Surface-enhanced Raman spectroscopy as a probe of competitive binding by anions to citrate-reduced silver colloids
Surface-enhanced Raman spectroscopy as a probe of competitive binding by anions to citrate-reduced silver colloids
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DOI：
10.1021/jp052184f
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发表时间：
2005-08-25
影响因子：
2.9
通讯作者：
Sirimuthu, NMS
中科院分区：
文献类型：
--
作者：
Bell, SEJ;Sirimuthu, NMS
柠檬酸盐还原的银胶体（CRSC）被广泛用于阳离子的表面增强拉曼散射（Sers）研究，但通常被发现对于阴离子的检测是无效的，除非它们被给予它们带正电荷的涂层的化合物处理。在这项工作中，通过用不与银表面强烈结合的聚集剂处理来产生适合于检测阴离子的CRSC。在这些条件下，决定增加的阴离子的主要因素是它们取代已经存在的任何阴离子的能力。在CRSC的情况下，当胶体与硫酸盐聚集时，观察到残留的柠檬酸盐，因为硫酸盐和残留的硝酸盐都没有取代它。在添加更强结合的阴离子（如卤化物）时，柠檬酸盐被取代，并且出现添加的分析物的条带，允许它们被检测而不需要创建带正电的涂层。结果发现，阴离子的相对亲和力，确定由Sers监测的位移实验，遵循其银盐的溶解度，大概是因为这两个属性是强烈依赖于Ag-阴离子键的强度。相对亲和力决定了哪些阴离子可以在其他阴离子存在的情况下被检测到;硝酸盐，硫酸盐和高氯酸盐在系列中低于柠檬酸盐，因此没有观察到。置换实验表明，吡啶二羧酸（DPA）与Cl-具有相似（较强）的结合，但它们可以依次被亲和力最高、溶解度最低的Br-和I-置换。该模型允许广泛的以前的观察结果被合理化，并允许实验条件适合于检测特定的新的分析物被设计在合理的原则。
Citrate-reduced silver colloids (CRSCs) are used extensively for surface-enhanced Raman scattering (SERS) studies of cations but are typically found to be ineffective for detection of anions unless they are treated with compounds that give them positively charged coatings. In this work CRSCs which were suitable for detection of anions were generated by treatment with aggregating agents that did not bind strongly to the silver surface. Under these conditions the major factor determining the enhancement of added anions was their ability to displace whatever anions were already present. In the case of CRSCs, residual citrate was observed when the colloids were aggregated with sulfate salts, since neither sulfate nor the residual nitrate displaced it. On addition of more strongly binding anions, such as halides, the citrate was displaced and the bands of the added analyte appeared, allowing them to be detected without the need for creation of positively charged coatings. It was found that the relative affinities of the anions, as determined by displacement experiments monitored by SERS, followed the solubilities of their silver salts, presumably because both properties are strongly dependent on the strength of the Ag-anion bonds. The relative affinities determine which anions can be detected in the presence of which others; nitrate, sulfate, and perchlorate are lower in the series than citrate and so are not observed. Displacement experiments show that dipicolinic acid (DPA) and Cl- have similar (stronger) binding, but they can be displaced in turn by Br- and I-, which have the highest affinity and lowest solubility. This model allows a broad range of previous observations to be rationalized and allows the experimental conditions suitable for detection of particular new analytes to be designed on rational principles.