Real‐Time Spatiotemporal Measurement of Extracellular Signaling Molecules Using an Aptamer Switch‐Conjugated Hydrogel Matrix

Cells rely on secreted signaling molecules to coordinate essential biological functions including development, metabolism, and immunity. Unfortunately, such signaling processes remain difficult to measure with sufficient chemical specificity and temporal resolution. To address this need, an aptamer‐conjugated hydrogel matrix that enables continuous fluorescent measurement of specific secreted analytes – in two dimensions, in real‐time is developed. As a proof of concept, real‐time imaging of inter‐cellular cyclic adenosine 3',5'‐monophosphate (cAMP) signals in Dictyostelium discoideum amoeba cells is performed. A set of aptamer switches that generate a rapid and reversible change in fluorescence in response to cAMP signals is engineered. By combining multiple switches with different dynamic ranges, measure cAMP concentrations spanning three orders of magnitude in a single experiment can be measured. These sensors are embedded within a biocompatible hydrogel on which cells are cultured and their cAMP secretions can be imaged using fluorescent microscopy. Using this aptamer‐hydrogel material system, the first direct measurements of oscillatory cAMP signaling that correlate closely with previous indirect measurements are achieved. Using different aptamer switches, this approach can be generalized for measuring other secreted molecules to directly visualize diverse extracellular signaling processes and the biological effects that they trigger in recipient cells. Cells communicate through secreted biomolecules, however, there are few tools to directly record these signals. Embedding fluorescent aptamer sensors within a biocompatible hydrogel enables tracking of cell‐to‐cell signaling with molecular specificity and high temporal resolution, demonstrated by monitoring of the molecular signals driving slime mold cell migration. This technology shall be applicable for studying a wide range of biological systems.