An integrated hybrid interference and absorption filter for fluorescence detection in lab-on-a-chip devices

We present a hybrid optical filter design that combines interference and absorbing components for enhanced fluorescence detection in miniaturized highly-integrated lab-on-a-chip devices. The filter is designed in such a way that the advantages of each technology are used to offset the disadvantages of the other. The filter is fabricated with microfabrication compatible processes and materials for monolithic integration with microelectronics and microfluidics devices. The particular embodiment of the filter described herein is designed to discriminate fluorescence emission at 650 nm from excitation at 532 nm. The 9-layer interference filter component is fabricated with alternating TiO₂ and SiO₂ thin-film layers and has an attenuation of −12.6 dB at 532 nm and −0.76 dB at 650 nm. The absorbing filter component is fabricated using a dyed photopolymer (KMPR + Orasol Red) having an attenuation of −32.6 dB at 532 nm and −1.28 dB at 650 nm. The total rejection ratio of the hybrid filter is 43 dB. The filter exhibits very low autofluorescence and performs equally well at off-axis incidence angles.