An electrochemical L-tryptophan sensor based on tellurium nanorods modified glassy carbon electrode was proposed. The tellurium nanorods were synthesized by a chemical reduction method. The morphology and structures of the nanorods were characterized by scanning electron microscope (SEM) and transmission electron microscope (TEM). Owing to the special structure of the tellurium nanorods, the sensor exhibits excellent electrocatalytic ability towards the oxidation of L-tryptophan and shows linearity in the range from 0.02 to 11.48 mM with a sensitivity of 256 mA mM−1 cm−2 with a correlation coefficient of 0.9945. The detection limit was 0.01 mM with signal-to-noise ratio of 3, and the response time was found to be 2 s. Moreover, the sensor also exhibited long-term stability, good reproducibility and anti-interference, thus holding promise for sensing of L-tryptophan in practice.

One of the important molecules in homeostasis, especially for hormone metabolism, cellular membrane production, and vitamin D synthesis is cholesterol. However, studies showed that increased levels of this molecule would be associated with increased incidence of cardiovascular diseases including heart failure and myocardial infarction (MI). Thus, the measurement of the blood level of cholesterol is an important step for early detection and prevention of several diseases. Electrochemical sensors with high accuracy could be useful for the detection of cholesterol in body fluids. Due to the outstanding chemical and physical properties that nanoparticles possess, they are perfectly suited for the development of new and improved sensing devices. In particular, electrochemical sensors and biosensors are two types of sensing devices that could benefit from the use of nanoparticles. Many different kinds of nanoparticles, such as metal nanoparticles, oxide nanoparticles, semiconductor nanoparticles, and even composite nanoparticles, have found widespread application in electrochemical sensors and biosensors, respectively. This review has covered a variety of electrochemical biosensors for cholesterol detection, including conductometric, amperometric, and potentiometric-based biosensors, as well as their detection techniques and limitations.

A thin film of epinephrine (EP) was electrochemically deposited on the surface of glassy carbon electrode previously activated in NaHCO3 solution. The cyclic voltammograms of the modified electrode indicate that the surface confined EP is strongly dependent on the solution pH, as expected for quinone/hydroquinone functionalities. The EP-modified glassy carbon electrode exhibited catalytic activity towards the electrooxidation of hydrazine, which appeared as a reduced overpotential especially in pH = 7.5. The diffusion coefficient of hydrazine was estimated using chronoamperometry. The catalytic rate constant, Kh, of the modified electrode for the oxidation of hydrazine was determined using the cyclic voltammograms recorded at low scan rates as well as the RDE voltammetric approach. It has been shown that the EP-modified electrode can be used as an amperometric sensor in the analysis of trace amount of hydrazine with high sensitivity and good limit of detection (0.83 µM). Amperometry by EP-modified electrode was used for determination of hydrazine in boiler feed water and the accuracy of the results was verified by comparison with those obtained from standard ASTM method.

The polyaniline-glucose oxidase (PANI-GOD) electrode has been investigated in the present work. Polyaniline (PANI) film via cyclic voltammetric method was synthesized at room temperature, in a standard three-electrode cell. Aniline films were deposited from 1 M acidic (H2SO4) aqueous media containing 0.2 M aniline by voltammetric sweep between -0.1 V and 1 V, Ag/AgCl, at 50 mV/s. The sweep was stopped after 30 cycles at -0.1 V Ag/AgCl and the working electrode was deposited by polyaniline. Platinum plate (0.4cm×0.4cm), platinum rod and Ag/ AgCl electrodes were used as working, counter and reference electrodes, respectively. The synthesized PANI films were characterized by electrochemical technique, electrical conductivity, UV-visible spectroscopy, Fourier transform infrared (FTIR) spectroscopy and electrochemical impedance spectroscopy (EIS). A simple technique was used for fabrication of a glucose sensor. In this method glucose oxidase as an enzyme was immobilized by glutaraldehyde 0.1% as cross-linking agent and kept pH around 7 using 0.1 M phosphate over polyaniline thin films, glucose oxidase was deposited on a platinum plate in phosphate or acetate buffer. The results of EIS indicated the successful immobilization of enzyme over polymer films. Effects of some experimental variables such as cross-linking agent volume content, pH, applied potential, and temperature on the amperometric response of the sensor were investigated. It was obsereved that the activity of modified electrodes changed with various amounts of cross-linking agent volume percent. The activation energy for polyaniline-modified electrode in acetate and phosphate buffer were obtained as 41 and 37 kJ/mol, respectively. A maximum current response was resulted at pH 7 and potential 0.65 V (versus Ag/AgCl).

