Confinement of AuAg NCs in a Pomegranate-Type Silica Architecture

Subscriber access provided by Stockholm University Library

Applications of Polymer, Composite, and Coating Materials

Confinement of AuAg NCs in Pomegranate-Type Silica Architecture for Improved Copper Ion Sensing and Imaging Jie Meng, Shuang E, Xing Wei, Xuwei Chen, and Jian-Hua Wang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • Publication Date (Web): 22 May 2019 Downloaded from http://pubs.acs.org on May 27, 2019

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 35 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

Confinement of AuAg NCs in Pomegranate-Type Silica Architecture for Improved Copper Ion Sensing and Imaging Jie Meng, Shuang E, Xing Wei, Xuwei Chen* and Jianhua Wang* Research Center for Analytical Sciences, Department of Chemistry, College of Sciences, Northeastern University, Box 332, Shenyang 110819, China

KEYWORDS: AuAg nanoclusters, dendritic silica spheres, pomegranate-type architecture, spatial confinement, Cu2+ sensing and imaging ABSTRACT: Metal nanoclusters (NCs) have been being a focus due to their superior optical properties, while their biomedical applications are limited by the relative low quantum yield and poor cellular uptaking behaviors. In present study, a pomegranate-type architecture with densely-packed AuAg NCs is constructed, where the amino-terminated dendritic silica spheres (dNSiO2) with ultralarge central-radial pore channels act as an efficient absorbent host for the self-assemble of AuAg NCs. The spatial confinement of AuAg NCs within the pomegranate-type silica architecture not only avoid the time-tedious purification procedure in metal NCs fabrication, but also offer significant improvement on the photoluminescence performance of AuAg NCs, i.e., the quantum yield (17.0%) is nearly doubled when compared to that of free AuAg NCs. The presence of Cu2+ induces the efficient quenching of the photoluminescence of obtained dNSiO2-AuAg NCs, achieving the sensitive detection

ACS Paragon Plus Environment

ACS Applied Materials & Interfaces 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

of Cu2+ with a detection limit of 0.060 M. Moreover, the pomegranate-type silica architecture serve itself as excellent nanocarrier to deliver AuAg NCs into living cells, making dNSiO2-AuAg NCs an efficient probe for intracellular Cu2+ sensing and imaging.


Page 2 of 35

Page 3 of 35 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


INTRODUCTION Noble metal nanoclusters (NCs), such as Au, Ag, Cu and Pt NCs, are a new class of luminescent nanomaterials with ultrasmall size, unique molecule-like properties and discrete electronic energy levels.1-5 These metal NCs are merited with nonblinking, large Stokes shift, favorable dispersity, good biocompatibility as well as strong resistance against photobleaching, making them promising spectral probes in the fields of sensing, imaging, molecular recognition and biomedical studies.6-11 Up to now, quite a few works have been focusing on the fabrication of highly luminescent metal NCs as their normal quantum yields (QYs) is significantly lower than those well-established chromophores (such as quantum dots and fluorescent dyes).12-14 Despite the attracting progress in fabricating luminescent metal NCs, the preparation of highly luminescent metal NCs with integrated biological functions and favorable biocompatibility for biomedical applications remains extremely challenging. Au NCs are an important class of metal NCs, and there are two strategies reported effectively on improving the QY of Au NCs. The first one is to fabricate bimetallic NCs by doping other metals into Au NCs, i.e., the preparation of AuAg NCs with enhanced luminescence by introduction of Ag into Au NCs,15-17 and the preparation of AuCu NCs with strong luminescence induced by the aggregation of Cu(I) complexes with Au(0) species.18 The another one is to make use of the spatial confinement effect, i.e., by encapsulating Au NCs into a polymer matrixes,19,20 layered double hydroxides (LDHs) nanosheets2 or metal-organic frameworks (MOFs)12,21 as a result of the mechanism of aggregation-induced emission (AIE).22-24



As a novel kind of porous material, dendritic mesoporous silica nanoparticles have become an attractive nanostructure for biomedical applications due to their distinctive structural and inherent features, including ultralarge central-radial pore channels, highly accessible inner surface, tunable pore size and dimension, facile surface functionalization and excellent biocompatibility.25,26 These prominent features make dendrimer-like silica nanoparticle a powerful nanocarrier platform, and demonstrate their potential in intracellular delivery of plasmid DNA27 and proteins.28,29 It is well recognized that intracellular and in vivo detecting of targets requires the full entry of fluorescent probe into the cells. For the applications of noble metal NCs in intracellular sensing and imaging, their up-taking by cells is rather difficult due to their poor surface functionality.6 Meanwhile metal NCs with ultrasmall size typically suffer from inadequate tumor accumulation due to their rapid clearance.30,31 At this juncture, dendritic silica spheres might provide an efficient answer to these challenges, as the introduction of dendritic silica spheres with appropriate size can improve tumor penetration for cancer diagnosis and therapy owing to the significant enhanced permeability and retention (EPR) effect.30,32 In this work, pomegranate-type silica architecture is fabricated, and then AuAg NCs is efficiently encapsulated into the pore channels of silica architecture via self-assembly. The secondary nanostructure integrates the merits of metal NCs and dendritic silica spheres, achieving enhanced performance for biomedical applications. This pomegranate-type silica architecture with high-density AuAg NCs (dNSiO2-AuAg NCs) is characterized systematically in


Page 4 of 35

Page 5 of 35 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


respect of morphology, AuAg NCs distribution and loading content within silica matrix as well as photoluminescent (PL) properties. Compared with the free AuAg NCs, the PL efficiency of the obtained dNSiO2-AuAg NCs is greatly improved due to the spatial confinement effect of AuAg NCs inside the dendritic silica architecture, making dNSiO2-AuAg NCs an efficient probe for sensitive and selective Cu2+ detection with a detection limit of 0.060 M. Moreover, the dendritic silica architecture can serve as an effective nanocarrier for the delivery of fluorescent AuAg NCs into live cells, demonstrated by the intracellular imaging and sensing of Cu2+ in HeLa Cells.

