www.sciencemag.org/cgi/content/full/341/6142/154/DC1
Supplementary Materials for
One-Step Assembly of Coordination Complexes for Versatile Film and Particle
Engineering
Hirotaka Ejima, Joseph J. Richardson, Kang Liang, James P. Best, Martin P. van Koeverden,
Georgina K. Such, Jiwei Cui, Frank Caruso*
*Corresponding author. E-mail: [email protected]
Published 12 July 2013, Science 341, 154 (2013)
DOI: 10.1126/science.1237265
This PDF file includes:
Materials and Methods
Figs. S1 to S18
References
Materials and Methods
Materials
Tannic acid (TA, ACS reagent), iron(III) chloride hexahydrate (FeCl3 6H2O),
vanadium(III) chloride (VCl3), gadolinium(III) chloride hexahydrate (GdCl3 6H2O),
chromium(III) chloride hexahydrate (CrCl3 6H2O), 3-(N-morpholino)propanesulfonic
acid (MOPS), poly(sodium 4-styrenesulfonate) (PSS, Mw ~70,000), polyethyleneimine
(PEI, Mw ~10,000), sodium phosphate buffer saline (PBS), sodium acetate, glycine,
dimethyldiethoxysilane (DMDES), iron oxide nanoparticles (Fe3O4) (D = 5 nm),
ammonium hydroxide, fluorescein isothiocyanate (FITC), FITC-dextran with various
average molecular weights (4, 10, 70, 250, 500, 2,000 kDa), bovine serum albumin
(BSA), lysozyme, rhodamine B, (-)-Epigallocatechin gallate (EGCG), and
ethylenediaminetetraacetic acid (EDTA) were purchased from Sigma-Aldrich.
Tetrahydrofuran (THF) and ethanol were purchased from Chem Supply. Polystyrene (PS)
particles (D = 0.124 ± 0.005, 0.836 ± 0.024, 3.55 ± 0.07, 10.02 ± 0.08 μm), silica
particles (D = 3.08 ± 0.13 μm), aminated silica particles (D = 3.07 ± 0.12 μm), and
melamine formaldehyde (MF) particles (D = 2.98 ± 0.06 μm) were purchased from
Microparticles GmbH. Escherichia coli (ATCC number 14948) and Staphylococcus
epidermidis (ATCC number 14990) were obtained from American Type Culture
Collection (ATCC). Alexa Fluor 633 carboxylic acid succinimidyl ester, Dulbecco’s
modified eagle medium (DMEM), and GlutaMAX were obtained from Life
Technologies. All these materials were used as received. Ellipsoidal PS particles were
prepared according to the reported stretching method (27) from commercially obtained
spherical PS particles (D = 3.55 μm). Fe3O4-loaded and non-loaded low-molecularweight polydimethylsiloxane (PDMS) emulsions were prepared by the base-catalyzed
hydrolysis and polymerization of DMDES (28, 29). The emulsion templates were
dialyzed against water before use (pH 6.5). Rhodamine B or protein (Alexa 633-labeled
lysozyme) loaded CaCO3 particles were synthesized via a precipitation reaction in the
presence of PSS (30). PSS was removed by thermal annealing (550 °C, 6 h) for mesopore
formation. High-purity water with a resistivity of 18.2 MΩ.cm was obtained from an
inline Millipore RiOs/Origin water purification system.
FeIII-TA Coating on Planar Substrates
PS, glass, Au, PDMS or quartz substrates were soaked in water in a 50 ml tube.
Solutions of FeCl3 6H2O and TA were added to this aqueous solution to yield the
following final concentrations (FeCl3 6H2O: 0.1 mg ml-1, TA: 0.4 mg ml-1 in 20 ml of
water). The solution was vigorously mixed by a vortex mixer for 10 s immediately after
the individual additions of FeCl3 6H2O and TA. The pH of this solution was subsequently
raised by adding 1 N NaOH solution to ca. pH 8. Then, the substrates were rinsed with
water. In Fig. 1A and 2A, this coating process was repeated five times to enhance the
color difference.
