We are attempting charge mapping and potentiometry on biological and molecular systems using a modified Atomic Force Microscope (AFM)--Electrostatic Force Microscope (EFM). With an interferometric detection system, we have obtained potentiometric sensitivity better than 0.1 mV and spatial resolution of about 200 angstroms. The images of red blood cells in air clearly show surface potential variation, independent of topography. We imaged FEP ((poly)tetrafluororethylene -co- hexafluoropropylene) films lithographically patterned with APS (poly(aminopropyl)siloxane). We have been able to positively identify the modified regions (APS) from the unmodified regions (FEP) using charge information. The charge density we estimated on the unmodified FEP regions of our samples is about 10-9C/cm2.