Assay of serum cholinesterase activity by an amperometric biosensor based on a co-crosslinked choline oxidase/overoxidized polypyrrole bilayer

Identification of a Novel Dual Inhibitor of Acetylcholinesterase and Butyrylcholinesterase: In Vitro and In Silico Studies

The enhancement of cholinergic functions via acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) inhibition is considered a valuable therapeutic strategy for the treatment of Alzheimer's disease. This study aimed to evaluate the in vitro effect of ZINC390718, previously filtered using computational approaches, on both cholinesterases and to characterize, using a molecular dynamics (MD) simulation, the possible binding mode of this compound inside the cholinesterase enzymes. The in vitro cytotoxicity effect was also investigated using a primary astrocyte-enriched glial cell culture. ZINC390718 presented in vitro dual inhibitory activity against AChE at a high micromolar range (IC₅₀ = 543.8 µM) and against BuChE (IC₅₀ = 241.1 µM) in a concentration-dependent manner, with greater activity against BuChE. The MD simulation revealed that ZINC390718 performed important hydrophobic and H-bond interactions with the catalytic residue sites on both targets. The residues that promoted the hydrophobic interactions and H-bonding in the AChE target were Leu67, Trp86, Phe123, Tyr124, Ser293, Phe295, and Tyr341, and on the BuChE target, they were Asp70, Tyr332, Tyr128, Ile442, Trp82, and Glu197. The cytotoxic effect of Z390718, evaluated via cell viability, showed that the molecule has low in vitro toxicity. The in vitro and in silico results indicate that ZINC390718 can be used as chemotype for the optimization and identification of new dual cholinesterase inhibitors.

Substrate-free fluorescence ratiometric detection of serum acetylcholinesterase activity with a self-assembled CsPbBr3 perovskite nanocrystals/tetraphenylporphyrin tetrasulfonic acid nanocomposite

A dual-emission fluorescent nanoprobe was successfully constructed through self-assembling CsPbBr₃ perovskite nanocrystals (CsPbBr₃ PNCs) and tetraphenylporphyrin tetrasulfonic acid (TPPS). Acetylcholinesterase (AChE) is observed to directly quench the green fluorescence of CsPbBr₃ PNCs at 520 nm in the absence of an enzyme substrate, but has no significant influence on the red emission of TPPS at 650 nm. The decreased value of the fluorescence intensities ratio at 520 to 650 nm (ΔF₅₂₀/F₆₅₀) is proportional to the logarithmic value of AChE activity ranging from 0.05 to 1.0 U/L. The limit of detection is as low as 0.0042 U/L. The relative standard deviation is 3.6% in eleven consecutive measurements of 0.2 U/L AChE. The method exhibits a good anti-interference capacity since it does not respond to most concomitant species. Satisfactory results are acquired for the determination of AChE activity in human serum samples.

A novel imine-linked covalent organic framework for rapid detection of methyl paraoxon

Methyl paraoxon (MP) has attracted more and more attention in recent years because of its severe neurotoxicity and respiratory toxicity. Therefore, it is very urgent to develop new and sensitive MP detection methods for health protection and public safety. Covalent organic frameworks (COFs) are widely used in fluorescence detection because they can effectively transmit and amplify probe signals with multiple identical binding sites within an extended framework. Here, COF_ML-DHTA nanosheet material was synthesized by the solvothermal reaction of melem (ML) and 2,5-dihydroxyterephthalaldehyde (DHTA). The resulting COF_ML-DHTA exhibits remarkable luminescence quenching toward MP due to the relationship of competitive absorption and Förster resonance energy transfer between MP and COF_ML-DHTA. COF_ML-DHTA can be used for sensitive and selective detection of MP in a wide concentration range of 0.57 ng mL^-1 to 30 μg mL^-1 with a detection limit of 0.19 ng mL^-1. The material has good chemical stability, excellent selectivity, good reusability and hydrophilicity, which provide more possibilities for COFs in the detection of pesticides.