For preparation of samples for ellipsometric analysis, sequential buildup of FeIIITA layers was performed on Au-coated silicon wafers prepared immediately prior to use.
Silicon wafers (<100> orientation, n-type, MMRC Pty. Ltd.) were cut to approximately
1.5 × 3 cm slides and soaked for 20 min in Piranha solution (98% H2SO4:30% H2O2
(7:3)) – Caution! Piranha solution is highly oxidizing and corrosive! Extreme care
1
should be taken during preparation and use. The slides were then sonicated in
isopropanol:water (1:1) solution for 20 min and finally heated to 60 °C for 20 min in
RCA SC-1 solution (H2O:30% NH4OH:30% H2O2 (5:1:1)). The slides were washed
thoroughly with water after each step. The cleaned wafers were dried under a nitrogen
stream then sputter-coated (Emitech K575X) with a ca. 20 nm Cr adhesion layer (50 mA
sputter current, 2 min) followed by ca. 50 nm Au (50 mA sputter current, 3 min).
FeIII-TA Coating on Particulate Substrates
The standard condition is described as follows. Aliquots (5 μl) of FeCl3 6H2O (10
mg ml-1) and then TA (40 mg ml-1) solutions were added to the aqueous PS template (D =
3.55 μm) suspension (490 μl) to yield the following final concentrations (PS: 10 mg ml-1,
FeCl3 6H2O: 0.1 mg ml-1, TA: 0.4 mg ml-1 in 0.5 ml of water). The suspension was
vigorously mixed by a vortex mixer for 10 s immediately after the individual additions of
FeCl3 6H2O and TA. The pH of this suspension was subsequently raised by adding 0.5 ml
of MOPS buffer (20 mM, pH 7.4). The particles were washed with water three times to
remove excess TA and FeCl3. In the washing step, the particles were spun down by
centrifugation (2,000 g, 30 s) and the supernatant was removed. The remaining pellet was
redispersed in the desired solvents.
The concentration of FeCl3 6H2O (0.06 − 0.20 mg ml-1) and TA (0.10 − 1.80 mg
-1
ml ) were altered from the standard conditions described above while the other variable
were kept constant. The starting amounts of the different templates were calculated so
that their surface areas were constant. To obtain capsules, the PS, low-molecular-weight
PDMS emulsion and CaCO3 templates were removed by washing with THF, ethanol or
100 mM EDTA (pH 7.4) five times, respectively. For fluorescent labeling of the FeIII-TA
film, the suspension was incubated with FITC-BSA (1 mg ml-1) for 15 min.
For sequential assembly experiments (fig. S7), standard conditions described
above were repeated, although the order of reagent addition was reversed (i.e., TA and
then FeIII). We adsorbed TA and then FeIII to avoid rapid depletion of free FeIII from
solution into the preformed film, as the FeIII concentration is below that required for
saturation of the film binding sites. This is confirmed by XPS data (fig. S5), which show
that the film stoichiometry is dependent on the [FeIII] used.
