A sensitive orange fluorescent calcium ion indicator for imaging neural activity

Abhi Aggarwal; Heather A. Baker; Céline D. Dürst; I-Wen Chen; Pablo de Chambrier; Carrie Stine; Julia Marie Gonzales; Jonathan S. Marvin; Milène Vandal; Torgny Lundberg; Cherie A. Brown-Panton; Kenryo Sakoi; Ronak H. Patel; Chenger Wang; Frank Visser; Yannick Fouad; Smrithi Sunil; Matthew D. Wiens; Takuya Terai; Kei Takahashi; Roger J. Thompson; Timothy A. Brown; Yusuke Nasu; Minh Dang Nguyen; Grant Robert Gordon; Sarah McFarlane; Kaspar Podgorski; Anthony J. D. G. Holtmaat; Robert E. Campbell; Alexander W. Lohman

doi:10.1038/s41467-026-74553-4

NeuroscienceNature CommunicationsJun 22, 2026

Peer-reviewed journal article

A sensitive orange fluorescent calcium ion indicator for imaging neural activity

Abhi Aggarwal iD, Heather A. Baker iD, Céline D. Dürst iD, I-Wen Chen iD, Pablo de Chambrier, Carrie Stine iD, Julia Marie Gonzales iD, Jonathan S. Marvin iD, Milène Vandal iD, Torgny Lundberg, Cherie A. Brown-Panton, Kenryo Sakoi, Ronak H. Patel iD, Chenger Wang iD, Frank Visser iD, Yannick Fouad, Smrithi Sunil iD, Matthew D. Wiens iD, Takuya Terai iD, Kei Takahashi iD, Roger J. Thompson iD, Timothy A. Brown iD, Yusuke Nasu iD, Minh Dang Nguyen iD, Grant Robert Gordon iD, , Alexander W. Lohman iD

Abstract

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. Here, we introduce OCaMP (also known as O-GECO2), 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, kinetics, and signal-to-noise ratio. These properties establish OCaMP as a robust tool for high-fidelity neural imaging optimized for 1030 nm excitation and a compromise-free option within the spectral gap between existing green and red GECIs.

PDF DOI