Hydroxyapatite/Graphene oxide composite for electrochemical detection of L-Tryptophan

Electrochemical Sensors and Biosensors for the Determination of Food Nutritional and Bioactive Compounds: Recent Advances

The significance of food nutrients and bioactive compounds in human health has driven the development of many methods for their determination in different matrices. Among these, electroanalysis has gained popularity due to its cost-effectiveness, rapidity, and, in many cases, portability and minimal sample treatment. This review highlights key advances in electrochemical sensors and biosensors from 2019 to the present. Given the variability and the challenges of managing food matrices, the focus is limited to methods that have been thoroughly assessed for their applicability to real samples. The technical characteristics and analytical performance of the proposed sensors are discussed, along with breakthrough features and future trends.

Cuprospinel decorated biopolymer functionalized CNFs based electrocatalytic platform integrated with grid search optimized neural network for detection of vital amino acid in beverages

An electrocatalytic platform based on a novel nanocomposite integrated with a grid search-optimized neural network (GSNN) was proposed for intelligent sensing of tryptophan. The cuprospinel-decorated chitosan-functionalized carbon nanofibers (CuFe2O4/Chit-CNFs) fabricated on a disposable electrode revealed exceptional electrocatalytic activity with a low detection limit (2 nM) and good sensitivity (79.18 μAμM-1 cm-2) over a broad linear range (0.05-152.55 μM). Cyclic voltammetry and differential pulse voltammetry were employed, and the sensing mechanism of tryptophan entails its electrocatalytic oxidation, where the synergistic impact of CuFe2O4 and Chit-CNFs boosts electrochemical response owing to their high surface area and conductivity. GSNN-based intelligent sensing returned a root mean square error (RMSE) of 2.76 and a mean absolute error (MAE) of 1.12. Moreover, the sensor's performance was tested on samples from apple juice, tomato juice, pineapple juice, and milk for assessing practicality, demonstrating recovery between 96.93 and 101.06 % and maximum relative standard deviation of 2.63 %. The proposed sensor showcased excellent selectivity, repeatability, reproducibility, and stability.

Rapid Tryptophan Assay as a Screening Procedure for Quality Protein Maize

Tryptophan is an essential amino acid deficient in cereals, especially maize. However, maize (Zea mays L.) is the main source of protein in some developing countries in Africa and Latin America. In general, the nutritional profile of cereals is poor, because they are deficient in essential amino acids such as tryptophan and lysine due to a relatively higher proportion of alcohol-soluble proteins. Quality protein maize (QPM) has been developed through genetic manipulation for the nutritional enrichment of maize to address these problems. Nevertheless, methods for protein, lysine and tryptophan are time-consuming and require relatively large amounts of samples. Therefore, we have advanced here a simple, cheap, fast, reliable and robust procedure for the determination of protein and tryptophan in the same biuret supernatant, which can also be used for chemical characterization of other cereals. Samples of 50 mg maize ground to pass through a 0.1 mm screen were sonicated for 5 min. in eppendorf vials with 1.5 mL of a biuret reagent each. After centrifugation and protein determination by biuret, 0.2 mL of supernatant was treated with 0.8 mL of a tryptophan reagent. Both total protein and tryptophan can be determined in microplates at 560 nm to speed up the measurements. The main advantage of the new micro-method is the rapid estimation of the nutrient quality of maize samples by a single weighing of a small amount of valuable plant materials.

Nanomaterial-based electrochemical sensors for detection of amino acids

Amino acids are the building blocks of proteins and muscle tissue. They also play a significant role in physiological processes related to energy, recovery, mood, muscle and brain function, fat burning and stimulating growth hormone or insulin secretion. Accurate determination of amino acids in biological fluids is necessary because any changes in their normal ranges in the body warn diseases like kidney disease, liver disease, type 2 diabetes and cancer. To date, many methods such as liquid chromatography, fluorescence mass spectrometry, etc. have been used for the determination of amino acids. Compared with the above techniques, electrochemical systems using modified electrodes offer a rapid, accurate, cheap, real-time analytical path through simple operations with high selectivity and sensitivity. Nanomaterials have found many interests to create smart electrochemical sensors in different application fields e.g. biomedical, environmental, and food analysis because of their exceptional properties. This review summarizes recent advances in the development of nanomaterial-based electrochemical sensors in 2017-2022 for the detection of amino acids in various matrices such as serum, urine, blood and pharmaceuticals.

Molecularly Imprinted Polymer-Amyloid Fibril-Based Electrochemical Biosensor for Ultrasensitive Detection of Tryptophan

A tryptophan (Trp) sensor was investigated based on electrochemical impedance spectroscopy (EIS) of a molecularly imprinted polymer on a lysozyme amyloid fibril (MIP-AF). The MIP-AF was composed of aniline as a monomer chemically polymerized in the presence of a Trp template molecule onto the AF surface. After extracting the template molecule, the MIP-AF had cavities with a high affinity for the Trp molecules. The obtained MIP-AF demonstrated rapid Trp adsorption and substantial binding capacity (50 µM mg⁻¹). Trp determination was studied using non-Faradaic EIS by drop drying the MIP-AF on the working electrode of a screen-printed electrode. The MIP-AF provided a large linear range (10 pM–80 µM), a low detection limit (8 pM), and high selectivity for Trp determination. Furthermore, the proposed method also indicates that the MIP-AF can be used to determine Trp in real samples such as milk and cancer cell media.

