Au/Pt-Egg-in-Nest Nanomotor for Glucose-Powered Catalytic Motion and Enhanced Molecular Transport to Living Cells

Article abstract of DOI:10.1002/anie.202103827

Nanostructures converting chemical energy to mechanical work by using benign metabolic fuels, have huge implications in biomedical science. Here, we introduce Au/Pt-based Janus nanostructures, resembling to “egg-in-nest” morphology (Au/Pt-ENs), showing enhanced motion as a result of dual enzyme-relay-like catalytic cascade in physiological biomedia, and in turn showing molecular-laden transport to living cells. We developed dynamic-casting approach using silica yolk-shell nanoreactors: first, to install a large Au-seed fixing the silica-yolk aside while providing the anisotropically confined concave hollow nanospace to grow curved Pt-dendritic networks. Owing to the intimately interfaced Au and Pt catalytic sites integrated in a unique anisotropic nest-like morphology, Au/Pt-ENs exhibited high diffusion rates and displacements as the result of glucose-converted oxygen concentration gradient. High diffusiophoresis in cell culture media increased the nanomotor-membrane interaction events, in turn facilitated the cell internalization. In addition, the porous network of Au/Pt-ENs facilitated the drug-molecule cargo loading and delivery to the living cells.

Full text of DOI:10.1002/anie.202103827

A Journal of the Gesellschaft Deutscher Chemiker
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Accepted Article
Title: Au/Pt-Egg-in-Nest Nanomotor for Glucose-Powered Catalytic
Motion and Enhanced Molecular Transport to Living Cells
Authors: Taewan Kwon, Nitee Kumari, Amit Kumar, Jongwon Lim,
Chang Yun Son, and In Su Lee
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To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.202103827
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10.1002/anie.202103827
Angewandte Chemie International Edition
RESEARCH ARTICLE
Au/Pt-Egg-in-Nest Nanomotor for Glucose-Powered Catalytic
Motion and Enhanced Molecular Transport to Living Cells
Taewan Kwon,[a,b,†] Nitee Kumari,[a,b,†] Amit Kumar,[a,b] Jongwon Lim,[a,b] Chang Yun Son,[b] In Su
Lee*[a,b,c]
[a]
T. Kwon, Dr. N. Kumari, Dr. A. Kumar, J. Lim, Prof. Dr. I. S. Lee
Center for Nanospace-confined Chemical Reactions (NCCR)
Pohang University of Science and Technology (POSTECH)
Pohang 37673, South Korea
E-mail: insulee97@postech.ac.kr (I. S. L.)
[b]
[c]
[†]
T. Kwon, Dr. N. Kumari, Dr. A. Kumar, J. Lim, Prof. Dr. C. Y. Son, Prof. Dr. I. S. Lee
Department of Chemistry
Pohang University of Science and Technology (POSTECH)
Pohang 37673, South Korea
Prof. I. S. Lee
Institute for Convergence Research and Education in Advanced Technology (I-CREATE)
Yonsei University
Seoul 03722, South Korea
These authors contributed equally to this work.
Supporting information for this article is given via a link at the end of the document.
Abstract: Nanostructures converting chemical energy to mechanical
work by using benign metabolic fuels, have huge implications in
biomedical science. Here, we introduce Au/Pt-based Janus
nanostructures, resembling to ‘egg-in-nest’ morphology (Au/Pt-ENs),
showing enhanced motion as a result of dual enzyme-relay-like
catalytic cascade in physiological biomedia, and in turn showing
molecular-laden transport to living cells. We developed dynamic-
casting approach using silica yolk-shell nanoreactors: first, to install a
large Au-seed fixing the silica-yolk aside while providing the
anisotropically confined concave hollow nanospace to grow curved
Pt-dendritic networks. Owing to the intimately interfaced Au and Pt
catalytic sites integrated in a unique anisotropic nest-like morphology,
Au/Pt-ENs exhibited high diffusion rates and displacements as the
result of glucose-converted oxygen concentration gradient. High
diffusiophoresis in cell culture media increased the nanomotor-
membrane interaction events, in turn facilitated the cell internalization.
