Optics Subsystem for GeneSat Experimental Payload
NASA Ames Research Center, Moffett Field, CA 94035

Introduction
The GeneSat experimental payload was designed to perform both fluorescence and optical density assays of biological specimens in an automated fashion. Below is a brief look at the functionality and components which comprise the optics subsystem. For a more detailed description of the device, see the Contact Information at the end of this page.

Functionality
The biological sample of interest, in this case E. coli, is placed inside the fluidic card wells. A complete optics unit sits below each well for a fully redundant assay system. The sample is excited with blue light (wavelengths of approximately 460 - 490 nm). The tagged fluorescent proteins of the sample respond by emitting green light (wavelengths of approx. 505 - 530 nm) which is detected by a photodiode. A set of off-the-shelf lenses and color filters ensure that only blue light of the desired wavelengths reaches the sample and only green light of the desired wavelengths reaches the detector. An optical density measurement is taken by placing a green LED atop the fluidic card well and again using the collection optics to measure light scattered by the sample. The goal for both the fluorescence and optical density measurement techniques is to achieve a detection sensitivity comparable to the benchtop equipment. Results for the fluorescence assay are shown to the left.

Figure 1. Separately packaged illumination and collection legs allow for minimal background signal on the detector, increasing sensitivity.		Figure 2. Fluorescence emission of GFP vs. non-GFP E. coli. The top plot shows data recorded by a full-size benchtop Molecular Devices Gemini fluorometer. The bottom plot shows the same measurements taken by our EDU (engineering design unit).
Figure 3. 3D model of the fluorescence and optical density measurement device.