In situ molecular self-assembly and sensitive label-free detection of streptavidin via a wavelength interrogated surface plasmon resonance sensor

The sensing sensitivity of wavelength interrogated surface plasmon resonance(WISPR) biosensor is improved by self-assembly of polyelectrolyte multilayer(PEM) film of poly(allylamine hydrochloride)(PAH)/poly(sodium-p-styrenesulfonate)(PSS) on the Au film coated glass chip via the layer-by-layer(LBL) technique. The home-made WISPR with Krestchmann configuration consists of a tungsten-halogen lamp as a photon source and a charge coupled device(CCD) camera as the detector. The influence of PEM film thickness on the optical properties of WISPR biosensors was investigated theoretically and experimentally. In order to achieve higher sensing sensitivity, the PEM film thickness has to be designed as ca.14 nm at an Au layer thickness of 50 nm and an incidental angle of 11.8A degrees. Furthermore, the PEM coated WISPR biosensor can serve as highly sensitive biosensor, in which the biotin-streptavidin is used as bioconjugate pair. After deposition of the PEM film of (biotin/PAH)(PSS/PAH)(3), the modified WISPR biosensor is more sensitive to the low concentration(< 0.01 mg/mL) of streptavidin. And the sensing sensitivity can be further increased by one order of magnitude compared with that of the biotin/PAH coated WISPR biosensor. Thus, such low-cost, high-performance and efficient PEM-coated WISPR biosensors have great potentials in a diverse array of fields such as medical diagnostics, drug screening, food safety analysis, environmental monitoring, and homeland security.