Signal enhancement by a multi-layered substrate for mutagen detection using an SOS response-induced green fluorescent protein in genetically modified Escherichia coli

In this paper, we describe a method to enhance the fluorescence signal of mutagen detection using SOS response-induced green fluorescence protein (GFP) in genetically modified Escherichia coli using a multi-layered substrate. To generate E. coli that express SOS response-induced GFP, we constructed a plasmid carrying the RecA promoter located upstream of the GFP gene and used it to transform E. coli BL21. The transformed strain was incubated with mitomycin C (MMC), a typical mutagen, and then immobilized on a multi-layered substrate with Ag and a thin Al(2)O(3) layer on a glass slide. Since the multi-layered substrate technique is an optical technique with potential to enhance the fluorescence of fluorophore placed on top of the substrate, the multi-layered substrate was expected to improve the fluorescence signal of mutagen detection. We obtained an average 14-fold fluorescence enhancement of MMC-induced GFP in the concentration range 1 to 1000 ng/ml. In addition, the lower detection limit of MMC was improved using this technique, and was estimated to be 1 ng/ml because of an enlargement of the difference between the blank and the signal of 1 ng/ml of MMC.