Integrated Nanophotonic Excitation and Detection of Fluorescent Microparticles

Biological microentities, such as cells and bacteria, are often detected and identified by bulky optical setups such as fluorescent microscopes and flow cytometers. Integrated photonics provides the prospect of dramatically miniaturizing these setups, enabling highly parallelized on-chip detection. In this work we designed, fabricated, and characterized a SiN photonic circuit for fluorescence detection of microentities. A tailored diffraction grating excites fluorescent particles, whose emitted light is collected in a single-mode waveguide by a second neighboring diffraction grating. Both fluorescent polystyrene microparticles and labeled peripheral blood mononuclear cells were detected in a microfluidic channel integrated on top of the waveguide circuit. We quantified both numerically and experimentally the efficiency of this grating system and obtained a good agreement. The presented on-chip fluorescent detection structure and the obtained results will strongly contribute to the development of on-chip cytometry and spectroscopy applications.