A novel immunosensor based on surface plasmon resonance(SPR) has been developed for the recognition of antigen. The sensor was designed on the basis of the fixed angle of incidence and measuring the reflected intensities in a wavelength range of 430―750 nm in real-time. An ultra-bright white light-emitting diode(LED) was used as the light source. Molecular self-assembling in solution was used to form the sensing membrane on gold substrate. It has been seen that the sensitivity of the SPR sensor with 3-mercaptopropionic acid(MPA)/protein A(SPA) sensing membrane is considerably higher than that with MPA or SPA modified sensing membrane. The kinetic processes on the sensing membrane were studied. The human B factor(Bf), an activator of complement 3(C3), was recognized among the other antigens. This sensor can also be used for other antigen/antibody or adaptor/receptor recognition. Under optimized experimental conditions, the sensor has good selectivity, repeatability, and reversibility. A novel immunosensor based on surface plasmon resonance (SPR) has been developed for the recognition of antigen. The sensor was designed on the basis of the fixed angle of incidence and measuring the reflected intensities in a wavelength range of 430-750 nm in real- time. An ultra-bright white light-emitting diode (LED) was used as the light source. Molecular self-assembling in solution was used to form the sensing membrane on gold substrate. It has been seen that the sensitivity of the SPR sensor with The kinetic processes on the sensing membrane were studied. The human B factor (Bf), an activator of complement This sensor can also be used for other antigen / antibody or adapter / receptor recognition. Under optimized experimental conditions, the sensor has good selectivity, repeatability, and reversibility.