Ultraviolet-visible Absorption Spectroscopy Research Articles

Synthesis of Nitrogen-Doped Carbon Quantum Dots (N-CQDs) as a Fluorescent Probe for the Determination of Tartrazine

Herein, nitrogen-doped carbon quantum dots (N-CQDs) were synthesized by a solvothermal reaction for the determination of tartrazine in food. The microscopic structures and optical properties were examined by high resolution transmission electron microscopy, x-ray diffraction, x-ray photoelectron spectroscopy, Fourier-transform infrared and ultraviolet-visible absorption spectroscopy. The fluorescence emission of the N-CQDs were 450 nm upon the excitation of 350 nm with a quantum yield of 14%. The N-CQDs provide a good linear range from 0.8 to 100 μM and low detection limit of 0.078 μM. The constructed fluorescent probe was successfully adopted to determine tartrazine in food samples with good accuracy. The fluorescence quenching mechanism of tartrazine by the N-CQDs are likely due to the static quenching and inner filter effect. Overall, a wide linear range, sensitive and stable fluorescent probe is provided which indicates a new method for the determination of tartrazine.

Increasing Reduction Potentials of Type 1 Copper Center and Catalytic Efficiency of Small Laccase from Streptomyces coelicolor through Secondary Coordination Sphere Mutations.

The key to type 1 copper (T1Cu) function lies in the fine tuning of the CuII/I reduction potential (E°'T1Cu ) to match those of its redox partners, enabling efficient electron transfer in a wide range of biological systems. While the secondary coordination sphere (SCS) effects have been used to tune E°'T1Cu in azurin over a wide range, these principles are yet to be generalized to other T1Cu-containing proteins to tune catalytic properties. To this end, we have examined the effects of Y229F, V290N and S292F mutations around the T1Cu of small laccase (SLAC) from Streptomyces coelicolor to match the high E°'T1Cu of fungal laccases. Using ultraviolet-visible absorption and electron paramagnetic resonance spectroscopies, together with X-ray crystallography and redox titrations, we have probed the influence of SCS mutations on the T1Cu and corresponding E°'T1Cu . While minimal and small E°'T1Cu increases are observed in Y229F- and S292F-SLAC, the V290N mutant exhibits a major E°'T1Cu increase. Moreover, the influence of these mutations on E°'T1Cu is additive, culminating in a triple mutant Y229F/V290N/S292F-SLAC with the highest E°'T1Cu of 556 mV vs. SHE reported to date. Further activity assays indicate that all mutants retain oxygen reduction reaction activity, and display improved catalytic efficiencies (kcat /KM ) relative to WT-SLAC.

Potential Linkage between Heavy Metal Pollution Risk Assessment and Dissolved Organic Matter Spectra in the WWTPs-River Integrated Area-Case Study from Ashi River.

Direct sewage discharge can cause severe damage to the water environment of the river. However, the impacts of dissolved organic matter (DOM) in the discharge on the original pattern of DOM and the distribution of heavy metals (HMs) in the river are little known. How to monitor such areas in a long-term and systematic manner also needs to be urgently addressed. In this paper, we characterized the DOM of the sediments in the WWTPs (wastewater treatment plants)-river integrated zone by ultraviolet-visible absorption spectroscopy (UV-vis), three-dimensional excitation-emission matrix (3D-EEM) combined with parallel factor (PARAFAC) method. The effects of WWTP on receiving waters were investigated, and the potential link between DOM and HM pollution was explored. Hg (Igeo: 3.94 ± 0.65; EF: 44.83 ± 31.11), Cd (Igeo: 1.81 ± 0.69; EF: 8.02 ± 2.97), Cu (Igeo: 1.61 ± 0.83; EF: 6.85 ± 2.37), Zn (Igeo: 1.55 ± 0.54; EF: 7.24 ± 3.58), and Ni (Igeo: 1.46 ± 0.56; EF: 6.12 ± 1.99) in rivers were the primary risk sources of HM. The combined pollution risk indicates that the WWTPs-river integrated area is in a high pollution risk state. Moreover, α(254) has a significant correlation with pollution indicators and can be used as a proxy indicator. These results help to understand better the impact of WWTPs on receiving water bodies and the potential connection between DOM and HM pollution and provide new ideas for monitoring the water environment in highly polluted areas.