Characterization
Differential interference contrast (DIC) and fluorescence microscopy images were
taken with an inverted Olympus IX71 microscope. Confocal laser scanning microscopy
(CLSM) images were acquired with a Leica TCS SP2 laser scanning microscope. Atomic
force microscopy (AFM) experiments were carried out with a JPK NanoWizard II
BioAFM. Typical scans were conducted in intermittent contact mode with MikroMasch
silicon cantilevers (NSC/CSC). The film thickness and roughness of the FeIII-TA capsules
(spherical, D = 3.55 μm) were analyzed using JPK SPM image processing software
(version V.3.3.32). Transmission electron microscopy (TEM) images and energy
dispersive X-ray spectroscopy (EDS) profiles were acquired using a FEI Tecnai TF20
instrument with an operation voltage of 200 kV. Scanning electron microscopy (SEM)
images were obtained on a FEI Quanta 200 field emission scanning electron microscope
operated at an accelerating voltage of 10 kV. In AFM, TEM/EDS and SEM experiments,
the capsule suspensions (2 μl) were allowed to air-dry on PEI-coated glass slides,
2
formvar-carbon coated copper grids and Piranha cleaned silicon wafers, respectively. The
SEM samples were then sputter coated with Au. Zeta-potential measurements were
carried out in water by using a Zetasizer Nano ZS (Malvern). UV-Vis absorption
measurements were carried out on a Nano drop ND-1000 UV-Vis spectrophotometer
(Thermo Scientific) or a Varian Cary 4000 UV-Vis spectrophotometer. Flow cytometry
assays were performed on a Cyflow Space (Partec GmbH) flow cytometer.
X-ray photoelectron spectroscopy (XPS) was performed on a VG
ESCALAB220i-XL spectrometer equipped with a hemispherical analyzer. The incident
radiation was monochromatic Al Kα X-rays (1486.6 eV) at 220 W (22 mA and 10 kV).
Survey (wide) and high resolution (narrow) scans were taken at analyzer pass energies of
100 eV and 50 eV, respectively. Survey scans were carried out with a 1.0 eV step size
and a 100 ms dwell time. Narrow high resolution scans were run over a 20 eV binding
energy range with a 0.05 eV step size and a 250 ms dwell time. Base pressure in the
analysis chamber was below 8.0 × 10-9 mbar. A low energy flood gun was used to
compensate the surface charging effect. All data were processed using CasaXPS software
and the energy calibration was referenced to the C 1s peak at 285.0 eV. For the sample
preparation, concentrated capsule suspensions were cast onto Piranha cleaned silicon
wafers and allowed to air dry.
Spectroscopic ellipsometry of air-dried films was performed using an Auto SE
spectroscopic ellipsometer (Horiba Jovin Yvon). Spectroscopic data were acquired
between 400 and 800 nm with a 2 nm increment over at least five spots on the wafer.
Ellipsometric thicknesses were modeled using the integrated software (DeltaPsi 2) using
a two layer optical model consisting of FeIII-TA on Au. Optical parameters for Au, as
provided by Horiba from published reference data, were used to model the substrate. The
overlying FeIII-TA film was modeled using a two oscillator Tauc Lorentz dispersion
model.
Disassembly Experiments
The 2 ml capsule suspensions (prepared from D = 3.55 μm PS templates, 1.0 ×
107 capsules ml-1) in 20 mM MOPS (pH 7.4), 100 mM EDTA (pH 7.4), 50 mM sodium
acetate (pH 4.0, pH 5.0) or 50 mM Gly-HCl (pH 3.0) were incubated in a thermostated
shaker bath at 37 °C for the desired time. The suspensions were diluted with water and
subjected to flow cytometry assays to count the number of capsules.
Permeability Tests
The dispersion of FeIII-TA capsules (prepared from PS templates, D = 3.55 μm,
4.0 × 107 capsules ml-1) was mixed with an equal volume of FITC-dextran solution (1 mg
ml-1). CLSM images of the capsules were taken within 10 min after mixing and the
capsules with dark interiors were considered to be impermeable, whereas capsules with
interiors of similar fluorescent intensity as the outer environment were considered to be
permeable. 100 capsules were examined.