In addition, the porous network of Au/Pt-ENs facilitated the drug-
molecule cargo loading and delivery to the living cells.
navigation by utilizing the different propulsion mechanisms such
as chemotaxis, magnetotaxis and bubble propulsion to deliver the
therapeutics directly in to the cells.[5] However, in the lack of
proper design of such nano-devices, it is highly challenging to
realize the movement in response to bioavailable fuel, mainly due
to the dominant Brownian forces in the regime of low Reynolds
number.[6] While reactive metal (such as Pt, Mg etc.)-modified
Janus nano/micro structures are known to show chemical
diffusiophoresis,[7] they can only be operated using biologically
harmful concentrations of H2O2 and other non-native fuels or in
the response to external light or magnetic fields.[8] We intended to
devise a biocompatible nanomotor, powered by glucose, which is
abundant and the most effective essential metabolic energy
source, functioning as the major pathological indicator,
biosynthetic precursor and biochemical signaling molecules in
living systems.[9] However, reaction with glucose as the fuel for
motility would require the multi-enzyme-like specific catalytic
power of integrated single nanostructure, carrying out chemical
cascades and anisotropic nanoscale convex-concave surface-
features to endow directional propulsion. We adopted the
inspiration from natural enzyme-designs, where multiple active
sites are precisely positioned for cooperative catalytic function
and surrounding poly-peptide-networks provide asymmetric
environment for substrate approach and product release. As
crucial design parameters: (i) gold (Au) and platinum (Pt) NCs
have unique catalytic properties and interfacing these metals in a
single nanostructure at right position can co-localize distinct
active sites for synergistic catalytic function; (ii) dendritic porous
metal network around Au-Pt active sites can expose enormous
surface area for substrate sequestration and facile approach; (iii)
judicious molding of nanostructure into overall anisotropic and
nanosized bowl-like shape, while positioning the reactive
interfaces in the bottom of bowl, will add the directional modality
in response to reaction with glucose; (iv) resulting enhanced
motion and in turn high frequency of interaction with cell-
membrane with porous morphology can be used for high loading
and cellular delivery of probes or therapeutic molecules.[10] Here,
Introduction
Metabolically driven autonomous motility is the key signature of
life, ubiquitous at all scales in living organisms, cells, organelles,
ion/molecular pumps and cytoskeletal motor proteins.[1] For
instance: bacteria can ingeniously swim towards higher glucose
concentration or escape from toxic chemical environment for
survival.[2] Biochemical stochastic forces exerted by native
protein-based nanomotors and enzymes can trigger key
mechano-biological events even at low concentration or
temperature gradients.[3] In a huge advantage over conventional
microscale objects showing motion, miniaturized autonomously
mobile nano-devices (< 100 nm) have potential applications in
intracellular targeted drug-delivery, precise cell manipulation,
noninvasive surgery, biosensing and diagnostics.[4] Recently,
several nanomotors have been reported to perform the controlled
1
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10.1002/anie.202103827
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RESEARCH ARTICLE
Figure 1. Schematic illustration of fabrication and performance of glucose fueled Au/Pt-Egg in Nest (Au/Pt-EN) nanomotors for efficient cellular uptake and
enhanced molecular carriage.
we introduce dendritic hollow hybrid metal nanostructures,
resembling to ‘egg-in-nest’ morphology (designated by Au/Pt-
ENs; AuNP as egg fixed to the bottom of dendritic Pt-Nest),
showing enhanced motion through diffusiophoresis as a result of
catalytic cascade reaction in physiological biomedia containing
glucose, and in turn affecting highly useful molecular-laden
transport to living cells. As a key synthetic strategy to target hybrid
nanostructures, which cannot be accessed by the conventional
colloidal ligand/surfactant and template-based methods,[11] we
d = 40 ± 1 nm of yolk] with multiple Au seeds (d = 6 ± 1 nm)
installed inside the hollow space (designated as dy-Au@yolk-
shell-SiO2) (details in SI, Figure S1).[12-13] Due to the rattle-like
structure having small size Au-seeds and freely movable SiO2-
yolk inside the hollow interior, dy-Au@yolk-shell-SiO2 was
expected unfavorable for the intended anisotropic metal. We
strategized to fix the dynamic cast by further growing the Au-
seeds into larger size until the SiO2-yolk moved aside and got
fixed with internal shell-surface while creating an asymmetric
developed dynamic-casting approach using silica yolk-shells: first, concave hollow nanospace. Employing Ostwald ripening
to install a large Au-seed fixing the silica yolk while leaving the
anisotropically confined concave hollow nanospace, followed by
the internal silica-surface-directed laterally curved Pt-growth
selectively originated at silica-free exposed Au-seed facets and
assuming nest-like negative curvature composed of Pt-dendritic
network. Owing to the intimately interfaced Au and Pt catalytic
sites integrated in a unique anisotropic morphology, Au/Pt-ENs
exhibited high diffusion and displacements as the result of
glucose oxidation reaction. High diffusiophoresis of Au/Pt-ENs in
cell culture media increased the nanomotor-membrane
interaction events, in turn increasing their cell internalization. As
an additional advantage, porous network of Au/Pt-ENs facilitated
the molecular cargo loading and delivery to the living cells.
