Peking 2018 joined the fifth Interlab measurement study. This year we helped to answer this question: Can we reduce lab-to-lab variability in fluorescence measurements by normalizing to absolute cell count or colony-forming units (CFUs) instead of OD?

The introduction of this year Interlab:


Equipment Information

Plate Reader: Perkin Elemer EnSpire TM Multilabel Reader 2300

Flow Cytometry: BD LSRFortessa TM Cell Analyzer

96 - Well Pate: Corning Incorporated Costar®️ 3603





Calibration 1: OD600 Reference point - LUDOX


Figure. 1 The result of LUDOX calibration. The correction factor of our plate reader is 3.316



Calibration 2: Particle Standard Curve – Microsphere


Figure. 2 The result of particle calibration.

(a) Particle Standard Curve - Linear (b) Particle Standard Curve - Log Scale
Figure. 3 The result of particle standard curve



Calibration 3: Fluorescence standard curve – Fluorescein


Figure. 4 The result of fluorescein calibration.

(a) Fluorescence Standard Curve - Linear (b) Fluorescence Standard Curve - Log Scale
Figure. 5 The result of fluorescence standard curve


Cell Measurement



Competent cells (Escherichia coli strain DH5α)
LB (Luria Bertani) media
Chloramphenicol (stock concentration 25 mg/mL dissolved in EtOH)
50 ml Falcon tube (or equivalent, preferably amber or covered in foil to block light) Incubator at 37°C
1.5 ml eppendorf tubes for sample storage
Ice bucket with ice
Micropipettes and tips
96 well plate, black with clear flat bottom preferred

Figure. 6 The required test devices.

Figure. 7 The localization of each device on the 96-well plate.


Plate Reader

Figure. 8 The raw readings of Abs 600 and fluorescence by the plate reader.

Figure. 9 The fluorescence per OD.

Figure. 10 The fluorescence per particle.


Flow Cytometry

(a) Colony 1 (b) Colony 2
Figure. 11 The result of flow cytometry at 0h.

(a) Colony 1 (b) Colony 2
Figure. 12 The result of flow cytometry at 6h.
Colony Forming Units per 0.1 OD600 E. coli cultures

Figure. 13 The count of colony forming units per 0.1 OD600 E. coli cultures.