Mechanical Tests
AFM force spectroscopy measurements were performed in water with a JPK
NanoWizard II BioAFM using colloidal probe (D = 32.4 μm) modified cantilever tips
(spring constant 36.4 mN m-1). Glass slides and cantilevers were cleaned with 30 vol%
3
isopropanol, water, and plasma treatment to remove any contaminant material. PEI was
adsorbed to cleaned glass substrates prior to measurement for electrostatic
immobilization of the capsules. For fabrication of the modified cantilevers, tipless
cantilevers (MikroMasch) were first calibrated on a cleaned glass substrate to determine
the inverse optical lever sensitivity (InvOLS), and then the spring constant was
determined using a modified thermal noise method. A spherical glass bead (Polysciences)
was attached to the calibrated cantilever using an epoxy resin (Selleys Araldite Super
Strength, Selleys) via careful micromanipulation using the AFM and associated optics,
and allowed to dry overnight. To obtain force-distance curves on FeIII-TA capsules
prepared from PS templates (D = 3.55 μm), the probe was optically positioned above
individual capsules, and an approach-retract cycle initiated with a constant piezo velocity
of 750 nm s-1. The temperature was regulated to 19 – 21 °C during force measurements,
and monitored using a JPK BioCell. Collected force spectra were analyzed using JPK
data processing software. A baseline was first subtracted from the non-contact z-range of
the force-displacement data, a probe/surface contact point assigned, and the effect of
cantilever bending subtracted to result in force-deformation (F-δ) data. The EY of the
spherical capsule could be estimated using the Reissner model for thin-walled spherical
shells. A wall thickness (h) of 10.4 nm, a Poisson ratio (ν) of 0.5, and an effective radius
(Reff) of 1.60 μm were used. Using the Reissner equation:
EY =
FReff 3(1− ν 2 )
4δ h 2
the EY was estimated to be 1.0 ± 0.2 GPa. Only deformation data over the capsule shell
thickness was used (fig. S6A). This result was also confirmed with measurements using a
stiffer cantilever (spring constant 72.6 mN m-1, probe diameter 31.9 μm), and at least 10
single capsules were analyzed. Additionally, it was found that deformations were elastic
to at least 450 nm (fig. S6B).
Adsorption Isotherms
Five mg of PS particles (D = 0.836 μm) and TA (0.0005, 0.005, 0.01, 0.02, 0.04,
0.05, 0.075, 0.125, 0.175, 0.2 mg) were mixed in 0.5 ml of water. After 10 s of vortex
mixing to adsorb TA, the particle suspensions were centrifuged (10,000 g, 5 min). 50 μl
of supernatant was transferred to new tubes. The absorbance at 275 nm of these solutions
(2 μl) was measured with a Nano drop ND-1000 UV-Vis spectrophotometer. Adsorbed
amounts of TA (mg/g of PS) at each concentration were calculated from a separately
constructed calibration curve.
Cell Viability Assays
Early passage HeLa cells were seeded in a 96-well plate at a density of 1 × 104
cells well-1 and cultured in DMEM supplemented with 10% FBS and 2 mM GlutaMAX
at 37 °C in 5% CO2. The cells were exposed to varying amounts of FeIII-TA capsules in a
total volume of 200 μl for 72 h. After aspirating the supernatant of each well and washing
three times with PBS, 180 μl of the medium and 20 μl of MTT solution (5 mg ml-1 in
PBS) were added to the wells. Plates were further incubated at 37 °C in 5% CO2 for 3 h.
After the addition of 150 μl of solubilization mixture (0.04 N HCl in isopropanol), the
absorbance at 560 nm (blue formazan) was measured with a plate reader (Multiskan
Ascent, Thermo Scientific). The absorbance of control wells without MTT was
4
subtracted. All experiments were performed in quadruplicate and the relative cell
viability was normalized relative to the untreated control cells.
Different Metals and Polyphenol
VIII-TA capsules were prepared in the same way as described above except that
VCl3 was used in place of FeCl3 6H2O at same final concentration of 0.1 mg ml-1. After
the PS template removal, a loss of capsules occurred during the washing steps with water.
Thus, the AFM samples were prepared by casting from the THF solution directly.
