Tolerance analysis of a micro-optical detection unit for fluorescence and absorbance measurements in lab-on-a-chip micro-channels for chromatographic applications

The integration of optical components on microfluidic devices is needed for downscaling analytical processes to portable, integrated and low-cost lab-on-a-chip systems for point-of-care applications. We have developed a micro-optical detection unit for both laser induced fluorescence and absorbance analysis in fused silica capillaries for microfluidic chromatographic applications. We present the use of non-sequential ray tracing simulations to design the system and to perform a tolerance analysis to define theoretically for each parameter in the system the acceptable fabrication and alignment errors. The system is prototyped using Deep Proton Writing and characterized by means of an optical non-contact profiler, in order to check for every parameter if the realized alignment and fabrication errors do not exceed the theoretically acceptable tolerance ranges. These measurements show that Deep Proton Writing is appropriate for the fabrication of the designed micro-optical detection system. In addition the tolerance study shows for which parameters the alignment is most critical. Finally we demonstrate by means of optical simulations that the same micro-optical design can be applied in different materials (index of refraction between 1.3 and 1.5) and used for sensing fluorescence of a variety of molecules in a wide spectral window (from 400nm up to 1550nm).