聚合物薄膜对表面等离子体共振光谱的调制

Modulation of polymer thin films on surface plasmon resonance spectroscopy

为了研究聚合物薄膜结构对表面等离子体共振光谱的调制作用,以波长调制型表面等离子体共振（WISPR）分析仪为传感器件,采用层层组装法,分别在传感器芯片表面原位制备聚丙烯胺盐酸盐（PAH）/聚苯乙烯磺酸钠（PSS）及聚二烯丙基二甲基氯化铵（PDDA）/PSS多层薄膜,系统地研究在空气与水条件下这2种薄膜对共振光谱的影响,并通过理论模拟分析其内在规律.实验结果表明：对于致密的PAH/PSS薄膜,WISPR分析仪（检测范围为500~1 000nm）所能测量的最大双层数分别为11（约70nm,水）和45（约158nm,空气）;每一双层PAH/PSS薄膜在水中所引起的波长移动远大于在空气中的波长移动.对于环境响应性比较强的PDDA/PSS薄膜,WISPR分析仪所能测量的最大双层数为5（约128nm,水）,在空气中即使双层数大于40,也有共振峰出现.随着组装层数的增加,PDDA/PSS薄膜引起的共振峰在空气中交替出现,如共振峰分别在双层数4~11、19~26、29~40出现,而在双层数12~18、27~28、46~90处消失,这表明薄膜的增厚使光波导的共振模式从表面等离子体共振模式转变为横磁模的一阶模式与二阶模式.结果表明：通过调节聚合物膜的种类和结构可以有效改变表面等离子体共振光谱的共振波长及共振模式.

Wavelength-interrogated surface plasmon resonance（WISPR）analyzer was used as sensors,and muiltlayer films of polyallylamine hydrochloride（PAH）/poly（sodium-p-styrenesulfonate）（PSS）and poly（diallyl-dimethylammonium chloride）（PDDA）/PSS were in situ fabricated on chips by layer-by-layer selfassembly method,respectively,in order to understand the effect of polymer films structure on the the resonance spectra.The effects of two kinds of polymer films on the resonance spectra of WISPR analyzer in air and in water were systematically investigated.The experimental results were further explained and discussed theoretically.Experimental results showed that,for the dense PAH/PSS film,maximum of bilayer number measured by WISPR analyzer with detection range of 500~1 000 nm was 11（about 70 nm,in water）and 45（about 158 nm,in air）,respectively.Wavelength shift caused by each PAH/PSS was much greater in water than that in air.As for PDDA/PSS thin films which has the relatively strong response to the environment,maximum of bilayer number was 5（about 128 nm,in water）.However,resonance peaks could be observed even if n was more than 40 in air.Moreover,resonance peaks appeared and disappeared alternately with increment of bilayer number.For instance,resonance peaks could be found at 4~11,19~26and 29~40,but no peaks at 12~18,27~28and 46~90.This indicated that the increase in film thickness make the resonance mode of waveguide transformed from surface plasmon resonance mode to first-order mode and second-order mode in transverse magnetic modes.Therefore,resonance wavelength and resonance mode can be effectively changed by adjusting the type and structure of film.