From the results of transformation experiments, the colour and fluorescence was used to identify colonies of XL-1 Blue E. coli cells that expressed GFP as a result of being transformed with the pQE30-GFP construct. In addition, the transformed cells were used to synthesize large quantities of hexahistidine-tagged GFP. The synthesis of GFP in cells transformed with the pQE30-GFP construct was induced  with the lactose analogue isopropyl ß-D-thiogalactopyranoside (IPTG). The bulk of the induced cells were then harvested and stored until later when the hexahistidine-tagged GFP protein was purified using IMAC (immobilised metal affinity chromatography) on nickel agarose. Plates from the 4°C cold-room were collected and the colonies on each examined. Typically, the number and “type” of colony present on each plate was thus determined based on whether the colony expresses GFP (“+” GFP) or does not express GFP (“-“GFP). Thereafter, four overnight cultures of cells were setup, two from GFP producing colonies and another two cultures of cells from non GFP-producing colonies which were then inoculated. The tubes were then incubated overnight at 37°C with shaking after capping them tightly. Finally an induction process was initiated after the tubes had stayed overnight whereby 1.5ml of each culture was set aside in microfuge tubes for later use. 25mg/ml ampicillin stock was added to the LB to give a final concentration of 100μg/ml. Thereafter, a spectrophotometer