Dynamic Hybrid Colloidosomes via Electrostatic Interactions for pH

Subscriber access provided by Access provided by University of Liverpool Library

Communication

Dynamic Hybrid Colloidosomes via Electrostatic Interactions for pH-Balanced Low Premature Leakage and Ultrafast Cargo Release Ting Guo, Tao Meng, Guang Yang, Yi Wang, Rui Su, and Shaobing Zhou Nano Lett., Just Accepted Manuscript • DOI: 10.1021/acs.nanolett.9b01949 • Publication Date (Web): 26 Aug 2019 Downloaded from pubs.acs.org on August 26, 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 23 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

Nano Letters

89x30mm (150 x 150 DPI)

ACS Paragon Plus Environment

Nano Letters 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

Page 2 of 23

Dynamic Hybrid Colloidosomes via Electrostatic Interactions for pH-Balanced Low Premature Leakage and Ultrafast Cargo Release Ting Guo,†,‡ Tao Meng,‡ Guang Yang,†,§ Yi Wang,†,‡ Rui Su,† and Shaobing Zhou*,† †Key

Laboratory of Advanced Technologies of Materials, Ministry of Education, School of Materials Science

and Engineering, Southwest Jiaotong University, Chengdu 610031, China ‡School

of Life Sciences and Engineering, Southwest Jiaotong University, Chengdu 610031, China

§College

of Medicine, Southwest Jiaotong University, Chengdu 610031, China

* Fax: +86 (028) 87634649. E-mail: [email protected] (S.B. Zhou) ABSTRACT: A trade-off between minimized premature leakage and rapid cargo release on demand is an intractable obstacle faced by smart delivery systems that restrains them from lab to market. To address this dilemma, dynamic hybrid colloidosomes relying on strong yet reversible electrostatic interactions are developed, simply through one-pot cooperative self-assembly of silica nanoparticles and fluorescent carbon dots at the interface of emulsion droplets. Specifically, pHdriven charge reversal of zwitterionic carbon dots leads to immediate electrostatic conversion between the two building blocks from attraction to repulsion. This makes robust locking and instantaneous breakdown of the colloidosomes to be subtly balanced, thus enabling low off-state leakage (10.5% over 7 days) while ultrafast on-state release (>90% within 5 minutes) upon an


1

Page 3 of 23 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

Nano Letters

acidic stimulus. We envision that such biocompatible, traceable and smart colloidosomes will offer unique opportunities for a broad application as on-demand release is desired. KEYWORDS: colloidosomes, dynamic binding, electrostatic interactions, pH-triggered release, self-assembly Smart delivery systems capable of responding to changes of local environment for triggered release of active cargoes have been widely explored in drug delivery, functional foods, corrosion protection, agriculture, cosmetics and catalysis, benefiting from spatiotemporal control over cargo release.1-7 Despite considerable progress in the development of stimuli-responsive micro/nano carriers, premature leakage of encapsulated cargoes is a common problem resulting in undesired off-target effects like harmful side effects, compromised efficacy and need for over-dosage.8 On the other hand, rapid cargo release upon target stimuli to achieve dramatically increased local concentration of actives (e.g. agents, catalysts or inhibitors) is highly desirable in many applications, such as cancer treatment, process control of chemical reactions, as well as feedbackactive anticorrosion protection, providing therapeutic and economic values.9-13 In order to circumvent leakage problem, current methods rely on strengthening of the carrier shell.14 However, overly rigid shells that first serve as protective barrier for cargo entrapment will become diffusion hindrance subsequently, which hamper the on-demand cargo release. Taken together, a trade-off between minimized premature leakage and rapid cargo release is a prerequisite for lab-to-market transition of smart delivery systems, but still an ongoing challenge. Colloidosomes, a type of promising carriers, have shown great potential to address those issues. They are hollow microcapsules with a solid shell constructed from densely packed nanoparticles (NPs), possessing superior mechanical robustness over their soft counterparts such as polymersomes and liposomes to withstand pressure-induced leakage.15,16 Colloidosomes are


