The　lack　of　analytical　strategies　to　directly　determine　the　bacteriostatic　activity　of　nanomaterials　in　complex　aqueous　media　(e.g.,　environmentally　relevant　scenarios)　seriously　hampers　the　harvest　of　reliable　data　for　nanomaterial　risk　assessment.　Here,　we　created　an　automated　phenotypic　method　based　on　a　developed　multi-channel　contactless　conductometric　sensor.　Bacterial　growth　kinetics　of　E.　coli　and　S.　aureus　were　determined　via　on-line　monitoring　of　conductivity　changes　in　simple　media　(e.g.,　liquid　LB　broth)　and　complex　media　(e.g.,　relevant　river　water　and　seawater　samples　with　diverse　pH,　salinity,　conductivity,　turbidity,　chemical　oxygen　demand　and　total　suspended　solids).　The　high　temporal　resolution　growth　curves　provide　detailed　information　on　the　bacteria　inhibition　of　the　model　nanomaterial　-　Au　nanospheres,　Au　nanorods,　Ag　nanospheres　and　Ag　nanocubes　-　at　each　growth　stage,　thus　enabling　users　to　directly　obtain　minimum　inhibitory　concentrations.　The　method　highlights　the　advantages　of　universality,　simplicity　and　affordability.　It　opens　up　possibilities　for　the　development　of　a　powerful　analytical　platform　for　researches　in　the　field　of　nanoscience,　e.g.　to　assess　ecotoxicity　of　nanomaterials.