Electrochemical investigation of tryptophan at gold nanoparticles modified electrode in the presence of sodium dodecylbenzene sulfonate

An ionic liquid-modified PEDOT/Ti3C2TX based molecularly imprinted electrochemical sensor for pico-molar sensitive detection of L-Tryptophan in milk

L-Tryptophan (L-Trp) is essential for the human body and can only be obtained externally. It is important to develop a method to efficiently detect L-Trp in food. In this work, ionic liquid (IL) modified poly(3,4-ethylendioxythiophene)/ Titanium carbide (PEDOT/Ti3C2TX) was used as a substrate material to improve detection sensitivity. Molecular imprinted polymers (MIP) film for specific recognition of L-Trp was fabricated on the surface of modified electrodes using electrochemical polymerization. The monitoring results showed that the molecularly imprinted electrochemical sensors (MIECS) exhibited good linearity ranges (10-6 - 0.1 μM and 0.1-100 μM) with a low detection limit (LOD) of 2.09 × 10-7 μM. In addition, the MIECS exhibited remarkable stability, reproducibility, and immunity to interference. A good recovery (93.54-99.59%) was demonstrated in the detection of milk. The sensor was expected to be developed as a highly selective and sensitive portable assay, and applied to the detection of L-Trp in food.

The Development of Reagentless Amperometric Glucose Biosensor Based on Gold Nanostructures, Prussian Blue and Glucose Oxidase

Precise blood glucose detection plays a crucial role in diagnosing and medicating diabetes, in addition to aiding diabetic patients in effectively managing their condition. In this research, a first-generation reagentless amperometric glucose biosensor was developed by combining the graphite rod (GR) electrode modification by gold nanostructures (AuNS) and Prussian blue (PB) with glucose oxidase (GOx)-an enzyme that can oxidize glucose and produce H2O2. Firstly, AuNS was electrochemically deposited on the GR electrode (AuNS/GR), and then PB was electrochemically synthesized on the AuNS/GR electrode (PB/AuNS/GR). Finally, GOx was immobilized over the PB/AuNS nanocomposite with the assistance of Nafion (Nf) (Nf-GOx/PB/AuNS/GR). An application of PB in the design of a glucose biosensor enables an easy electrochemical reduction and, thus, the determination of the H2O2 produced during the GOx-catalyzed oxidation of glucose in the sample at a low operation potential of -0.05 V vs. Ag/AgCl/KCl3 mol L-1. In addition, AuNS increased the electrochemically active surface area, improved the GOx immobilization and ensured a higher analytical signal. The developed glucose biosensor based on the Nf-GOx/PB/AuNS/GR electrode exhibited a wide linear range, from 0.025 to 1 mmol L-1 of glucose, with a 0.0088 mmol L-1 limit of detection, good repeatability and high selectivity over electroactive interfering substances. The developed biosensor is convenient for the determination of glucose in the physiological environment.

Sensitive Voltammetric Sensor for Tryptophan Detection by Using Polyvinylpyrrolidone Functionalized Graphene/GCE

In this paper, an electrochemical method for the measurement of tryptophan (Trp) was developed based on a glassy carbon electrode modified with polyvinylpyrrolidonefunctionalized graphene (PVP-GR)/glassy carbon electrode (GCE). In 0.1 M phosphate buffer solution (PBS, pH = 2.2), compared with bare GCE, PVP/GCE, and GR/GCE, the oxidation peak current of Trp increased dramatically at PVP-GR/GCE. The oxidation mechanism of Trp on the PVP-GR/GCE was discussed and the experimental conditions were optimized. Under the best experimental conditions, the oxidation peak current of Trp was proportional to its concentration in the range of 0.06 µM–10.0 µM and 10.0–100.0 µM, and the limit of detection (LOD) was 0.01 µM (S/N = 3). The target modified electrode with excellent repeatability, stability and selectivity, was successfully applied to detectTrp in drugs and biological samples.