2

Nano Letters 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

Page 4 of 23

featured by intrinsic porosity originating from interstices between adjacent shell-forming NPs, thus their permeability is strongly depended on pore/shell adjustment. Accordingly, a variety of smart colloidosomes have been developed, which are sensitive to diverse stimuli including temperature, pH, light, magnetic, enzyme, gas and ethanol.17-23 Unlike traditional strategies that release of cargoes via passive diffusion through adjustable pores,24 straightforward release via capsule breakdown would benefit from diffusion-controlled rate limit to be overcome,25 and from free release of large or insoluble cargoes without shell hindrance. However, strong robustness and fast responsiveness for on-demand cargo release are inherently mutually exclusive. A promising way to address this dilemma is to employ dynamic binding instead of permanent shell locking (sintering or covalent crosslinking), by which assembly and disassembly of colloidosomes can be flexibly controlled with the aid of desired stimuli. Until now, only a few mechanisms for fabricating dynamic colloidosomes have been reported, including hydrophobic-hydrophilic transition, hostguest interactions and electrostatic actuation.26-28 Additionally, unsatisfactory ratio between onand off-state release rates, tedious and harsh preparation process, as well as lack of traceability greatly limit their subsequent applications. In the present work, we report novel dynamic hybrid colloidosomes based on a reliable electrostatic strategy, showing pH-triggered ultrafast cargo release. It is well konwn that pH changes are typical endogenous signals frequently observed at many target sites. The colloidosomes are constructed by a simple one-pot Pickering emulsion approach. Polyethylenimine modified silica (SiO2-PEI) NPs and fluorescent carbon dots (CDs) are coassembled at the interface of emulsion droplets (Figure 1a, b), where they spontaneously lock together via strong electrostatic attraction under a near-neutral pH condition (Figure 1c). Differing from slow cleavage of chemical bonds, the zwitterionic CDs undergo immediate charge reversal


3

Page 5 of 23 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

Nano Letters

in response to an acidic stimulus, which results in electrostatic repulsion between the two building blocks (BBs) and therefore promotes instantaneous colloidosome disintegration (Figure 1d). Note that, the prepared colloidosomes possess a multilayer hybrid shell structure, which makes their permeability tolerant to packing defects, thereby a better steric hindrance for cargo retention.

Figure 1. Fabrication of dynamic hybrid colloidosomes for on-demand cargo release triggered by pH. (a) Positively charged SiO2-PEI NPs are prepared by modification of commercial SiO2 NPs with PEI. Zwitterionic CDs are synthesized by a bottom-up hydrothermal route. (b) One-pot fabrication of cargo-loaded colloidosomes via Pickering emulsion co-assembly. (c) Electrostatic attractions between adjacent SiO2-PEI NPs and CDs at pH 7.4, enabling robust capsule locking and low cargo leakage. (d) Electrostatic repulsions between adjacent SiO2-PEI NPs and CDs at pH 5.0, leading to instantaneous capsule disassembly and ultrafast cargo release.


4

Nano Letters 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

Page 6 of 23

RESULTS AND DISCCUSSION Preparation and Characterization of the Two BBs. Our initial attempt started with the design of the two BBs. Here, a commercial colloidal SiO2 suspension with an average size of 22 nm was used. The surface charge of the SiO2 suspension was negative above pH 3, while turning to be positive after electrostatic bonding with strong cationic PEI (Table S1, Figure S1).29 As determined by thermogravimetric analysis (TGA), for the SiO2-PEI NPs obtained by an optimal PEI/SiO2 mass ratio of 0.25, the adsorbed amount of PEI on SiO2 was 10.4% (Figure S2). Although PEI was physically adsorbed onto the SiO2 NPs, desorption was negligible at pH 7.4 as evidenced by zeta potential measurements (Figure S3). Considering excellent biocompatibility, bright fluorescence emission and pH-driven charge reversal,30,31 CDs were used as another class of BBs. In this study, zwitterionic CDs were prepared by ethylenediamine (EDA) and citric acid (CA) through a bottom-up hydrothermal route according to an earlier report with modification.32 The transmission electron microscopy (TEM) image shows discrete and quasi spherical shape of as-prepared CDs with an average size of 5.5 ±1.2 nm (Figure S4a,b, S5). High-resolution TEM (HR-TEM) image clearly revealed that the CDs were amorphous carbon particles without any lattices (inset of Figure S4a), which was consistent with the results of selected area electron diffraction (SAED) (a diffuse halo, Figure S4c), Raman spectrum (no obvious D or G bands, Figure S4d), as well as X-ray diffraction (XRD) pattern (a broad peak centered at 25o, Figure S4e). Good stability of the CDs was demonstrated by their UV-vis absorption spectra (Figure S6a). According to attenuated total reflection Flourier transform infrared (ATR-FTIR, Figure S4f) and X-ray photoelectron spectroscopy (XPS, Figure S7) analysis, the CDs carried both amino and carboxyl groups on their surface stemming from EDA and CA, respectively, endowing them with amine acid-like charge character: electronegative at pH above


