Electrochemical determination of L-Tryptophan based on a multiwall carbon nanotube/Mg–Al layered double hydroxide modified carbon paste electrode as a sensor

Electrochemical sensor based on molecularly imprinted copolymer for selective and simultaneous determination of riboflavin, dopamine, and L-tryptophan

This research shows the exact detection of riboflavin (RF), dopamine (DA), and L-tryptophan (Trp) through molecularly imprinted polymer (MIP) based on the electropolymerization method. MIP was placed on the surface of the glassy carbon electrode (GCE) by electropolymerization of monomers such as catechol and para-aminophenol, in the presence of all three analytes. The introduced sensor was investigated using field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), Fourier-transform infrared spectroscopy (FTIR), and electrochemical methods, for example, electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and differential pulse voltammetry (DPV). The MIP/GCE performs well in terms of selectivity, reproducibility, repeatability, and stability. This sensor revealed good linear ranges of 0.005-500 μM for RF, 0.05-500 μM for DA, and 0.1-250 μM for Trp with limits of detection (LOD) as 0.0016 μM, 0.016 μM, and 0.03 μM for RF, DA, and Trp, respectively. The modified GCE was successfully applied to detect RF, DA, and Trp in serum and milk samples with satisfactory results.

Copper oxide nanoflowers/poly-l-glutamic acid modified advanced electrochemical sensor for selective detection of l-tryptophan in real samples

The main objective of this research work is to develop a low-cost sensor to detect l-tryptophan (L-tryp) in real sample medium based on a modified glassy carbon electrode. For this, copper oxide nanoflowers (CuONFs) and poly-l-glutamic acid (PGA) were used to modify GCE. The prepared NFs and PGA coated electrode was characterized using field emission scanning electron microscope (FE-SEM) with energy dispersive X-ray (EDX) and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. Furthermore, the electrochemical activity was performed by cyclic voltammetry (CV), differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS). The modified electrode showed excellent electro-catalytic activity towards L-tryp detection in PBS solution at neutral pH 7.0. Based on the physiological pH condition, the proposed electrochemical sensor can detect L-tryp concentration with a linear range of 1.0 × 10^-4-8.0 × 10^-8 molL^-1 with having a detection limit of 5.0 × 10^-8 molL^-1 and sensitivity of 0.6μA/μMcm². The selectivity of L-tryp was tested with a mixture of salt and uric acid solution at the above conditions. Finally, this strategy demonstrated excellent recovery value in real sample analysis like milk and urine.

Electrochemical Amino Acid Sensing: A Review on Challenges and Achievements

The rapid growth of research in electrochemistry in the last decade has resulted in a significant advancement in exploiting electrochemical strategies for assessing biological substances. Among these, amino acids are of utmost interest due to their key role in human health. Indeed, an unbalanced amino acid level is the origin of several metabolic and genetic diseases, which has led to a great need for effective and reliable evaluation methods. This review is an effort to summarize and present both challenges and achievements in electrochemical amino acid sensing from the last decade (from 2010 onwards) to show where limitations and advantages stem from. In this review, we place special emphasis on five well-known electroactive amino acids, namely cysteine, tyrosine, tryptophan, methionine and histidine. The recent research and achievements in this area and significant performance metrics of the proposed electrochemical sensors, including the limit of detection, sensitivity, stability, linear dynamic range(s) and applicability in real sample analysis, are summarized and presented in separate sections. More than 400 recent scientific studies were included in this review to portray a rich set of ideas and exemplify the capabilities of the electrochemical strategies to detect these essential biomolecules at trace and even ultra-trace levels. Finally, we discuss, in the last section, the remaining issues and the opportunities to push the boundaries of our knowledge in amino acid electrochemistry even further.

Sulfur and nitrogen co-doped graphene quantum dot-assisted chemiluminescence for sensitive detection of tryptophan and mercury (II)

A simple one-step thermal treatment to prepare strong fluorescent sulfur and nitrogen co-doped graphene quantum dots (SN-GQD) using citric acid and l-cysteine as precursors was developed. The ultra-weak chemiluminescence (CL) from the reaction of hydrogen peroxide (H₂ O₂ ) and periodate (IO₄ ^- ) was significantly enhanced by SN-GQD in acidic medium. The enhanced CL was induced by excited-state SN-GQD (SN-GQD*), which was produced from the transfer energy of (O₂ )₂ * and ¹ O₂ to SN-GQD and recombination of oxidant-injected holes and electrons in SN-GQD. In the presence of tryptophan (Trp), the CL intensity of the SN-GQD-H₂ O₂ -KIO₄ system was greatly diminished. This finding was used to design a novel method for determination of Trp in the linear range 0.6-20.0 μM, with a limit of detection (LOD) of 58.0 nM. Furthermore, Hg²⁺ was detectable in the range 0.1-9.0 μM with a LOD of 64.0 nM, based on its marked enhancement of the SN-GQD-H₂ O₂ -KIO₄ CL system. The proposed method was successfully applied to detect Trp in milk and human plasma samples and Hg²⁺ in drinking water samples, with recoveries in the range 95.7-107.0%.

A highly selective and sensitive chemosensor forl-tryptophan by employing a Schiff based Cu(ii) complex

Construction of a new Cu(ii) complex (1) based modified glassy carbon electrode (1-GCE) for highly selective and sensitive detection ofl-tryptophan (l-Trp).

Delphinidin immobilized on silver nanoparticles for the simultaneous determination of ascorbic acid, noradrenalin, uric acid, and tryptophan

In the present study, the fabrication of a new modified electrode for electrocatalytic oxidation of noradrenalin, based on the delphinidin immobilized on silver nanoparticles modified glassy carbon electrode. Cyclic voltammetry was used to investigate the redox properties of this modified electrode. The surface charge transfer rate constant (k_s) and the charge transfer coefficient (α) for the electron transfer between the glassy carbon electrode and the immobilized delphinidin were calculated. The differential pulse voltammetry exhibited two linear dynamic ranges and a detection limit of 0.40μM for noradrenalin determination. Moreover, the present electrode could separate the oxidation peak potentials of ascorbic acid, noradrenalin, uric acid, and tryptophan in a mixture. The usefulness of this nanosensor was also investigated for the determination of ascorbic acid, noradrenalin, and uric acid in pharmaceutical and biological fluid samples with satisfactory results.

An electrochemical sensor for determination of tryptophan in the presence of DA based on poly(l-methionine)/graphene modified electrode

Electrocatalytic oxidation of l-Trp at poly(l-methionine)/graphene composite film modified glassy carbon electrode (PLME/GR/GCE) were investigated by differential pulse voltammetry.

A multi-walled carbon nanotube/poly-2,6-dichlorophenolindophenol film modified carbon paste electrode for the amperometric determination of l-tyrosine

An electrochemically induced oxa-Michael addition reaction for electro-polymerization of 2,6-dichlorophenolindophenol at CPE/MWCNT for the electro-catalytic oxidation of tyrosine.