Peroxidase activity of the coronene bisimide supramolecular architecture and its applications in colorimetric sensing of H2O2 and glucose

Ultrasensitive determination of α-glucosidase activity using CoOOH nanozymes and its application to inhibitor screening

In this work, a novel method for the colorimetric sensing of α-glucosidase (α-Glu) activity was developed based on CoOOH nanoflakes (NFs), which exhibit efficient oxidase-mimicking activity. Colorless 3,3',5,5'-tetramethylbenzidine (TMB) can be oxidized by CoOOH NFs into blue-colored oxidized TMB (oxTMB) in the absence of H₂O₂. L-Ascorbic acid-2-O-α-D-glucopyranose (AAG) can be hydrolysed by α-glucosidase to produce ascorbic acid, resulting in a significant decrease of catalytic activity of CoOOH NFs. Thus, a colorimetric α-glucosidase activity detection method was designed with a limit of detection of 0.0048 U mL^-1. Furthermore, the designed sensing platform exhibits favorable applicability for the α-glucosidase (α-Glu) activity assay in real samples. Meanwhile, this method can be expanded to study the inhibitors of α-Glu. Finally, the as-proposed method combined with a smartphone would be a color recognizer, which was successfully applied for the determination of α-Glu activity in human serum samples.

Diels-Alder Cycloaddition to the Bay Region of Perylene and Its Derivatives as an Attractive Strategy for PAH Core Expansion: Theoretical and Practical Aspects

PAHs (polycyclic aromatics hydrocarbons), the compound group that contains perylene and its derivatives, including functionalized ones, have attracted a great deal of interest in many fields of science and modern technology. This review presents all of the research devoted to modifications of PAHs that are realized via the Diels–Alder (DA) cycloaddition of various dienophiles to the bay regions of PAHs, leading to the π-extension of the starting molecule. This type of annulative π-extension (APEX) strategy has emerged as a powerful and efficient synthetic method for the construction of polycyclic aromatic hydrocarbons and their functionalized derivatives, nanographenes, and π-extended fused heteroarenes. Then, [4 + 2] cycloadditions of ethylenic dienophiles, -N=N-, i.e., diazo-dienophiles and acetylenic dienophiles, are presented. This subject is discussed from the organic synthesis point of view but supported by theoretical calculations. The possible applications of DA cycloaddition to PAH bay regions in various science and technology areas, and the prospects for the development of this synthetic method, are also discussed.

Sensitive colorimetric sensor for point-of-care detection of acetylcholinesterase using cobalt oxyhydroxide nanoflakes

Point-of-care monitoring of acetylcholinesterase (AChE) is of significant importance for pesticide poisoning and disease diagnosis because it plays a pivotal role in biological nerve conduction systems. Herein, we designed a colorimetric strategy for the facile and accurate detection of AChE based on tandem catalysis with a multi-enzyme system, which is constituted by cobalt oxyhydroxide nanoflakes (CoOOH NFs) and choline oxidase (CHO). In this sensor, AChE catalytically hydrolyzed acetylcholine (ACh) to produce choline, which was further efficiently oxidized by CHO to yield H₂O₂. CoOOH NFs, as a nanozyme, efficiently catalyzed 3,3',5,5'-tetramethylbenzidine (TMB) into blue oxTMB with the help of H₂O₂, accompanied by an enhancement of absorbance intensity. The resulting intensity could be employed as the signal output of the CHO/CoOOH/ACh system in monitoring AChE. Under optimal conditions, the developed sensor possessed a sensitive response to AChE with a detection limit of 33 μU mL^-1. Interestingly, the proposed platform was applied to fabricate a paper-based sensor for rapidly recognizing AChE by direct observation with the naked eyes. Combined with a smartphone and ImageJ software, we further developed an image-processing algorithm for the quantitative detection of AChE with highly promising results, which validated the outstanding potential of on-site application in clinical diagnostics and pesticide poisoning.

Mustard seeds derived fluorescent carbon quantum dots and their peroxidase-like activity for colorimetric detection of H2O2 and ascorbic acid in a real sample

Herein, we were synthesized fluorescent carbon quantum dots via facile one-step hydrothermal treatment of mustard seeds (M-CQDs). It showed excellent optical property with fluorescent quantum yield 4.6%. The as-prepared M-CQDs exhibited peroxidase-like mimetic activity and catalyzed the oxidation of chromogenic substrate 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H₂O₂ to produce a blue color reaction mixture with the prominent peak at 652 nm. Furthermore, the peroxidase-like catalytic performance of M-CQDs followed the steady-state kinetics behavior and exhibited similar catalytic activity as that of natural enzyme Horseradish peroxidase (HRP). In addition to this, the double reciprocal plot showed a parallel line which suggested the occurrence of Ping-Pong type of mechanism. The H₂O₂ dependent oxidation of TMB was helpful for the colorimetric detection of H₂O₂ in the linear range of 0.02-0.20 mM with the limit of detection (LOD) of 0.015 mM. Interestingly, the oxidized TMB (ox-TMB) was further reduced to native TMB by the reducing agent ascorbic acid. Hence M-CQDs showed its potential towards the selective and sensitive detection of ascorbic acid in the linear range of 10-70 μM having a correlation coefficient of 0.998 with LOD of 3.26 μM. The practical feasibility of the proposed detection method of AA was also investigated in common fresh fruits.

Peroxidase mimetic activity of fluorescent NS-carbon quantum dots and their application in colorimetric detection of H2O2 and glutathione in human blood serum

Interest is growing in the development of artificial enzymes to overcome the drawbacks of natural enzymes. Herein, we have synthesized nitrogen-sulphur dual-doped carbon quantum dots (NS-CQDs) via a one-step hydrothermal method; the NS-CQDs possess excellent optical properties and a high fluorescent quantum yield (46%). Significantly, the NS-CQDs exhibited peroxidase mimetic enzyme activity without support from metals or polymeric materials and efficiently catalyzed the oxidation of peroxidase substrate 3,3,5,5-tetramethylbenzidine (TMB) in the presence of H₂O₂ to produce a blue solution with an absorption maximum at 652 nm. Mechanistic studies suggest that the small size and high electron density of NS-CQDs play vital roles and accelerate the reduction of H₂O₂ to generate ˙OH radical, which facilitates the oxidation of TMB. The catalytic activity is based on Michaelis-Menten kinetic behavior, and steady state kinetic analysis suggests that the NS-CQDs exhibit a higher affinity for H₂O₂ than TMB, similar to the natural enzyme horseradish peroxidase (HRP). Moreover, the catalytic pathway follows a ping-pong mechanism. Therefore, these findings offer a worthy platform for colorimetric detection of H₂O₂ in a linear range of 0.02 mM to 0.1 mM with a limit of detection of 0.004 mM. Interestingly, the blue colour of oxidized TMB showed excellent selectivity over non-thiolate biological molecules, especially amino acids, and glutathione can be detected up to 0.07 μM via colorimetric and fluorimetric assays. Additionally, this system showed excellent recovery (96.0-108.3%) of GSH from human blood serum. Thus, the proposed sensing system is simple, convenient, and straightforward and can be potentially applied for real time monitoring of H₂O₂ and glutathione in biological samples.

A colorimetric biosensor based on enzyme-catalysis-induced production of inorganic nanoparticles for sensitive detection of glucose in white grape wine

Sensitive and selective colorimetric sensors have come into a high demand due to their simplicity, rapidity, precision and use of common laboratory instruments.