Bonding with a UV Ozone Cleaner – A Practical Guide to Prepare a Microfluidic Chip

This study describes a procedure for preparing microfluidic chips made from polydimethylsiloxane (PDMS). It uses a UV ozone cleaner for surface activation instead of the more common oxygen plasma treatment. Although this process has some limitations compared to oxygen plasma bonding, it can be used when a low-cost procedure for a small number of microfluidic chips is required or when an oxygen plasma etcher is unavailable. The challenges of this process arise from the slight hardening of the PDMS surface when it is activated for 70 minutes, which is necessary for reliable bonding. It is demonstrated that damage resulting from this hardening in conjunction with careless handling of the microfluidic chip is mitigated by incorporating predetermined break structures and using tubes with an outer diameter that is smaller than the inlets. Additionally, pre-polymerized PDMS glue and PDMS seals are suggested to ensure that the tubes are properly sealed. To demonstrate the concept, two microfluidic structures were prepared and tested, achieving flow rates of at least 170 µL/min at ±180 mbar. Bonding remains stable up to a pressure of approximately 0.5 bar.