GdIII/FeIII-TA and CrIII/FeIII-TA capsules were prepared by first coating the PS particles
(D = 3.55 μm) with a GdIII-TA or CrIII-TA layer, then capped with a FeIII-TA layer. PS
templates were removed by THF treatment.
FeIII-EGCG coatings were deposited in a slightly modified way as described
above, with TA being replaced by EGCG. Aliquots of FeCl3 6H2O (5 μl, 10 mg ml-1) and
EGCG (20 μl, 10 mg ml-1) solutions were added to the aqueous PS template (D = 3.55
μm) suspension (475 μl) to yield the following final concentrations (PS: 10 mg ml-1,
FeCl3 6H2O: 0.1 mg ml-1, EGCG: 0.4 mg ml-1 in 0.5 ml of water). The pH of this
suspension was subsequently raised by adding 0.5 ml of MOPS buffer (20 mM, pH 7.4).
The coated particles were washed three times with water and subjected to zeta-potential
measurements. For planar substrates (quartz slide), solutions of FeCl3 6H2O and EGCG
were added to the aqueous solution containing the substrate to yield the following final
concentrations (FeCl3 6H2O: 0.1 mg ml-1, EGCG: 0.4 mg ml-1 in 20 ml of water). The
solution was vigorously mixed by a vortex mixer for 10 s immediately after the
individual additions of FeCl3 6H2O and EGCG. The pH of this solution was subsequently
raised by adding 1 N NaOH solution to ca. pH 8. The substrates were then rinsed with
water and dried under a nitrogen stream.
5
Fig. S1. Schematic illustration of the one-step assembly of coordination complexes
on a range of substrates.
By simply mixing FeIII and TA, substrates are instantaneously coated with films that can
disassemble in response to pH.
6
Fig. S2. Sequential video frames depicting rapid FeIII-TA film assembly on particle
templates.
7
Fig. S3. Molecular weight dependent permeability of FeIII-TA capsules.
(A) CLSM images of FeIII-TA capsules incubated with FITC-dextran (4, 250, 2,000 kDa,
from left to right). Scale bars are 10 μm. (B) The percentage of permeable capsules
plotted against different molecular weights of FITC-dextran.
8
Fig. S4. EDS analysis of FeIII-TA capsules.
The signals of Cu and part of C/O are from the formvar-carbon coated copper grid.
9
Fig. S5. XPS spectra of FeIII-TA capsules.
Capsules were prepared from the following FeIII and TA concentrations. [FeCl3 6H2O] =
(A) 0.06 mg ml-1, (B) 0.12 mg ml-1, (C) 0.2 mg ml-1. [TA] = 0.4 mg ml-1 for (A-C).
10
Fig. S6. AFM force analysis of FeIII-TA capsules.
(A) Representative force-deformation curves for the small deformation regime of FeIIITA capsules. (B) Force-deformation approach curves for large deformations of the first,
third and tenth force cycle on the same individual FeIII-TA capsule, demonstrating
reversible shell deformation/reformation.
11
Fig. S7. FeIII-TA film growth with sequential deposition cycles on template particles.
(A) Film thickness of FeIII-TA capsules prepared from PS templates (D = 3.55 μm)
measured by AFM (mean ± S.D., N = 20). (B) Representative AFM images and
corresponding height profiles of the FeIII-TA capsules with the indicated number of
deposition cycles.
12
Fig. S8. FeIII-TA film growth with sequential deposition cycles on planar substrates.
(A) UV-Vis absorption spectra for FeIII-TA films (up to five deposition cycles) deposited
on quartz. (B) AFM height image of a scratched zone of a FeIII-TA film (five deposition
cycles) on a quartz substrate showing bare substrate (left) and a 20 nm-thick FeIII-TA film
(right). (C) Ellipsometric thickness of FeIII-TA films on Au substrates (mean ± S.D., N =
5).
13
Fig. S9. Effect of iron(III) chloride hexahydrate concentration ([FeCl3 6H2O]) on
film thickness.
