supplementary information10.1038... · junling guo, blaise l. tardy, andrew j. christofferson,...

© 2016 Macmillan Publishers Limited, part of Springer Nature. All rights reserved.

SUPPLEMENTARY INFORMATIONDOI: 10.1038/NNANO.2016.172

NATURE NANOTECHNOLOGY | www.nature.com/naturenanotechnology 1

1

Supplementary Information

Modular assembly of superstructures from polyphenol-

functionalized building blocks

Junling Guo, Blaise L. Tardy, Andrew J. Christofferson, Yunlu Dai, Joseph J. Richardson, Wei

Zhu, Ming Hu, Yi Ju, Jiwei Cui, Raymond R. Dagastine, Irene Yarovsky and Frank Caruso*

*Correspondence to: Prof. F. Caruso (E-mail: [email protected])

Modular assembly of superstructures frompolyphenol-functionalized building blocks

http://dx.doi.org/10.1038/nnano.2016.172


2 NATURE NANOTECHNOLOGY | www.nature.com/naturenanotechnology

SUPPLEMENTARY INFORMATION DOI: 10.1038/NNANO.2016.172

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Table of Contents

Section S1. General materials ................................................................................................. 3

Section S2. Building block particles ........................................................................................ 3

Purchased particles ............................................................................................................. 3

Synthesized particles .......................................................................................................... 3

Human microvascular endothelial cells (HMECs) ............................................................. 4

Section S3. Three-dimensional (3D) collagen matrix ............................................................ 4

Section S4. General characterization ..................................................................................... 4

Instruments and software ................................................................................................... 4

SEM and TEM sample preparation .................................................................................... 5

Section S5. Modularly-assembled SPs with single-type building block particles ............... 6

Metal coordination-based particle functionalization .......................................................... 6

Oxidation reaction-based particle functionalization .......................................................... 6

Supraparticle assembly ....................................................................................................... 7

Formation of hollow SPs .................................................................................................... 7

Nomenclature of superstructures ........................................................................................ 8

Section S6. Modularly-assembled hierarchical SPs with multiple level structures ........... 8

First-level generation .......................................................................................................... 8

Secondary-level generation ................................................................................................ 8

Section S7. Modularly-assembled one-dimensional (1D) superstructure through magnetic field application ........................................................................................................ 9

Section S8. Macroscopic bio/inorganic hybrid materials ..................................................... 9

Section S9. Colloidal-probe atomic force microscopy (AFM) measurements .................... 9

Preparation of colloidal probes .......................................................................................... 9

Surface functionalization of colloidal probes and glass substrate .................................... 10

Approach–retraction process ............................................................................................ 10

Section S10. Molecular dynamics (MD) simulation models and methods ........................ 11

Model construction ........................................................................................................... 11

Force-field parameterization and partial charge calculation by QM calculations............ 12

MD simulation details ...................................................................................................... 12

Section S11. Figures and Tables ............................................................................................ 14

Section S12. Notes and discussion ......................................................................................... 41

Section S13. Supplementary references ............................................................................... 47





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Section S1. General materials

Tannic acid (TA), dopamine hydrochloride, iron(III) chloride hexahydrate (FeCl3·6H2O), aluminum(III)

chloride (AlCl3), zirconium(IV) chloride (ZrCl4), cerium(III) chloride heptahydrate (CeCl3·7H2O), zinc

sulfate heptahydrate (ZnSO4·7H2O), polyethylenimine (PEI), tris(hydroxymethyl)aminomethane (Tris), and

3-(N-morpholino)propansulfonic acid (MOPS) were purchased from Sigma-Aldrich (Australia). Fetal

bovine serum (FBS) and epidermal growth factor were purchased from Sigma-Aldrich (USA). MCDB131

medium, L-glutamine, hydrocortisone, and penicillin-streptomycin were purchased from Life Technologies

(USA). Tetrahydrofuran (THF) and ethanol were purchased from Chem-Supply. All of these materials were

used as received. High-purity Milli-Q (MQ) water with a resistivity of 18.2 MΩ cm was obtained from an

inline Millipore RiOs/Origin water purification system.

Section S2. Building block particles

Purchased particles

Polystyrene (PS) particles (3.5 μm, 10 μm, 50 μm), amino-functionalized silica (SiO2) particles (365 nm, 1

μm), melamine resin (MF) particles with green, red, and blue fluorescence colours (500 nm, 900 nm),

magnetic and red fluorescence PS particles (1 μm), and magnetic SiO2 particles (500 nm) were purchased

from Microparticles GmbH (Germany). Zinc oxide (ZnO) nanowires and Micrococcus lysodeikticus

particles were purchased from Sigma-Aldrich (Australia).

Synthesized particles

Mesoporous SiO2 particles (500 nm) were synthesized according to reported methods1. Ytterbium and

erbium co-doped sodium yttrium fluoride (NaYF4:Yb/Er) nanoparticles (~100 nm) were prepared

according to literature methods2. Rod-like SiO2 particles (500 nm) were prepared according to methods

reported elsewhere3. Iron oxyhydroxides akaganeite (β-FeOOH) nanorods, silver cyanide (AgCN)

nanowires, nickel nickeltetracyanonickelate (Ni[Ni(CN)4]) polygons, and cubic Prussian blue

(Fe4[Fe(CN)6]3) nanoparticles were prepared according to literature methods4. Gold (Au) and silver (Ag)

nanoparticles were prepared according to methods described elsewhere5. All the chemicals involved in the





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particle synthesis were purchased from Sigma-Aldrich (Australia).

Human microvascular endothelial cells (HMECs)

Human microvascular endothelial cell line-1 (HMEC-1) was obtained from Prof. Christoph E. Hagemeyer

(Baker IDI Heart and Diabetes Institute, Australia). HMEC-1 were cultured in MCDB131 medium supplied

with 10% FBS, 2 mM L-glutamine, 1 µg/mL hydrocortisone, 10 ng/mL epidermal growth factor, and 100

u/mL penicillin-streptomycin at 37 °C with 95% humidity and 5% CO2. The HMEC particles were

suspended in Dulbecco's phosphate-buffered saline (DPBS) buffer solution and used as core particles in the

magnetic supraparticle assembly process.