EXPERIMENTAL SECTION Materials and Instrumentations (see Supporting Information). Synthesis of AuAg NCs. AuAg NCs are prepared according to a typical procedure. Briefly, HAuCl4 (4 mL, 5 mM) and AgNO3 (1 mL) of different concentrations at varied Ag/Au molar ratio are added to freshly-prepared GSH solution (5 mL, 6 mM). The resultant mixture is heated under 70 °C for 24 h under gentle stirring. After cooling to room temperature, the reaction mixture is filtered through a 0.22 m filter membrane to remove the white precipitate of AgCl, and afterwards purified by dialysis process (MWCO: 3500). The final product is stored at 4 °C for further use. Preparation of Amino-Terminated Dendritic Silica Spheres. The dendritic silica spheres (dSiO2) are synthesized following a previously reported method.26,33 Typically, TEA (68 mg) is first dissolved in 25 mL deionized water at 80 °C under gentle stirring, then CTAB (380 mg) and sodium salicylate (168 mg) are added into



the above solution. After stirring for 1 h, 4 mL of TEOS is added and stirred for another 2 h. The product is collected by centrifugation (9000 rpm) and washed with ethanol for several times to remove the residual reactants. The collected product is dispersed in a solution of 50 mL methanol and 3 mL HCl, and refluxed at 60 °C for 6 h to eliminate the residual organic templates. This procedure is repeated for two times and the final product is dispersed in 100 mL ethanol. To prepare amino-terminated dendritic silica spheres (dNSiO2), 2.5 mL ammonia and 1 mL APTES are added into the above dSiO2 ethanol solution, then the mixture is stirred vigorously at room temperature for 12 h. The obtained product is washed with ethanol and deionized water thoroughly, and finally dispersed in 50 mL deionized water. The amount of dNSiO2 is achieved by freeze-drying under vacuum. Synthesis of dNSiO2-AuAg NCs Fluorescent Spheres. In order to assemble AuAg NCs, the wet precipitate from 1 mL dNSiO2 suspension (1 mg mL−1) are mixed with 2 mL AuAg NCs aqueous solution (1.7 mg mL-1), and then the mixture is sonicated for 10 min. The dNSiO2-AuAg NCs composites are harvested by centrifugation and washed with deionized water to remove excess AuAg NCs. This precipitate is finally re-suspended in 2 mL deionized water for further use. Note that the supernatant of AuAg NCs used for assembly is not further purified. Fluorescence Detection of Cu2+. The procedure for detection of Cu2+ with AuAg NCs or dNSiO2-AuAg NCs as probe is as following. 200 μL Cu2+ of various concentrations (prepared with 10 mM PBS buffer, pH = 7.4) are mixed with 50 μL AuAg NCs or dNSiO2-AuAg NCs solution. After incubation for 2 min at room


Page 6 of 35

Page 7 of 35 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


temperature, the photoluminescent (PL) spectra are recorded under excitation of 370 nm. Cytotoxicity Assay. HeLa cells are cultured in DMEM supplemented with 10% fetal bovine serum, 100 units mL-1 penicillin, and 100 g mL-1 streptomycin in a humidified incubator (37 C, 5% CO2). To evaluate the cytotoxicity of AuAg NCs and dNSiO2-AuAg NCs, MTT assays are performed using HeLa cells as model. At first, HeLa cells are cultivated in a 96-well cell culture plate and cultured for 12 h. The original medium is then removed, and different concentrations of AuAg NCs or dNSiO2-AuAg NCs in DMEM is put into each well and incubated for 24 h. Subsequently, the medium is abandoned and 100 L fresh DMEM containing 10 L MTT solution (5 mg mL-1) is introduced into each well and further incubated for 4 h. Finally, the medium is removed and 150 L dimethyl sulfoxide is added. The absorbance (A) of the resultant mixture at 490 nm is measured with an ELISA plate reader after shaking for 5 min. The cell viability is assessed according to following equation: Cell viability (%) = Atreat / Acontrol  100% Fluorescence Imaging of Cu2+ in Living Cells. HeLa cells are plated on a Petri dish with 20-mm bottom well, and cultured for 24 h in a humidified incubator (37 C, 5% CO2). To investigate the cellular uptake behaviors of AuAg NCs and dNSiO2-AuAg NCs, the cells were incubated with 100 g mL-1 AuAg NCs or dNSiO2-AuAg NCs in DMEM for 6 h respectively, then washed with PBS buffer (10 mM, pH = 7.4) for three times to remove the residual material before fluorescence imaging.



For fluorescent assay of Cu2+ in live cells, HeLa cells are incubated with dNSiO2-AuAg NCs in DMEM with the final concentration of 100 g mL-1 for 6 h and washed with PBS buffer (10 mM, pH = 7.4) for three times. Thereafter, different concentrations of Cu2+ (0, 2.5, and 5 M) is added and incubated for 30 min. The fluorescence imaging is performed on a confocal fluorescence microscope with a 40× objective lens (yellow fluorescence channel, Ex = 405 nm, Em = 560-620 nm). The optical density is evaluated using software Image J (National Institutes of Health).

RESULTS AND DISCUSSION Preparation and Characteristics of dNSiO2-AuAg NCs. The synthetic strategy of a pomegranate-type silica architecture is outlined in Scheme 1, which comprises the synthesis of AuAg NCs, the preparation of amino-terminated dendritic silica spheres (dNSiO2) and the self-assembly of AuAg NCs on dendritic silica framework. In the synthesis protocol of AuAg NCs, glutathione (GSH) is adopted as the protecting ligand. Au(III) is first reduced to Au(I) by the thiol group of GSH, followed immediately by the coordination of Au(I) and Ag(I) to the thiol group to form Au(I)/Ag(I)-thiolate complexes, the complexes is then condensed into a compact shell on an situ generated Au(0) core.17,22,34 As revealed in Figure 1a, the obtained AuAg NCs are well monodispersed with an average size of about 1.7  0.4 nm. The magnified HR-TEM image shows that the lattice fringe spacing of the obtained AuAg NCs is 0.233 nm (the bottom inset in Figure 1a), which is ascribed to the (111) lattice spacing of the face-centered cubic Au.35,36


Page 8 of 35

Page 9 of 35 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Scheme 1. Schematic illustration for the preparation of pomegranate-type AuAg NCs incorporated silica spheres.

The fabrication of highly luminescent metal NCs has always been a hot concern in biosensing and bioimaging. At this juncture, the strategy of bimetallic NCs has been proved to be an efficient way37, which also gains the support from the improved photoluminescence of AuAg NCs by silver doping17,38-41. As we all know, the purification procedure is a necessary step in order to ensure the characteristic luminescence of fabricated metal NCs. Due to the ultrasmall size and excellent dispersion of metal NCs, it is difficult to achieve purification by simple centrifugation, therefore, purification techniques such as dialysis, chromatographic separation and precipitation via organic reagent are usually adopted, which unavoidably leads to the problems such as long-time manipulations, large-volume consumption of organic reagent, easy coagulation and damaged luminescent properties of metal NCs in the purification process. To address this issue and further improve the PL performance of



