Micro-Opto-Electro-Mechanical-Systems (MOEMS) become widely accepted in sensor technology. In this context planar emitter-receiverdevices with silicon photodiodes vertical emitting laser, and integrated micro-optics to measure the concentration of particles in fluids are presented. Two different variations of the sensor, with and without micro-optics to shape the primary light, are compared. The arrangements with integrated micro-optics achieve a clearly increased sensitivity. This is demonstrated by experiments.