A sensitive colori/fluorimetric nanoprobe for detection of polyphenols using peroxidase-mimic plasma-modified MoO3 nanoparticles

Synthesis, characterization, and application of Cu-substituted LaNiO3 perovskites as photocatalysts and/or catalysts for persulfate activation towards pollutant removal

The presence of emerging contaminants in environmental aqueous matrices is an ever-growing problem, since conventional wastewater treatment methods fail to adequately remove them. Therefore, the application of non-conventional methodologies such as advanced oxidation processes is of great importance to tackle this modern problem. Photocatalysis as well as catalytic activation of persulfates are promising techniques in this field as they are capable of eliminating various emerging contaminants, and current research aims to develop new materials that can be utilized for both processes. In this light, the present study focused on the use of a simple sol-gel-combustion methodology to synthesize Cu-substituted LaNiO3 perovskite materials in an attempt to improve the photocatalytic and catalytic performance of pure LaNiO3, using molar ratios of Cu:Ni that have not been previously reported in the literature. The morphological, structural, and optical features of the synthesized materials were characterized by a series of analytical techniques (e.g., X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, diffuse reflectance spectroscopy, etc.). Also, their performance as photocatalysts, persulfate anion activators and simultaneously as photocatalysts/persulfate anion activators (hybrid) was evaluated by conducting laboratory-scale experiments using phenol (phenolics) as a model emerging contaminant. Interestingly, the results revealed that LaCu0.25Ni0.75O3 exhibited the best efficiency in all the applied processes, which was mainly attributed to the introduction of oxygen vacancies in the structure of the substituted material. The contribution of selected reactive species in the hybrid photocatalytic/catalytic experiments utilizing LaCu0.25Ni0.75O3 as a (photo)catalyst was investigated using appropriate scavengers, and the results suggested that singlet oxygen is the most dominant. Additionally, the stability of all synthesized perovskites was assessed by monitoring the concentration of the leached Cu and/or Ni cations at the end of every applied process. Finally, the reusability of LaCu0.25Ni0.75O3 was evaluated in three consecutive catalytic cycles using the hybrid experiment methodology, as this process demonstrated the best efficiency in terms of phenolics removal, and the results were rather promising.

Design and application of histidine-functionalized ZnCr-LDH nanozyme for promoting bacteria-infected wound healing

Excessive use of antibiotics can lead to an increase in antibiotic-resistant bacteria, which makes it a serious health threat. Therefore, developing new materials with antibacterial activity, such as nanozymes, has gained considerable attention. Reactive oxygen species (ROS) produced by nanozymes have rapid and effective antibacterial efficacy. Here, histidine (His) modified ZnCr layered double hydroxide (LDH) was synthesized inspired by the natural enzyme, and the enzyme-like activity of His/ZnCr-LDH was tested using a colorimetric method. Then, we developed an acid-enhanced antibacterial method based on the high peroxidase-like activity of His/ZnCr-LDH, and its ROS-generating capability in the presence of glucose oxidase (GOx) and glucose (Glu) as a source of hydrogen peroxide (H2O2). Gluconic acid (GA), the main product of the GOx reaction, provides an acidic environment and promotes ROS generation. The mentioned strategy shows high antibacterial activity at a low minimum inhibitory concentration (MIC) which represents the potential of His/ZnCr-LDH for effective bacterial elimination (3.5 μg mL-1 for S. aureus and 6 μg mL-1 for E. coli). In addition, animal experiments illustrated that the His/ZnCr-LDH can successfully boost the curing of infected wounds. The outcomes indicate that amino acid modified LDHs offer a new strategy for effective bacterial removal in different medical applications.

Proficient sonophotocatalytic degradation of organic pollutants using Co3O4/TiO2 nanocomposite immobilized on zeolite: Optimization, and artificial neural network modeling

The health of all living organisms is greatly influenced by the quality of the water. Therefore, developing cost-effective, eco-friendly, and easily accessible methods is desperately needed to meet the high global demand for clean water. Recently, nanozyme-based dye degradation methods have been promising for the remediation of water pollution. In this work, peroxidase-mimic Co3O4/TiO2 nanocomposite was synthesized and characterized for its size, morphology, and crystalline structure. Colorimetric assay results showed that the peroxidase-like activity of the Co3O4/TiO2 nanocomposite was considerably enhanced compared to the pure Co3O4 NPs and TiO2 NPs. Besides excellent enzyme-mimic activity, the higher sonophotocatalytic dye degradation capability of the nanocomposite after immobilization on zeolite (Co3O4/TiO2@Ze) was also demonstrated. Under optimal conditions (pH = 5.0, 25 °C), 0.1 g/L of catalyst was able to degrade 100 % of methylene blue (MB) with 600 μM in the presence of 30 μM H2O2 within 12 min. GC/MS analysis and toxicity studies revealed less toxic metabolite production after treatment of MB with sonophotocatalytic Co3O4/TiO2@Ze. Modeling of MB degradation using artificial neural networks (ANN) with a 5:6:1 topology was successfully performed, and the results confirmed the fitness of theoretical and experimental outputs according to the calculated correlation coefficient values. The prepared nanocomposite could thus be used as a promising and highly effective catalyst for the removal of organic dyes from polluted water.

