Current Analytical Chemistry - Volume 13, Issue 1, 2017

Electrochemical techniques are powerful tools for trace analysis of important food, clinical and environmental compounds in real samples. In between electrochemical methods, stripping voltammetry technique is a very selective and highly sensitive method for the determination of nanomolar level of electroactive species in solution. Detection limits for electroactive compounds at sub-ppb concentrations have been reported using stripping voltammetric methods. Therefore, in this review, we focus on application of stripping voltammetric sensor for trace level analysis of metal ion, drug and environmental compounds. This review describes basic stripping voltammetric sensors and ability of them in the real sample analysis. Stripping voltammetric sensors can be used in industry for the analysis of food samples and they are a good alternative for HPLC method. Fast response and good limit of detection are the main reason that encourages us to write a review.

The interdisciplinary field of materials science involves the discovery and design of new materials. Because of this, materials science has effective interest in the fabrication of biosensors/ nanosensors. In this review, we have focused on molecular imprinted electrochemical sensors based nanomaterials such as graphene oxide/carbon nanotubes molecular imprinting has been very effective method to achieve high selectivity and sensitivity for the fabrication of sensors. It is based on the formation of three-dimensional nano-cavities in crosslinking polymer matrix, where the functional and crosslinking monomers are copolymerised in the presence of target molecule (imprint molecule), which acts as a molecular template. In an imprinted polymer, the chemically active moieties of the target molecules are held in position by the highly crosslinked polymeric networks. In addition, the novel nanomaterials such as graphene/carbon nanotubes have many applications in sensor technology. The review presents the recent developments related to molecularly imprinted electrochemical sensors based carbon nanomaterials.

Aptamers are specific oligonucleotides selected invitro which bind to target molecules with high affinity and specificity like antibody-antigen interactions. For that reason, these synthetic oligonucleotides also known as “artificial antibodies”, offer great potential as bio-recognition elements in biosensors. Electrochemical sensors, as biosensors, are very attractive to early diagnosis of cancer as these devices are fast, portable, extremely sensitive and selective towards their targets, especially when a biorecognition element is integrated with the electrode surface. This review presents electrochemical aptasensors reported in the literature which is sensitive to and specific to cancer cells or their marker proteins, and their possible improvements by combining nanotechnology.

Background: Determination of heavy and transition metal ions, like lead, especially with the aid of portable, user fiendly, and accurate and precise devices has long been an interesting area in analytical applications, especially in the case of environmental and biological samples. In this light, and given the facility, speed, accuracy, precision and also moderate costs of electrochemical monitoring techniques, these methods have been brought into the spotlight. Among the various areas of research used for such purposes, the preparation, modification and application of carbon paste electrodes (CPEs), as sensors which offer rather unique advantages of renewability of their surface, stable responses, low Ohmic resistance, and above all, the possibility of modifying and fine tuning their composition to meet the requirements of specific analytical applications, have given these devices a unique role among the other comparable techniques and hence this field has turned to a very attractive area of scientific endeavor. The composition of the carbon pastes usually consists of graphite powder dispersed in a binding solvent, but the characteristics of CPEs have been further improved through the addition of various modifiers. A rather recent step in the area of modification of CPEs, is the application of nano-materials to form nanocomposite carbon paste electrodes (NC-CPEs). Objective: The application of NC-CPEs has been widely developed, and the current review tends to offer an overview on the development and applications of NC-CPEs for the analysis of lead, as a significant transition metal with various biological roles. This manuscript furtehr tends to provide the reader with a classification of the nano-composite modified CPEs for lead ions, which might surve as a general outlook for planing for further research, for the same analyte as well as others.

The electrochemical bahaviour of cysteamine (CA) has been investigated by synergic effect of acetylferrocene (AF) and NiO/CNT nanocomposite at a surface of carbon paste electrode (AF/NiO/CNTs/CPE). Voltammetric techniques were used to investigate the suitability of AF/NiO/CNTs/CPE for the electrocatalytic oxidation of CA in pH=7.0 as a suitable condition in voltammetric analysis. AF/NiO/CNTs/CPE shows a dynamic range to electrocatalytic analysis of CA in the range of 0.1-600 μM with a detection limit of 0.07 μM by square wave voltammetric method (SWV). The ability of AF/NiO/CNTs/CPE as a sensor checked analysis of CA in real samples.

Background: Benserazide is an important catechol drug that has been comprehensively used as an irreversible inhibitor of peripheral aromatic amino acid decarboxylase. It is an important drug with wide application in treatment of Parkinson's disease. Therefore, the determination of this drug is very important in biological samples. Methods: According to importance of BZ in biological and pharmaceutical samples, we focused on determination of this drug in real samples. In between and analytical methods, electrochemical based sensors have good choice for the determination of drug samples. Results: The aim of the present study was using CdO/SWCNTs nanocomposite and Ionic liquid (n-hexyl-3- methylimidazolium bromide) for modification of carbon paste electrode. The proposed sensor was applied to the determination of benserazide (BZ). Under optimum pH of 7.0, the electro-oxidation of BZ at a surface of modified electrode occurred at a potential of about 250 mV and oxidation current was more than bare carbon paste electrode. The plot of oxidation signal vs. concentration of BZ was linear in the range of 0.1 to 450.0 μM BZ and detection limit was calculated to be 0.06 μM BZ. The new sensor was also examined for the determination of BZ in real samples. Conclusion: In this study, we describe synthesis of CdO/SWCNTs by direct chemical precipitation method and synthesized nanocomposite characterized with XRD and TEM methods. In continuation, a carbon paste electrode modified with CdO/SWCNTs and 1-methyl-3-butylimidazolium bromide has been utilized for voltammetric analysis of BZ in pharmaceutical and water samples. In the best electrochemical condition, the oxidation peak current was proportional to the BZ concentration in the range of 0.1–450.0 μM with the detection limit of 0.06 μM.

