A novel material,Poly(4,4'-diazobenzene-2,5-thiophene) (PDABTh) was synthesized and its third-order optical
nonlinearity was studied using Z-scan technique with 20 ps laser pulse at 1064 nm. We measured the nonlinear refractive
index n<sub>2</sub>=8.4x10-19 m<sup>2</sup>/w with positive sign and nonlinear absorption coefficient β=1.8x10<sup>-12</sup> m/w with reverse saturable
absorption. The molecular second-order hyperpolarizability was calculated to be 4.2x10<sup>-30</sup> esu. The special Π-electron
structure may contribute to these relatively large non-linear optical properties. This suggests that the PDABTh may have
a potential application in nonlinear optical devices.
We report the experimental demonstration of a novel label-free optical immunosensor based on porous silicon
microcavity for the detection of Hydroxysafflor yellow A (HYSA). HYSA antibodies were immobilized into the porous
silicon using standard amino-silane and glutaraldehyde chemistry. We monitor the shift of the resonance dip in the
reflectance spectrum when HYSA-BSA is attached to the porous silicon microcavity. The label-free immunosensor is
simple and exhibit excellent sensitivity for HYSA antibodies with a sensitivity of 0.91nm/ng.