In Situ Detection of a Biphasic Pericellular Chemical Potential Field Generated by a Single Prokaryotic Cell

We report a direct, pre-registered experimental test demonstrating that a single metabolically active prokaryotic cell (Escherichia coli) generates a stable, spatially structured chemical potential field in its immediate aqueous environment. Using Scanning Electrochemical Microscopy (SECM), we performed real-time, in situ mapping of local gradients for both consumed and produced chemical species surrounding an immobilized single cell. We test the minimal hypothesis that an active cellular overdensity generates a biphasic pericellular field: a negative chemical potential gradient for consumed substrates (O₂) and a positive chemical potential gradient for produced metabolites (H⁺). Measurements are benchmarked against two null controls—a chemically fixed cell and an inert microsphere of comparable dimensions—processed under identical conditions. Only the metabolically active cell exhibits a persistent, coherent biphasic gradient structure. The null hypothesis of a homogeneous chemical field is rejected at high statistical significance (>10σ). This result establishes the formation of a stable, density-driven chemical potential field as a directly measurable feature of single-cell biophysics.