Electrochemical determination of L-tryptophan in food samples on graphite electrode prepared from waste batteries

One of the goals of this research was to develop an electrochemical sensor that had the ability to determine the target analyte and was both cheap and non-toxic. Another goal was to influence the reduction of electronic waste. In accordance with these, a graphite rod from zinc-carbon batteries was used to prepare an electrochemical sensor for the determination of L-tryptophan in Britton–Robinson buffer solution. Two electrochemical methods were used in the experimental research, differential pulse voltammetry and cyclic voltammetry. The effect of different parameters, including the pH value of supporting solution, scan rate, as well as the concentration of L-tryptophan on the current response, was studied. The pH value of Britton–Robinson buffer influenced the intensity of L-tryptophan oxidation peak, as well as the peak potential. The intensity of the current response was the highest at pH 4.0, while the peak potential value became lower as the pH increased, indicating that protons also participated in the redox reaction. Based on the obtained data, electrochemical oxidation of L-tryptophan at the graphite electrode was irreversible, two electron/two proton reaction. In addition, it was observed that the oxidation peak increased as the scan rate increased. According to the obtained electrochemical data, it was suggested that the oxidation of L-tryptophan was mixed controlled by adsorption and diffusion. The linear correlation between oxidation peak and L-tryptophan concentration was investigated in the range 5.0–150.0 µM and the obtained values of limit of detection and limit of quantification were 1.73 µM and 5.78 µM, respectively. Also, the prepared electrochemical sensor was successful in determination of target analyte in milk and apple juice samples.

Surface functionalization of natural hydroxyapatite by polymerization of β-cyclodextrin: application as electrode material for the electrochemical detection of Pb(II)

A composite material prepared by polymerization of β-cyclodextrin (β-CD) on the surface of natural hydroxyapatite using citric acid as cross linker, was employed as electrode material for the detection of Pb(II). Hydroxyapatite was obtained from bovine bones, following a three-step procedure including pre-calcination, chemical treatment with (NH₄)₂HPO_4, and calcination. The structure and morphology of the pristine hydroxyapatite (NHAP_P0.5) and its functionalized counterpart (NHAP_p0.5-CA-β-CD) were examined using XRD, FTIR, and SEM. Upon deposition as thin film on a glassy carbon electrode (GCE), the ion exchange ability of NHAP_p0.5-CA-β-CD was exploited to elaborate a sensitive sensor for the detection of lead. The electroanalytical procedure was based on the chemical accumulation of Pb(II) ions under open-circuit conditions, followed by the detection of the preconcentrated species using differential pulse anodic stripping voltammetry. The reproducibility of the proposed method, based on a series of 8 measurements in a solution containing 2 μM Pb(II) gave a coefficient of variation of 1.27%. Significant parameters that can affect the stripping response of Pb(II) were optimized, leading to a linear calibration curve for lead in the concentration range of 2 × 10^-8 mol L^-1 - 20 × 10^-8 mol L^-1 (R² = 0.998). The detection limit (3S/m) and the sensitivity of the proposed sensor were 5.06 × 10^-10 mol L^-1 and 100.80 μA.μM^-1, respectively. The interfering effect of several ions expected to affect the determination of lead was evaluated, and the proposed sensor was successfully applied in the determination of Pb(II) ions in spring water, well water, river water and tap water samples.

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.

Preparation and biological properties of silk fibroin/nano-hydroxyapatite/hyaluronic acid composite scaffold

In this study, the silk fibroin/nano-hydroxyapatite/hyaluronic acid (SF/nHAp/HA) composite scaffolds with different HA contents were developed by blending, cross-linking and freeze-drying, and their physicochemical properties and cell biocompatibilityin vitrowere subsequently studied. It was observed that the molecular conformation of the composite scaffolds was mainly composed of silk I and a small amount of theβ-sheets structure. On enhancing the HA content, the pore size of the scaffold decreased, while the porosity, water absorption, swelling ratio and mechanical properties were observed to increase. In particular, the SF/nHAp/HA scaffold with a 5.0 wt% ratio exhibited the highest water absorption and mechanical properties among the developed materials. In addition, thein vitrocytocompatibility analysis showed that the bone marrow mesenchymal stem cells exhibited excellent cell proliferation and osteogenic differentiation ability on the SF/nHAp/5.0 wt%HA scaffolds, as compared with the other scaffolds. It can be concluded that the developed composite scaffolds represent a promising class of materials for the bone tissue repair and regeneration.