Incubation well with an unvented gas cavity for use in a microfluidic chip

An incubation segment for use in a microfluidic chip for microbiological assays, wherein said incubation segment is formed in a substrate with a first major face and a second major face, said segment comprises an incubation well, an inlet channel through which a sample may be inputted into said incubation well, and a gas cavity connected to said incubation well by a microfluidic communication channel, wherein said gas cavity is unvented and a base of the gas cavity is connected to a base of the incubation well by the communication channel, wherein the incubation well comprises an optical window, the optical window comprising a through hole extending from said first major face through said substrate to said second major face, a first impermeable, transparent layer covering the incubation well on said first major face, and a second impermeable, transparent layer covering the incubation well on said second major face.