Three-in-One: Sensing, Self-Assembly, and Cascade Catalysis of Cyclodextrin Modified Gold Nanoparticles
三合一：环糊精改性金纳米颗粒的传感、自组装和级联催化

Yan Zhao, $^{†}$ Yucheng Huang, $^{†}$ Hui Zhu, Qingqing Zhu, and Yunsheng Xia*©
赵燕、 $^{†}$ 黄玉成、 $^{†}$ 朱慧、朱青青和夏云生* ©Key Laboratory of Functional Molecular Solids, Ministry of Education; College of Chemistry and Materials Science, Anhui Normal University, Wuhu 241000, China
功能分子固体教育部重点实验室;安徽师范大学化学与材料科学学院，安徽芜湖 241000

S Supporting Information S 支持信息

Abstract 抽象

We herein present a three-in-one nanoplatform for sensing, self-assembly, and cascade catalysis, enabled by cyclodextrin modified gold nanoparticles (CD@AuNPs). Monodisperse AuNPs $15 - 20 nm$ in diameter are fabricated in an eco-friendly way by the proposed one-step colloidal synthesis method using CD as both reducing agents and stabilizers. First, the as-prepared AuNPs are employed as not only scaffolds but energy acceptors for turn-on fluorescent sensing based on guest replacement reaction. Then, the macrocyclic supramolecule functionalized AuNPs can be controllably assembled and form well-defined one- and two-dimensional architectures using tetrakis(4-carboxyphenyl)porphyrin as mediator. Finally, in addition to conventional host-guest interaction based properties, the CD@AuNPs possess unpredictable catalytic activity and exhibit mimicking properties of both glucose oxidase and horseradish peroxidase simultaneously. Especially, the cascade reaction (glucose is first catalytically oxidized and generates gluconic acid and $H_{2} O_{2}$ ; then the enzymatic $H_{2} O_{2}$ and preadded TMB ( $3, 3^{'}, 5, 5^{'}$ -tetramethylbenzidine) are further catalyzed into $H_{2} O$ and oxTMB, respectively) is well-achieved using the AuNPs as the sole catalyst. By employing a joint experimental-theoretical study, we reveal that the unique catalytic properties of the $CD @ A u N P s$ probably derive from the special topological structures of CD molecules and the resulting electron transfer effect from the AuNP surface to the appended CD molecules.
我们在此提出了一种用于传感、自组装和级联催化的三合一纳米平台，该平台由环糊精改性金纳米颗粒（CD@AuNPs）实现。直径为直径的单分散 AuNPs $15 - 20 nm$ 是通过所提出的一步胶体合成方法以环保方式制备的，该方法使用 CD 作为还原剂和稳定剂。首先，所制备的 AuNP 不仅用作支架，还用作基于客体替代反应的开启荧光传感的能量受体。然后，使用四（4-羧基苯基）卟啉作为介质，可以可控地组装大环超分子官能化的 AuNPs 并形成明确的一维和二维结构。最后，除了基于主客体相互作用的常规特性外，CD@AuNPs还具有不可预测的催化活性，并同时表现出葡萄糖氧化酶和辣根过氧化物酶的模拟特性。特别是，使用 AuNP 作为唯一催化剂，可以很好地实现级联反应（葡萄糖首先被催化氧化并生成葡萄糖酸和 $H_{2} O_{2}$ ;然后酶和 $H_{2} O_{2}$ 预添加的 TMB（ $3, 3^{'}, 5, 5^{'}$ -四甲基联苯胺）分别进一步催化成 $H_{2} O$ oxTMB）。通过采用联合实验理论研究，我们揭示了其 $CD @ A u N P s$ 独特的催化性质可能源于 CD 分子的特殊拓扑结构以及由此产生的从 AuNP 表面到附加的 CD 分子的电子转移效应。

- INTRODUCTION -介绍

Gold nanoparticles (AuNPs) are a continuous research interest in the fields of nanoscience and nanotechnology due to their unique optical/electrical properties and versatile application potentials.

^{1}

Their physicochemical features and corresponding applications have aroused strong repercussions in several aspects. First, AuNPs possess a distance dependent surface plasmon resonance (SPR) band, which has been extensively employed for designing assembly/disassembly modulated colorimetric sensors.

^{Ic, d, 2^{2}}

Second, the extinction coefficient of AuNPs is as high as

10^{8} - 10^{10} M^{- 1} {cm}^{- 1}^{3}

So, they are one of the ideal energy acceptors in constructing a fluorescence resonance energy transfer (FRET) system for sensing and biosensing.

