Session: 14-10-02: Micro/Nanofluidics 2025 II

Paper Number: 166403

The Effect of Different Cations on Surface Charge Density and Wetting Behaviors in Plastic Nanofluidic Devices 

The surface charge density of plastic nanofluidic walls plays a significant role in controlling molecular transport in nanochannels, which is crucial for optimizing the performance of nanofluidic devices, especially in single biomolecular transport and their applications. Low surface charge density is usually preferred to achieve molecular transport into nanostructures (nanochannels and nanopores) by minimizing the effect of electroosmotic flow. However, most thermoplastics have highly negative surface charges, making it difficult to drive molecules. Another issue with plastic nanofluidic devices is the difficulty in wetting the device, which is associated with the hydrophobic nature of polymer chemistry. It is challenging to achieve good wetting and low surface charge density simultaneously. In this study, we show a new method of modifying surfaces of plastic nanofluidic devices by different cationic treatment to achieve surfaces with low surface energy and good wetting behavior.

Polymer nanochannels were fabricated from a UV-resin using nanoimprint lithography (NIL), and the surfaces of imprinted nanochannels were treated by soaking in different electrolytes with different cationic valences including KCl, MgCl₂ and AlCl₃. The thermoplastic substrate used was cyclic olefin polymer (COP). The COP substrates treated with different electrolytes were then irradiated with UV/O3 for 1.5 min to activate the surface, which was followed by bonding with a COC cover plate. Then, the degree of wetting and translocation of single biomolecules were tested by measuring transient current flowing through the channels. The surface charge density on the flat COC substrate treated under different conditions was characterized by measuring zeta potential using the SurPASS3 electrokinetic analyzer across a pH range of 10 to 2.

Our results show that, compared to the untreated sample, the use of MgCl₂ significantly impacts the zeta potential, leading to a noticeable change in surface charge density of the COP substrate. After the cover plate bonding, the wetting of the COP chip treated with 2% v/v MgCl₂ in 1 M KCl w became significantly enhanced compared to that of untreated COP. The zeta potential of the COP substrate treated with AlCl₃ further decreased and the degree of wetting was further enhanced. We will also show the effect of different types of cations in electrolyte solutions on the capture of single molecules through nanochannels. The findings of this work pave the way to overcome the limitations of polymer-based nanofluidic devices regarding wetting of the nanostructured channels and capturing of single molecules, which are pre-requisite operational procedures of using nanofluidic devices for biosensing and lab-on-chip devices.

Presenting Author: POURIA POURHOSSEINHENDABAD Louisiana State University

Presenting Author Biography: I am a first-year Ph.D. student at Louisiana State University (LSU), specializing in biosensing of biomolecules using
in-plane polymeric nanopores. My research focuses on the development behaviors in plastic nanofluidic devices.
My work integrates nanotechnology, polymer science, and biosensing, aiming to enhance the sensitivity and
efficiency of nanopore-based detection systems. My contributions to the field include experimental and theoretical
advancements in nanopore design and characterization.

Authors:

POURIA POURHOSSEINHENDABAD Louisiana State University
Sarah Stenhouse Louisiana State University
Hooman Abdolvand Louisiana State University
Sunggook Park Louisiana State University