Semester of Graduation

2020 Summer

Degree

Master of Science in Mechanical Engineering (MSME)

Department

Mechanical Engineering

Document Type

Thesis

Abstract

Polymer nanofluidic devices have great potential to replace silicon (Si) and glass-based nanofluidic devices in biomedical applications due to their advantages such as low material and fabrication cost, various physicochemical properties, well-developed surface modification protocol, and low electrical noises for electrical measurements. In nanofluidic sensing applications, single molecules such as DNA are introduced into the fabricated nanochannel or nanopore, measuring their physicochemical properties optically or electrically. The properties of materials for nanofluidic devices have a significant role in the performance of the devices, such as DNA translocation and device stability.

Among several nanoscale fluidic physics, surface charge density is a key material property of nanofluidic devices related to the capture of single molecules because it determines the magnitude of electrophoresis and electroosmosis in the nanostructures. To facilitate the capture of single molecules into nanofluidic devices, polymers containing poly(ethylene glycol) (PEG) are preferred due to their low surface charge density and reduction of surface fouling of biomolecules. However, a drawback of PEG-based polymers is a weak chemical and mechanical stability due to swelling effect and low surface hardness when in contact with electrolytes.

This work presents an improvement in the chemical and mechanical stability of a nanofluidic device formed in poly(ethylene glycol) diacrylate (PEGDA), a PEG-based UV resin for UV-NIL, by adding a cross-linking agent (e.g. TMPTA). First, we defined the surface charge density of polymers such as PMMA, COC 6013, and PEGDA with the different O2 treatment time because these three polymers have low surface charge density compared to other polymers. Then, we studied the effect of the cross-linking agent content on the surface charge density of PEGDA-TMPTA material and on the translocation of DNA molecules through the nanopore. Five different compositions of PEGDA resins with varied amounts of a cross-linking

1 agent, trimethylolpropane triacrylate (TMPTA), were used (pure PEGDA, ratio 5:1, 1:1, 1:2, and 1:5). The surface hardness of PEGDA-TMPTA resin increases according to the crosslinking agent concentration from 139 MPa (pure PEGDA resin) to 205 MPa (1:5 resin). To be specific, the surface hardnesses of pure PEGDA, 5:1, 1:1, 1:2, and 1:5 were 139 MPa, 158 MPa, 196 GPa, 204 MPa, and 205 MPa, respectively. The surface charge densities at 0.001M KCl (pH 8.0) of pure PEGDA, 5:1, 2:1, 1:1, and 1:5 were −9.5 ± 0.09 ����/�� ! ,

−7.9 ± 0.97 ����/�� ! , −7.1 ± 1.06 ����/�� ! , −7.5 ± 1.10 ����/�� ! , and −7.4 ± 0.57 ����/

�� ! , respectively. These observed surface charge densities of PEGDA-TMPTA resin exhibit a decreasing trend which is beneficial for DNA translocation into nanostructures. In conclusion, this approach has a positive influence on the chemical and mechanical stability of nanofluidic devices concerning DNA translocation into a nanopore or a nanochannel.

Committee Chair

Dr. Sunggook Park

DOI

10.31390/gradschool_theses.5201

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