diluting a sample comprising the infectious agent with a dilutive solution to yield a diluted sample;

separating the diluted sample into a first aliquot and a second aliquot, wherein the second aliquot is used as a control solution;

mixing an anti-infective at a first concentration into the first aliquot to yield a test solution;

introducing the test solution to a first sensor such that the test solution is in fluid communication with a redox-active material of the first sensor, wherein the first sensor comprises an active electrode and a reference electrode, the active electrode comprising a redox-active layer positioned on top of at least one conductive metallic layer;

introducing the control solution to a second sensor such that the control solution is in fluid communication with the redox-active material of the second sensor, wherein the second sensor comprises an active electrode and a reference electrode, the active electrode comprising a redox-active layer positioned on top of at least one conductive metallic layer;

monitoring an oxidation reduction potential (ORP) of the test solution and the control solution over a period of time using one or more parameter analyzers coupled to the first sensor, the second sensor, or a combination thereof, wherein the ORPs are monitored in the absence of any added reporter molecules in the test solution or the control solution; and

comparing the ORP of the test solution with the ORP of the control solution to determine the susceptibility of the infectious agent to the anti-infective.