Amperometric choline biosensors based on multi-wall carbon nanotubes and layer-by-layer assembly of multilayer films composed of Poly(diallyldimethylammonium chloride) and choline oxidase

Enhanced Electrocatalytic Detection of Choline Based on CNTs and Metal Oxide Nanomaterials

Choline is an officially established essential nutrient and precursor of the neurotransmitter acetylcholine. It is employed as a cholinergic activity marker in the early diagnosis of brain disorders such as Alzheimer's and Parkinson's disease. Low levels of choline in diets and biological fluids, such as blood plasma, urine, cerebrospinal and amniotic fluid, could be an indication of neurological disorder, fatty liver disease, neural tube defects and hemorrhagic kidney necrosis. Meanwhile, it is known that choline metabolism involves oxidation, which frees its methyl groups for entrance into single-C metabolism occurring in three phases: choline oxidase, betaine synthesis and transfer of methyl groups to homocysteine. Electrocatalytic detection of choline is of physiological and pathological significance because choline is involved in the physiological processes in the mammalian central and peripheral nervous systems and thus requires a more reliable assay for its determination in biological, food and pharmaceutical samples. Despite the use of several methods for choline determination, the superior sensitivity, high selectivity and fast analysis response time of bioanalytical-based sensors invariably have a comparative advantage over conventional analytical techniques. This review focuses on the electrocatalytic activity of nanomaterials, specifically carbon nanotubes (CNTs), CNT nanocomposites and metal/metal oxide-modified electrodes, towards choline detection using electrochemical sensors (enzyme and non-enzyme based), and various electrochemical techniques. From the survey, the electrochemical performance of the choline sensors investigated, in terms of sensitivity, selectivity and stability, is ascribed to the presence of these nanomaterials.

Protein-based polyelectrolyte multilayers

The immobilization of proteins to impart specific functions to surfaces is topical for chemical engineering, healthcare and diagnosis. Layer-by-Layer (LbL) self-assembly is one of the most used method to immobilize macromolecules on surfaces. It consists in the alternate adsorption of oppositely charged species, resulting in the formation of a multilayer. This method in principle allows any charged object to be immobilized on any surface, from aqueous solutions. However, when it comes to proteins, the promises of versatility, simplicity and universality that the LbL approach holds are unmet due to the heterogeneity of protein properties. In this review, the literature is analyzed to make a generic approach emerge, with a view to facilitate the LbL assembly of proteins with polyelectrolytes (PEs). In particular, this review aims at guiding the choice of the PE and the building conditions that lead to the successful growth of protein-based multilayered self-assemblies.

Detection of toxic choline based on Mn2O3/NiO nanomaterials by an electrochemical method

In this study, a novel in situ choline sensor was assembled by attaching the binary Mn₂O₃/NiO nanoparticles (NPs) onto a glassy carbon electrode (GCE). Initially, Mn₂O₃/NiO NPs were synthesized via a wet-chemical process and fully characterized via XRD, XPS, FESEM, EDS, FTIR and UV-Vis methods. The analytical performances of the choline sensor were evaluated by an electrochemical method in the phosphate buffer phase. The estimated linear dynamic range (LDR) was found to be 0.1 nM to 0.1 mM. The other analytical performances of the choline sensor, such as sensitivity (16.4557 μA μM⁻¹ cm⁻²) and detection limit (5.77 ± 0.29 pM), were also calculated very carefully from the calibration plot. Overall, the choline sensor exhibited a reliable reproducibility, in situ validity, selectivity, interference effect, stability, and intra-day and inter-day performances with high accuracy in a short response time. Moreover, the probe was successfully applied to detect choline in real human, mouse and rabbit serum. This fabrication route would be a novel approach for the detection of selective biochemical sensor in the healthcare and biomedical fields.

In this study, a novel in situ choline sensor was assembled by attached the binary Mn₂O₃/NiO nanoparticles onto glassy carbon electrode, which might be a reliable way to develop of future sensor in the field of biomedical and healthcare fields.

Nanoparticle-based biocompatible and targeted drug delivery: characterization and in vitro studies

Paclitaxel nanoparticles (PAX NPs) prepared with the size of 110 ± 10 nm and ζ potential of -40 ± 3 mV were encapsulated in synthetic/biomacromolecule shell chitosan, dextran-sulfate using a layer-by-layer self-assembly technique. Zeta potential measurements, analysis of X-ray photoelectron spectroscopy, and scanning electron microscopy confirmed the successful adsorption of each layer. Surface modifications of these core-shell NPs were performed by covalently conjugating with poly(ethylene glycol) (H(2)N-PEG-carboxymethyl, M(w) 3400) and fluorescence labeled wheat germ agglutinin (F-WGA) to build a biocompatible and targeted drug delivery system. 32% of PAX was released from four bilayers of biomacromolecule assembled NPs within 8 h as compared with >85% of the drug released from the bare NPs. Moreover, high cell viability with PEG conjugation and high binding capacity of WGA-modified NPs with Caco-2 cells were observed. This biocompatible and targeted NP-based drug delivery system, therefore, may be considered as a potential candidate for the treatment of colonic cancer and other diseases.