Overview

METHODS

Background

“All of the 2016 iGEM teams are invited and encouraged to participate in the Third International InterLaboratory Measurement Study in synthetic biology.” Our team took part in this study which aimed to standardize the measurements of fluorescence in different labs. The main task was to quantify expression of GFP in common, comparable or absolute units. In our case, we measured fluorescence using plate reader.

Design

Fluorescence is widely used as a proxy for promoter activity by expressing fluorescent proteins such as green fluorescent protein (GFP). Despite this is an indirect measurement, it provides a useful insight into expression levels and has significant advantage that it could be ontinuously monitored without disrupting cells.

Fluorescence/OD600 is routinely used to give an adjustment of the relative expression per cell.

We aim to do this using the supplied FITC as a standard reference material. The standard curve could be constructed via measuring the fluorescence of a dilution series. We have previously performed this standard curve on our own instrument alongside a standard curve for purified GFP. Using these standard curves alongside your own standard curve for FITC it is thus possible to transform your relative measurements of fluorescence into absolute measurements of GFP molecules.

However, we aim to contain instrument variability, at least to some degree, by measuring a standard scattering solution of a mono-dispersed silica suspension (LUDOX). The objective is to see if a simple, single fixed-point measurement can be used as a ratiometric adjustment to provide greater uniformity in fluorescence/OD600 measurements across sites.

Materials and methods