Betamethasone-based chiral electrochemical sensor coupled to chemometric methods for determination of mandelic acid enantiomers

Overoxidation of Intrinsically Conducting Polymers

Intrinsically conducting polymers may undergo significant changes of molecular structure and material properties when exposed to highly oxidizing conditions or very positive electrode potentials, commonly called overoxidation. The type and extent of the changes depend on the experimental conditions and chemical environment. They may proceed already at much lower rates at lower electrode potentials because some of the processes associated with overoxidation are closely related to more or less reversible redox processes employed in electrochemical energy conversion and electrochromism. These changes may be welcome for some applications of these polymers in sensors, extraction, and surface functionalization, but in many cases, the change of properties affects the performance of the material negatively, contributing to material and device degradation. This report presents published examples, experimental observations, and their interpretations in terms of both structural and of material property changes. Options to limit and suppress overoxidation are presented, and useful applications are described extensively.

A disposable dual-signal enantioselective electrochemical sensor based on stereogenic porous chiral carbon nanotubes hydrogel

As the highest form of molecular recognition, the chiral molecular recognition is the most difficult measurements. Herein, a disposable dual-signal enantioselective platform was fabricated based on stereoscopic porous chiral carbon nanotubes hydrogel modified screen printed electrode. This kind of chiral hydrogel was prepared by a simple heating method with l-cysteine and chiral single-walled carbon nanotubes of chirality (6,5), and its dispersion and morphology were characterized by several techniques including scanning electron microscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and electrochemical impedance spectroscopy. The stereogenic chiral interface was successfully employed to discriminate mandelic acid enantiomers via both oxidation peak intensity and peak potential value of cyclic voltammetry. The chiral recognition mechanism was discussed specifically, which resulted from the formation of an efficient three-dimensional chiral nanospace. The inherent chirality of chiral carbon nanotubes hydrogel, together with their orderly spatial arrangement, can significantly improve the efficiency of chiral recognition compared with traditional electrochemical chiral sensors. As a novel chiral sensing interface, such chiral carbon nanotubes hydrogel was simple to prepare, fast to operate, with good sensitivity and excellent stability for the construction of efficient and practical electrochemical chiral sensors.

Chiral Graphene Hybrid Materials: Structures, Properties, and Chiral Applications

Chirality has become an important research subject. The research areas associated with chirality are under substantial development. Meanwhile, graphene is a rapidly growing star material and has hard-wired into diverse disciplines. Rational combination of graphene and chirality undoubtedly creates unprecedented functional materials and may also lead to great findings. This hypothesis has been clearly justified by the sizable number of studies. Unfortunately, there has not been any previous review paper summarizing the scattered studies and advancements on this topic so far. This overview paper attempts to review the progress made in chiral materials developed from graphene and their derivatives, with the hope of providing a systemic knowledge about the construction of chiral graphenes and chiral applications thereof. Recently emerging directions, existing challenges, and future perspectives are also presented. It is hoped this paper will arouse more interest and promote further faster progress in these significant research areas.

A simple voltammetric electronic tongue for the analysis of coffee adulterations

This work presents a simple and low-cost analytical approach to detect adulterations in ground roasted coffee by using voltammetry and chemometrics. The voltammogram of a coffee extract (prepared as simulating a home-made coffee cup) obtained with a single working electrode is submitted to pattern recognition analysis preceded by variable selection to detect the addition of coffee husks and sticks (adulterated/unadulterated), or evaluate the shelf-life condition (expired/unexpired). Two pattern recognition methods were tested: linear discriminant analysis (LDA) with variable selection by successive projections algorithm (SPA), or genetic algorithm (GA); and partial least squares discriminant analysis (PLS-DA). Both LDA models presented satisfactory results. The voltammograms were also evaluated for the quantitative determination of the percentage of impurities in ground roasted coffees. PLS and multivariate linear regression (MLR) preceded by variable selection with SPA or GA were evaluated. An excellent predictive power (RMSEP = 0.05%) was obtained with MLR aided by GA.