Fast microwave synthesis and white luminescent emission from Pb1–2xCaxSrxMoO4 (x=0; 0.3; and 0.5) particles

Scheelite with ABO4 structure has been increasingly highlighted in the optoelectronic field. In this study, PbMoO4, Pb0.4Ca0.3Sr0.3MoO4, and Ca0.5Sr0.5MoO4 particles were fast synthesized via microwave-assisted hydrothermal method for 1, 2, 4, and 8 min. The particles were characterized by X-ray diffraction (XRD) and Rietveld refinement, ultraviolet-visible (UV–vis) absorption spectroscopy, photoluminescence (PL), and field emission scanning electron microscopy (FE-SEM). The diffractogram showed a scheelite-type tetragonal structure and a unit cell with space group I41/a, as well as the presence of defects with an increase in the synthesis time in PbMoO4 and Pb0.4Ca0.3Sr0.3MoO4 samples. Rietveld refinement data possibilities the evaluation of distortions in the tetrahedral [MoO4] clusters and FE-SEM images showed octahedral, spherical particles, and flower-like morphology due to the additions of calcium and strontium in the structure. The bandgap of the materials varied between 3.32 and 4.18 eV, which was affected by the increase in the presence of dopants in the materials. The photoluminescence presented by the PL emission spectral showed a typical emission peak in green with the PL signal intensity decreasing with the synthesis time increase for the PCSMO samples, and the longer the synthesis time, the higher the PL signal for CSMO samples. CCT coordinates have been calculated for all samples and its value exhibited that, overall emission is near white light. This parameter infers that Pb0.4Ca0.3Sr0.3MoO4 sample, synthesized in 1 min, may have potential application in commercial LEDs, due to near white emission and fast microwave synthesis.

Insight into the effect of large yellow croaker roe phospholipids on the physical properties of surimi gel and their interaction mechanism with myofibrillar protein.

The present study aimed to investigate the effects of large yellow croaker roe phospholipids (LYCRPLs) on the physical properties of surimi gels and to clarify their interaction mechanism with myofibrillar proteins (MPs) in terms of chemical forces and the spatial conformation. LYCRPLs could improve the gel strength, textural properties, rheological properties and water-holding capacity of surimi gels. Moreover, the interaction mechanism between LYCRPLs with MPs was revealed through intermolecular forces, Fourier transform infrared spectroscopy and ultraviolet visible absorption spectroscopy. The findings demonstrated that LYCRPLs enhanced the surface hydrophobicity and particle size of MPs, facilitating expansion and cross-linking of MPs. These results provide a theoretical basis for improving the characteristics of surimi gels and thus facilitate the application of LYCRPLs in the aquatic food industry. © 2023 Society of Chemical Industry.

Interactions between gold nanoparticles with different morphologies and human serum albumin

Introduction: Three different shapes of gold nanoparticles were synthesized in this experiment. At the same time, studies compared their effects with human serum albumin (HSA).Methods: Gold nanoparticles (AuNPs) with three different morphologies, such as, nanospheres (AuNSs), nanorods (AuNRs), and nanoflowers (AuNFs) were synthesized via a seeding method and their characteristic absorption peaks were detected using ultraviolet-visible (UV-vis) absorption spectroscopy, Telectron microscopy (TEM), Dynamic Light Scattering (DLS) and Zeta potential measurements, circular dichroism (CD), and Fourier transform infrared spectroscopy (FTIR) to study the interactions between them and HSA. By comparing the thermodynamic parameters and quenching mechanism of the three materials, similarities and differences were determined in their interactions with HSA.Results: The results showed that with an increase in the concentration of the AuNPs with the three different morphologies, the UV-vis absorption peak intensity of the mixed solution increased, but its fluorescence intensity was quenched. This indicates that the three types of AuNPs interact with HSA, and that the interactions between them represent a static quenching process, which is consistent with the conclusions derived from three-dimensional fluorescence experiments. Through variable-temperature fluorescence experiments, the binding constants, number of binding sites, and thermodynamic parameters of the interactions between the three types of AuNPs and HSA were determined. The Gibbs free energy changes were <0, indicating that the reactions of the three types of AuNPs with HSA are spontaneous, resulting in associated matter. Binding constant measurements indicated that the strongest binding took place between the AuNFs and HSA. In addition, the results of fluorescence, CD spectroscopy, and FTIR showed that three different shapes of AuNPs can induce conformational changes in HSA and reduce the α-helix content. Among them, AuNFs have the smallest ability to induce conformational changes.Discussion: According to studies, AuNFs interact more favorably with HSA. This can be used as a reference for the administration of drugs containing AuNPs.

