Recent advances in single-photon avalanche diode (SPAD) cameras, with higher detection efficiencies, fill factors, and pixel densities, have opened new frontiers in fluorescence lifetime imaging microscopy (FLIM). FLIM offers a quantitative, motion-robust view into cellular physiology by reporting fluorescence lifetimes rather than intensities, providing intrinsic calibration of molecular states. In cardiac research, this capability is transformative: conventional electrophysiological techniques such as patch clamp or multi-electrode arrays are either invasive, low-throughput, or compromised by motion artifacts, limiting their utility in live, contracting cells. Likewise, conventional FLIM systems are too slow to resolve fast events such as action potentials (APs) or calcium (Ca²⁺) transients—key to understanding excitation-contraction coupling and the mechanisms underlying cardiovascular disease.
We have recently demonstrated a breakthrough in this space with fluorescence-lifetime optical electrophysiology (FLOE) [1], employing a dual-gated, 500 × 500 SPAD array (SwissSPAD3) [2] to capture lifetime-resolved voltage and calcium signals at 192 frames per second across beating cardiomyocyte monolayers. FLOE enables calibrated mapping of membrane voltage and Ca²⁺ concentrations in contracting cells without pharmacological uncouplers, treating natural movement as meaningful physiological data rather than a confound. This establishes a new paradigm for quantitative, high-speed optical electrophysiology.
This PhD project will take FLOE to the next level by extending both instrumentation and applications. On the instrumentation side, the doctoral researcher will develop a hybrid photometry system that integrates intensity-based detection via photomultiplier tubes with lifetime-resolved imaging from a SPAD camera. This dual-modality approach will combine the photon efficiency and dynamic range of conventional detectors with the temporal precision of SPADs, pushing towards kilohertz-rate acquisition with picosecond timing. The project will also explore computational approaches (such as temporal cleaning and Poisson-limited lifetime estimation) to enhance resolution and reduce noise.
On the application side, the student will use this next-generation FLIM platform to interrogate excitation-contraction coupling in both human induced pluripotent stem cell (iPSC)-derived cardiomyocytes and ex-vivo rabbit heart tissue. Using voltage- and calcium-sensitive lifetime dyes, the project will capture absolute AP and Ca²⁺ dynamics across fields of view spanning hundreds of microns, revealing emergent phenomena such as late-phase repolarization. Calibration protocols established in our preliminary work will allow translation of fluorescence lifetime signals into absolute physiological values, enabling rigorous quantitative analysis.
The project will be carried out in close collaboration with Clyde Biosciences, an industrial partner developing cardiotoxicity assays. By advancing motion-robust, high-throughput optical assays, this work has strong translational potential for cardiotoxicity screening, regenerative medicine, and drug discovery. More broadly, the methodological advances in high-speed FLIM will extend to neuroscience, organoid systems, and mechanobiology, where dynamic processes unfold too rapidly for conventional imaging approaches.
This PhD will therefore not only deliver a unique optical technology but also establish its biological relevance in one of the most pressing health contexts: cardiovascular disease, the leading cause of mortality worldwide. The student will gain expertise in ultrafast optics, advanced imaging, and quantitative physiology, while contributing to a paradigm shift in how we study excitable systems in their native, contractile state.