The Measurement Committee is committed to achieving reliable and repeatable measurement. Therefore the interlab study is established, measurements made in different laboratories by measuring the expression of GFP will be no more variable than measurements taken within the same lab.
After several years of hard work, the committee concluded a universal protocol for measuring GFP expression. In recent years, the interlab study aims to improve the protocol and identify and correct the sources of systematic variability as much as possible.
This year’s interlab study aims to reduce a major source of variability during fluorescence measurements: the number of cells in the sample. Normally, we take the Abs600 of a sample as a representation of its cell density, but still many previous studies showed that there was significant lab-to-lab variability(?). Therefore, we followed the protocols delivered by the iGEM authority and carried out this verification.
According to the protocol, we performed three calibration experiments (OD600 reference point, particle standard curve and the fluorescence standard curve) before the body part began. Results shown below.
Table 1. OD600 reference point
4 replicates are measured respectively to acquire the average Abs600 of LUDOX CL-X solution and dH2O. Reference OD600 is given by the iGEM authority. The ratio of OD600/Abs600 is 3.652.
Figure 1A Particle Standard Curve
Figure 1B Particle Standard Curve (log scale)
We use the silica beads delivered by iGEM and made a serial dilution in the 96-well plate according to the protocol. 4 replicates were measured in total. Origin data presented at the bottom of this page.
Figure 2A Fluorescein Standard Curve
Figure 2B Fluorescein Standard Curve(log scale)
We use the fluorescein powder delivered by iGEM and made a serial dilution in the 96-well plate according to the protocol. 4 replicates were measured in total. Origin data presented at the bottom of this page.
After finishing the calibration, we carried out the cell culturing and the measurements of Abs600 and fluorescein.
First of all, we transformed the given plasmids into E.coli K-12 DH5-alpha on the plates of LB medium with chloramphenicol of 25μg/ml in 37℃, and picked 2 colonies of each plate over night, inoculating into 5ml Luria- Bertani liquid medium with 25 μg/mL chloramphenicol, incubating in 37°C at the speed of 220 rpm for 16hrs.
Secondly, the cell cultures were diluted to the concentration of Abs600=0.02 for target start and were transferred to the same LB medium of 12mL in 50mL falcon tubes, at the same incubator above. At the time of 0 and 6 hours of incubation, we took off 500μL into 1.5 ml eppendorf tubes of each colony of 8 devices, and placed them on ice to prevent from further growth.
Last but most importantly, we pipetted 4 replicates samples of each devices, 100μL per well, into a 96-well plate. Samples were laid out according to the plate diagram shown in the protocol.