In addition to various high resolution imaging approaches, atom probe tomography (APT) has the unique potential towards 3D compositional mapping of biological cells at the atomic scale [1]. However, applying APT for atomic-scale mapping of biological samples still remains a challenge due to insufficient sample conductivity. Although adding pulsed-laser can facilitate probing of electrically insulated materials, difficulties with the thermal evaporation process still prevents proliferation of APT in the biology domain. The thermal evaporation process of organic materials using the pulse laser is more sensitive to the experimental conditions resulting in a more costly solution with less spatial resolution [2]. In this study, we report the first successful APT imaging of bacterial cells with a pulse voltage atom probe through engineering an ultrathin metallic layer to enable compelling local field evaporation on cells. An optimal coating strategy was first developed, followed by deriving the empirical model of minimal achievable layer for APT biological samples. 3D compositional maps of various regions in a single bacterial cell have been acquired with over 106 -107 number of ions collected in each run. Mass spectra and reconstructed 3D volumes obtained from the intracellular domain and cell envelope regions highlight the significant compositional and structural variations in the bacterial architectures and reveal distinct concentrations of elements and proteins. We expect that this study will not only provide a technical solution for engineering nanoscale coating, but also contribute a novel and repeatable solution to explore the cells at the “ultimate” resolution.