Search Results (40)

In order to improve the charge transfer properties and reduce the recombination of photogenerated carriers, an Fe₂O₃/C₃N₄ heterojunction was constructed to increase the built-in field. The grain boundary of the Fe₂O₃/C₃N₄ nanocomposite was filled with Cu, Au, Pt, and Pd nanoparticles using in situ synthesis. The nanometal-modified heterostructures showed good absorption in the visible and near-infrared (NIR) regions. The photocurrent responses to the light sources with wavelengths of 405, 532, 650, 780, 808, 980, and 1064 nm were investigated using Au electrodes. The results indicated that the nanocomposite exhibits photocurrent switching behaviour towards the visible-light and NIR regions. Interestingly, the reversible photocurrent response phenomenon (transition from negative to positive photoconductivity) was observed before and after passivation of the grain boundary defects of the Fe₂O₃/C₃N₄ heterojunction with metal nanoparticles. The physical mechanisms involved were discussed. The Cu nanomaterials played donor effects in the interfacial tailoring of the Fe₂O₃/C₃N₄ heterojunction since Cu nanoparticles possess a high concentration of free electrons. It was shown that defects in the nanocomposites play an important role in the photoelectric behaviour and that modulation of the defects not only enhances photocurrent acquisition but also determines the polarity of the photocurrent. This study provides useful guidance not only for microstructure modulation and interdisciplinary applications of the materials themselves but also for the study of light–matter interactions. Full article

The early monitoring and inactivation of bacteria are of crucial importance in preventing the further spread of foodborne pathogens. Staphylococcus aureus (S. aureus), a prototypical foodborne pathogen, is widely present in the natural environment and has the capability to trigger a range of diseases at low concentrations. In this work, we designed Fe₃O₄@SiO₂-Au core–shell–satellite nanocomposites (NCs) modified with aptamer for efficient capture, high-sensitivity surface-enhanced Raman scattering (SERS) detection, and photothermal therapy (PTT) against S. aureus. Fe₃O₄@SiO₂-Au NCs with tunable Au nanocrystal nanogaps were prepared. By combining the finite-difference time-domain (FDTD) method and experimental results, we studied the electric field distribution of Fe₃O₄@SiO₂-Au under different Au nanogaps and ultimately obtained the optimal SERS substrate FSA-60. The modification of aptamer on the surfaces of FSA-60 could be used for the specific capture and selective detection of S. aureus, achieving a detection limit of as low as 50 cfu/mL. Furthermore, Apt-FSA-60 possessed excellent photothermal properties, demonstrating the strong photothermal killing ability against S. aureus. Therefore, Apt-FSA-60 is a promising high-sensitivity SERS substrate and efficient photothermal agent and is expected to be widely applied and promoted in future disease prevention and treatment. Full article

Organic–inorganic nanocomposites have the potential to be used in photovoltaic materials due to their eco-friendliness, suitable band gaps, and high stability. In this work, we integrated gold and Fe₃O₄ magnetic nanoparticles with poly-m-amino benzene sulfonic (m-ABS) to synthesize Fe₃O₄@Au@poly-(m-aminobenzenesulfonic acid) (Fe₃O₄@Au@m-ABS) magneto-plasmonic nanoparticles (MPNPs) to enhance the performance of the organic photovoltaic (OPV). These MPNPs exhibit broad UV-Vis absorption and a low band gap of 2.878 eV, enhancing their suitability for photovoltaic applications. The MPNPs were introduced into the ZnO electron transporting layer (ETL) and active layer to investigate the influence of MPNPs on the power conversion efficiency (PCE) of the OPVs. When 0.1 vol% MPNPs were incorporated in the ETL, the OPVs achieved a PCE of 14.24% and a fill factor (FF) of 69.10%. On the other hand, when 0.1 vol% MPNPs were incorporated in the active layer, the OPVs showed a PCE of 14.11% and an FF of 68.83%. However, the OPVs without MPNPs only possessed a PCE of 13.15% and an FF of 63.69%. The incorporation of MPNPs increased the PCE by 8.3% in the OPV device. These findings suggest that Fe₃O₄@Au@m-ABS MPNPs are promising nanocomposite materials for enhancing the performance of OPVs. Full article

