pH 10.0. The influence of parameters such as concentration, pH and reaction time were inspected. A linear relationship (R² = 0.9992) between absorbance and the concentration of Cu(II) was obtained at themaximum absorptionpeak of 474 nm within 1.6-9.6 × 10^-6 mol L^-1 concentration range. The limit of detection for Cu(II) ion and limit of quantitation were 1.1 × 10^-7 mol L^-1 and 3.7 × 10^-7 mol L^-1, respectively.The potentiometric method is based on a novel poly(vinyl chloride) membrane, containing the synthesized azo dye as an ionophore, was used to developed a Cu(II)- selective sensor. This newly developed sensor revealed a Nernstian response over Cu²⁺ ion in a concentration range 1.0 × 10^-6-1.0 × 10^-2 mol L^-1 with cationic slopes of 29.5 ± 0.2 mV decade^-1 and detection limits of 3.0 × 10^-6 mol L^-1 copper(II) for o-nitrophenyl-octyl ether (o-NPOE) based membrane sensor. The electrode showed good discrimination toward Cu²⁺ ions with respect to most common cations. The advantages of the proposed methods are their simplicity, selectivity, and high sensitivity. In addition, the sensor has been used as indicator electrode in the potentiometric titration of Cu²⁺ ion against EDTA. The structure and geometry of the complex formed between Cu(II) and H₂L ligand was identified via isolation of the solid complex; Co(II) an Ni(II) complexes were synthesized as well. The geometrical structure around the metal centers were proved to be square planar for Cu(II) complex and tetrahedral for Co(II) an Ni(II) complexes.

Applications of Potentiometric Sensors for the Determination of Drug Molecules in Biological Samples

Potentiometry is extensively studied by researchers as one of the electrochemical methods due to its multiple advantages. Until today, thousands of potentiometric sensors have been developed and applied successfully in many fields such as medicine, environmental monitoring, agriculture, industry and pharmaceutical sciences. Clinical drug analyses and determination of drugs in biological samples are highly important from a medical point of view. These analyses are carried out using various analytical devices including potentiometric sensors. These potentiometric sensors are superior to other devices in terms of several performance parameters, and thus present a good alternative for researchers. Using potentiometric sensors, very successful results in the identification of drug molecules in body fluids have been obtained and reported in the literature up to now. In this study, we review potentiometry-based sensors developed for the determination of drug molecules in various biological samples such as blood serum and urine, and touch upon their performance features in these applications.

A carbon paste electrode modified with Al2O3-supported palladium nanoparticles for simultaneous voltammetric determination of melatonin, dopamine, and acetaminophen

The authors have modified a carbon paste electrode with Al₂O₃-supported palladium nanoparticles (PdNP@Al₂O₃) to obtain a sensor for simultaneous voltammetric determination of melatonin (MT), dopamine (DA) and acetaminophen (AC). The PdNP@Al₂O₃ was characterized by scanning electron microscopy and energy-dispersive X-ray spectra. The sensor can detect DA, AC, MT and their mixtures by giving distinct signals at working voltages of typically 236, 480 and 650 mV (vs. Ag/AgCl), respectively. Differential pulse voltammetric peak currents of DA, AC and MT increase linearly in the 50 nmol L^-1 - 1.45 mmol L^-1, 40 nmol L^-1 -1.4 mmol L^-1, and 6.0 nmol L^-1 - 1.4 mmol L^-1 concentration ranges. The limits of detection are 36.5 nmol L^-1 for DA, 36.5 nmol L^-1 for AC, and 21.6 nmol L^-1 for MT. The sensor was successfully used to detect the analytes in (spiked) human serum and drug samples. Graphical abstract Schematic presentation of Al2O3-supported palladium nanoparticles (PdNP@Al2O3) for modification of a carbon paste electrode (CPE) to develop a voltammetric sensor for the simultaneous determination of dopamine (DA), acetaminophen (AC) and melatonin (MT).

Facile and novel synthesis of palladium nanoparticles supported on a carbon aerogel for ultrasensitive electrochemical sensing of biomolecules

Highly stable palladium nanoparticles (Pd NPs) supported on a porous carbon aerogel (Pd/CA) prepared by a facile microwave reduction route is reported. The as-prepared Pd/CA composites were characterized by various techniques, viz. XRD, Raman, SEM-EDX, FE-TEM, BET, and TGA. The Pd NPs were found to disperse uniformly in the porous carbon matrix, which possesses a large surface area (851.8 m² g^-1) and pore volume (3.021 cm³ g^-1). The Pd/CA composite was found to possess extraordinary electrocatalytic activity and excellent selectivity for simultaneous detection of dopamine (DA) and melatonin (ML). The Pd/CA-modified electrode exhibited a wide linear response range for electrochemical sensing of DA (0.01-100 μM) and ML (0.02-500 μM) with a detection limit of 0.0026 and 0.0071 μM, respectively. In addition, the electrochemical sensor reported herein was successfully applied for the detection of DA and ML in human serum and urine samples, revealing perspective practical applications.

Graphene and Co-polymer composite based molecularly imprinted sensor for ultratrace determination of melatonin in human biological fluids

A novel molecularly imprinted polymer (MIP) sensor based on a composite of graphene (GR) and a co-polymer of 4-amino-3-hydroxy-1-naphthalenesulfonic acid (AHNSA) and melamine (MM) has been fabricated for detecting melatonin.