A bimetallic chip was designed to improve the performance of a surface plasmon resonance (SPR) sensor based on angular interrogation, which demonstrated a relatively low noise level and a high resolution compared with a single gold chip. The calculated refractive index resolution of the bimetallic chip is 5.3 × 10<sup>-7</sup> RIU. In addition, the electric field intensity at the surface of the chip is enhanced. This can guarantee a high sensitivity in a larger sensing region for the measurement of macromolecules, especially in the field of biological sensing. The bimetallic chip SPR sensor was combined with molecularly imprinted polymer (MIP) film as artificial receptor to detect antibiotics. The molecularly imprinted polymer was prepared by photo-polymerization of ciprofloxacin capped with itaconic acid as functional monomer on the bimetallic chip. The thickness of the MIP film was 16 ±2 nm, which was measured with a stylus profiler. The MIP exhibited high selectivity to ciprofloxacin compared with dopamine and penicillin, and the selectivity coefficients of ciprofloxacin，penicillin, and dopamine were 1, 0.22, and 0.19, respectively. The SPR response was proportional to the concentration of ciprofloxacin, the limit of detection (LOD) of which was 0.1 pM or 0.04 ppt，while the LOD for a single gold chip was 0.5 pM. The adsorption of CIP by the MIP bimetallic-coated chip was reversible. Taking the reproducibility of MIP into consideration, a combination of SPR sensing with MIP is a promising method for the detection of ciprofloxacin.
Abstracts A method, based on particle swarm optimization (PSO) and finite-difference time-domain (FDTD) simulation, is proposed to optimize micro-well structural parameter of SPRi sensor with polarization contrast modulation. According to PSO algorithm, these six structural parameters are optimized. Following that, the electromagnetic field characteristics of the gold micro-well structure involving the background gold film thickness are simulated and optimized by FDTD. It is proved that the sensitivity of the optimized structure is four times higher than the traditional one, which shows the practicability of the home-built SPRi sensor, in addition, as a result of the high signal-to-noise ratio, the refractive index resolution of the sensor is two order of the magnitude lower. Besides that, optimization algorithm provides a new way for other SPR sensor optimization.