Research on 3D bioprinting of living cells has strong focus on printable biocompatible materials and monitoring of cell growth in printed constructs, while cell metabolism is mostly measured in media surrounding the constructs or by destructive sample analyses. Bioprinting is combined with online imaging of O₂ by functionalizing a hydrogel bioink via addition of luminescent optical sensor nanoparticles. Rheological properties of the bioink enable 3D printing of hydrogel layers with uniform response to O₂ concentration. Co-immobilization of sensor nanoparticles with green microalgae and/or mesenchymal stem cells does not affect cell viability over several days. Interference from microalgal autofluorescence on the O₂ imaging is negligible, and no leakage or photobleaching of nanoparticles is observed over 2–3 days. Oxygen dynamics due to respiration and photosynthesis of cells can be imaged online and the metabolic activity of different cell types can be discriminated in intact 3D structures. Bioinks containing chemical sensor particles enable noninvasive mapping of cell metabolism and spatiotemporal dynamics of their chemical microenvironment in 3D-printed structures. This major advance now facilitates rapid evaluation of cell activity in printed constructs as a function of structural complexity, metabolic interactions in mixed species bioprints, and in response to external incubation conditions.