Electrophoretic Separation of Single Particles Using Nanoscale Thermoplastic Columns

Area of Science:

• Nanotechnology and Materials Science
• Analytical Chemistry
• Separation Science

Background:

• Microscale electrophoresis phenomena are not directly applicable to nanoscale separations.
• Understanding nanoscale electrophoretic characteristics is crucial for optimizing separation performance in sub-150 nm devices.
• Key nanoscale processes influencing separation efficiency include electric double layer (EDL) overlap, diffusion, adsorption/desorption, and dielectrophoretic effects causing stick/slip motion.

Purpose of the Study:

• To investigate the performance characteristics of electrophoretic separations in poly(methyl methacrylate) (PMMA) nanoslits.
• To demonstrate the size-based separation of silver nanoparticles (AgNPs) using PMMA nanoslit devices.
• To evaluate the impact of operational parameters (electric field strength, nanoslit dimensions, buffer composition) on electrophoretic performance (efficiency and resolution).

Main Methods:

• Fabrication of PMMA nanoslit devices.
• Utilized silver nanoparticles (AgNPs) capped with citrate groups as the model system.
• Tracked AgNP transport using dark field microscopy and localized surface plasmon resonance.
• Investigated separations in nanoslits with negatively charged PMMA walls (induced by O2 plasma modification).

Main Results:

• Demonstrated size-based separation of AgNPs in PMMA nanoslits without buffer additives.
• Achieved separations not observed in microscale columns.
• High electric field strengths (>200 V/cm) resulted in higher plate numbers (improved efficiency) compared to lower fields due to the absence of stick/slip motion.
• Successfully separated 60 nm AgNPs from 100 nm AgNPs in free solution using 100 μm long columns.

Conclusions:

• PMMA nanoslit devices enable effective nanoscale electrophoresis.
• Nanoscale electrophoresis can achieve size-based separation of nanoparticles without buffer additives.
• Optimizing electric field strength is critical for enhancing separation efficiency in nanoscale electrophoresis by mitigating stick/slip motion.