The present invention relates to a method of producing a nanocomposite for fabricating an electrochemical biosensor, the method characterized by the steps of preparing carboxylated reduced graphene oxide-titanium dioxide (rGO-TiO2); wherein the carboxylated rGO-TiO2 nanocomposite is deposited on a working electrode of an electrochemical biosensor. The present invention also relates to the electrochemical biosensor and the method for detecting foodborne bacteria using the electrochemical biosensor.