Section S3. Three-dimensional (3D) collagen matrix

Skin collagen fibre matrix was prepared from cattle hide according to the literature methods6. Briefly, cattle

pelt was cleaned, limed, split, and delimed, according to approaches used in leather processing, to remove

non-collagen components such as impurities (blood and non-protein components), fats, and grease. Then,

the pelt was treated with 150% aqueous solution of acetic acid (concentration 16 g/L) thrice to remove

mineral substances. Finally, the pH of the pelt was adjusted to 4.8–5.0 before cross-linking by chromium

salt (Cr3+) or glutaraldehyde, or dehydrating and drying.

Section S4. General characterization

Instruments and software

Differential interference contrast (DIC) images were obtained with an inverted Olympus IX71 microscope.

Transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS) were

performed on a FEI Tecnai TF20/Spirit instrument, operating at a voltage of 200 or 100 kV. Scanning

electron microscopy (SEM) images were obtained on a FEI Quanta 200/XL30 field-emission scanning

electron microscope, operating at an accelerating voltage of 10 or 2 kV. The pseudo colours in the SEM





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images were added by image processing in Photoshop CS6 (Adobe Systems Inc.). UV-Visible absorption

and fluorescence measurements were conducted on an Infinite M200 PRO microplate reader (Tecan Group,

Switzerland). Flow cytometry assays were carried out on a Cyflow Space (Partec GmbH, Germany) flow

cytometer for Fig. S4, and an A50 Apogee flow cytometer (Apogee Flow System, UK) for Fig. S21. 3D-

structured illumination microscopy (3D-SIM) imaging was performed using a DeltaVision OMX V4 Blaze

SIM super-resolution microscope equipped with a 60× 1.42 NA oil immersion objective, with a set of

standard filters for DAPI/CFP/FITC/AF488/AF568/Cy5/AF647. Image processing and 3D models were

analyzed and generated with Imaris (Bitplane) software using the maximum intensity projection.

Deconvolution images were taken on a series of z-sections within the top and bottom of a supraparticle

(SP). Coverslips were prepared by smearing 22 mm × 22 mm square glass coverslips with a 0.1% solution

of PEI, followed by drying by heating under a flame. Upconversion luminescence emission spectra were

obtained using a 980 nm LD Module (K98D08M-30W, China) as the excitation source and a R955

(Hamamatsu Photonics, Japan) detector in the range of 400–900 nm. The iron concentrations were detected

by inductively coupled plasma optical emission spectrometry (ICP-OES) using an ICP Varian Vista MPX

instrument.

SEM and TEM sample preparation

SP suspensions (2.0 μL) were allowed to air-dry on Piranha-cleaned silicon wafers and Formvar carbon-

coated gold grids (Piranha solution: 98% H2SO4/30% H2O2, 7:3 v/v; Caution! Piranha solution is highly

oxidizing and corrosive! Extreme care should be taken during preparation and use). For the preparation of

3D-structured spherical hollow SP samples, the critical point drying (CPD) method was applied7. Briefly,

SP suspensions (10.0 μL) were incubated on PEI-coated glass coverslips for 1 h. Following incubation, the

excess culture was drained, and coverslips with adhered capsules were immersed in 100% ethanol to

dehydrate for 30 min. The coverslips were then dried in a Balzers CPD030 critical point dryer (Balzers,

Liechtenstein) and mounted onto 25-mm aluminum stubs with double-sided carbon tabs. The coverslips

were coated with gold using a Xenosput sputter coater (Dynavac, Wantirna South, Australia). The SPs on

the coverslips were imaged with a Philips XL30 field-emission scanning electron microscope (Philips,

Eindhoven, Netherlands) at a voltage of 2.0 kV and a spot size of 2.0.





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Section S5. Modularly-assembled SPs with single-type building block particles

Metal coordination-based particle functionalization

The building block particles were suspended in MQ water or DPBS buffer solution (0.5–5% w/v). TA and

FeCl3 solutions were added to the building block particles suspension to achieve the final concentrations of

TA (0.24 mM) and Fe3+ (0.24 mM)8,9. Then, MOPS buffer solution (pH 8.0, 100 mM) was added to raise

the solution pH. An Fe-TA (iron-phenolic) network (FePN) was formed and used for functionalizing the

surface of the building block particles with catechol/galloyl (C/G) groups. The functionalized building

block particles were washed with MQ water 3–4 times to remove the excess Fe-TA complexes. In the

washing process, the particles were spun down by centrifugation and the supernatant was removed. The

centrifugation speeds used for the different particles were varied and optimized to avoid particle

aggregation: ~50 nm – 8000 g, 10 min; 100–200 nm – 800 g, 15 min; ~500 nm – 1000 g, 5 min; ~800 nm –

1000 g, 2 min; and ~1 μm – 1000 g, 1.5 min. The monodispersity of the particles was necessary for the

particle assembly process.

Oxidation reaction-based particle functionalization

It has been demonstrated that the functionalization of building blocks could be achieved through mussel-

inspired polydopamine (PDA) coating10,11. This functionalization process was used for the formation of

core–satellite and hollow SPs, thus highlighting the versatility of surface chemistry in the modular

assembly method. Briefly, dopamine (12 mg) was dissolved in MQ water (4.4 mL). The suspensions of

building blocks were mixed with the dopamine solution to achieve the final concentration of dopamine of 2

mg/mL. Polymerization of dopamine was allowed to proceed for 2–3 h in Tris buffer solution (pH 8.5, 10

mM) with constant shaking in ambient air at room temperature (~25 °C, or ~298 K) at 1 atmosphere

pressure. The PDA-functionalized building block particles were obtained after washing with MQ water 3–4

times to remove the excess PDA. The monodispersity of the resulting particles was necessary for the

subsequent particle assembly process on larger core particles. Therefore, the centrifugation speeds were

optimized to avoid aggregation.





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Supraparticle assembly

The superstructural assembly of building block particles can occur after mixing with larger core particles

(or templates, e.g., PS, MF particles (0.1–5% w/v), cells, collagen matrix). During the assembly process,

the mixing suspension was vortexed for 10–60 s to instigate collisions between the building blocks and

cores (templates). Sonication may be applied to assist the dispersion of particles. After particle mixing,

inter-particle locking was achieved by adding metal ions (final concentration: 0.24 mM FeCl3, AlCl3, ZrCl4,

CeCl3, or ZnSO4) and an equal volume of MOPS buffer solution (pH 8.0, 100 mM). The C/G groups from

two different particles can complex with the same metal ions (clusters) to form the inter-particle bridging.

