No abstract

12Cardiac regeneration and stem cell therapies depend critically on the ability to locally resolve the 13 contractile properties of heart tissue 1,2 . Current regeneration approaches explore the growth of 14 cardiac tissue in vitro and the injection of stem cell-derived cardiomyocytes 3-6 (CMs) but scientists 15 struggle with low engraftment rates and marginal mechanical improvements, leaving the estimated 16 26 million patients suffering from heart failure worldwide without effective therapy 7-9 . One 17 impediment to further progress is the limited ability to functionally monitor injected cells as 18 currently available techniques and probes lack speed and sensitivity as well as single cell specificity. 19 Here, we introduce microscopic whispering gallery mode (WGM) lasers into beating cardiomyocytes 20to realize all-optical recording of transient cardiac contraction profiles with cellular resolution. The 21 brilliant emission and high spectral sensitivity of microlasers to local changes in refractive index 22

Characterizing single cell contractility in the beating heart is strongly limited by light scattering and extreme tissue dynamics. Here, we use tissue-integrated microlasers to measure contractility in live zebrafish and living myocardial slices at a depth several times deeper than multiphoton microscopy-based techniques.

Microscopic whispering gallery mode lasers detect minute changes in cellular refractive index inside individual cardiac cells and in live zebrafish. We show that these signals encode cardiac contractility that can be used for intravital sensing.

Microscopic whispering gallery mode lasers detect minute changes in cellular refractive index inside individual cardiac cells and in live zebrafish. We show that these signals encode cardiac contractility that can be used for intravital sensing.