Real-time tracking of hydrogen peroxide secreted by live cells using MnO2 nanoparticles intercalated layered doubled hydroxide nanohybrids

We report a facile and green method for the fabrication of new type of electrocatalysts based on MnO₂ nanoparticles incorporated on MgAl LDH P-type semiconductive channel and explore its practical applications as high-performance electrode materials for electrochemical biosensor. A series of MgAl layered doubled hydroxide (LDH) nanohybrids with fixed Mg/Al (M²⁺/M³⁺ atomic ratio of 3) and varied amount of MnCl₂.4H₂O are fabricated by a facile co-precipitation method. This approach demonstrates the combination of distinct properties including excellent intercalation features of LDH for entrapping nanoparticles and high loading of MnO₂ nanoparticles in the host layers of LDH. Among all samples, Mn5–MgAl with 0.04% loaded manganese has a good crystalline morphology. A well-dispersed MnO₂ nanoparticles encapsulated into the host matrix of hydrotalcite exhibit enhanced electrocatalytic activity towards the reduction of H₂O₂ as well as excellent stability, selectivity and reproducibility due to synergistic effect of good catalytic ability of MnO₂ and conductive MgAl LDH. Glass carbon electrode (GCE) modified with Mn5–MgAl possesses a wide linear range of 0.05–78 mM, lowest detection limit 5 μM (S/N = 3) and detection sensitivity of 0.9352 μAmM⁻¹. This outstanding performance enables it to be used for real-time tracking of H₂O₂ secreted by live HeLa cells. This work may provide new insight in clinical diagnosis, on-site environmental analysis and point of care testing devices.     

A Convenient Synthesis of Pyridophenanthroline Derivatives under Catalyst Free Conditions

A three‐component reaction between an aromatic aldehyde, quinolin‐6‐amine or quinolin‐5‐amine, and tert‐butyl 2,4‐dioxopiperidine‐1‐carboxylate in reflux EtOH gave pyrido phenanthroline derivatives in high yields under catalyst free conditions. The rare C‐H…F hydrogen bond is found in the crystal structure of 6h .     

Nanobody-based electrochemical immunoassay for Bacillus thuringiensis Cry1Ab toxin by detecting the enzymatic formation of polyaniline

We describe an electrochemical immunoassay for the Cry1Ab toxin that is produced by Bacillus thuringiensis. It is making use of a nanobody (a heavy-chain only antibody) that was selected from an immune phage displayed library. A biotinylated primary nanobody and a HRP-conjugated secondary nanobody were applied in a sandwich immunoassay where horseradish peroxidase (HRP) is used to produce polyaniline (PANI) from aniline. PANI can be easily detected by differential pulse voltammetry at a working voltage as low as 40 mV (vs. Ag/AgCl) which makes the assay fairly selective. This immunoassay for Cry1Ab has an analytical range from 0.1 to 1000 ng∙mL^-1 and a 0.07 ng∙mL^-1 lower limit of detection. The average recoveries of the toxin from spiked samples are in the range from 102 to 114 %, with a relative standard deviation of <7.5 %. The results demonstrated that the assay represented an attractive alternative to existing immunoassays in enabling affordable, sensitive, robust and specific determination of this toxin.

Nanobodies specific to Cry1Ab toxin were isolated from an immunized camel. A biotinylated primary nanobody and a HRP-conjugated secondary nanobody were applied in a sandwich immunoassay with horseradish peroxidase being used to produce polyaniline, which can be easily detected by differential pulse voltammetry.

     

Glassy carbon electrode modified with gold nanoparticles and hemoglobin in a chitosan matrix for improved pH-switchable sensing of hydrogen peroxide

Hemoglobin (Hb) has been demonstrated to endow electrochemical sensors with pH-switchable response because of the presence of carboxyl and amino groups. Hb was deposited in a chitosan matrix on a glassy carbon electrode (GCE) that was previously coated with clustered gold nanoparticles (Au-NPs) by electrodeposition. The switching behavior is active (“on”) to the negatively charged probe [Fe(CN)₆ ³⁻] at pH 4.0, but inactive (“off”) to the probe at pH 8.0. This switch is fully reversible by simply changing the pH value of the solution and can be applied for pH-controlled reversible electrochemical reduction of H₂O₂ catalyzed by Hb. The modified electrode was tested for its response to the different electroactive probes. The response to these species strongly depends on pH which was cycled between 4 and 8. The effect is also attributed to the presence of pH dependent charges on the surface of the electrode which resulted in either electrostatic attraction or repulsion of the electroactive probes. The presence of Hb, in turn, enhances the pH-controllable response, and the electrodeposited Au-NPs improve the capability of switching. This study reveals the potential of protein based pH-switchable materials and also provides a simple and effective strategy for fabrication of switchable chemical sensors as exemplified in a pH-controllable electrode for hydrogen peroxide.

A pH “on-off” switchable nanobiosensor was fabricated by casting a chitosan-hemoglobin biocomposite onto nano-gold electrode. This composite film exhibits not only excellent pH-responsive on (pH 4.0)-off (pH 8.0) behavior but also excellent pH-tunable on-off bioelectrocatalysis of H₂O₂.

     

N‐Arylation of Heterocycles Promoted by Cyclen Derivatives

An efficient copper‐catalyzed N‐arylation reactions of imidazole, indole, and triazole with aryl or heteroaryl halides using cyclen derivatives as efficient organic base and ligand at moderate temperature have been investigated. The cross‐couplings proceed smoothly with good to excellent yields.