Core–satellite SPs were obtained after washing with MQ water for 3–5 times to remove the free building

blocks and template particles. The centrifugation speeds used for the different core–satellite SPs were

varied and optimized to avoid particle aggregation: 100–200 nm – 800 g, 15 min; ~1 μm – 1000 g, 1.5 min,

and ~3.5 μm – 1000 g, 1 min.

Formation of hollow SPs

Metal-phenolic coordination bonds between particles provide robust linkages for the construction of hollow

superstructures. In the core (template) removal process, the core–satellite SPs were spun down by

centrifugation and washed with THF for 3–4 times. The arrangement of the building particles could be

stabilized accordingly to maintain a hollow superstructural architecture. During the THF washing process,

the hollow SPs were spun down by centrifugation, and the supernatant was removed. The centrifugation

speeds used for the different hollow SPs were varied and optimized to avoid particle aggregation: 100–200

nm – 800 g, 15 min; ~1 μm – 1000 g, 1.5 min, and ~3.5 μm – 1000 g, 1 min. After removal of the core, the

hollow SPs were transferred to the desired solvents (MQ water or buffer solutions). Note that metal ions

were required for SP formation.





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Nomenclature of superstructures

The names used to denote the core–satellite, hollow SPs, and hybrid composites prepared were as follows.

Core–satellite SPs and hybrid composites were denoted as (diameter size, μm)(building block name)@(diameter size,

μm)(core/template/substrate name). Hollow SPs were denoted as hollow (diameter size, μm)(building block name)

SPs.

Section S6. Modularly-assembled hierarchical SPs with multiple level structures

The C/G-functionalized building blocks do not easily form free linkages with each other owing to

electrostatic repulsion forces between them. Therefore, the interactions between the C/G groups and core

particles play a dominant role in the dynamic force interactions, leading to subsequent assembly of the SPs

with larger cores.

First-level generation

Green fluorescence PS particles (280 nm) were functionalized with C/G groups using the protocol in

Section S5. The functionalized particles were then mixed with 930 nm blue fluorescence MF particles and

vortexed for 10–30 s (sonication may be applied to assist the dispersion of particles). FeCl3 solution and an

equal volume of MOPS buffer solution (pH 8.0, 100 mM) were added to effect inter-particle locking (final

concentration of Fe3+: 0.24 mM). [email protected] core–satellite SPs were obtained by washing with MQ thrice.

Secondary-level generation

[email protected] core–satellite SPs were directly mixed with 15-μm red fluorescence PS particles and vortexed

for 10–30 s. FeCl3 solution and an equal volume of MOPS buffer solution (pH 8.0, 100 mM) were added to

induce secondary inter-particle locking (final concentration of Fe3+: 0.24 mM). Hierarchical

15PS@([email protected]) core–satellite SPs were obtained by washing with MQ thrice.





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Section S7. Modularly-assembled one-dimensional (1D) superstructure through

magnetic field application

The magnetic red fluorescence PS particles were functionalized according to the metal coordination-based

method described in Section S5. The C/G-functionalized particles were suspended in MQ water and

dropped on a glass slide (1–2 μL). A neodymium-iron-boron alloy magnet, Nd2Fe14B, was positioned on

the left side of the glass slide in a coplanar direction. In the presence of the magnet, the C/G-functionalized

magnetic particles assembled into a liner superstructure. After 20 s, a drop of FeCl3 solution was added to

achieve the final concentration of Fe3+ (0.24 mM). The addition of FeCl3 linked and stabilized the 1D linear

superstructure, which was retained even after removal of the magnet.

Section S8. Macroscopic bio/inorganic hybrid materials

The pretreated 3D collagen matrix (3D CM) was further cross-linked by chromium salts (Cr3+) or

glutaraldehyde according to leather manufacturing processes6. The cross-linked 3D CM was mixed with a

suspension of C/G-functionalized Ag nanoparticles (500–1000 mL, depending on the CM weight) at 318 K

at pH 6.5 for 5 h. Subsequently, the CM@Ag nanoparticles composites were collected after thorough

washing with MQ water.

Section S9. Colloidal-probe atomic force microscopy (AFM) measurements

Preparation of colloidal probes

The larger silica colloidal probes used for the indentation experiments on bare PS particles and planar glass

substrates were prepared by the method described in Ducker et al.12, in which spherical colloidal silica

particles were attached to V-shaped silicon nitride MLCT cantilevers (Bruker Corporation, USA) using a

small amount of two-part epoxy adhesive (Super Glue Corporation, USA) with a 30-min delayed setting

time. Specifically, an MLCT cantilever was lowered into a small amount of adhesive that was then





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promptly used to pick up a colloidal silica particle deposited on a glass slide. The cantilever with the

particle glued at the cantilever tip was left at room temperature to allow the adhesive to dry and set for 24 h.

The diameter of the colloidal probe (silica particle) was determined to be 11.7 μm. Additionally, 5-μm

spherical silica particles were purchased from Novascan Technologies (USA) and used in the indentation

test. The spring constants of the 11.7-μm and 5-μm probes were 0.064 N/m and 0.034 N/m, respectively, as

measured by the method of Hutter–Bechhoefer13.

Surface functionalization of colloidal probes and glass substrate

The silica particles on the cantilevers were coated with three layers of FePN based on the protocol given in

Section S5 (metal coordination-based particle functionalization)8. Briefly, the cantilevers were placed in a

Petri dish containing MQ water (5 mL). Then, FeCl3 solution (50 μL, 24 mM) and TA solution (50 μL, 24

mM) were added to the Petri dish. The solution was mixed several times with a pipette. Finally, MOPS

buffer solution (5 mL; pH 8.0, 100 mM) was added to the solution to raise the pH. The cantilevers were

then washed with MQ water thrice to remove excess FeIII-TA complexes. The whole process was repeated

three times to build up three FePN coating layers on the colloidal probes. Note that all of these processes

were conducted with care to avoid damage of the cantilevers. Additionally, a glass substrate was coated

with three layers of FePN using the same protocol as that used for the cantilever coating. The FePN-coated

glass substrate was used to examine the interactions between two FePN surfaces to understand the inter-

particle locking process.

