Physical basis of colors seen in Congo red-stained amyloid in polarized light
Physical basis of colors seen in Congo red-stained amyloid in polarized light
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DOI：
10.1038/labinvest.3700714
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发表时间：
2008-03-01
影响因子：
5
通讯作者：
Jones, Adrian P.
中科院分区：
文献类型：
--
作者：
Howie, Alexander J.;Brewer, Douglas B.;Jones, Adrian P.
淀粉样蛋白被刚果红染色，传统上被认为在偏振光下显示苹果绿双折射，尽管在实践中，在精确交叉的偏振滤光片（称为偏振器和分析器）之间可以看到各种颜色。当偏光镜和检偏镜不交叉时，有时当载玻片旋转时，会看到其他颜色。以前，一直没有令人满意的解释这些属性。双折射意味着材料具有两个折射率，这取决于其在偏振光中的取向。双折射可以将线偏振光改变为椭圆偏振光，这允许光通过交叉检偏器。取向的刚果红的双折射随波长而变化，并且在其吸收峰附近最大，从峰的短波侧的负（垂直于涂片或淀粉样纤维的透射慢轴）变为长波侧的正（平行于慢轴）。这可以用任何光吸收物质的一种性质来解释，这种性质被称为吸收峰周围折射率的异常色散。负双折射给出蓝色的透射，正双折射给出黄色的透射，并且混合物被感知为绿色。这解释了绿色是如何在理想条件下出现的。光学系统中的附加或应变双折射，例如在载玻片中，部分或完全消除蓝色或黄色，产生黄色/绿色或黄色，以及蓝色/绿色或蓝色，这在实践和插图中常见。当起偏器或检偏器不交叉时，双折射效应减弱，出现二向色效应，当偏振面靠近吸收轴时，由绿色逐渐变为红色，反之，由绿色逐渐变为无色。这种效应的不对称性对于病理学家确认淀粉样蛋白是有用的。与通常报道的“偏振光下的苹果绿双折射”不同，当在偏光镜和检偏镜之间检查时，刚果红染色的淀粉样蛋白应该更准确地说是显示出异常颜色。
Amyloid stained by Congo red is traditionally said to show apple-green birefringence in polarized light, although in practice various colors may be seen between accurately crossed polarizing filters, called polarizer and analyzer. Other colors are seen as the polarizer and analyzer are uncrossed and sometimes when the slide is rotated. Previously, there has been no satisfactory explanation of these properties. Birefringence means that a material has two refractive indices, depending on its orientation in polarized light. Birefringence can change linearly polarized light to elliptically polarized, which allows light to pass a crossed analyzer. The birefringence of orientated Congo red varied with wavelength and was maximal near its absorption peak, changing from negative (slow axis of transmission perpendicular to smears or amyloid fibrils) on the shortwave side of the peak to positive ( slow axis parallel) on the longwave side. This was explained by a property of any light-absorbing substance called anomalous dispersion of the refractive index around an absorption peak. Negative birefringence gave transmission of blue, positive gave yellow, and the mixture was perceived as green. This explains how green occurs in ideal conditions. Additional or strain birefringence in the optical system, such as in glass slides, partly or completely eliminated blue or yellow, giving yellow/green or yellow, and blue/green or blue, which are commonly seen in practice and in illustrations. With uncrossing of polarizer or analyzer, birefringent effects declined and dichroic effects appeared, giving progressive changes from green to red as the plane of polarization approached the absorbing axis and from green to colorless in the opposite way. This asymmetry of effects is useful to pathologists as a confirmation of amyloid. Rather than showing 'apple-green birefringence in polarized light' as often reported, Congo red-stained amyloid, when examined between crossed polarizer and analyzer, should more accurately be said to show anomalous colors.