Direct and Indirect Effects of Land Use on Dissolved Organic Matter in a Typical Karst River

Land use can directly affect the abundance of riverine dissolved organic matter (DOM) by transporting terrestrial organic matter to rivers and can also indirectly enhance local production of DOM by increasing riverine nutrient loading. This study investigated the characteristics and spatial distribution of DOM components in the Furong River during the rainy season (July) using ultraviolet-visible light absorption spectroscopy (UV-VIS) and three-dimensional excitation emission matrix fluorescence spectroscopy-parallel factor analysis (EEM-PARAFAC) techniques. Furthermore, correlation analysis and the partial least squares path model (PLS-PM) were used to identify and quantify the direct and indirect impacts of land use on DOM at multiple scales. The results revealed that:① the direct effects of land use on DOM were generally stronger than the indirect effects. ② The responses of different DOM components to riverine nutrient status and land use varied, with dissolved organic carbon (DOC) and colored dissolved organic matter (CDOM) components being more susceptible to riverine nutrient status and fluorescent dissolved organic matter (FDOM) being more sensitive to land use. ③ The direct impact intensity of land use on DOC and CDOM fluctuated slightly with the spatial scale, but the total impact intensity had no visible spatial scale difference, and the direct impact intensity on the FDOM component decreased with the increase in spatial scale. ④ Dryland, urban and other construction land, patch density (PD), edge density (ED), and Shannon's diversity index (SHDI) were typical land use metrics that exacerbated DOM abundance, whereas paddy field, shrubland, largest patch index (LPI), and aggregation index (AI) were typical land use metrics that effectively mitigated DOM abundance. Total nitrogen (TN), nitrate nitrogen (NO3--N), and dissolved total phosphorus (DTP) were water quality parameters that were significantly affected by land use and were closely related to DOM components, that is, nitrogen and phosphorus played an important "intermediary" role in "land use-riverine DOM." FDOM could be used as indicators to measure the strength of terrestrial organic matter directly input to rivers by land use.

Enhanced photocatalytic degradation of rhodamine B using Fe/Ba-doped Bi4Ti3O12 nanostructures: Mechanism and performance evaluation

This research paper aims to synthesize nano-sheets of Bi4Fe0.08Ti2.92O12, Bi3.75Ba0.25Ti3O12, and Bi3.75Ba0.25Fe0.08Ti2.92O12 using the molten salt technique. The investigation focuses on examining the structural, morphological, optical properties, and photocatalytic activities of these materials. Specifically, we study the individual and collective impact of ion substitution at sites A and B (with Ba2+ at site A and Fe3+ at site B). Our analysis incorporates various characterization techniques such as X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM/EDX), photoluminescence (PL), and ultraviolet–visible absorption spectroscopy (UV-VIS). We select Rhodamine B (Rh–B) as a representative organic contaminant to evaluate the photocatalytic efficiency of the catalysts under sunlight. Additionally, we assess the influence of doping on photocatalytic activity. Remarkably, substituting iron and barium at sites B and A, respectively, results in maximum degradation rates of Rh–B, achieving 97.11 % and 96.75 % degradation, respectively. The synthesis procedure yields well-formed crystals of suitable size in all nano samples, leading to enhanced performance of the photocatalysts in degrading Rh–B. This study significantly contributes to the advancement of wastewater purification methodologies.

