The aim of the 2016 iGEM InterLab was to quantify the expression of GFP under different promoters and Ribosomal Binding Regions (RBRs). The use of GFP to indirectly measure the expression of a specific protein in cells is a key approach in biology. It enables us to monitor expression levels without killing the cells. The ability measure expression levels per cell is important to be able to quantify strength of promotors. In order to achieve this, population size is indirectly measured using OD600. Expression per cell is then obtained by Fluorescence/OD600.
Both Fluorescence and OD600 are relative measurements, meaning the instruments used and their settings play a crucial role.
To calibrate the instrument and transform relative measurements into absolutes ones, FITC is used as reference material to construct a standard calibration curve for fluorescence. FITC standard is constructed by serial dilution. The resulting FITC curve is used in combination with another FITC standard curve and a GFP standard curve provided by iGEM.
OD600 is a measure of light scattering, therefore light detection is dependent on the physical geometry of the machine. Calibration experiments using a flow cytometer do not involve standard curves. In order to give uniformity to Fluorescence/OD600 data, a standard scattering solution of a mono-dispersed silica suspension (LUDOX) is used.