5

Page 7 of 23 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

Nano Letters

their isoelectric point (IEP), while electropositive below that. Zwitterionic CDs with different IEP values can be flexibly modulated by the mole ratio of EDA to CA (Table S2), and in the present work, CDs with IEP around pH 5.5 were obtained by a ratio of 0.8. Formation and Characterization of Dynamic Hybrid Colloidosomes. Next, dynamic hybrid colloidosomes were fabricated by a modified method as Liu et al. reported,33 utilizing Pickering emulsion as template. The scanning electron microscopy (SEM) image shows the successful preparation of highly spherical colloidosomes without collapse even under high vacuum, suggesting their superior robustness (Figure 2a). The average size distribution of the colloidosomes was 3.6 ± 1.1 μm determined by particle sizing instrument. As highly magnified SEM image displays (Figure 2b), the colloidosome shell is constructed with closely packed SiO2-PEI NPs free of obvious defects. The image of a freeze fractured colloidosome shows its multilayer hollow structure (Figure 2c). TEM image of an ultrathin sliced specimen further confirmed the hollow interior of the colloidosomes (Figure 2e), which was not clearly visible in an ordinary top-tobottom projection when an air-dried specimen was used (Figure 2d). It should be pointed out that, CDs are too small to be observed by SEM, or be distinguished by TEM due to their relatively lower contrast compared with SiO2-PEI NPs. However, a confocal laser scanning microscope (CLSM) image of the ultrathin sliced sample shows the uniform blue fluorescence of the shell, indicating the existence of the CDs (Figure 2f), by which directly reveals the homogeneous coassembly of the two classes of BBs to form the colloidosome shell.


6

Nano Letters 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

Page 8 of 23

Figure 2. Microscopy images of dynamic hybrid colloidosomes. (a) SEM, (b) highly magnified SEM and (c) cryo-SEM images. (d) TEM image upon an air-dried specimen. (e) TEM and (f) CLSM images upon ultrathin sliced specimens. Insets of (d) and (e) represent ‘top-to-bottom’ and ‘cross-section’ views, respectively. Co-Assembly Mechanism via One-Pot Pickering Emulsion Approach. To explore the mechanism underlying Pickering emulsion templated co-assembly for producing stable colloidosomes, the fabrication conditions have been investigated in detail. By fixing the concentration of CDs in starting suspension at 1 mg·mL-1, with the concentration of SiO2-PEI NPs increasing from 10 to 60 mg·mL-1, the mean colloidosome size decreased and a better spherical shape with more regular and complete capsules was obtained (Figure 3a). Further control experiment was carried out with fabrication in the absence of CDs, resulting in unstable colloidosomes with irregular morphology (Figure 3b,

60

SiO2-PEI/0CD) and a broad size

distribution (Figure 3c, fuchsia solid curve). As shown in Figure 3c (dotted curves), the hydrodynamic diameters of the newly prepared colloidosomes obtained without or with insufficient CDs (e.g. 0.5 mg·mL-1) sharply decreased over a period of 2 hours, suggesting fast


7

Page 9 of 23 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

Nano Letters

disassembly of these capsules. In contrast, when the CD concentration was raised to 1 mg·mL-1, the resultant colloidosomes possessed a narrow size distribution and high stability over 12 hours (Figure 3d, fuchsia curves); no significant changes in size and stability were observed for a higher CD concentration of 2 mg·mL-1 (Figure 3d, green curves). Notably, colloidosomes formed by CDs and PEI-free SiO2 NPs also failed to keep their integrity (Figure 3e), whose CDs tended to detach from the like-charged SiO2 shell. It can be directly observed by the stepwise colour fading from yellow (colour of CDs) to white during post-treatment, and by the non-fluorescent of the resultant colloidosomes under UV exposure (Figure 3f versus Figure 3g).


8

Nano Letters 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

Page 10 of 23

Figure 3. Fabrication condition investigation of colloidosomes. Bright-field images of colloidosomes dispersed at pH 7.4, (a) prepared by CDs of 1 mg·mL-1 and different SiO2-PEI concentrations of 10, 30 and 60 mg·mL-1, respectively; (b) or by SiO2-PEI NPs of 60 mg·mL-1 and different CD concentrations of 0, 0.5 and 2 mg·mL-1, respectively. Size changes of colloidosomes at pH 7.4 prepared by different concentrations of CDs: (c) 0 and 0.5 mg·mL-1 CDs, observed at original and 2 hours, respectively; (d) 1 and 2 mg·mL-1 CDs, observed at original and 12 hours, respectively. (e) Colloidosomes prepared by 60 mg·mL-1 SiO2 NPs (without PEI modification) and 1 mg·mL-1 CDs. The digital photographs of colloidosomes prepared (f) by SiO2-PEI NPs and CDs, and (g) by SiO2 NPs and CDs, under room light and UV light, respectively. Nomenclature of the colloidosomes, for example, the colloidosomes generated by 60 mg·mL-1 SiO2-PEI NPs and 1 mg·mL-1 CDs are denoted as 60SiO2-PEI/1CD. Based on the results presented above as well as the mechanism that Liu and co-workers have reported,33 we propose an electrostatic-dependent cooperative self-assembly process for the fabrication of the colloidosomes. Firstly, water in oil (w/o) emulsions form during ultrasonic emulsification, and the two BBs dispersed in the water phase adsorb spontaneously at the droplet interface to form initial monolayer shell driven by the decrease of interface energy.34 Subsequently, the inner BBs continuously migrate and jam to the shell due to slight solubility of water in 1butanol, along with the outward diffusion of the water until exhausted. As a consequence, hybrid colloidosomes with a multilayer shell of close-packed BBs and hollow superstructure are finally fabricated. Note that, only a sufficient amount of oppositely charged CDs anchoring at the shell could finally form the stable colloidosomes, via strong electrostatic locking of adjacent shellforming NPs. In contrast, colloidosomes whose shell holding together merely by relatively weak


