Abstract
This paper outlines a straightforward, fast, and low-cost method to fabricate polydimethylsiloxane (PDMS) chips. Termed sandwich bonding (SWB), this method requires only a laboratory oven. Initially, SWB relies on the reversible bonding of a coverslip over PDMS channels. The coverslip is smaller than the substrate, leaving a border around the substrate exposed. Subsequently, a liquid composed of PDMS monomers and a curing agent is poured onto the structure. Finally, the cover is cured. We focused on PDMS/glass chips because of their key advantages in microfluidics. Despite its simplicity, this method created high-performance microfluidic channels. Such structures featured self-regeneration after leakages and hybrid irreversible/reversible behavior. The reversible nature was achieved by removing the cover of PDMS with acetone. Thus, the PDMS substrate and glass coverslip could be detached for reuse. These abilities are essential in the stages of research and development. Additionally, SWB avoids the use of surface oxidation, half-cured PDMS as an adhesive, and surface chemical modification. As a consequence, SWB allows surface modifications before the bonding, a long time for alignment, the enclosure of sub-micron channels, and the prototyping of hybrid devices. Here, the technique was successfully applied to bond PDMS to Au and Al.
Highlights
Substrates play an important role in microfluidics by affecting the properties and performance of analytical chips because large surface-to-volume ratios are observed in microchannels
This paper addresses a groundbreaking method for prototyping PDMS microfluidic chips that represents a potential way to fabricate powerful and low-cost PDMS chips
A rounded profile of microchannels represents a positive aspect concerning the deployment of elastomeric valves and the execution of further photolithography steps such as thin film deposition and UV exposure inside the microchannel[38,39]
Summary
Substrates play an important role in microfluidics by affecting the properties and performance of analytical chips because large surface-to-volume ratios are observed in microchannels. SWB ensured great adhesion strengths without the use of surface oxidation, half-cured PDMS as an adhesive layer, solvents, or surface chemical modification, requiring only a laboratory oven for enclosing the microfluidic channels. In addition to drawbacks such as additional apparatuses (vacuum pump and magnets) and key restrictions for devices with high densities of microfluidic structures, these methods generate poor adhesion strength, ranging from 0.05 to only 0.16 MPa. The following assays are included here: mold characterization, channel cross-section imaging, and tests of adhesion strength, self-regeneration, reversibility, and repeatability through measurements of electroosmotic flow.
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