Synthesis of Carbohydrate-Functionalized Quantum Dots in Microreactors
Synthesis of Carbohydrate-Functionalized Quantum Dots in Microreactors
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DOI：
10.1002/anie.200905053
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发表时间：
2010-01-01
影响因子：
16.6
通讯作者：
Seeberger, Peter H.
中科院分区：
文献类型：
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作者：
Kikkeri, Raghavendra;Laurino, Paola;Seeberger, Peter H.
电子学和生命科学的应用需要大量的单分散半导体纳米晶体，[1]量子点。[2]对于生物应用，量子点的表面通常用羧酸功能化以结合蛋白质[3]或直接与碳水化合物结合。[4]传统的间歇工艺由于温度控制有限和缺乏均匀混合而限制了大规模生产量子点的效用。[5]连续流动微反应器提供对包括温度在内的反应条件的精确控制，并且生产时间与工艺规模无关。6]微反应器通道的高表面积与体积比[5]能够实现精确的温度控制和有效的混合，从而能够制备尺寸分布窄的量子点。[7]已经使用微型气液和液液流动反应器制备了量子点。[8]在温和的液相反应条件下制备表面功能化的量子点仍然具有挑战性。理想情况下，一个连续的过程既能产生量子点，又能使其功能化。在这里，我们提出了一种单相微流控系统，用于合成高发光、表面功能化的CdSe和CdTe纳米粒子。与需要250-3008C温度的间歇过程相比，1608C的温度在流动过程中是足够的。[8]硫化锌外壳的形成和带有羧基和碳水化合物的纳米颗粒的功能化都在连续流动系统中完成(图1)。在流动反应器中简单地改变反应时间就可以得到不同尺寸的量子点。[9]较高的反应温度通常会导致快速成核，并且很快就会得到大的纳米晶。在低温下，纳米晶的尺寸和未反应前驱体在混合物中的浓度可以达到平衡。因此，连续成核被抑制，停留时间分布(RTD)变窄，并且通过改变反应时间获得了均匀的QD分数。均匀的反应混合物和缓慢的成核导致了使用微反应器生产量子点的温和过程。将Cd前驱体[8]与Se或Te前驱体以1：1的比例混合，制备了具有不同发射峰值的Cd前驱体[8]和Cd-Te纳米粒子。将油酸和油胺加入氧化镉溶液中，于1508℃下溶解于月桂酸中，制备了Cd前驱体。在Syrris微型反应器中，通过将元素硒或碲粉溶解于三正辛基膦(TOP)中制备了Se和Te前驱体。反应时间从3到30分钟不等。用甲醇/氯仿/正己烷沉淀法提纯了Cd Se和Cd Te磁芯，并在真空下干燥。根据吸收光谱计算出每个样品的平均尺寸分布(请参阅支持信息中的图1)。[12]量子点的光学性质显示出带边发射和增强强度随时间发生的红移。CdSe量子点的光致发光峰尖锐，其带边发光的fWHM(半高全宽)值在40-50 nm之间(图2)，这表明量子点的尺寸分布很窄。然而，在反应时间30分钟后，FWHM从40 nm增加到90 nm，量子产率的下降表明饱和成核发生在20-20分钟之后。
Large quantities of monodisperse semiconductor nanocrystals,[1] quantum dots (QDs), are needed for applications in electronics and the life sciences.[2] For biological applications, the surface of QDs is often functionalized with carboxylic acids for the attachment of proteins [3] or directly with carbohydrates.[4] Traditional batch processes are of limited utility for the production of QDs on a larger scale owing to limited temperature control and lack of homogeneous mixing.[5] Continuous-flow microreactors provide precise control over reaction conditions, including temperature, and the production time is independent of the process scale.[2, 6] The high surface-to-volume ratio [5] of the microreactor channels enables precise temperature control as well as efficient mixing, allowing for the preparation of QDs with narrow size distribution.[7] QDs have been prepared using microfabricated gas–liquid and liquid–liquid flow reactors.[8] The preparation of surface-functionalized QDs under mild reaction conditions in the liquid phase remains challenging. Ideally, a continuous process would serve to both produce the quantum dots and to functionalize them. Herein we present a single-phase microfluidic system for the synthesis of highly luminescent, surface-functionalized CdSe and CdTe nanoparticles. In contrast to batch processes, which require temperatures of 250–3008C, temperatures of 1608C are sufficient in the flow process.[8] Both the formation of the zinc sulfide shell and the functionalization of the nanoparticles with carboxy groups and carbohydrates were perfomed in a continuous-flow system (Figure 1). Differentsized quantum dots were obtained by simply varying the reaction time in the flow reactor.[9] High reaction temperatures usually result in fast nucleation, and large nanocrystals are quickly obtained. At low temperatures, the size of the nanocrystals and the concentration of the unreacted precursors in the mixture can be balanced. Thus, continuous nucleation is suppressed, the residence time distribution (RTD) is narrowed, and homogeneous QD fractions are obtained by varying the reaction time. The homogenous reaction mixture and slow nucleation results in a mild process for the production of QDs using microreactors. CdSe and CdTe nanoparticles with different emission maxima were prepared by injection of a 1: 1 mixture of Cd precursor [8] and Se or Te precursor. The Cd precursor was prepared by the addition of oleic acid and oleylamine to a solution of cadmium oxide dissolved in lauric acid at 1508C. The Se and Te precursors were prepared by dissolving elemental selenium or tellerium powder in tri-n-octylphosphine (TOP) in a Syrris microreactor. Reaction times ranged from 3 to 30 minutes. The CdSe and CdTe cores were purified by precipitation from methanol/chloroform/n-hexane and dried under vacuum. The average size distribution of each sample was calculated from the absorbance spectra (see Figure 1 in the Supporting Information).[12] The optical properties of the QDs show a time-dependent bathochromic shift in the band-edge emission and enhanced intensity. The photoluminescence peaks of CdSe QDs are sharp, with fwhm (full width at half maximum) values of the band-edge luminescence between 40 and 50 nm (Figure 2), which indicates the narrow size distribution of the QDs. However, after 30minutes of reaction time the fwhm increased from 40 to 90nm, and a decrease in quantum yield indicated that saturated nucleation occurred after 20–