Magnetic Fluorescent Quantum Dots Nanocomposites in Food Contaminants Analysis: Current Challenges and Opportunities

The presence of food contaminants can cause foodborne illnesses, posing a severe threat to human health. Therefore, a rapid, sensitive, and convenient method for monitoring food contaminants is eagerly needed. The complex matrix interferences of food samples and poor performance of existing sensing probes bring significant challenges to improving detection performances. Nanocomposites with multifunctional features provide a solution to these problems. The combination of the superior characteristics of magnetic nanoparticles (MNPs) and quantum dots (QDs) to fabricate magnetic fluorescent quantum dots (MNPs@QDs) nanocomposites are regarded as an ideal multifunctional probe for food contaminants analysis. The high-efficiency pretreatment and rapid fluorescence detection are concurrently integrated into one sensing platform using MNPs@QDs nanocomposites. In this review, the contemporary synthetic strategies to fabricate MNPs@QDs, including hetero-crystalline growth, template embedding, layer-by-layer assembly, microemulsion technique, and one-pot method, are described in detail, and their advantages and limitations are discussed. The recent advances of MNPs@QDs nanocomposites in detecting metal ions, foodborne pathogens, toxins, pesticides, antibiotics, and illegal additives are comprehensively introduced from the perspectives of modes and detection performances. The review ends with current challenges and opportunities in practical applications and prospects in food contaminants analysis, aiming to promote the enthusiasm for multifunctional sensing platform research.

Synthesis and characterization of a flexible fluorescent magnetic Fe3O4@SiO2/CdTe-NH2 nanoprobe

In this study, we designed and synthesized two novel fluorescent magnetic nanoparticles. Fe₃O₄@SiO₂-NH-GSH-CdTe (FSGC) (GSH = glutathione) nanoparticles were synthesized using amino-functionalized Fe₃O₄@SiO₂ nanoparticles and GSH-stabilized CdTe quantum dots (CdTe QDs), while flexible Fe₃O₄@SiO₂-NH-GSH-CdTe-NH-NH₂ (FSGCN) nanoparticles were synthesized using the FSGC precursor and 1,6-hexamethylenediamine. These two kinds of nanoprobes exhibited excellent magnetic and fluorescent properties. By comparing the fluorescence quenching effect of folic acid (FA) on FSGC and FSGCN, we found that the quenching effect of FA on FSGC was acute and the process was too fast to determine the FA content. However, the quenching effect of FA on flexible FSGCN was mild and hence it could be used as a nanoprobe to determine FA concentration. At physiological pH, the fluorescence quenching effect of FA on the FSGCN nanoprobes was fitted according to the Stern-Volmer equation with a linear response in the concentration range of 0.14 to 4.20 μg mL^-1 with a detection limit of 15.1 × 10^-9 g mL^-1 (S/N = 3) under optimized experimental conditions. The proposed flexible nanoprobe was successfully used to determine the content of FA in folic acid tablets. Recovery was found to be in the range of 92.7%-105.6% with a relative standard deviation of 1.12%-3.84%. Owing to their good stability, environment-friendly characteristics, high selectivity, and good optical properties and biocompatibility, these nanoprobes have potential for usage in practical applications.

Design, synthesis and in vitro evaluation of anticancer and antibacterial potential of surface modified Tb(OH)3@SiO2core–shell nanoparticles

In the current study, we modified the surface of Tb(OH)₃nanoparticles with a silica layer to enhance their solubility and biocompatibility.

A type of novel fluorescent magnetic carbon quantum dots for cells imaging and detection

A new type of multifunctional fluorescent magnetic carbon quantum dots SPIO@CQDs(n) ([superparamagnetic iron oxide nanoparticles (SPIO), carbon quantum dots, (CQDs)]) with magnetic and fluorescence properties was designed and prepared through layer-by-layer self-assembly method. The as-synthesized SPIO@CQDs(n) exhibited different emission colors including blue, green, and red when they were excited at different excitation wavelengths, and its fluorescent intensity increased as the increase of CQD layer (n). SPIO@CQDs(n) with quite low toxicity could mark cytoplasm with fluorescence by means of nonimmune markers. The mixture sample of liver cells L02 and hepatoma carcinoma cells HepG2 was taken as an example, and HepG2 cells were successfully separated and detected effectively by SPIO@CQDs(n), with a separation rate of 90.31%. Importantly, the designed and prepared SPIO@CQDs( n ) are certified to be wonderful biological imaging and magnetic separation regents.

Recent progress on magnetic iron oxide nanoparticles: synthesis, surface functional strategies and biomedical applications

This review focuses on the recent development and various strategies in the preparation, microstructure, and magnetic properties of bare and surface functionalized iron oxide nanoparticles (IONPs); their corresponding biological application was also discussed. In order to implement the practical in vivo or in vitro applications, the IONPs must have combined properties of high magnetic saturation, stability, biocompatibility, and interactive functions at the surface. Moreover, the surface of IONPs could be modified by organic materials or inorganic materials, such as polymers, biomolecules, silica, metals, etc. The new functionalized strategies, problems and major challenges, along with the current directions for the synthesis, surface functionalization and bioapplication of IONPs, are considered. Finally, some future trends and the prospects in these research areas are also discussed.