^{1 c, 4}

Last but not least, AuNPs exhibit catalytic activity, which makes them a potential candidate for the replacement of expensive Pt in some fields.

^{1 b, c, 5}

It is widely accepted that the specific properties/applications of AuNPs are dependent on a series of factors including particle size, shape, surface chemistry, aggregation state, and preparation method.

^{6}

For example, a relatively large size (

> 10 nm

) is essential for distinct SPR bands;

^{6 b}

in contrast, catalytic activity is commonly believed to be the privilege of ultrasmall AuNPs

(\sim 2 nm) .^{5 c, e, 7}

In parallel, macrocyclic supramolecules, such as crown ether, cyclodextrin (CD), and calixarene, possess unique and sizetunable cavity structures and exhibit special properties.

^{8}

On the basis of host-guest interactions, they have been well-applied for self-assembly, drug/gene delivery, separation, sensing, etc.

^{9}

金纳米颗粒（AuNPs）由于其独特的光学/电学特性和广泛的应用潜力，是纳米科学和纳米技术领域的持续研究兴趣。

^{1}

它们的物理化学特性和相应的应用在几个方面引起了强烈的反响。首先，AuNP 具有距离依赖性表面等离子体共振（SPR）带，该带已广泛用于设计组装/拆卸调制比色传感器。

^{Ic, d, 2^{2}}

其次，AuNPs 的消光系数高达

10^{8} - 10^{10} M^{- 1} {cm}^{- 1}^{3}

因此，它们是构建用于传感和生物传感的荧光共振能量转移（FRET）系统的理想能量受体之一。

^{1 c, 4}

最后但并非最不重要的一点是，AuNP 表现出催化活性，这使它们成为某些领域替代昂贵 Pt 的潜在候选者。

^{1 b, c, 5}

人们普遍认为，AuNPs 的具体性质/应用取决于一系列因素，包括颗粒大小、形状、表面化学、聚集状态和制备方法。

^{6}

例如，相对较大的尺寸（

> 10 nm

）对于不同的 SPR 波段至关重要;

^{6 b}

相比之下，催化活性通常被认为是超小 AuNP

(\sim 2 nm) .^{5 c, e, 7}

的特权同时，大环超分子，如冠醚、环糊精（CD）和卡利沙雷，具有独特且尺寸可调的空腔结构，并表现出特殊性能。

^{8}

在主客交互的基础上，它们已广泛应用于自组装、药物/基因递送、分离、传感等。

^{9}

So, the integration of AuNPs and macrocyclic supramolecules not only provides a kind of hybrid nanomaterial but is expected to bring new properties, functions, and applications.

^{1 l, 10 a - g}

因此，AuNPs 和大环超分子的整合不仅提供了一种杂化纳米材料，而且有望带来新的特性、功能和应用。

^{1 l, 10 a - g}

To date, the hybrid nanomaterials consisting of macrocyclic supramolecules and AuNPs have been well-studied.

^{10}

Despite these substantial achievements, there are a few issues and/or potential problems that are still of concern. First, in the fabrication of the hybrid entities, a few harsh reagents or conditions

({NaBH}_{4}, NaOH

, thiols, etc.) are commonly adopted.

^{10 e - h}

In addition to being environmentally unfriendly, their extremely high binding affinity and/or strong interactions might passivate/block the surface properties of AuNPs. Second, previous studies often only focus their attention on one certain aspect of properties/applications, which is unfavorable for comprehensive understanding of the features and for better tapping of the potential of the hybrid materials. Third, in terms of the hybrid materials, pre-existing research studies mainly concentrate on their host-guest interaction based properties/ functions/applications. Considering that macrocyclic supramolecules possess unique topological structures, their interactions with AuNPs might unusually modulate the particle surface chemistry and result in novel properties and corresponding potential applications.
迄今为止，由大环超分子和 AuNPs 组成的杂化纳米材料已经得到了很好的研究。

^{10}

尽管取得了这些重大成就，但仍有一些问题和/或潜在问题值得关注。首先，在制造杂交实体时，一些苛刻的试剂或条件

({NaBH}_{4}, NaOH

、硫醇等）通常被采用。

^{10 e - h}

除了对环境不友好之外，它们极高的结合亲和力和/或强相互作用可能会钝化/阻断 AuNP 的表面特性。其次，以前的研究往往只关注特性/应用的某个特定方面，这不利于全面理解特性和更好地挖掘混合材料的潜力。第三，就混合材料而言，现有的研究主要集中在基于其主客体相互作用的特性/功能/应用上。考虑到大环超分子具有独特的拓扑结构，它们与 AuNPs 的相互作用可能会异常调节颗粒表面化学并产生新的性质和相应的潜在应用。

