While polydimethylsiloxane (PDMS) has proven to be a popular material in the construction of microfluidic devices, the polymer network structure of PDMS makes it permeable to some molecules. This feature can be problematic for applications where thin PDMS walls are used to separate two different molecular streams or cell populations. Therefore, a better understanding of factors affecting small molecule absorption in PDMS is important for better design and operation of microfluidic devices.
We report on studies of various factors in the absorption of fluorescent dyes in PDMS. Results show significant effects of thermal aging of PDMS on the absorption of the hydrophobic molecule Nile Red. In addition, the short-term hydrophobic recovery of the PDMS devices after being plasma bonded to a glass slide was investigated. Furthermore, we have tested the effects of aspiration and flushing, which show that the wetting property (hydrophilic or hydrophobic) of the flushing solvents can significantly affect the absorption of the Nile Red dye. Finally, parallel tests of PDMS absorption of fluorescein isothiocyanate (FITC) were conducted with no absorption observed.