Voltage Imaging

Electrical signals help cells communicate and coordinate their activity. Neurons and heart muscle cells are familiar examples, but pancreatic islet cells also rely on changes in membrane voltage. We develop fluorescent probes and imaging methods that make these electrical signals visible, allowing us to watch where they begin, how they spread, and how they relate to other cellular events.

Our hybrid chemigenetic indicators bring together the brightness of synthetic dyes and the targeting specificity of genetically encoded proteins. We attach a dye to a light-sensitive protein called rhodopsin, whose absorption changes with membrane voltage. Through electrochromic Förster resonance energy transfer (eFRET), these changes alter the dye’s brightness, turning voltage fluctuations into optical signals. Our early Flare indicators allowed us to map electrical coupling between cells. We then developed hybrid voltage indicators (HVIs) with an expanded color palette, including far-red probes that can be combined with other fluorescent sensors and light-driven stimulation (Angew. Chem. Int. Ed. Engl., 2018; Nat. Chem., 2021).

Recording for longer brings another challenge: illumination can bleach the probe and damage the cell, changing the very signals we want to measure. By incorporating protective cyclooctatetraene groups into our dyes, we reduced both effects and extended reliable voltage recordings to 30 minutes in cultured neurons (PNAS, 2023).

More recently, we developed HVI⁺ indicators that brighten when cells depolarize. Their lower fluorescence at rest helps reduce background, enabling recordings in neurons, heart muscle cells, and pancreatic islets (Sci. Adv., 2025).

We also build fully genetically encoded indicators, in which a fluorescent protein takes the place of the synthetic dye. Our initial multicolor eFRET sensors offered a choice of colors for watching neurons fire (Nat. Commun., 2014). By improving both the rhodopsin sensor and its fluorescent partner, we developed the red indicators Cepheid1b and Cepheid1s. Their increased sensitivity, brightness, and photostability let us capture both action potentials and smaller voltage fluctuations in brain slices, and examine how electrical activity and calcium signals are coupled in pancreatic islets (Sci. Adv., 2023).

Even a fast probe needs a camera that can keep up. Our imaging methods address the trade-off between recording speed and how much of a sample we can see at once. Precisely timed flashes of light increased the effective acquisition rate fivefold while removing timing artifacts from the camera’s rolling shutter (Chem. Biomed. Imaging, 2023). In collaborative work, we extended kilohertz voltage imaging to larger fields of view using repetitive optical selective exposure (ROSE). We also helped develop a compressive-imaging method that uses the frame-transfer process of an EMCCD camera to visualize action potential propagation with microsecond temporal resolution (Optica, 2025; ACS Photonics, 2026).