the obtained AuAg NCs, dendritic silica spheres with center-radial open pores and highly accessible inner surface are adopted as the nanocarrier for the self-assembly of AuAg NCs. The dendritic silica spheres are firstly prepared via a one-pot synthesis protocol with TEOS as silica source, cationic surfactant CTAB and sodium salicylate as structure directing agent.26 Subsequently, the surface of dSiO2 is aminated by APTES for the assembling of AuAg NCs. The as-prepared dNSiO2 spheres are monodispersed with a uniform size of ∼235 nm (Figure 1b), and the unique structure with central-radial pore channels can be clearly observed (Figure 1c), which is favorable to load nanoparticle guests. By dispersing the dNSiO2 templates into the AuAg NCs, the self-assembly of AuAg NCs on the dNSiO2 framework is facilely achieved under ultrasonication due to free diffusion of AuAg NCs in the pore channels of dNSiO2 and strong interaction between the amino-groups of dNSiO2 and the carboxyl-groups AuAg NCs. Moreover, the time-consuming dialysis process for the purification of AuAg NCs in conventional protocol is avoided as only AuAg NCs are encapsulated inside the dNSiO2 framework during the self-assembly process. The successful encapsulation of AuAg NCs can be clearly observed in the TEM image of dNSiO2-AuAg NCs nanospheres. (Figure 1d). In order to further demonstrate the self-assembly of AuAg NCs, scanning transmission electron microscopy (STEM) is performed. As illustrated in Figure 1e, a large number of AuAg NCs (white dots) distribute evenly throughout the whole dNSiO2 matrix. Moreover, the corresponding energy-dispersive X-ray spectroscopy (EDS) elemental mapping of Au, Ag, and S from AuAg NCs (Figure 1f), and the central peaks of Au


Page 10 of 35

Page 11 of 35 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


and Ag from the EDS elemental line scanning spectra of single dNSiO2-AuAg NCs sphere (Figure S1) further indicate the homogenous distribution of AuAg NCs within the silica framework. ICP-MS assays indicate that the Au and Ag content are 411.4 and 32.0 μg mg-1 in AuAg NCs, 230.4 and 20.9 μg mg-1 in dNSiO2-AuAg NCs, respectively.

Figure 1. (a) HR-TEM image of AuAg NCs. The insets show the size-distribution histogram (top) and the magnified HR-TEM image (bottom) of AuAg NCs. (b) SEM



Page 12 of 35

image of dNSiO2 templates. TEM images of (c) dNSiO2 templates and (d) dNSiO2-AuAg NCs nanospheres. (e) STEM image of dNSiO2-AuAg NCs nanospheres and (f) corresponding EDS elemental mapping.

Figure 2a illustrates the nitrogen adsorption-desorption results of the dNSiO2 spheres before and after the self-assembly of AuAg NCs. The dNSiO2 spheres exhibit a typical type IV isotherm with a distinct capillary condensation step and hysteresis loop.

The

corresponding

pore

size

distribution

curve

shows

that

the

Barrett-Joyner-Halenda (BJH) pore diameter of the original dNSiO2 templates is about 27-43 nm. The self-assembly of AuAg NCs on silica walls leads to the decrease on the Brunauer-Emmett-Teller (BET) surface area from 446 to 254 m2 g−1, and the total pore volume from 1.99 to 1.43 cm3 g−1. The assembly of AuAg NCs within the silica framework are further confirmed by FT-IR spectra, Zeta potential, and X-ray diffraction (XRD) pattern. FT-IR spectra of AuAg NCs, dNSiO2 and dNSiO2-AuAg NCs composites are demonstrated in Figure 2b. The intense peak appearing at ca. 1083 cm−1 belongs to Si–O–Si antisymmetric stretching vibration. The two characteristic peaks at ca. 798 cm−1 and ca. 464 cm−1 are attributed to symmetric stretching vibration and bending vibration of Si–O, respectively.42,43 As for the GSH-protected AuAg NCs, the stretching vibrations of C=O at ca. 1645 cm1, the bending vibrations of NH at ca. 1529 cm1 and the stretching vibrations of CO at ca. 1396 cm1 are clearly observed. Comparing the FT-IR spectra of dNSiO2, several distinct absorption peaks derived from AuAg NCs at ca. 1400, 1537 and 1646 cm1 appear in the FT-IR spectra of dNSiO2-AuAg NCs,


Page 13 of 35 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


demonstrating the successful self-assembly of AuAg NCs within the silica framework. The zeta potential analysis indicate that the dNSiO2 is positively charged (7.3 mV), and the obtained AuAg NCs are strong negative charged (34.9 mV). After AuAg NCs are self-assembled into the pores of dNSiO2 via interaction between amino-groups of dNSiO2 and carboxyl-groups of AuAg NCs including electrostatic attraction and hydrogen bonding, a partly neutralized zeta potential of −19.6 mV for the final product dNSiO2-AuAg NCs is obtained (Figure 2c). The wide-angle XRD patterns of dNSiO2, AuAg NCs and dNSiO2-AuAg NCs are revealed in Figure 2d. A typical diﬀraction peak of dNSiO2 appears at around 22.5° in the XRD pattern of dNSiO2, indicating the existence of amorphous silica.43,44 The XRD pattern of AuAg NCs displays two diffraction peaks at 32.9° and 51.2°, confirming the formation of metal nanoclusters, rather than metallic nanoparticles. Because the diffraction angle at 32.9° deviate from the peaks of 38.2° corresponding to the (111) plane of Au fcc structure, and the extra peak at 51.2° is non-existent for the fcc structure.34,45 Unsurprisingly, both of the distinct diffraction peaks of dNSiO2 and AuAg NCs are clearly observed in the XRD pattern of dNSiO2-AuAg NCs. X-ray photoelectron spectroscopy (XPS) is applied to identify the oxidation states of Au and Ag in as-prepared dNSiO2-AuAg NCs. The survey spectrum in Figure S2a reveals the elemental composition of dNSiO2-AuAg NCs, containing C, N, O, S, Au, Ag and Si. The lower binding energies of Au 4f7/2 (84.0 eV) indicates that the existence of some Au(I), but Au(0) is dominant (Figure S2b).34,39,46 Meanwhile, the Ag 3d5/2 peak is centered at 367.5 eV which is lower than bulk Ag (367.9 eV),



illustrating the Ag atoms are positively charged (Figure S2c).34,47,48

Figure 2. (a) Nitrogen adsorption-desorption isotherms and pore size distribution curves (inset) of dNSiO2 and dNSiO2-AuAg NCs. (b) FTIR spectra of AuAg NCs, dNSiO2 and dNSiO2-AuAg NCs. (c) Zeta potential of AuAg NCs, dNSiO2 and dNSiO2-AuAg NCs in PBS buffer (pH 7.4, 10 mM). (d) The wide-angle XRD patterns of dNSiO2, AuAg NCs and dNSiO2-AuAg NCs.