Received: July 22, 2016 收稿日期： 2016-07-22
Published: December 7, 2016
发布时间：2016 年 12 月 7 日

Figure 1. As-prepared

CD @ A u N P s

. Three kinds of products made from chloroauric acid and

α - CD (A - D), β - CD (E - H)

, and

γ - CD (I - L)

, respectively. The four rows show TEM (A, E, I), scanning electron microscopy (SEM) (B, F, J), absorption spectra (C, G, K), and histograms of size distribution (

D, H, L

) results, respectively.
图 1.原样

CD @ A u N P s

.三种产品分别由氯金酸和

α - CD (A - D), β - CD (E - H)

、和

γ - CD (I - L)

制成。四行分别显示 TEM （A， E， I）、扫描电子显微镜（SEM）（B、F、J）、吸收光谱（C、G、K）和尺寸分布直方图（

D, H, L

）结果。

Figure 2. Structural characterizations of the

β

-CD@AuNPs. (A) High-resolution TEM image of the

β

-CD@AuNPs. (B) FT-IR spectra of the

β

CD@AuNPs (red curve) and

β

-CD (black curve). High-resolution XPS survey scan of O 1s © and C 1s (D) of the

β

-CD@AuNPs. (E)

^{1} H

NMR spectrum (in

D_{2} O

) of the

β

-CD@AuNPs. ( F ) The schematic diagram for the surface chemistry of the

β

-CD@AuNPs. The cartoon mode in the left of part F only shows the probable structure of the as-prepared

β

-CD@AuNPs, which does not consider (i) the size proportion between

β

- CD and the AuNPs, and (ii) the precise amounts of

β

-CD molecules on each AuNP.
图 2.

β

-CD@AuNPs的结构特征。（A）

β

-CD@AuNPs 的高分辨率 TEM 图像。（B）

β

CD@AuNPs（红色曲线）和

β

-CD（黑色曲线）的 FT-IR 光谱。

β

-CD@AuNPs 的 O 1s © 和 C 1s （D）的高分辨率 XPS 巡测扫描。（E）

^{1} H

β

-CD@AuNPs 的 NMR 谱图（in

D_{2} O

）。（ F ）

β

-CD@AuNPs 表面化学示意图。F 部分左侧的卡通模式仅显示了制备

β

的 -CD@AuNPs 的可能结构，它没有考虑（i） - CD 和 AuNPs 之间的

β

大小比例，以及（ii）每个 AuNP 上 -CD 分子的

β

精确数量。

In this study, we first demonstrate a three-in-one nanoplatform for sensing, self-assembly, and cascade catalysis enabled by CD modified AuNPs (CD@AuNPs). Monodisperse AuNPs

15 - 20 nm

in diameter are fabricated in an eco-friendly way using CD molecules as both reducing agents and stabilizers. Different from previous approaches for the fabrication of macrocycle-AuNP hybrid nanomaterials, no harsh reagents and/or conditions are used here.

^{10 e - g}

Because the AuNPs possess supramolecular cavities on their surface, they can be
在这项研究中，我们首先展示了一个由 CD 修饰的 AuNPs （CD@AuNPs）实现的用于传感、自组装和级联催化的三合一纳米平台。直径

15 - 20 nm

的单分散 AuNP 是使用 CD 分子作为还原剂和稳定剂以环保方式制造的。与以前制造大环 AuNP 杂化纳米材料的方法不同，这里没有使用苛刻的试剂和/或条件。

^{10 e - g}

因为 AuNP 在其表面具有超分子腔，所以它们可以
employed as scaffolds and energy acceptors for turn-on fluorescent sensing by host-guest interactions. Then, the CD@AuNPs can act as building blocks and assemble into welldefined one- and two-dimensional (1D/2D) superstructures with the assistance of tetrakis(4-carboxyphenyl)porphyrin (TCPP) as mediator. Finally, despite being tens of nanometers in diameter, the AuNPs possess unpredictable catalytic activity and exhibit mimicking properties of both glucose oxidase (GOx) and horseradish peroxidase (HRP) simultaneously.
用作支架和能量受体，通过主客体交互打开荧光传感。然后，CD@AuNPs可以作为构建块，在四（4-羧基苯基）卟啉（TCPP）作为介质的帮助下组装成明确的一维和二维（1D/2D）超结构。最后，尽管直径为数十纳米，但 AuNPs 具有不可预测的催化活性，并同时表现出葡萄糖氧化酶（GOx）和辣根过氧化物酶（HRP）的模拟特性。

