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The gist of biosensor is the sensing layer itself due to the ability to sense bio components such as bacteria. Graphene is an example of a promising material used as biosensor. Graphene material possess unique and superior properties and promised material to use as sensing layer due to its advantages in conductivity and large surface area. Escherichia coli is a group of bacteria causes harmful disease to human health due to its spreading in environment through faecal contaminated water. This study reports on biocompatibility of graphene against E. coli through visible growth inhibitory test and SEM image that evidently showed no inhibition growth and undamaged bacteria cell. Graphene wettability over water contact angle performed by hydrophobicity with 108.90° which preferably attached by the cells due to its surface energy condition. Negativity charge of bacteria enables to induce the holes of graphene then formed ohmic contact between the sheets and electrode. Based on its resistance, graphene could detect E. coli with limit detection of 4 CFU. Therefore, a compact and portable design of E. coli sensor was successfully fabricated with the device average error about 12.23%. • A novel, compact and portable design of E. coli sensor was successfully fabricated. • Biocompatibility of graphene against E. coli through visible growth inhibitory test and SEM image were presented. • Graphene material characterization was presented. • The negativity charge of bacteria could induce graphene film then produced ohmic contact between the sheets and electrode. • Increasing number of bacteria could decrease graphene resistivity. [ABSTRACT FROM AUTHOR]