Present work bridges the sophisticated nanoscale synthesis and
structure modulation with life-like active biological functions and
will invoke the discoveries of new motile nanomaterials interfacing
with biology for range of applications.
process[14] resulted in transformation of multiple Au-seeds into a
single large-size spheroidal Au-nanocrystal (Au-NC, d = 20 ± 3
nm), giving desired fixed cast configuration (fix-Au@yolk-shell-
SiO2), as characterized by transmission electron microscopy
(TEM), high-angle annular dark-field-scanning transmission
electron microscopy (HAADF-STEM) and energy-dispersive X-
ray spectroscopy (EDX)-based elemental line-profiling (Figures
2a, S2 and S3). The sufficiently grown Au-NC within confined
space acted like a lock to fix all constituents of the cast viz. the
Au-NC, the silica-yolk and the outer silica shell together. Next, we
immersed fix-Au@yolk-shell-SiO2 in
a Pt-growth solution
containing Na2PtCl4 (24 mM) and ascorbic acid (103 mM), to
conduct seed-mediated growth of surfactant-free Pt
nanodendrites within asymmetric nanoconfined space (Figure
1).[15] As shown in time-course TEM images (Figure 2b), reductive
growth of Pt-grains originated at the available Au-surface first
covering all of its silica-free Au-part followed by autocatalytic Pt-
on-Pt dendritic growth (granules size ca. 3 nm) of interconnected
branching network, filling the whole internal void-space of the cast
and constructing a nest-like architecture around the Au-NC
(designated as Au/Pt@yolk-shell-SiO2). The locked yolk inside
the cast guided the overall structure to assume a negative
curvature, decreasing the Pt-volume consecutively and leaving a
Pt-free mouth-area in the end. After Pt-growth, the SiO2-cast was
Results and Discussion
Synthesis of Au/Pt-ENs through Dynamic Casting Approach
For the cast-directed growth of Au/Pt-ENs: first, we obtained
dynamic silica yolk-shells [diameters (d) = 80 ± 1 nm of shell and
2
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Figure 2. (a) EDX line profile for fix-Au@yolk-shell-SiO2. (b) Time course TEM images of growth of Pt dendrites from Au seeds in fix-Au@yolk-shell-SiO2. (c-h)
Characterization of Au/Pt-ENs: TEM (c), HRTEM (d) and HAADF STEM images (left of e), EDX elemental mapping and line profile (right of e), SEM image (f),
Deconvoluted Pt XPS spectra (g), and Voxel projections from the tomography reconstructions of a tilt series and BF-TEM images of from various projections (h).
easily etched away by the treatment with aqueous NaOH solution,
leading to Au/Pt-EN, an hollow Pt-structure (overall diameter 62
± 3 nm) having Au-NC embedded and well-connected to the thick
5% and 10% glucose conversion, respectively (Figure S8b).
These results validated the influence of Au-Pt heterojunction on
Au/Pt-ENs catalytic activity. Owing to the intimately interfaced Au
Pt-bottom (Au-Pt junctions), overall resembling to the ‘egg-in-nest’ and Pt catalytic sites integrated in a unique anisotropic nest-like
structure as characterized by HRTEM, STEM-EDS, SEM, X-ray
diffraction spectroscopy (XRD) and X-ray photoelectron
spectroscopy (XPS) (Figures 2c-g, S4, S5). The accurate
visualization of the three-dimensional (3D) bowl-like morphology
of Au/Pt-EN was reconstructed using energy-filtered-TEM-
tomography (Figure 2h, Video S1). In a control experiment, dy-
Au@yolk-shell-SiO2 afforded symmetrical hollow Pt-structure
(sym-h-Au/Pt) due to the unrestricted Pt growth originated at
multiple small size Au seeds and filling the available internal
volume in all directions while adjusting the mobile yolk in the
center (Figure S6).
morphology, Au/Pt-ENs were able to oxidize glucose and
generate O2 gas (Figure S9).[17] This is similar to the one shown
by coupled enzyme cascade consisting of glucose oxidase and
peroxidase.[18] The nest-like morphology with a wide opening
facilitated the glucose fuel entry and product mass transfer along
Au-Pt active site located at one end and in turn affected the
enzyme-like cascade reactions.
