Rhodium(III)‐Catalyzed [3+2]/[5+2] Annulation of 4‐Aryl 1,2,3‐Triazoles with Internal Alkynes through Dual C(sp2)?H Functionalization

A rhodium(III)‐catalyzed [3+2]/[5+2] annulation of 4‐aryl 1‐tosyl‐1,2,3‐triazoles with internal alkynes is presented. This transformation provides straightforward access to indeno[1,7‐cd]azepine architectures through a sequence involving the formation of a rhodium(III) azavinyl carbene, dual C(sp²) H functionalization, and [3+2]/[5+2] annulation.     

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.

     

Rapid and ultrasensitive colorimetric detection of mercury(II) by chemically initiated aggregation of gold nanoparticles

The article describes a method for rapid and visual determination of Hg(II) ion using unmodified gold nanoparticles (Au-NPs). It involves the addition of Au-NPs to a solution containing Hg(II) ions which, however, does not induce a color change. Next, a solution of lysine is added which induces the aggregation of the Au-NPs and causes the color of the solution to change from wine-red to purple. The whole on-site detection process can be executed in less than 15 min. Other amines (ethylenediamine, arginine, and melamine) were also investigated with respect to their capability to induce aggregation. Notably, only amines containing more than one amino group were found to be effective, but a 0.4 μM and pH 8 solution of lysine was found to give the best results. The detection limits for Hg (II) are 8.4 pM (for instrumental read-out) and 10 pM (for visual read-out). To the best of our knowledge, this LOD is better than those reported for any other existing rapid screening methods. The assay is not interfered by the presence of other common metal ions even if present in 1000-fold excess over Hg(II) concentration. It was successfully applied to the determination of Hg(II) in spiked tap water samples. We perceive that this method provides an excellent tool for rapid and ultrasensitive on-site determination of Hg(II) ions at low cost, with relative ease and minimal operation.

Rapid and ultrasensitive detection of mercury ions using gold nanoparticle based label-free colorimetric method with excellent sensitivity, easy operation and low cost.

     

Colorimetric method for determination of bisphenol A based on aptamer-mediated aggregation of positively charged gold nanoparticles

A sensitive, specific and rapid colorimetric aptasensor for the determination of the plasticizer bisphenol A (BPA) was developed. It is based on the use of gold nanoparticles (AuNPs) that are positively charged due to the modification with cysteamine which is cationic at near-neutral pH values. If aptamers are added to such AuNPs, aggregation occurs due to electrostatic interactions between the negatively-charged aptamers and the positively-charged AuNPs. This results in a color change of the AuNPs from red to blue. If a sample containing BPA is added to the anti-BPA aptamers, the anti-BPA aptamers undergo folding via an induced-fit binding mechanism. This is accompanied by a conformational change, which prevents the aptamer-induced aggregation and color change of AuNPs. The effect was exploited to design a colorimetric assay for BPA. Under optimum conditions, the absorbance ratio of A ₅₂₇/A ₆₈₀ is linearly proportional to the BPA concentration in the range from 35 to 140 ng∙mL⁻¹, with a detection limit of 0.11 ng∙mL⁻¹. The method has been successfully applied to the determination of BPA in spiked tap water and gave recoveries between 91 and 106 %. Data were in full accordance with results obtained from HPLC. This assay is selective, easily performed, and in our perception represents a promising alternative to existing methods for rapid quantification of BPA.

The negatively-charged anti-BPA aptamers can absorb onto the positively-charged cysteamine-capped AuNPs (cysteamine-AuNPs) via electrostatic interactions, which can cause the aggregation of AuNPs accompanied by a red-to-blue color change. In the presence of BPA, the specific binding of BPA to the aptamers induces the conformation changes of anti-BPA aptamers, which can release the aptamers from cysteamine-AuNPs and thus prevent the aggregation and color change of cysteamine-AuNPs.

     

Poly(o-phenylenediamine) nanosphere-conjugated capture antibody immobilized on a glassy carbon electrode for electrochemical immunoassay of carcinoembryonic antigen

We report on a new electrochemical immunosensor for the carcinoembryonic antigen (CEA; a model analyte). First, poly(o-phenylenediamine) nanospheres (PPDNSs) were synthesized by using a wet-chemistry method. The nanospheres were utilized as the support for immobilizing horseradish peroxidase-labeled polyclonal rabbit anti-human CEA antibody (HRP-anti-CEA) on a pretreated glassy carbon electrode (GCE) using glutaraldehyde as a crosslinker. In the presence of target CEA, an antigen-antibody immunocomplex formed on the electrode. This results in a partial inhibition of the active center of HRP and decreases the activity of HRP in terms of H₂O₂ reduction. The performance and factors influencing the performance of the immunoelectrode were studied. Under optimal conditions, the reduction current obtained from the anti-CEA-conjugated HRP (best at a working voltage of −265 mV vs. Ag/AgCl) is proportional to the CEA concentration in the 0.01 to 60 ng mL⁻¹ range, with a detection limit of 3.2 pg mL⁻¹. Non-specific adsorption was not observed. Relative standard deviations for intra-assay and inter-assay are <8.3 % and <9.7 %, respectively. The method was applied to the analysis of nine human serum samples, and a good relationship was found between the electrochemical immunoassay and the commercialized ELISA kit for human CEA.

A new electrochemical immunosensor based on poly(o-phenylenediamine) nanospheres was developed for the rapid detection of carcinoembryonic antigen via the inhibition of enzymatic activity.

     

Simultaneous determination of hydroquinone and catechol using a glassy carbon electrode modified with gold nanoparticles,ZnS/NiS@ZnS quantum dots and L-cysteine

We describe an electrochemical sensor for simultaneous determination of hydroquinone (HQ) and catechol (CC). A glassy carbon electrode (GCE) was modified with gold nanoparticles, L-cysteine, and ZnS/NiS@ZnS quantum dots using a layer-by-layer technique. The materials were characterized by X-ray diffractometry, field emission scanning electron microscopy, and electrochemical impedance and Fourier transform infrared spectroscopy. Cyclic voltammetry and differential pulse voltammetry revealed this modified GCE to represent a highly sensitive sensor for the simultaneous determination of HQ and CC. The anodic peak current for HQ at a working voltage of 80 mV (vs. Ag/AgCl) is related to its concentration in the 0.1 to 300 μM range (even in the presence of 0.1 mM of CC). The anodic peak current for CC at a working voltage of 184 mV is related to its concentration in the 0.5 to 400 μM range (even in the presence of 0.1 mM of HQ). The detection limits (at an S/N ratio of 3) are 24 and 71 nM for HQ and CC, respectively. The modified GCE was successfully applied to the determination of HQ and CC in aqueous solutions and gave satisfactory results.

A glassy carbon electrode was modified with gold nanoparticles, ZnS/NiS@ZnS quantum dots and L-cysteine and used for simultaneous determination of hydroquinone and catechol.