(A) Representative AFM height images (5 × 5 μm) of capsules prepared at different
[FeCl3 6H2O]. (B) Film thickness of the capsules prepared at the indicated [FeCl3 6H2O].
Film thicknesses of 20 capsules were measured. The results are average values with
standard deviations (mean ± S.D., N = 20).
14
Fig. S10. Film thicknesses of the capsules prepared at the indicated TA
concentrations.
The results are average values with standard deviations (mean ± S.D., N = 20).
15
Fig. S11. Adsorption isotherm of TA.
(A) A 3D structure of TA. The structure was modeled using Chem3D software
(CambridgeSoft Corporation), and subjected to energy minimization by the molecular
mechanics method (MM2). Red: oxygen; gray: carbon; white: hydrogen. (B) Adsorbed
amount of TA onto PS particles (D = 836 nm) plotted against the initial concentration of
TA. Approximately 10 s was allowed for TA adsorption. The plot was fitted to the
following Langmuir equation; y = ymax × αx / (1 + αx), where y is the adsorbed amount of
TA, ymax is the maximum y, x is the concentration of TA, α is a constant. By assuming
that a TA molecule is monodisperse (Mw = 1701.2 g mol-1) and occupies 4 nm2, the
adsorption amount of 100% coverage was calculated to be 2.42 mg/g of PS. This value is
similar to the ymax value, suggesting that TA molecules can form a densely packed layer
on the template surface, even without FeIII.
16
Fig. S12. Schematic illustration of the FeIII-TA film formation processes at different
FeIII concentrations.
Excess FeIII results in the small aggregates in bulk solution. These small aggregates attach
to the surface, leading to the increase in roughness of the capsules.
17
Fig. S13. FeIII-TA coating on various particles.
(A) A 3D CLSM image of Rhodamine B-loaded CaCO3 particles (red) coated with FeIIITA films (green). (B) A SEM image of mesoporous CaCO3 templates. (C–E) DIC, SEM,
and TEM images of FeIII-TA replica particles. (F) A TEM image of Au NPs coated with
FeIII-TA films. (G) TEM images of a FeIII-TA capsule loaded with Fe3O4 nanoparticles.
18
Fig. S14. A DIC image of FeIII-TA capsules prepared from PS templates (D = 3.55
μm), showing that they shrink at pH 2.
19
Fig. S15. Representative AFM image (left) and height profile (right) of a FeIII-TA
capsule after incubation at pH 5.0 for two days.
20
Fig. S16. MTT assay of FeIII-TA capsules on HeLa cells.
Cells were incubated at the indicated capsule ratio for 72 h. The results are average
values with standard deviations (mean ± S.D., N = 4).
21
Fig. S17. Capsules prepared from various metals.
(A) AFM image of VIII-TA capsules. (B) EDS analysis of VIII-TA capsules. (C) DIC
image of GdIII/FeIII-TA hybrid capsules. (D) EDS analysis of GdIII/FeIII-TA hybrid
capsules. (E) DIC image of CrIII/FeIII-TA hybrid capsules. (F) EDS analysis of CrIII/FeIIITA hybrid capsules. The Cu signals in the EDS spectra are from the copper grids used for
TEM.
22
Fig. S18. Film deposition of another polyphenol compound, (-)-Epigallocatechin
gallate (EGCG), with FeIII.
(A) A suspension of PS particles (D = 3.55 μm) uncoated (left) and FeIII-EGCG-coated
(right). The zeta-potential shifted from -27 ± 3 mV to -37 ± 6 mV after FeIII-EGCG
coating, indicating successful film deposition. (B) Pellets of uncoated (left) and FeIIIEGCG coated PS particles (right). (C) UV-Vis spectra monitoring of sequential Fe IIIEGCG coatings (seven coatings) on a quartz slide. (D) A photograph of an uncoated (left)
and FeIII-EGCG coated (right) quartz slide.
23
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