Approach–retraction process

The AFM head was slowly lowered into the fluid cell containing a glass disk coated with the iron-phenolic

network (FePN) film or on which PS particles of diameters of 10 or 50 μm were immobilized using a PEI-

coated glass substrate. The fluid cell was left to equilibrate to room temperature (from 21 to 23 °C) for at

least 30 min. Prior to the force measurements, the sensitivity of the colloidal probe was measured by

indenting the bare glass base of the fluid cell until a constant compliance was achieved. The spring constant

was then determined. The colloidal probe was then engaged and slowly lowered onto the glass substrate or

the PS particles until a distinct probe deflection was recorded. The vertical alignment of the colloidal probe





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with that of the particles was achieved by adjusting the position of the fluid cell with a micromanipulation

stage. To eliminate hydrodynamic effects, all force–distance curves were obtained at a velocity of 200 nm/s.

The approach–retraction process was repeated several times on each surface.

Section S10. Molecular dynamics (MD) simulation models and methods

Model construction

TA molecules were constructed based on the commercial formula, C76H52O46, and solvated in a cubic water

box of 50 × 50 × 50 Å3 and equilibrated by 200 ns of MD simulation. Complexes comprising a FeIII ion and

three TA per complexes (FeIII-TA3) were constructed from the equilibrated TA molecules. The geometry

around Fe was obtained from quantum mechanics (QM) geometry optimizations of FeIII-galloyl3 fragments

(Fig. S15). Three sodium ions were added to the solvated systems to maintain a net neutral charge. Our

previous work has shown that a relaxed polymer surface is critical for the accurate modelling of adhesion

or adsorption14. For the PS surface, five atactic oligomers of polystyrene of 10 monomer units each were

packed into a confined layer using the Theodorou–Suter algorithm15,16. The constant pressure and

temperature (NPT) ensemble simulations conducted at 1 atm and 298 K, maintained with the Berendsen

barostat and Andersen thermostat, respectively, were used to compress the layer into a 20 × 20 × 20 Å3 unit

cells, producing a target density of 0.99 g/cm3. This quasi two-dimensional (2D) model of the PS layer of

20 Å thickness was replicated in the x- and y-directions to create larger-sized layers in unit cells of 60 × 60

× 20 Å3 and 80 × 80 × 20 Å3 for use in simulations as PS substrates for TA and FeIII-TA3 complexes,

respectively. The 20-Å-thick polystyrene layers were solvated in 60 × 60 × 80 Å3 and 80 × 80 × 100 Å3

boxes, and the polystyrene surfaces were relaxed in water at 298 K by MD for up to 200 ns in the constant

volume and temperature (NVT) ensemble until no significant surface rearrangements were observed and

the potential energy fluctuations were within 1%. Following the surface relaxation, the TA3 and FeIII-TA3

complexes were added to the respective substrates in four different initial orientations, with a separation of

at least 10 Å between the TA and polystyrene surface to create multiple starting configurations for the

adsorption simulations.





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Force-field parameterization and partial charge calculation by QM calculations

For all MD simulations, the published parameters from the Condensed-phase Optimized Molecular

Potentials for Atomistic Simulation Studies (COMPASS) force field17 complemented as described herein

were applied. We have used COMPASS previously to model adhesion at polymer surfaces14, and the force

field has been shown to be reliable for modelling polymers, nanomaterials, and interfaces18-21. To

accurately determine the FeIII coordination complex geometry, QM calculations were performed on the X-

ray crystal structure of ferrioxalate22 and on a FeIII-galloyl3 fragment (Table S1). The density functional

theory calculations with B3LYP hybrid functional were employed, the 6-31G(d,p) basis set was used for

non-metal atoms and the LANL2DZ(f) basis set and effective core potential were used for iron. The

polarizable continuum model was used to assess the effects of water implicitly. All calculations were

performed using Gaussian 0923. The bond lengths, angles, and force constants obtained to reproduce the

distorted octahedral geometry shown in Fig. S15 are listed in Table S2. For the C–C–O–Fe dihedrals, a

QM dihedral scan was performed, and dihedral force constants were applied to reproduce the QM

rotational barrier of ~20 kcal/mol (Table S2). The Lennard-Jones parameters for iron, and missing angles

and dihedrals for non-metal interactions were taken from the Polymer Consistent Force Field (PCFF)24.

Atomic partial charges on the iron and chelating oxygens were taken from QM calculations (Table S1), and

the remaining atomic charges were calculated by the charge equilibration (QEq) method25.

MD simulation details

To enable extensive conformational sampling using an efficient MD implementation, the open-source MD

code LAMMPS26 was used. Production simulations were run in the NPT ensemble, using the Nosé–Hoover

thermostat and barostat, to maintain a temperature of 298 K and pressure of 1 atm. All systems used a time

step of 1 fs and an output frequency of 10 ps. Electrostatics beyond a 15.5 Å cut-off were evaluated with

the PPPM summation method with an accuracy of 10−5 kcal/mol, and van der Waals interactions were

assessed with an atom-based summation using a 15.5 Å cut-off and tail correction. All simulations were run

for up to 200 ns, with at least three different initial velocity distributions for each system. Equilibration was

defined as the point where the TA heavy-atom root-mean-square deviation reached a steady value with a

standard deviation of less than 1 Å. All analyses were performed on 10 ns of equilibrated trajectory.

Additional analysis of the initial interactions between FeIII-TA3 and the PS surface was performed on the





13

first 20 ns of simulation following stabilization of the temperature and pressure. To ensure statistical

validation of the adsorption mechanism, 100 independent simulations of FeIII-TA3 adsorption on the PS

surface were performed. Hydrogen bonds were calculated with a maximum donor–acceptor distance of 2.5

Å and a minimum angle of 120°. Atomic density profiles were created using the VMD Density Profile

Tool27.