The Optical Properties of dNSiO2-AuAg NCs. The photoluminescent (PL) spectra and the corresponding photographs of AuAg NCs with different Ag/Au molar ratio are shown in Figure 3a. Compared to the pure Au NCs, improved photoluminescence behaviors of AuAg NCs are observed due to the “silver effect”.39,46 The photoluminescence of Au NCs is induced by the Au(I)-thiolate complexes on the NCs surface via aggregation-induced emission (AIE). After the introduction of Ag(I) ions,


Page 14 of 35

Page 15 of 35 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Ag(I) ions serve as linker to turn the small Au(I)-thiolate motifs into large Au(I)/Ag(I)-thiolate complexes, and the AIE of the complexes on the entire NCs surface17 offers the as-prepared AuAg NCs with improved photoluminescence. It can be seen that the bimetallic AuAg NCs with Ag/Au molar ratio of 0.2, 0.3 and 0.5 displays considerable photoluminescence, and then the AuAg NCs prepared with an Ag/Au molar ratio of 0.2 is chosen for ensuing studies based on the comprehensive considerations of economy and toxicity. Figure S3 shows the UV-vis absorption spectra, PL excitation and emission spectra of the AuAg NCs. The absorption spectra displays shoulder peaks at near 400 nm. Moreover, no localized surface plasmon resonance (LSPR) absorption peaks belonging to the typical characteristic of spherical Au and Ag NPs are observed, indicating that the core diameter of the obtained AuAg NCs is less than 2 nm.49 The excitation and emission maxima of the AuAg NCs are centralized at 370 and 570 nm, respectively. It has been demonstrated that the PL performance of metal NCs can be efficiently enhanced by the “spatial confinement” strategy,1,2,20 and dendritic silica spheres are expected to serve as an effective confining nanocarrier in present study. The photoluminescence of Au NCs and AuAg NCs is mainly related to the AIE effect, which is closely associated with the restriction of intramolecular motion (RIM)12,22 When AuAg NCs is confined in the pore of dNSiO2, the photoluminescence of AuAg NCs is further enhanced due to the fact that the free movement of Au(I)/Ag(I)-thiolate complexes is restricted, resulting in the reduction of non-radiative transition.12 The effect of AuAg NCs loading content (defined as mass ratio of captured AuAg NCs to



dNSiO2) on the PL behaviors of final dNSiO2-AuAg NCs are thus investigated. It can be seen in Figure 3b that the PL intensity of dNSiO2-AuAg NCs gradually increases with the loading content of AuAg NCs, therefore, dNSiO2-AuAg NCs with maximal AuAg NCs loading content, i.e., ca 231.7%, is adopted for ensuing investigations. Afterwards, the absolute quantum yield (QY) of Au NCs, AuAg NCs and the ultimate dNSiO2-AuAg NCs are determined by a quantum yield spectrometer (Hamamatsu Photonic K.K., Japan). The QY of free Au NCs is about 3.8%, and the Ag-doping facilitates to improve the QY of AuAg NCs to 9.4%. The spatial confinement of AuAg NCs within dNSiO2 architecture further improves the QY to 17.0%, which might be favorable for biomedical application.

Figure 3. (a) The photoluminescent spectra of the AuAg NCs with different Ag/Au molar ratio. Inset shows the corresponding photographs of the AuAg NCs in aqueous media under visible (upper) and UV light of 365 nm (lower). (b) The


Page 16 of 35

Page 17 of 35 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


photoluminescent spectra of the dNSiO2-AuAg NCs with varied AuAg NCs loading content from 34% to 231.7%. (c) Cumulative release behaviors of AuAg NCs from dNSiO2-AuAg NCs nanospheres in PBS buffer (10 mM, pH = 7.4). Inset shows the corresponding photographs of the supernatant. (d) Photoluminescent stabilities of Au NCs, AuAg NCs and dNSiO2-AuAg NCs against continuous irradiation with a 150 W Xenon lamp.

Considering the possible biomedical applications of dNSiO2-AuAg NCs, the leakage of loaded AuAg NCs in physiological environment (pH 7.4) is studied by luminescent quantitation. Nearly no release of AuAg NCs from the dNSiO2 architecture is observed within a week (Figure 3c), indicating the excellent stability of dNSiO2-AuAg NCs, which should attribute to the strong interaction between the amino-groups

of

dNSiO2

and

the

carboxyl-groups

of

AuAg

NCs.

The

photoluminescence stabilities of Au NCs, AuAg NCs and dNSiO2-AuAg NCs have been investigated by continuous irradiation with a 150 W Xenon lamp, and almost no changes on the luminescence of these three NCs is observed (Figure 3d), suggesting that the obtained dNSiO2-AuAg NCs is merited with favorable photo-stability, and it might be used as powerful fluorescent probe to handle with real samples. Fluorescence Sensing of Cu2+ with dNSiO2-AuAg NCs. As this pomegranate-type nanostructure with high-density AuAg NCs has been illustrated to be highly luminescent, which might pose itself as excellent probe in biosensing and imaging. Delightedly, we find that the luminescence of dNSiO2-AuAg NCs is effectively quenched in the presence of Cu2+. The reason might lie in the fact that the complexation of Cu2+ with GSH molecules would induce the aggregation of



GSH-protected AuAg NCs.50-52 At the same time, the unstable valence electron structure of Cu2+ (3d9) would impede the ligand-Au/Ag charge transfer. The aggregation of AuAg NCs is further verified by HR-TEM. As presented in Figure S4, AuAg NCs are uniformly dispersed in aqueous solution, and the aggregation of AuAg NCs is clearly observed after the addition of Cu2+. Then the performance of dNSiO2-AuAg NCs as a luminescent probe on Cu2+ detection is investigated. Figure 4a-d show the luminescent emissions of AuAg NCs and dNSiO2-AuAg NCs in the presence of different concentration of Cu2+. It can be seen that the PL intensity of AuAg NCs and dNSiO2-AuAg NCs both decrease gradually with the increasing Cu2+ concentration. The linear range for Cu2+ detection with AuAg NCs as probe is 2-10 M, and the detection limit is derived to be 0.31 M obtained via the 3σ criterion. While for dNSiO2-AuAg NCs, the linear range is from 0.2 to 2 μM. Meanwhile, a detection limit of 0.060 M is obtained, which is evidently more lower than that of AuAg NCs. For comparison, the detection performance of recently reported Cu2+ sensors are summarized in Table S1. It can be seen that dNSiO2-AuAg NCs offers improved sensitivity in Cu2+ detection when compared with the reported metal NPs/NCs probes, contributed by the enhanced quantum yield induced by the spatial confinement of AuAg NCs. Impressively, the sensitivity of Cu2+ detection is improved due to the application of dendritic silica spheres. We have demonstrated that there are ultralarge central-radial pore channels in the obtained dendritic silica colloids. After the assembly of AuAg NCs, the surface of pore channels of dNSiO2 are coated with large


Page 18 of 35

Page 19 of 35 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


number of negative-charged AuAg NCs. The electrostatic interactions between nagetive-charged AuAg NCs and cations such as Cu2+ leads to the migration of cations into the pores of dNSiO2, and the local concentration amplification effect caused by the cations accumulation eventually offer an improved detection sensitivity on Cu2+ detection.

