Real-time electrochemical determination of phenolic compounds after benzene oxidation

Adsorptive transfer cyclic square-wave voltammetry and HPLC with tandem electrochemical detection - Two novel methods for determination of chili peppers pungency

The pungency of chili peppers, the most popular hot spice used worldwide, is caused by capsaicinoids (CPDs), the content of which can vary greatly due to varietal differences and growing conditions. For the first time, a novel simple method for the fast determination of CPDs in chili peppers and chili products was developed based on adsorptive transfer cyclic square-wave voltammetry (AdTCSWV), using adsorption of lipophilic CPDs on an unmodified glassy carbon electrode surface from methanolic extracts of chili pepper samples. The CSWV is based on short oxidation of adsorbed CPDs to quinoid products, and their subsequent reduction and re-oxidation to provide specific analytical signals with a linear range from 0.05 to 1.00 mg L-1. This principle was also implemented in tandem coulometric and amperometric detection of CPDs after HPLC separation. The two-step electrochemical detection provides increased selectivity for CPDs in case of CPDs co-elution with other electrochemically oxidizable components that cannot be reversibly reduced.

Colorimetric sensing strategy for detection of cysteine, phenol cysteine, and phenol based on synergistic doping of multiple heteroatoms into sponge-like Fe/NPC nanozymes

Nanozymes have both the high catalytic activity of natural enzymes and the stability and economy of mimetic enzymes. Research on nanozymes is rapidly emerging, and the continuous development of highly catalytic active nanozymes is of far-reaching significance. This work reports heteroatomic nitrogen (N) and phosphorus (P) double-doped mesoporous carbon structures and metallic Fe coordination generated sponge-like nanozymes (Fe/NPCs) with good peroxidase activity. On this basis, we constructed a highly sensitive colorimetric sensor with cysteine and phenol as simulated analytes using Fe/NPCs nanozymes, and the response limits reached 53.6 nM and 5.4 nM, respectively. Besides, the method has high accuracy in the detection of cysteine and phenol at low concentrations in serum and tap water, which lays a foundation for application in the fields of environmental protection and biosensors.

Azaporphyrins Embedded on Carbon-Based Nanomaterials for Potential Use in Electrochemical Sensing-A Review

Phthalocyanines and porphyrazines as macrocyclic aza-analogues of well-known porphyrins were deposited on diverse carbon-based nanomaterials and investigated as sensing devices. The extended π-conjugated electron system of these macrocycles influences their ability to create stable hybrid systems with graphene or carbon nanotubes commonly based on π-π stacking interactions. During a 15-year period, the electrodes modified by deposition of these systems have been applied for the determination of diverse analytes, such as food pollutants, heavy metals, catecholamines, thiols, glucose, peroxides, some active pharmaceutical ingredients, and poisonous gases. These procedures have also taken place, on occasion, in the presence of various polymers, ionic liquids, and other moieties. In the review, studies are presented that were performed for sensing purposes, involving azaporphyrins embedded on graphene, graphene oxide or carbon nanotubes (both single and multi-walled ones). Moreover, possible methods of electrode fabrication, limits of detection of each analyte, as well as examples of macrocyclic compounds applied as sensing materials, are critically discussed.

New insight into monitoring degradation products during the TiO2-photocatalysis process by multivariate molecular spectroscopy

This study focuses on the feasibility of a spectroscopic multivariate method for monitoring the concentration of phenol and its main degradation products during heterogeneous photocatalysis. Phenolic compounds were chosen as model to evaluate the degradation process due to their toxicity and persistence in the environment and also their well-known degradation pathway. The predictive capability of the multivariate method developed by partial least squares regression (PLSR) over the spectral range of 200-350 nm was satisfactory, allowing mean predicted errors below 5.0 % in the simultaneous determination of the target compounds using six latent variables and smoothing spectra. Suitable results were reported for the simultaneous determination of hydroquinone, resorcinol, pyrocatechol, and p-benzoquinone in accordance to the chromatographic method. Characteristics such as simplicity, low cost, and fast data acquisition are remarkable in this procedure, which makes it appropriate for this type of analytical control.

NiCu Alloy Nanoparticle-Loaded Carbon Nanofibers for Phenolic Biosensor Applications

NiCu alloy nanoparticle-loaded carbon nanofibers (NiCuCNFs) were fabricated by a combination of electrospinning and carbonization methods. A series of characterizations, including SEM, TEM and XRD, were employed to study the NiCuCNFs. The as-prepared NiCuCNFs were then mixed with laccase (Lac) and Nafion to form a novel biosensor. NiCuCNFs successfully achieved the direct electron transfer of Lac. Cyclic voltammetry and linear sweep voltammetry were used to study the electrochemical properties of the biosensor. The finally prepared biosensor showed favorable electrocatalytic effects toward hydroquinone. The detection limit was 90 nM (S/N = 3), the sensitivity was 1.5 µA µM⁻¹, the detection linear range was 4 × 10⁻⁷–2.37 × 10⁻⁶ M. In addition, this biosensor exhibited satisfactory repeatability, reproducibility, anti-interference properties and stability. Besides, the sensor achieved the detection of hydroquinone in lake water.

Preparation of a graphene-loaded carbon nanofiber composite with enhanced graphitization and conductivity for biosensing applications

G/CNF was prepared for the first time by a facile method and it was successfully applied in laccase based biosensor.