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Section S11. Figures and Tables

Figure S1. Molecular structures of TA (a) and dopamine (b). TA originates from plants and can form a

coordination supramolecular network with metal ions9. Dopamine is derived from marine animals (mussel

foot protein) and can be polymerized into PDA under alkaline conditions10. These polyphenols were used

to functionalize the various building block particles examined with C/G groups. The latter functional

moieties enabled transformation of the particles into LEGO brick-inspired modular bricks with the same

functional surface.





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Figure S2. Schematic representation of the modular assembly method. The formation of core–satellite

SPs involves the surface functionalization of building blocks (with C/G groups), particle assembly of the

functionalized building blocks on larger core particles, and inter-particle locking (during the assembly

process). To obtain hollow SPs, the PS core particles were removed by washing with THF.





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Figure S3. TEM images of bare, FePN-functionalized, and PDA-functionalized SiO2 building block

particles. The nanoscale coating confers the various building block particles with same surface chemistry,

enabling transformation of the particles into easy-to-use modular building blocks. The surface is

functionalized with C/G groups, which can further interact with other surfaces to provide the driving forces

for particle assembly and instigate inter-particle locking through metal coordination complexation

(similarly to the connecting structures of “knob-stud” in LEGO superstructuring). Scale bars are 100 nm in

images depicting whole particles and 50 nm in images showing magnified parts of the particles.





17

Figure S4. Size distribution of building block particles via 2D mapping of the corresponding particle

size distributions. The 2D mapping images were generated from forward-scattered light (FSC) and side-

scattered light (SSC) using flow cytometry. a and b show the monodisperse building block particles (960

nm SiO2) before and after FePN functionalization. The particle size distribution depicted in c was obtained

after mixing with 10 μm PS particles for assembly, adding Fe3+ ions to lock the assembled particles, and

washing with THF to remove the PS cores. The particle size distribution following the processes described

in c was shifted towards to that of the 10-μm bare PS particles in d.





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Figure S5. Supraparticle formation through metal binding. a, The formation of SPs was achieved

through Fe binding between the FePN- or PDA-functionalized building block particles. b, Fe

concentrations of discrete and assembled FePN- or PDA-functionalized particles were measured by ICP-

OES. Distinct Fe concentration increases were observed after the assembly process. n = 3.





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Figure S6. DIC images of the core–satellite and hollow SPs assembled from PDA-functionalized SiO2

particles on larger PS particles. The core–satellite SPs were constructed from PDA-functionalized 960-

nm PS particles on 10-μm PS particles (a,b). The hollow SPs were constructed from PDA-functionalized

465-nm SiO2 particles on 3.5-μm PS particles (c). Scale bars are 10 μm (a) and 5 μm (b,c).





20

Figure S7. a, 3D surface of adsorbed particle number on larger template particles; r1 and r2 represent the

radii of template particles and building block particles, respectively. b, Plot of actual counted particle

numbers (squares) and theoretically calculated values (lines) based on maximum geometrically close-

packed structure (Mm) or complete kinetically driven assembled structure (Mp). n = 3.





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Figure S8. Representative force–distance curves of FePN-coated SiO2-attached probes approaching

and retracting from the FePN-coated planar glass substrate.





22

Figure S9. Interactions between FeIII-TA3 (FePN) and a PS surface in atomic detail. a, Representative

snapshots obtained from the MD simulation, showing the anchoring, lockdown, and stable adsorption steps.

b, Close-up view of the aromatic interactions between FeIII-TA3 and the PS surface. c, Running average of

(C/G)–PS aromatic contacts over the first 20 ns of simulation. d, Exemplar number density of FeIII-TA3

normal to the PS–water interface (dashed line). Hydrogen atoms and water molecules are omitted for

clarity. To ensure statistical validation of the adsorption mechanism, a total of 100 independent simulations

of FeIII-TA3 adsorption on the PS surface were performed.





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Figure S10. Disassembly of hollow SPs by sonication or treatment under acidic conditions. a,

Schematic representation of hollow SPs disassembling into well-dispersed discrete building block particles.

b,c, DIC images of 0.3SiO2 SPs suspensions and the disassembled particles obtained upon sonication (b)

and immersion of the SPs suspension under acidic pH conditions (0.5 M HCl, c). Scale bars are 5 μm.





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Figure S11. TEM image of the integration system of hollow [email protected]:Yb/Er SPs. The

hollow SPs were prepared by modular co-assembly of DOX-loaded msp-SiO2 (600 nm) and upconversion

NaYF4:Yb/Er (100 nm) nanoparticles. Scale bar is 1 μm. Because of the assembly of these particles into a

highly integrated system, the multicomponent building blocks can exert near-field coupling effects within a

single particle system.





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Figure S12. Schematic representation of modularly-assembled hierarchical SPs with multiple level

structures. The formation process involves two levels of core–satellite SPs. The length scales of the

hierarchical assembled SPs range from 280 nm to 15 μm (~50 times larger than fundamental building

blocks).





26

Figure S13. Modular assembly of 1D linear superstructures with the assistance of a magnetic field.

After assembly of the particles under a magnetic field (B), Fe3+ ions were added to the suspension. The

linearly assembled superstructure can be retained even after removal of the magnetic field. Fluorescence

microscopy images show the free monodisperse PS particles (a) and linearly assembled superstructures

(b,c). Scale bars are 10 μm (a,b) and 5 μm (c).





27

Figure S14. Assembly of C/G-functionalized Ag nanoparticles (AgNPs) on a CM for preparing

macroscopic bio/inorganic hybrid composites. The interactions between the C/G groups and collagen

protein can provide the driving force for the particle assembly (a). One of the most important advantages of

this approach is the post-assembly process, which allows the use of diverse building block combinations.

For example, CM, which is a protein-based material, is highly sensitive to thermal and chemical

conditions28. Therefore, the in situ synthesis of functional particles on CM can only be performed under

mild conditions29. However, the C/G-based post-assembly can circumvent such a restriction, potentially

allowing a diversity of functional particles to integrate on the biological substrate. The photographs in b

and c show the colour change from ivory (pure CM) to black (CM@Ag nanoparticles). d and e show the

stretchable ability and the centimetre-size scale of the CM@Ag nanoparticles material. f, SEM image

depicting the hierarchical structure of the collagen fibrils (scale bar is 500 nm). Inset in f shows a TEM

image of the assembled Ag nanoparticles on CM (scale bar is 20 nm).





