Enzyme-Activated Surfactants for Dispersion of Carbon Nanotubes
Enzyme-Activated Surfactants for Dispersion of Carbon Nanotubes
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DOI：
10.1002/smll.200801184
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发表时间：
2009-03-06
期刊：
影响因子：
13.3
通讯作者：
Ulijn, Rein V.
中科院分区：
文献类型：
--
作者：
Cousins, Brian G.;Das, Apurba K.;Ulijn, Rein V.
碳纳米管（cnt）的加工仍然是开发其独特性能的一个重要障碍碳纳米管分散是通过使用表面活性剂和具有芳香官能团的聚合物通过p-p相互作用组装到纳米管表面的非共价改性来实现的。[2,3]合成芳香配体，如芘及其衍生物，也被用作碳纳米管同时分散和功能化的低成本表面活性剂。[4-7]对于需要碳纳米管和生物系统之间的界面的系统（例如，生物传感），已经研究了含有芳香残基的生物大分子，如多糖、DNA、RNA和肽。[8-9]在这种情况下，肽尤其具有吸引力，因为它们具有丰富的适应性化学，并且可以利用噬菌体展示利用大量组合文库识别碳纳米管结合肽序列。[10-11]这些序列通常包含12个或更多的残基，并且总是富含芳香氨基酸，如色氨酸(W)和组氨酸(H)。将这些芳香族氨基酸与合成的芳香族配体结合起来，可能会提供表面活性剂，将生物学的多功能性与合成系统的稳健性和成本效益结合起来。N-（氟酰-9-甲氧基羰基）（Fmoc）被选为特别有前途的配体，因为它通常在固态肽合成中用作保护基团，也就是说，Fmoc肽是合成肽系统的中间体，可以直接用于碳纳米管固定。此外，已知Fmoc氨基酸可以通过p-p相互作用相互作用，因为这样的分子可以自组装成纳米结构。[12-13]作为第二个目标，我们研究了基于fmoc肽的表面活性剂是否可以转化为酶寻的体系[14-16]，在恒定的pH、离子强度和温度条件下，这些体系可用于按需组装、分散或稳定碳纳米管。选择了四种fmoc保护的芳香氨基酸，W， H，酪氨酸(Y)和苯丙氨酸(F)，甘氨酸(G)作为非芳香对照（图1a）。通过检测这些分子在磷酸缓冲盐水（PBS）中分散碳纳米管的能力，研究了它们与单壁和多壁纳米管（SWNTs和MWNTs）的相互作用。然后用紫外可见光谱法评估分散程度（见辅助资料）。这些单壁碳纳米管由英国Thomas Swan & Co. Ltd （Elicarb®）提供，采用化学气相沉积（CVD）方法在公司内部制造在分散之前，用镊子将纳米碳纳米管的物理聚集体手动分解，而纳米碳纳米管是作为排列阵列生长的，因此不需要任何机械预处理。在辅助信息中讨论了碳纳米管的表征和尺寸。制备分散体时，每个小瓶含有1mg的CNTs，其中加入氨基酸衍生物溶液（3ml, 0.6 mM）。然后用微探针和低功率浴对混合物进行超声处理4分钟。两分钟的超声处理使样品的局部温度升高108c，在室温下使用低功率水浴再浸泡2min。通过浊度来评估分散程度，利用比尔定律计算纳米管的浓度（见支持信息）。浊度是通过测量从分散体中提取并稀释10倍的等分液在550 nm （A550 nm）和700 nm （A700 nm）处的吸收来获得的。使用……获得了最高水平的分散。
The processing of carbon nanotubes (CNTs) remains a significant barrier in the exploitation of their unique properties.[1] CNT dispersions have been achieved by noncovalent modification using surfactants and polymers with aromatic functionalities that assemble onto nanotube surfaces via p–p interactions.[2, 3] Synthetic aromatic ligands, such as pyrene and its derivatives, have also been used as low-cost surfactants for simultaneous CNT dispersion and functionalization.[4–7] For systems where an interface between CNTs and biological systems is required (eg, biosensing) biological macromolecules containing aromatic residues such as polysaccharides, DNA, RNA, and peptides have been studied.[8–9] Peptides are especially attractive in this context because of their rich, adaptable chemistry and the possibility of identifying CNT binding peptide sequences using massive combinatorial libraries by exploiting phage display.[10–11] These sequences usually contain 12 or more residues and are invariably rich in aromatic amino acids such as tryptophan (W) and histidine (H). Combining these aromatic amino acids with synthetic aromatic ligands may provide surfactants that combine biology’s versatility with the robustness and cost-effectiveness of synthetic systems. N-(Fluorenyl-9-methoxycarbonyl)(Fmoc) was selected as a particularly promising ligand since it is used commonly as a protecting group in solid-state peptide synthesis, that is, Fmoc-peptides are intermediates in synthetic peptide systems and may be used directly for CNT immobilization. Furthermore, it is known that Fmoc amino acids can interact via p–p interactions, as such molecules can self-assemble into nanostructures.[12–13] As a second aim, we studied whether Fmoc-peptide-based surfactants could be converted into enzymatically addressable systems [14–16] that might be used to assemble, disperse, or stabilize CNTs on-demand under constant conditions of pH, ionic strength, and temperature. Four Fmoc-protected aromatic amino acids, W, H, tyrosine (Y), and phenylalanine (F), were selected, with glycine (G) as a nonaromatic control (Figure 1a). The interactions of these molecules with single-and multiwalled nanotubes (SWNTs and MWNTs) were studied by examining their ability to disperse CNTs in phosphate buffer saline (PBS). The degree of dispersion was then assessed using UV–Vis spectroscopy (see Supporting Information). The SWNTs were provided by Thomas Swan & Co. Ltd, UK (Elicarb®) and the MWNTs were manufactured in-house by chemical vapor deposition (CVD) using previous published protocols.[17] The physical aggregates of SWNTs were broken up manually using tweezers before dispersion, whereas the MWNTs were grown as aligned arrays and therefore did not require any mechanical pretreatment. The characterization and dimensions of CNTs are discussed in the supporting information. The dispersions were prepared with each vial containing CNTs (1mg) to which a solution of amino acid derivatives (3 mL, 0.6 mM) was added. The mixture was then ultrasonicated using a microprobe and a low power bath for 4 min. Two minutes of sonication increased the local temperature of the samples by 10 8C and the low-power water bath was used at room temperature for a further 2min. The degree of dispersion was assessed by the turbidity from which the concentration of nanotubes was calculated using Beer’s law (see Supporting Information). The turbidity was obtained by measuring the absorption at 550 nm (A550 nm) and 700 nm (A700 nm) on aliquots taken from the dispersions and diluted ten-fold. The highest level of dispersions was obtained using …