Surface-enhanced Raman spectroscopy for trace arsenic detection in contaminated water
Surface-enhanced Raman spectroscopy for trace arsenic detection in contaminated water
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DOI：
10.1002/anie.200800776
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发表时间：
2008-01-01
影响因子：
16.6
通讯作者：
Yang, Peidong
中科院分区：
文献类型：
--
作者：
Mulvihill, Martin;Tao, Andrea;Yang, Peidong
孟加拉国、印度和中国部分地区饮用水的低水平砷污染构成了一场国际公共卫生危机，仅在孟加拉国就有30多万人死于慢性中毒。1993年，世界卫生组织将地下水中砷的最高含量暂定为10 ppb（0.01 mg LH 4 N1）。[1]然而，暴露于这些浓度的砷仍然会导致皮肤癌、肺癌、膀胱癌和肾癌的发病率增加。[1]新技术允许可靠地检测低于10 ppb的砷，应该鼓励更严格的标准。目前的实验室分析技术（如电感耦合等离子体质谱、原子荧光光谱、高效液相色谱-质谱）允许在这些水平上进行检测，但发展中国家既不容易获得这些技术，也不能进行现场检测。[2，3]已审查了现场兼容技术的现状，仍有很大的改进余地。[3，4]即使改进当前的化学现场测试以满足这些标准，也没有可以区分砷物质氧化状态的化学指示剂的例子。对于接触研究，这方面的知识对于毒理学、补救和监测当地人群的影响是必要的。通过开发一种用于表面增强拉曼光谱（Sers）的高活性基底，并与便携式拉曼技术结合使用，[5]这些挑战中的许多都可以克服。自从20世纪70年代后期发现Sers以来，人们一直在不断地推动使纳米结构表面附近的分子的拉曼信号最大化。当传导电子的集体振荡与入射光同相共振时，金属表面附近的电场的强烈局部放大导致Sers增强。纳米结构的大小、形状和接近程度都会影响局部表面等离子体激元（LSP）的频率和幅度，[6，7]因此直接影响所表现出的拉曼增强程度。已经使用实验技术直接观察到LSP，例如扫描近场[8]和TEM相关暗场[9]显微镜。这些实验，沿着更传统的光散射技术，证明了尺寸和形状对LSP的巨大影响。[7]最近对几乎接触的纳米结构之间的电磁耦合的研究表明，这种集体效应可以激发导致更高电磁增强的LSP。[10-13]虽然众所周知银显示出最强的等离子体响应，[7]金通常用于传感应用，因为它的化学稳定性和与许多激光激发波长的兼容性。[14]对于我们Sers传感器，我们引入了两个关键特性，可以在典型的传感条件下实现更好的分析能力。首先，利用LB组装法制备了银纳米晶体的密集阵列。这些紧密堆积的单层表现出宽带散射分布，使它们与许多不同的激发波长兼容。[13]第二个关键特征是吸附聚合物的银颗粒的表面钝化。表面吸附的聚（乙烯基吡咯烷酮）（PVP）具有双重目的：它的功能作为钝化配体在合成过程中，它稳定的银颗粒氧化，同时仍然促进银和砷酸盐之间的相互作用在传感实验。PVP涂层使这些银纳米结构比其他钝化配体在更长的时间内对空气和水稳定。
Low-level arsenic contamination of drinking water in Bangladesh, India, and parts of China presents an international public health crisis, with over 300000 deaths attributed to chronic poisoning in Bangladesh alone. In 1993, the World Health Organization set a provisional guideline of 10 ppb (0.01 mg LÀ1) for maximum arsenic content in groundwater.[1] However, exposure to arsenic at these concentrations still results in increased rates of skin, lung, urinary bladder, and kidney cancer.[1] New technologies allowing reliable detection of arsenic below 10 ppb should instigate a stricter standard. Current technologies for laboratory analysis (eg inductively coupled plasma (ICP) MS, atomic fluorescence spectroscopy (AFS), HPLC-MS) allow detection at these levels, but they are neither readily available in developing countries nor capable of on-site field detection.[2, 3] The current state of field-compatible technologies has been reviewed, and there remains significant room for improvement.[3, 4] Even if current chemical field tests are improved to meet these standards, there are no examples of chemical indicators that can distinguish the oxidation state of the arsenic species. For exposure studies, this knowledge is necessary for toxicology, remediation, and monitoring of the effects within the local populations. By developing a highly active substrate for surface-enhanced Raman spectroscopy (SERS) that can be used in conjunction with portable Raman technology,[5] many of these challenges can be surmounted. Since the discovery of SERS in the late 1970s there has been a continual push to maximize the Raman signal for molecules near nanostructured surfaces. SERS enhancement results from an intense local amplification of the electric field near a metal surface when collective oscillations of conduction electrons resonate in phase with the incident light. The size, shape, and proximity of nanostructures all affect the frequency and magnitude of the localized surface plasmons (LSPs),[6, 7] thus directly influencing the degree of Raman enhancement exhibited. LSPs have been directly observed using experimental techniques such as scanning near field [8] and TEM-correlated dark field [9] microscopy. These experiments, along with more conventional light-scattering techniques, demonstrate the dramatic effects that size and shape have on the LSPs.[7] Recent studies on electromagnetic coupling between nanostructures that are nearly touching indicate that such collective effects can excite LSPs that lead to even higher electromagnetic enhancement.[10–13] Although it is widely known that silver shows the strongest plasmonic response,[7] gold is often used for sensing applications because of its chemical stability and compatibility with many laser excitation wavelengths.[14] For our SERS sensor, we have introduced two key features that lead to better analytical capability under typical sensing conditions. First, dense arrays of silver nanocrystals are fabricated using Langmuir–Blodgett (LB) assembly. These close-packed monolayers exhibit broadband scattering profiles, making them compatible with many different excitation wavelengths.[13] The second key feature is the surface passivation of the silver particles with adsorbed polymer. Surface-adsorbed poly (vinyl pyrrolidone)(PVP) serves dual purposes: it functions as the passivating ligand during nanocrystal synthesis, and it stabilizes the silver particles to oxidation while still facilitating interaction between silver and arsenate during sensing experiments. The PVP coating makes these silver nanostructures air-and water-stable over much longer periods then other passivating ligands.The synthesis of the …