Apparatuses and methods of optically analyzing fluid within a pipette are described herein. In an embodiment, an optical reader subassembly includes a pipette configured to aspirate and hold a fluid sample within its tip, a housing configured to receive at least the tip of the pipette through a reentrant seal so that the tip of the pipette is located in a light tight manner within an internal area, a light source positioned to be in proximity to the tip of the pipette when the tip of the pipette is received by the housing, the light source configured to project light through the tip of the pipette and onto the fluid sample held within the tip, and an optical sensor configured to take a reading of the fluid sample held within the tip of the pipette without any of the fluid sample being injected from the pipette.