Monitoring fluorescent calcium signals in neural cells with organic photodetectors

Optical imaging of biological activities is used to monitor the functional aspects of neural circuits by reporting activities via fluorescent and molecular probes. Current imaging approaches encompass different optical components, inorganic sensors-based detection units and image processing elements, in order to measure optical activities. Inorganic sensors have important drawbacks that create certain difficulties for biological studies, such as high energy consumption and high dark-noise at physiological temperature. Organic photodetectors (OPD) as optical sensors have numerous advantages including high temporal resolution and sensitivity. They have also demonstrated a high performance at both room and relatively high temperatures, without needing cooling systems, unlike inorganic-based sensors. However, their performance in detecting fluorescent biological signals, reported by molecular probes or genetically encoded-indicators, remains to be established. In this work, we fabricated a standalone simple-structure OPD in open-air, with an active layer consisting of eXtra Large bandgap Polymer (XPL) blended with fullerene. We demonstrate the excellent performance of OPDs in the sensing of fluorescent calcium signals reported by chemical and genetically encoded fluorescent calcium indicators from living brain cells with a high temporal resolution. This work paves the way for the integration of OPDs as highly sensitive optical sensors in a broad range of biomedical devices.