Innovative Graphene-Based Nanocomposites for Improvement of Electrochemical Sensors: Synthesis, Characterization, and Applications.

Graphene, renowned for its exceptional physicochemical attributes, has emerged as a favored substrate for integrating a wide array of inorganic and organic materials in scientific endeavors and innovations. Electrochemical graphene-based nanocomposite sensors have been developed by incorporating diverse nanoparticles into graphene, effectively immobilized onto electrodes through various techniques. These graphene-based nanocomposite sensors have effectively detected and quantified various electroactive species in samples. This review delves into using graphene nanocomposites to fabricate electrochemical sensors, leveraging the exceptional electrical, mechanical, and thermal properties inherent to graphene derivatives. These nanocomposites showcase electrocatalytic activity, substantial surface area, superior electrical conductivity, adsorption capabilities, and notable porosity, which are highly advantageous for sensing applications. A myriad of characterization techniques, including Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), BET surface area analysis, and X-ray diffraction (XRD), have proven effective in exploring the properties of graphene nanocomposites and validating the adjustable formation of these nanomaterials with graphene. The applicability of these sensors across various matrices, encompassing environmental, food, and biological domains, has been evaluated through electrochemical measurements, such as cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and differential pulse voltammetry (DPV). This review provides a comprehensive overview of synthesis methods, characterization techniques, and sensor applications pertinent to graphene-based nanocomposites. Furthermore, it deliberates on the challenges and future prospects within this burgeoning field.

Selection, alkaline phosphatase fusion, and application of single-chain variable fragment (scFv) specific to NT-proBNP as electrochemical immunosensor for heart failure.

Heart failure has a high global prevalence, with symptoms such as breathlessness, fatigue, and swelling. Early detection is crucial, as the condition worsens over time and can be fatal. This study identified the single-chain variable fragment (scFv) that specifically binds to the heart failure biomarker N-terminal pro B-type natriuretic peptide (NT-proBNP) using biopanning techniques for the development of an alternative diagnostic tool. Ten clones were identified that bound to the target peptide, with two clones (scFv-16 and scFv-36) selected for further analysis. Soluble scFv-16 and scFv-36 were produced and fused with alkaline phosphatase (AP) for potential applications. The binding efficiency and specificity levels of scFv to natriuretic peptides were evaluated using surface plasmon resonance (SPR) analysis. The values of the dissociation constant (KD) for NT-proBNP of scFv-16, scFv-36, scFv-16-AP, and scFv-36-AP were in the range 3.72 × 10-7-3.42 × 10-8 M with high specificity. All constructed scFvs had specificity to NT-proBNP, while not binding to A-type (ANP) and C-type (CNP) natriuretic peptides. When AP was combined, the scFv had a slightly higher yield of expression. The enzyme activity of scFv-36-AP was observed first by the absorption at 405 nm at a minimum of 44 nM and then by the naked eye at a minimum of 88 nM. Additionally, the potential application of NT-proBNP binding scFv was preliminarily investigated using an electrochemical technique to directly detect NT-proBNP in phosphate buffer saline. The results revealed the limit of detection at 69.09 pg/mL, which was less than the cutoff value (150 pg/mL) to discharge patients or healthy people. These findings provided promising biomolecules for the development of a reliable and sensitive diagnostic tool for heart failure.

Generation of a Single-Chain Variable Fragment Antibody against Feline Immunoglobulin G for Biosensor Applications.

For many decades, feline infectious disease has been among the most common health problems and a leading cause of death in cats. These diseases include toxoplasmosis, feline leukemia virus (FeLV), and particularly feline immunodeficiency virus (FIV) disease. Early diagnosis is essential to increase the chance of successful treatment. Generally, measurement of the IgG level is considered to be indicative of an individual's immune status for a particular pathogen. The antibodies specific to feline IgG are crucial components for the development of a detection kit. In this study, feline IgG-bound scFv was selected using phage display technology. Three rounds of biopanning were conducted against purified feline IgG. Through an indirect enzyme-linked immunosorbent assay (ELISA), two scFv clones demonstrating the best binding ability to feline IgG were chosen for biochemical characterization. In addition, the selected scFv (N14) was expressed and purified in a bacterial system. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed that the size of the purified N14 was 29 kDa. A sandwich ELISA was used to evaluate the binding capacity of the purified scFv to feline IgG. As expected, the purified N14 had the capacity to bind feline IgG. Furthermore, N14 was modified to create a scFv-alkaline phosphatase (scFv-AP) fusion platform. The surface plasmon resonance (SPR) results revealed that N14-AP bound to feline IgG with an affinity binding value of 0.3 ± 0.496 µM. Additionally, the direct ELISA demonstrated the binding capacity of N14-AP to feline IgG in both cell lysate and purified protein. Moreover, N14-AP could be applied to detect feline IgG based on electrosensing with a detection limit of 10.42 nM. Overall, this study successfully selected a feline IgG-bound scFv and developed a scFv-AP platform that could be further engineered and applied in a feline infectious disease detection kit.

Application of oxygen scavengers in gel electromembrane extraction: A green methodology for simultaneous determination of nitrate and nitrite in sausage samples.