28

Figure S15. a, FeIII-galloyl3 used in the QM calculations. b, Bonds, angles, and the shown force-field atom

types are consistent with those listed in Table S2.





29

Figure S16. a, Solvated TA with numbering of galloyl groups around the central sugar ring. b, Distance

between galloyl pairs (by centre of mass) measured in the final 10 ns of simulation.





30

Figure S17. Typical equilibrium adsorption configuration of TA on a PS surface. PS carbons are

coloured grey and TA carbons are coloured pink. Hydrogen atoms and water molecules are omitted for

clarity.





31

Figure S18. Representative snapshots of FeIII-TA3 (a) showing the increase in π–π stacking around Fe

that is not observed in the free TA aggregate (b). Carbon, oxygen, and iron atoms are coloured pink, red,

and yellow, respectively. Hydrogen atoms and water molecules are omitted for clarity. c, Radial distribution

function of oxygen–oxygen distances in FeIII-TA3 and TA3.





32

Figure S19. Representative snapshots from MD simulations of FeIII-TA3 and TA3 adsorption on a PS

surface. a, Fully adsorbed FeIII-TA3; b, partially adsorbed FeIII-TA3; c, fully adsorbed TA3; and d, partially

adsorbed TA3. PS carbon atoms are coloured grey, and TA carbon, oxygen, and iron atoms are coloured

pink, red, and yellow, respectively. Hydrogen atoms and water molecules are omitted for clarity.





33

Figure S20. Number density profiles of FeIII-TA3 and TA without Fe averaged over all simulations. a,

Fully adsorbed on the PS surface. b, Partially adsorbed on the PS surface. The PS–water interface is

represented by the dashed line.





34

Figure S21. RDF profiles of oxygen–oxygen distances in FeIII-TA3 and TA3 in solution (dotted lines),

fully adsorbed on PS (solid lines), and partially adsorbed on PS (dashed lines).





35

Figure S22. a, Particle adsorption of florescent 0.28PSgreen on human prostate PC-3 cells, as measured

using area counting of 2D flow cytometry data from the 488 green and small angle light scattering

(SALS) channels. n = 3. ***P < 0.001, student’s t-test. b, DIC and florescence images of PC-3 cells

incubated with discrete 280 nm florescent PS particles (0.28PSgreen) and their core-satellite

[email protected] SPs after 6 h (37 °C, particle number ratio of 0.28PS to cell is 100:1). Scale bars are 5

μm.





36

Table S1. Bond lengths and partial charges in ferrioxalate and a FeIII-galloyl3 fragment obtained from QM

optimizations that were employed for force field parameterization and MD simulations.

Atoms QM

Ferrioxalate Bond length (Å) Fe–O 2.03

Partial atomic charge

Fe 0.83

O1 −0.58

O2 −0.59

O3 −0.58

O4 −0.59

O5 −0.58

O6 −0.59

FeIII-galloyl3 fragment Bond length (Å) Fe–O 2.02–2.10

Partial atomic charge Fe 0.70

O1 −0.70

O2 −0.67

O3 −0.65

O4 −0.69

O5 −0.65

O6 −0.69





37

Table S2. Force-field parameters developed in this work.

Fe–O bond E = kb2(b − b0)2 + kb3(b − b0)2 + kb4(b − b0)2

where b0 is the equilibrium bond length and kb2, kb3, and kb4 are the force constants

Atom type b0 (Å) kb2

(kcal/mol/Å2) kb3 kb4

fe3o–ofn, where n = 1–6 2.05 500 0 0

O–Fe–O angle E = kθ2(θ − θ0)2 + kθ3(θ − θ0)2 + kθ4(θ − θ0)2

where θ0 is the equilibrium angle and kθ2, kθ3, and kθ4 are the force constants

Atom type θ0 (°) kθ2

(kcal/mol/rad2) kθ3 kθ4

of1–fe3o–of4 of2–fe3o–of5 of3–fe3o–of6 166 150 0 0

of1–fe3o–of2 of3–fe3o–of4 of5–fe3o–of6 79.7 150 0 0


of1-fe3o-of3 of1–fe3o–of5 of2–fe3o–of6


C–C–O–Fe dihedral E = kϕ1(1 – cos ϕ) + kϕ2(1 – cos 2ϕ) + kϕ3(1 – cos 3ϕ)

where kϕ1, kϕ2, and kϕ3 are the force constants

Atom type kϕ1 (kcal/mol) kϕ2 (kcal/mol) kϕ3

c3a–c3a–ofn–fe3o, where n = 1–6 5 15 0





38

Table S3. Hydrogen bond population and lengths in TA.

Hydrogen bonding pairs

Hydrogen bond

population (%) Average hydrogen bond length (Å)

TA hydroxylwater 93 ± 7 1.95 ± 0.03

TA ether oxygenwater 38 ± 13 1.93 ± 0.13

TA carbonyl oxygenwater 72 ± 15 2.01 ± 0.09

Total TAwater 82 ± 5 1.96 ± 0.05

TA hydroxylTA hydroxyl 2 ± 2 2.13 ± 0.16

TA ether oxygenTA hydroxyl 1 ± 3 2.19 ± 0.11

TA carbonyl oxygenTA hydroxyl 4 ± 6 2.04 ± 0.24

Total TATA 2 ± 1 2.11 ± 0.18





39

Table S4. Average hydrogen bond population for FeIII-TA3 and TA3.

Hydrogen bonding pairs FeIII-TA3 TA3

Total TAwater (74 ± 1)% (67 ± 1)%

Total TATA (6.0 ± 0.3)% (4.9 ± 0.3)%





40

Table S5. Average population of hydrogen bonds in FeIII-TA3 and TA3 adsorbed on a PS surface.

Hydrogen bonding

pairs Fully adsorbed Partially adsorbed

FeIII-TA3 TA3 FeIII-TA3 TA3

Total TAwater (60 ± 1)% (59 ± 1)% (63 ± 1)% (58 ± 1)%

Total TATA (6.9 ± 0.3)% (3.9 ± 0.3)% (6.8 ± 0.3)% (3.9 ± 0.3)%





41

Section S12. Notes and discussion

Note and discussion: Amino-functionalized SiO2 particles were used instead of bare SiO2 particles for SP

assembly because of the higher affinity of the FePN coating on the positively charged amino-functionalized

SiO2 particles. To functionalize bare SiO2 particles, the FePN coating process requires three repeat coatings.

