An infrared IgG immunoassay based on the use of a nanocomposite consisting of silica coated Fe3O4 superparticles

A reliable, rapid and ultrasensitive immunoassay is described for determination of immunoglobulin G (IgG). It is making use of biofunctional magnetite (Fe₃O₄) superparticles coated with SiO₂ and serving as an infrared (IR) probe. The unique IR fingerprint signals originating from the transverse and longitudinal phonon modes, respectively, of the asymmetric stretching of the Si-O-Si bridges display a satisfactory resistance to optical interference from the environment. The adoption of Fe₃O₄ superparticles instead of Fe₃O₄ nanoparticles as the magnetic core warrants a controllable structure and a strong magnetic response. This facilitates the efficient purification of the probes and the alleviation of the interfacial resistance between the liquid-solid interfaces by using a magnet. The gold-coated substrate was used to immobilize goat-anti-human IgG. The analyte (human IgG) was incubated with the IR probes, and then captured by the substrate immobilized antibody with the assistance of an external magnetic field. The integral area of the IR absorption band between 1250 cm^-1 - 900 cm^-1 was chosen for quantitative assay. The limit of detection is 95 fM, which is two orders of magnitude better than that without the magnetic field. The assay time was shortened from 2 h to 1 min. High selectivity, specificity, and long-term stability of the immunoassay were achieved. The performance of the assay when analyzing blood samples confirmed the practicability of the method. Graphical abstract Schematic presentation of the infrared (IR) immunoassay based on Fe₃O₄ superparticle@SiO₂ nanocomposites. The assistance of an external magnetic field reduces the incubation time and improves the detection sensitivity.

Silica-Assisted Nucleation of Polymer Foam Cells with Nanoscopic Dimensions: Impact of Particle Size, Line Tension, and Surface Functionality

Core-shell nanoparticles consisting of silica as core and surface-grafted poly(dimethylsiloxane) (PDMS) as shell with different diameters were prepared and used as heterogeneous nucleation agents to obtain CO₂-blown poly(methyl methacrylate) (PMMA) nanocomposite foams. PDMS was selected as the shell material as it possesses a low surface energy and high CO₂-philicity. The successful synthesis of core-shell nanoparticles was confirmed by Fourier transform infrared spectroscopy, thermogravimetric analysis, and transmission electron microscopy. The cell size and cell density of the PMMA micro- and nanocellular materials were determined by scanning electron microscopy. The cell nucleation efficiency using core-shell nanoparticles was significantly enhanced when compared to that of unmodified silica. The highest nucleation efficiency observed had a value of ∼0.5 for nanoparticles with a core diameter of 80 nm. The particle size dependence of cell nucleation efficiency is discussed taking into account line tension effects. Complete engulfment by the polymer matrix of particles with a core diameter below 40 nm at the cell wall interface was observed corresponding to line tension values of approximately 0.42 nN. This line tension significantly increases the energy barrier of heterogeneous nucleation and thus reduces the nucleation efficiency. The increase of the CO₂ saturation pressure to 300 bar prior to batch foaming resulted in an increased line tension length. We observed a decrease of the heterogeneous nucleation efficiency for foaming after saturation with CO₂ at 300 bar, which we attribute to homogenous nucleation becoming more favorable at the expense of heterogeneous nucleation in this case. Overall, it is shown that the contribution of line tension to the free energy barrier of heterogeneous foam cell nucleation must be considered to understand foaming of viscoelastic materials. This finding emphasizes the need for new strategies including the use of designer nucleating particles to enhance the foam cell nucleation efficiency.