Evanescent wave-based particle tracking velocimetry for nanochannel flows

Area of Science:

• Fluid dynamics
• Nanotechnology
• Analytical chemistry

Background:

• Understanding fluid behavior in the 10-1000 nm range (extended nanospace) is crucial for developing advanced nanofluidic devices.
• Existing methods face challenges in accurately measuring flow dynamics at the nanoscale.

Purpose of the Study:

• To develop and validate a particle tracking velocimetry (PTV) technique for measuring velocity distribution in nanochannel flows.
• To investigate fluid behavior, including slip velocity, in nanochannels using evanescent wave illumination.

Main Methods:

• Developed a PTV system utilizing evanescent wave illumination to track 64 nm fluorescent nanoparticles.
• Achieved high spatial resolution (< light wavelengths) and temporal resolution (260 μs) to minimize Brownian motion effects.
• Employed multi-time particle tracking image processing to detect weak fluorescent signals from tracer nanoparticles.

Main Results:

• Successfully measured pressure-driven water flow in a 50 μm wide, 410 nm deep nanochannel.
• Observed velocity distributions that generally agreed with macroscopic fluid dynamics predictions.
• Detected slip velocities at the channel walls, even in a hydrophilic channel, suggesting nanoscale fluid behavior.

Conclusions:

• The developed PTV method is effective for characterizing fluid dynamics in extended nanospace.
• Slip flow at hydrophilic nanochannel walls indicates unique molecular behavior within approximately 10 nm of the surface.
• Findings contribute to the design and optimization of nanofluidic devices for analytical chemistry applications.