Figure 4. (a) The photoluminescent spectra of AuAg NCs upon addition of various concentrations of Cu2+. (b) The relationship of the photoluminescent intensity of AuAg NCs versus the Cu2+ concentrations. Inset: the fitted calibration curve in the



linear region of 2-10 M Cu2+. (c) The photoluminescent spectra of dNSiO2-AuAg NCs upon addition of various concentrations of Cu2+. (d) The relationship of the photoluminescent intensity of dNSiO2-AuAg NCs versus the Cu2+ concentrations. Inset: the fitted calibration curve in the linear region of 0.2-2 M Cu2+. (e) Selectivity of the dNSiO2-AuAg NCs probe toward metal ions, anions, amino acids and various ROS. (500 M for Na+, K+, Ca2+ and Mg2+, 10 M for other cations, 10 M for anions, 10 M for amino acids and 10 M for ROS).

To detect targets in real samples of complicated matrices, selectivity is also a vital factor for the detection method except sensitivity.53 Hence, the selectivity of the dNSiO2-AuAg NCs probe in Cu2+ detection is investigated. The luminescence responses of dNSiO2-AuAg NCs towards the common metal ions (Na+, K+, Ca2+, Mg2+, Cd2+, Fe2+, Fe3+, Mn2+, Zn2+, Cr3+, Pb2+, Ag+, Al3+, Hg2+ and Ba2+), anions (S2−, I−, CO32−, NO3−, SO42− and NO2−), physiological relevant amino acids, as well as reactive oxygen species (ROS) such as 1O2, ClO−, H2O2, ONOO− and •OH under the identical testing conditions are recoded. As illustrated in Figure 4e, only Cu2+ is found to pose significant effect on the luminescence of dNSiO2-AuAg NCs, and negligible interferences are observed for other metal ions and amino acids. Though Cu2+ may lead to the formation of ROS in living cells,54 while the presence of ROS (1O2, ClO−, H2O2, ONOO− and •OH) offers no obvious variation on the photoluminescence of dNSiO2-AuAg NCs, suggesting the favorable selectivity of dNSiO2-AuAg NCs on Cu2+ detection. The excellent response selectivity might attribute to the high constant of Cu2+-GSH complexation51,55 and the unstable valence electron structure of Cu2+ (3d9).


Page 20 of 35

Page 21 of 35 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Fluorescence Imaging of Cu2+ in Live Cells. Encouraged by the excellent performance of dNSiO2-AuAg NCs on Cu2+ detection, the potential of this probe in cell imaging is further investigated. The biocompatibility of AuAg NCs and dNSiO2-AuAg NCs was first evaluated by a standard MTT assay. Compared with the free AuAg NCs, dNSiO2-AuAg NCs exhibit lower cytotoxicity. Cell viability of higher than 90% can be obtained even the concentration of dNSiO2-AuAg NCs is high up to 500 g mL−1 (in which the net amount of AuAg NCs is about 280 g mL−1 according to ICP-MS results) (Figure S5), indicating the excellent biocompatibility of dNSiO2-AuAg NCs. The imaging results of HeLa cells after culturing with 100 g mL–1 AuAg NCs/dNSiO2-AuAg NCs are shown in Figure 5. It has been demonstrated that free AuAg NCs can not serve as imaging probe due to the difficulty in entering cells caused by the electrostatic repulsion between AuAg NCs and cell membrane.6 While in present study, it can be seen that dNSiO2-AuAg NCs can be readily taken up by cells and bright imaging are observed, indicating that the effectiveness of this pomegranate-type silica architecture as an powerful carrier in delivering AuAg NCs into living cells. Since dNSiO2-AuAg NCs is negative charged, the endocytosis might be the main routes for the entry of dNSiO2-AuAg NCs into cells. The endosomes wrapped dNSiO2-AuAg NCs are first formed by nonspecific cellular uptake due to their strong affinity for clathrin-coated vesicles, and then dNSiO2-AuAg NCs escape from the endosomes into cytoplasm due to the ‘‘Proton Sponge’’ effect.56



Figure 5. The confocal fluorescence microscopy images of HeLa cells after incubation with 100 g mL-1 (a) AuAg NCs and (b) dNSiO2-AuAg NCs for 3 h and 6 h, respectively. Scale bar is 20 μm.

Thereafter, the dNSiO2-AuAg NCs probe is employed for visualizing Cu2+ in living cells. HeLa cells are first cultured with dNSiO2-AuAg NCs for 6 h and then treated with different concentrations of Cu2+ for 30 min. ICP-MS assay indicate that the Cu content in living cells after incubating with 2.5 μM and 5 μM Cu2+ solutions are determined to be about 24.8 fg cell-1 and 53.6 fg cell-1, respectively (Figure S6). It is obvious that intracellular Cu content increase gradually with the concentration of Cu2+ incubating solution. As illustrated in Figure 6a-c, the intracellular fluorescence decreases gradually when the concentration of Cu2+ increases from 0 to 5 μM. The mean fluorescence intensity of cell regions is thus estimated and compared via ImageJ software (National Institutes of Health). The relationship between optical density and Cu2+ concentration is shown in Figure 6d. These results indicate that dNSiO2-AuAg NCs nanoprobes can be applied for Cu2+ sensing in living cells.


Page 22 of 35

Page 23 of 35 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 6. The confocal fluorescence microscopy images of HeLa cells cultured with 100 g mL-1 dNSiO2-AuAg NCs for 6 h and then treated with various concentrations of Cu2+. (a) 0 μM, (b) 2.5 μM, (c) 5 μM. All the fluorescence images were taken at a 405 nm laser. Scale bar is 20 μm. (d) The relationship between optical density and Cu2+ concentration.

CONCLUSIONS In summary, we propose a novel, simple and effective strategy for the preparation of highly luminescent AuAg NCs with integrated biological functions and favorable biocompatibility for biomedical application. High density of AuAg NCs are self-assembled into dendritic silica matrix due to their highly accessible inner surface of dendritic silica and the host-guest interaction. The as-prepared dNSiO2-AuAg NCs displays high quantum yield of 17.0%, which is greatly improved by the “silver effect” and the “spatial confinement” strategy compared with free AuAg NCs. Significantly, this pomegranate-type nanostructure is readily up-taken by living cells and show high sensitivity in Cu2+ detection, making the obtained dNSiO2-AuAg NCs a powerful nanoprobe for Cu2+ sensing and imaging in living cells. This strategy is expected to expand the application of metal nanoclusters in bioanalysis, bioimaging,



cancer therapy, and catalysis by exploiting dendritic silica spheres as a scaffold, where functional groups such as amino-groups, mercapto-groups can be grafted for anchoring metal nanoclusters, and the ultralarge pore channel can serve as efficient nanoreactor.