Hydrothermal synthesis of ZnO Crystals: Diverse morphologies and characterization of the photocatalytic properties

Zinc oxide (ZnO) microstructures including the ZnO nanorods (R-ZnO), ZnO nanopillars (C-ZnO), and multistage microspheres composed of ZnO nanosheets (M-ZnO) have been synthesized using a two-step hydrothermal approach by adjusting the concentrations of the growth solution. Scanning Electron Microscopy (SEM) was employed to observe the surface morphology of the fabricated samples. X-ray diffraction (XRD) was utilized for the structure characterization, which the results reveal a hexagonal wurtzite ZnO structure in all three samples with different microstructures. X-ray Photoelectron Spectroscopy (XPS) was used to investigate their defects, indicating that the oxygen vacancy ratios were 34.3 %, 21.8 %, and 51.5 % respectively for R-ZnO, C-ZnO, and M-ZnO. The band gaps of R-ZnO, C-ZnO, and M-ZnO, determined through Ultraviolet–Visible Absorption Spectroscopy (UV–Vis), were found to be 3.35 eV, 3.6 eV, and 3.19 eV, respectively. Finally, the photocatalytic performances of the prepared ZnO samples were investigated under simulated sunlight irradiation by observing the degradation of methyl orange, which the M-ZnO samples obtained a superior photocatalytic efficiency of 79 %.

Atomic Layer Deposition of Defective Amorphous TiOx Thin Films with Improved Photoelectrochemical Performance.

A proper control of defects in TiO2 thin films is challenging work for enhancing the photoelectrochemical (PEC) efficiency in water splitting processes. Additionally, a deep understanding of how defects affect the PEC performance of TiO2 thin films is of great interest for achieving better performance. With these aims, we prepared defective amorphous TiOx thin films at various growth temperatures by atomic layer deposition using tetrakis(dimethylamido)titanium as the Ti precursor. Careful X-ray photoelectron spectroscopy and electron spin resonance spectroscopy analyses revealed that the defect concentration in the TiOx thin films can be controlled by adjusting the growth temperature during the ALD process. We also evaluated the light absorption properties of the deposited TiOx thin films using ultraviolet-visible absorption spectroscopy. And it was found that the TiOx thin film deposited at a growth temperature of 200 °C exhibited the highest defect concentration and the highest photocurrent density of 0.051 mA/cm2 at 1.23 V vs reversible hydrogen electrode (RHE) compared to those of the other films. The light absorption efficiency, photogenerated charge separation efficiency, and charge transfer efficiency of defective amorphous TiOx thin films were carefully studied to understand the correlation between the defect concentration in the prepared TiOx thin film and its PEC activity. This study provides insight into the PEC properties of defective amorphous ALD-TiOx thin films.

Effect of ultraviolet exposure and thermal treatment on NaF micro-crystallization mechanism in photo-thermo-refractive glasses

Photo-thermo-refractive (PTR) glass is a promising recording medium for volume-holographic devices. The recording processes involve a series of steps including ultraviolet (UV) exposure, nucleation, and crystallization thermal treatment. Sodium fluoride (NaF) microcrystals precipitate after crystallization, and modulate the refractive index locally of the glass matrix. In this study, to simulate the volume Bragg grating recording processes and study the effect of photothermal-induced processes on the crystallization kinetics in PTR glass, Si-Al-Na-Zn-K PTR glasses with and without Br− ions were prepared using the melt-quenching method. The UV exposure duration, thermal treatment temperature and crystallization time were regulated during subsequent treatment. During these processes, Br-free samples were used for comparison to demonstrate the potential roles of Br−ion in the nucleation and crystallization. The Ag nanoparticle (NP) nuclei surrounded by AgBr (AgF) microcrystals were characterized using UV–visible absorption spectroscopy and transmission electron microscopy, and the changes in the precipitated NaF were characterized using X-ray diffraction, Raman spectroscopy as well as XPS. The mechanism of NaF micro-crystallization is disclosed based on above experimental results. It is found the formation of Ag nanoparticle surrounded by AgBr (AgF) microcrystals inhibits the crystallization kinetics of NaF microcrystals in PTR glass.

An effective and simple strategy for highly selective and anti-interference detection of dopamine based on the carbon quantum dots-molecularly imprinted polymers modified electrode

