Single-Cell Mapping of Colloidal Phase Transitions via Dielectrophoretic Control of Particle Concentration

Colloidal systems offer a versatile platform for probing condensed matter behavior through tunable interactions and direct imaging. While dielectrophoresis (DEP) has previously been used to crystallize colloids, its broader potential for systematically resolving multiple phase transitions within a single system remains underexplored. Here, we build on prior DEP-based approaches by demonstrating a unified single-sample platform that enables continuous, reversible modulation of local volume fraction and interparticle potential via electric field gradients and surfactant-controlled ionic strength. This platform accesses a range of phase states including liquid-BCC, BCC-FCC, and melting, within a sealed sample. Using real-time confocal microscopy and quantitative structural analysis, we track the evolution of order and capture reversible transitions. Our results highlight the ability to controllably switch between distinct crystal symmetries and phase boundaries in situ, offering a powerful tool for studying nonequilibrium transitions and interface dynamics.