A nanocomposite prepared from copper(II) and nitrogen-doped graphene quantum dots with peroxidase mimicking properties for chemiluminescent determination of uric acid.

Nitrogen-doped graphene quantum dots (N-GQD) were employed along with Cu(II) ions under alkaline conditions and room temperature to synthesize nanocomposites of type Cu(II)/Cu2O/N-GQDs. These nanocomposites exhibit excellent stability and dispersity, and also display a peroxidase-like activity that is superior to pure Cu2O nanoparticles and natural peroxidase (POx). A chemiluminescence (CL) method was designed that is based on the use of uricase which oxidizes uric acid under formation of H2O2. The nanocomposites were used as a POx mimic in the luminol-H2O2 CL system. Under optimized conditions, a linear relationship between CL intensity and the uric acid (UA) concentration in the range of 0.16-4.0 µM, and a detection limit of 0.041 µM (at S/N = 3) were obtained. The CL method was applied to the determination of UA in spiked serum and urine, and recoveries ranged from 85.0 to 121.3%. Graphical abstract Schematic presentation of synthesis strategy of Cu(II)/Cu2O/N-GQDs and the CL method based Cu(II)/Cu2O/N-GQDs for H2O2-meidated uric acid detection. The method can be used for the determination of uric acid (UA) with the detection limit of 0.041 µM.

Removal of Lead(II) Ions from Aqueous Solution Using L. Seed Husk Ash as a Biosorbent.

The removal of heavy metals, especially from wastewater, has attracted significant interest because of their toxicity, tendency to bioaccumulate, and the threat they pose to human life and the environment. Many low-cost sorbents have been investigated for their biosorption capacity toward heavy metals. However, there are no reports available on the removal of Pb(II) from aqueous solution by of L. seed husk ash. In this work, use of seed husk ash for the removal of Pb(II) from wastewater was investigated as a function of contact time and the initial pH of the solution. Kinetics and equilibrium constants were obtained from batch experiments. Our study shows that the adsorption process follows pseudo-second-order kinetics. Moreover, the Langmuir absorption model gave a better fit to the experimental data than the Freundlich equation. The maximum adsorption capacity of the husk ash was 263.10 mg g at 298 K and pH 5.0, and this is higher than the previously reported data obtained using other sorbents. The results obtained confirm that seed husk ash is an effective sorbent for the removal of Pb(II) from aqueous solution. Analysis of infrared spectra of the husk ash after absorption of Pb(II) suggested that OH, C=O, C-O, Si-O-Si, and O-Si-O groups were important for the Pb(II) ion removal. Moreover, practical tests on this biosorbent for Pb(II) removal in real wastewater samples successfully demonstrated that seed husk ash constitutes an efficient and cost-effective technology for the elimination of heavy metals from industrial effluent.

Distribution and source apportionment of polycyclic aromatic hydrocarbons in the surface soil of Baise, China.

To estimate the distribution and sources of polycyclic aromatic hydrocarbons (PAHs) in the soils of Baise, in southwest China, soil sampling sites were selected from industry, traffic, rubbish, gas station, residential, and suburban areas for analysis of PAHs. The average concentrations of ∑16PAHs in the present study varied significantly, depending on the sampling location, and ranged from 16.8 to 6,437.0 µg/kg (dry weight basis), with a mean value of 565.8 µg/kg. PAH concentrations decreased significantly along the industry-traffic-rubbish-gas station-residential-suburban transect. The PAH profiles in the surface soil of the different areas imply that either source proximity to the sampling sites, or transport and deposition effects influenced PAH distributions. Two diagnostic ratios were selected and used to apportion PAH sources in the surface soil, and bivariate plots show general trends of covariation. Principal component analysis and multivariate linear regression were used to determine the primary sources and their contributions of PAHs to the soils. The model showed that factors 1 (coal and wood combustion) and 2 (petroleum combustion) contributed over 52.1 and 32.5% of the total source of soil PAHs, respectively. The remaining 15.4% came from evaporative and uncombusted petroleum.

