如何指揮和控制納米粒子的自組裝是納米技術(shù)的一個(gè)關(guān)鍵問題。
密歇根大學(xué)的研究人員發(fā)現(xiàn)了一種將流體聚集納米晶體轉(zhuǎn)為自由浮動(dòng)薄片的方法,，生命有機(jī)體中一些蛋白質(zhì)組裝的過程也是采用這種方式,。
化學(xué)工程、材料科學(xué)和工程教授Sharon Glotzer說,，“這在生物學(xué)和納米科學(xué)的兩個(gè)基本組成元件蛋白質(zhì)和納米粒子之間建立了一個(gè)重要銜接,，這項(xiàng)突破對(duì)從下而上地將材料聚集起來用于藥物投遞和能源等應(yīng)用是相當(dāng)振奮人心的,。”
博士后研究生Kotov說，“這項(xiàng)工作的重要性在于它在蛋白質(zhì)世界和納米科技世界之間建立了一個(gè)關(guān)鍵銜接,，一旦我們知道如何控制納米粒子與它們自組裝能力之間的力量,，這將使我們?cè)谝幌盗袘?yīng)用中受益，例如光捕獲納米粒子裝置和像蛋白質(zhì)一樣但實(shí)質(zhì)上卻是納米粒子的新藥,。”
根據(jù)納米粒子的大小,，在紫外照射之下薄片能呈現(xiàn)從鮮綠色到深紅的顏色。薄片由碲化鎘晶體（太陽能電池材料）做成,，薄片的寬度大約2微米,，厚度約為人頭發(fā)的1/5。Glotzer說,，科學(xué)家早已知道如何將納米粒子制成薄片,，但那些薄片僅僅在粒子處于兩種流體之間時(shí)才能獲得，從未在單流體表面上獲得過,。
該項(xiàng)工作三年前始于Kotov的實(shí)驗(yàn)室,，他和他的團(tuán)隊(duì)在實(shí)驗(yàn)中發(fā)現(xiàn)了薄片，雖然得到了薄片,，但是他們不能確定是如何制造出來的,。
Kotov說，“我們知道某些特定蛋白質(zhì)在生命體內(nèi)自組裝到稱為S-layers的層里,，”S-layers蛋白包括各種各樣的細(xì)菌及其他稱為archaea的單細(xì)胞原核生物的最外層的細(xì)胞被膜蛋白,，他們?cè)诒砻婧徒缑婺苄纬烧叫巍⒘切位蚱渌庑蔚牡?薄片,，并被困在流體中,。研究團(tuán)隊(duì)致力于建立控制S-layer蛋白質(zhì)自組裝的力量與控制納米粒子自組裝的力量之間的聯(lián)系。Glotzer的團(tuán)隊(duì)也參與到這項(xiàng)工作當(dāng)中,，專門從事計(jì)算機(jī)建模和仿真,。
“很可能S-layer蛋白質(zhì)之間的力量是高度異向性的，并且我們猜測(cè)這也是納米粒子的特點(diǎn)”,，Glotzer說,，“計(jì)算機(jī)仿真允許我們進(jìn)一步拓展和檢驗(yàn)這個(gè)假設(shè)”。
Glotzer的研究團(tuán)隊(duì)發(fā)現(xiàn),，CdTe納米晶體的獨(dú)特形狀提升了一種組合力量,，從而導(dǎo)致形成異常的二維外形。Kotov研究團(tuán)隊(duì)隨后的實(shí)驗(yàn)表明,，其中任一力量的缺失,，薄片都不能形成，這種結(jié)果證實(shí)了上述模仿預(yù)言,。
“自組裝是生產(chǎn)具有特定的幾何和物理化學(xué)表面特性的生物學(xué)分子組織序列的基本自然組裝原則”,，Glotzer認(rèn)為,，“在生產(chǎn)功能納米材料和設(shè)備時(shí)，如果我們可以適當(dāng)?shù)卦O(shè)計(jì)模塊,，自組裝較傳統(tǒng)制造業(yè)方法有實(shí)質(zhì)的優(yōu)勢(shì),，這是我們?cè)O(shè)法做的。”
背景資料：
密歇根大學(xué)工程學(xué)院在全美工程學(xué)院之中處于前列,，學(xué)院預(yù)算超過1.3億美元,。學(xué)院有11個(gè)系和二個(gè)NSF工程研究中心，這些系和研究中心對(duì)三個(gè)領(lǐng)域特別重視：納米科技和綜合性微系統(tǒng),、多孔與分子生物技術(shù)和信息技術(shù),。學(xué)院努力在這些領(lǐng)域?yàn)橘Y本建設(shè)計(jì)劃和項(xiàng)目尋求增加1.1億美元，從而支持進(jìn)一步研究發(fā)現(xiàn),。學(xué)院的目標(biāo)是推進(jìn)學(xué)術(shù)發(fā)展和推廣尖端研究以提高公共健康和福利,。
英文原文：
Researchers make nanosheets that mimic protein formation
How to direct and control the self-assembly of nanoparticles is a fundamental question in nanotechnology.