A Crosstalk- and Interferent-Free Dual Electrode Amperometric Biosensor for the Simultaneous Determination of Choline and Phosphocholine

Choline (Ch) and phosphocholine (PCh) levels in tissues are associated to tissue growth and so to carcinogenesis. Till now, only highly sophisticated and expensive techniques like those based on NMR spectroscopy or GC/LC- high resolution mass spectrometry permitted Ch and PCh analysis but very few of them were capable of a simultaneous determination of these analytes. Thus, a never reported before amperometric biosensor for PCh analysis based on choline oxidase and alkaline phosphatase co-immobilized onto a Pt electrode by co-crosslinking has been developed. Coupling the developed biosensor with a parallel sensor but specific to Ch, a crosstalk-free dual electrode biosensor was also developed, permitting the simultaneous determination of Ch and PCh in flow injection analysis. This novel sensing device performed remarkably in terms of sensitivity, linear range, and limit of detection so to exceed in most cases the more complex analytical instrumentations. Further, electrode modification by overoxidized polypyrrole permitted the development of a fouling- and interferent-free dual electrode biosensor which appeared promising for the simultaneous determination of Ch and PCh in a real sample.

Natural Polymeric Materials: A Solution to Plastic Pollution from the Agro-Food Sector

Conventional petroleum-derived plastics represent a serious problem for global pollution because, when discarded in the environment, are believed to remain for hundreds of years. In order to reduce dependence on fossil resources, bioplastic materials are being proposed as safer alternatives. Bioplastics are bio-based and/or biodegradable materials, typically derived from renewable sources. Food waste as feedstock represents one of the recent applications in the research field of bioplastics production. To date, several food wastes have been used as raw materials for the production of bioplastics, including mostly fruit and vegetable wastes. The conversion of fruit and vegetable wastes into biomaterials could occur through simple or more complex processes. In some cases, biopolymers extracted from raw biomass are directly manufactured; on the other hand, the extracted biopolymers could be reinforced or used as reinforcing agents and/or natural fillers in order to obtain biocomposites. The present review covers available results on the application of methods used in the last 10 years for the design of biomaterials obtained from formulations made up with both fruits and vegetables by-products. Particular attention will be addressed to the waste pre-treatment, to the bioplastic formulation and to its processing, as well as to the mechanical and physical properties of the obtained materials.

Assay of Phospholipase D Activity by an Amperometric Choline Oxidase Biosensor

A novel electrochemical method to assay phospholipase D (PLD) activity is proposed based on the employment of a choline biosensor realized by immobilizing choline oxidase through co-crosslinking on an overoxidized polypyrrole film previously deposited on a platinum electrode. To perform the assay, an aliquot of a PLD standard solution is typically added to borate buffer containing phosphatidylcholine at a certain concentration and the oxidation current of hydrogen peroxide is then measured at the rotating modified electrode by applying a detection potential of +0.7 V vs. SCE. Various experimental parameters influencing the assay were studied and optimized. The employment of 0.75% (v/v) Triton X-100, 0.2 mM calcium chloride, 5 mM phosphatidylcholine, and borate buffer at pH 8.0, ionic strength (I) 0.05 M allowed to achieve considerable current responses. In order to assure a controlled mass transport and, at the same time, high sensitivity, an electrode rotation rate of 200 rpm was selected. The proposed method showed a sensitivity of 24 (nA/s)⋅(IU/mL)⁻¹, a wide linear range up to 0.33 IU/mL, fast response time and appreciable long-term stability. The limit of detection, evaluated from the linear calibration curve, was 0.005 IU/mL (S/N = 3). Finally, due to the presence of overoxidized polypyrrole film characterized by notable rejection properties towards electroactive compounds, a practical application to real sample analysis can be envisaged.

Detection of choline in biological fluids from patients on haemodialysis by an amperometric biosensor based on a novel anti-interference bilayer

A new and highly selective amperometric biosensor able to analyse choline in clinical samples from patients suffering from renal diseases and receiving repetitive haemodialysis treatment is described. The proposed biosensor is based on choline oxidase immobilized by co-crosslinking onto a novel anti-fouling and anti-interferent membrane. Between the several polymeric films electrosynthesized on a Pt electrode whose permselective behaviours were here investigated, those based on overoxidized polypyrrole/poly(o-aminophenol) bilayer revealed the most effective in rejecting common interferents usually present in biological fluids. The so realized biosensor showed notably analytical performances, displaying linear choline responses up to 100 μM, a sensitivity of 156 nA mM^-1 mm^-2 and a limit of detection, calculated at a signal-to-noise ratio equal to 3, of 1 μM; further, the within-a-day coefficients of variation for replicate (n = 3) were 2.7% and 1.2% at 100 μM and 10 μM choline levels, respectively. The remarkable performances and anti-interference behaviour allowed us the use of the proposed biosensor for the selective and fouling-free detection of choline in dialysate coming from patients on haemodialysis and even in their unpretreated human sera. Preliminary results gave choline levels in good agreement with the expected values.