Distribution and source apportionment of polycyclic aromatic hydrocarbons in soils and leaves from high-altitude mountains in southwestern china.

Several studies have investigated the distribution patterns and geographic sources of polycyclic aromatic hydrocarbons (PAHs) in mountainous areas. Little is known about how different sources contribute to PAH concentrations at different elevations along mountain slopes. To estimate the distribution and sources of PAHs at different altitudes in mountainous areas of southwestern China, samples of soils and leaves from trees were collected from 1000 to 1500 m asl in the Dawangling forest and analyzed for PAHs. Total PAH concentrations ranged from 93.9 to 802.3 ng g (average, 252.3 ng g) in soils and from 4.1 to 100.9 ng g (average, 23.1 ng g) in leaves. Our results suggest that soil PAH levels in the study area could be classified as "weakly contaminated." The PAH levels in leaves from the Dawangling forest were lower than those found in Himalayan spruce needles from the central Himalayas in China and from an agricultural station in southern England. Total PAHs in the Dawangling forest soils increased with elevation, primarily due to the low-molecular-weight PAHs, which accumulated in samples from higher altitudes. In contrast, high-molecular-weight PAHs were inversely related to or unrelated to elevation. The PAH profiles were similar in soils and leaves from all mountainous regions. Diagnostic ratios showed that the PAHs in soils at different altitudes were from different pollution emission sources; therefore, PAHs in the entire study area were probably derived from mixed sources. Cluster analyses confirmed that liquefied petroleum gas, coal/wood combustion, and petroleum combustion were likely the predominant PAH sources in this region.

Colorimetric detection of creatinine based on specifically modulating the peroxidase-mimicking activity of Cu-Fenton system.

Creatinine (CR) has always been considered as a prime important indicator for evaluating of renal dysfunction. Nevertheless, the literature still lacks in methods that fulfill the requirements for detecting CR effectively. Therefore, the development of a visual sensing method for the detection of CR specifically and sensitively is definitely desirable. To provide a solution, a colorimetric sensing platform for monitoring CR was constructed based on the regulation effect of CR on the peroxidase-mimicking activity of MoO3-Cu2+ system. Here, the prepared MoO3 itself does not have the catalytic activity of peroxidase mimics, but it can be used as a co-catalyst. In the presence of CR, the Cu2+ Fenton-like reaction can be promoted through co-catalysis of MoO3, so as to facilitate the production of more reactive oxygen species (ROS) and accelerate the oxidation process of 3,3',5,5'-tetramethylbenzidine (TMB). As a result, the regulation of MoO3-Cu2+ peroxidase-like activity can be achieved by adding different concentrations of CR. The higher the concentrations of CR, the stronger the catalytic activity for MoO3-Cu2+/CR. Experimental results showed that the colorimetric sensing strategy proposed in this paper can be successfully applied to the analysis of CR in human serum samples.

Enhancing the peroxidase-like activity of MIL-88B by ligand exchange with polydopamine.

Metal-organic frameworks (MOFs) as nanozymes have been widely used in biosensing. However, MOFs have inherent defects of easy agglomeration, leading to the stacking of active surfaces. In addition, the low conductivity of MOFs is not conducive to the electron migration in the Fenton-like reaction, which leads to a further decrease in catalytic activity and severely restricts their application. In response to the above problems, it makes sense to develop a method to improve both the dispersion and conductivity of MOFs. Here, a simple ligand exchange method with polydopamine (PDA) was used to synthesize MOF PDA-MIL-88B. PDA-MIL-88B shows stronger peroxidase-like activity than MIL-88B. One reason is the good dispersibility of PDA-MIL-88B, which is conducive to exposing the active surface. In addition, the reduced electrochemical impedance of PDA-MIL-88B increases its electrical conductivity, which is favorable for electron migration in the Fenton-like reaction. As a result, PDA-MIL-88B can better catalyze 3,3',5,5'-tetramethylbenzidine to achieve redoximorphic color changes. PDA-MIL-88B can be used to detect glucose in human serum with good sensitivity and selectivity. This work can provide a strategy for MOFs to enhance the enzyme-like activity.