Next, we analyzed the nanomotion behavior of Au/Pt-ENs in the
presence of glucose at different concentrations (Figure 3) using
nanoparticle tracking analysis (NTA) and deduced the
corresponding average mean square displacements (MSDs).[20]
As compared to DI media, the presence of glucose (10 mM),
showed directional movement of Au/Pt-ENs (Figure S10). The
MSD of 100 Au/Pt-ENs at three glucose concentrations (10, 20,
and 50 mM) were measured as a function of the time interval (Δt)
from the parabolic fit of the MSD dependency on time according
to the equation ⟨MSD⟩ = 4DeΔt + (vt)2 (Figure 3b, S11, Video S2)
with Deff being the effective diffusion coefficient and v, the speed
of the nanomotors. The MSDs showed a parabolic shape over a
short period of time (Figure S12), corresponding to the dominant
Catalytic Activity and Glucose-fueled Motion Behavior of
Au/Pt-ENs
Next, we confirmed Au/Pt-ENs, to catalyze the cascade oxidation
of glucose (50 mM solution) to form D-gluconic acid (detected by
1H NMR, Figure S7) and H2O2 followed by decomposition of H2O2
into water and oxygen, overall conversion reaching to ~ 20% (by
commercial GOx assay kit) within 1h at r.t. and physiological pH
(Figure S8).[16] In two separate control experiments: using Pt-Nest
(obtained after removing Au) and Au-NC (no Pt) could only afford
3
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Figure 3. Analysis of the motion behaviour of Au/Pt ENs. (a) Representative tracking trajectories of Au/Pt ENs with different glucose concentrations. (b)
Correspondent mean-squared displacement (MSD) plots. (c) Effective diffusion coefficient obtained by analyzing the MSD of Au/Pt ENs at different glucose
concentrations in DMEM (error bars represent SE). (d) Representative tracking trajectories of sym-h-Au/Pts with different glucose concentrations. (e) Effective
diffusion coefficient obtained by analyzing the MSD of sym-h-Au/Pts. (f) Velocity (mean ± SD) of Au/Pt ENs, sym-h-Au/Pts and other control particles in the
presence of 50 mM, glucose as fuel. (g) Effective diffusion coefficient of Au/Pt EN and Pt-Nest at different H2O2 concentrations. Simulation results of the O2
concentration distribution around Au/Pt-EN (h) and Pt-Nest (i).
propulsive displacement over random Brownian motion and its
slope increased with increasing glucose concentrations.[21] As
expected, the trajectory of the Au/Pt-ENs without the glucose fuel
followed the random walk typical of a Brownian motion (Figure 3a,
b, Video S3). We further evaluated the self-propulsion capabilities
of Au/Pt-ENs in physiological biomedia [Dulbecco’s Modified
Eagle’s-Medium (DMEM)] at different glucose concentrations (0
mM, 20 mM, 50 mM, and 100 mM): similar to the trend in the case
of DI, the calculated Deff in DMEM were deduced to be following
increasing order (1.3 ± 0.5, 2.3 ± 0.7, 3 ± 1, and 3.7 ± 0.9 μm2s−1,
respectively) (Figure 3c, S13). The observed difference in Deff
values at each added glucose concentration in the case of DMEM
and DI is due to their different compositions in pristine states.