Dopamine (DA) dysfunction is known to cause neurological and physiological disorders, such as schizophrenia, Parkinson's disease, and addictive behavior. Therefore, dopamine detection is essential for both diagnosis and disease prevention. In this study, a novel and effective electrochemical sensor was fabricated based on a carbon quantum dots (CQDs)@molecularly imprinted polymers (MIPs) modified electrode for dopamine detection. The CQDs were obtained by an eco-friendly hydrothermal carbonization method, using sycamore leaves as a natural carbon source. The structure of the prepared CQDs@MIPs composite was confirmed through techniques including Ultraviolet–visible absorption spectroscopy, dynamic light scattering technique, scanning electron microscopy, and transmission electron microscopy. By combining the rapid electron transfer rate of the CQDs with the selective activity of the MIPs, the prepared CQDs@MIPs composite-modified electrode demonstrated greatly enhanced electrochemical performance. The developed sensor exhibited a good response towards dopamine detection, with a considerably lower detection limit (5 × 10−9M) and a wider linear range (5 × 10−9–5 × 10−4M) compared to current publications. In addition to the outstanding reproducibility and anti-interference ability, this ‘green sourced’ sensor showed great potential for practical applications, as validated by the satisfactory recovery analysis of dopamine from goat blood serum.

Studies on <i>in vitro</i> binding of parecoxib to p38MAPK using spectroscopic methods

Purpose: To investigate the interaction between parecoxib and p38MAPK under simulated physiological conditions.Methods: The interaction between parecoxib and p38MAPK was studied under simulated physiological conditions using spectroscopy-based methods. The effect of parecoxib on the microenvironment and conformation of p38MAPK chromophore was studied by synchronous fluorescence spectroscopy, three-dimensional fluorescence, time-resolved fluorescence spectroscopy, circular dichroism spectroscopy, and ultraviolet-visible absorption spectroscopy.Results: Synchronous fluorescence spectroscopy showed that addition of parecoxib changed the structure of p38MAPK and destroyed the original stable structure. Three-dimensional fluorescence spectroscopy showed that the hydrophilicity of the microenvironment in which the fluorescent chromophore is located was enhanced, and the polarity increased such that the serum protein macromolecules tend to be unfolded, and the alpha-helix content reduced. Time-resolved fluorescence spectroscopy showed that the presence of parecoxib hardly affected the fluorescence quenching of p38MAPK, and the combination of parecoxib and p38MAPK forms a stable complex (static quenching). Circular dichroism spectroscopy revealed the combined parecoxib change, the secondary structure of p38MAPK and reduced the alpha-helix content. Ultraviolet-visible absorption spectroscopy revealed changes in the microenvironment of the three amino acid residues as well as the tertiary structure of the protein.Conclusion: The results shows that parecoxib has a significant effect on the structure of p38MAPK. In addition to explicitly inhibiting COX-2 and blocking arachidonic acid synthesis of prostaglandins, it inhibits the pathway involved in p38MAPK.

Preparation of silver nanoparticles by Osbeckia stellata aqueous extract via green synthesis approach: Characterization and assessment of their antioxidant, antidiabetic, cytotoxicity, and antibacterial properties.

Silver nanoparticles (Ag NPs) via green synthesis using medicinal plants have been widely used in natural product research due to the economical and eco-friendly properties of NPs. The plant-derived Ag NPs biosynthesis comprises the interaction between silver nitrate (precursor) and bioactive components of plant extract (reducing agents). In this work, Ag NPs were biosynthesized using Osbeckia stellata leaves aqueous extract. Characterization of Ag NPs was done by using ultraviolet-visible absorption (UV-Vis) spectroscopy, dynamic light scattering (DLS), Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive X-ray analysis (EDX). Further, antioxidant, antidiabetic, cytotoxicity, and antimicrobial activities were evaluated to establish the pharmacological properties of Ag NPs. UV-Vis spectroscopy and FTIR showed an absorption peak of Ag NPs due to the surface plasmonic resonance. In contrast, the particle size in the nanometer range was analyzed by XRD and DLS. The size of the particle was confirmed by the SEM, TEM, and EDX in the nanometer range. This study showed the spherical shape and crystalline nature of NPs. Zeta potential was used to determine the stability of Ag NPs. Biosynthesized Ag NPs showed significantly potent antioxidant, antidiabetic, and cytotoxicity activity. Ag NPs also showed effectiveness against gram-positive (Escherichia coli) and gram-negative (Staphylococcus aureus) bacteria in the antimicrobial activity study. The result concluded that these Ag NPs might be used in biomedical and pharmacological fields.

