Light Scattering Contrast Inversion of Single Metal Nanoparticles Inside a Nanofluidic Channel

Area of Science:

• Nanoscale science and engineering
• Optical physics
• Materials science

Background:

• Nanofluidics offers precise control of nanoscale fluid flow and particle manipulation.
• Optical microscopy and spectroscopy enable the study of single nanoentities using light.
• Contradictory light scattering properties of metal nanoparticles in nanofluidics are poorly understood.

Purpose of the Study:

• To systematically investigate the light scattering properties of platinum (Pt) and gold (Au) nanodisks within nanofluidic structures.
• To understand the underlying physics governing the optical appearance of metal nanodisks in nanofluidic systems.
• To demonstrate dynamic optical tuning for potential applications in nanoscale sensing.

Main Methods:

• Fabrication of Pt and Au nanodisks into nanotrenches within a poly(methyl methacrylate) matrix.
• Development of an analytical model based on electrostatic approximation to explain light scattering interference.
• Experimental demonstration of dynamic optical tuning in a fully enclosed nanofluidic channel by adjusting liquid refractive index.

Main Results:

• Light scattering signatures of nanodisks varied, appearing brighter, darker, or invisible compared to the trench alone, depending on geometry.
• The analytical model successfully explained the observed optical effects through interference between nanodisk and nanofluidic structure scattering.
• Dynamic optical tuning from dark to bright to invisible states was achieved by changing the refractive index of the internal liquid.

Conclusions:

• The interplay between nanodisk and nanofluidic structure geometry dictates light scattering properties.
• Interference effects are fundamental to understanding and controlling the optical appearance of metal nanodisks in nanofluidics.
• This tunable optical effect holds promise for developing optical sensors for sub-diffraction-limit volumes in nanofluidic systems.