9

Page 11 of 23 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

Nano Letters

van der Waals forces, such as those produced by pure SiO2-PEI NPs or by SiO2 NPs and CDs of similarly charged, quickly dissociate apart when they are moved to a fresh fluid. pH-Dominated Stabilization and Destabilization of Dynamic Hybrid Colloidosomes. Since it is the electrostatic interactions that dominate the stability of the colloidosomes, we were curious to know whether destabilization of these capsules could be initiated by destroying such interactions by pH adjustment. The colloidosomes formed by 60 mg·mL-1 SiO2-PEI NPs and 1 mg·mL-1 CDs were employed as typical samples, which contained 1.68% of CDs (determined by UV absorption calibration curve, Figure S6b) thereby permitting fluorescence observation. As expected, colloidosomes remained intact in phosphate-buffered saline (PBS: 10 mM, pH 7.4) over the experimental period of 1 month (Figure 4a), which was consistent with the DLS and zeta potential measurements (Figure S8). Corresponding 3D reconstitution revealed the superstructure of a typical colloidosome as a well-defined spherical micro-compartment (Figure 4b). In contrast, once acetate buffer (AB: 10 mM, pH 5.0) was added, the colloidosomes lost their integrity via structure evolution of swelling, deformation, rupture and finally disintegration within 3 minutes (Figure 4c, Movie S1, Figure S9). To show clearly the swelling process, a few drops of 0.1 M HCl were added to the margin of the colloidosome dispersion, which leaded to instantaneous swelling and subsequent rupture of the colloidosomes once HCl diffused to the field of view (Figure S10). In addition, the disassembly of the colloidosomes at pH 5.0 could be observed by 3D reconstitution (Figure 4d) and optical transmittance transition of the suspension from opaque (inset of Figure 4a) to transparent (inset of Figure 4c).


10

Nano Letters 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

Page 12 of 23

Figure 4. pH-Dominated stabilization and destabilization of dynamic hybrid colloidosomes. (a) Time sequence of fluorescence images that shows high stability of the colloidosomes at pH 7.4 for 1 month. (b) 3D reconstruction of a single colloidosome dispersed at pH 7.4. (c) Top row, time sequence of in situ CLSM images that shows instantaneous colloidosome disassembly at pH 5.0; bottom row, corresponding bright-field images of a typical colloidosome. See Movie S1 for the complete sequence. (d) 3D reconstruction of a single colloidosome dispersed at pH 5.0. Insets of (a) and (c), digital photographs of the colloidosomes stored at pH 7.4 over 1 month and at pH 5.0 over 3 minutes, respectively. Insets of (b) and (d), the corresponding one-half 3D images for viewing purpose. Fluorescence images were observed at DAPI channel; CLSM images were captured at Ex/Em = 405/462 nm.


11

Page 13 of 23 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

Nano Letters

Electrostatic Interaction Identification for the Dynamic Binding. In view of pH sensitivity of dynamic hybrid colloidosomes, zeta potential measurements and ATR-FTIR analysis were utilized to further explore the mechanism of their stabilization and destabilization. As shown in Figure 5a, the zeta potential of SiO2-PEI NPs increased from 44.2 ±1.8 to 58.7 ±1.7 mV when the pH value of buffer solution decreased from 8.0 to 5.0. A charge reversal was shown in the CDs with an IEP at pH ≈ 5.5, which can be ascribed to the pH-induced deprotonation or protonation of both amino and carboxyl groups of CD bearing. Furthermore, pH-dependent electrostatic adsorption/desorption between SiO2-PEI NPs and CDs were identified by the corresponding 2nd derivative spectra of the interested area marked in ATR-FTIR spectra (Figure S11). From the spectrum of CD adsorbed SiO2-PEI sample (Figure 5b, fuchsia curve), the absorption peak at 1632 cm-1 is assigned to the asymmetric COO− stretch of carboxylate groups35 of CD bearing at pH 7.4. Such a characteristic peak appears to be sharper and shifts to 1645 cm-1 in the desorption sample (Figure 5b, green curve), which assigns to the C=O stretch of corresponding protonated free acid at pH 5.0. In the former case, proton transfer in ammonium-carboxylate ion pairs36 existing between SiO2-PEI NPs and CDs accounts for the diminished absorption and relatively low wavenumber. In the latter case, the breakup of such ionic hydrogen bonds due to protonation of carboxylic acid groups of CD bearing leads to blue-shift together with the increased absorption. Also, shifts of the NH bending vibration peak of amino groups of SiO2-PEI bearing from 1562 cm1

