University of Delaware, Department of Chemistry and Biochemistry, Newark, DE 19716, United States.
Talanta. 2011 Sep 15;85(3):1369-75. doi: 10.1016/j.talanta.2011.06.020. Epub 2011 Jun 17.
Surface plasmon resonance spectroscopy is sensitive to near-surface (<300 nm) chemical and physical events that result in refractive index changes. The non-specific nature of the stimulus implies that chemical selectivity in SPR sensing configurations entirely relies upon the chemical recognition scheme employed. Biosensing applications commonly use surface layers composed of antibodies or enzymes for biomolecular recognition. Monitoring of volatile compounds with SPR spectroscopy, however, has not been widely discussed due to the difficulty in selectively responding to small molecules (<100 Da) in addition to the limited refractive index changes resulting from the interaction between the plasmon wave and volatile compounds. Different strategies explored thus far for sensing of small molecules have relied on optical and electrical changes of the recognition layer upon exposure to the analyte, yielding an indirect measurement. Examples of coatings used for gas-phase sensing with SPR include conducting metal oxides, polymers and organometallic dyes. Electrically conducting polymers, like polyaniline and polypyrrole, display dramatic conductivity changes in the presence of certain compounds. This property has resulted in their routine incorporation into different sensing schemes. However, application of electrically conducting polymers to SPR gas-phase sensing has been limited to a few examples, despite encouraging results. The emeraldine salt form of polyaniline (PAni) demonstrates a decreased electrical conductivity correlated to NH(3) concentration. In this contribution, PAni doped with camphorsulfonic acid (PAni-CSA) was applied to gas-phase sensing of NH(3) by way of SPR spectroscopy. Spectroscopic ellipsometry was used to determine the optical constants (n and k) for emeraldine salt and emeraldine base forms of PAni, confirming the wavelength-dependent response observed via SPR. The analytical performance of the coatings show that a limit of detection of 32 ppm NH(3) based on precision of the mass-flow controllers used and an estimated method limit of detection of ∼0.2 ppm based on three standard deviations of the blank. This is directly comparable to other, more established sensing architectures.
表面等离子体共振光谱学对近表面（<300nm）的化学和物理事件敏感，这些事件会导致折射率变化。刺激的非特异性意味着 SPR 传感配置中的化学选择性完全依赖于所采用的化学识别方案。生物传感应用通常使用由抗体或酶组成的表面层进行生物分子识别。然而，由于SPR 光谱法难以选择性地响应小分子（<100Da），以及等离子体波与挥发性化合物相互作用导致的折射率变化有限，SPR 光谱法对挥发性化合物的监测尚未得到广泛讨论。迄今为止，为了检测小分子而探索的不同策略依赖于暴露于分析物时识别层的光学和电学变化，从而得到间接测量。SPR 用于气相传感的涂层示例包括导电金属氧化物、聚合物和有机金属染料。电导率聚合物，如聚苯胺和聚吡咯，在存在某些化合物时表现出显著的电导率变化。这一特性导致它们被常规地纳入不同的传感方案中。然而，尽管有令人鼓舞的结果，但电导率聚合物在 SPR 气相传感中的应用仅限于少数几个例子。聚苯胺的emeraldine 盐形式（PAni）表现出与 NH3 浓度相关的电导率降低。在本研究中，通过表面等离子体共振光谱学，将樟脑磺酸掺杂的聚苯胺（PAni-CSA）应用于 NH3 的气相传感。光谱椭圆光度法用于确定 emeraldine 盐和 PAni 的 emeraldine 碱形式的光学常数（n 和 k），证实了通过 SPR 观察到的波长依赖性响应。涂层的分析性能表明，基于所使用的质量流量控制器的精度，NH3 的检出限为 32ppm，基于空白的三个标准偏差估计的方法检出限约为 0.2ppm。这与其他更成熟的传感架构直接可比。
