A sensitive orange fluorescent calcium ion indicator for imaging neural activity
Aggarwal et al. develop OCaMP, an orange fluorescent calcium indicator optimised for imaging neural activity at wavelengths above 1000 nm, enabling improved deep tissue imaging and expanded compatibility with existing sensors.
Genetically encoded calcium indicators (GECIs) are vital tools for fluorescence-based visualization of neuronal activity with high spatial and temporal resolution. However, current highest-performance GECIs are predominantly green or red fluorescent, limiting multiplexing options and efficient excitation with fixed-wavelength femtosecond lasers operating at 1030 nm. In an effort to overcome these limitations, we developed OCaMP, an orange fluorescent GECI engineered from O-GECO1 through targeted substitutions to improve calcium affinity while retaining the favorable photophysical properties of mOrange2. OCaMP exhibits improved two-photon cross-section, responsiveness, photostability, and calcium affinity relative to O-GECO1. In cultured neurons, zebrafish, and mouse cortex, OCaMP outperforms the red GECIs jRCaMP1a and jRGECO1a in sensitivity, photostability, and signal-to-noise ratio. Here we show that OCaMP, an orange fluorescent GECI, is a robust tool for high-fidelity neural imaging optimized for wavelengths above 1000 nm and a practical option within the spectral gap between existing green and red GECIs.