Spectrally filtered passive Si photodiode array for on-chip fluorescence imaging of intracellular calcium dynamics

On-chip fluorescence imaging devices are recognized for their miniaturized and implantable nature that can benefit the study of intracellular dynamics at a variety of settings. However, it is challenging to integrate a spectral filter onto such devices (to block the excitation light) that has similar performance to the state-of-the-art emission filters used in fluorescence microscopes. In this work, we report a 100%-yield, spectrally filtered passive Si photodiode array designed for on-chip fluorescence imaging of intracellular Ca²⁺ dynamics. Coated with a spectral filter layer that has a high extinction ratio (>10³), our array features high wavelength selectivity (>10²), high linearity (R² > 0.98), and low detection limit (45.1 μW 640/30 nm light). Employing fluorescence microscopy as the reference, we demonstrate that our array can conduct on-chip Ca²⁺ imaging in C2C12 cells that were chemically triggered to increase their intracellular Ca²⁺ levels. Importantly, our array-level data qualitatively captured the static fluorescence image of the cells and the intracellular Ca²⁺ dynamics, both of which are correlated with the microscope-collected data. Our results suggest the possible use of the spectrally filtered array towards a miniaturized on-chip fluorescence imaging device, which may open up new opportunities in tissue-level pharmaceutical screening and fundamental studies on cell networks.