Figure 3. Fluorescent sensing of cholesterol using the composite made of the

β

CD @ A u N P

and RB molecules. (A) Fluorescence spectra of RB in the presence of different concentrations of the AuNPs. (B) Plots of RB fluorescence intensities versus the AuNP concentrations. © Fluorescence spectra of the (

β - CD @ A u N P - RB

) composite after adding varying amounts of cholesterol. (D) Plots of the (

β

-CD@AuNP-RB) composite fluorescence intensities versus cholesterol concentrations. (E) Selectivity of the (

β

-CD@AuNP-RB) composite toward various potential interfering substances. The concentration of cholesterol is

4.0 μ M

; the concentrations of the added various substances (from alanine to lecithin) are 0.3 , 0.1 ,

0.08, 0.12, 0.12, 0.16, 0.2, 0.02, 0.08, 0.26, 0.14, 0.06, 0.08, 0.16, 0.25, 1.0, 0.1, 0.28, 0.161 .04, 2.5 μ M

, respectively; the concentrations of dopamine, bile acid, bilirubin, progesterone, and HSA (human serum albumin) are

3.0 pM, 4.9 nM, 9.4 nM, 4.5 pg / mL

, and

0.035 g / L

, respectively. The concentrations of both the analytes and various potential interfering substances correspond to 1000 times dilution of those in serum. (F) DFT models for the interactions of

β

-CD with tryptophan (I), cholesterol (II), and RB (III), respectively. Also, the chemical structures of the three kinds of guest molecules are displayed. (G) Schematic illustration of fluorescent turn-on detection of cholesterol using the (

β

-CD@AuNP-RB) composite.
图 3.使用由

β

CD @ A u N P

和 RB 分子制成的复合材料对胆固醇进行荧光感应。（A）不同浓度 AuNPs 存在下 RB 的荧光光谱。（B） RB 荧光强度与 AuNP 浓度的关系图。© 添加不同量胆固醇后（

β - CD @ A u N P - RB

）复合物的荧光光谱。（D）（

β

-CD@AuNP-RB）复合荧光强度与胆固醇浓度的关系图。（E）（

β

-CD@AuNP-RB）复合物对各种潜在干扰物质的选择性。胆固醇的浓度是

4.0 μ M

;添加的各种物质（从丙氨酸到卵磷脂）的浓度分别为 0.3 、 0.1 、

0.08, 0.12, 0.12, 0.16, 0.2, 0.02, 0.08, 0.26, 0.14, 0.06, 0.08, 0.16, 0.25, 1.0, 0.1, 0.28, 0.161 .04, 2.5 μ M

;多巴胺、胆汁酸、胆红素、孕酮和 HSA（人血清白蛋白）的浓度分别为

3.0 pM, 4.9 nM, 9.4 nM, 4.5 pg / mL

和

0.035 g / L

。分析物和各种潜在干扰物质的浓度相当于血清中浓度的 1000 倍。（F）

β

-CD 分别与色氨酸（I）、胆固醇（II）和 RB （III）相互作用的 DFT 模型。此外，还显示了三种客体分子的化学结构。（G）使用（

β

-CD@AuNP-RB）复合材料对胆固醇进行荧光开启检测的示意图。

Especially, the cascade reaction (glucose is first catalytically oxidized and form gluconic acid and

H_{2} O_{2}

; then the enzymatic

H_{2} O_{2}

and preadded

3, 3^{'}, 5, 5^{'}

-tetramethylbenzidine (TMB) are further catalyzed into

H_{2} O

and oxTMB, respectively) is wellachieved using the AuNPs as the sole catalyst. By combination of experiments and density functional theory (DFT) calculations, the unpredictable catalytic properties of the

C D @ A u N P s

probably derive from the unique topological structures of CD molecules and the resulting electron transfer effect from the AuNP surface to the appended CD molecules.
特别是，使用 AuNPs 作为唯一催化剂，可以很好地实现级联反应（葡萄糖首先被催化氧化并形成葡萄糖酸和

H_{2} O_{2}

;然后酶和

H_{2} O_{2}

预添加

3, 3^{'}, 5, 5^{'}

的四甲基联苯胺（TMB）分别进一步催化成

H_{2} O

oxTMB）。通过实验和密度泛函理论（DFT）计算的结合，其不可预测的催化性质

C D @ A u N P s

可能源自 CD 分子独特的拓扑结构以及由此产生的从 AuNP 表面到附加 CD 分子的电子转移效应。

- RESULTS AND DISCUSSION - 结果与讨论

We found that AuNPs could be facially fabricated using CD molecules as both stabilizers and reducing agents in mild conditions. After the mixture of CD molecules, chloroauric acid, and phosphate buffer solution (PBS, pH 7.0 ) was heated to