Enhanced luminescence of CaMoO₄:Eu by core@shell formation and its hyperthermia study after hybrid formation with Fe₃O₄: cytotoxicity assessment on human liver cancer cells and mesenchymal stem cells

Highly water dispersible Eu³⁺ doped CaMoO₄ nanoparticles (core) covered by CaMoO₄ (shell) have been prepared using the polyol method. Significant enhancement in luminescence intensity by core@shell formation is observed due to the decrease of non-radiative rate arising from surface/defect of particles. Effect of 266 nm laser excitation (Mo-O charge transfer band) on the asymmetric ratio (A₂₁ = intensity ratio of electric to magnetic dipole transitions) has been studied and compared with a xenon lamp source. Luminescence intensity increases with the increase of power at 532 nm laser excitation. In order to explore materials, which can show dual functionalities such as luminescence as well as magnetic properties (magnetization of ∼14.2 emu g⁻¹), water dispersible Fe₃O₄-CaMoO₄:Eu hybrid magnetic nanoparticles (MN) have been prepared. This shows good heating ability up to ∼42 °C (hyperthermia) and luminescence in the red region (∼612 nm), which is in a biological window (optical imaging). Biocompatibility of the synthesized Fe₃O₄-CaMoO₄:Eu hybrid magnetic nanoparticles has been evaluated in vitro by assessing their cytotoxicity on human liver cancer cells (HepG2 cells) and hTERT cells using the MTT assay and fluorescent microscopy studies.

Multifunctional Nanostructures: Synthesis and Applications

Free identical nanoobjects include metals, semiconductors, magnetic materials, polymers, bio molecules, are integrated together to form as multifunctional nanomaterials (MFNs), in which more than one behaviour can be rendered simultaneously. This summary showcases their exciting properties which are providing the emerging properties in applications like visualizing and targeting in drug delivery, recoverable and reusable photocatalytic materials. Various application areas, where the multifunctional nanomaterials are now getting the constant place in cutting edge technologies, are highlighted. And also in this, various multifunctional materials and their criteria involving during the integration of assorted materials based on their properties and to be applied according to the requirements of the applications are also explained in detail.

Preparation of novel magnetic and fluorescent CS–Fe3O4@CdSeS nanoparticles for simultaneous removal and optical determination of trace copper ions

Simultaneous removal and detection of copper ions by CS–Fe₃O₄@CdSeS is achieved with high saturation adsorption capacity and high sensitivity.

Development of Fe/Fe3O4 core-shell nanocubes as a promising magnetic resonance imaging contrast agent

Here, we report the synthesis, characterization, and properties of Fe/Fe3O4 core-shell nanocubes prepared via a simple route. It includes NaBH4 reduction of FeCl3 in an ethylene glycol solution in the presence of 2-mercaptopropionic acid (surfactant) and trisodium citrate (cosurfactant) followed by surface oxidation with trimethylamine N-oxide. The morphology and structure of Fe/Fe3O4 core-shell nanocubes were characterized using transmission electron microscopy (TEM), high-resolution TEM, selected area electron diffraction, X-ray powder diffraction, and X-ray photoelectron spectroscopy. All of the methods confirm a Fe/Fe3O4 core-shell structure of nanocubes. Magnetic measurements revealed that the Fe/Fe3O4 core/shell nanocubes are superparamagnetic at 300 K with a saturation magnetization of 129 emu/g. The T2 weighted imaging and the T2 relaxation time showed high MRI contrast and sensitivity, making these nanocubes viable candidates as enhanced MRI contrast agents.

Single cell detection using a magnetic zigzag nanowire biosensor

A magnetic zigzag nanowire device was designed for single cell biosensing. Nanowires with widths of 150, 300, 500, and 800 nm were fabricated on silicon trenches by electron beam lithography, electron beam evaporation, and lift-off processes. Magnetoresistance measurements were performed before and after the attachment of a single magnetic cell to the nanowires to characterize the magnetic signal change due to the influence of the magnetic cell. Magnetoresistance responses were measured in different magnetic field directions, and the results showed that this nanowire device can be used for multi-directional detection. It was observed that the highest switching field variation occurred in a 150 nm wide nanowire when the field was perpendicular to the substrate plane. On the other hand, the highest magnetoresistance ratio variation occurred in a 800 nm wide nanowire also when the field was perpendicular to the substrate plane. Besides, the trench-structured substrate proposed in this study can fix the magnetic cell to the sensor in a fluid environment, and the stray field generated by the corners of the magnetic zigzag nanowires has the function of actively attracting the magnetic cells for detection.