Au/Pt-EN has an asymmetric nest-like Pt-structure with a
socketed AuNP in the closed bottom (Figure 2e). The nest-like
morphology with a wide opening facilitated the glucose fuel entry
and product mass transfer along [Au-Pt] active site located at one
end of NP. This asymmetrically localized chemical cascade
reactions on Au/Pt-ENs generated a chemical gradient around
S14) even at high glucose concentrations (> 50 mM). When
compared to the other control nanostructures such as Pt-Nest
(after removing Au having the cavity open on both side), Au-NC
and sym-h-Au/Pt, the velocity of Au/Pt-EN was highest (20.4
μm/s) (Figure 3f). The low MSD of Au-NC may be due to the
deformed spherical shape (Figure S15) having low catalytic
activity.[22] In Au/Pt-ENs, catalytic glucose oxidation produced
H2O2, which in turn was decomposed to O2 releasing from the
particle without detectable bubble formation (Figure S16a),
pointing toward the exclusion of O2-bubble-mediated propulsion
mechanism. Also, we measured the MSDs (Figure S17) of Au/Pt-
ENs by directly using H2O2 at various concentration (0.01, 0.03,
0.05, 0.08% v/v), again showing no detectable O2-bubbles (Figure
S16). In Au/Pt-ENs, both the outer surface and the cavity can
catalyze the decomposition of H2O2 to form O2 gradient, so the
motion of Au/Pt-ENs is controlled by two competitive effects: the
concentration gradient at the outer surface and the concentration
gradient at the cavity, leading to the generation of a force with the
direction from higher to lower O2 concentration, affording
directional motility. The comparative simulation study conducted
on nanomotor models[23] also corroborated the claim of higher O2
gradient in the case of Au/Pt-ENs (details in SI, Figure 3h, S17,
S18).
NP-surface
to
trigger
directional
self-propulsion
as
nanomotors.[19,22a] In the control experiments (Figure 3d-e):
despite exhibiting glucose oxidation at comparable rates (up to
20% conversion) similar to Au/Pt-ENs, sym-h-Au/Pt (with closed
hollow spherical shape) demonstrated much lower MSDs (Figure
4
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Figure 4. (a) Snapshots of a real time monitoring of Rh 110 modified Au/Pt-ENs interaction with MDA-MB cells through CLSM. (b) CLSM images of MDA-MB
cells after 10 min of treatment with Au/Pt-ENs in presence and absence of glucose (100mM). Scale bar: 25 μm (c) TEM images of fixed and sectioned MCF-7
cells after treatment with Au/Pt-ENs showing their cytosolic internalization. (d-f) Flow cytometry analysis showing a population of cells treated with Rh 110
modified Au/Pt-ENs with (red) and without (grey) glucose.
Motion Induced Cellular Uptake and Anticancer Drug
Delivery Studies of Au/Pt-ENs
enhanced motion. Additionally, the locations of the Au/Pt-ENs
inside cytoplasm were confirmed by Bio-TEM of fixed and
sectioned cells (Figure 4c). Cellular internalization of Au/Pt-ENs
in MDA-MB-231 cells was also quantified by flow-cytometry
(Figure 4d-f), where the larger number of dye-positive cells was
found in presence of glucose. Next, we investigated Au/Pt-ENs
as effective drug carriers, by their cargo loading and pH-induced
release capabilities using doxorubicin (Dox).[10a,25] Au/Pt-ENs
demonstrated good Dox (0.8 mg/mL) loading efficiency [18%
(w/w)] due to the porous network of Pt-Nest (Figure S22).
Subsequently, in a drug release experiment: at pH 7, only ca. 10%
drug was released after 4 h, but at acidic condition (pH 5) notably
much faster drug release (ca. 60%) was noticed and almost 100%
drug was released within 24h at pH 5 (Figure 5a). Next, we tested
the anti-cancer in vitro therapeutic application of Dox-loaded-
Au/Pt-ENs in MDA-MB-231 cells. Dox-free Au/Pt-ENs did not
affect cell viability at concentrations as high as 50 μg mL−1 after
the 24 h (Figure S23). After the treatment of cells with Dox-
loaded-Au/Pt-ENs in the presence of glucose, concentration-
dependent cell viability was observed (89% at 10 μg mL−1 73% at
Next, we tested Au/Pt-EN for motion-induced cellular uptake
behaviors. Rhodamine 110-labeled-Au/Pt-ENs were treated with
different cell-lines [MCF-7 (human breast cancer cells) and MDA-
MB-231 cells (epithelial breast cancer cells)] with and without
spiked glucose (100 mM glucose). In the time-lapse confocal laser
scanning microscopy (CLSM) images, (Figure 4a, S19, & Video
S4-5) demonstrated Au/Pt-EN-movements were apparently
much faster in the cell-culture containing 100 mM glucose (Video
S4) and they quickly (within 10 min) started accumulating on to
cell and internalizing into the cytoplasmic region most likely as a
result of frequent membrane-interactions, as confirmed by CLSM-
based Z-stacking mages (Figure S 20, Video S6).[24] The mobile
black-spots visualized in the real-time monitoring experiments
were the clusters of Au/Pt-EN nanomotors formed in the cell-
growth media/buffer (Figure S21). As shown in Figure 4b, the
numbers of red fluorescencent punctate spots in the cytoplasmic
region were much larger with spiked glucose, signifying much
higher cellular uptake of Au/Pt-ENs due to the glucose-fueled
5
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Figure 5. (a) Release profiles for Dox from the Au/Pt-ENs in different pH buffer solution. Glucose-dependent biocompatibility of (b) the Dox-loaded-Au/Pt-ENs
and (c) physical mixture of Dox and Au/Pt-ENs at different concentration, with increased efficacy as Dox delivery vehicles (N = 5, error bars represent SE,
Asterisks indicate significant differences (*p < 0.01, **p < 0.001 vs. DOX and Au/Pt-ENs free cells)). (d) CLSM imaging of MDA-MB cells and doxorubicin after
treatment with Dox-loaded-Au/Pt-ENs in presence and absence of glucose (100 mM). Scale bars: 25 μm.