Developing photocatalytic nanomaterials with unique physical and chemical features using low-cost and eco-friendly synthetic methods is highly desirable in wastewater treatment. In this work, the magnetically separable α-Fe₂O₃-CeO₂ nanocomposite (NC), with its respective metal oxides of α-Fe₂O₃ and CeO₂ nanoparticles, was synthesized using a combination of hexadecyltrimethylammonium bromide (CATB) and ascorbic acid via the hydrothermal method. To tune the band gap, the heterojunction nanocomposite of α-Fe₂O₃-CeO₂ was decorated with plasmonic Au nanoparticles (Au NPs). The various characterization methods, such as FTIR, UV-vis DRS, XRD, XPS, TEM, EDX, SEM, and PL, were used to determine the properties of the materials, including their morphology, elemental composition, optical properties, band gap energy, and crystalline phase. The nanocomposite of α-Fe₂O₃-CeO₂@Au was utilized to remove Rose Bengal (RB) dye from wastewater using a photocatalytic technique when exposed to visible light. A comprehensive investigation of the impact of the catalyst concentration and initial dye concentration was conducted to establish the optimal photodegradation conditions. The maximum photocatalytic efficiency of α-Fe₂O₃-CeO₂@Au (50 mg L⁻¹) for RB (20 ppm) dye removal was found to be 88.9% in 120 min under visible-light irradiation at a neutral pH of 7 and 30 °C. Various scavengers, such as benzoquinone (BQ; 0.5 mM), tert-butyl alcohol (TBA; 0.5 mM), and ethylenediaminetetraacetic acid (EDTA; 0.5 mM), were used to investigate the effects of different free radicals on the photocatalytic process. Furthermore, the reusability of the α-Fe₂O₃-CeO₂@Au photocatalyst has also been explored. Furthermore, the investigation of the potential mechanism demonstrated that the heterojunction formed between α-Fe₂O₃ and CeO₂, in combination with the presence of deposited Au NPs, led to an enhanced photocatalytic efficiency by effectively separating the photogenerated electron (e⁻)–hole (h⁺) pairs. Full article

Gold nanoclusters (AuNCs) with fluorescence in the Near Infrared (NIR) by both one- and two-photon electronic excitation were incorporated in mesoporous silica nanoparticles (MSNs) using a novel one-pot synthesis procedure where the condensation polymerization of alkoxysilane monomers in the presence of the AuNCs and a surfactant produced hybrid MSNs of 49 nm diameter. This method was further developed to prepare 30 nm diameter nanocomposite particles with simultaneous NIR fluorescence and superparamagnetic properties, with a core composed of superparamagnetic manganese (II) ferrite nanoparticles (MnFe₂O₄) coated with a thin silica layer, and a shell of mesoporous silica decorated with AuNCs. The nanocomposite particles feature NIR-photoluminescence with 0.6% quantum yield and large Stokes shift (290 nm), and superparamagnetic response at 300 K, with a saturation magnetization of 13.4 emu g⁻¹. The conjugation of NIR photoluminescence and superparamagnetic properties in the biocompatible nanocomposite has high potential for application in multimodal bioimaging. Full article

An electrochemical sensor with high sensitivity for the detection of sodium nitrite was constructed based on the peroxidase-like activity of Au magnetic nanocomposites (Au@Fe₃O₄). The Au@Fe₃O₄ composite nanoparticles were green-synthesized via the reduction of gold nanoparticles (AuNPs) from waste chestnut skins combined with the sonochemical method. The nanoparticles have both the recoverability of Fe₃O₄ and the advantage of being able to amplify electrical signals. Furthermore, the synergistic effect of green reduction and sonochemical synthesis provides a functional approach for the preparation of Au@Fe₃O₄ with significant peroxidase-like activities. The physicochemical properties were characterized using transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), the Brunauer–Emmett–Teller (BET) method, and Fourier transform infrared spectroscopy (FT-IR). The electrochemical properties of sodium nitrite were determined with cyclic voltammetry (CV) and chronoamperometry (i-t). The results revealed that Au@Fe₃O₄ acted as a peroxidase mimic to decompose hydrogen peroxide to produce free radicals, while ·OH was the primary free radical that promoted the oxidation of sodium nitrite. With the optimal detection system, the constructed electrochemical sensor had a high sensitivity for sodium nitrite detection. In addition, the current response had a good linear relationship with the sodium nitrite concentration in the range of 0.01–100 mmol/L. The regression equation of the working curve was y = 1.0752x + 4.4728 (R² = 0.9949), and the LOD was 0.867 μmol/L (S/N = 3). Meanwhile, the constructed detection system was outstanding in terms of recovery and anti-interference and had a good detection stability of more than 96.59%. The sensor has been successfully applied to a variety of real samples. In view of this, the proposed novel electrochemical analysis method has great prospects for application in the fields of food quality and environmental testing. Full article