Construction of visible light driven silver sulfide/graphitic carbon nitride p-n heterojunction for improving photocatalytic disinfection.

Compared with the Z-scheme and type-II heterojunctions, p-n type heterojunctions are more favorable for the migration of photo-induced carriers owing to the advantage of built-in electric fields. In addition, it is still of great significance to understand the carrier migration properties of the p-n heterojunction. Therefore, the development of new p-n heterojunctions and the development of high-efficiency catalysts with effective modulation of light responsiveness and rapid transfer of charge to achieve photocatalytic inactivation have attracted much attention. In this study, we synthesized a Ag2S/g-C3N4 heterojunction via the in situ deposition of Ag2S onto the g-C3N4 substrate. The prepared Ag2S/g-C3N4 composite facilitated photo-generated charge carrier transfer and exhibited outstanding photocatalytic inactivation of bacteria compared to that of a single catalyst under visible light irradiation. In addition, the ACN-2 composites fully deactivated 7 log10 CFU/mL E. coli and 7 log10 CFU/mL S. aureus cells in 90 min under visible light. The quenching experiments confirmed that photo-generated active species (O2-, OH, and h+) were the major reactive oxygen species that contributed to the inactivation of bacteria. Energy band alignment analysis indicated that a type-II band alignment was formed in the p-n heterostructure, thereby providing strong support for the photocatalytic mechanism. This study not only provides insights into the design of p-n heterostructures, but also presents a promising strategy to enhance the photocatalytic capacities of g-C3N4 based materials for pathogen inactivation.

Colorimetric Detection of Salicylic Acid in Aspirin Using MIL-53(Fe) Nanozyme.

The impurity of salicylic acid (SA) in aspirin is a required inspection item for drug quality control. Since free SA is significantly toxic for humans, the content determination of free SA is absolutely necessary to ensure people's health. In this work, a facile colorimetric method was developed for the detection of SA in aspirin by utilizing the MIL-53(Fe) nanozyme. As MIL-53(Fe) possesses enzyme mimicking catalytic activity, 3,3,5,5-tetramethylbenzidine (TMB) can be easily oxidized to blue-oxidized TMB (oxTMB) with the existence of H2O2. Moreover, an inhibition effect on the catalytic activity of the MIL-53(Fe) nanozyme is induced due to the specific complexation between SA and Fe3+ in the center of MIL-53(Fe), which results in a lighter color in the oxTMB. The color change of oxTMB can be seen easily by the naked eye with the addition of different concentrations of SA. Thus, a simple colorimetric platform was established for effectively monitoring SA. A good linear relationship (R 2 = 0.9990) was obtained in the concentration range of 0.4-28 µmol L-1, and the detection limit was 0.26 µmol L-1. In particular, the rationally designed system has been well-applied to the detection of SA impurity in aspirin. Satisfyingly, the detection results are highly in accord with those of HPLC. This novel colorimetric platform broadens the application prospects of nanozymes in the field of pharmaceutical analysis.

Cu-Doped Carbon Dots as Catalysts for the Chemiluminescence Detection of Glucose.

Development of metal-doped carbon dots (CDs) to effectively modulate their electronic properties and surface chemical reactivities is still in its early stage. In this paper, a facile solid-phase synthesis strategy was developed to synthesize Cu-doped CDs (Cu-CDs) using citric acid as the carbon source and Cu(NO3)2·3H2O as the dopant, respectively. The as-prepared Cu-CDs exhibited superior peroxidase-like activity to horseradish peroxidase and were stable under a wide range of pH and temperatures. Consequently, the Cu-CD-based chemiluminescence sensing was applied to sensitively detect glucose with a low detection limit of 0.32 µM, and the recoveries and the relative standard deviation of the serum sample are 87.2-112.2 and 8.16% (n = 6), respectively. Notably, the proposed chemiluminescence sensing was also successfully applied for label-free detection of glucose in complex biological samples, which envisioned its potential applications in clinical diagnosis and other analytical assays.