The generation of oxygen from electrolysis in gel electromembrane extraction (G-EME) causes a negative error when applied to the analysis of easily oxidized species such as nitrite. Nitrite in G-EME is oxidized by oxygen to nitrate, leading to the negative error and the impossibility of simultaneous analysis. In this work, the application of oxygen scavengers to the acceptor phase of the G-EME system was attempted to minimize the oxidation effect. Several oxygen scavengers were selected and examined according to their compatibility with ion chromatography. The mixture of sulfite and bisulfite (14 mg L-1) showed the highest efficiency in preventing the oxidation of nitrite to nitrate. Under the optimized conditions, a good linear range was obtained (10-200 µg L-1; R2 > 0.998) with a detection limit of 8 µg L-1 for both nitrite and nitrate. This method was applied to the simultaneous determination of nitrite and nitrate in sausage samples.

Ratiometric Fluorescent Sensor for Copper(II) and Phosphate Ions from Aminopyrene Derivatives.

Three derivatives of 1-aminopyrene are functionalized with 2-picolyl and 2-picolinyl groups and are tested as fluorescent sensors for metal ions. The target compounds are successfully synthesized in yields of 50-90% and characterized by 1 H-NMR, 13 C-NMR, and HRMS. The compound with an amino picolyl group (P1) exhibits an excellent selectivity toward Cu(II) ion as the fluorescent signal shifts from 433 to 630 nm. From a fluorescence titration experiment, the limit of detection for Cu(II) ion is estimated as 0.19 µm. The fluorescence spectral shift by Cu(II) ion is reliant on the use of acetonitrile as a co-solvent, and the results from cyclic voltammetry and UV-Vis spectroscopy suggest that the sensing mechanism involves a coordination complex between the P1, acetonitrile and Cu(II) ion. Furthermore, this P1-Cu complex can also be used as a selective fluorescent sensor for PO4 3- ion with a detection limit of 0.44 µm.

Biosensors for the detection of organophosphate exposure by a new diethyl thiophosphate-specific aptamer.

OBJECTIVE: An aptamer specifically binding to diethyl thiophosphate (DETP) was constructed and incorporated in an optical sensor and electrochemical techniques to enable the specific measurement of DETP as a metabolite and a biomarker of organophosphate exposure. RESULTS: A DETP-bound aptamer was selected from the library using capillary electrophoresis-systematic evolution of ligands by exponential enrichment (CE-SELEX). A colorimetric method revealed that the aptamer had the highest affinity for DETP, with a mean Kd value (± SD) of 0.103 ± 0.014 µM. The docking results and changes in resistance showed that the selectivity of the aptamer for DETP was higher than that for the similar structures of dithiophosphate (DEDTP) and diethyl phosphate (DEP). The altered amplitude of cyclic voltammetry showed a linear range of DETP detection covering 0.0001-10 µg/ml with a limit of detection of 0.007 µg/ml. The recovery value of a real sample of pH 7 was 97.2%. CONCLUSIONS: The current method showed great promise in using the DETP-specific aptamer to detect the exposure history to organophosphates by measuring their metabolites, although degradation of organophosphate parent compounds might occur.

Gel electromembrane microextraction followed by ion chromatography for direct determination of iodine in supplements and fortified food samples: Green chemistry for food analysis.

In this study, a sensitive, selective, and environmentally friendly analytical method for direct extraction and preconcentration of iodine was developed. Iodine, as an iodate ion or iodide ion, was simultaneously extracted and preconcentrated by gel electromembrane microextraction (G-EME) and analyzed for total iodine by ion chromatography. The total iodine was determined by combining the peak areas of both iodate and iodide ions. Under the optimized conditions, linear calibration for iodine using a mixture of iodate and iodide ions was obtained from 10 to 100 µg L-1 (r2 > 0.996). The detection limit was 7.0 µg L-1. Recoveries of spiked iodine (as iodate) in the samples were greater than 90%. The method was applied for the determination of iodine in dietary supplements and fortified food samples, i.e., iodine-enriched eggs. Our developed method could be directly applied for the determination of iodine in different matrix samples including eggs without a pretreatment step.

Control of ferrous iron oxidation within circumneutral microbial iron mats by cellular activity and autocatalysis.

Ferrous iron (Fe2+) oxidation by microbial iron mat samples, dominated by helical stalks of Gallionella ferruginea or sheaths of Leptothrix ochracea, was examined. Pseudo-first-order rate constants for the microbial mat samples ranged from 0.029 +/- 0.004 to 0.249 +/- 0.042 min(-1) and correlated well with iron content (R2 = 0.929). Rate constants for Na azide-treated (1 mM) samples estimated autocatalytic oxidation by iron oxide stalks or sheaths, with values ranging from 0.016 +/- 0.008 to 0.062 +/- 0.006 min(-1). Fe2+ oxidation attributable to cellular activities was variable with respect to sampling location and sampling time, with rate constants from 0.013 +/- 0.005 to 0.187 +/- 0.037 min(-1). Rates of oxidation of the same order of magnitude for cellular processes and autocatalysis suggested that bacteria harnessing Fe2+ as an energy source compete with their own byproducts for growth, not chemical oxidation (under conditions where aqueous oxygen concentrations are less than saturating). The use of cyclic voltammetry within this study for the simultaneous measurement of Fe2+ and oxygen allowed the collection of statistically meaningful and reproducible data, two factors that have limited aerobic, circumneutral, Fe2+ -oxidation rate studies.