Preparation and characterization of a silicone RAFT-modified aqueous acrylic resin coating for wood antifouling

Anionic emulsifiers, synthesized from novel silicone RAFT reagents (RAFT-PDMS), acrylic acid, lauryl methacrylate, and methyl methacrylate, were used to create a macromolecular silicone-modified polyacrylate aqueous emulsion. This emulsion was prepared by copolymerizing the custom-made anionic emulsifier with hydroxyethyl acrylate and other monomers. The emulsion underwent crosslinking with isocyanate, leading to a novel aqueous wood varnish incorporating polydimethylsiloxane chain segments. The structural features of RAFT-PDMS were characterized using 1HNMR, Fourier Transform Infrared Spectroscopy (FTIR), Ultraviolet-Visible Absorption Spectroscopy (UV–VIS), and Energy-Dispersive X-ray Spectroscopy (EDS). By adjusting the degree of polymerization and content of RAFT-PDMS, emulsions with a core-shell structure were generated. The impact of RAFT-PDMS on the molecular weight, particle size, and thermal properties of the latex was evaluated. Studies demonstrated that the applied wood coatings reduced surface roughness while enhancing gloss and hydrophobicity. Further tests revealed excellent antifouling properties and resistance to both acid and alkali for the coating. This type of wood paint could address challenges associated with the difficulty of combining large molecule organosilicones with wood, thereby offering a novel approach for wood paint applications.

Optical Properties of Heterostructured ZnO/NiO Nanocomposites Synthesized via Facile Precipitation Process

The semiconductor zinc oxide/nickel oxide (ZnO/NiO) heterostructured nanocomposites have been successfully synthesized via facile and eco-friendly homogeneous precipitation process with ethanol and water as solvents. The prepared nanocomposites were studied by means of structural and optical characteristics by using X-ray diffraction, ultraviolet visible absorption and photoluminescence emission spectro-scopies. The peaks in the XRD pattern attributed to the hexagonal wurtzite structure of ZnO and face-centered cubic structure of NiO, as a result the XRD analysis further confirmed that the solvents play a powerful role in size of the crystallite of the synthesized nanocomposites. Strong UV absorption may be seen in UV-vis absorbance spectra and samples of ZnO/NiO nanocomposite materials had greater energy gap (Eg) values than those of pure NiO and ZnO materials. The synthesized materials have demonstrated high photoluminescence emission in UV-blue region in the range of 241-498 nm, it might be a valuable source for future display applications. According to the aforementioned finding, the ZnO/NiO nanocomposites showed significant promise and were a viable material for optoelectronic devices.

Magneto-Plasmonic Nanoparticles Generated by Laser Ablation of Layered Fe/Au and Fe/Au/Fe Composite Films for SERS Application

Magneto-plasmonic nanoparticles were fabricated using a 1064 nm picosecond-pulsed laser for ablation of Fe/Au and Fe/Au/Fe composite thin films in acetone. Nanoparticles were characterized by electron microscopy, ultraviolet-visible (UV-VIS) absorption, and Raman spectroscopy. Hybrid nanoparticles were arranged on an aluminum substrate by a magnetic field for application in surface-enhanced Raman spectroscopy (SERS). Transmission electron microscopy and energy dispersive spectroscopy analysis revealed the spherical core-shell (Au-Fe) structure of nanoparticles. Raman spectroscopy of bare magneto-plasmonic nanoparticles confirmed the presence of magnetite (Fe3O4) without any impurities from maghemite or hematite. In addition, resonantly enhanced carbon-based bands were detected in Raman spectra. Plasmonic properties of hybrid nanoparticles were probed by SERS using the adsorbed biomolecule adenine. Based on analysis of experimental spectra and density functional theory modeling, the difference in SERS spectra of adsorbed adenine on laser-ablated Au and magneto-plasmonic nanoparticles was explained by the binding of adenine to the Fe3O4 structure at hybrid nanoparticles. The hybrid nanoparticles are free from organic stabilizers, and because of the biocompatibility of the magnetic shell and SERS activity of the plasmonic gold core, they can be widely applied in the construction of biosensors and biomedicine applications.

