An optical biosensor based on waveguided metallic photonic crystals (MPCs) is reported for the sensitive testing of biomolecular interactions, which provides practical approaches for the label-free detection of specific bioreactions. The enhancement of the sensitivity or the amplification of the sensor signal by the coupling between the waveguide resonance mode and particle-plasmon resonance (PPR) breaks through the bottle-neck of the intrinsic response sensitivity defined by the spectral shift of the PPR. The success of this sensor is demonstrated by sensing the specific reaction between the HIV-1 capsid protein (p24) antigen and the monoclonal anti-p24 antibody, where the dynamics of the bioreactions can be recorded with a potentially high time resolution. This new sensor stands out due to its compact design and its new physics, compared with conventional devices, its simple operation, the simple fabrication of the MPC chip and the low cost of the whole system.