A novel photodetector integrated microfluidic system for chemiluminescence (CL) detection is reported. The system incorporates a polycarbazole/fullerene photodiode whose optical characteristics (i.e. dark current, external quantum efficiency and photosensitivity) are described here. Using a CL immunoassay for detecting the stress hormone cortisol, the integrated photodetector achieved a detection sensitivity of 1.775 pA × nM(-1) and a detection limit of less than 0.28 nM. The device would be a powerful low-cost alternative to silicon photodiode and photomultiplier tube for bioanalytical assays, with potentially wide-ranging applications within point-of-care diagnostics.