Facile sonochemical synthesis of perovskite-type SrTiO3 nanocubes with reduced graphene oxide nanocatalyst for an enhanced electrochemical detection of α-amino acid (tryptophan)

In this paper, perovskite-type SrTiO₃ nanocubes decorated reduced graphene oxide is synthesized by sonochemical method. The as-synthesized SrTiO₃@RGO nanocomposite was confirmed by XRD, TEM, SEM, elemental mapping and electrochemical technique. Furthermore, surface morphological and X-ray diffraction studies revealed the formation and high loading of SrTiO₃ nanocubes on reduced graphene oxide matrix. The SrTiO₃@RGO nanocomposite modified electrode shows an excellent electrochemical detection towards of amino acid (tryptophan). The developed sensor was showed a wide linear range from 30 nM to 917.3 µM and detection limit is 7.15 nM. Furthermore, the sensitivity was calculated to be 9.11 µA µM^-1 cm². In addition, the proposed modified sensor is exhibited good selectivity, stability, reproducibility and repeatability. The SrTiO₃@RGO catalyst modified electrode was successfully applied to tryptophan analysis in biological samples.

A Simple and Efficient Molecularly Imprinted Electrochemical Sensor for the Selective Determination of Tryptophan

In this paper, a tryptophan (Trp) molecularly imprinted chitosan film was prepared on the surface of an acetylene black paste electrode using chitosan as the functional polymer, Trp as the template molecule and sulfuric acid as the crosslinking agent. The surface morphologies of non-imprinted and imprinted electrodes were characterized by scanning electron microscopy (SEM). The formation of hydrogen bonds between the functional polymer and the template molecule was confirmed by infrared spectroscopy. Some factors affecting the performance of the imprinted electrode such as the concentration of chitosan, the mass ratio of chitosan to Trp, the dropping amount of the chitosan-Trp mixture, the solution pH, and the accumulation potential and time were discussed. The experimental results show that the imprinted electrode exhibit good affinity and selectivity for Trp. The dynamic linear ranges of 0.01–4 μM, 4–20 μM and 20–100 μM were obtained by second derivative linear sweep voltammetry, and the detection limit was calculated to be 8.0 nM. The use of the imprinted electrode provides an effective method for eliminating the interference of potentially interfering substances. In addition, the sensor has high sensitivity, reproducibility and stability, and can be used for the determination of Trp in pharmaceutical preparations and human serum samples.

Facile Preparation of Fe3O4/C Nanocomposite and Its Application for Cost-Effective and Sensitive Detection of Tryptophan

In this study, we reported facile synthesis of Fe₃O₄/C composite and its application for the cost-effective and sensitive determination of tryptophan (Trp) in human serum samples. Fe₃O₄/C composites were prepared by a simple one-pot hydrothermal method followed by a mild calcination procedure, using FeCl₃∙6H₂O as Fe₃O₄ precursor, and glucose as reducing agent and carbon source simultaneously. The Fe₃O₄/C composite modified glassy carbon electrode (Fe₃O₄/C/GCE) was prepared by drop-casting method. The microstructure and morphology of Fe₃O₄/C composite was characterized by powder X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. Due to large specific surface area and synergistic effect from Fe₃O₄ nanoparticles and carbon coating, Fe₃O₄/C composite showed excellent electrocatalytic activity toward the oxidation of Trp. As a result, the proposed Fe₃O₄/C/GCE displayed superior analytical performances toward Trp determination, with two wide detection ranges (1.0–80 μM and 80–800 μM) and a low detection limit (0.26 μM, S/N = 3). Moreover, successful detection of Trp in human serum samples further validate the practicability of the proposed sensor.

Electrochemical Sensor for Rapid and Sensitive Detection of Tryptophan by a Cu2O Nanoparticles-Coated Reduced Graphene Oxide Nanocomposite

In this paper, a nanocomposite of cuprous oxide and electrochemically reduced graphene oxide (Cu₂O–ERGO) was prepared by a simple and low-cost method; hereby, a new method for the electrochemical determination of tryptophan (Trp) by this composite modified glassy carbon electrode (GCE) is proposed. The prepared materials and modified electrodes were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and cyclic voltammetry (CV). The results showed that Cu₂O–ERGO/GCE had good electrocatalytic activity for Trp. The effects of supporting electrolyte, scanning rate, accumulation potential, and accumulation time on the determination of Trp were studied. Under the optimum experimental conditions, Trp was quantitatively analyzed by square-wave voltammetry (SWV). The oxidation peak current of Trp had a good linear relationship with its concentration in the range of 0.02–20 μM, and the detection limit was 0.01 μM (S/N = 3). In addition, the modified electrode has high sensitivity, good repeatability, and long-term stability. Finally, the proposed method has been successfully applied in the determination of Trp concentration in practical samples.