Background: Application of room temperature ionic liquids (RTILs) in making potentiometric drug sensors is a new strategy to improve the response mechanism. The response of the sensors generally depends on the polymeric membrane ingredients; amount of sensing material, type of plasticizer and ionic additive. Sensing element of a drug sensor which is the most important component of the membrane can be an ion-pair complex or a molecularly imprinted polymer (MIP). In the potentiometric sensors, drug molecules should be able to form a cationic or anionic species to exchange with the similar species in interaction with the sensing element placed in the membrane. Hydrophobicity of the drug and the membrane properties affect the extraction of the drug ions from aqueous phase to the organic layer of the membrane. Rather recently, ionic liquids have found important roles as ionic additives to help better extraction of these organic ions. In addition, due to their particular electrochemical properties, they improve the membrane conductivity which may be more important in case of MIP-based membrane sensors. Also, since they better compatibility with polymers, they plasticize the membrane more properly and improve the performance of the sensor. Miscibility of RTILs with water is the key factor to limit their selection. RTILs can be water-immiscible or hydrophobe compounds depending on the type of cationic and anionic bases. Objective: From the early introduction of the potentiometric methods up to now, there are many reports on PVC membrane sensors for the wide range of pharmaceutical compounds. However, this review considers those ones which used ionic liquids in the composition of the membrane.

Background: Mercury is a highly hazardous heavy metal which can seriously affect the human health. Many analytical methods such as cold vapor atomic absorption spectroscopy, inductively coupled plasma optical emission spectrometry (ICP-OES), and inductively coupled plasma mass spectrometry (ICP-MS), have been reportedly used for the the determination of mercury in different samples. These techniques analyze the total mercury content (ionic form or complex species) accurately but they are very expensive and time consuming. In comparison, electrochemical sensors present inexpensive procedures that are able to analyze only the ionic forms of metallic ions, including mercury fast and simple. The devices can be further easily miniaturized and applied in portable applications. As opposed to these mertious advantages, they unfortunately suffer certain drawbacks especially if used for the analysis of heavy metal ions. The disadvantages include the fact that most selectophores used in designing mercury selective sensors, suffer from interference by the copper ions particularly when the analyte concentration is low. The application of ionic imprinted polymers (IIPs) as biomimetic selectophores in the design of the electrochemical sensing devices can be a good way to overcome this problem. The high extraction ability of IIPs make them suitable for the analysis of races of various analytes including mercury, making the analysis of very dilute sample viable. Objective: The present review tends to provide the reader with an overview of the methods used for the synthesis of Hg-IIPs as well as their applications to the analysis of various samples through their incorporation into the different electrochemical sensing devices such as potentiometric and voltammetric sensors.

Background: Many instruments have been developed for use in a variety of situations to facilitate the application of nano-based sensors, avoiding expensive and time-consuming procedures. Modified electrochemical methods are precise and sensitive analytical methods with excellent limits of detection. In these systems the analytical information is obtained from the electrical signal that results from the interaction of the drug and the recognition layer at the sensing electrode. Depending on the nature of the electrical signal, which is measured, those techniques are divided into capacitive, impedimetric, admittometric and voltammetric techniques. These methods offer a number of advantages for sensitive quantitative studies, mainly well-defined and peak-shaped responses, where undesirable effects are greatly minimized. Therefore, these techniques are very valuable in mechanistic and kinetic quantitative studies. In addition, the electrochemical systems provide monitoring of interest analytes for in-vivo and in-situ measurements. Objective: Increasing concern about the drug analysis from analytical methodologies has led to design new field of electroanalytical measurements. This paper presents the new advanced electrochemical instrument and micro and nano-based sensors capable of detecting and identifying drugs.

Vanillin (VAL) is an important flavoring agent in foods, beverages, and pharmaceuticals samples. It is a more atractive food additive as flavor enhancer. Therefore, determination of VAL is important in food industrials. A new method for the determination of VAL in food samples was developed by sqaure wave voltammetry using carbon paste electrode modified with CuFe2O4 nanoparticles and ionic liquid as a working electrode. The obtained CuFe2O4 nanoparticles were characterized by transmission electron microscopy (TEM) method. The modfied electrode shows high electrocatalytic activity for VAL electrooxidation at pH=7.0 as an optimum condition. A linear calibration plot was obtained in the concentration range of 0.1–700.0 μM with a detection limit of 0.07 μM. The proposed electrode was successfully applied for the detectermination of VAL in biscuit, chocolate and coffee milk samples.