In summary, we generated a library of 40 structurally diverse quinone mediators to gain a better understanding of the important physicochemical properties and biochemical interactions driving Nhd2-dependent EET in L. plantarum, a commensal gut bacterium. The library consists of twenty-nine naphthoquinones, six benzoquinones, and five anthraquinones that were obtained through semi-synthesis, natural product isolation and commercial sources. A particular focus of the library was to assemble mediators with diverse LogD, E o , and ΔGcomp. Correlation of these properties to the Ndh2-dependent EET activity in an iron(III) oxide nanoparticle reduction assay revealed a significant relationship between Ndh2-dependent EET activity and both LogD (p < 0.0001) and ΔGcomp (p = 0.0115). Analysis of some of the mediators in a BES confirmed that they are each capable of generating a detectable current, and the current of one of the mediators generated was stable over 5 d. This study has significantly increased our library of known mediators, provided insights into the properties that make a mediator successful, and has led to a mediator (23) that generates stable current outputs for potential use in a variety of biosensing applications.