Provided herein, among other things, is method comprising: a) placing a planar absorbent support comprising an in vitro transcription and translation (IVTT) mix impregnated therein in contact with an array of in situ-assembled expression cassettes; and b) incubating the planar absorbent support and array under conditions by which the expressed cassettes are transcribed and translated by the impregnated IVTT components, thereby producing an array of proteins. Screening methods that employ the array of proteins are also provided.