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This review article aims to provide an overview of the recent advances in the voltammetric and amperometric sensing of cysteine (Cys). The introduction summarizes the important role of Cys as an essential amino acid, techniques for its sensing, and the utilization of electrochemical methods and chemically modified electrodes for its determination. The main section covers voltammetric and amperometric sensing of Cys based on glassy carbon electrodes, screen printed electrodes, and carbon paste electrodes, modified with various electrocatalytic materials. The conclusion section discusses the current challenges of Cys determination and the future perspectives., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The new Co(ii) compound [Co(5,5'-dmbpy) 2 (NCS) 2 ] (a1) was prepared by reacting Co(NO 3 ) 2 ·6H 2 O, 5,5'-dimethyl-2,2'-bipyridine ligand, and Na(SCN). The nano-scale size of [Co(5,5'-dmbpy) 2 (NCS) 2 ] (a1) was synthesized using sonochemical process. The size of the nanoparticles (a2) was ∼13 ± 2 nm. We have also provided a new platform of electrochemical sensing for simultaneous detection of acetaminophen and naproxen using (a2) surface modified graphite screen printed electrode (SPE) in 0.1 M phosphate buffer solution (PBS, pH 7.0). In contrast to bare SPE, the modified SPE could significantly improve the electrooxidation activity of acetaminophen along with the rise in the current of an anodic peak. The peak currents acquired using differential pulse voltammetry (DPV) raised linearly with the raising of acetaminophen concentration and the sensor had a detection range over the concentration range of 0.009-325.0 μM, with a detection limit of 5.0 nM (S/N = 3). In the case of naproxen peak, currents of naproxen oxidation at the modified SPE were linearly dependent on the naproxen amounts in the range of 1.0-500.0 μM. The detection limit (S/N = 3) was calculated to be 0.03 μM. The DPV responses show that the peaks of acetaminophen and naproxen oxidation were vividly separated from one other with a potential difference of 410 mV between them. The low detection limit, high sensitivity, and stability made the relevant electrode applicable for the analysis of acetaminophen and naproxen in real samples. Further, its practical applicability was reliable and desirable in the analysis of pharmaceutical compounds and biological fluids. The benefits of using this modified electrode for the determination of analytes are compared with other works in the manuscript., Competing Interests: The authors declare no competing interests., (This journal is © The Royal Society of Chemistry.)

It is essential to develop easy-to-use sensors towards a better monitoring of food additives so that human health can be positively influenced. A type of critical food additive that is widely used in making soft drinks and diverse foodstuff is called amaranth. This study aimed at presenting a novel Pd/GO nanomaterial-modified screen-printed electrode (Pd/GO/SPE), which is responsible for providing a sensing interface during the process of specifying the electrochemical features of amaranth. The morphology and structure of the Pd/GO nanomaterial was investigated by Fourier-transform infrared spectroscopy, thermal gravimetric analysis, X-ray photoelectron spectroscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy, scanning transmission electron microscopy, and high-resolution transmission electron microscopy. When the optimized conditions was adjusted, Pd/GO/SPE proved to be a capable sensor for conducting a very sensitive sensing towards the amaranth under a common working situation of 575 mV. In this regard, it was embarked on measuring some of the sensor features, including its sensitivity, linear dynamic range, and detection limit for amaranth with the values of 0.0948 μA μM -1 , 0.08 μM-360.0 μM and 30.0 nM were obtained, respectively., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Scientists have categorized conductive polymers as materials having strongly reversible redox behavior and uncommon combined features of plastics and metal. Because of their multifunctional characteristics, e.g. , simplistic synthesis, acceptable environmental stability, beneficial optical, electronic, and mechanical features, researchers have largely considered them for diverse applications. Therefore, their capability of catalyzing several electrode reactions has been introduced as one of their significant features. A thin layer of the conducting polymer deposited on the substrate electrode surface can augment the electrode process kinetics of several solution species. Such electrocatalytic procedures with modified conducting polymer electrodes can create beneficial utilization in diverse fields of applied electrochemistry. This review article explores typical recent applications of conductive polymers (2016-2020) as active electrode materials for energy storage applications, electrochemical sensing, and conversion fields such as electrochemical supercapacitors, lithium-ion batteries, fuel cells, and solar cells., Competing Interests: The authors declare no competing interests., (This journal is © The Royal Society of Chemistry.)

The detection of hydrazine (HZ) is an important application in analytical chemistry. There have been recent advancements in using electrochemical detection for HZ. Electrochemical detection for HZ offers many advantages, e.g. , high sensitivity, selectivity, speed, low investment and running cost, and low laboriousness. In addition, these methods are robust, reproducible, user-friendly, and compatible with the concept of green analytical chemistry. This review is devoted to the critical comparison of electrochemical sensors and measuring protocols used for the voltammetric and amperometric detection of the most frequently used HZ in water resources with desirable recovery. Attention is focused on the working electrode and its possible modification which is crucial for further development., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Nanostructured metal oxides, such as zinc oxide (ZnO), are considered as excellent materials for the fabrication of highly sensitive and selective electrochemical sensors and biosensors due to their good properties, including a high specific surface area, high catalytic efficiency, strong adsorption ability, high isoelectric point (IEP, 9.5), wide band gap (3.2 eV), biocompatibility and high electron communication features. Thus, ZnO nanostructures are widely used to fabricate efficient electrochemical sensors and biosensors for the detection of various analytes. In this review, we have discussed the synthesis of ZnO nanostructures and the advances in various ZnO nanostructure-based electrochemical sensors and biosensors for medical diagnosis, pharmaceutical analysis, food safety, and environmental pollution monitoring.

