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  3. Antiseptics(杀菌剂) have saved countless lives, but they are most effective when the bacteria they are attacking are individual cel

Antiseptics(杀菌剂) have saved countless lives, but they are most effective when the bacteria they are attacking are individual cel

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问题      Antiseptics(杀菌剂) have saved countless lives, but they are most effective when the bacteria they are attacking are individual cells in suspension. Once bacteria have attached themselves to solid surfaces and formed films, they are far harder to eradicate with standard disinfectants. Bacterial pollution of medical devices is a particular problem, as those devices are then used on people whose immune systems may be in less than best condition. Surgical instruments may be treated with ultraviolet light, but that is not appropriate for everything. The result is that infections arising from bacteria attached to surfaces in clinics and hospitals are reckoned to cause up to 1.4m deaths per year.
     In order to develop a better method of disinfection, a team led by David Whitten of the University of New Mexico and Kirk Schanze of the University of Florida set out to design the equivalent of a mousetrap for bacteria. The device they came up with is an empty capsule five microns across. It is made of alternating layers of two polymers’(聚合体) ,one of which is positively charged, and the other negatively so. These opposite charges serve to hold the capsule together.
     The polymers in question also absorb light in a way that is likely to transfer the absorbed energy to nearby oxygen molecules (氧分子) to create what is known as singlet oxygen, a particularly reactive form of the element that would kill any bacteria inside the capsule.
     To test this idea, the two researchers ran a series of experiments in which they exposed their newly built microcapsules to Pseudomonas aeruginosa, a fatal bacterium commonly, found in hospitals, and also to Cobetia marina, a bacterium that frequently adheres to ships and marine equipment, causing dirt. They found that in both cases the microcapsules attracted and captured bacteria that were nearby. After one hour of exposure to light, they report in a forthcoming issue of Applied Materials & Interfaces, the capsules killed more than 95% of the bacteria used in the study.
     What kills the bacteria is clear: it is the singlet oxygen. What is attracting them into the microcapsules, though, is not well understood. The researchers infer that the positive electric charge may have the function of attracting bacteria, since many bacteria are negatively charged and would thus be attracted to the polymer in question. Alternatively, because both bacteria and polymers are repelled by water they may be pushed together by this joint repulsion. However it works, the result is what Dr. Whitten describes as a micro-sized Roach Motel ("Bacteria check in, but they don’t check out"). If the idea can be scaled up, it may prove a useful weapon in the fight against hospital-caused infection and marine-dirt alike.  
What can we learn about the device designed by David Whitten and Kirk Schanze?
选项 A、The two layers of polymers are charged differently.
B、The empty capsule they designed is used to trap mouse.
C、The absorbed-light can kill bacteria inside the capsule directly.
D、Singlet oxygen is an insulated form of element.
答案A
解析 细节题。由定位句可知，第二段开始讨论David Whitten and Kirk Schanze的实验设计，其中本段最后一句处提到It is made of alternating layers of two polymers，one of which is positively charged，and the other negatively so，两个聚合体交换层电极正负不同，A符合题意。
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