100^{\circ} C

for 60 min (Figures S1-S4 in Supporting Information), Au colloidal solution was reliably obtained (Figure S5 in Supporting Information). Figure 1 shows three kinds of AuNPs synthesized by the CD molecules with different sized cavities, namely,

α

β

-, and

γ

-CD, respectively. The three corresponding AuNPs are

19 \pm 1.8, 20 \pm 1.6

, and

15 \pm 1.8 nm

in diameter, as determined by transmission electron microscopy (TEM). According to dynamic light scattering (DLS), their average hydrodynamic diameters are 22,24 , and 19 nm , respectively, in agreement with TEM measurements, despite some apparent enlargement because of a hydration layer and a stronger contribution of larger particles to DLS signal.

^{11}

For the

β - CD @ A u N P s

, their shape is spherical/quasispherical with only

8 %

size distribution (Figure 1E,F). The AuNP solution is wine red and possesses a sharp SPR band centered at 520 nm (Figure 1 G ), indicating the typical features of gold nanosphere. While for the

α

- and

γ

-CD@AuNPs (Figure 1A,I), slightly elongated NPs are occasionally observed. Accordingly, the solutions are somewhat purple, and the SPR bands exhibit a
我们发现，在温和的条件下，可以使用 CD 分子作为稳定剂和还原剂进行面部制造。将 CD 分子、氯金酸和磷酸盐缓冲溶液（PBS，pH 7.0）的混合物加热至

100^{\circ} C

60 分钟后（支持信息中的图 S1-S4），可靠地获得 Au 胶体溶液（支持信息中的图 S5）。图 1 显示了由具有不同空腔大小的 CD 分子合成的三种 AuNPs，分别是

α

-、

β

- 和

γ

-CD。三个相应的 AuNP 是

19 \pm 1.8, 20 \pm 1.6

，直径

15 \pm 1.8 nm

由透射电子显微镜（TEM）确定。根据动态光散射（DLS），它们的平均流体动力学直径分别为 22,24 和 19 nm，与 TEM 测量一致，尽管由于水合层和较大颗粒对 DLS 信号的贡献更大而明显扩大。

^{11}

对于

β - CD @ A u N P s

，它们的形状是球形/准球形，只有

8 %

尺寸分布（图 1E，F）。AuNP 溶液呈酒红色，具有以 520 nm 为中心的尖锐 SPR 带（图 1 G），表明金纳米球的典型特征。而对于

α

- 和

γ

-CD@AuNPs（图 1A、I），偶尔会观察到略微拉长的 NP。因此，溶液有点紫色，SPR 条带表现出
little broadening with small trailing over 750 nm (Figure 1C,K). Because

β

-CD had the best performances in the AuNP fabrication, the corresponding products were then employed for further study.
在 750 nm 以上略加宽，有小拖尾（图 1C，K）。由于

β

-CD 在 AuNP 制备中具有最佳性能，因此采用相应的产品进行进一步研究。

As shown in Figure 2A, the

β

-CD@AuNPs are 5 -fold twin crystalline, similar to the products obtained by the conventional Turkevich method.

^{12}

The AuNPs possess distinct lattice fringes, indicating good crystallinity. We then employed various characterization techniques to detect the surface chemistry of the products. The Fourier transform infrared spectroscopy (FT-IR) spectra of

β

-CD and the

β - CD @ A u N P s

were first detected. As shown in Figure 2B, the similar profiles of the two curves preliminarily indicate that the major feature groups of

β

CD molecules are retained in the obtained products. Furthermore, the hydroxy band (

3354.7 {cm}^{- 1}

) of the products is obviously narrower than that of the original

β - CD

Three-in-One: Sensing, Self-Assembly, and Cascade Catalysis of Cyclodextrin Modified Gold Nanoparticles 三合一：环糊精改性金纳米颗粒的传感、自组装和级联催化

S Supporting Information S 支持信息

Abstract 抽象

- INTRODUCTION -介绍

- RESULTS AND DISCUSSION - 结果与讨论

Three-in-One: Sensing, Self-Assembly, and Cascade Catalysis of Cyclodextrin Modified Gold Nanoparticles
三合一：环糊精改性金纳米颗粒的传感、自组装和级联催化