to 1548 cm-1 and back to 1556 cm-1 is considered as the result of ion pair formation or

decomposition. Taken together, strong yet reversible electrostatic interactions between the two BBs, which is dominated by pH, are responsible for the dynamic binding of the colloidosomes. Adsorption of oppositely charged CDs on SiO2-PEI NPs via electrostatic ion pair interaction significantly


12

Nano Letters 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

Page 14 of 23

alleviates the electrostatic repulsion between SiO2-PEI NPs and efficiently interlocks the shell by electrostatic attraction to form the robust colloidosomes (Figure 1c). Negative to positive charge reversal of the CDs prompted by pH decrease would in turn destroy such ion pairs and even generate strong electrostatic repulsion between those of like-charged BBs, resulting in sudden colloidosome disassembly (Figure 1d). As a consequence, the assembly-disassembly of the colloidosomes is reversible. As shown in Figure S12, the colloidosomes disintegrated into fragments when they were exposed to acetate buffer, as detected by DLS measurements. However, when the pH value of the resultant dispersion was increased to pH 8 by 1 M NaOH, and fresh 1butanol was added as oil phase subsequently, well-formed colloidosomes could be obtained again after ultrasonic emulsification. Accordingly, the pH-reversible electrostatic interactions between the two classes of BBs enable a satisfactory recyclability of the materials up to three times, which is meaningful especially in catalytic field.

Figure 5. Identification of the electrostatic interactions between the two BBs. (a) Zeta potential measurements of SiO2-PEI NPs and CDs as a function of pH, respectively. Data are presented as mean ±SD based on three independent experiments. (b) ATR-FTIR 2nd derivative spectra of SiO2, SiO2-PEI, CD adsorbed SiO2-PEI and CD desorbed SiO2-PEI NPs, respectively.


13

Page 15 of 23 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

Nano Letters

pH-Balanced Low Premature Leakage and Ultrafast Cargo Release. Drug encapsulation and triggered release of the colloidosomes was subsequently investigated, using fluorescein isothiocyanate–dextran (FD10) as a model drug (Figure S13). At a typical SiO2-PEI: CD: FD10 feeding weight ratio of 60: 1: 12, a loading efficiency as high as 86.9% and a loading content of 24.3% were obtained. As expected, the release of FD10 was strongly pH-dependent, with 10.5% minimal leakage over a period of 7 days at pH 7.4 (Figure S14a), whereas up to 90% ultrafast release within 5 minutes at pH 5.0 (Figure S14b), exhibiting an outstanding ratio between on/off release rate reported to date via colloidosomes (Table S3). High storage stability of the FD10loaded colloidosomes was further confirmed by DLS and zeta potential measurements, and the premature release under pH 7.4 at 4 ℃ was as low as 5.5% over a month (Figure S15). To evaluate whether the proposed smart colloidosomes can be applied in biomedical field, the biocompatibility experiments for both the intact and the disintegrated colloidosomes were carried out, utilizing live/dead staining and Alamar Blue assay. According to Figure S17, few dead cells were observed in blank colloidosomes or the fragment group shown as red fluorescence of endothelial cells (ECs). Alamar Blue assay results also displayed a high cell viability above 87% up to a concentration of 200 μg·mL-1 (Figure S18), suggesting the negligible toxicity of the proposed materials. Encouraged by the unique properties mentioned above, the colloidosomes were further evaluated as vehicles for pH-triggered release of active biomacromolecules, where catalase that can efficiently decompose hydrogen peroxide (H2O2) into H2O and O2 was employed as model cargo. As expected, the catalases were well entrapped within the capsules with negligible leakage (8%) over 3 days in the off state (Figure 6a, blue curve), while it took only 5 minutes to be completely released (93%) in the on state (Figure 6b, red curve), regardless of their large size (10.5


14

Nano Letters 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

Page 16 of 23

nm) owing to capsule disassembly. Importantly, the catalase retained their high activity once released from the capsules compared to the free enzymes under the same conditions (Figure 6, black curves).

