Sensing Modalities Across the Biological Hierarchy From Single Cells to Organs for Cellular Efflux Monitoring

ABSTRACT Cellular efflux provides a direct readout of homeostasis, metabolic activity, and pathological changes. As biological systems progress from single cells to 2D planar models, 3D constructs, and whole organs, rising biological complexity reshapes efflux behavior through shifts in ionic fluctuations, diffusion patterns, matrix composition, and tissue mechanics. Because each level introduces distinct efflux information that reflects individual cell behavior, collective signaling, or integrated physiological activity, dedicated sensing strategies are required to capture these signals with fidelity across the full hierarchy. In this review, we outline recent sensing strategies and interface designs that enable efflux monitoring across these biological hierarchies, and then describe how these concepts emerge in the major transducing modalities, including optical, electrochemical, and electrical approaches that define which efflux signatures can be measured. We highlight implementations that use photonic nanomaterials, nanostructured electrodes, and field effect architectures to sustain quantitative readout in increasingly complex microenvironments. We further discuss how diffusion behavior, reaction kinetics, and sensor response characteristics shape efflux feature extraction across scales, and highlight the key directions this field must advance toward. Combined with advances in materials and interface engineering, these developments establish efflux sensing as a central analytical framework for tissue engineering, drug evaluation, and bioprocess control.