External random factors have a great influence on the fabrication of accurate photonic crystal, especially porous silicon-based photonic crystals. Compared with the binary photonic crystal, polybasic structure photonic crystal shows more stability and smaller effect of the random fluctuation. In this paper, we have fabricated a novel simple porous silicon polybasic Bragg's mirror combined with excellent specific antigen-antibody inmunoreaction as an immunosensor for determining Hydroxysafflor yellow A (HSYA), which is the main chemical component of Carthamus tinctorius L. The binding of HSYA and the polyclonal anti-HSYA antibodies causes red shifts in the reflection spectrum of the sensor, and the red shift was proportional to the HSYA concentration with linear relationship ranging from 1 to 3 mu g mL(-1) with a detection limit of 0.78 mu g mL(-1). Importantly, this research offers hope for development of a commercial porous silicon-based immunosensor for component determination of C. tinctorius L. or other antigens. (C) 2010 Elsevier B.V. All rights reserved.