Nickel oxide nanoparticles/ionic liquid crystal modified carbon composite electrode for determination of neurotransmitters and paracetamol

Ionic liquid crystals mimic the natural bio-based ionic liquid crystals such as cell membrane structures in their interactions with drugs.

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.

An amperometric sensor for detection of tryptophan based on a pristine multi-walled carbon nanotube/graphene oxide hybrid

A pMWCNT/GO hybrid shows excellent catalytic activity towards tryptophan oxidation and can thus be used as electrode material in a biosensor for sensing tryptophan sensitively and selectively.

Supramolecular p-sulfonated calix[4,6,8]arene for tryptophan detection

Numerous techniques have focused on the ability of p-sulfonated calix[n]arene to form complexes with tryptophan. Scanning electron microscopy and Fourier transform infrared spectroscopy were utilized to study the organization and molecular structure of different layers of the electrode surface. Scanning electron microscopy results showed that SC4A displayed a cubic structure whereas SC6A and SC8A displayed dendrite structures. The electrochemical properties and potential complex formation between SCnA and tryptophan were characterized by cyclic voltammetry and electrochemical impedance spectroscopy. Cyclic voltammetry experiments showed that the gold electrode was successfully functionalized by self-assembled cysteamine and SC4A. Electrochemical impedance spectroscopy results showed the observation of the tryptophan–SCnA interaction and indicated that SC4A had the highest sensitivity to tryptophan and allowed 2.04 μg L−1 tryptophan to be detected. Electrochemical impedance spectroscopy analysis and molecular modeling calculation confirmed that SC4A has higher tryptophan sensitivity than SC6A and SC8A.

In situ generation of a high-performance Pd-polypyrrole composite with multi-functional catalytic properties

We report on a bottom up approach for the synthesis of a Pd-polypyrrole nanocomposite material. The composite material was characterized by means of different techniques, such as UV-vis, IR, and Raman spectroscopy, which offered information about the chemical structure of the polymer, whereas electron microscopy images provided information regarding the morphology of the composite material and the distribution of the metal particles in the polymer matrix. During the synthesis of the nanocomposite, the Pd nanoparticles act as a catalyst for a model proton-coupled electron transfer reaction. The Pd-polypyrrole nanocomposite material was also used as a catalyst for the electro-catalytic detection of tryptophan, a precursor for some neurotransmitters.

Simultaneous electrochemical determination of dopamine, ascorbic acid and uric acid in the presence of sodium dodecyl sulphate using a multi-walled carbon nanotube modified carbon paste electrode

A carbon paste electrode modified with multi-walled carbon nanotubes (CPE/MWCNT) was prepared as a biosensor for the simultaneous determination of dopamine (DA), ascorbic acid (AA) and uric acid (UA) in the presence of sodium dodecyl sulphate (SDS).

Synthesis and application of FePt/CNTs nanocomposite as a sensor and novel amide ligand as a mediator for simultaneous determination of glutathione, nicotinamide adenine dinucleotide and tryptophan

In this study, we report the synthesis and application of a FePt/CNTs nanocomposite as a highly sensitive sensor and novel amide ligand (9,10-dihydro-9,10-ethanoanthracene-11,12-dicarboximido)-4-ethylbenzene-1,2-diol as a mediator for the determination of glutathione (GSH), nicotinamide adenine dinucleotide (NADH) and tryptophan (Trp). The synthesized materials were characterized with different methods such as NMR, IR spectroscopy, TEM, XRD, FESEM, cyclic voltammetry, electrochemical impedance spectroscopy and square wave voltammetry (SWV). The modified electrode exhibited a potent and persistent electron mediating behavior followed by well-separated oxidation peaks of GSH, NADH and Trp. The peak currents were linearly dependent on GSH, NADH and Trp concentrations in the range of 0.08-220, 1.0-400 and 5.0-500 μmol L(-1), with detection limits of 0.05, 0.8 and 1.0 μmol L(-1), respectively. The modified electrode was used for the determination of these compounds in real samples.