To minimize cross talk in systems and methods for detecting two or more different optical signals emitted from each of a plurality of reaction receptacles, an excitation signal associated with each of the optical signals has a known excitation frequency, and any detected signal having a frequency that is inconsistent with the excitation frequency is discarded. The receptacles are moved relative to optical sensors configured to detect each unique optical signal from an associated receptacle, and to further minimize cross talk, the optical sensors are arranged so that only one reaction receptacle at a time is in a signal detecting position with respect to one of its associated optical sensors, and the optical sensors are grouped by the optical signal they are configured to detect so that a first optical signal is detected from each of the reaction receptacles before a second optical signal is detected from the reaction receptacles.