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.

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 analytes-distinctive features on the PCA plots allows us to recognize polarity as a key property which affects the AuNCs_MSS response. In addition, density functional theory (DFT) calculations suggest that corners and edges of the nanocages play important roles on the binding energy.

The assembly of biomolecules onto mechanically and chemically stable inorganic structures is advantageous for practical applications considering the potential for improvements in the stability and catalytic functionality of biomaterials. In this research, we have utilized hierarchically-structured, radially porous silica hollow spheres as a platform for hemoprotein self-assembly. Proteins adsorbed onto silica surfaces through electrostatic interactions remained intact and exhibited rapid gas-phase sensing activity towards hydrogen sulfide gas. The nanoscale molecular interactions between hemoproteins and the analyzed gases were transduced into measurable variations in electric signals using a nanomechanical Membrane-type Surface stress Sensor (MSS).