A seamless microchannel with aligned microelectrodes structure can be prepared to include a polymeric body defining a surface of a seamless microchannel. The microchannel is seamless in that it is formed by a single body of material having a conduit that is open at one surface and extends to another opening aligned with microelectrodes in another surface of the body. The rest of the microchannel is closed and defined by the single body of material. The seamless microchannel structure can be used in methods that include biosensors, coupling waveguides, capillary electrophoresis chips, microreactors, polymerase chain reaction-chips, and solving mathematical problems.