An LED-induced fluorescence detection system with integrated on-chip lens based on microfluidic chips technology

Background: The power density of optical excitation on microfluidic chips is attenuated due to the beam divergence of the optical fiber, making it difficult to collect either the emission or scattering light. The excitation power and coupling efficiency can be significantly increased by using an on-chip microlens system with integrated optical fibers, specially designed and simulated to reshape and collect the optical signal within the microfluidic chip. Objective: This article presents research work for designing, fabricating, and testing a type of on-chip microlens. The on-chip microlens was designed by Code V → lens design software, and numerical simulations were conducted to optimize the distance between the optical elements. The air microlens was produced using a direct lithograph of SU-8 photoresist. Results and conclusion: The export light beam could be focused to a very small point to satisfy the requirements of the fluorescence excitation of samples. On the other hand, the detection efficiency could also be increased with the help of the on-chip microlens. The presented fabrication method does not require any assembly process or external driving force. To fabricate a microlens with a different focus, it is only necessary to change the figures on the mask. This technique can be used in a variety of applications as it is possible to produce customized microlens for specific applications.