Development of long-term implantable luminescent biosensors for subcutaneous oxygen has proved challenging due to difficulties in immobilizing a biocompatible matrix that prevents sensor aggregation yet maintains sufficient concentration for transdermal optical detection. Here, we demonstrate that Pd-porphyrins can be used as PEG crosslinkers to generate a polyamide hydrogel with extreme porphyrin density (~5 mM). Dye aggregation was avoided due to the spatially constraining 3-D mesh formed by the porphyrins themselves. The hydrogel exhibited oxygen-responsive phosphorescence and could be stably implanted subcutaneously in mice for weeks without degradation, bleaching or host rejection. To further facilitate oxygen detection using steady state techniques, we developed an oxygen non-responsive companion hydrogel by blending copper and free base porphyrins to yield intensity-matched luminescence for ratiometric detection.