Hong,

I personally use  Dow-Corning 734 silicone sealant/adhesive and it
works great for attaching PDMS to platinum-cured silicone tubing, so I
am sure that it will work well for PDMS-PDMS bonding. It is also a
PDMS-based polymer, so less concern for biocompatibility...

Philip D. Hewes
Department of Biomedical Engineering (Undergraduate)
University of Michigan: School of Engineering