Figure 6. On-demand enzyme release from dynamic hybrid colloidosomes. (a) Release profile of catalase performed at pH 7.4; the corresponding specific activities of enzymes after release, as well as free enzymes in the same medium. (b) Release profile of catalase performed at pH 5.0; the corresponding specific activities of enzymes after release, as well as free enzymes in the same medium. Data are presented as mean ±SD based on three independent experiments. CONCLUSION In summary, we demonstrate a reliable strategy to engineer dynamic hybrid colloidosomes, which shows reversible assembly and disassembly property by simple pH variations. In this platform, an acidic pH change leads to a sharp “pull-to-push” electrostatic force conversion between the two BBs, resulting in the instantaneous breakdown of the colloidosomes accompanied by the on-demand cargo release. Owing to the rate limit and the shell diffusion hindrance to be conquered, ultrafast and complete macromolecule release on a timescale of minutes can be achieved. The proposed one-pot Pickering emulsion approach is bio-friendly, as the encapsulated


15

Page 17 of 23 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

Nano Letters

enzymes maintain their high catalytic activity. In fact, colloidosomes in response to tailored pH values are required to serve various applications, for example, pH-triggered drug delivery for cancer therapy at pH 6.5 is needed. Therefore, besides pH 5.0, colloidosomes sensitive to other pH values should be developed, and they may be obtained by using CDs with different IEP values as BBs. More intriguingly, considering a wide choice of NPs as modular BBs, dynamic colloidosomes with magnetic, plasmonic, thermal or even multifunctional properties can be obtained in a similar bottom-up process to meet specific applications. In view of easy preparation, fluorescence, biocompatibility, rapid pH-responsiveness and recyclability of our smart colloidosomes, they will find numerous potentials in biomedicine, catalysis, production of fine chemicals, as well as in protocell studies.

ASSOCIATED CONTENT Supporting Information The following files are available free of charge. Materials and Methods (materials, synthesis of SiO2-PEI NPs, synthesis of zwitterionic CDs, fabrication of colloidosomes, ultrathin sliced specimen preparation for TEM, 3D-reconstruction of the colloidosomes, ATR-FTIR specimen preparation, cargo loading and release assay, the Bradford protein assay, enzymatic activity assay, cytocompatibility assay, characterization) (PDF) Figures S1-S16 (digital photographs of SiO2-PEI dispersions prepared by 0, 0.10 and 0.25 mass ratios of PEI to SiO2, TGA curves of bare SiO2 NPs and SiO2-PEI NPs prepared by 0.25 mass ratio of PEI to SiO2, stability of the SiO2-PEI NPs stored at pH 7.4 identified by zeta potential measurements, characterization of zwitterionic CDs, HPLC chromatogram of zwitterionic CDs, UV-vis absorption of zwitterionic CDs, XPS spectra of zwitterionic CDs, storage stability of blank


16

Nano Letters 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

Page 18 of 23

colloidosomes, SEM image of dynamic hybrid colloidosomes undergo acid-triggered disassembly, in situ bright-field images of dynamic hybrid colloidosomes upon exposure to acid solution, ATRFTIR spectra of SiO2, SiO2-PEI, CD adsorbed SiO2-PEI and CD desorbed SiO2-PEI NPs, respectively, reversible assembly-disassembly behavior of the colloidosomes, fluorescence spectra of FD10, CDs and SiO2-PEI in AB, respectively, on-demand FD10 release from dynamic hybrid colloidosomes, storage stability of FD10-loaded colloidosomes, raw fluorescence curves of FD10 in the release solutions, live/dead staining, Alamar Blue assay, calibration curves of FD10, catalase and H2O2) (PDF) Tables S1-S3 (preparation and characterization of SiO2-PEI NPs, preparation and zeta potential data of CDs, typical examples of stimuli-responsive colloidosomes for triggered release) (PDF) Movie S1 (CLSM observation of instantaneous disassembly of dynamic hybrid colloidosomes at pH 5.0) (MOV) AUTHOR INFORMATION Corresponding Author * Fax: +86 (028) 87634649. E-mail: [email protected] (S.B. Zhou). ORCID Shaobing Zhou: 0000-0002-6155-4010 Notes The authors declare no competing financial interest. ACKNOWLEDGMENTS This work was partially supported by the China National Funds for Distinguished Young Scientists (No. 51725303), National Natural Science Foundation of China (Nos. 21574105, 51703189), the Sichuan Province Youth Science and Technology Innovation Team (Grant