This review summarizes the progress that has been made in the past ten years in the field of electrochemical sensing using nanomaterial-based carbon paste electrodes. Following an introduction into the field, a first large section covers sensors for biological species and pharmaceutical compounds (with subsections on sensors for antioxidants, catecholamines and amino acids). The next section covers sensors for environmental pollutants (with subsections on sensors for pesticides and heavy metal ions). Several tables are presented that give an overview on the wealth of methods (differential pulse voltammetry, square wave voltammetry, amperometry, etc. ) and different nanomaterials available. A concluding section summarizes the status, addresses future challenges, and gives an outlook on potential trends., Competing Interests: The authors declare that they have no competing interests., (This journal is © The Royal Society of Chemistry.)

Neuro-transmitters have been considered to be essential biochemical molecules, which monitor physiological and behavioral function in the peripheral and central nervous systems. Thus, it is of high pharmaceutical and biological significance to analyze neuro-transmitters in the biological samples. So far, researchers have devised a lot of techniques for assaying these samples. It has been found that electro-chemical sensors possess features of robustness, selectivity, and sensitivity as well as real-time measurement. Graphene quantum dots (GQDs) and carbon QDs (CQDs) are considered some of the most promising carbon-based nanomaterials at the forefront of this research area. This is due to their characteristics including lower toxicity, higher solubility in various solvents, great electronic features, strong chemical inertness, high specific surface areas, plenty of edge sites for functionalization, and versatility, in addition to their ability to be modified via absorbent surface chemicals and the addition of modifiers or nano-materials. Hence in the present review, the synthesis methods of GQDs and CQDs has been summarized and their characterization methods also been analyzed. The applications of carbon-based QDs (GQDs and CQDs) in biological and sensing areas, such as biological imaging, drug/gene delivery, antibacterial and antioxidant activity, photoluminescence sensors, electrochemiluminescence sensors and electrochemical sensors, have also been discussed. This study then covers sensing features of key neurotransmitters, including dopamine, tyrosine, epinephrine, norepinephrine, serotonin and acetylcholine. Hence, issues and challenges of the GQDs and CQDs were analyzed for their further development., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The present investigation examines a sensitive electrochemical technique to detect desipramine through Fe 3 O 4 /CuO nanoparticles (NPs). Fe 3 O 4 /CuO NPs were synthesized via a coprecipitation procedure, and the products were characterized via energy disperse spectroscopy, X-ray diffraction, transmission electron microscopy, scanning electron microscopy, and vibrating sample magnetometer. The voltage-current curve and differential pulse voltammetry examinations of Fe 3 O 4 /CuO-modified screen-printed electrode (Fe 3 O 4 /CuO/SPE) were followed by the determination of electro-catalytic activities toward desipramine oxidation in a phosphate buffer solution (pH = 7.0). In addition, the value of diffusion coefficient ( D = 3.0 × 10 -6 cm 2 s -1 ) for desipramine was calculated. Then, based on the optimum conditions, it was observed that the currents of the oxidation peak were linearly proportionate to the concentration of desipramine in the broad range between 0.08 and 400.0 μM and LOD of 0.03 μM (S/N = 3). Finally, our new sensor was successfully utilized to detect desipramine in the real samples, with reasonable recovery in the range of 97.2% to 102.7%., Competing Interests: All the authors declare no conflict of interest., (This journal is © The Royal Society of Chemistry.)

This study introduces the sensitive electrochemical detection of clozapine with the use of a ruthenium(iv) oxide nanoparticle (RuO 2 NP)-modified screen-printed electrode (RuO 2 NPs/SPE). The electrochemical behaviors of clozapine at RuO 2 NP/SPE have been examined via cyclic voltammetry (CV), differential pulse voltammetry (DPV) and chronoamperometry (CHA). According to the results, the modified electrode has been accompanied by a decreasing over-potential ( ca. 170 mV) and enhancement in the peak current (3 times) in comparison with the bare SPE. The results indicated that RuO 2 NP/SPE markedly augmented electro-catalytic activities toward clozapine oxidation. In addition, linear responses have been observed in the range between 0.2 and 500.0 μM with a sensitivity of 0.076 μA μM -1 and a limitation of detection of 0.07 μM (3 σ ). Moreover, the successful application of RuO 2 NP/SPE has been seen in detecting clozapine in real samples, which showed satisfied recoveries. Therefore, outputs suggest that RuO 2 NP/SPE will be promising for functional utilization., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)