Apparatuses and methods of optically analyzing fluid within a pipette are described herein. In an embodiment, an optical reader subassembly includes a housing including an internal area, a container configured to hold a fluid sample at a sample position in a light tight manner within the internal area of the housing, a light source configured to project light onto the fluid sample within the container, and an optical sensor configured to move between different sensor positions while the fluid sample remains stationary at the sample position, the different sensor positions including at least two of: (i) a first sensor position for taking a luminescence reading of the fluid sample; (ii) a second sensor position for taking a dark current or other background measurement; and (iii) a third sensor position for taking a fluorescence reading of the fluid sample.