Fig. 1.

Design of a microfabricated probe. a) Zemax simulation of the optical pathway of the probe coupled to a microfluidic system. The optics include mirrors (M) and lenses (L), which are designed to focus 100 µm below the coverslip. Fiber 1 is used for guiding excitation (Ex.) light from a light source, which corresponds to 90° incidence, and Fiber 2 is used for guiding emitted light (Em.) to a detector, which corresponds to 65° incidence (° incidence= angle at which the light ray strike the sample surface. L1 and M1 reflect and focus excitation light from Fiber1 onto a sample in a microfluidic chip. L2 and M2 gather and focus the emitted light to Fiber 2. b) Drawing of a mold used to fabricate the PDMS probes. Mold is made from SU-8 photoresist on a Si substrate. The inset shows a cross-sectional view of the mold with fiber optic inserted. The mold is fabricated from 3-layers of SU-8. The drawings are color-coded by layer thickness. The blue layer (#1) is the thinnest and serves to hold the fibers at the proper height like “skids”. The green layer (#2) consists of the posts for guiding and holding the fiber in place. The green layer also creates the optics on the probe tip. The red layer (#3) creates the outer boundary of the mold and therefore defines the overall probe size. Optical fibers are inserted to act as part of the mold and create a defined space for the fibers. The optical fibers are butted to the optical lenses. c) Drawing (left) and microphotograph (right) of PDMS probe created using mold in Figure 1b. The probe includes 2 optical fibers which are inserted through the guide created by the molding process. Optical components formed by air gaps (white-text label) created from the mold. The final overall probe dimensions are 1.1 mm wide × 0.52 mm thick.