University of Michigan researchers have discovered a way to make nanocrystals in a fluid assemble into free-floating sheets the same way some protein structures form in living organisms.
"This establishes an important connection between two basic building blocks in biology and nanotechnology, that is, proteins and nanoparticles, and this is very exciting for assembling materials from the bottom up for a whole slew of applications ranging from drug delivery to energy," said Sharon Glotzer, professor of chemical engineering and materials science and engineering.
Glotzer and Nicholas Kotov, associate professor of chemical engineering, and their students who are post doctoral researchers have co-authored a paper scheduled to appear Oct. 13 in the journal Science.
"The importance of this work is in making a key connection between the world of proteins and the world of nanotechnology" Kotov said. "Once we know how to manipulate the forces between the nanoparticles and their ability to self-organize, it will help us in a variety of practical applications from light-harvesting nanoparticle devices to new drugs which can act like proteins, but are actually nanoparticles."
The sheets, which can appear colored under UV illumination from bright green to dark red depending on the nanoparticle size, are made from cadmium telluride crystals, a material used in solar cells. The sheets are about 2 microns in width, about 1/5 the thickness of a human hair.
Scientists have long known how to coax nanoparticles into forming sheets, Glotzer said. But those sheets have only been achieved when the particles were on a surface or at an interface between two fluids, never while suspended in a single fluid.
The work started in Kotov's lab three years ago, when he and his team observed the sheets in experiments. Though they created them, they weren't sure how.
"We were aware of certain proteins in living organisms that self-assemble into layers, called S-layers," Kotov said. S-layer proteins comprise the outermost cell envelope of a wide variety of bacteria and other single-celled, prokaryotic organisms called archaea, and they are able to form 2-d sheets with square, hexagonal, and other packings at surfaces and interfaces, as well as suspended in fluid. The group sought to make the connection between the forces governing S-layer protein assembly and the forces governing the nanoparticle assembly. That's when Glotzer's group, whose expertise is in computer modeling and simulation, became involved.
"It's likely that the forces between S-layer proteins are highly anisotropic, and we suspected this was also a feature of the nanoparticles," Glotzer said. "Computer simulations allowed us to further develop and test this hypothesis."
Post doctoral researcher Zhenli Zhang of Glotzer's group tried various combinations of forces based on information gleaned from experiments performed by post doctoral Zhiyong Tang of Kotov's group. The team discovered that the unique shape of the CdTe nanocrystals gave rise to a combination of forces that conspired to produce the unusual two-dimensional packing. Subsequent experiments by Kotov's group showed that if any of the forces were missing, the sheets would not form, confirming the simulation predictions.
"Self-assembly is nature's basic building principle for producing organized arrays of biomolecules with controlled geometrical and physicochemical surface properties," Glotzer said. "In the fabrication of functional nanoscale materials and devices, self-assembly offers substantial advantages over traditional manufacturing approaches, if we can design the building blocks appropriately. This is what we're trying to do."
The paper is called Self-assembly of CdTe Nanocrystals into Free-Floating Sheets. The work was partially supported by seed funds provided by the U-M College of Engineering's Nanotechnology Initiative and by the Department of Energy, the Air Force Office of Scientific Research, and the National Science Foundation.
