TEXT ONE
Most cells are transparent in other words, they are not very good at reflecting or absorbing light. To look at them under a microscope thus requires trickery. Many of these tricks kill the cells, and even those that keep them alive look only at slices through each cell, rather than seeing the whole thing in three dimensions.
Michael Feld, of the Massachusetts Institute of Technology, and his colleagues, think they can change that. They have invented a way to look at cells that are still alive. Moreover, they can do so in three dimensions. Their method is called tomographic phase microscopy, and it is reported in this weeks Nature Methods. Instead of relying on absorbed or reflected light, Dr Felds technique celebrates transparency by looking at light that gets through unaltered. It does so by measuring a property called the refractive index.
This index measures the speed of light in a material. The different components of a cell, though transparent, have different refractive indices. Dr Feld and his team therefore set out to map what these differences are, with a view to using them to distinguish between cellular components.
To measure the refractive indices of different parts of a cell they use a technique called interferometry, which involves splitting a beam of light in two. One half, known as the object beam, passes through the cell; the other is directed along a different path and acts as a reference. The length of the reference path is such that if no sample is present, the two daughter beams will be as perfectly in phase when they meet as they were when they were separated. The crests and the troughs of their waves will reinforce each other, and the result will be brightness. The more that the light passing through the sample is slowed down, however, the more the two beams will be out of phase. Crest will fall on trough, and the result will be darkness. It is this phase shift that gives Dr Felds new form of microscopy its name.
A single pair of beams does not, however, produce a useful image. To do that requires scanning the object beam through the target about a hundred different ways. From the refractive index of each path it is possible with the application of some suitably crunchy computing power to produce a three-dimensional image.
To test his idea, Dr Feld looked at cervical-cancer cells. If you identify this cancer early, the patient will probably survive. Miss it, and she will die. Dr Feld wondered if the changes that occur during cancer would show up using his new method. They did, in a part of the cell called the nucleolus. This is the place where the components of protein factories are made. Since cancer cells grow rapidly, and thus have a high demand for proteins, it was a likely place to expect changes.
Dr Feld also has plans to use beams of different colours, since each colour has a slightly different refractive index in a given material. That would provide extra data for the computer to chew on, and probably result in better pictures. With enough pictures, Dr Felds technique may make biology as transparent as the cells it studies.
小学一年级英语下册Unit2 Small animals教案1
一年级英语教案Module1 unit6 Mid-Autumn Festival
上海牛津版一年级英语Unit7 My family教案
上海牛津版一年级英语Unit3 This is my mum教案
牛津版一年级英语上册Unit 2 Good morning 教案
一年级英语上册教案 Unit1My classroom 第三课时
牛津版一年级英语上册unit5 Fruit教案(3)
沪教版小学英语一年级下册教案unit1单元分析
新起点小学一年级英语下册Unit11 Toys教案
牛津版一年级英语上册unit5 Fruit教案(2)
沪教牛津版小学英语一年级上册 Unit 3 第二课时教案
上海牛津版一年级英语下册Unit9 Revision第二课时教案
上海牛津版一年级英语Unit 9 Revision单元分析教案
牛津版小学一年级英语上册Unit1 Hello教案
上海牛津版一年级英语下册Unit2 Small animals教案
一年级英语上册Unit1 My classroom第三课时教案
新课标小学英语第一册期末考试百词范围
苏教版小学一年级英语下册Unit5 On the road教案
一年级英语上册教案Unit1 My classroom第一课时
一年级英语Module1 unit6 Mid-Autumn Festival教案
上海牛津版一年级英语下册Unit3 Colours教案(1)
沪教牛津版小学英语一年级上册 Unit3 period2教案
上海版牛津一年级英语教案 Unit 3 My abilities
沪教版小学英语一年级下册教案unit1课时1
上海牛津版一年级英语Unit2 Small animals第四课时教案
新起点小学一年级英语教案Unit7 Fruit
上海牛津版一年级英语下册Unit2 Small animals第五课时教案
一年级英语下册Unit2 Small animals第三课时教案
沪教版小学英语一年级下册教案unit1课时2
牛津小学一年级英语Unit5 Fruit教案(五个课时)
不限 |
英语教案 |
英语课件 |
英语试题 |
不限 |
不限 |
上册 |
下册 |
不限 |