Interposer with first and second adhesive layers

An interposer comprising:

• a base layer having a first surface and a second surface opposite the first surface;
• a first adhesive layer disposed on the first surface of the base layer;
• a first release liner disposed on the first adhesive layer;
• a second adhesive layer disposed on the second surface of the base layer;
• a second release liner disposed on the second adhesive layer;
• and a plurality of microfluidic channels disposed within the interposer, the plurality of microfluidic channels extending fully through each of the base layer, the first adhesive layer, and the second adhesive layer, and the second release liner, but not through the first release liner.