17

Page 19 of 23 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

Nano Letters

No.2016TD0026). The authors thank Analysis and Testing Center of Southwest Jiaotong University. REFERENCES (1) El-Sawy, H. S.; Al-Abd, A. M.; Ahmed, T. A.; El-Say, K. M.; Torchilin, V. P. StimuliResponsive nano-architecture drug-delivery systems to solid tumor micromilieu: past, present, and future perspectives. ACS Nano 2018, 12, 10636−10664. (2) Vallet-Regí, M.; Colilla, M.; Izquierdo-Barba, I.; Manzano, M. Mesoporous silica nanoparticles for drug delivery: current insights. Molecules 2018, 23, 47. (3) Augustin, M. A.; Hemar, Y. Nano- and micro-structured assemblies for encapsulation of food ingredients. Chem. Soc. Rev. 2009, 38, 902–912. (4) Jakab, M. A.; Scully, J. R. On-demand release of corrosion-inhibiting ions from amorphous Al–Co–Ce alloys. Nat. Mater. 2005, 4, 667–670. (5) Xu, X. H.; Bai, B.; Wang, H. L.; Suo, Y. R. A near-infrared and temperature-responsive pesticide release platform through core–shell polydopamine@PNIPAm nanocomposites. ACS. Appl. Mater. Interfaces 2017, 9, 6424–6432. (6) Martins, I. M.; Barreiro, M. F.; Coelho, M.; Rodrigues, A. E. Microencapsulation of essential oils with biodegradable polymeric carriers for cosmetic applications. Chem. Eng. J. 2014, 245, 191-200. (7) Wang, H.; Zhao, Z.; Liu, Y. X.; Shao, C. M.; Bian, F. K.; Zhao, Y.J. Biomimetic enzyme cascade reaction system in microfluidic electrospray microcapsules. Sci. Adv. 2018, 4, eaat2816. (8) Rosenblum, D.; Joshi, N.; Tao, W.; Karp, J. M.; Peer, D. Progress and challenges towards targeted delivery of cancer therapeutics. Nat. Commun. 2018, 9, 1410.


18

Nano Letters 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

Page 20 of 23

(9) Lukianova-Hleb, E. Y.; Belyanin, A.; Kashinath, S.; Wu, X. W.; Lapotko D. O. Plasmonic nanobubble-enhanced endosomal escape processes for selective and guided intracellular delivery of chemotherapy to drug-resistant cancer cells. Biomaterials 2012, 33, 1821-1826. (10) Liu, G. N.; Zhao, X.; Zhang, Y. L.; Xu, J. C.; Xu, J. Q.; Li, Y.; Min, H.; Shi, J.; Zhao, Y.; Wei, J. Y.; Wang, J.; Nie G. J. Engineering biomimetic platesomes for pH-responsive drug delivery and enhanced antitumor activity. Adv. Mater. 2019, 31, 1900795. (11) Mabrouk, E.; Cuvelier, D.; Brochard-Wyart, F.; Nassoy, P.; Li, M. H. Bursting of sensitive polymersomes induced by curling. Proc. Natl. Acad. Sci. USA 2009, 106, 7294-7298. (12) Fu, J. J.; Chen, T.; Wang, M. D.; Yang, N. W.; Li, S. N.; Wang, Y.; Liu, X. D. Acid and alkaline dual stimuli responsive mechanized hollow mesoporous silica nanoparticles as smart nanocontainers for intelligent anticorrosion coatings. ACS Nano 2013, 7, 11397-11408. (13) Sheng, Z. Z.; Liu, X.; Min, L. L.; Wang, H. L.; Liu, W.; Wang, M.; Huang, L. Z.; Wu, F.; Hou, H. Bioinspired approaches for medical devices. Chin. Chem. Lett. 2017, 28, 1131–1134. (14) Zieringer, M. A.; Carroll, N. J.; Abbaspourrad, A.; Koehler, S. A.; Weitz, D. A. Microcapsules for enhanced cargo retention and diversity. Small 2015, 11, 2903-2909. (15) Dinsmore, A. D.; Hsu, M. F.; Nikolaides, M. G.; Marquez, M.; Bausch, A. R.; Weitz, D. A. Colloidosomes: selectively permeable capsules composed of colloidal particles. Science 2002, 298, 1006-1009. (16) Kim, J. W.; Fernández-Nieves, A; Dan N.; Utada, A. S.; Marquez M.; Weitz, D. A. Colloidal assembly route for responsive colloidosomes with tunable permeability. Nano Lett. 2007, 7, 28762880.


