This paper reports the magnetic control of nanoparticle collisions on gold ultramicroelectrode surface. Magnetite nanoparticles with diameters of 10 nm and modified with Prussian blue (Fe3O4-NPs-PB) were directed by gravitational force on the electrode surface, and spikes in current-time transients were observed. By modulating a magnetic field parallel to the electrode surface, the number of nanoparticle collisions and the nanoparticle positions could be controlled.
The controlled assembly of metal nanoparticles into ordered structures interacting with biological molecules is an emerging concept in surface science. Here, bare magnetite nanoparticles (Fe 3 O 4 −NPs) were employed as nanoadhesives to capture hollow metallic nanostructures (Au−Ag nanocages) from aqueous suspensions, and these coupled nanostructures were patterned onto various types of substrate via magnetolithography. Microwires of Au−Ag nanocages patterned onto an Au substrate behaved as optical antennas, providing a plasmonic enhancement exploited in surface-enhanced infrared absorption spectroscopy (SEIRAS) to investigate the proteins cytochrome c, bilirubin oxidase, alcohol dehydrogenase, bovine serum albumin, and glucose oxidase. Chemical maps containing more than 4000 spectra, acquired within only 2 min with a focal plane array detector, indicate that proteins were adsorbed along the microwires with their secondary structure preserved according to the spatial distribution of their amide groups. We believe there are significant practical aspects of the methodology proposed here to develop an alternative label-free assay for investigating biological molecules.
Magnetite decorated with gold nanoparticles (Fe3O4-AuNPs) is a ferrimagnetic material with unprecedented applications in immunosensors, as a contrast agent for imaging diagnosis, and for the photothermal ablation of tumor cells. Here, we show the preparation of controlled amounts of Fe3O4-AuNPs without organic solvents, surfactants, or heat treatment. For this, we have developed a customized natural-rubber-based microfluidic device (NRMD) as a flexible lab-on-a-chip for the decoration of Fe3O4 with AuNPs. With a novel NRMD configuration, monodisperse Fe3O4-NPs (ϕ = 10 nm) decorated with AuNPs (ϕ = 4 nm) were readily obtained. The AuNPs were homogenous in terms of their size and their distribution on the Fe3O4-NP surfaces. Furthermore, the lab-on-a-chip was projected with an internal system for magnetic separation, an innovation in terms of aqueous/carrier phase separation. Finally, the nanomaterials produced with this NRMD are free of organic solvents and surfactants, allowing them to be used directly for medical applications.
Here,
we show that gold nanocages (AuNCs) can be used as receptor
materials for nanomechanical membrane-type surface stress sensor (MSS).
The fabricated AuNCs-coated MSS (AuNCs_MSS) was employed successfully
for the recognition of small volatile molecules. Each AuNCs_MSS exhibited
a specific pattern of the response signal to each analyte, enabling
groupwise discrimination of the compounds by means of principal component
analysis (PCA). The application of contour maps of analyte-distinctive
features on the PCA plots allows us to recognize polarity as a key
property that affects the AuNCs_MSS response. In addition, density
functional theory (DFT) calculations suggest that corners and edges
of the nanocages play important roles in binding energy.
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