Plasmonic Interactions in Nano-Structured Voids

我们南安普顿大学的团队正在使用纳米尺度的古老铸造艺术来开发超灵敏探测器，这些探测器正在进行健康筛查和可编程彩色织物的测试。我们的纳米科学家团队已经开发出纳米铸造技术，以制造纳米级的黄金结构，从而能够通过光检测微小数量的分子。美索不达米亚文明用沙子制作模具来铸造熔化的铜。我们使用纳米级塑料球作为模具和电镀技术来构建我们的结构。这些球体悬浮在水中，一滴水在镀金玻璃上蒸发，留下一层球体。然后使用电镀技术在球“模具”周围生长黄金。最后，球被溶解，留下一个带有“纳米盘”和空腔的金金属结构。这些微小的空腔与光的波长相当，因此它们可以捕获光并以非凡的效率集中其能量。集中的能量增强了被称为拉曼散射的现象超过一百万倍，从而能够在非常低的浓度下可靠地检测分子。但是光被困在这些空腔中的确切方式（以一种称为“等离子体”的形式）仍然有些神秘，因为它非常难以预测。我们在这里的项目是了解和开发可以在整个光谱范围内进行颜色调谐的等离子体激元。为此，我们可以对各种金属、腔体形状和外涂层进行研究。有几种应用是有前景的：当激光形式的光聚焦在样品上时，拉曼散射产生一种分子指纹。样品中分子的振动键吸收一些光并将其“散射”，使得从样品发射的光根据存在的分子以特征方式改变颜色。使用拉曼光谱仪测量这种效应，其输出是散射的拉曼光的光谱。然而，问题是拉曼散射非常弱，难以检测，并且其本身在诊断中几乎没有实际用途。我们的金纳米材料放大了拉曼散射，因此即使只有极微量的物质存在，也可以很容易地检测到分子指纹。对同一样品进行重复测量，得到的结果相同，误差在百分之几以内，而以前观察到的结果差异很大。在筛选患者时，这种准确性显然至关重要。灵敏地观察分子有许多应用。了解分子如何与表面结合是揭开催化奥秘的关键（一个数十亿美元的产业）。污染物的环境监测或生物危害检测依赖于这种可能性。使用这种技术对患者的眼泪进行诊断结膜炎，通过节省药物，实验室时间和患者就诊次数，可以在10年内为NHS节省约4.71亿英镑。还有许多其他可能的疾病，包括肝炎，艾滋病，糖尿病和衣原体，都可能在你的眼泪中发现。另一个潜在的应用是生产低成本的太阳能电池，它可以非常薄，并涂在塑料上。使用有机涂层的金纳米腔，光可以被非常有效地吸收并提取能量，但我们必须确定这一过程的有效性。最后一个有趣的可能性是制造色彩强烈的薄膜，但不使用有毒和致癌染料。通过拉伸薄膜，或者将它们连接到电池上，它们的颜色可能会改变。因此，我们计划测试我们的结构对这种新的可调颜色的限制。

The ancient art of casting but at the nano-metre scale is being used by our team at the University of Southampton to develop ultra sensitive detectors which are being tested for health screening, and programmable coloured fabrics. Our team of nano-scientists have developed the technique of nano-casting to make nano scale gold structures that enable detection by light of tiny numbers of molecules. The Mesopotamian civilization made moulds from sand to cast molten copper. We use nano-scale plastic spheres for moulds and electroplating techniques to build up our structures. The spheres are suspended in water, a drop of which is evaporated on gold-coated glass leaving a single layer of spheres. The gold is then grown up around the ball 'mould' using electroplating techniques. Finally the balls are dissolved leaving a gold metal structure with 'nano-dishes' and cavities.It is the optical properties of the structure that are key. The tiny cavities are on the scale of the wavelength of light, so they trap the light and concentrate its energy with extraordinary efficiency. The concentrated energy enhances a phenomenonknown as Raman scattering more than a million-fold enabling the reliable detection of molecules at very low concentrations. But the exact way that light is trapped inside these cavities (in a form called a 'plasmon') is still somewhat mysterious, as it is extremely hard to predict. Our project here is to understand and develop the plasmons which can be colour-tuned over the entire spectrum. To do this we can play tricks with a large variety of metals, cavity shapes, and over-coatings.Several applications are in prospect:Raman scattering produces a kind of molecular fingerprint when light in the form of a laser is focused on a sample. The vibrating bonds of the molecules in the sample absorb some of the light and 'scatter' it so that the light emitted from the sample changes colour in a characteristic way depending on the molecules present. A Raman spectrometer is used to measure this effect with the output being a spectrum of the scattered Raman light. The problem however is that Raman scattering is very weak, hard to detect, and on its own is of little practical use in diagnostics. Our gold nano materials amplify Raman scattering so that the molecular fingerprints can easily be detected even when only tiny traces ofsubstances are present. Repeating measurements on the same sample gives the same results within a few per cent, whereas previously huge variations are observed. Such accuracy is obviously vital when screening patients. There are many applications for seeing molecules sensitively. Understanding how molecules bind to surfaces is key for unraveling the mysteries of catalysis (a multi-billion industry). And environmental monitoring of pollutants or bio-hazard detection rely on such possibilities. Diagnosing conjunctivitis using this technique on tears from patients could save the NHS an estimated 471m over 10 years through savings in drugs, laboratory time and the number of patient visits. And there are many other possible diseases including hepatitis, HIV, diabetes and chlamydia that it might be possible to spot in your tears.Another prospective application is in producing low cost solar cells, which can be extremely thin and coated onto plastics. Using the organically-coated gold nano-cavities, light can potentially be very efficiently absorbed and the energy extracted, but we have to ascertain how effective this process can be made.A final intriguing possibility is in making thin films which are strongly coloured, but don't use toxic and carcinogenic dyes. By stretching the films, or connecting them to a battery, their colour can potentially be changed. Hence we plan to test thelimits to this new tuneable colour from our structures.