[2008.08.09] 法医技术：指上乾坤

Forensic technology
法医技术

Sticky fingers
指上乾坤

From The Economist print edition
Aug 7th 2008

A new and more powerful fingerprinting technology is at hand
更新更强的指纹识别技术即将登场

AS ANY aficionado of whodunnits will know, lifting and analysing fingerprints is a tedious task. Fiddling with the little brushes, fine powders and sticky tape can test the patience of the most fastidious crime-scene investigator. And then there is all the lab work, which can require even greater care. However, real-life forensic experts may soon look less like their counterparts in “CSI” and more like sci-fi sleuths armed with extremely clever hand-held fingerprint analysers.
任何悬疑小说迷都知道提取和分析指纹是件很乏味的工作。摆弄小刷子，洒下细粉，贴上胶带对大多数挑剔的犯罪现场调查人员来说都是耐心的考验。然后就都是实验室的工作，那更需要小心翼翼。不过现实生活中的法医专家可能很快就不会像他们在美剧《犯罪现场调查》中的同行那样，而是更像科幻小说中装备着极度智能便携式指纹分析仪的侦探了。

This could be the upshot of a new fingerprinting method developed by Demian Ifa and his colleagues at Purdue University in Indiana. Their innovation, reported this week in Science, is based on desorption electrospray ionisation (DESI), an analytical technique which can be deployed in the field. It involves spraying a tiny (0.15×0.15mm) area of a fingerprint with an electrically charged mixture of methanol and water. When these charged droplets come into contact with the surface of the print they collect any substances deposited on it, creating a thin liquid film. As more drops are sprayed on the same spot, some of this film is scattered and sucked into a mass spectrometer, which can identify the molecules collected. All this takes only a few tenths of a second. Then the spray is moved along to the next patch on the fingerprint and the process is repeated. It will work on any surface on which there are fingerprints.
印第安纳州州普渡大学的Demian Ifa和他同事开发的指纹识别新技术可能让这一设想变为现实。本周的《科学》杂志报道了他们的这一基于解吸附电喷雾离子化（desorption electrospray ionisation）的新检测方式。解吸附电喷雾离子化是一种能在实地使用的技术。这种技术首先往指纹上一小块区域喷上（0.15×0.15毫米）充上电流的甲醇与水的混合溶液。这些充了电的液滴与指纹表面接触后会吸走其表现上存积的任何物质，产生一块液体薄膜。当更多的小滴喷在同一点上时，某些薄膜就会扩散并被吸入一个质谱计用以鉴别收集到的分子。整个过程只需几个十分之一秒，然后继续往指纹上其他小块喷射并不断重复。这一技术在任何有指纹的表面上都能使用。

Each reading by the mass spectrometer creates a kind of chemical “pixel”. However, instead of each pixel representing a colour, as in the image on a screen, these readings show all the different chemical compounds present in each of the thousands of tiny patches that together make up the sample. The overall distribution of these readings can be converted into an image of the fingerprint that is accurate enough to identify who left it with standard recognition software.
质谱计每次读取的数据最后生成一种所谓化学”像素”。然而，这些数据并非如组成荧屏上图像的像素一样每个点表示一种颜色，而是显示组成样本的数千小块中的每一个不同的化学成分。这些数据构成的整体结果能被转换成一个指纹图像，其精度足够由标准识别软件分辨出留下指纹的人。

But DESI also presents an additional boon to gumshoes. Because it is based on chemical rather than purely visual data, it can discover what else people touched before leaving their prints. In their experiments, Dr Ifa and his team identified minute traces of drugs, such as cocaine and marijuana, as well as explosives.
但吸附电喷雾离子化技术对刑警还有额外的好处。因为它是基于化学而不是纯粹的视觉数据，能够检测出留下指纹的人之前碰过的其他物体。Ifa博士和他的小组在实验中检测出了微量的毒品痕迹，比如可卡因和大麻，同样也能识别爆炸物。

Moreover, besides indicating what substances had been deposited on the skin of the person who left the print, DESI can discern traces of substances that have been secreted through it. Since such secretions are the end result of chemical processes going on inside the body, they can provide indirect evidence of a person’s health, which could also help with identification. One day such techniques may even help doctors diagnose illnesses by scanning a portion of the skin of their patients.
此外，解吸附电喷雾离子化技术除了能检测出吸留下指纹者皮肤上的积存物质，还能辨别通过皮肤渗透出来物质的痕迹。因为这些分泌物都是身体内部进行的化学反应的最终成果，所以能间接说明一个人的健康状况，这也能有助于身份的鉴别。也许某一天，这种技术甚至能帮助医生通过扫描病人身上一部分皮肤来诊断疾病。

Given that different people tend to handle different things (and not necessarily illicit ones), and that they secrete slightly different substances, this method can even help to disentangle overlapping sets of fingerprints, which is very difficult with optical analysis alone. Graham Cooks, a member of the Purdue team, has already built a functioning portable DESI device with a built-in miniature mass spectrometer that is no bigger than a doctor’s case. With such technology virtually at policemen’s fingertips, crooks are well advised to keep their hands clean.
因为不同的人一般都会做不同的事情（不一定要是违法的），所以他们的分泌物都会有所不同。这种方法甚至能帮助分解一些叠在一起的指纹，只用光学分析是很难做到的。普渡大学小组成员Graham Cooks已经制作了一个能够运作的便携式解吸附电喷雾离子化装置，其内置了小型的质谱计，体积不比医药箱大。当这种技术成为警察的掌中利器时，就得奉劝那些作恶之人不要弄脏手了。

译者：xcz2  http://www.ecocn.org/forum/viewthread.php?tid=13222&page=1&extra=page%3D1#pid83004