Miniaturized fluorescence measurement system with novel dichroic beam splitter cubes with 3 by 3 by 3 cubic millimeters and special optical direction-selective filters

We present highly miniaturized optical and electronic components for a two-channel fluorimeter with pin photodiodes with a very small detection limit (with an excitation of 100 μW and 590 nm, we detect one nW at 650 nm). One potential application lies in continuous monitoring of blood glucose levels. In a first step, novel dichroic beam splitter cubes made of fused silica with an edge length of 3 mm were developed. The diagonally dividing surface of the cubes was provided with a new dichroic layer system using the PARMS (Plasma Assisted Reactive Magnetron Sputtering) coating technology, which made it possible to achieve an angle of incidence of 45° (the current state of the art is more like 30°). The wavelength ranges are between 560 and 800 nm. In a second step, a special LED lighting unit with dimensions of 4 mm by 6 mm by 5 mm was developed. The angular distribution in the excitation beam that hits a dichroic beam splitter cube is limited to 3 degrees. In addition, very thin optically direction-selective filters have been developed to reduce stray light on the photodiodes. Here, glass substrates with a 100 μm thick Si-layer were used. This silicon layer was structured using inductively coupled plasma etching (ICP). Breakthroughs measuring 40 μm by 40 μm were created with inner walls made of black silicon. The transmission of these filters is 0.4 at angle of incidence at zero degrees and is less than 0.01 at angles of incidence greater than 13°.