In this work a new electrochemical method will be presented for the determination of enalapril in pharmaceutical tablets using unmodified screen printed electrode (SPE). The studies were done using amperommetric detection. Enalapril provides well defined, oval-shape oxidation peak at +1. 05 V (vs. Ag/AgCl, 3. 0 M KCl) in Britton-Robinson buffer solution (BRBS) at pH 5. 0. After optimization of the experimental conditions, the influence of most common interferent compounds was tested. Under optimized experimental conditions, the signals were linearly proportional to the concentration of enalapril in the range from 2. 5 to 90 μ M with a detection limit of 0. 9 μ M. Repeatability of ten replicate measurements of 5 μ M enalapril was estimated to be 1. 5%. Proposed method was successfully applied for the determination of the total amount of enalapril content in pharmaceutical preparations. Nevertheless, proposed method could be beneficial for the quick quantifications of enalapril in drugs using unmodified SPE electrode without any further treatment.

In this research work, at first, bimetallic Pt-Pd particles/ ERGO nanohybrid was prepared on glassy carbon electrode (GCE) and then was used to determine bisphenol A (BPA). The morphology of modified electrode was studied by using field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM) and energy dispersive spectroscopy (EDS). Cyclic voltammetry (CV) of modified electrode in the presence of BPA in phosphate buffer indicated an oxidation peak at 0. 44 V which means the irreversible oxidation process of this compound. In addition, electrochemical impedance spectroscopy results showed that charge transfer of Pt-Pd/ERGO/GCE is lower than GCE and ERGO/GCE. Amperometric method was applied as a sensitive analytical method for the determination of BPA. A linear relationship between the oxidation peak current and BPA concentration was obtained in the range from 5 to 201. 5 µ M with a detection limit of 0. 75 µ M and sensitivity of 0. 13 µ A µ M-1. Moreover, the proposed electrode exhibits good selectivity for electrooxidation of BPA.

The effect of Pd nanoparticles geometry has been studied on modifying Fc and Fc-COOH-based electrodes. It has been found to have more reliable results before and after Pd use with Fc-COOH modified electrode. The sensing activity has been performed for ascorbic acid and found quite good results with Fc-COOH-based electrode and surprising results with Pd-modified Fc and Fc-COOH-based electrode, which is further confirmed by performing amperometry titration and observed much high current in case of PdNPs modified Fc-COOH based electrode. The rise in anodic peak current from 14.5A to 33.01A and 1.30A to 3.63 A for Fc and Fc-COOH modified electrodes under a similar environment. The current function continuously rises from 10 to 16A/(mV)0.5 and 6.5 to 13.4A/(mV)0.5. The Rct value decreases from 12.8 k to 1.9 k and 8.3 k to 1.5 krespectively. Electrochemical impedance spectroscopy has also been studied, confirming that PdNPs modified Fc and Fc-COOH-based electrodes having low Rct value, the faster charge transfer is compassionate toward ascorbic acid. Transmission electron microscopy, PXRD, and CV have all been used to characterize the nanomaterial with the following major investigation:(i) The average size of PdNPs1&PdNPs2 is found 18nm & 8nm, (ii) It has been discovered that the palladium content influences both the electrocatalytic effectiveness of novel modified electrode materials and the oxidoreduction electrochemistry of ferrocene and Fc-COOH, and(iii) The modified electrode has an extremely low detection limit for ascorbic acid of < 5 μM