Microfluidic diagnostic device with a three-dimensional (3D) flow architecture

A microfluidic diagnostic device with a three-dimensional (3D) flow architecture comprises a polymeric body having first and second opposing surfaces and comprising first flow channels in the first opposing surface, second flow channels in the second opposing surface, and connecting flow passages extending through a thickness of the polymeric body to connect the first flow channels to the second flow channels, thereby defining a continuous 3D flow pathway in the polymeric body. The microfluidic diagnostic device also includes a first cover adhered to the first opposing surface to seal the first flow channels, a second cover adhered to the second opposing surface to seal the second flow channels, and one or more access ports in fluid communication with the continuous 3D flow pathway for introducing liquid reagent(s) and/or a sample into the polymeric body.