A robust and facile label-free method for highly sensitive colorimetric detection of ascorbic acid in fresh fruits based on peroxidase-like activity of modified FeCo-LDH@WO3 nanocomposite

Many compounds such as amino acids and oligonucleotides have been shown to effectively change peroxidase-like activity of nanoparticles. While a few studies have focused on mimicking the active site of natural enzymes on nanozymes and thus increasing their substrate affinity. Therefore, in this work, the surface of FeCo@WO3 nanocomposite was modified using guanosine triphosphate (GTP) to mimic the histidine of peroxidase enzyme's active site and its modification was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Fourier-transform infrared spectroscopy (FT-IR). Then, the peroxidase-mimicking activity of the modified nanocomposite was tested using a colorimetric method, based on the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide (H2O2). It was found that GTP improves the activity of FeCo@WO3 as a natural peroxidase active site's distal histidine residue. Ascorbic acid (AA) is a powerful antioxidant that induces the reduction of blue color (oxidized TMB) ox-TMB to colorless TMB. The colorimetric method was applied for the sensitive detection of AA in common fruits. The linear range of AA was 10-100 μM with a limit of detection (LOD) of 0.27 μM, which provides a rapid and sensitive method for testing AA in the field of food analysis.

Construction of ratiometric fluorescence sensor and test strip with smartphone based on dual-emission carbon dots for the specific detection of chlortetracycline

Concerns about environmental and food contamination caused by chlortetracycline (CTC) residues have prompted people to explore efficient and convenient CTC monitoring platforms. However, the reported fluorescent probes generally fail to selectively detect CTC due to the structural similarity of tetracycline antibiotics. Herein, an intrinsic dual-emission carbon dots (D-CDs) ratiometric fluorescence sensor was prepared for highly sensitive and selective determination of CTC over other tetracyclines by one-step synthesis. The sensor exhibited a significant fluorescence enhancement at 425 nm after introducing CTC. The fluorescence "turn on" of the sensing system is due to aggregation-induced emission (AIE) phenomenon formed by hydrogen bonds and π conjugation promoting the specific recognition of CTC by D-CDs. The linear detection varied from 0.98 to 143.67 ng mL^-1 with a low limit of detection (LOD) of 1.29 ng mL^-1 (R² = 0.998), which was lower than most reported in the literature. The D-CDs sensor was applied to detect CTC in spiked milk, blocked normal human serum, and fish samples with recoveries of 95.5-104.2% and relative standard deviations (RSDs) of 2.6%. Particularly, D-CDs based test papers with a smartphone were prepared for portable and visual detection of CTC by analyzing the various color changes of RGB of fluorescence color, with an LOD of 7.18 ng mL^-1 (R² = 0.9909). The fluorescence sensor designed in this work could be used as a rapid tool with high performance and selectivity for monitoring control in foods.

CeO2/Co3O4@N-doped hollow carbon microspheres with improved peroxidase-like activity for the determination of quercetin

Nanozymes, as substitutes for natural enzymes, have been used to construct some fast cheap sensing platforms by virtue of the high catalytic activity. Herein, we firstly study the peroxidase-like activity of CeO₂/Co₃O₄@N-doped hollow carbon microspheres as nanozymes. In the presence of H₂O₂, CeO₂/Co₃O₄@NCH exhibits high peroxidase-like activity evaluated by the catalytic oxidation of the chromogenic substrate, 3,3',5,5'-tetramethylbenzidine (TMB) into a blue oxTMB visually in 1 min. The larger surface area, pore-like structure, and oxygen vacancies contribute to the enhanced peroxidase-like activity of CeO₂/Co₃O₄@NCH. The active species •O^2- is detected during the catalytic process. Thus, based on the excellent peroxidase-like activity of CeO₂/Co₃O₄@NCH, a facile and effective biosensor is fabricated for sensitive and selective determination of H₂O₂ and quercetin, respectively. CeO₂/Co₃O₄@NCH shows high affinity towards H₂O₂ (K_m = 4.001 mM) and TMB (K_m = 0.086 mM). The detection limit of H₂O₂ and quercetin is as low as 0.086 mM and 1.19 μM (3σ/slope), respectively. This work remarkably extends the utilization of CeO₂/Co₃O₄@NCH in designing a colorimetric sensing platform related to biosensing, food, and environmental monitoring. A fast colorimetric sensing platform for quercetin based on the excellent peroxidase-like activity of CeO₂/Co₃O₄@NCH.

Interaction of bovine serum albumin with ellagic acid and urolithins A and B: Insights from surface plasmon resonance, fluorescence, and molecular docking techniques

Human serum albumin (HSA) shows the sequence homology and structural similarity with bovine serum albumin (BSA). Therefore, here, the interaction of natural phenolic antioxidants, ellagic acid (ELA), and its derivatives-urolithins A (ULA) and B (ULB)-with BSA was investigated. The results of surface plasmon resonance (SPR) indicated a high affinity of ELA, ULA, and ULB to BSA, with KD value < 1 × 10-6 M. The KD values of binding of the studied compounds to BSA increased with temperature, revealing a reduction in affinity with an increase in temperature. Fluorescence data showed that the quenching of BSA by tested compounds occurred via a static quenching. However, the affinity of ELA for BSA was higher than that of ULA and ULB, which may be because of the presence of a large number of hydroxyl groups in its structure. The assessment of the antioxidant activity of BSA and BSA-ELA/ULA/ULB complexes using the DPPH assay indicated that the DPPH scavenging activity of BSA increased after complex formation with ELA/ULA/ULB in the following order: BSA-ELA > BSA-ULA > BSA-ULB > BSA, which was due to their structural differences. The results of the docking analysis were in agreement with the experimental results.