Capsaicinoids, mostly from chili peppers, are widely used in daily life. Capsaicinoids are considered to be markers for the identification of illegal cooking oil (ICO), which is a serious threat to public health. The identification of capsaicinoids can help reveal food-related fraud, thereby safeguarding consumers’ health. Here, a novel and ultrasensitive method was established with a signal amplification strategy for the detection of capsaicinoids. AuNPs@Fe₃O₄ nanocomposites were functionalized with 4-aminothiophenol (4-atp). After diazotization, 4-atp on AuNPs@Fe₃O₄ reacted with capsaicinoids and formed capsaicinoids-azo-atp-AuNPs@Fe₃O₄. Ultimately, capsaicinoids-azo-atp-AuNPs@Fe₃O₄ was dropped onto the surface of a screen-printed carbon electrode (SPCE) and detected via the differential pulse voltammetry (DPV) method. AuNPs@Fe₃O₄ nanocomposites increased the specific surface area of the electrode. Moreover, the diazotization–coupling reaction enriched the analytes on the electrode surface. Liquid–liquid extraction was used for sample pretreatment. Under a pH value of 9.0 and concentration of 0.20 mol/L for the supporting electrolyte, the linearity of capsaicinoids in ICO is from 0.10 to 10.00 ng/mL, and the limit of detection (S/N = 3) is 0.05 ng/mL. This method is ultra-sensitive, reliable, and cost-effective for the detection of capsaicinoids. Herein, this method provides a promising tool for the identification of ICO. Full article

Metal-organic frameworks (MOFs) are often used as carriers in the preparation of electrochemiluminescent (ECL) materials, and ECL materials stabilized in the aqueous phase can be prepared by encapsulating chromophores inside MOFs by an in situ growth method. In this study, nanocomposites MIL-88B(Fe)-NH₂@Ru(py)₃²⁺ with excellent ECL response were prepared by encapsulating Tris(2,2′-bipyridine)ruthenium dichloride (Ru(py)₃²⁺) inside MIL-88B(Fe)-NH₂ using the one-step hydrothermal method. MIL-88B(Fe)-NH₂ possesses abundant amino groups, which can accelerate the catalytic activation process of K₂S₂O₈, and its abundant pores are also conducive to the enhancement of the transmission rate of co-reactant agents, ions, and electrons, which effectively improves the ECL efficiency. In order to obtain more excellent ECL signals, we prepared aminated biochar (NH₂-biochar) using Pu-erh tea dregs as precursor and loaded gold nanoparticles (Au NPs) on its surface as substrate material for modified electrodes. Both NH₂-biochar and Au NPs can also be used as a co-reactant promoter to catalyze the activation process of co-reactant K₂S₂O₈. Therefore, a sandwich-type ECL immunosensor was prepared based on a dual signal-enhanced strategy for the highly sensitive and selective detection of aflatoxin B1 (AFB1). Under the optimal experimental conditions, the sensitive detection of AFB1 was achieved in the range of 1 pg·mL⁻¹~100 ng·mL⁻¹ with a detection limit of 209 fg·mL⁻¹. The proposed dual signal-enhanced ECL immunosensor can provide a simple, convenient, and efficient method for the sensitive detection of AFB1 in food and agricultural products. Full article

In this paper, a core-shell based on the Fe₃O₄@SiO₂@Au nanoparticle amplification technique for a surface plasmon resonance (SPR) sensor is proposed. Fe₃O₄@SiO₂@AuNPs were used not only to amplify SPR signals, but also to rapidly separate and enrich T-2 toxin via an external magnetic field. We detected T-2 toxin using the direct competition method in order to evaluate the amplification effect of Fe₃O₄@SiO₂@AuNPs. A T-2 toxin–protein conjugate (T2-OVA) immobilized on the surface of 3-mercaptopropionic acid-modified sensing film competed with T-2 toxin to combine with the T-2 toxin antibody–Fe₃O₄@SiO₂@AuNPs conjugates (mAb-Fe₃O₄@SiO₂@AuNPs) as signal amplification elements. With the decrease in T-2 toxin concentration, the SPR signal gradually increased. In other words, the SPR response was inversely proportional to T-2 toxin. The results showed that there was a good linear relationship in the range of 1 ng/mL~100 ng/mL, and the limit of detection was 0.57 ng/mL. This work also provides a new possibility to improve the sensitivity of SPR biosensors in the detection of small molecules and in disease diagnosis. Full article

