Functionalized-Graphene Field Effect Transistor-Based Biosensor for Ultrasensitive and Label-Free Detection of -Galactosidase Produced by Escherichia coli

The detection of beta-galactosidase (beta-gal) activity produced by Escherichia coli (E. coli) can quickly analyze the pollution degree of seawater bodies in bathing and fishing grounds to avoid large-scale outbreaks of water pollution. Here, a functionalized biosensor based on graphene-based field effect transistor (GFET) modified with heat-denatured casein was developed for the ultrasensitive and label-free detection of the beta-gal produced by E. coli in real water samples. The heat-denatured casein coated on the graphene surface, as a probe linker and blocker, plays an important role in fabricating GEFT biosensor. The GFET biosensor response to the beta-gal produced by E. coli has a wide concentration dynamic range spanning nine orders of magnitude, in a concentration range of 1 fgmL(-1)-100 ngmL(-1), with a limit of detection (LOD) 0.187 fgmL(-1) (1.61 aM). In addition to its attomole sensitivity, the GFET biosensor selectively recognized the beta-gal in the water sample and showed good selectivity. Importantly, the detection process of the beta-gal produced by E. coli can be completed by a straightforward one-step specific immune recognition reaction. These results demonstrated the usefulness of the approach, meeting environmental monitoring requirements for future use.