25 μg mL−1 42% at 50 μg mL−1, 40% at 75 μg mL−1 34% at 100 μg
mL−1) (Figure 5b) and after the 50 µg mL−1 the viability of cells did
not change significantly. Interestingly, cell viability was much
higher (ca. 60%-90%) in the absence of glucose. When physical
mixture of Dox and Au/Pt-ENs was treated with cells, we
In conclusion, we developed a silica-dynamic-casting approach
for in-solution growth of Au/Pt-ENs as nanosized bi-metallic
open-mouth-shells, possessing multi-enzyme-mimetic catalytic
capabilities. Due to the unique Janus nest-like hollow
nanostructures having asymmetrically on-end-located catalytic
Au-Pt-interface, Au/Pt-ENs overpowered random Brownian
forces and endowed life-like directional mechanical movements
in response to the bio-abundant and non-toxic fuel such as
glucose. Such motion-behavior endowed efficient cellular uptake
of NPs due to the high frequency of cell-membrane-interactions,
which in turn rendered their potential as self-powered cargo
delivery vehicles for anti-cancer drug molecules loading and pH-
induced intracellular release. This work opens new avenues to
design and synthesize nature-inspired mobile nanodevices
demonstrating enzyme-like catalytic functions and performing
mechanical work in response to the benign biochemical fuels.
Such nanosized automotive platforms will be highly useful for
observed
> 85% cell viability regardless of the particles
concentration and glucose. Further the confocal images of MDA-
MB cells, also showed a clear increase in red fluorescence spots
in the cytoplasmic region of the cells treated with the Dox-loaded-
Au/Pt-ENs incubated with glucose solutions compared with the
control group (absence of glucose) (Figure 5d). Since the DOX is
adsorbed onto Au/Pt-ENs via hydrophobic interaction, the
protonation of amino group in Dox (at pH 6.0-6.5) facilitated its
aqueous propensity and intracellular release.[26]
Conclusion
6
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Peng, A. A. M. André, Y. Men, M. Srinivas, D. A. Wilson, ACS Nano 2017,
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Acknowledgements
This work was supported by the Basic Science Research Program
through the National Research Foundation of Korea (NRF)
funded by the Ministry of Science, ICT & Future Planning (MSIP)
(NRF-2016R1A3B1907559)
2020R1I1A1A01071762) (N.K.).
(I.S.L.)
and
(NRF-
Keywords: nanobowl • nanocasting synthesis • nanomotor • glucose fuel •
intracellular delivery carrier
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10.1002/anie.202103827
Angewandte Chemie International Edition
RESEARCH ARTICLE
Entry for the Table of Contents
Open-mouth hollow Au/Pt-based nanostructures, resembling to “egg-in-nest” morphology, have been synthesized by a dynamic-
casting approach utilizing the silica yolk-shell cast. These nanosized motors are capable of propelling themselves in response to
biocompatible glucose as fuel, via a catalytic cascade oxidation reaction. In response to autonomous motion they can effectively
internalize into living cells, and deliver the cargo anti-cancer drug molecules efficiently.
8
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