In this paper, the luminescent complex Eu(3-thenoyltrifluoroacetonate)₃ was integrated with Fe₃O₄ and gold (Au) nanoparticles to form a multifunctional nanocomposite, Fe₃O₄/Au/Eu(TTA)₃ (FOASET NC), for dual magnetic-photothermal therapy and biomedical imaging. Upon functionalization with amine-NH₂, the FOASET NC exhibits a small size of 60–70 nm and strong, sharp emission at λ_max = 614 nm, enhanced by surface plasmon resonance (SPR) of Au nanoparticles that provided an effective label for HT29 colorectal cancer cells by fluorescence microscopy imaging. In addition, a hyperthermia temperature (42–46 °C) was completely achieved by using these FOASET NCs in an aqueous solution with three heating modes for (i) Magnetic therapy (MT), (ii) Photothermal therapy (PT), and (iii) Dual magnetic-photothermal therapy (MPT). The heating efficiency was improved in the dual magnetic-photothermal heating mode. Full article

A dual-mode lab-on-paper device based on BiVO₄/FeOOH nanocomposites as an efficient generating photoelectrochemical (PEC)/colorimetric signal reporter has been successfully constructed by integration of the lab-on-paper sensing platform and PEC/colorimetric detection technologies for sensitive detection of carcinoembryonic antigen (CEA). Concretely, the BiVO₄/FeOOH nanocomposites were in situ synthesized onto the paper-working electrode (PWE) through hydrothermal synthesis of the BiVO₄ layer on cellulose fibers (paper-based BiVO₄) which were initially modified by Au nanoparticles for improving the conductivity of three dimensional PWE, and then the photo-electrodeposition of FeOOH onto the paper-based BiVO₄ to construct the paper-based BiVO₄/FeOOH for the portable dual-mode lab-on-paper device. The obtained nanocomposites with an FeOOH needle-like structure deposited on the BiVO₄ layer exhibits enhanced PEC response activity due to its effective separation of the electron–hole pair which could further accelerate the PEC conversion efficiency during the sensing process. With the introduction of CEA targets onto the surface of nanocomposite-modified PWE assisted by the interaction with the CEA antibody from a specific recognition property, a signal-off PEC signal state with a remarkable photocurrent response decreasing trend can be achieved, realizing the quantitative detection of CEA with the PEC signal readout mode. By means of a smart origami paper folding, the colorimetric signal readout is achieved by catalyzing 3,3′,5,5′-tetramethylbenzidine (TMB) to generate blue oxidized TMB in the presence of H₂O₂ due to the satisfied enzyme-like catalytic activity of the needle-like structure, FeOOH, thereby achieving the dual-mode signal readout system for the proposed lab-on-paper device. Under the optimal conditions, the PEC and colorimetric signals measurement were effectively carried out, and the corresponding linear ranges were 0.001–200 ng·mL⁻¹ and 0.5–100 ng·mL⁻¹ separately, with the limit of detection of 0.0008 and 0.013 ng·mL⁻¹ for each dual-mode. The prepared lab-on-paper device also presented a successful application in serum samples for the detection of CEA, providing a potential pathway for the sensitive detection of target biomarkers in clinical application. Full article

