Optical MEMS-based fluorescence detection scheme with applications to capillary electrophoresis

A new laser-induced fluorescence (LIF) detection system for capillary electrophoresis (CE) has been designed, built, and tested in this work. Multi-mode optical fibers were incorporated on-chip to couple laser light into the detection area on a borosilicate glass substrate. A metal-semiconductor-metal (MSM) GaAs photodiode was fabricated and mounted over the separation capillary using a new conductive polymer flip-chip bonding approach, replacing the traditional photomultiplier tube (PMT) in the detection scheme. Proper operation of the photodiode after interconnection was verified by directly impinging light into the detector using two laser sources. For both dry and filled channels, several laser source-fluorescent dye combinations were employed in order to generate a fluorescence signal (≈ few nA) detected by the photodiode. We thus demonstrate the feasiblity of integrating optical MEMS into chemical micro total analysis systems (μ-TAS). In the future, this has the potential to improve functionality, throughput, and ease of operation of these 'laboratories on chip'.