Page 24 of 35

Page 25 of 35 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


ASSOCIATED CONTENT Supporting Information

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] (X.-W. Chen); [email protected] (J.-H. Wang). Tel: +86-24-83688944. Fax: +86-24-83676698. ORCID Xuwei Chen: 0000-0001-7189-5022 Jianhua Wang: 0000-0003-2175-3610 Notes The authors declare no competing financial interest.

ACKNOWLEDGMENTS The authors appreciate financial support from National Natural Science Foundation of China (21475017, 21727811). Supporting Information Available: Materials and Instrumentations; STEM images and corresponding EDS elemental line scanning of dNSiO2-AuAg NCs nanospheres; The XPS spectra of dNSiO2-AuAg NCs, High resolution Au4f and Ag3d peaks of dNSiO2-AuAg NCs; The UV-vis absorption spectra, photoluminescent excitation and emission spectra of the AuAg NCs (Ag/Au = 0.2); HR-TEM images of AuAg NCs in water and 100 μM Cu2+ solution; The



Page 26 of 35

viability of HeLa cells after incubation with different concentrations of AuAg NCs and dNSiO2-AuAg NCs nanospheres for 24 h; Intracellular Cu content in HeLa cells measured by ICP-MS after incubation with 0, 2.5, and 5 μM of Cu2+ for 30 min; Comparisons on the performance of recent reported sensors for Cu2+ detection.

REFERENCES (1) Bai, X. L.; Xu, S. Y.; Wang, L. Y. Full-Range pH Stable Au-Clusters in Nanogel for Confinement-Enhanced Emission and Improved Sulfide Sensing in Living Cells. Anal. Chem. 2018, 90, 3270-3275. (2) Tian, R.; Zhang, S. T.; Li, M. W.; Zhou, Y. Q.; Lu, B.; Yan, D. P.; Wei, M.; Evans, D. G.; Duan, X. Localization of Au Nanoclusters on Layered Double Hydroxides

Nanosheets:

Confinement-Induced

Emission

Enhancement

and

Temperature-Responsive Luminescence. Adv. Funct. Mater. 2015, 25, 5006-5015. (3) Luo, Z. T.; Zheng, K. Y.; Xie, J. P. Engineering Ultrasmall Water-Soluble Gold and Silver Nanoclusters for Biomedical Applications. Chem. Commun. 2014, 50, 5143-5155. (4) Tao, Y.; Li, M. Q.; Ren, J. S.; Qu, X. G. Metal Nanoclusters: Novel Probes for Diagnostic and Therapeutic Applications. Chem. Soc. Rev. 2015, 44, 8636-8663. (5) Chakraborty, I.; Pradeep, T. Atomically Precise Clusters of Noble Metals: Emerging Link between Atoms and Nanoparticles. Chem. Rev. 2017, 117, 8208-8271. (6) Xie, Y. Z. Y.; Xianyu, Y. L.; Wang, N. X.; Yan, Z. Y.; Liu, Y.; Zhu, K.; Hatzakis, N. S.; Jiang, X. Y. Functionalized Gold Nanoclusters Identify Highly Reactive Oxygen Species in Living Organisms. Adv. Funct. Mater. 2018, 28, 1702026.


Page 27 of 35 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(7) Zang, J. C.; Li, C. A.; Zhou, K.; Dong, H. S.; Chen, B.; Wang, F. D.; Zhao, G. H. Nanomolar Hg2+ Detection Using β-Lactoglobulin-Stabilized Fluorescent Gold Nanoclusters in Beverage and Biological Media. Anal. Chem. 2016, 88, 10275-10283. (8) Sun, J.; Jin, Y. D. Fluorescent Au Nanoclusters: Recent Progress and Sensing Applications. J. Mater. Chem. C 2014, 2, 8000-8011. (9) Chen, L. Y.; Wang, C. W.; Yuan, Z. Q.; Chang, H. T. Fluorescent Gold Nanoclusters: Recent Advances in Sensing and Imaging. Anal. Chem. 2015, 87, 216-229. (10) Zhang, L. B.; Wang, E. K. Metal Nanoclusters: New Fluorescent Probes for Sensors and Bioimaging. Nano Today 2014, 9, 132-157. (11) Shang, L.; Dong, S. J.; Nienhaus, G. U. Ultra-Small Fluorescent Metal Nanoclusters: Synthesis and Biological Applications. Nano Today 2011, 6, 401-418. (12) Cao, F. F.; Ju, E. G.; Liu, C. Q.; Li, W.; Zhang, Y.; Dong, K.; Liu, Z.; Ren, J. S.; Qu, X. G. Encapsulation of Aggregated Gold Nanoclusters in a Metal-Organic Framework for Real-Time Monitoring of Drug Release. Nanoscale 2017, 9, 4128-4134. (13) Le Guevel, X.; Trouillet, V.; Spies, C.; Li, K.; Laaksonen, T.; Auerbach, D.; Jung, G.; Schneider, M. High Photostability and Enhanced Fluorescence of Gold Nanoclusters by Silver Doping. Nanoscale 2012, 4, 7624-7631. (14) Oh, E.; Delehanty, J. B.; Field, L. D.; Mäkinen, A. J.; Goswami, R.; Huston, A. L.; Medintz, I. L. Synthesis and Characterization of PEGylated Luminescent Gold Nanoclusters Doped with Silver and Other Metals. Chem. Mater. 2016, 28,