19

Page 21 of 23 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

Nano Letters

(17) Huang, X.; Li, M.; Green, D. C.; Williams, D. S.; Patil, A. J.; Mann, S. Interfacial assembly of protein–polymer nano-conjugates into stimulus-responsive biomimetic protocells. Nat. Commun. 2013, 4, 2239. (18) Li, M.; Harbron, R. L.; Weaver, J. V. M.; Binks, B. P.; Mann, S. Electrostatically gated membrane permeability in inorganic protocells. Nat. Chem. 2013, 5, 529-536. (19) Lin, J.; Wang, S. J.; Huang, P.; Wang, Z.; Chen, S. H.; Niu, G.; Li, W. W.; He, J.; Cui, D. X.; Lu., G. M.; Chen, X. Y.; Nie, Z. H. Photosensitizer-loaded gold vesicles with strong plasmonic coupling effect for imaging-guided photothermal/photodynamic therapy. ACS Nano 2013, 7, 5320-5329. (20) Long, Y.; Liu, C. Y.; Zhao, B.; Song, K.; Yang, G. Q.; Tung, C. H. Bio-inspired controlled release through compression–relaxation cycles of microcapsules. NPG Asia Mater. 2015, 7, e148. (21) Song, J. B.; Pu, L.; Zhou, J. J.; Duan, B.; Duan, H. W. Biodegradable theranostic plasmonic vesicles of amphiphilic gold nanorods. ACS Nano 2013, 7, 9947–9960. (22) Lei, L.; Zhang, Q.; Shi, S. X.; Zhu, S. P. Breathable microgel colloidosome: gas-switchable microcapsules with O2 and CO2 tunable shell permeability for hierarchical size-selective control release. Langmuir 2017, 33, 6108−6115. (23) Jiang, H.; Hong, L. Z.; Li, Y. X.; Ngai, T. All-Silica submicrometer colloidosomes for cargo protection and tunable release. Angew. Chem. Int. Ed. 2018, 57, 11662-11666. (24) Zhou, S. B.; Fan, J.; Datta, S. S.; Guo, M.; Guo, X.; Weitz, D. A. Thermally switched release from nanoparticle colloidosomes. Adv. Funct. Mater. 2013, 23, 5925–5929. (25) Qu, J. B.; Chu, L. Y.; Yang, M.; Xie, R.; Hu, L.; Chen, W. M. A pH‐responsive gating membrane system with pumping effects for improved controlled release. Adv. Funct. Mater. 2006, 16, 1865-1872.


20

Nano Letters 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

Page 22 of 23

(26) Song, J. B.; Zhou, J. J.; Duan, H. W. Self-Assembled plasmonic vesicles of SERS-encoded amphiphilic gold nanoparticles for cancer cell targeting and traceable intracellular drug delivery. J. Am. Chem. Soc. 2012, 134, 13458−13469. (27) Zhang, J.; Coulston, R. J.; Jones, S. T.; Geng, J.; Scherman, O. A.; Abell, C. One-Step fabrication of supramolecular microcapsules from microfluidic droplets. Science 2012, 335, 690694. (28) Li, S.; Moosa, B. A.; Croissant, J. G.; Khashab, N. M. Electrostatic assembly/disassembly of nanoscaled colloidosomes for light-triggered cargo release. Angew. Chem. Int. Ed. 2015, 54, 6804– 6808. (29) Williams, M.; Armes, S. P. Double emulsions and colloidosomes-in-colloidosomes using silica based Pickering emulsifiers. Langmuir 2014, 30, 2703−2711. (30) Hassan, M.; Gomes, V. G.; Dehghani, A.; Ardekani, S. W. Engineering carbon quantum dots for photomediated theranostics. Nano Res. 2018, 11, 1–41. (31) Feng, T.; Ai, X. Z.; An, G. H.; Yang, P. P.; Zhao, Y. L. Charge-Convertible carbon dots for imaging-guided drug delivery with enhanced in vivo cancer therapeutic efficiency. ACS Nano 2016, 10, 4410–4420. (32) Zhu, S. J.; Meng, Q. N.; Wang, L.; Zhang, J. H.; Song, Y. B.; Jin, H.; Zhang, K.; Sun, H. C.; Wang, H. Y.; Yang, B. Highly photoluminescent carbon dots for multicolor patterning, sensors, and bioimaging. Angew. Chem. Int. Ed. 2013, 52, 3953–3957. (33) Liu, D. L.; Zhou, F.; Li, C. C.; Zhang, T.; Zhang, H. H.; Cai, W. P.; Li, Y. Black gold: plasmonic colloidosomes with broadband absorption self-assembled from monodispersed gold nanospheres by using a reverse emulsion system. Angew. Chem. Int. Ed. 2015, 54, 9596–9600.


21

Page 23 of 23 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

Nano Letters

(34) Binks, B. P.; Clint, J. H. Solid wettability from surface energy components: relevance to Pickering emulsions. Langmuir 2002, 18, 1270−1273. (35) Sarma, B.; Nath, N. K.; Bhogala, B. R.; Nangia, A. Synthon competition and cooperation in molecular salts of hydroxybenzoic acids and aminopyridines. Cryst. Growth Des. 2009, 9, 15461557. (36) Mani, R.; Rietveld, I. B.; Nicolaï,B.; Varadharajan, K.; Louhi-Kultanen, M.; Narasimhan, S. Fluorescence and physical properties of the organic salt 2-chloro-4 nitrobenzoate–3-ammoniumphenol. Chem. Phys. 2015, 458, 52–61.

For Table of Contents Only


22

Dynamic Hybrid Colloidosomes via Electrostatic Interactions for pH

Recommend Documents