Dual-mode cholesterol sensor based on gold nanorods and carbon quantum dots

A novel dual-mode cholesterol biosensor was developed based on gold nanorods-carbon quantum dots-Cholesterol oxidase (AuNRs-CQDs-COD) complex synthesized by the cross-linking method. The specific reaction to/against cholesterol and cholesterol oxidase can produce hydrogen peroxide. Due to the etching effect between the hydrogen peroxide and AuNRs, the absorption peaks of AuNRs would drift so that the fluorescence quenching occurred because of the electronic charge transfer between the hydrogen peroxide and CQDs. The spectrum properties, structure and micromorphology of AuNRs-CQDs-COD complex were characterized by transmission electron microscope (TEM), Fourier transform infrared (FTIR), Fluorescence and Ultraviolet–Visible absorption spectroscopy, respectively. There was a good linear correlation between the fluorescence response and absorption peak shift of AuNRs-CQDs-COD probe in cholesterol solution within the concentration in the range 0.1–1 mM, and the limit of detection (LOD) is 0.028 μM. This dual-mode cholesterol biosensor based on AuNRs-CQDs-COD complex has good anti-interference and selectivity.

Investigation through the antimicrobial activity of electrospun PCL nanofiber mats with green synthesized Ag–Fe nanoparticles

Wound or device infections with drug resistant microorganisms are a major challenge in medicine that could increase morbidity and mortality rate, with a great financial burden on the health care system. Nanofibers with antimicrobial coating have been widely applied in wound dressing and tissue engineering to decrease the risk of infections. In the present study, Ag–Fe core-shell NPs were green synthesized by applying Ducrosia anethifolia plant extracted as a stabilizing and reducing agent. The novel nanocomposites by a combination of Ag–Fe and polymeric polycaprolactone (PCL) nanofibers were produced. Synthesized nanoparticles and nanocomposites were characterized using several physical and mechanical techniques, including scanning electron microscopy (SEM), dynamic light scattering method (DLS), X-ray diffraction (XRD), transmission electron microscopy (TEM), fourier transform infrared (FT-IR) spectroscopy, ultraviolet–visible absorption spectroscopy (UV–vis), and tensile test. The mean size of the synthesized Ag and Ag–Fe core-shell nanoparticles were 4.1 and 18.4 nm. Silver nanoparticles were successfully coated with Fe shell and nearly spherical core-shell shape. SEM images showed that PCL nanofibers have an average size of 265 nm. The results revealed that the increase in the Ag–Fe core-shell NPs' concentration leads to the smaller size of nanofibers. The antimicrobial properties of Ag–Fe core-shell and PCL/Ag–Fe nanocomposites were evaluated against some clinically important bacteria and fungi. Also, the cytotoxicity of PCL/Ag–Fe nanocomposites on fibroblast cells Natural man (NHDF) was assessed for 24, 48, and 72 h. The results of the study confirmed minimal cellular toxicity and considerable antimicrobial properties of green synthesized PCL/Ag–Fe nanocomposites, especially against some drug resistant pathogens, which could be promising new insight to improve the PCL-based composites applications in wound dressings or medical devices.

Purification, Identification, Chelation Mechanism, and Calcium Absorption Activity of a Novel Calcium-Binding Peptide from Peanut (Arachis hypogaea) Protein Hydrolysate.

A novel calcium-binding peptide was purified from peanut protein hydrolysate using gel filtration chromatography and identified using HPLC-MS/MS. Its amino acid sequence was determined as Phe-Pro-Pro-Asp-Val-Ala (FPPDVA, named as FA6) with the calcium-binding capacity of 15.67 ± 0.39 mg/g. Then, the calcium chelating characteristics of FPPDVA were investigated using ultraviolet-visible absorption spectroscopy, fluorescence spectroscopy, Fourier transform infrared spectroscopy, particle size, and zeta potential. The results showed that FPPDVA interacted with calcium ions, the chelation of calcium ions induced FPPDVA to fold and form a denser structure, the calcium-binding sites may mainly involve oxygen atoms from the carboxyl residues of Asp and Ala, and Phe possessed contact energy and carbonyl residues of Val. Microstructure analysis showed that FPPDVA-calcium chelate exhibited a regularly ordered and tightly aggregated sheets or block structures. Additionally, FPPDVA-calcium chelate had good gastrointestinal digestive stability and thermal stability. The results of everted rat intestinal sac and Caco-2 cell monolayer experiments showed that FPPDVA-calcium chelate could promote calcium absorption and transport through the Cav1.3 and TRPV6 calcium channels. These data suggest that FPPDVA-calcium chelate possesses the potential to be developed and applied as calcium supplement.