8676-8688. (15) Wang, S. X.; Meng, X. M.; Das, A.; Li, T.; Song, Y. B.; Cao, T. T.; Zhu, X. Y.; Zhu, M. Z.; Jin, R. C. A 200-fold Quantum Yield Boost in the Photoluminescence of Silver-Doped AgxAu25-x Nanoclusters: The 13th Silver Atom Matters. Angew. Chem. Int. Ed. 2014, 53, 2376-2380. (16) Zhou, T. Y.; Lin, L. P.; Rong, M. C.; Jiang, Y. Q.; Chen, X. Silver-Gold Alloy Nanoclusters as a Fluorescence-Enhanced Probe for Aluminum Ion Sensing. Anal. Chem. 2013, 85, 9839-9844. (17) Dou, X. Y.; Yuan, X.; Yu, Y.; Luo, Z. T.; Yao, Q. F.; Leong, D. T.; Xie, J. P. Lighting up Thiolated Au@Ag Nanoclusters via Aggregation-Induced Emission. Nanoscale 2014, 6, 157-161. (18) Kang, X.; Wang, S. X.; Song, Y. B.; Jin, S.; Sun, G. D.; Yu, H. Z.; Zhu, M. Z. Bimetallic Au2 Cu6 Nanoclusters: Strong Luminescence Induced by the Aggregation of Copper(I) Complexes with Gold(0) Species. Angew. Chem. Int. Ed. 2016, 55, 3675-3678. (19) Pyo, K.; Thanthirige, V. D.; Kwak, K.; Pandurangan, P.; Ramakrishna, G.; Lee, D. Ultrabright Luminescence from Gold Nanoclusters: Rigidifying the Au(I)-Thiolate Shell. J. Am. Chem. Soc. 2015, 137, 8244-8250. (20) Goswami, N.; Lin, F. X.; Liu, Y. B.; Leong, D. T.; Xie, J. P. Highly Luminescent Thiolated Gold Nanoclusters Impregnated in Nanogel. Chem. Mater. 2016, 28, 4009-4016. (21) Gao, Q.; Xu, S. Y.; Guo, C.; Chen, Y. G.; Wang, L. Y. Embedding Nanocluster


Page 28 of 35

Page 29 of 35 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


in MOF via Crystalline Ion Triggered Growth Strategy for Improved Emission and Selective Sensing. ACS Appl. Mater. Interfaces 2018, 10, 16059-16065. (22) Luo, Z. T.; Yuan, X.; Yu, Y.; Zhang, Q. B.; Leong, D. T.; Lee, J. Y.; Xie, J. P. From Aggregation-Induced Emission of Au(I)-Thiolate Complexes to Ultrabright Au(0)@Au(I)-Thiolate Core-Shell Nanoclusters. J. Am. Chem. Soc. 2012, 134, 16662-16670. (23) Wu, Z. N.; Liu, J. L.; Gao, Y.; Liu, H. W.; Li, T. T.; Zou, H. Y.; Wang, Z. G.; Zhang, K.; Wang, Y.; Zhang, H.; Yang, B. Assembly-Induced Enhancement of Cu Nanoclusters Luminescence with Mechanochromic Property. J. Am. Chem. Soc. 2015, 137, 12906-12913. (24) Le Guével, X.; Perez Perrino, M.; Fernández, T. D.; Palomares, F.; Torres, M. J.; Blanca, M.; Rojo, J.; Mayorga, C. Multivalent Glycosylation of Fluorescent Gold Nanoclusters Promotes Increased Human Dendritic Cell Targeting via Multiple Endocytic Pathways. ACS Appl. Mater. Interfaces 2015, 7, 20945-20956. (25) Du, X.; Qiao, S. Z. Dendritic Silica Particles with Center-Radial Pore Channels: Promising Platforms for Catalysis and Biomedical Applications. Small 2015, 11, 392-413. (26) Yang, Y. N.; Bernardi, S.; Song, H.; Zhang, J.; Yu, M. H.; Reid, J. C.; Strounina, E.; Searles, D. J.; Yu, C. Z. Anion Assisted Synthesis of Large Pore Hollow Dendritic Mesoporous Organosilica Nanoparticles: Understanding the Composition Gradient. Chem. Mater. 2016, 28, 704-707. (27) Du, X.; Shi, B. Y.; Liang, J.; Bi, J. X.; Dai, S.; Qiao, S. Z. Developing



Functionalized Dendrimer-Like Silica Nanoparticles with Hierarchical Pores as Advanced Delivery Nanocarriers. Adv. Mater. 2013, 25, 5981-5985. (28) Xu, C.; Yu, M. H.; Noonan, O.; Zhang, J.; Song, H.; Zhang, H. W.; Lei, C.; Niu, Y. T.; Huang, X. D.; Yang, Y. N.; Yu, C. Z. Core-Cone Structured Monodispersed Mesoporous Silica Nanoparticles with Ultra-Large Cavity for Protein Delivery. Small 2015, 11, 5949-5955. (29) Shen, D. K.; Yang, J. P.; Li, X. M.; Zhou, L.; Zhang, R. Y.; Li, W.; Chen, L.; Wang, R.; Zhang, F.; Zhao, D. Y. Biphase Stratification Approach to Three-Dimensional Dendritic Biodegradable Mesoporous Silica Nanospheres. Nano Lett. 2014, 14, 923-932. (30) Li, H. J.; Du, J. Z.; Du, X. J.; Xu, C. F.; Sun, C. Y.; Wang, H. X.; Cao, Z. T.; Yang, X. Z.; Zhu, Y. H.; Nie, S. M.; Wang, J. Stimuli-Responsive Clustered Nanoparticles for Improved Tumor Penetration and Therapeutic Efficacy. Proc. Natl. Acad. Sci. U.S.A. 2016, 113, 4164-4169. (31) Zhang, X. D.; Luo, Z. T.; Chen, J.; Shen, X.; Song, S. S.; Sun, Y. M.; Fan, S. J.; Fan, F. Y.; Leong, D. T.; Xie, J. P. Ultrasmall Au10-12(SG)10-12 Nanomolecules for High Tumor Specificity and Cancer Radiotherapy. Adv. Mater. 2014, 26, 4565-4568. (32) Chen, Y.; Chu, C.; Zhou, Y. C.; Ru, Y. F.; Chen, H. R.; Chen, F.; He, Q. J.; Zhang, Y. L.; Zhang, L. L.; Shi, J. L. Reversible Pore-Structure Evolution in Hollow Silica Nanocapsules: Large Pores for siRNA Delivery and Nanoparticle Collecting. Small 2011, 7, 2935-2944. (33) Huang, L.; Liao, T.; Wang, J.; Ao, L. J.; Su, W.; Hu, J. Brilliant Pitaya-Type


