Microfabricated rubber microscope using soft solid immersion lenses
Soft lithography with surface tension control is used to microfabricate extremely efficient solid immersion lenses (SILs) out of rubber elastomeric material for use in microscope type applications. In order to counteract the surface tension of the mold material in a negative mold that causes creep on a positive mold, material such as RTV is partially cured before use in order to allow the reticulation of polymer chains to change the viscosity of the uncured material in a controllable manner. In a specific embodiment, the techniques of soft lithography with surface tension control are used to make molded SILs out of the elastomer polydimethylsiloxane. The lenses achieve an NA in the range of 1.25. The principle of compound lens design is used to make the first compound solid immersion lens, which is corrected for higher light gathering ability and has a calculated NA=1.32. An important application of these lenses is integrated optics for microfluidic devices, specifically in a handheld rubber microscope for microfluidic flow cytometry.
1. A microfabricated microscope comprising:
a first elastomeric solid immersion lens formed of a cured elastomer in a shape greater than a hemisphere and less than a sphere;
a second elastomeric solid immersion lens formed of a cured elastomer in a shape greater than a hemisphere and less than a sphere, said second elastomeric lens being juxtaposed to said first elastomeric solid immersion lens so as to share a common focal point, thereby to yield a numerical aperture greater than 1.
2. The microscope according to claim 1 wherein the first and second elastomeric solid immersion lenses are formed by partially curing an elastomeric material forming a negative mold to a controlled semicured state with surface tension control to establish a selected mold depth and thereby a precise surface plane.
3. The microscope according to claim 1 further including a cytometer at the common focal point.