Nanoparticle Supracrystals and Layered Supracrystals as Chemical Amplifiers
Nanoparticle Supracrystals and Layered Supracrystals as Chemical Amplifiers
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DOI：
10.1002/anie.201002295
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发表时间：
2010-01-01
影响因子：
16.6
通讯作者：
Grzybowski, Bartosz A.
中科院分区：
文献类型：
--
作者：
Kowalczyk, Bartlomiej;Walker, David A.;Grzybowski, Bartosz A.
金属纳米颗粒（NPs）的主要应用之一是检测生物学上重要的[1]或有毒物质[2]，通常通过光谱或表面等离子体共振（SPR）变化[3]伴随着颗粒聚集[4]或分散[2c，5]在分析物的存在下。然而，除了高灵敏度的基于DNA的方法之外，[6]大多数报道的比色检测方案需要每个NP大量过量的分析物分子（大约一千个，[2c，5]参见支持信息，第1节）来影响纳米颗粒SPR带中甚至很小的偏移。[7]因此，提高现有的检测限需要放大组装/拆卸过程。不幸的是，与基于纳米颗粒的测定相容的扩增程序的全部内容目前限于银在表面固定的AuNP上的催化沉积。[8]在本文中，我们表明，NP超晶体和以前未报道的核-壳（CS）超晶体（图1）稳定的分析物特异性交联剂可以显着提高（超过两个数量级相比，非结晶NP聚集体）的NP为基础的检测灵敏度。交联的晶体不溶于水，并且由于NP聚集，在可见光范围内不表现出SPR。然而，当存在分析物（阴离子、小分子或酶）时，它切割交联剂，使得每个晶体释放出数百万个单独的NP，就像一个被挤压的“气球”（图2、图3），这些NP在可见光区强烈吸收，并有效地将分子尺度的“切割”事件放大为肉眼可见的明显颜色变化（图4）。此外，在CS超晶体中，“壳”和“核”区域具有不同的NP组成，并且用不同的交联剂稳定;因此，这些晶体可以在两种不同分析物的作用下以逐步方式溶解（图5）。这种特性允许空间分布的传感，从而晶体仅在它们穿过分析物的特定浓度景观时才释放它们的货物。我们使用了直径约为（5.6 ± 0.5）nm的AuNP和直径为（5.6 ± 0.5）nm的AgNP。2)用带正电荷的N，N，N-三甲基（11-巯基十一烷基）氯化铵（HS（CH 2）11N（CH 3）3+，TMA，ProChimia，波兰）或带负电荷的去质子化巯基十一烷酸（HS（CH 2）10 COOH 4，MUA，ProChimia;图1a）的自组装单层（SAM）涂覆的纳米。AuNP具有强的表面等离子体共振（SPR）带，其最大值在Imax = 520 nm处，并且它们的水溶液呈现鲜红色;对于AgNP，Imax % 420 nm，并且颗粒溶液呈现黄色。通过从含有相等数量的带相反电荷的NP的DMSO/水混合物中缓慢蒸发水来生长超晶体（此后，简称为“晶体”）（参见参考文献104）。[9]和支持信息，第2节，以了解详细信息）。1-2 μm的晶体（图1b）因此组装（约。2.2 107个晶体/mL）通过纳米颗粒之间的静电相互作用保持在一起，每个纳米颗粒包含数百万个纳米颗粒（约107个晶体/mL）。2.5通过SEM成像测定的106个NP），并且可溶于水。然而，在暴露于使附近的NP交联的烷烃二硫醇时，晶体在水中变得稳定（图2a），并且可以用作晶种或核以外延存款另外的NP壳。这些壳纳米粒子再次从带相反电荷的粒子的水溶液中沉积，[10]其材料性质可能与晶体核心中的材料性质不同。以这种方式，核-壳晶体（每一个高达约。2.5微米宽...
One of the main applications of metal nanoparticles (NPs) is in the detection of biologically important [1] or toxic substances,[2] usually by the spectral or surface plasmon resonance (SPR) changes [3] accompanying particle aggregation [4] or dispersion [2c, 5] in the presence of an analyte. With the exception of highly sensitive DNA-based methods,[6] however, most reported colorimetric detection schemes require large excesses of analyte molecules per one NP (on the order of one thousand,[2c, 5] see the Supporting Information, Section 1) to affect even small shifts in the nanoparticles SPR bands.[7] Improving the existing detection limits therefore requires amplification of the assembly/disassembly process. Unfortunately, the repertoire of amplification procedures compatible with nanoparticle-based assays is currently limited to the catalytic deposition of silver on surface-immobilized AuNPs.[8] Herein, we show that NP supracrystals and previously unreported core–shell (CS) supracrystals (Figure1) stabilized by analyte-specific cross-linkers can enhance dramatically (by over two orders of magnitude compared to noncrystalline NP aggregates) the sensitivity of NP-based detection. The cross-linked crystals are insoluble in water and, owing to NP aggregation, do not exhibit SPR in the visible regime. When, however, an analyte (an anion, a small molecule, or an enzyme) is present, it cuts the cross-linkers so that each crystal liberates, like a pinched “balloon”(Figure 2, Figure 3), millions of individual NPs absorbing strongly in the visible regime and effectively amplifying the molecular-scale “cutting” events into pronounced color changes visible to a naked eye (Figure 4). Moreover, in the CS supracrystals, the “shell” and the “core” regions have different NP compositions and are stabilized with different cross-linkers; consequently, these crystals can dissolve in a step-wise fashion under the action of two different analytes (Figure 5). This property allows for spatially distributed sensing, whereby the crystals release their cargo only if they travel through specific concentration landscapes of the analytes. We used AuNPs with an approximate diameter of (5.6 Æ 0.5) nm and AgNPs of diameter (5.6 Æ1. 2) nm coated with self-assembled monolayers (SAMs) of either positively charged N, N, N-trimethyl (11-mercaptoundecyl) ammonium chloride (HS (CH2) 11N (CH3) 3+, TMA, ProChimia, Poland) or negatively charged, deprotonated mercaptoundecanoic acid (HS (CH2) 10COOÀ, MUA, ProChimia; Figure 1a). The AuNPs had a strong surface plasmon resonance (SPR) band with maximum at lmax= 520 nm, and their aqueous solutions appeared bright red; for AgNPs, lmax% 420 nm and particle solutions appeared yellow. Supracrystals (henceforth, simply “crystals”) were grown by slow evaporation of water from DMSO/water mixtures containing equal numbers of oppositely charged NPs (see Ref.[9] and the Supporting Information, Section 2 for details). The 1–2 μm crystals (Figure 1b) thus assembled (ca. 2.2 107 crystals per mL) were held together by electrostatic interactions between the NPs, comprised several million nanoparticles each (ca. 2.5 106 NPs as determined by SEM imaging), and were soluble in water. Upon exposure to alkane dithiols that cross-linked the nearby NPs, however, the crystals became stable in water (Figure 2a) and could be used as seeds or cores to epitaxially deposit an additional shell of NPs. These shell NPs were again deposited from an aqueous solution of oppositely charged particles,[10] the material properties of which could be different from those in the crystal core. In this way, core–shell crystals (each up to ca. 2.5 μm across …