Page 30 of 35

Page 31 of 35 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Silica Colloids with Central-Radial and High-Density Quantum Dots Incorporation for Ultrasensitive Fluorescence Immunoassays. Adv. Funct. Mater. 2018, 28, 1705380. (34) Zhang, J.; Yuan, Y.; Wang, Y.; Sun, F. F.; Liang, G. L.; Jiang, Z.; Yu, S. H. Microwave-Assisted Synthesis of Photoluminescent Glutathione-Capped Au/Ag Nanoclusters: A Unique Sensor-on-a-Nanoparticle for Metal ions, Anions, and Small Molecules. Nano Res. 2015, 8, 2329-2339. (35) Shang, L.; Azadfar, N.; Stockmar, F.; Send, W.; Trouillet, V.; Bruns, M.; Gerthsen, D.; Nienhaus, G. U. One-Pot Synthesis of Near-Infrared Fluorescent Gold Clusters for Cellular Fluorescence Lifetime Imaging. Small 2011, 7, 2614-2620. (36) Shang, L.; Yang, L. X.; Stockmar, F.; Popescu, R.; Trouillet, V.; Bruns, M.; Gerthsen, D.; Nienhaus, G. U. Microwave-Assisted Rapid Synthesis of Luminescent Gold Nanoclusters for Sensing Hg2+ in Living Cells using Fluorescence Imaging. Nanoscale 2012, 4, 4155-4160. (37) Yuan, X.; Dou, X. Y.; Zheng, K. Y.; Xie, J. P. Recent Advances in the Synthesis and Applications of Ultrasmall Bimetallic Nanoclusters. Part. Part. Syst. Char. 2015, 32, 613-629. (38) Zhou, Q.; Lin, Y. X.; Xu, M. D.; Gao, Z. Q.; Yang, H. H.; Tang, D. P. Facile Synthesis of Enhanced Fluorescent Gold-Silver Bimetallic Nanocluster and Its Application for Highly Sensitive Detection of Inorganic Pyrophosphatase Activity. Anal. Chem. 2016, 88, 8886-8892. (39) Zhang, N.; Si, Y. M.; Sun, Z. Z.; Chen, L. J.; Li, R.; Qiao, Y. C.; Wang, H.



Page 32 of 35

Rapid, Selective, and Ultrasensitive Fluorimetric Analysis of Mercury and Copper Levels in Blood using Bimetallic Gold-Silver Nanoclusters with “Silver Effect”-Enhanced Red Fluorescence. Anal. Chem. 2014, 86, 11714-11721. (40) Guan, G. J.; Cai, Y. Q.; Liu, S. H.; Yu, H. D.; Bai, S. Q.; Cheng, Y.; Tang, T.; Bharathi, M. S.; Zhang, Y. W.; Han, M. Y. High-Level Incorporation of Silver in Gold Nanoclusters: Fluorescence Redshift upon Interaction with Hydrogen Peroxide and Fluorescence Enhancement with Herbicide. Chem. Eur. J. 2016, 22, 1675-1681. (41) Huang, H.; Li, H.; Feng, J. J.; Wang, A. J. One-Step Green Synthesis of Fluorescent Bimetallic Au/Ag Nanoclusters for Temperature Sensing and in Vitro Detection of Fe3+. Sens. Actuators, B 2016, 223, 550-556. (42) Chen, L. L.; Li, L.; Zhang, L. Y.; Xing, S. X.; Wang, T. T.; Wang, Y. A.; Wang, C. G.; Su, Z. M. Designed Fabrication of Unique Eccentric Mesoporous Silica Nanocluster-Based Core-Shell Nanostructures for pH-Responsive Drug Delivery. ACS Appl. Mater. Interfaces 2013, 5, 7282-7290. (43)

Chen,

Y.;

Zuo,

C.

Z.;

Ma,

X.

Y.;

Chen,

A.

L.

Solid-Silica

Core/Mesoporous-Silica Shell Composite Abrasives: Synthesis, Characterization, and the Effect of Mesoporous Shell Structures on CMP. J. Mater. Sci.-Mater. Electron. 2017, 29, 3817-3828. (44) Deshmukh, P.; Bhatt, J.; Peshwe, D.; Pathak, S. Determination of Silica Activity Index and XRD, SEM and EDS Studies of Amorphous SiO2 Extracted from Rice Husk Ash. Trans. Indian Inst. Met. 2012, 65, 63-70. (45) Qian, H. F.; Jin, R. C. Ambient Synthesis of Au144(SR)60 Nanoclusters in


Page 33 of 35 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Methanol. Chem. Mater. 2011, 23, 2209-2217. (46) Sun, J.; Wu, H. X.; Jin, Y. D. Synthesis of Thiolated Ag/Au Bimetallic Nanoclusters

Exhibiting

an

Anti-Galvanic

Reduction

Mechanism

and

Composition-Dependent Fluorescence. Nanoscale 2014, 6, 5449-5457. (47) Weaver, J. F.; Hoflund, G. B. Surface Characterization Study of the Thermal Decomposition of Ag2O. Chem. Mater. 1994, 6, 1693-1699. (48) Wagner, C. D.; Riggs, W. M.; Davis, L. E.; Moulder, J. F.; Muilenberg, G. E. Handbook of X-ray Photoelectron Spectroscopy; Physical Electronics Division, Perkin-Elmer Corp.: Eden Prairie, MN, 1979. (49) Daniel, M. C.; Astruc, D. Gold Nanoparticles: Assembly, Supramolecular Chemistry, Quantum-Size-Related Properties, and Applications toward Biology, Catalysis, and Nanotechnology. Chem. Rev. 2004, 104, 293-346. (50) Fang, C.; Zhou, X. Y. Voltammetry and EQCM Investigation of Glutathione Monolayer and Its Complexation with Cu2+. Electroanalysis 2003, 15, 1632-1638. (51) Chen, W. B.; Tu, X. J.; Guo, X. Q. Fluorescent Gold Nanoparticles-Based Fluorescence Sensor for Cu2+ Ions. Chem. Commun. 2009, 1736-1738. (52) Tu, X. J.; Chen, W. B.; Guo, X. Q. Facile One-Pot Synthesis of Near-Infrared Luminescent Gold Nanoparticles for Sensing Copper (II). Nanotechnology 2011, 22, 095701. (53) Huang, H.; Dong, F. Y.; Tian, Y. Mitochondria-Targeted Ratiometric Fluorescent Nanosensor for Simultaneous Biosensing and Imaging of O2•– and pH in Live Cells. Anal. Chem. 2016, 88, 12294-12302.



(54) Ostrakhovitch, E. A.; Lordnejad, M. R.; Schliess, F.; Sies, H.; Klotz, L. O. Copper Ions Strongly Activate the Phosphoinositide-3-Kinase/Akt Pathway Independent of the Generation of Reactive Oxygen Species. Arch. Biochem. Biophys. 2002, 397, 232-239. (55) Liu, A. C.; Chen, D. C.; Lin, C. C.; Chou, H. H.; Chen, C. H. Application of Cysteine Monolayers for Electrochemical Determination of sub-ppb Copper (II). Anal. Chem. 1999, 71, 1549-1552. (56) Huang, X. L.; Teng, X.; Chen, D.; Tang, F. Q.; He, J. Q. The effect of the Shape of Mesoporous Silica Nanoparticles on Cellular Uptake and Cell Function. Biomaterials 2010, 31, 438-448.


Page 34 of 35

Page 35 of 35


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Confinement of AuAg NCs in a Pomegranate-Type Silica Architecture

Recommend Documents