Due to the abuse of antibiotics, the sensitivity of patients to antibiotics is gradually reduced. This work develops a Fe₃O₄@SiO₂@Au/PDA nanochain which shows an interesting magnetic-field-induced improvement of its photothermal antibacterial property. First, SiO₂ was wrapped on Fe₃O₄ nanospheres assembled in a chain to form a Fe₃O₄@SiO₂ nanocomposite with a chain-like nanostructure. Then, the magnetic Fe₃O₄@SiO₂@Au/PDA nanochains were prepared using in situ redox-oxidization polymerization. Under the irradiation of an 808 nm NIR laser, the temperature rise of the Fe₃O₄@SiO₂@Au/PDA nanochain dispersion was obvious, indicating that they possessed a good photothermal effect. Originating from the Fe₃O₄, the Fe₃O₄@SiO₂@Au/PDA nanochain showed a typical soft magnetic behavior. Both the NIR and magnetic field affected the antimicrobial performance of the Fe₃O₄@SiO₂@Au/PDA nanochains. Escherichia coli and Staphylococcus aureus were used as models to verify the antibacterial properties. The experimental results showed that the Fe₃O₄@SiO₂@Au/PDA nanochains exhibited good antibacterial properties under photothermal conditions. After applying a magnetic field, the bactericidal effect was further significantly enhanced. The above results show that the material has a broad application prospect in inhibiting the growth of bacteria. Full article

Nanocomposite thin film materials present great opportunities in coupling materials and functionalities in unique nanostructures including nanoparticles-in-matrix, vertically aligned nanocomposites (VANs), and nanolayers. Interestingly the nanocomposites processed through a non-equilibrium processing method, e.g., pulsed laser deposition (PLD), often possess unique metastable phases and microstructures that could not achieve using equilibrium techniques, and thus lead to novel physical properties. In this work, a unique three-phase system composed of BaTiO₃ (BTO), with two immiscible metals, Au and Fe, is demonstrated. By adjusting the deposition laser frequency from 2 Hz to 10 Hz, the phase and morphology of Au and Fe nanoparticles in BTO matrix vary from separated Au and Fe nanoparticles to well-mixed Au-Fe alloy pillars. This is attributed to the non-equilibrium process of PLD and the limited diffusion under high laser frequency (e.g., 10 Hz). The magnetic and optical properties are effectively tuned based on the morphology variation. This work demonstrates the stabilization of non-equilibrium alloy structures in the VAN form and allows for the exploration of new non-equilibrium materials systems and their properties that could not be easily achieved through traditional equilibrium methods. Full article

As a typical representative of endocrine-disrupting chemicals (EDCs), bisphenol A (BPA) is a common persistent organic pollutant in the environment that can induce various diseases even at low concentrations. Herein, the magnetic Fe₃O₄-Au@Ag@(Au@Ag) nanocomposites (CSSN NCs) have been prepared by self-assembly method and applied for ultra-sensitive surface-enhanced resonance Raman scattering (SERRS) detection of BPA. A simple and rapid coupling reaction of Pauly’s reagents and BPA not only solved the problem of poor affinity between BPA and noble metals, but also provided the SERRS activity of BPA azo products. The distribution of hot spots and the influence of incremental introduction of noble metals on the performance of SERRS were analyzed by a finite-difference time-domain (FDTD) algorithm. The abundance of hot spots generated by core–shell–satellite structure and outstanding SERRS performance of Au@Ag nanocrystals were responsible for excellent SERRS sensitivity of CSSN NCs in the results. The limit of detection (LOD) of CSSN NCs for BPA azo products was as low as 10⁻¹⁰ M. In addition, the saturation magnetization (Ms) value of CSSN NCs was 53.6 emu·g⁻¹, which could be rapidly enriched and collected under the condition of external magnetic field. These magnetic core–shell–satellite NCs provide inspiration idea for the tailored design of ultra-sensitive SERRS substrates, and thus exhibit limitless application prospects in terms of pollutant detection, environmental monitoring, and food safety. Full article

We report the successful synthesis and a complete magnetic characterization of CoFe₂O₄@SiO₂@Au magnetoplasmonic nanoparticles. The CoFe₂O₄ magnetic nanoparticles were prepared using the hydrothermal method. A subsequent SiO₂ shell followed by a plasmonic Au shell were deposited on the magnetic core creating magnetoplasmonic nanoparticles with a core–shell architecture. A spin-glass-type magnetism was shown at the surface of the CoFe₂O₄ nanograins. Depending on the external magnetic field, two types of spin-glass were identified and analyzed in correlation with the exchange field acting on octahedral and tetrahedral iron sites. The magnetization per formula unit of the CoFe₂O₄ core is not changed in the case of CoFe₂O₄@SiO₂@Au nanocomposites. The gold nanoparticles creating the plasmonic shell show a giant diamagnetic susceptibility, dependent on their crystallite sizes. Full article