This is probably due to the small deposition of FePN complexes on the SiO2 substrate. It was generally

observed that repeated FePN coating on building block particles could enhance the surface

functionalization.

Note and discussion: The polyphenol-based particle functionalization can be achieved through either

metal-phenolic coordination complexation or oxidation. Both of these methods are well established and

exhibit high simplicity and efficiency. Therefore, both methods could be used in the surface

functionalization of the building block particles. In this work, we demonstrate the phenolic-based particle

functionalization mainly through the metal coordination-based method. The oxidative polymerization-

based particle functionalization and SP assembly are also reported herein (Fig. S6).

Note and discussion: The concentrations of the building blocks and template particles in aqueous

suspensions need to be carefully adjusted. Namely, the number of building blocks should be sufficient for

the formation of a continuous network on the template particles. Although the building blocks can adsorb

and form coordination-based bridging on the templates, a near-close packed arrangement is required for the

formation of a hollow structure.

Note and discussion: Size matching between the building block particles and core particles is important to

generate superstructures. If the size of the building block particles is similar to that of the template particles,

a near-close packed arrangement of the building blocks on the template particles is unlikely. As a general

rule, the building block-to-core (template) size ratio of less than 1:8 should be used to design

superstructures.





42

Note and discussion: The monodispersity of the functionalized building blocks is important for particle

assembly on the templates. Polydispersity facilitates aggregation and therefore the building blocks will be

prone to aggregation to form large clusters30; larger cluster particles have a smaller area (relative to their

size) for effective interaction with the template particles. Sonication may be applied to assist the particle

dispersion before the addition of metal ions.

Note and discussion: The thickness of the coating layer achieved via either the metal-coordination or

oxidative polymerization of polyphenol can be varied with different substrates and building blocks.

Therefore, generally, it is necessary that the thickness of the coating layer on the building blocks is

considerably smaller than the size of the building blocks. As a general rule, the ratio of the thickness of the

phenolic layer to the diameter of the building block should be kept below 1:5.

Note and discussion (Calculation and statistical analysis of assembled particles on larger core

particles): The packing density of spherical building blocks on spherical templates has been well studied

by Mansfield and coworkers31. The theoretical analysis and descriptions show that when the ratio of

building blocks per template is larger than 13, the maximum geometrical packing is equivalent to ~ 83% of

the surface area of the template extended by the radius of the building block32. For particle numbers per

template >13, the maximum number of particles per template (Mm) can be described as:

2

1

2

2 13m

rMr

where r1 is the radius of the core template particles and r2 represents the radius of the building block

particles. While the average maximum for kinetic assembly (where each collision leads to adhesion) is

described by:

2

1

2

1p prM Kr

where Kp is a unit-less constant with value of ~2.18731. Fig. S7a shows the 3D surface of adsorbed particle

number (based on Mp) on larger template particles. Additionally, the numbers of spherical particles per

template in the hollow SPs presented in this work were counted through TEM images. As shown in Fig.

S7b, the counted particle numbers with different radii of assembled (r2) and core particles (r1) were





43

between the calculated values based on a geometrically close-packed structure (Mm) and a kinetically

driven assembled structure (Mp). Based on these results, it can be assumed that each single collision

between a building block and the template does not necessarily lead to adhesion, suggesting that the

particle assembly is driven by combinational process consist of kinetic and also thermodynamic processes,

and there is also a statistical contribution due to the number of collisions required for adhesion.

Note and discussion (Solvated TA, MD simulation): In the equilibrated TA, the galloyl groups were

extended perpendicular to the plane of the sugar ring (Fig. S16a) and paired off consistently with the next

nearest neighbour galloyl rather than the nearest neighbour (Fig. S16b). The equilibrated TA has an average

end-to-end distance of 26.2 ± 1.4 Å and a radius of gyration of 8.4 ± 0.2 Å. Hydrogen bond populations

and lengths for TA are presented in Table S3. On average, (82 ± 5)% of TA hydrogen bond sites are

populated by water; however, only (2 ± 1)% of the sites are populated by intramolecular hydrogen bonds.

This indicates that the stability of the galloyl pairings is dominated by aromatic interactions rather than

hydrogen bonding.

Note and discussion (Solvated TA on a PS surface, MD simulation): Following the initial recognition

event between a galloyl group and a benzene ring of the PS surface, TA typically adsorbed within 2–5 ns

and remained fairly flat on the surface (Fig. S17) with no significant diffusion across the surface and an

average number of TA–PS aromatic contacts of 8.4 ± 1.8. The radius of gyration of TA decreased slightly

from 8.4 ± 0.2 Å in solution to 7.9 ± 0.2 Å, and the population of TAwater hydrogen bonds decreased,

whereas the TATA hydrogen bond population increased relative to TA in solution.

Note and discussion (Solvated FeIII-TA3 complex versus free TA3, MD simulation): To examine the role

of Fe, simulation studies were conducted for FeIII-TA3 complexes and three free TA molecules (TA3) in

solution (Fig. S18a,b). The FeIII-TA3 complexes were more ordered than TA3, as shown by the larger

hydrogen bond population (Table S4) and the radial distribution functions (RDFs) (Fig. S18c).

Interestingly, the FeIII-TA3 complex exhibited a high degree of intramolecular π–π stacking (which is not

seen in TA3) owing to the attraction of the galloyl hydroxyl groups to the oxygen groups coordinating FeIII.

The rigidity imposed by the FeIII coordination provides a point of stability for the rest of the complex not





44

found in TA3, where each TA continually re-adjusts owing to flexibility and interactions with the other two

TAs.

Note and discussion (Solvated FeIII-TA3 complex versus TA3 on a PS surface, MD simulation): The

extent of adsorption of the FeIII-TA3 complex and TA3 on the PS surface was dependent on the approach

vector (i.e., initial orientation and atomic velocities) of the molecule(s). Complete adsorption was observed

for ~40% of the sampled adsorption configurations, with TA coming into contact with the PS surface (Fig.

S19a,c). However, in ~60% of the adsorbed configurations, at least one TA remained unadsorbed and

extended away from the PS surface into solution (Fig. S19b,d).

