Fabrication of Hybrid Micro-Nanofluidic Devices With Centimeter Long Ultra-Low Aspect Ratio Nanochannels

Abstract

Hybrid microfluidic and nanofluidic devices have a variety of applications including water desalination, molecular gates and DNA sieving among several other lab-on-chip uses. Most microfluidic and nanofluidic devices currently are fabricated in glass, silicon, polydimethylsiloxane (PDMS), or with a combination of these materials. In order to impart functionality, metals, polymers or auxiliary components are often integrated with these devices. Ultra-low aspect ratio channels have several advantages including critical dimensions on the nanoscale but increased throughput compared to higher aspect ratio channels with the same critical dimension, which is important for applications where a higher volumetric flow rate is desired. Additionally, theoretical analysis is significantly easier as ultra-low aspect ratio channels can be modeled as 1-D systems. The fabrication methods for achieving low aspect ratios (< 0.005) usually require extensive facilities with several innovative fabrication and bonding schemes being previously reported. In this paper, we report on fabrication and bonding of ultra-low aspect ratio microfluidic and nanofluidic devices with aspect ratios at 0.0005 in glass/PDMS devices in contrast to the previous best reported result of 0.005 achieved in a silica device using stamp and stick PDMS bonding. The simplicity of our approach presents a new pathway to achieving the lowest aspect ratio nanochannels ever reported for channels fabricated using an interfacial layer for bonding. Centimeter long nanochannels on a borosilicate substrate were fabricated by standard UV photolithography followed by wet etching. Surface roughness of the fabricated channels is on the same order as the roughness of the initial substrate (2–3 nm) and therefore can enable fabrication of channels with critical dimensions approaching 15 nm or less. Devices were then bonded using a second borosilicate substrate with a thin PDMS adhesion layer (∼ 2 μm). The PDMS adhesion layer allows rapid, facile, and alignment-free bonding compared to traditional fusion or anodic bonds. Successful verification of device operation and functionality was determined by verifying flow in operational devices and with scanning electron microscopy to confirm bonding for the formation of nanochannels.