Apparatus for storing food and for keeping it warm and moist comprising a substantially water impermeable pouch that bounds an insulated food warming chamber, the pouch having opposing substantially coextensive lips capable of being moved apart for providing passage to the warming chamber and for providing a partial vapor lock for inhibiting moisture from building up in the warming chamber. The object is to reliably detect the material of the surface of the object that was taken from the stack before it is provided for further processing. 8,where X represents the reduction in film thickness per 1\xd7107 mm of the traveling distance of the photoreceptor for black development and Y represents the reduction in film thickness per 1\xd7107 mm of the traveling distance of the photoreceptors for the other development colors. According to the present invention, the PCB can be tested simply by connecting the PCB tester to the miniature USB connector, and the components can be easily plugged in without need of such operations as windowing and positioning. Analyte gas pumps for the inventive sensor include dual pumping electrodes situated on opposite sides of the membrane, and include a means for applying a DC power across the membrane to the sensing and counter electrodes. The present invention provides a wide range of dyes and kits containing the same, which are applicable for labeling a variety of biomolecules such as nucleic acids, cells and microorganisms.