An on-chip spectral surface plasmon resonance (SPR) biosensor with three parallel channels has been built for biomolecule detections. It is capable of updating intensity baselines to suppress errors induced by light source instability. In order to minimize structure and reduce positional regression uncertainty, the scan operations are achieved by timely changing optical media instead of conventional mechanical scan. The detection results of human immunoglobulin G (hIgG) demonstrated that the baseline updating improves the limitation of detection of hIgG concentration from ~86.1 to ~17.4 ng/mL.