The atomic density profiles revealed that when Fe was present, TA displayed both greater penetration into

PS and greater extension into solution. In contrast, in the absence of Fe, TA was more concentrated along

the plane of the PS–water interface (Fig. S20). The radius of gyration increased slightly for the fully

adsorbed FeIII-TA3, but not for the partially adsorbed molecules, and decreased slightly for TA3. For the

fully adsorbed TA complexes, the average interaction enthalpy between TA and the PS surface was similar

with or without Fe, with a value of −232 ± 60 kcal/mol for FeIII-TA3 and −214 ± 58 kcal/mol for TA3. For

the partially adsorbed TA systems, the average interaction enthalpy was −131 ± 46 kcal/mol for FeIII-TA3

and −140 ± 54 kcal/mol for TA3. The most extended TA in FeIII-TA3 was bonded through the coordinated

Fe to the TA adsorbed on the surface. In contrast, in the TA3 systems, the most extended TA had almost no

direct contact with the PS surface and was only held to the other TA through hydrogen bonding and

aromatic interactions.

TA–PS adsorption and stabilization is mainly driven by two factors: aromatic interactions between TA and

PS and displacement of water from TA and the PS surface during adsorption. The fully adsorbed TA3 have

the highest number of TA–PS aromatic interactions, totalling to 9.2 ± 3.0 per TA. The number of TA–PS

aromatic interactions in fully adsorbed FeIII-TA3 is 5.5 ± 2.5 per TA. For the partially adsorbed systems,

there is little difference in the number of TA–PS aromatic interactions with and without Fe (i.e., 3.3 ± 1.5

and 3.6 ± 1.8 per TA, respectively).





45

Though accurate determination of the water displacement is difficult owing to constant fluctuations in both

the PS surface and TA, the fully adsorbed FeIII-TA3 displaces on average (47 ± 13)% of the water molecules

from the PS surface, whereas the partially adsorbed FeIII-TA3 displaces (38 ± 12)%. The relative

proportions of the FeIII-TA3 solvent accessible surface area (SASA) in contact with PS are (34 ± 3)% and

(21 ± 1)% for the fully and partially adsorbed systems, respectively. In contrast, for TA3, the contact area is

~32% for both the fully and partially adsorbed systems. In all cases, there is an increase in SASA for the

fully adsorbed systems and a decrease in SASA for the partially adsorbed systems relative to the

corresponding fully solvated systems. Once the partially absorbed system is stable, there appears to be a

free energy barrier to further adsorption. Owing to the rigid geometry imposed by the Fe coordination, for

the partially adsorbed FeIII-TA3 to fully adsorb, some of the established aromatic interactions must be

broken, and the PS surface must be partially resolvated to allow the non-adsorbed TA to anchor adequately

to the PS surface. No such constraints are imposed on the free TA.

Table S5 presents the hydrogen bond population in FeIII-TA3 and TA3 on a PS surface. Relative to the free

FeIII-TA3 and TA3 in solution, there is a greater reduction in the waterTA hydrogen bonds population in

FeIII-TA3 when compared with that in TA3. In general, there is an increase in the TATA hydrogen bonds

population in FeIII-TA3 and a reduction in TA3 when adsorbed on a PS surface. For TA3, in general, a

reduction in the amount of all types of hydrogen bonds is observed when adsorbed onto PS. However,

slightly more TATA hydrogen bonds are observed on PS when Fe is present. The total amount of

waterTA hydrogen bonds is similar with or without Fe. The RDFs of FeIII-TA3 and TA3 adsorbed onto PS

(Fig. S21) revealed that TA was more ordered when adsorbed on the PS surface in the presence of Fe.

Additionally, both FeIII-TA3 and TA3 were more ordered when adsorbed on PS than in solution. The trends

observed in the RDFs could be explained as follows. The increased ordering of FeIII-TA3 upon adsorption

on the PS surface is due to both the existing PS–TA interactions and the rigidity imposed by the FeIII

coordination. In contrast, the increased ordering of TA3 observed upon adsorption on the PS surface is only

due to the existing PS–TA interactions. In any case, PS (rather than the presence of Fe) has a greater effect

on TA ordering.

Note and discussion (Role of Fe in FePN functionalization, MD simulation): Our simulations suggest





46

that when the FeIII-TA3 complex adsorbs on a PS surface, in general, two TAs are strongly (closely) bound

to the surface, whereas the remaining TA can extend away from the surface (up to 4.5 nm) in a stable and

ordered fashion, thus providing an anchoring point for further complexation with free FeIII ions in solution

or direct adsorption on another PS particle. In contrast, in the absence of Fe, the TA3 molecules tend to

concentrate along the plane of the PS–water interface, and any TA extending away from the PS is less

ordered, extended to a shorter distance, and has little direct contact with the PS surface. It is suggested that

if this extended free TA were to come in contact with another PS particle, it is likely to be easily desorbed

from the initial PS surface and to subsequently adsorb on the second PS particle, rather than providing a

link between the two particles. Although comprehensive simulations of the free energy of adsorption for the

systems of interest here cannot be performed owing to current computational limitations, these observations

may provide an atomic-level rationale for the role of FeIII ions in facilitating inter-particle locking.

Note and discussion (Particle adsorption on cells: comparison between supraparticles and discrete

particles): SPs formed through the assembly of building block particles are expected to have a higher

particle adsorption ability than free building block particles when interacting with cells, due to the

concentration of the building blocks around a single template in the SPs. Human prostate PC-3 cells were

incubated with discrete 280 nm green florescent PS particles (0.28PSgreen) and their core-satellite

[email protected] SPs at 37 °C with the same particle(0.28PSgreen)–cell ratio (100:1). After 6 h, flow

cytometry demonstrated that, in the same feed concentrations of 0.28PSgreen particles, the SPs led to higher

particle adsorption with PC-3 cells (Fig. S22a). DIC and florescence images (Fig. S22b) showed that a

single SP anchored to the cells was able to confer a number of 0.28PSgreen particles. This could lead to

potential applications in engineering enhanced florescence targeting probes and sustained drug release

systems33.





47

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supplementary information10.1038... · junling guo, blaise l. tardy, andrew j. christofferson,...

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