Ruach-Nir Irit, Bendikov Tatyana A, Doron-Mor Ilanit, Barkay Zahava, Vaskevich Alexander, Rubinstein Israel
Department of Materials and Interfaces, Weizmann Institute of Science, Rehovot 76100, Israel.
J Am Chem Soc. 2007 Jan 10;129(1):84-92. doi: 10.1021/ja064919f.
Ultrathin gold films prepared by evaporation of sub-percolation layers (typically up to 10 nm nominal thickness) onto transparent substrates form arrays of well-defined metal islands. Such films display a characteristic surface plasmon (SP) absorption band, conveniently measured by transmission spectroscopy. The SP band intensity and position are sensitive to the film morphology (island shape and inter-island separation) and the effective dielectric constant of the surrounding medium. The latter has been exploited for chemical and biological sensing in the transmission localized surface plasmon resonance (T-LSPR) mode. A major concern in the development of T-LSPR sensors based on Au island films is instability, manifested as change in the SP absorbance following immersion in organic solvents and aqueous solutions. The latter may present a problem in the use of Au island-based transducers for biological sensing, usually carried out in aqueous media. Here, we describe a facile method for stabilizing Au island films while maintaining a high sensitivity of the SP absorbance to analyte binding. Stabilization is achieved by coating the Au islands with an ultrathin silica layer, ca. 1.5 nm thick, deposited by a sol-gel procedure on an intermediate mercaptosilane monolayer. The silica coating is prepared using a modified literature procedure, where a change in the reaction conditions from room temperature to 90 degrees C shortened the deposition time from days to hours. The system was characterized by UV-vis spectroscopy, ellipsometry, XPS, HRSEM, AFM, and cyclic voltammetry. The ultrathin silica coating stabilizes the optical properties of the Au island films toward immersion in water, phosphate buffer saline (PBS), and various organic solvents, thus providing proper conditions where the optical response is sensitive only to changes in the effective dielectric constant of the immediate environment. The silica layer is thin enough to afford high T-LSPR sensitivity, while the hydroxyl groups on its surface enable chemical modification for binding of receptor molecules. The use of silica-encapsulated Au island films as a stable and effective platform for T-LSPR sensing is demonstrated.
通过将亚渗流层（通常名义厚度可达10纳米）蒸发到透明基板上制备的超薄金膜形成了阵列明确的金属岛。此类薄膜呈现出特征性的表面等离子体（SP）吸收带，可通过透射光谱方便地进行测量。SP带的强度和位置对薄膜形态（岛的形状和岛间间距）以及周围介质的有效介电常数敏感。后者已被用于透射局域表面等离子体共振（T-LSPR）模式下的化学和生物传感。基于金岛薄膜的T-LSPR传感器开发中的一个主要问题是不稳定性，表现为浸入有机溶剂和水溶液后SP吸光度的变化。后者可能会给通常在水性介质中进行的基于金岛的生物传感换能器的使用带来问题。在此，我们描述了一种简便的方法来稳定金岛薄膜，同时保持SP吸光度对分析物结合的高灵敏度。通过用约1.5纳米厚的超薄二氧化硅层涂覆金岛来实现稳定化，该二氧化硅层通过溶胶 - 凝胶法沉积在中间的巯基硅烷单层上。二氧化硅涂层采用改进的文献方法制备，其中反应条件从室温变为90摄氏度将沉积时间从数天缩短至数小时。该系统通过紫外 - 可见光谱、椭偏仪、X射线光电子能谱、高分辨率扫描电子显微镜、原子力显微镜和循环伏安法进行表征。超薄二氧化硅涂层使金岛薄膜在浸入水、磷酸盐缓冲盐水（PBS）和各种有机溶剂时的光学性质稳定，从而提供了光学响应仅对紧邻环境的有效介电常数变化敏感的合适条件。二氧化硅层足够薄以提供高T-LSPR灵敏度，而其表面的羟基能够进行化学修饰以结合受体分子。展示了使用二氧化硅封装的金岛薄膜作为T-LSPR传感的稳定且有效平台。
