The aim of POSEIDON is to develop a radically new bottom-up approach toward multi-scale, on-chip self-assembly of active colloids based on low-cost colloid technology. For the first time this encompasses the entire process chain of computer-aided design, controlled synthesis, hierarchical assembly, optoelectronic integration and device fabrication. By controlling and designing self-assembly processes directly on a device, addressing length scales from nm to 100’s of μm simultaneously, the POSEIDON approach allows to fabricate functional nanophotonic components with 3D, single-nm resolution integrated into complex PICs. The goal of POSEIDON is to develop electrically pumped light sources that can be monolithically integrated into the back end of CMOS chips. So far, the key bottleneck that is holding back integrated photonic applications is the lack of a monolithically integrable, mass-manufacturable light source because Si does not emit light efficiently. All top-down approaches of heterogeneous integration of III-V light sources are costly, have low integration density and low throughput, creating massive cost and complexity barriers for the application and commercialization of Si photonics in general and PICs in particular. Packaging costs including fibers for external light sources currently constitute around 80% of the total cost of Si photonic PICs and are hence a showstopper for many applications. The breakthrough targeted by POSEIDON overcomes the limitations of top-down PIC fabrication and tears down the massive cost and complexity barriers initially mentioned. The developed technology will enable further applications from optical computing, to quantum optics for ultra-secure communications, to personalized health monitoring devices able to detect molecules at ultralow concentrations. The aim of POSEIDON is to develop a radically new approach toward multi-length-scale, on-chip assembly of active colloids for the creation of on-chip light sources.