Ultra-high integrated silicon nitride fluorescence excitation chip for point-to-point excitation of biofluorescence signals

Current research is focused on the miniaturization and integration of detection devices for biological targets in order to adapt to outdoor and emergency field settings, as well as to enhance the flexibility and practicality of detection. This study proposes an ultra-high integrated silicon nitride fluorescence excitation chip for point-to-point excitation of biological fluorescence signals. By employing the finite-difference time-domain(FDTD) method and utilizing silicon nitride as the functional material, a visible light fluorescence excitation chip operating at the wavelength of 645nm was designed and fabricated. The chip is composed of an input grating coupler, multiple multimode interferometers, and output grating couplers. A grating array containing 2016 excitation points is constructed cascading multiple multimode interference splitters and connecting excitation gratings at the terminals. The single grating coupling efficiency of the chip is 30% with a total excitation light area of 4×4mm² and an emitted light angle of around 80 degrees. By adjusting the positions of different output grating couplers, the chip can adapt to excitation requirements at different locations, making it suitable for various applications such as fluorescence quantitative polymerase chain reaction(PCR) and digital PCR. With the help of microfluidic chambers and a photodetector, the chip successfully achieved the detection limit of 0.5 µmol/L Cyanine 5(Cy5) fluorescent reagent solution, which is sufficient for direct detection of PCR fluorescence signals.